RES 1193RESOLUTION NO.//^3
A RESOLUTION adopting the Camas Stormwater Design
Standards Manual supplemental to the Stormwater Management
Manual for Western Washington.
WHEREAS,by Ordinance No.2582,the City of Camas added a new Chapter 14.02 to the
Camas Municipal Code regulating Stormwater control;and
WHEREAS,to provide stormwater management requirements and design standards
supplemental to the Stormwater Management Manual for Western Washington,the City of Camas
constituted a Stormwater Ordinance Committee consisting of representatives from the Camas City
Council,local business representatives,civil engineers,and City staff;and
WHEREAS,said Committee has adopted requirements and design standards as set forth in a
document known as the "Camas Stormwater Design Standards Manual";and
WHEREAS,the Council of the City of Camas desires to approve the Camas Stormwater
Design Standards Manual,
NOW,THEREFORE,BE IT RESOLVED BY THE COUNCIL OF THE CITY OF CAMAS
as follows:
SECTION I
The Camas Stormwater Design Standards Manual is hereby adopted,supplemental to the
Stormwater Management Manual for Western Washington.
ADOPTED BY THE COUNCIL AND APPROVED BY THE MAYOR AT A REGULAR
MEETING this lT^day of July,2010.
FS *SIGNED:
Mayor
\ATTEST:
Clerk
>
ts tolform :APP
City Attorney
Resolution #1193
Table of Contents
Page
Chapter 1:General Requirements
1.01 Purpose
1.02 Applicability
1.03 Exemptions
1.04 Relationship to Other City of Camas Codes
1.05 Basin Plans
1.06 Regional and Subregional Facilities
Chapter 2:Submittal Requirements
2.01 Introduction
2.02 Erosion Prevention and Sediment Control Plan
2.03 Construction Stormwater Pollution Prevention Plan (SWPPP)
2.04 Preliminary Stormwater Site Plan
2.05 Final Stormwater Plan
2.06 Stormwater Plan Changes
Chapter 3:Erosion and Sediment Control
3.01 Applicability
3.02 Construction SWPPP Requirements
3.03 Small Parcel Erosion and Sediment Control Requirements ....
3.04 Sediment Trap and Temporary Sediment Pond Sizing
Chapter 4:Flow Control and Infiltration Systems
4.01 Applicability
4.02 Flow Control
4.03 Flow Control -Small Parcel Requirements
4.04 Retrofit of Existing Flow Control Facilities
4.05 Flow Control Facilities:Side slopes,Fencing,and Setbacks ...
4.06 Closed Depressions
4.07 Infiltration Systems
1-1
1-1
1-1
1-5
1-7
1-8
1-8
2-1
2-1
2-1
2-1
2-5
2-12
2-19
3-1
3-1
3-1
3-7
3-7
4-1
4-1
4-1
4-3
4-4
4-6
4-8
4-8
City of Camas —Stormwater Design Standards Manual TOC-i
TableofContentsContinued4-94.08OtherApplicableInfiltrationRegulations4.09InfiltrationInvestigation4.10GroundwaterMonitoring4.11GroundwaterMounding4.12InfiltrationTestingMethods4.13InfiltrationDesignRates4.14InfiltrationDesignGuidelines4.15InfiltrationFacilitySetbacks4.16InfiltrationConstructionObservationandConfirmationTestingChapter5:RunoffTreatment5.01Applicability5.02GeneralRequirements5.03TreatmentFacilitySizing5.04Treatment-TypeThresholds5.05AdditionalRequirementsforPublicFacilities5.06EmergingTechnologiesChapter6:LowImpactDevelopment6.01Applicability6.02Bioretentionareas(RainGardens)6.03PermeablePavementsChapter7:ConveyanceSystems7.01Introduction7.02DesignandConstructionStandards7.03Manholes7.04DesignStormFrequency7.05HydraulicMethods7.06OpenChannels7.07Outfalls7.08OutfallstoDetentionPonds4-104-104-104-114-114-124-134-135-15-15-15-15-25-45-46-16-16-16-37-17-17-17-47-47-57-87-97-10CityofCamas—StormwaterDesignStandardsManualTOC-ii
7.09 Conveyance System Easements
Chapter 8:Drainage of Roadway Pavements...
8.01 General Requirements
8.02 Catch Basin Locations
8.03 Catch Basin Construction Standards
Chapter 9:Offsite Analysis and Mitigation
9.01 Introduction
9.02 Exemptions
9.03 Offsite Analysis
9.04 Mitigation
Chapter 10:Definitions
Appendix A:Hydrology Data
7-10
8-1
8-1
8-1
8-2
9-1
9-1
9-1
9-2
9-4
10-1
A-1
Figures
Figure 1.1:Flow Chart for Determining Stormwater Requirements .
Figure 1.2:New Development Minimum Requirements Flow Chart
Figure 1.3:Redevelopment Minimum Requirements Flow Chart ....
Figure 4.1:Pond Volume Correction Factor
Figure A -1 :Type IA Rainfall Distribution
Figure A-2:2-Year,24-Hour Clark County Isopluvial Map
Figure A-3:10-Year,24-Hour Clark County Isopluvial Map
Figure A-4:25-Year,24-Hour Clark County Isopluvial Map
Figure A-5:100-Year,24-Hour Clark County Isopluvial Map
1-2
1-3
1-4
4-4
A -7
A-9
A -10
A-11
A-12
Tables
Table 4-1 :Coefficient of Permeability Correction Factors
Table 7-1 :Allowable Storm Sewer Pipes
Table 7-2 :Storm Sewer Pipe Capacity and Minimum Slopes
Table 7-3:Maximum Pipe Slopes and Velocities
Table 7-4:Open Conveyance Protection
Table 7-5:Rock Requirements for Rock Splash Pad Outfalls
4-12
7-2
7-7
7-7
7-7
7-10
City of Camas —Stormwater Design Standards Manual TOC-iii
TableofContentsContinuedTableA-1:Sheetflow“n”Valuesand“k”ValuesUsedinTimeCalculationsforHydrographsTableA-2:TypeIARainfallDistributionTableA-3:RunoffCurveNumbersA-3A-4A-13A-14TableA-2:HydrologicSoilsGroupsCityofCamas—StormwaterDesignStandardsManualTOC-iv
Chapter 1:General Requirements
1.01 Purpose
The purpose of the Camas Stormwater Design Standards Manual (CSDSM)is to identify
stormwater management requirements for new development and redevelopment projects in
accordance with Camas Municipal Code (CMC)Chapter 14.02.
Camas’s National Pollutant Discharge Elimination System (NPDES)Phase II permit identifies
stormwater management requirements for the City.One of the requirements is that the City must
adopt the Stormwater Management Manual for Western Washington (Stormwater Manual;
Department of Ecology 2005)or an equivalent.The City has elected to adopt the Stormwater
Manual.
Local jurisdictions may modify or add to the Stormwater Manual requirements,as long as the
requirements are equivalent to or stricter than the Stormwater Manual requirements.This manual
supplements and clarifies sections of the Stormwater Manual to provide guidance for and tailor
to local conditions.It does not repeat the contents of the Stormwater Manual,so both manuals
must be consulted.If a topic or standard is not addressed in these design standards,refer to the
Stormwater Manual for guidance.
Where portions of the Camas SDSM and the Stormwater Manual conflict the requirements in
the Camas SDSM apply.Where a provision of the CAMAS SDSM is not equivalently addressed
in the Stormwater Manual the Camas SDSM provisions shall be deemed as a supplemental
requirement.
Where provisions of the Camas SDSM conflict with other City Code,state,or federal
requirements,the more stringent provisions apply,as determined by the Director.
1.02 Applicability
All new development and redevelopment activities shall refer to Figure 1.1 on the following
page to determine the stormwater requirements that will apply to the project.
City of Camas —Stormwater Design Standards Manual 1-1
Chapter1:GeneralRequirementsContinuedFigure1.1:FlowChartforDeterminingStormwaterRequirementsWilltheprojectsitedischargestormwaterdirectlyorindirectlyintoaMunicipalSeparateStormSewerSystemownedoroperatedbytheCityofCamas?ProjectMeetstheSmallParcelRequirements.ApplySmallParcelErosionandSedimentControlRequirementsperSection3.03.No>NextQuestionYesApplytheMinimumRequirementsasoutlinedinFigures1.2and1.3.Willtheprojectsitedisturbone(1)acreormore?Willtheprojectcreatemorethan5,000squarefeetofimpervioussurface?ORORYesApplyMinimumRequirements1,3,4,and5,andtheSmallParcelFlowControlrequirementsasoutlinedinSection4.03,andtherunofftreatmentrequirementsinSectionIstheprojectsitelessthanone(1)acreandpartofalargercommonplanofdevelopmentorsale?>NoNoYesNoFurtherRequirements.RefertoFigure1.2andFigure1.3.5.CityofCamas—StormwaterDesignStandardsManual1-2
Chapter 1:General Requirements
Continued
Figure 1.2:New Development Minimum Requirements Flow Chart
Does the site have 35%or
more of existing
impervious coverage?
See Redevelopment
Minimum Requirements
Flow Chart (Figure 1-3).
Yes >
No
Does the project convert
%acres or more of
native vegetation to lawn
or landscaped areas,or
convert 2.5 acres or
more of native
vegetation to pasture?
Does the project have
2,000 square feet or more
of new,replaced,or new
plus replaced
impervious surfaces?
Does the project add
5,000 square feet or
more of new
impervious surfaces?
NoNo
>*
YesYes No
Yes
All Minimum
Requirements (#1 -
#9)apply to the new
impervious surfaces
AND converted
pervious surfaces.
Does the project have
land-disturbing
activities of 7,000
square feet or more?Minimum Requirements
#1 through #5 apply to
the new AND replaced
impervious surfaces
AND the land
disturbed .
Yes
No
See Minimum
Requirement #2,
Construction
Stormwater Pollution
Prevention.
1-3CityofCamas—Stormwater Design Standards Manual
Chapter1:GeneralRequirementsContinuedFigure1.3:RedevelopmentMinimumRequirementsFlowChartDoestheareaofnew,replaced,ornewplusreplacedimpervioussurfacestotal2,000squarefeetormore?ORDoestheareaoflanddisturbingactivitytotal7,000squarefeetormore?YestoeitherNotobothApplyMinimumRequirement#2,ConstructionStormwaterPollutionPrevention.MinimumRequirements#1through#5applytothenewANDreplacedimpervioussurfacesANDthelanddisturbed.NextQuestionDoestheprojectadd5,000squarefeetofmoreofnewimpervioussurfaces?ORConvert%acresormoreofnativevegetationtolawnorlandscapedareas?ORConvert2.5acresormoreofnativevegetationtopasture?YesNoMinimumRequirements#1through#9applytothenewimpervioussurfacesandtheconvertedpervioussurfaces.NextQuestionIsthisaroad-relatedproject?NoDoestheprojectadd5,000squarefeetormoreofnewimpervioussurfaces?YesNoIsthetotalofthenewPLUSreplacedimpervioussurfaces5,000squarefeetormore,ANDdoesthevalueoftheproposedimprovements-includinginteriorimprovements-exceed50%oftheassessedvalue(orreplacementvalue)oftheexistingsiteimprovements?Dothenewimpervioussurfacesadd50%ormoretotheexistingimpervioussurfaceswithintheprojectlimits?NoYesNoadditionalrequirements.*lrN°MinimumRequirement#1through#9appliestothenewANDreplacedimpervioussurfaces.YesNoadditionalrequirements.1-4CityofCamas—StormwaterDesignStandardsManual
Chapter 1:General Requirements
Continued
Minimum Requirements that may apply to a new development or redevelopment activity
include:
Preparation of Stormwater Site Plans
Construction Stormwater Pollution Prevention Plan
Source Control of Pollution
Preservation of Natural Drainage Systems &Outfalls
On-site Stormwater Management
Runoff Treatment
Flow Control
Wetlands Protection
Operation and Maintenance
1.
2.
3.
4.
5.
6 .
7.
8 .
9.
In addition to the applicable Minimum Requirements,all new underground injection control
wells shall meet the requirements of the Washington State Department of Ecology Underground
Injection Control (UIC)Program.Information regarding Ecology's requirements can be found on
their website:http://www.ecy.wa.gov/programs/wq/gmdwtr/uic/.
Projects that disturb less than one acre and are not part of a larger common plan of development
or sale that will disturb one acre or more,but create more than 5,000 square feet of impervious
surface shall meet Minimum Requirements 1,3,4,and 5 and the Small Project requirements for
erosion and sediment control,mnoff treatment and quantity control as specified in Chapters 3,4
and 5 of this manual,or shall meet the applicable minimum requirements as described in Figures
1.2 and 1.3,this manual and the Stormwater Manual.
1.03 Exemptions
Total Exemptions
The following types of projects are exempt from Camas Municipal Code 14.02 and this manual.
Other state and federal requirements may apply.
Forest practices regulated under Title 222 Washington Administrative Code,except for
Class IV General Forest practices that are conversions from timber land to other uses.
Commercial agricultural practices involving working the land for production.However,
the conversion from timberland to agriculture and the construction of new impervious
surfaces are not exempt.
Oil and gas field activities or operations,including construction of drilling sites,waste
management pits,and access roads,as well as construction of transportation and treatment
infrastructure such as pipelines,natural gas treatment plants,natural gas pipeline compressor
1 .
2.
3.
City of Camas —Stormwater Design Standards Manual 1-5
Chapter1:GeneralRequirementsContinuedstations,andcrudeoilpumpingstations.Operatorsareencouragedtoimplementandmaintainbestmanagementpracticestominimizeerosionandcontrolsedimentduringandafterconstructionactivitiestohelpensureprotectionofsurfacewaterqualityduringstormevents.Thefollowingroadmaintenancepractices:a.Potholeandsquarecutpatching.b.Overlayingexistingasphaltorconcretepavementwithoutexpandingtheareaofcoverage.c.Shouldergrading.d.Regrading/reshapingdrainagesystems.e.Cracksealing.f.Resurfacingwithin-kindmaterialwithoutexpandingtheroadprism.g.Vegetationmanagement.4.PartialExemptionsThefollowingtypesofprojectsareexemptfromCamasMunicipalCode14.02andthismanualexceptasdescribed:Residentialshortplatsoflotslessthanoneacrethatcreatelessthan5,000squarefeetofnewimpervioussurfaceshallsubmitastormwaterplanlimitedtoconveyanceanddisposal,andanErosionandSedimentControlPlanasoutlinedinChapter3ofthismanual.Theconstructionofsingle-familyhomes,duplexes,andtheiraccessorystructuresareexemptfromMinimumRequirements6through9,providedthefollowingconditionsaremet:a.TheprojectsiteisincludedinastormwaterplanpreviouslyapprovedbytheCity.b.Thestormwaterplanprovidesforrunofftreatment,anddetentionorretentionofrunofffromresidentiallots.Undergroundutilityprojectsthatreplacethegroundsurfacewithin-kindmaterialormaterialswithsimilarrunoffcharacteristicsshallbeexemptfromalloftheMinimumRequirementsexceptMinimumRequirement#2,ConstructionStormwaterPollutionPrevention.DrainageProjectsareexemptfromMinimumRequirement#6,andtheDirectormayalsowaiveallorpartsofMinimumRequirement1,iftheprojectmeetstheotherappropriatepartsofthischapter.NewdevelopmentandredevelopmentthatmeetthecriteriainAppendixI-E(Flow1.2.3.4.5.1-6CityofCamas—StormwaterDesignStandardsManual
Chapter 1:General Requirements
Continued
Control-Exempt Surface Waters)of the Stormwater Manual and all of the following criteria
are exempt from Minimum Requirement 7 (Flow Control):
a.Project meets the exemption requirements (described in Volume I,Section 2.5.7 of the
Stormwater Manual)for discharges to one of the following water bodies:
o Columbia River
o Lacamas Lake
o Round Lake
b.Runoff is treated in accordance with Minimum Requirement 6 (Runoff Treatment).
c.The discharge structure is designed to avoid erosion during all storms up to the
100-year storm.
d.If an existing discharge structure is used the discharge structure and conveyance system
leading to the discharge must have adequate capacity to meet the requirements of
Chapter 7 (Conveyance Systems)of this manual.
1.04 Relationship to Other City of Camas Codes
1.CMC 16.53;Wetlands
This section describes wetland buffer widths for stormwater facilities,requirements for
locating stormwater facilities in buffers,and requirements for locating stormwater
facilities in wetlands.
2.CMC 16.55;Critical Aquifer Recharge Areas (CARAs)
This section describes allowable and restricted uses in CARAs,including limitations for
the use of injection wells and dry wells.Contact City of Camas personnel to determine if
the project site is within a CARA.
3.CMC 16.59;Geologically Hazardous Areas
This section of code describes standards for geologically hazardous areas,including
Erosion Hazard Areas,Landslide Hazard Areas,Seismic Hazard Areas,and other areas
determined by the City to be susceptible to other geological events,including mass
wasting,debris flows,rock falls,and differential settlement,as defined in CMC
16.59.020.
See this section for requirements when locating detention facilities within 200 feet of the
top of a Landslide Hazard Area.
4.CMC 16.61;Fish and Wildlife Habitat Conservation Areas
City of Camas —Stormwater Design Standards Manual 1 -7
Chapter1:GeneralRequirementsContinuedThissectiondiscussesrequirementsforplacementofstormwaterconveyancefacilitiesinHabitatConservationAreas.CMC17.19.040(C)3;DesignandImprovementStandards;StormDrainageThissectionprovidesgeneralstormwaterrequirements,anditdescribesrequirementsforplacementofstormdrainagefacilitiesonproperties.5.1.05BasinPlansAsallowedbytheCity’spermit,basinplanningmaybeusedbytheCityasanavailableoptiontotailorMinimumRequirement6RunoffTreatment,MinimumRequirement7FlowControl,and/orMinimumRequirement8Wetlandprotection.Basinplanningmaybeusedtosupportalternativestotreatment,flowcontrol,and/orwetlandprotectioncontainedinSection4ofAppendix1oftheCity’sNPDESpermit.Itmayalsobeusedtodemonstrateanequivalentleveloftreatment,flowcontrol,and/orwetlandprotectionthroughtheconstructionanduseofregionalstormwaterfacilities.Inorderforabasinplantoserveasameansofmodifyingtheminimumrequirements,thefollowingconditionsmustbemet:Theplanmustbeformallyadoptedbyalljurisdictionswithresponsibilitiesundertheplan.Allordinancesorregulationscalledforbytheplanmustbeineffect.ThebasinplanmustbereviewedandapprovedbytheWashingtonStateDepartmentofEcology.1.2.3.1.06RegionalandSubregionalFacilitiesTheCityencouragesmultipleusersofstormwaterfacilities.Ifregionalorsubregionalfacilitiesareusedtomeetsomeoralloftherequirementsforstormwaterqualitytreatmentandquantitycontrol,thefollowingconditionsshallbemet:1.Stormwaterrunoffshallbetransportedfromaprojectsitetoaregional/subregionalfacilitythroughapipeormanmadeopenchannelconveyancesystem,orthroughanaturaldrainagewayifapprovedbytheDirector.2.Iftheregional/subregionalfacilitydoesnotyetexist,interimquantitycontrolandtreatmentmethodsshallbeusedtomeettherequirementsofthischapter.AllinterimmethodsshallbereviewedandshallrequirewrittenapprovalbytheDirector.3.Thefacilitymusthavesufficientcapacitytomeetapplicablewaterqualitytreatmentand/orquantitycontrolrequirements.CityofCamas—StormwaterDesignStandardsManual1-8
Chapter 2:Submittal Requirements
2.01 Introduction
A Stormwater Site Plan is a comprehensive plan and report containing all the technical
information and analyses necessary for the City to evaluate proposed new development or
redevelopment activities for compliance with stormwater requirements.The contents of the
Stormwater Site Plan will vary with the type and size of the project and the individual site
characteristics.
This section describes the submittal package that is required for projects within the City of
Camas.Additional guidance on preparing a Stormwater Site Plan is contained in Volume I,
Chapter 3 of the Stormwater Manual.
2.02 Erosion Prevention and Sediment Control Plan
An Erosion Prevention &Sediment Control Plan (EPSCP)is required for Small Parcels,as
defined in Figure 1.1.
The plan shall be submitted to and approved by the City prior to demolition,street cuts,clearing,
grading,filling or issuance of City permits.Items that are to be included in an EPSCP:
Existing and proposed contours for the site and adjacent properties.
Location of all existing drainage facilities and water resource features.
Identification of all sensitive lands including wetlands and steep slopes.
Areas of cuts and fills.
Site plan showing significant trees,as defined in Camas Municipal Code Section
18.62.030.
Existing and proposed structures.
Proposed erosion prevention and sediment control BMPs.
1.
2.
3.
4.
5.
6 .
7.
See Chapter 3 of this manual for more information on erosion control requirements.
2.03 Construction Stormwater Pollution Prevention Plan (SWPPP)
In accordance with Minimum Requirement 2,a Construction Stormwater Pollution Prevention
Plan (SWPPP)is required for all project sites where the new,replaced,or new plus replaced
impervious surfaces total 2,000 square feet or more or where 7,000 square feet or more of land is
disturbed.The Construction SWPPP shall be submitted before undertaking any land-disturbing
activity.The Construction SWPPP shall be stamped by an engineer licensed in the state of
Washington and submitted with the final stormwater plan.Chapter 3 of this manual provides
guidance for developing the Construction SWPPP.
City of Camas —Stormwater Design Standards Manual 2-1
Chapter2:SubmittalRequirementsContinuedTheConstructionSWPPPshallconsistoftwoparts:anarrativeandthedrawings.Thefollowingtwosectionsdescribethecontentsofthenarrativeandthedrawings.NotethatanNPDESConstructionSiteStormwaterDischargepermitismaystillberequiredbytheWashingtonDepartmentofEcology.ConsultEcologyregulationstodeterminewhetherthispermitisrequired.SectionA-NarrativeThenarrativeshalladdressthefollowing:Twelve(12)Elements-DescribehowtheConstructionSWPPPaddresseseachofthe12requiredelements(SeeChapter3ofthismanual).IncludethetypeandlocationofBMPsusedtosatisfytherequiredelement.Ifanelementisnotapplicabletoaproject,provideawrittenjustificationforwhyitisnotnecessary.Projectdescription-Describethenatureandpurposeoftheconstructionproject.Includethetotalsizeofthearea,anyincreaseinexistingimperviousarea;thetotalareaexpectedtobedisturbedbyclearing,grading,excavationorotherconstructionactivities,includingoff-siteborrowandfillareas;andthevolumesofgradingcutandfillthatareproposed.Existingsiteconditions-Describetheexistingtopography,vegetation,anddrainage.Includeadescriptionofanystructuresordevelopmentontheparcelincludingtheareaofexistingimpervioussurfaces.Adjacentareas-Describeadjacentareas,includingstreams,lakes,wetlands,residentialareas,androadsthatmightbeaffectedbytheconstructionproject.Provideadescriptionofthedownstreamdrainageleadingfromthesitetothereceivingbodyofwater.Criticalareas-Describeareasonoradjacenttothesitethatareclassifiedascriticalareas.Criticalareasthatreceiverunofffromthesiteshallbedescribedupto%mileaway.ThedistancemaybeincreasedbytheDirector.Describespecialrequirementsforworkingnearorwithintheseareas.Soil-Describethesoilonthesite,givingsuchinformationassoilnames,mappingunit,erodibility,settle-ability,permeability,depth,texture,andsoilstructure.Potentialerosionproblemareas-Describeareasonthesitethathavepotentialerosionproblems.Constructionphasing-Describetheintendedsequenceandtimingofconstructionactivitiesandanyproposedconstructionphasing.Constructionschedule-Describetheconstructionschedule.Ifthescheduleextendsintothewetseason,describewhatactivitieswillcontinueduringthewetseasonandhowthetransportofsedimentfromtheconstructionsitetoreceivingwaterswillbeprevented.Financial/ownershipresponsibilities-Describeownershipandobligationsfortheproject.1.2.3.4.5.6.7.8.9.10.CityofCamas—StormwaterDesignStandardsManual2-2
Chapter 2:Submittal Requirements
Continued
Include bond forms and other evidence of financial responsibility for environmental
liabilities associated with construction.
Engineering calculations -Attach any calculations made for the design of such items as
sediment ponds,diversions,and waterways,as well as calculations for runoff and stormwater
detention design (if applicable).Engineering calculations must bear the signature and stamp
of an engineer licensed in the state of Washington.
A responsible,certified erosion control specialist shall be identified.Telephone and/or
pager numbers should be included.
11.
12.
Section B -Drawings
1.Vicinity map -Provide a map with enough detail to identify the location of the construction
site,adjacent roads,and receiving waters.
Site map -Provide a site map(s)showing the following features:
a.A legal description of the property boundaries or an illustration of property lines
(including distances)in the drawings.
b.The direction of north in relation to the site.
c.Existing structures and roads,if present.
d.The boundaries of and label the different soil types.
e.Areas of potential erosion problems.
f.Any on-site and adjacent surface waters,critical areas,their buffers,FEMA base flood
boundaries,and Shoreline Management boundaries.
g.Existing contours and drainage basins and the direction of flow for the different
drainage areas.
h.Final and interim grade contours as appropriate,drainage basins,and the direction of
stormwater flow during and upon completion of construction.
i.Areas of soil disturbance,including all areas affected by clearing,grading and
excavation.
j.Locations where stormwater discharges to surface waters during and upon completion
of construction.
k.Existing unique or valuable vegetation and the vegetation that is to be preserved.
l.Cut and fill slopes indicating top and bottom of slope catch lines.
m.Stockpile,waste storage,and vehicle storage/maintenance areas.
n.Total cut and fill quantities and the method of disposal for excess material.
2.
City of Camas —Stormwater Design Standards Manual 2-3
Chapter2:SubmittalRequirementsContinuedConveyancesystems-Showonthesitemapthefollowingtemporaryandpermanentconveyancefeatures:a.Locationsforswales,interceptortrenches,orditches.b.Drainagepipes,ditches,orcut-offtrenchesassociatedwitherosionandsedimentcontrolandstormwatermanagement.c.Temporaryandpermanentpipeinvertsandminimumslopesandcover.d.Grades,dimensions,anddirectionofflowinallditchesandswales,culverts,andpipes.e.Detailsforbypassingoff-siterunoffarounddisturbedareas.f.Locationsandoutletsofanydewateringsystems.3.LocationofdetentionBMPs-Showonthesitemapthelocationsofstormwaterdetention4.BMPs.ErosionandSedimentControl(ESC)BMPs-ShowonthesitemapallmajorstructuralandnonstructuralESCBMPsincluding:a.Thelocationofsedimentpond(s),pipesandstructures.b.Dimensionpondbermwidthsandinsideandoutsidepondslopes.c.Thetrap/pondstoragerequiredandthedepth,length,andwidthdimensions.d.Typicalsectionviewsthroughpondandoutletstructure.e.Typicaldetailsofgravelconeandstandpipe,and/orotherfilteringdevices.f.Stabilizationtechniquedetailsforinletsandoutlets.g.Control/restrictordevicelocationanddetails.h.Stabilizationpracticesforberms,slopes,anddisturbedareas.i.Rockspecificationsanddetailforrockcheckdam,ifused.j.Spacingforrockcheckdamsasrequired.k.Frontandsidesectionsoftypicalrockcheckdams.l.Thelocation,detail,andspecificationforsiltfence.m.Theconstructionentrancelocationandadetail.Detaileddrawings-Anystructuralpracticesusedthatarenotreferencedinthismanualorotherlocalmanualsshouldbeexplainedandillustratedwithdetaileddrawings.OtherpollutantBMPs-IndicateonthesitemapthelocationofBMPstobeusedforthecontrolofpollutantsotherthansediment.Monitoringlocations-Indicateonthesitemapthewaterqualitysamplinglocations,if5.6.7.8.CityofCamas—StormwaterDesignStandardsManual2-4
Chapter 2:Submittal Requirements
Continued
required by the Department of Ecology.Sampling stations shall be located in accordance
with applicable permit requirements.
Notes addressing construction phasing and scheduling shall be included on the drawings.9.
2.04 Preliminary Stormwater Site Plan
In accordance with Minimum Requirement #1,a preliminary stormwater site plan is required for
all new development and redevelopment projects that are not exempt from all Minimum
Requirements (as described in Section 1.01).The purpose of the preliminary stormwater site plan
is to allow the City to determine whether a proposal can meet the requirements of Camas
Municipal Code Chapter 14.02.
The preliminary stormwater site plan shall be submitted with the land use application and shall
consist of:
A preliminary development plan.1.
A preliminary Technical Information Report,bound,and prepared in the standardized
format described in the sections below.
2.
The preliminary stormwater site plan shall identify how stormwater runoff that originates on the
site,or flows through the site,is currently controlled and how this will change with the proposed
development or redevelopment project.If the site is within a region covered by a basin plan,the
information needed in the preliminary stormwater site plan may be reduced.
The project engineer shall include a statement that all the required information is included in the
preliminary stormwater site plan and that the proposed stormwater facilities are feasible.All
plans,studies,and reports that are part of the preliminary and final stormwater site plans shall be
stamped,signed and dated by the professional civil engineer(s),registered in the state of
Washington,responsible for preparation of the report.
Modification of Content Requirements
The Director may waive in writing some or all of the content requirements in the preliminary
stormwater plan if:
•The development project is included in an approved final stormwater plan that meets the
requirements of this chapter;or
•A basin plan exists that makes some of the information irrelevant.
•The City determines,upon receipt of a letter of request from the applicant,that less
information is required to accomplish the purposes of this chapter.
City of Camas —Stormwater Design Standards Manual 2-5
Chapter2:SubmittalRequirementsContinuedThewaiverofsomeortheentirepreliminarystormwaterplandoesnotrelievetheapplicantoftherequirementtoprepareafinalstormwaterplan.PreliminaryDevelopmentPlanThepreliminarydevelopmentplanshallconsistof22-inchx34-inchor24-inchx36-inchdrawings.Thepreliminarydevelopmentplanshallshowthecharacteroftheexistingsiteandproposedfeatures,includingbutnotlimitedto:1.Existingandproposedpropertyboundaries,easements,andrights-of-way.2.Existingandproposedcontourswitha2-footmaximumcontourinterval,unlesstheDirectordeterminesalesserintervalissufficienttoshowdrainagepatternsandbasinboundaries.3.Offsiteareascontributingrunofftothesite.4.Naturalandmanmadedrainagefeaturesadjacenttothesite,includingexistingandproposed(ifknown)stormwaterfacilities.5.Existingonsitewaterwells,knownagriculturaldraintiles,areasofpotentialslopeinstability,structures,utilities,andseptictanksanddrainfields.6.Locationofthe100-yearfloodplainandfloodwaysandshorelinemanagementarealimitsonthesite.7.Existingwaterresourcefeaturesonandadjacenttothesite,includingstreams,wetlands,springs,sinks,andstormwaterfacilities.8.Existingandproposeddrainageflowroutesforeachthresholddischargearea(TDA)toandfromthesite,includingbypassflows.9.ProposedlocationofstructuralsourcecontrolBMPsimplementedinaccordancewithMinimumRequirement3(SourceControlofPollution),whereapplicable.10.Pointofdischargelocationsfromtheproposedprojectsitethatpreservethenaturaldrainagepatternsandexistingoutfalllocations,inaccordancewithMinimumRequirement4(PreservationofNaturalDrainageSystemsandOutfalls).11.AreasoftheprojectsitewhereonsitestormwatermanagementBMPswillbeeffectivelyimplemented,inaccordancewithMinimumRequirement5(OnsiteStormwaterManagement),includinglowimpactdevelopmentBMPs.Theplanmustshowtheareasofretainednativevegetation,requiredflowlengths,andvegetatedflowpathsforproperimplementationoftheseBMPs.12.Allexistingdrainagefacilities,includingstructuralwaterqualityorflowcontrolBMPsandconveyancesystems.13.Existingandproposedpollution-generatingpervioussurfaces(PGPS),includinglawn,CityofCamas—StormwaterDesignStandardsManual2-6
Chapter 2:Submittal Requirements
Continued
landscaped areas,and pasture areas.
Existing areas of the site predominantly covered by native vegetation (i.e.,native trees,
shrubs,and herbaceous plants as defined by the Washington State Department of Ecology
(Ecology))and areas of native vegetation to be preserved under proposed conditions.
Approximate location and size of proposed runoff treatment and flow control facilities
implemented in accordance with Minimum Requirements 6 and 7.
The delineated wetland boundary (for sites that discharge stormwater to a wetland,either
directly or indirectly through a conveyance system,and must meet Minimum Requirement 8,
Wetlands Protection).
A conceptual grading plan that verifies the constructability of a stormwater facility (for
sites with slopes greater than five percent).
The Director may require additional site or vicinity information if needed to determine
the feasibility of the stormwater proposal.
14.
15.
16.
17.
18 .
Preliminary Technical Information Report (TIR)
The preliminary TIR shall be bound and contain all technical information and analyses necessary
to determine that the proposed stormwater facilities are feasible.The required contents of the
preliminary TIR are identified below.
Table of Contents
List of section headings and their respective page numbers.
List of tables with page numbers.
List of figures with page numbers.
List of attachments,numbered.
List of references.
1 .
2.
3.
4 .
5.
Map Submittals
All maps shall contain a scale and north arrow.
Vicinity Map:All vicinity maps shall clearly show the project site.
Soils Map:The soils map shall show soils within the contributing area that drains to the
site itself.Soils maps may be obtained from the following sources:
a.Updated version of the Soil Survey of Clark County,Washington,originally published
in 1972,and updated by the Natural Resources Conservation Service (NRCS).
b.Geographic information system (GIS)maps of soils from Clark County GIS.
1.
2 .
City of Camas —Stormwater Design Standards Manual 2-7
Chapter2:SubmittalRequirementsContinuedc.WashingtonsoilsurveydataasavailableontheNRCSwebsite(http://websoilsurvey.nrcs.usda.gov).d.Ifthemapsdonotappeartoaccuratelyrepresentthesoilsforthesite,theapplicantisresponsibleforverifyingtheactualsoilsforthesite.OtherMaps:Thefollowingadditionalmapsshallberequiredinthesituationsnoted:a.Floodplains.IfafloodplainmappedbytheFederalEmergencyManagementAgency(FEMA)existsonoradjacenttothesite,amapshowingthefloodplainisrequired.b.ShorelineManagementArea.IfthesitecontainsorisadjacenttoastreamorlakeregulatedundertheWashingtonShorelinesManagementAct,amapshowingtheboundaryoftheshorelinemanagementareainrelationtothesiteisrequired.3.SectionA-ProjectOverview1.Describethesitelocation.2.Describethetopography,naturaldrainagepatterns,vegetativegroundcover,andpresenceofcriticalareas(CMCTitle16).Criticalareasthatreceiverunofffromthesiteshallbedescribedtoaminimumof%mileawayfromthesiteboundary.3.Identifyanddiscussexistingonsitestormwatersystemsandtheirfunctions.4.Identifyanddiscusssiteparametersthatinfluencestormwatersystemdesign.5.Describedrainagetoandfromadjacentproperties.6.Describeadjacentareas,includingstreams,lakes,wetlandareas,residentialareas,androadsthatmightbeaffectedbytheconstructionproject.7.Generallydescribeproposedsiteconstruction,sizeofimprovements,andproposedmethodsofmitigatingstormwaterrunoffquantityandqualityimpacts.SectionB-MinimumRequirementsDescribetheland-disturbingactivityanddocumenttheapplicableminimumrequirementsfortheprojectsite.Includethefollowinginformationintableformat:Theamountofexistingimpervioussurface.Theamountofnewimpervioussurface.Theamountofreplacedimpervioussurface.Theamountofnativevegetationconvertedtolawnorlandscaping.Theamountofnativevegetationconvertedtopasture.Thetotalamountofland-disturbingactivity.1.2.3.4.5.6.CityofCamas—StormwaterDesignStandardsManual2-8
Chapter 2:Submittal Requirements
Continued
Provide a statement that confirms the minimum requirements that will apply to the development
activity.For land-disturbing activities where Minimum Requirements 1 through 9 must be met:
Provide the amount of effective impervious area in each TDA,and document through an
approved continuous runoff simulation model (e.g.,the Western Washington Hydrologic
Model (WWHM)or MGS Flood)the increase in the 100-year flood frequency from pre-
developed to developed conditions for each TDA.
List the TDAs that must meet the runoff control requirements listed in Minimum
Requirement 6.
List the TDAs that must meet the flow control requirements listed in Minimum
Requirement 7.
List the TDAs that must meet the wetlands protection requirements listed in Minimum
Requirement 8.
1.
2.
3.
4.
Section C -Soils Evaluation
Describe the site’s suitability for stormwater infiltration for flow control,runoff
treatment,and LID measures.
Identify water table elevations,flow directions (where available),and data on seasonal
water table fluctuations with minimum and maximum water table elevations where these may
affect stormwater facilities.
Identify and describe soil parameters and design methods for use in hydrologic and
hydraulic design of proposed facilities.
Report findings of testing and analysis used to determine the infiltration rate.
Where unstable or complex soil conditions exist that may significantly affect the design
of stormwater facilities,the Director may require a preliminary soils report that addresses
stormwater design considerations arising from soil conditions.The preliminary soils report
shall be prepared by a registered professional engineer proficient in geotechnical
investigation and engineering or a registered soil scientist.The preliminary soils report shall
include a soils map developed using the criteria set in the NRCS National Soil Survey
Handbook (NRCS 2007)and the SCS Soil Survey Manual (SCS 1993),at a minimum scale
of 1:5,000 (12.7 inch/mile).
1.
2 .
3.
4.
5.
Section D -Source Control
If the development activity includes any of the activities listed in Section 2.2 of Volume IV of
the Stormwater Manual,identify the source control BMPs to be used with the land-disturbing
activity.
Section E -Onsite Stormwater Management BMPs
City of Camas —Stormwater Design Standards Manual 2-9
Chapter2:SubmittalRequirementsContinuedOnthepreliminarydevelopmentplanorothermaps,showthesiteareaswhereonsitestormwatermanagementBMPswillbeeffectivelyimplemented.(SeeVolumeIII,Chapter3andVolumeV,Chapter5oftheStormwaterManual.)Theplanmustshowtheareasofretainednativevegetationandrequiredflowlengthsandvegetatedflowpaths,asrequiredforproperimplementationofeachonsitestormwaterBMP.ArrowsmustshowthestormwaterflowpathtoeachBMP.IdentifyanddescribegeotechnicalstudiesorotherinformationusedtocompletetheanalysisanddesignofeachonsitestormwaterBMP.Identifythecriteria(andtheirsources)usedtocompleteanalysesforeachonsitestormwaterBMP.DescribehowdesigncriteriawillbemetforeachproposedonsitestormwatermanagementBMP.DescribeanyonsiteapplicationofLIDmeasuresplannedfortheproject.ProvideaplanthatshowstheproposedlocationandapproximatesizeofeachLIDfacility.Identifyanddescribeanyassumptionsusedtocompletetheanalysis.Describesitesuitability,includinghydrologicsoilgroups,slopes,areaofnativevegetation,andadequatelocationofeachBMP.1.2.3.4.5.6.7.SectionF-RunoffTreatmentAnalysisandDesignForland-disturbingactivitieswherethethresholdswithinMinimumRequirement6indicatethatrunofftreatmentfacilitiesarerequired:Documenttheleveloftreatmentrequired(basic,enhanced,phosphorus,oil/waterseparation),basedonproceduresinVolumeV,Chapter2oftheStormwaterManualandChapter5ofthismanual.ProvidebackgroundanddescriptiontosupporttheselectionofthetreatmentBMPsbeingproposed.Includeananalysisofinitialimplementationcostsandlong-termmaintenancecosts.1.2.Identifygeotechnicalorsoilsstudiesorotherinformationusedtocompletetheanalysisanddesign.IdentifytheBMPsusedinthedesign,andtheirsources.Summarizetheresultsoftherunofftreatmentdesign,anddescribehowtheproposeddesignmeetstherequirementsofCMCChapter14.02andtheStormwaterManual.Provideatablethatliststheamountofpollution-generatingpervioussurfaces(PGPS)andpollution-generatingimpervioussurfaces(PGIS).3.4.5.6.CityofCamas—StormwaterDesignStandardsManual2-10
Chapter 2:Submittal Requirements
Continued
Section G -Flow Control Analysis and Design
For land-disturbing activities where the thresholds within Minimum Requirement 7 indicate that
flow control facilities are required:
Identify the site’s suitability for stormwater infiltration for flow control,including tested
infiltration rates,logs of soil borings,and other information.
1.
Identify and describe geotechnical or other studies used to complete the analysis and2.
design.
If infiltration cannot be provided for flow control,provide the following additional
information:
a.Identify the areas where flow control credits can be obtained for dispersion,LID,or
other measures,per the requirements in the Stormwater Manual.
b.Provide the approximate sizing and location of flow control facilities for each TDA,per
Volume III of the Stormwater Manual.
c.Identify the criteria (and their sources)used to complete the analyses,including pre-
developed and post-developed land use characteristics.
For sites considered to be historical prairie,submit a project site report prepared by a
wetland scientist or horticulturist experienced in identifying soils,plant,and other evidence
associated with historic prairies to demonstrate the existence of historic prairie on the project
site.Areas within Camas that were historically prairie include Fern and Lacamas prairies.
Contact City staff for a map showing potential prairie locations.
Complete a hydrologic analysis for existing and developed site conditions,in accordance
with the requirements of Chapter 4 of this manual and Chapter 2,Volume III of the
Stormwater Manual,using an approved continuous runoff simulation model.Compute
existing and developed flow durations for all subbasins.Provide an output table from the
continuous flow model.
Include and reference all hydrologic computations,equations,graphs,and any other aids
necessary to clearly show the methodology and results.
Include all maps,exhibits,graphics,and references used to determine existing and
developed site hydrology.
3.
4.
5.
6 .
7.
Section H -Wetlands Protection
For projects with stormwater discharges to a wetland,either directly or indirectly through a
conveyance system,the preliminary TIR shall describe wetland protection measures to be
implemented in accordance with Minimum Requirement 8.The narrative shall describe the
City of Camas —Stormwater Design Standards Manual 2-11
Chapter2:SubmittalRequirementsContinuedmeasuresthatwillmaintainthehydrologicconditions,hydrophyticvegetation,andsubstratecharacteristicsnecessarytosupportexistinganddesignateduses.2.05FinalStormwaterPlanPurposeInaccordancewithMinimumRequirement1,thefinalstormwaterplanprovidesfinalengineeringdesignandconstructiondrawingsforthestormwateraspectsofaproposednewdevelopmentorredevelopmentproject.ThefinalstormwaterplanshallbesubmittedandapprovedbytheDirectorbeforeconstructionofthedevelopmentcanbegin.ModificationofContentRequirementsTheDirectormaywaiveinwritingsomeorallofthecontentrequirementsinthefinalstormwaterplanif:•Thedevelopmentprojectisincludedinanapprovedfinalstormwaterplanthatmeetstherequirementsofthischapter;or•Abasinplanexiststhatmakessomeoftheinformationirrelevant.FinalStormwaterPlanSubmittalThefinalstormwaterplansubmittalshallincludethefollowing:Anyeasements,covenants,oragreementsnecessarytopermitconstruction.Finalengineeringplansthatprovidesufficientdetailtoallowconstructionofthestormwaterfacilities.Theseplansshallbestamped,signed,anddatedbytheengineer(s),registeredinthestateofWashington,responsibleforhydrologic,hydraulic,geotechnical,structuralandgeneralcivilengineeringdesignandbytheprojectengineerresponsibleforthepreparationofthefinalstormwaterplan.Thefinalengineeringplanshallshowallutilitiestoensurethatconflictsbetweenproposedutilitylinesdonotexist.Theapprovedpreliminarystormwatersiteplan,withanexplanationofanydifferencesbetweenthedesignconceptsincludedinthepreliminaryandfinalstormwaterplans.Afinaldevelopmentplan(whichmaybeapartofthefinalengineeringplansoraseparateplan).Seetherequirementsidentifiedbelow.Aboundcopyofthefinaltechnicalinformationreport(TIR).Seetherequirementsidentifiedbelow.TheEPSCPorSWPPPpreparedinaccordancewithSection2.02or2.03.1.2.3.4.5.6.FinalDevelopmentPlanCityofCamas—StormwaterDesignStandardsManual2-12
Chapter 2:Submittal Requirements
Continued
The final development plan shall be consistent with the preliminary development plan and may
be combined with the final engineering plans.In addition to the information required in the
preliminary development plan,the final plan requires the following information :
Threshold discharge area (TDA)delineations,and total impervious and pervious area
delineations and acreages by TDA.
The acreage of pollution-generating pervious surfaces (PGPS)and pollution-generating
impervious surfaces (PGIS)used in the hydraulic/hydrologic calculations both onsite and
offsite that contribute surface runoff.
Directions and lengths of overland,pipe,and channel flow.
Outfall points from each TDA and overflow routes for the 100-year storm.
Onsite conveyance systems,including pipes,catch basins,channels,ditches,swales,and
culverts.
Primary flow path arrows for drainage under developed conditions,with the calculated
flow rates.Cross-reference the flow rates to the hydrological model output file used to
calculate the flow rates.
The Director may require additional site or vicinity information if needed to determine
the feasibility of the stormwater proposal.
1 .
2 .
3.
4.
5.
6 .
7.
Final Technical Information Report (TIR)
The final TIR shall be a bound,comprehensive report,supplemental to the final engineering
plans,that contains all technical information and analyses necessary to complete final
engineering plans based on sound engineering practices and appropriate geotechnical,
hydrologic,hydraulic,and water quality design.
The final TIR shall be stamped,signed,and dated by the professional engineer(s),registered in
the state of Washington,responsible for the hydrologic,hydraulic,geotechnical,structural and
general civil engineering design.
The required contents of the final TIR,which is part of the final stormwater plan,are identified
below.
Table of Contents
See the preliminary TIR requirements in Section 2.04.
Map Submittals
See the preliminary TIR requirements in Section 2.04.
Section A -Project Overview
City of Camas —Stormwater Design Standards Manual 2-13
Chapter2:SubmittalRequirementsContinuedProvidetheinformationfromthepreliminaryTIR,withthefollowingadditionalelements:1.Referencetheconceptualdesignproposedinthepreliminarystormwaterplan.2.Identifyrevisionstotheconceptualdesigncontainedwithinthefinalengineeringplans.SectionB-MinimumRequirementsProvidetheinformationfromSectionBofthepreliminaryTIR,revisedasnecessaryforthefinaldesign.ConfirmtheapplicableminimumrequirementsidentifiedinthepreliminaryTIR.Forland-disturbingactivitieswhereMinimumRequirements1through9mustbemet,providetherequiredinformationlistedinSectionBofthepreliminaryTIR,revisedtoreflectthefinaldesign.SectionC-SoilsEvaluationSeethepreliminaryTIRrequirementsinSection2.04.SectionD-SourceControlSeethepreliminaryTIRrequirementsinSection2.04.SectionE-OnsiteStormwaterManagementBMPsProvidetheinformationfromthepreliminaryTIR,withthefollowingadditionalelements:1.Referencetheconceptualdesignproposedinthepreliminarystormwaterplan.2.Identifyrevisionstotheconceptualdesigncontainedwithinthefinalengineeringplans.3.Forbioretentionsystems,providethefollowing:a.Theproposedsoilmatrixforthefacility.b.Theplantingplan,listingproposedplanttypesandlocations.c.Detaildrawings,includingthefollowing:oIfanunderdrainisused,showdrainrock,pipe,andfilterfabricspecifications.oAllstormwaterpipingassociatedwiththefacility,includingcatchbasin,pipematerials,sizes,slopes,andinvertelevations.oRaingardenwidth,length,sideslopes,andmaximumdesignwaterdepth.oIrrigationsystem,ifinstalled.oDesignsforanyretainingwallsproposed.Structuralwallsshallmeetcitybuildingpermitrequirements.4.Forporouspavements:CityofCamas—StormwaterDesignStandardsManual2-14
Chapter 2:Submittal Requirements
Continued
a.Supporting design calculations showing adequate infiltration rates to accommodate
flows from all impervious surfaces directed onto any porous pavement.
b.Geotextile specification.
c.Base material gradation.
d.Asphalt mix design and void calculations.
e.Acceptance test procedures.
f.Detail drawings,including the following:
o Geotextile
o Base material
o Asphalt layer
Reversed slope sidewalks:
a.Details on the planting plan for any areas receiving water from reversed slope
sidewalks.
5.
Section F -Runoff Treatment Analysis and Design
For land-disturbing activities where the thresholds within Minimum Requirement 6 indicate that
runoff treatment facilities are required,provide the information from the preliminary TIR,with
the following additional elements:
Reference the conceptual runoff treatment design proposed in the preliminary stormwater1.
plan.
Identify revisions to the conceptual runoff treatment design contained in the preliminary
stormwater plan.
Complete a detailed analysis and design of all proposed runoff treatment system
elements,in accordance with Chapter 5 of this manual and Volume V of the Stormwater
Manual.Reference runoff treatment system elements to labeled points shown on the site
location map or final development plan.
Include and reference all computations,equations,charts,nomographs,detail drawings,
and other tabular or graphic aids used to design water quality system elements in the
technical appendix.
Summarize the results of the runoff treatment design and describe how the proposed
design meets the requirements of CMC Chapter 14.02 and the Stormwater Manual.
Section G -Flow Control Analysis and Design
For land-disturbing activities where the thresholds within Minimum Requirement 7 indicate that
flow control facilities are required:
2.
3.
4.
5.
City of Camas —Stormwater Design Standards Manual 2-15
Chapter2:SubmittalRequirementsContinued1.Identifyrevisionstotheconceptualdesignproposedinthepreliminarystormwaterplan.2.Identifyinitialconditions,includingstreambaseflows,beginningwatersurfaceelevations,hydraulicorenergygradelines,initialgroundwaterelevations,beginningstoragevolumes,andotherdataorassumptionsusedtocompletetheanalysesofinitialconditions.Referencethesourcesofinformation.3.Describeanyassumptionsusedtocompletetheanalysis,includingflowcreditsthroughtheuseofonsitestormwaterBMPsorLIDmeasures.4.Completeadetailedhydrologicanalysisforexistinganddevelopedsiteconditions,inaccordancewiththerequirementsofChapter2,VolumeIIIoftheStormwaterManual,usinganapprovedcontinuousrunoffsimulationmodel.Computepre-developedanddevelopedflowdurationsforallsubbasins.Provideanoutputtablefromthecontinuousflowmodel,includingthefollowing:a.Flowratesforthe2-,10-,and100-yearreturnperiodsforpre-developedanddevelopedconditions.b.Atablelistingthepass/failratesforeachflowlevelwheredurationstatisticswerecalculated.c.Agraphshowingtheflowrateontheyaxisandpercenttimeexceedingonthexaxisforpre-developedconditionsandpost-developedmitigatedconditions,from50percentofthe2-yearflowratethroughthe50-yearflowrate.5.Provideahydraulicanalysisofpipesand/orchannelsthatleadtoand/orfromtheoutletstructure.Theanalysisshouldconfirmthecapacityofpipesandchannelstoconveythepeakflowratesforthe2-,10-,50-,and100-yearreturnperiodflowratewiththewatersurfaceelevationofthepondattheelevationforthosereturnperiodflowrates.6.SubmitelectroniccopiesoftheWWHM(.wdm,.prj,.usi)projectfilestoallowreviewerstorunthemodelandconfirmthemodelresults.7.Refertolabeledpointsshownonthesitelocationmapanddevelopmentplan.8.Includeandreferenceallhydrologicandhydrauliccomputations,equations,ratingcurves,stage/storage/dischargetables,graphs,andanyotheraidsnecessarytoclearlyshowthemethodologyandresults.9.Includeallmaps,exhibits,graphics,andreferencesusedtodetermineexistinganddevelopedsitehydrology.FlowControlSystemPlan1.Provideanillustrativesketchoftheflowcontrolfacilityanditsappurtenances.2.Showbasicmeasurementsnecessarytoconfirmstoragevolumes.CityofCamas—StormwaterDesignStandardsManual2-16
Chapter 2:Submittal Requirements
Continued
3.Show all orifice,weir,and flow restrictor dimensions and elevations.
The sketch shall correspond with final engineering plans.Alternatively,a final site
grading plan that incorporates the above information may be included as an attachment to the
final stormwater plan.
Provide electronic copies of the drawings used for analysis,measurement,and design
inputs for the hydrologic analysis submitted with the final drawing in one of the following
approved file formats:Portable Document Format (.pdf ),or AutoCAD (.dwg,.dxf ).
4.
5.
Section H -Wetlands Protection
For projects with stormwater discharges to a wetland,either directly or indirectly through a
conveyance system,the TIR shall describe wetland protection measures to be implemented in
accordance with Minimum Requirement 8.The narrative shall describe the measures that will
maintain the hydrologic conditions,hydrophytic vegetation,and substrate characteristics
necessary to support existing and designated uses.
Section I -Other Permits
Construction of roads and stormwater facilities may require additional permits from other
agencies.These permits may contain requirements that affect the design of the stormwater
system.This section lists the titles of other possible required permits,the agencies that require
the permits,and the permit requirements,if known,that affect the final stormwater plan.
Approved permits that are critical to the feasibility of the stormwater facility design shall be
included in this section.
Underground injection control (UIC)well registration:DOE.Proposed public UIC wells
shall receive Washington State Department of Ecology UIC Program rule authorization prior
to civil plan approval.Provide a copy of the authorization during the plan review process.A
copy of the registration application will be accepted if rule authorization notification has not
been received from Ecology within 60 days of application for well registration.
1 .
Section J -Conveyance Systems Analysis and Design
Reference the conceptual drainage design proposed in the preliminary stormwater plan.
Identify revisions to the conceptual drainage design contained in the preliminary
stormwater plan.
Identify the criteria used to complete the analyses and their sources.
Identify and discuss initial conditions,including stream base flows,beginning water
surface elevations,hydraulic or energy grade lines,beginning storage elevations,and other
data or assumptions used to complete the analyses of initial conditions.Reference the sources
of information.
1 .
2 .
3.
4.
City of Camas —Stormwater Design Standards Manual 2-17
Chapter2:SubmittalRequirementsContinuedDescribeanyassumptionsusedtocompletetheanalyses.Completeadetailedhydraulicanalysisofallproposedcollectionandconveyancesystemelementsandexistingcollectionandconveyanceelements,includingoutfallstructuresandoutletprotection,thatinfluencethedesignorareaffectedbytheproposal,inaccordancewithChapter7(ConveyanceSystems)ofthismanual.Computeandtabulatethefollowing:a.Identifydesignflowsandvelocitiesandconveyanceelementcapacitiesforallconveyanceelementswithinthedevelopment.b.Identifythe10yearrecurrenceintervalstagefordetentionfacilityoutfalls(SeeChapter7).Providestage-frequencydocumentationfromthecontinuousrunoffmodel.c.Computeexisting100-yearfloodplainelevationsandlaterallimitsforallchannels,andverifynonetlossofconveyanceorstoragecapacityfromdevelopment.d.Referenceconveyancesystemelementstolabeledpointsshownonthesitelocationmapordevelopmentplan.e.Verifythecapacityofeachconveyancesystemelementtoconveydesignflowanddischargeatnon-erosivevelocities.Verifythecapacityoftheonsiteconveyancesystemtoconveydesignflowsthatresultfromultimatebuild-outofupstreamareas.f.Includeandreferenceallhydrauliccomputations,equations,pipeflowtables,flowprofilecomputations,charts,nomographs,detaildrawings,andothertabularorgraphicaidsusedtodesignandconfirmtheperformanceofconveyancesystems.g.Summarizetheresultsofsystemanalyses,anddescribehowtheproposeddesignmeetstherequirementsofthischapter.5.6.SectionK-Off-siteAnalysisIfapplicable,providetheresultsofanoffsiteanalysispreparedinaccordancewithChapter9(OffsiteAnalysisandMitigation)ofthismanual.(SeeexemptionsinChapter9.)SectionL-ApprovalConditionsSummaryListeachpreliminaryapprovalconditionrelatedtostormwatercontrol,wetlands,floodplains,andotherwater-relatedissues,andexplainhowthefinaldesignaddressesorconformstoeachcondition.SectionM-SpecialReportsandStudiesWheresite-specificcharacteristics,suchassteepslopes,wetlands,andsiteslocatedinwellheadprotectionareas,presentdifficultdrainageandwaterqualitydesignproblems,theDirectormayrequireadditionalinformationorthepreparationofspecialreportsandstudiesthatfurtheraddressthespecificsitecharacteristics,thepotentialforimpactsassociatedwiththedevelopment,andthemeasuresthatwouldbeimplementedtomitigateimpacts.SpecialreportsCityofCamas—StormwaterDesignStandardsManual2-18
Chapter 2:Submittal Requirements
Continued
shall be prepared by professionals with expertise in the particular area of analysis,who shall
date,sign,stamp,and otherwise certify the report.Subjects of special reports may include,but
are not be limited to:
1.Geotechnical
Wetlands
Floodplains and Floodways
Groundwater
Structural Design
Fluvial Geomorphology (erosion and deposition)
2 .
3.
4 .
5 .
6.
All special reports and studies shall be included in the technical appendix.
Section N -Maintenance and Operations Manual
The project engineer shall prepare maintenance and operations manual for each stormwater
control or treatment facility to be privately maintained,and for those that constitute an
experimental system to be maintained by the City.The manual shall be written in an orderly and
concise format that clearly describes the design and operation of the facility.The manual shall
also provide an outline of required maintenance tasks;with the recommended frequencies each
task should be performed.The manual shall contain or reference procedures from the Stormwater
Manual.
If the site has media filtration systems,the manual shall clearly describe a long-term plan for
maintaining these facilities,including who will provide the maintenance and how it will be
funded.
Technical Appendix
The TIR shall contain a technical appendix that includes all computations completed in the
preparation of the TIR,together with copies of referenced data,charts,graphs,nomographs,
hydrographs,stage-storage discharge tables,maps,exhibits,and all other information required to
clearly describe the stormwater flow control and runoff treatment design for the proposed
development activity.The format of the technical appendix shall follow as closely as possible the
section format of the TIR and shall be adequately cross-referenced to ensure that the design may
be easily followed,checked,and verified.The technical appendix shall also contain all special
reports and studies,other than those included as attachments to the TIR.
2.06 Stormwater Plan Changes
City of Camas —Stormwater Design Standards Manual 2-19
Chapter2:SubmittalRequirementsContinuedIfthedesignermustmakechangesorrevisionstothefinalstormwaterplanafterfinalapproval,theproposedrevisionsshallbesubmittedtoCamaspriortoconstruction.Thesubmittalsshallincludethefollowing:1.Substitutepagesfortheoriginallyapprovedfinalstormwaterplan,identifyingtheproposedchanges.Reviseddrawings,showinganystructuralchanges.Anyothersupportinginformationthatexplainsandsupportsthereasonforthechange.2.3.Acomplianceletterfromtheplanningdepartmentthatnoplatamendmentisrequired.4.Allrevisionsshallbestamped,signed,anddatedbytheprofessionalengineer(s),registeredinthestateofWashington,responsibleforhydrologic,hydraulic,geotechnical,structuralandgeneralcivilengineeringdesign.CityofCamas—StormwaterDesignStandardsManual2-20
Chapter 3:Erosion and Sediment Control
3.01 Applicability
All projects must provide erosion and sediment control per CMC 14.06.Projects that meet the
Small Parcel requirements per Figure 1.1 shall follow the standards in Section 3.03.Projects that
do not meet the Small Parcel Standards are required to follow the standards in the Stormwater
Manual,outlined in Minimum Requirement 2,except as revised by this chapter.
If a SWPPP is required,a copy shall be provided for review to the City of Camas.
3.02 Construction SWPPP Requirements
The Construction SWPPP shall include a narrative and drawings.The narrative shall include
documentation to explain and justify the pollution prevention decisions made for the project.
All BMPs shall be clearly referenced in the narrative and marked on the drawings.
Construction SWPPP Elements
Each of the 12 elements below shall be included in the Construction SWPPP,unless site
conditions render the element unnecessary and the exemption from that element is clearly
justified in the Construction SWPPP.Note that these elements shall be followed in place of the
elements listed in Section 2.5.2 of the Stormwater Manual.
1.Preserve Vegetation/Mark Clearing Limits
a.Prior to beginning land-disturbing activities,including clearing and grading,clearly
mark all clearing limits,sensitive areas and their buffers,and trees that are to be
preserved within the construction area.
b.The duff layer,native top soil,and natural vegetation shall be retained in an
undisturbed state to the maximum degree practicable.
Establish Construction Access
a.Construction vehicle access and exit shall be limited to one route,if possible.
b.Access points shall be stabilized with quarry spalls,crushed rock,or other equivalent
BMP to minimize the tracking of sediment onto public roads.
c.Wheel wash or tire baths shall be located onsite if the stabilized construction entrance is
not effective in preventing sediment from being tracked onto public roads.
d.If sediment is tracked offsite,roads shall be cleaned thoroughly at the end of each day
or more frequently during wet weather.Sediment shall be removed from roads by
shoveling or pickup sweeping and shall be transported to a controlled sediment disposal
area.
2 .
City of Camas —Stormwater Design Standards Manual 3-1
Chapter3:ErosionandSedimentControlContinuede.Streetwashingisallowedonlyaftersedimentisremovedinaccordancewith2.d.above.Streetwashwastewatershallbecontrolledbypumpingbackonsiteorotherwisebepreventedfromdischargingintosystemstributarytowatersofthestate.f.Constructionentrancesthathavebecomeineffectiveshallbereconstructedorreplaced.ControlFlowRatesa.Propertiesandwaterwaysdownstreamfromdevelopmentsitesshallbeprotectedfromerosionresultingfromincreasesinthevelocityandpeakvolumetricflowrateofstormwaterrunofffromtheprojectsite.b.Wherenecessarytocomplywith3.a.above,stormwaterretentionordetentionfacilitiesshallbeconstructedasoneofthefirststepsingrading.Detentionfacilitiesshallbefunctionalpriortoconstructionofsiteimprovements(e.g.,impervioussurfaces).c.Ifpermanentinfiltrationpondsareusedforflowcontrolduringconstruction,thesefacilitiesshouldbeprotectedfromsiltationduringtheconstructionphaseinaccordancewiththeprojectSWPPP,includingbutnotlimitedtotemporarysedimentationponds.InstallSedimentControlsa.StormwaterrunofffromdisturbedareasshallpassthroughasedimentpondorotherappropriatesedimentremovalBMPpriortoleavingaconstructionsiteorpriortodischargetoaninfiltrationfacility.RunofffromfullystabilizedareasmaybedischargedwithoutasedimentremovalBMP,butshallmeettheflowcontrolperformancestandardof3.a,above.b.SedimentcontrolBMPs(sedimentponds,traps,filters,etc.)shallbeconstructedasoneofthefirststepsingrading.TheseBMPsshallbefunctionalbeforeotherland-disturbingactivitiestakeplace.c.BMPsintendedtotrapsedimentonsiteshallbelocatedinamannertoavoidinterferencewiththemovementofjuvenilesalmonidsattemptingtoenteroff-channelareasordrainages.StabilizeSoilsa.ExposedandunworkedsoilsshallbestabilizedbyapplicationofeffectiveBMPsthatpreventerosion.b.Nosoilsshallremainexposedandunworkedformorethanthetimeperiodssetforthbelowtopreventerosion:iLDuringthedryseason(July6-September30):7days.xLDuringthewetseason(October1-July6):2days.c.Soilsshallbestabilizedattheendoftheshiftandbeforeaholidayorweekendifneeded,basedontheweatherforecast.3.4.5.l.li.CityofCamas—StormwaterDesignStandardsManual3-2
Chapter 3:Erosion and Sediment Control
Continued
d.Soil stockpiles shall be stabilized from erosion,protected with sediment trapping
measures,and,where possible,located away from storm drain inlets,waterways,and
drainage channels.
Protect Slopes
a.Cut and fill slopes shall be designed and constructed in a manner that will minimize
erosion.
b.Offsite stormwater (run-on)or groundwater shall be diverted away from slopes and
undisturbed areas with interceptor dikes,pipes and/or swales.Offsite stormwater shall
be managed separately from stormwater generated on the site.
c.At the top of slopes,drainage shall be collected in pipe slope drains or protected
channels to prevent erosion.Temporary pipe slope drains shall handle the expected
peak 10-minute flow velocity from a Type 1A,10-year,24-hour frequency storm for
the developed condition.Alternatively,the 10-year,1-hour flow rate predicted by an
approved continuous runoff model,increased by a factor of 1.6,may be used.The
hydrologic analysis shall use the existing land cover condition for predicting flow rates
from tributary areas outside the project limits.For tributary areas on the project site,the
analysis shall use the temporary or permanent project land cover condition,whichever
will produce the highest flow rates.If the Western Washington Hydrology Model is
used to predict flows,bare soil areas shall be modeled as “landscaped area.”
d.Excavated material shall be placed on the uphill side of trenches,consistent with safety
and space considerations.
e.Check dams shall be placed at regular intervals within constructed channels that are cut
down a slope.
Protect Drain Inlets
a.Storm drain inlets made operable during construction shall be protected so stormwater
runoff does not enter the conveyance system without first being filtered or treated to
remove sediment.
b.Inlet protection devices shall be cleaned or removed and replaced when sediment has
filled one-third of the available storage (unless a different standard is specified by the
product manufacturer).
Stabilize Channels and Outlets
a.All temporary onsite conveyance channels shall be designed,constructed,and
stabilized to prevent erosion from the following expected peak flows.Channels shall
handle the expected peak 10-minute flow velocity from a Type 1A,10-year,24-hour
frequency storm for the developed condition.Alternatively,the 10-year,1-hour flow
rate predicted by an approved continuous runoff model,increased by a factor of 1.6,
6.
7.
8.
City of Camas —Stormwater Design Standards Manual 3-3
Chapter3:ErosionandSedimentControlContinuedmaybeused.Thehydrologicanalysisshallusetheexistinglandcoverconditionforpredictingflowratesfromtributaryareasoutsidetheprojectlimits.Fortributaryareasontheprojectsite,theanalysisshallusethetemporaryorpermanentprojectlandcovercondition,whicheverwillproducethehighestflowrates.IftheWesternWashingtonHydrologyModelisusedtopredictflows,baresoilareasshallbemodeledas“landscapedarea.”b.Stabilization,includingarmoringmaterial,adequatetopreventerosionofoutlets,adjacentstreambanks,slopes,anddownstreamreachesshallbeprovidedattheoutletsofallconveyancesystems.ControlPollutantsa.Allpollutants,includingwastematerialsanddemolitiondebris,thatoccuronsiteshallbehandledanddisposedofinamannerthatdoesnotcausecontaminationofstormwater.b.Cover,containment,andprotectionfromvandalismshallbeprovidedforallchemicals,liquidproducts,petroleumproducts,andothermaterialsthathavethepotentialtoposeathreattohumanhealthortheenvironment.Onsitefuelingtanksshallincludesecondarycontainment.c.Maintenance,fueling,andrepairofheavyequipmentandvehiclesshallbeconductedusingspillpreventionandcontrolmeasures.Contaminatedsurfacesshallbecleanedimmediatelyfollowinganyspillincident.d.Wheelwashortirebathwastewatershallbedischargedtoaseparateonsitetreatmentsystemortothesanitarysewerwithlocalsewerdistrictapproval.e.Applicationoffertilizersandpesticidesshallbeconductedinamannerandatapplicationratesthatwillnotresultinlossofchemicaltostormwaterrunoff.Manufacturers’labelrequirementsforapplicationratesandproceduresshallbefollowed.f.BMPsshallbeusedtopreventortreatcontaminationofstormwaterrunoffbypH-modifyingsources.Thesesourcesinclude,butarenotlimitedto:bulkcement,cementkilndust,flyash,newconcretewashingandcuringwaters,wastestreamsgeneratedfromconcretegrindingandsawing,exposedaggregateprocesses,dewateringconcretevaults,concretepumpingandmixerwashoutwaters.ConstructionsiteoperatorsarerequiredtoadjustthepHofstormwaterifnecessarytopreventviolationsofwaterqualitystandards.g.ConstructionsiteoperatorsshallobtainwrittenapprovalfromtheCityandtheDepartmentofEcologypriortousingchemicaltreatmentotherthanC02ordryicetoadjustpH.9.CityofCamas—StormwaterDesignStandardsManual3-4
Chapter 3:Erosion and Sediment Control
Continued
City of Camas —Stormwater Design Standards Manual 3-5
Chapter3:ErosionandSedimentControlContinuedControlDewateringa.Foundation,vault,andtrenchdewateringwater,whichhavesimilarcharacteristicstostormwaterrunoffatthesite,shallbedischargedintoacontrolledconveyancesystempriortodischargetoasedimenttraporsedimentpond.b.Clean,non-turbiddewateringwater,suchaswell-pointgroundwater,canbedischargedtosystemstributarytoordirectlyintosurfacewatersofthestate,asspecifiedin8,above,providedthedewateringflowdoesnotcauseerosionorfloodingofreceivingwaters.Cleandewateringwatershallnotberoutedthroughstormwatersedimentponds.c.Otherdewateringdisposaloptionsmayinclude:(i)infiltration;(ii)transportoffsiteinavehicle,suchasavacuumflushtruck,forlegaldisposalinamaimerthatdoesnotpollutestatewaters;(iii)onsitechemicaltreatmentorothersuitabletreatmenttechnologiesapprovedbythecounty;(iv)sanitarysewerdischargewithlocalsewerdistrictapproval,ifthereisnootheroption;or(v)useofasedimentationbagwithoutfalltoaditchorswaleforsmallvolumesoflocalizeddewatering.d.Highlyturbidorcontaminateddewateringwatershallbehandledseparatelyfromstormwater.MaintainBMPsa.AlltemporaryandpermanenterosionandsedimentcontrolBMPsshallbeinspected,maintained,andrepairedasneededtoensurecontinuedperformanceoftheirintendedfunctioninaccordancewithBMPspecifications.b.AlltemporaryerosionandsedimentcontrolBMPsshallberemovedwithin30daysafterfinalsitestabilizationisachievedorafterthetemporaryBMPsarenolongerneeded.ManagetheProjecta.Developmentprojectsshallbephasedtothemaximumdegreepracticableandshalltakeintoaccountseasonalworklimitations.b.Constructionsiteoperatorsshallmaintain,andrepairasneeded,allsedimentanderosioncontrolBMPstoensurecontinuedperformanceoftheirintendedfunction.c.Constructionsiteoperatorsshallperiodicallyinspecttheirsites.SiteinspectionsshallbeconductedbyaCertifiedErosionandSedimentControlLeadwhoshallbeidentifiedintheConstructionSWPPPandshallbepresentonsiteoroncallatalltimes.d.Constructionsiteoperatorsshallmaintain,update,andimplementtheirConstructionSWPPP.ConstructionsiteoperatorsshallmodifytheirConstructionSWPPPwheneverthereisachangeindesign,construction,operation,ormaintenanceattheconstructionsitethathas,orcouldhave,asignificanteffectonthedischargeofpollutantstowatersofthestate.10.11.12.CityofCamas—StormwaterDesignStandardsManual3-6
Chapter 3:Erosion and Sediment Control
Continued
3.03 Small Parcel Erosion and Sediment Control Requirements
The following erosion/sediment control measures are required for small parcels:
Only construction vehicles are allowed off-street and must be utilized only on gravel
construction access areas.
Workers'personal vehicles shall be parked on adjacent streets or other approved areas.
All unworked and exposed soils must be stabilized by seeding,covering,or mulching
from the curb line to at least ten feet from the building envelope.
Pre-grade all sidewalk areas receiving runoff from the subject lot and stabilize for use as
sediment traps.
Gravel drives used as site entrances shall be constructed of minimum two-inch diameter
gravel and no finer materials are allowed.
Construction materials such as lumber shall be delivered and stored on designated
locations which are stabilized and protected from erosion.
Each owner,builder,or permit holder shall install and maintain inlet protection on street
storm drain inlets downslope from their site.
Erosion control measures shall be reviewed and inspected at the end of each day.In
nonwork periods,inspections shall take place after each rainfall or at least once a week,
whichever is more frequent.Needed corrections shall be made immediately.
1.
2 .
3.
4.
5.
6.
7.
8.
3.04 Sediment Trap and Temporary Sediment Pond Sizing
For sediment traps and temporary sediment ponds,it is acceptable to use an approved continuous
runoff model to calculate the design flows,Q2 and Q10,as follows:
Sediment Trap
Q2 =design inflow (cfs)based on the 2-year flow rate (1-hour time step in an approved
continuous runoff model)for the developed (unmitigated)site,multiplied by a factor of 1.3.The
10-year peak flow shall be used if the project size,expected timing and duration of construction,
or downstream conditions warrant a higher level of protection.Q10 is the 10-year flow rate (1-
hour time step in an approved continuous runoff model)for the developed (unmitigated)site,
multiplied by a factor of 1.6.
Temporary Sediment Pond Sizing
Q2 and Q10 are the same as those used for Sediment Trap,above.
If using a continuous runoff model to design the principal spillway,Q10 is the 10-year flow rate
(1-hour time step)for the developed (unmitigated)site,multiplied by a factor of 1.6.
City of Camas —Stormwater Design Standards Manual 3-7
Chapter3:ErosionandSedimentControlContinuedIfusingacontinuousrunoffmodeltodesigntheemergencyspillway,the100-yearflowisthe100-yearflowrate(1-hourtimestep)forthedeveloped(unmitigated)site,multipliedbyafactorof1.6.Notethatsingleeventmodelscanalsobeusedforsizingthesefacilities.SeetheStormwaterManualforfurtherinformation.CityofCamas—StormwaterDesignStandardsManual3-8
Chapter 3:Erosion and Sediment Control
Continued
City of Camas —Stormwater Design Standards Manual 3-9
mmmrn
Chapter 4:Flow Control and
Infiltration Systems
4.01 Applicability
Projects must provide flow control to reduce the impacts of stormwater runoff from impervious
surfaces and land cover conversions per the applicability thresholds in Chapter 1.That portion of
any development project in which the thresholds are not exceeded in a Threshold Discharge Area
shall apply On-site Stormwater Management BMPs in accordance with Minimum Requirement
5.
4.02 Flow Control
Refer to Volume I,Chapter 2.5.7 of the Stormwater Manual to fulfill Minimum
Requirement 7.
Flow control facilities,with the exception of UIC wells,shall use Volume III of the
Stormwater Manual for design requirements.
Runoff discharges from all new development and redevelopment sites shall follow
Minimum Requirement Number 4.
Infiltration is the preferred BMP if site conditions are appropriate and groundwater
quality will not be impaired.All applicable discharges to groundwater shall comply with the
requirements of the Washington State Department of Ecology Underground Injection Control
Program and the City’s CARA ordinance.
To insure the standards in this chapter are met,the volume available for storing runoff in
a stormwater facility shall be reduced by seasonal high groundwater and/or ordinary high
water unless a liner and buoyancy calculations are provided for the facility.
Residential and commercial structures meeting the requirements in Chapter 3.1,Volume
III of the Western Washington Manual shall direct roof runoff to roof downspout control
systems.
All facilities shall provide emergency overflow routes for storm events that exceed the
design capacity of the facility.
The Western Washington Hydrology Model (WWHM)and MGS Flood are currently the
only continuous simulation hydrologic models approved for use by the City of Camas.
1 .
2.
3.
4.
5.
6 .
7.
8 .
See Section 4.06 (Infiltration Systems)of this manual for infiltration requirements in9.
Camas.
10 .Closed depression analysis shall be performed as required in Chapter 2.4 of Volume III
of the Western Washington Manual.See Section 4.06 of this manual for more information.
City of Camas —Stormwater Design Standards Manual 4-1
Chapter4:FlowControlandInfiltrationSystemsContinuedCityofCamas—StormwaterDesignStandardsManual4-2
Chapter 4:Flow Control and Infiltration Systems
Continued
4.03 Flow Control -Small Parcel Requirements
New development,redevelopment,and construction site activities that meet the Small Parcel
Requirements as outlined in Figure 1.1 shall design flow control facilities using the following
methods:
Projects shall utilize the Santa Barbara Unit Hydrograph (SBUH)method for hydrologic
analysis and the level pool routing method for facility sizing.
Projects must limit the peak rate of runoff from individual development sites as follows:
a.The peak release rate for the 2-year design storm after development shall not exceed
one-half the pre-developed 2-year design storm peak runoff rate.
b.The peak release rate for the 10-and 100-year design storms after development shall
not exceed the respective pre-developed design storm peak runoff rates.
The pre-developed land cover shall be the existing land cover present at the time of
development.
A correction factor shall be applied to the detention facility depending on project site
impervious cover.The correction factor can be determined from Figure 4.lor from the
following equation:
1.
2 .
3.
4.
Multiplication Factor =(composite runoff curve number/46)-0.6
This correction factor is to be applied to the volume of the pond without changing its depth
or the design of its outlet structure,which shall result in an increase in surface area.
A Soil Conservation Society (SCS)Type 1A rainfall distribution resolved to a maximum
of 10-minute time intervals shall be used.This distribution can be found in Appendix A.
Time of Concentration shall be calculated as described in Section 4-4.6.2 of the
Washington Department of Transportation’s Highway Runoff Manual,“n”and “k”values
used in the equations may be found in Appendix A.
Isopluvial maps used for analysis shall be “Isopluvial Maps for Design Storms in Clark
County,”as published in National Oceanic and Atmospheric Administration (NOAA)Atlas
2,“Precipitation -Frequency Atlas for the Western United States,”Volume IX,Washington.
These isopluvial maps are included in Appendix A.
Curve numbers used for analysis shall be as specified in Appendix A.
Soil groups used for analysis shall be as defined in the most current version of
“Hydrologic Soil Groups for Soils in Clark County,”published by the SCS.Alternatively,
hydrological soil groups from the United States Department of Agriculture (USDA)“Web
Soil Survey”can be used,or soil groups can be developed by a Registered Soil Scientist.
These hydrologic soils groups can be found in Appendix A.
5.
6.
7.
8 .
9.
City of Camas —Stormwater Design Standards Manual 4-3
Chapter4:FlowControlandInfiltrationSystemsContinuedFigure4.1:PondVolumeCorrectionFactor4.04RetrofitofExistingFlowControlFacilitiesThisprocedureistobeusedforanewprojectsitewhereflowcontrolrequirementsaretobemetusingapondthatwasoriginallydesignedusingapeakflowcontrolstandardandsingle-eventmethodology.Theoriginalflowcontrolreleaseratesfortheexistingpondaretobeaddedtotheflowcontroltargetsforthenewproject.Iftheexistingdetentionfacilityisnotsizedsufficientlyforthenewflowtargets,thepondsizewillneedtoberevised.Step1:Estimatethepredevelopmenttargetpeakflowsfortheexistingdrainageareatributarytothefacility.Usethesamepredevelopmentlandcoversthatwereoriginallyapprovedfordesigningthepond.Donotincludetheareafromthenewproject.UsetheSBUHmethodtodeterminethetargetpeakflowsofthefollowing:•Viofthepredevelopmentpeakflowofa2-year,24-hourstorm.•Thepredevelopmentpeakflowofa10-year,24-hourstorm.•Thepredevelopmentpeakflowofa100-year,24-hourstorm.CityofCamas—StormwaterDesignStandardsManual4-4
Chapter 4:Flow Control and Infiltration Systems
Continued
Step 2:
Estimate the predevelopment runoff flows for the new project site.The pre-developed land cover
requirements of this manual shall be used for determining the pre-development flows.The pre-
development runoff flows of interest are:
•Vi of the peak flow of a 2-year,24-hour storm.
•The peak flow of a 2-year,24-hour storm.
•The peak flow from a 10-year,24-hour storm.
Restricted Variable Assumptions
The flow path length assumed for sheet flow runoff in the pre-developed condition
calculations shall not be less than 300 feet.
1.
2.The Manning’s effective roughness coefficient for pre-developed forested conditions
shall be 0.8.For pasture conditions,the coefficient shall be 0.15.
Curve numbers for pre-developed forest and pasture conditions shall be selected from the “fair”
category.
Step 3:
Determine the regulatory target flows by summing the flows of Steps 1 and 2,as follows:
Step 1 Regulatory Target Flows
Vi the 2-year +Vi the 2-year =the target control level for the 2-year post-development peak flow
Step 2
the target control level for the 10-year post-development peak flow10-year +2-year
the target control level for the 100-year post-development peak flow100-year +10-year
Step 4:
Determine the post-development flows of the entire drainage area for the 2-year,24-hour storm;
the 10-year,24-hour storm;and the 100-year,24-hour storm.For existing land areas not
proposed for improvement,use the same land covers and flow routing assumptions that were
used in the original design.For the land that is proposed for improvement in the project,use the
proposed land covers.
Step 5:
Using the existing detention basin and discharge structure,determine whether the post-
development flows of Step 4 are controlled to the regulatory target flows in Step 3.
City of Camas —Stormwater Design Standards Manual 4-5
Chapter4:FlowControlandInfiltrationSystemsContinuedStep6:Iftheexistingdetentionbasinanddischargestructuredonotmeettheregulatorytargetflows,modifythedetentionbasinvolumeand/orthedischargestructureuntilthetargetsareachieved.Volumecorrectionfactor:Ifthepre-developedconditionoftheprojectsitewasmodeledaspasture,thecubicfootincreaseinthedetentionvolumeofStep4mustbeincreasedbythepercentageindicatedinthey-axisinFigure4.1.Thepercentimperviouslandcoverofthex-axispertainsonlytotheprojectsite.4.05FlowControlFacilities:Sideslopes,Fencing,andSetbacksSideslopes1.Interiorsideslopesshallbe3:1orflatter,orconstructedwithretainingwalls.2.Exteriorsideslopessteeperthan3:1areallowedifitisdemonstratedthatthefacilitycanbeadequatelymaintained.Long-termerosioncontrolshallbeprovidedandanapprovedmaintenanceplanisrequired.3.UseofretainingwallsinstormwaterfacilitiestallerthanfourfeetrequiresapprovaloftheDirector.Theheightofthewallshallbemeasuredfromthebottomofthefootingtothetopofthewall.TheCitymaygrantadeviationfromthesideslopestandardswhentheDirectordeterminesthatthesafety,health,andwelfareofthepublicwillnotbecompromised.4.FencingFencesshallberequiredunderthefollowingconditions:1.Forallpondswithretainingwalls24-inchesorhigher(measuredfromthetopofwalltothepondbottom),2.Whereapondinteriorsideslopeissteeperthan3H:IV.3.Wherethereisanadjacentornearby(withintwoblocks)facilitythatprovidescarefortheelderlyorpersonswithdisabilitiesincludingbutnotlimitedtoAlzheimer’s,dementiaorvisionimpairment.4.Onschoolsites,parksandplaygroundswhereneededtocomplywithsafetystandardsdevelopedbytheDepartmentofHealth(DOH)andtheSuperintendentforPublicInstruction(SPI).Thesestandardsincludewhatiscalleda‘non-climbablefence’.Oneexampleofanonclimbablefenceisachain-linkfencewithatightermesh,sochildrencannotgetafoot-holdforclimbing.5.Whereapermanentpoolispresent,unlessa5-footwidesafetybenchisprovidedabovethepermanentpoolelevation,andsideslopesare4:1orflatter.FencesmayberequiredinotherinstancesasdeterminedbytheDirector.CityofCamas—StormwaterDesignStandardsManual4-6
Chapter 4:Flow Control and Infiltration Systems
Continued
Other fencing requirements:
1.Fences shall be a minimum of 42 inches high,of such materials that would effectively prevent entry
by small children,and complying with local permitting authority requirements (such as building
codes).
2.Fences installed along public rights-of-way and adjoining public spaces shall be of “see-through”
construction or materials,such that a person could not effectively hide behind the fence.
3.The use of other types of barriers (e.g.shrubs,split rail fences)or no barriers,are allowed for slopes
flatter than 3H:IV,except near the areas described in Numbers 3 and 4 above.
4 .Where less than 10 percent of the pond perimeter have side slopes steeper than 3:1,split rail fences
(3-foot minimum height)or densely planted thomed hedges (e.g.,barberry,holly,etc.)may be used.
5 .Other materials meeting the requirements listed above may be used for fencing with prior approval by
the director.
Gates are required for vehicle access and shall be a minimum of 16-feet wide.5.
Setbacks
Flow control facilities shall be setback as follows:
Per CMC 17.19.030(F)from streets and accessory structures.
At least 10-feet from neighboring property lines.
Per Washington Department of Health regulations for distances from septic system
drainfields.
At least 50-feet from slopes 15 percent or steeper,unless a geotechnical analysis and
report is prepared that includes an assessment of impoundment seepage on the stability of the
natural slope.This report must be signed and stamped by an engineer with geotechnical
expertise licensed in the state of Washington.
At least 100-feet from any well head.
A geotechnical analysis and report must be prepared for detention facilities located within
200 feet of the top of a Landslide Hazard Area.This report must include the assessment of
impoundment seepage on the stability of the natural slope.This report must be signed and
stamped by an engineer with geotechnical expertise licensed in the state of Washington.
Infiltration facilities shall also follow the setbacks in Section 4.15 of this manual.
1.
2 .
3.
4.
5.
6.
7.
City of Camas —Stormwater Design Standards Manual 4-7
Chapter4:FlowControlandInfiltrationSystemsContinuedAccessAccessroadsshallusethefollowingdesignguidelines:a.Maximumgradeof15percent.b.Outsideturningradiusof40feetminimum.c.Minimumof15feetwideoncurvesand12feetwideonstraightsections.d.Constructedwithasphalt,compactedgravel,orasimilarall-weathersurfacereceivingpriorapprovalforusefromtheDirector.Accessroadmustbepavedbetweentheabuttingstreetandthegate.Accesstothebottomofthefacilitymustbeprovided,unlessotherwiseapprovedbytheDirector,andsufficientevidenceisprovidedthatrequiredaccessandmaintenancecanbeaccomplishedfromtheperimeter.Accessperthissectionmustbeprovidedtotheflowcontrolstructureandtheemergencyoverflowstructure.1.2.3.4.4.06ClosedDepressionsCloseddepressionsrequirecarefulassessmentoftheexistinghydrologicperformanceinordertoevaluatetheimpactsofaproposedproject.Acalibratedcontinuousflowmodelmustbeusedforclosedepressionanalysis.InfiltrationratesusedintheanalysisofcloseddepressionsmustbedeterminedaccordingtotheproceduresinSection3.3oftheStormwaterManual,andperthismanual.Aminimumoffourinfiltrationtestsmustbeperformedtoestablishanaveragesurfaceinfiltrationrate.Closeddepressionsmustfirstbemodeledwiththepredevelopmentsitetodeterminethereturnfrequencyatwhichfloodingfirstoccursandthewaterlevelsassociatedwithreturnfrequenciesinexcessofthisfrequency.Proposeddetentionfacilitiesfortheprojectsiteshallbesizedsuchthatdischargefromthepost-developmentsitedoesnotincreasewatersurfacelevelsforthefrequenciesatwhichfloodingoccurs,uptoa100-yearevent.4.07InfiltrationSystemsStormwaterinfiltrationsystemscanbeusedforflowcontrolandrunofftreatmentwhereappropriate.Infiltrationfacilitiesforflowcontrolareusedtoconveystormwaterrunoffintothegroundafterappropriatetreatment.Infiltrationfacilitiesfortreatmentpurposesrelyonthesoilprofiletoprovidetreatment.Thefollowingsectionsdescribeapplicableregulations,soiltestingrequirements,andgeneraldesignmethodologyfornewinfiltrationfacilitiesusedforflowcontrolinCamas.RefertotheCityofCamas—StormwaterDesignStandardsManual4-8
Chapter 4:Flow Control and Infiltration Systems
Continued
Stormwater Manual and the latest edition of Ecology's “Guidance for UIC Wells that Manage
Stormwater”for additional information and requirements for infiltration facilities.
4.08 Other Applicable Infiltration Regulations
Washington State Department of Ecology Underground Injection Control Program
Some infiltration facilities are classified as Underground Injection Control (UIC)wells.UIC
wells include drywells and perforated pipes and are regulated under Department of Ecology’s
UIC Program (WAC 173-218).
The two basic requirements of the UIC Program are registration of new UIC wells with the
Washington State Department of Ecology and protection of groundwater from pollution
associated with stormwater runoff.
Registration:UIC wells are required to be registered with Washington State Department
of Ecology.Registration information can be found on Ecology’s website:
http://www.ecy.wa.gov/programs/wq /gmdwtr/uic/registration/reginfo.htm 1
Non-endangerment Standard:New UIC wells are required to meet a non-endangerment
standard ensuring discharges from a UIC well will not contaminate groundwater.Department
of Ecology’s guidelines for meeting this standard are found in “Guidance for UIC Wells that
Manage Stormwater”.This guidance shall be followed for UIC installation.The guidance has
requirements for minimum depth to groundwater,as well as siting and installation
requirements.It also lists activities that are prohibited from using UIC wells.This document
may be found at the following web site:
http://www.ecv.wa.gov/pubs/0510067.pdf
1 .
2.
Proposed public UIC wells must receive Washington State Department of Ecology UIC
Program rule authorization prior to civil plan approval.Provide a copy of the mle
authorization during the plan review process.A copy of the registration application will be
accepted if mle authorization notification has not been received from Ecology within 60 days
of application for well registration.
Private UIC wells are also required to meet WAC 173-218 and register with Ecology prior to
construction.The City will require verification of Ecology's authorization of a proposed
private infiltration facility or a demonstration by the applicant that the UIC facility will meet
Ecology’s water quality standards prior to civil plan approval.
When UIC regulations conflict with City of Camas requirements,the regulations that are
more protective as deemed by the Director shall apply.
City of Camas —Stormwater Design Standards Manual 4-9
Chapter4:FlowControlandInfiltrationSystemsContinuedAquiferRechargeAreas-CamasMunicipalCode16.55CamasMunicipalCode16.55.070(B),whichistheCity’sCriticalAquiferRechargeArea(CARA)ordinance,prohibitsdrywellsinCriticalAquiferRechargeAreas.SeeCMC16.55formoreinformationandcontactCitystafftodetermineiftheprojectsiteisinaCARA.4.09InfiltrationInvestigationProperevaluationofsoilsiscriticaltotheplacementanddesignofinfiltrationfacilities.Adetailedsoilsreportisrequiredwhereinfiltrationsystems,orLIDpracticesthatutilizeinfiltration,areproposed.Thisreportshallcharacterizethesoilprofile,theinfiltrationrateofthesoilandthedepthtogroundwater.Ataminimum,thisreportshallfollowthecontentguidelinesprovidedinSection4.2oftheSWWASCEInfiltrationStandards.ThereportshallbesignedandstampedbyageotechnicalengineerregisteredinthestateofWashington.Subsurfacecharacterizationshallbeconductedtoadepthofatleastsix-feetbelowtheproposedfacilitybaseelevation,orlowerifrecommendedbythegeotechnicalengineer.Subsurfacecharacterizationsandinfiltrationtestingshallbeconductedattheproposeddepthandlocationoftheproposedsystem.4.10GroundwaterMonitoringAminimumofonegroundwatermonitoringwellshallbeinstalledineachproposedinfiltrationfacilitylocation,unlessthehighestgroundwaterlevelisdemonstratedtobeatleast15feet,or5feetforsitessmallerthanoneacre,belowtheproposedfacility.Thesewellsshallbeinstalledandmonitoredduringatleastonewetseasonwithinthree(3)yearspriortothedateoffinalapproval.TheCitymayrequireadditionaltesting,monitoringorgroundwatermoundinganalysisinareasofknownhighgroundwaterorpoorinfiltrationrates.4.11GroundwaterMoundingAgroundwatermoundinganalysisshallberequiredif:•Thedepthtoeithertheseasonalgroundwatertableoralowpermeabilitysoilstratumislessthanfive(5)feetfromtheinfiltrationfacilitybottom;or•Ifrecommendedbythegeotechnicalprofessional.Iftheseasonalhighgroundwaterlevelislessthan15feetfromthebottomoftheproposedfacilityandagroundwatermoundinganalysisisnotbeingperformed,thegeotechnicalengineerCityofCamas—StormwaterDesignStandardsManual4-10
Chapter 4:Flow Control and Infiltration Systems
Continued
shall provide a discussion in the soils report explaining the rationale for not conducting the
analysis.
4.12 Infiltration Testing Methods
The Single-Ring Falling Flead Infiltration Test outlined in Section 4.1 of the SWWASCE
Infiltration Standards is allowed for determining infiltration rates in Camas.Other acceptable
test methods include:
1.The Pilot Infiltration Test (PIT)outlined in Volume III,Chapter 3 of the Stormwater
Manual.
The USDA Soil Textural Classification and the ASTM Gradation Testing correlations
provided in Chapter 3 of Volume III of the Stormwater Manual.In general these correlations
provide conservative long-term infiltration rates;however,the presence of cemented,
lithified,or indurated materials may make the use of these correlations unconservative.
Therefore,these correlations should only be used if a registered professional engineer or
engineering geologist proficient in geotechnical engineering has evaluated the site soils and
deemed these correlations appropriate for the site.
3.The alternative Auger Borehole Falling-Head Infiltration Test method outlined in Section
4.1.6,Alternative Test Methods,of the SWWASCE Infiltration Standards may be used where
explorations are conducted by advancing borings,as opposed to test pits.
Field test methods,such as the open test pit method discussed in 4.1.7 Specialized
Testing for Unique Sites of SWWASCE Infiltration Standards,may be used only if the other
test methods described above are not feasible or practical.
2.
4.
Regardless of the test methodology utilized,the Infiltration Investigation shall follow the
guidelines outlined in Section 4.1,Field Test Methods,of the SWWASCE Infiltration Standards
regarding frequency,location,and depth of testing;soil classification and testing;high
groundwater characterization;and groundwater mounding analysis.
A final report shall be prepared in conformance with Section 4.2,Infiltration Investigation
Report,of the SWWASCE Infiltration Standards.
Infiltration Testing Frequency
A minimum of one infiltration test shall be conducted at each proposed infiltration facility
location.
4.13 Infiltration Design Rates
The design infiltration rate shall be determined by dividing the calculated coefficient of
permeability or tested infiltration rate (depending on the testing method)by the appropriate
correction factor.However,if the USDA Soil Textural Classification and the ASTM Gradation
City of Camas —Stormwater Design Standards Manual 4-11
Chapter4:FlowControlandInfiltrationSystemsContinuedTestingcorrelationsareused,thennocorrectionfactorsareutilizedasthosecorrelationsprovidefactoredlong-terminfiltrationrates.Thefollowingtable(Table4-1)shallbeusedtodeterminethetotalcorrectionfactorstoobtaindesigninfiltrationratesforinfiltrationfacilities.Themaximumalloweddesigninfiltrationrateis250inches/hour.Table4-1:CoefficientofPermeabilityCorrectionFactorsCorrectionFactor(CF)DesignConditionBaseCorrectionFactorThebasecorrectionfactorismeanttoaccountforsoilvariabilityandlong-termsystemdegradationduetosiltation,crusting,orotherfactors.2SoilsCorrectionFactorAdditivecorrectionfactorrecommendedbyageotechnicalprofessionalasaresultofsoilorgroundwaterconditionsAsrecommendedbygeotechnicalprofessionalSystemDesignCorrectionFactorsIftheinfiltrationfacilityservesabasinwithanimperviousareagreaterthantwoacresandlessthanfiveacresAddV3IftheinfiltrationfacilityservesabasinwithanimperviousareagreaterthanfiveacresAdd1InfiltrationfacilitiesincloseddepressionsAdd2IfasacrificialsystemisprovidedandleftoperationalfollowingpermanentsitestabilizationSubtract*/2TotalCF=BaseCF+SoilsCF+SystemDesignCFWhenusingWWHM,theInfiltrationReductionFactoris1/CF.4.14InfiltrationDesignGuidelinesInfiltrationFacilitiesdesignedforflow/quantitycontrolshallbesizedpertheStormwaterManual.Anoverflowroutemustbeidentifiedintheeventthatcapacityisexceeded.AnyrunoffinexcessofinfiltrationcapacityshallalsocomplywiththeFlowControlrequirementifapplicable.Iftheoverflowrouteisapipedconnectionfacilitytosurfacewater,thenthefacilityshallbemodeledwithWWHMorMGSFloodandmeettheapplicableFlowControlrequirements.CityofCamas—StormwaterDesignStandardsManual4-12
Chapter 4:Flow Control and Infiltration Systems
Continued
Infiltration calculations for drywells and perforated pipe trench systems shall follow the
recommendations outlined in Section 5.3,Infiltration Calculations for Selected Facilities,of the
SWWASCE Infiltration Standards.
Public infiltration trenches shall have structures for access and maintenance on both ends of
infiltration piping systems,with a minimum of either a drywell or manhole on one pipe end.
4.15 Infiltration Facility Setbacks
The base of infiltration facilities shall be a minimum of five feet above seasonal high water or an
impermeable layer and meet Washington State Department of Ecology Underground Injection
Control Rules water quality standards.A separation down to three (3)feet may be considered if
the groundwater mounding analysis,the volumetric water holding capacity,and the design of an
overflow and/or bypass structure is adequate to prevent overtopping and meet the site suitability
criteria specified in the Stormwater Manual.
Infiltration facilities (except residential roof downspout systems)shall be set back a minimum of
20 feet down slope or 100 feet up slope from a building foundation.
Written justification from an appropriate qualified professional shall be submitted to and
approved by the City to reduce these setbacks.Setback reductions shall also meet other
applicable local,state and federal requirements.
Refer to the Stormwater Manual and the local building code for residential roof downspout
systems.
4.16 Infiltration Construction Observation and Confirmation Testing
The completed facility must be tested and monitored to demonstrate that the facility performs as
designed.If the tested coefficient of permeability determined at the time of construction is at
least 90 percent of the uncorrected coefficient of permeability used to determine the design rate,
construction shall be allowed to proceed.If the tested rate does not meet this requirement,the
applicant shall submit an additional testing plan to the City that follows the requirements in
Chapter 2 of this manual.This plan shall address steps to correct the problem,including
additional testing and/or resizing of the facility to ensure that the system complies with the
provisions of this chapter.
City of Camas —Stormwater Design Standards Manual 4-13
Chapter 5:Runoff Treatment
5.01 Applicability
Runoff from Pollution Generating Impervious Surfaces (PGIS)or Pollution Generating Pervious
Surfaces (PGPS)shall be treated per the applicability thresholds in Chapter 1.That portion of
any development project in which the PGIS or PGPS thresholds are not exceeded in a threshold
discharge area shall apply On-site Stormwater Management BMPs in accordance with Minimum
Requirement 5.
5.02 General Requirements
All sites with direct discharges to surface waters shall comply with the following state
laws:The Water Pollution Control Act (Chapter 90.48 RCW)and Water Quality Standards
for Surface Waters of the State of Washington (Chapter 173-201A WAC).
Treatment of runoff from sidewalks,separated bike paths,roofs,fenced fire lanes,and
infrequently used maintenance access roads is not required if the stormwater drains away
from pollution generating surfaces.Runoff from these surfaces that mix with runoff from
pollution generating surfaces will require treatment.
Phosphorus treatment is required in the Lacamas watershed above the dam at the south
end of Round Lake,for all development sites exceeding one (1)acre in size.All water
leaving the site during the water quality design storm shall be treated.
Projects that meet the Small Parcel Requirements as defined in Figure 1.1 are exempt
from the enhanced treatment requirements as defined in Volume V of the Western
Washington Manual.
Proprietary media filtration systems shall be designed and installed per the
manufacturer’s specifications and shall be easily accessible for maintenance and
replacement.
1.
2.
3.
4.
5.
5.03 Treatment Facility Sizing
Treatment BMPs shall be sized to capture,hold and treat the water quality design storm and shall
be sized based on the following:
1.Water Quality Design Storm Volume
The volume of runoff predicted from a 24-hour storm with a six-month return frequency
shall be used to size wetpool facilities.This volume is determined using single-event
hydrology and the NRCS curve number equations as described in Volume III,Chapter 2
of the Stormwater Manual and Chapter 4 of this manual.This storm shall be assumed to
be 70 percent of the 2-year,24-hour storm.Alternatively,the 91st percentile,24-hour
runoff volume indicated by a continuous runoff model may be used.
City of Camas —Stormwater Design Standards Manual 5-1
Chapter5:RunoffTreatmentContinuedWaterQualityDesignStormFlowRatea.ForprojectsthatarerequiredtocomplywithMinimumRequirement6:theflowrateatorbelowwhich91percentoftherunoffvolume,asestimatedbyacontinuousrunoffmodel,willbetreated.b.ForSmallProjectsasdefinedinFigure1.1,theflowratepredictedfroma24-hourstormwithasix-monthreturnfrequency(a.k.a.,70percentofthe2-year,24-hourstorm).c.Downstreamofdetentionfacilitiesthewaterqualitydesignflowratemustbethefulltwo-yearreleaseratefromthedetentionfacility.2.5.04Treatment-TypeThresholdsOilControl:TreatmenttoachieveOilControlappliesto“high-use”sites.High-usesitesarethosethattypicallygeneratehighconcentrationsofoilduetohightrafficturnoverorthefrequenttransferofoil.High-usesitesinclude:AnareaofacommercialorindustrialsitesubjecttoanexpectedAverageDailyTraffic(ADT)countequaltoorgreaterthan100vehiclesper1,000squarefeetofgrossbuildingarea.1.Anareaofacommercialorindustrialsitesubjecttopetroleumstorageandtransferinexcessof1,500gallonsperyear,notincludingroutinelydeliveredheatingoil.Anareaofacommercialorindustrialsitesubjecttoparking,storageormaintenanceof25ormorevehiclesthatareover10tonsgrossweight(trucks,buses,trains,heavyequipment,etc.).AroadintersectionwithameasuredADTcountof25,000vehiclesormoreonthemainroadwayand15,000vehiclesormoreonanyintersectingroadway,excludingprojectsproposingprimarilypedestrianorbicycleuseimprovements.2.3.4.PhosphorusTreatment:TherequirementtoprovidephosphorouscontrolisdeterminedbytheCity,ortheWashingtonStateDepartmentofEcology(e.g.,throughawasteloadallocation).PhosphorustreatmentisrequiredintheLacamaswatershedabovethedamatthesouthendofRoundLake,foralldevelopmentsitesexceedingone(1)acreinsize.Allwaterleavingthesiteduringthewaterqualitydesignstormshallbetreated.EnhancedTreatment:Enhancedtreatmentforreductionindissolvedmetalsisrequiredforthefollowingprojectsitesthatdischargetofish-bearingstreams,lakes,ortowatersorconveyancesystemstributarytofish-bearingstreamsorlakes:CityofCamas—StormwaterDesignStandardsManual5-2
Chapter 5:Runoff Treatment
Continued
Industrial project sites.
Commercial project sites.
Multi-family project sites.
High AADT roads as follows:
a.Fully controlled and partially controlled limited access highways with Annual
Average Daily Traffic (AADT)counts of 15,000 or more.
b.All other roads with an AADT of 7,500 or greater.
1.
2.
3.
4 .
However,such sites listed above that discharge directly (or,indirectly through a municipal storm
sewer system)to Basic Treatment Receiving Waters as specified in Volume I,Appendix I-C of
the Stormwater Manual,and areas of the above-listed project sites that are identified as subject to
Basic Treatment requirements,are also not subject to Enhanced Treatment requirements.
For developments with a mix of land use types,the Enhanced Treatment requirement shall apply
when the runoff from the areas subject to the Enhanced Treatment requirement comprises 50
percent or more of the total runoff within a threshold discharge area.
Basic Treatment:Basic Treatment generally applies to:
Project sites that discharge to the ground,UNLESS:
a.The soil suitability criteria for infiltration treatment are met;(see Volume III,Chapter 3
of the Stormwater Manual for soil suitability criteria),or
b.The project uses infiltration strictly for flow control -not treatment -and the discharge
is within 14-mile of a phosphorus sensitive lake (use a Phosphorus Treatment facility),
or within 14 mile of a fish-bearing stream,or a lake (use an Enhanced Treatment
facility).
Residential projects not otherwise needing phosphorus control as designated by the US
Environmental Protection Agency,the Washington State Department of Ecology,or by the
City of Camas;and
Project sites discharging directly to salt waters,river segments,and lakes listed in
Volume I,Appendix I-C of the Stormwater Manual;and
Project sites that drain to streams that are not fish-bearing,or to waters not tributary to
fish-bearing streams;and
Landscaped areas of industrial,commercial,and multi-family project sites,and parking
lots of industrial and commercial project sites that do not involve pollution-generating
sources (e.g.,industrial activities,customer parking,storage of erodible or leachable
material,wastes or chemicals)other than parking of employees’private vehicles.
1.
2 .
3.
4 .
5.
City of Camas —Stormwater Design Standards Manual 5-3
Chapter5:RunoffTreatmentContinuedFordevelopmentswithamixoflandusetypes,theBasicTreatmentrequirementshallapplywhentherunofffromtheareassubjecttotheBasicTreatmentrequirementcomprises50percentormoreofthetotalrunoffwithinathresholddischargearea.5.05AdditionalRequirementsforPublicFacilitiesTheCityencouragescreativitytodesignswalesandfilterstripstoreflectanaturalsettingandaddvisualappealtothedevelopment.Whiletheswalemustremainfunctional,accessibleandmaintainable,consideroptionstomakethefacilitymoreaestheticallypleasingsuchastheuseofperimeterplantmaterialandmeanderoftheflowline.Publicfacilitiesrequireadequatespacetoprovideforsafemaintenanceoperations.Allaspectsrelatedtothesafeoperationandmaintenanceoffacilities(i.e.,accessroads,vehicleparkingandmaneuveringspace,trafficconstraints,etc.)willbereviewedandapprovedwiththedesignofthefacility.Vaultsusedforpublicdrainagewillrequirehatchaccessdoors;manholeaccessportsarenotallowedonvaults.5.06EmergingTechnologiesTheCityhasconditionallyapprovedalternativemethodsforstormwaterqualitytreatmentforuseinbothpublicandprivateareasasfollows:CONTECHStormwaterSolutionsCDSStormwaterTreatmentSystemhasWashingtonStateDepartmentofEcology’s“GeneralUseLevelDesignationForPretreatment.”Thisbestmanagementpractice(BMP)maybeusedfortreatmentofstormwaterrun-offforstormsystemsinsomeareasthatutilizedrywellstodisposeofstormwater.CDSpollutioncontrolmanholesmaybeusedinsomeareastotreatrun-offfromPGISorPGPSthatutilizedrywellsandrequiretwostagedrywells,ornotreatmentperthe“GuidanceforUICWellsthatManageStormwater”(Ecology2006).Theycanbelocatedwithinthepublicrights-of-way.CDSmanholesarenotapprovedforuseinareasasdefinedbyEcologyUndergroundInjectionControlRules.CONTECHStormwaterSolutionsVortechsSystemhasEcology’s“GeneralUseLevelDesignationforPretreatment.”TheCityofCamaswillconsideruseofthisalternativeonprivatedevelopmentsitesandforuseaspublictreatmentonacase-by-casebasis.Usecouldincludetreatmentofstormwaterrun-offforstormsystemsinsomeareasthatutilizedrywellstodisposeofstormwater.Useforpublicdrainagewillrequirededicationofaseparatetractforaccessandmaintenance.VortechsarenotapprovedforuseinareasasdefinedbyEcologyUndergroundInjectionControlRules.OtherStormwaterTreatmentTechnologiesapprovedthroughEcology’sTAPEandCTAPEprogramsmaybeallowedbytheDirectoronacase-by-casebasis.CityofCamas—StormwaterDesignStandardsManual5-4
Chapter 6:Low Impact Development
6.01 Applicability
At this time,the use of Low Impact Development (LID)is not mandated by the City of Camas,
or by the Washington Department of Ecology.However,the City encourages the use of LID for
new development and redevelopment projects in appropriate conditions.The City will review
these on a case-by-case basis.Criteria to be considered include:
Availability of established design and maintenance procedures.
Other local agencies have used and approved the method proposed.
1.
2.
LID practices shall refer to the Low Impact Development Technical Guidance Manual for Puget
Sound (LID Manual)and Volume III,Appendix III-C of the Stormwater Manual for design
recommendations.All uses of LID practices shall meet applicable regulations and requirements,
and may require specific approval from other City departments (for example,Transportation or
Building).
6.02 Bioretention Areas (Rain Gardens)
Bioretention areas in City of Camas rights-of-way require specific approval by the City.
To receive credit for flow control,bioretention facilities (rain gardens,stormwater infiltration
planters,and curb extensions)must be designed and modeled in accordance with the bioretention
areas section of Volume III,Appendix III-C of the Stormwater Manual and the LID Manual.
Bioretention facilities soil mixes shall be one of the following:
•A soil mix with a minimum depth of 18-inches meeting the following criteria:
-The texture of the soil mix shall be loamy sand (USDA Soil Textural Classification)
with a clay content of less than five percent by dry weight.
-The pH for the soil mix shall be between 5.5 and 7.0.
-The final soil mix shall infiltrate water without immediate ponding on the surface.If
ponding occurs,the soil shall be retilled with additional sand and organic topsoil until
infiltration occurs.
-The completed facility shall infiltrate water at a rate of one (1)inch per hour or
greater.
•A soil mix with a minimum depth of 24-inches meeting the following criteria:
-The soil mix shall meet a minimum of five (5)milli-equivalents CEC/100 grams dry
soil.
-The soil mix shall contain a minimum 10 percent of organic content.
City of Camas —Stormwater Design Standards Manual 6-1
Chapter6:LowImpactDevelopmentContinued-Thesoilmustbecomposedoflessthan25percentgravelbyweightwithatleast75percentofthesoilpassingthe#4sieve,andtheportionpassingthe#4sievemustmeetoneofthefollowinggradations:oAtleast50percentmustpassthe#40sieveandatleasttwopercentmustpassthe#100sieve,ORoAtleast25percentmustpassthe#40sieveandatleastfivepercentmustpassthe#200sieve.•Asoilmixwithaminimumdepthof24-inchesmeetingthefollowingcriteria:-Thesoilmixshallmeetaminimumoffive(5)milli-equivalentsCEC/100gramsdrysoil.-Thesoilmixshallcontainaminimum10percentoforganiccontent.-Thesoilmusthaveameasuredinfiltrationrateofnineinchesperhourorless.CompostusedforbioretentionsoilmixmusteitherbeproducedbyaWashingtonStatepermittedcompostingfacilityunderWAC173-350-220and/ormeettheStateofWashingtonregulatorystandardsforpathogenandcontaminantstandards.Compostusedinbioretentionareasshouldbestable,matureandderivedfromorganicwastematerialsincludingyarddebris,woodwastesorotherorganicmaterialsthatmeettheintentoftheorganicsoilamendmentspecification.Biosolidsandmanurecompostscanbehigherinbio-availablephosphorusthancompostderivedfromyardorplantwaste,andtherefore,arenotallowedinbioretentionareas.Ifthecatchmentareaexceeds2,000squarefeetorthebioretentionareaisonaroadwayclassifiedasanarterialandflowisconcentrated,bioretentionshallbeprecededbyapresettlingBMP(e.g.,presettlingcatchbasin,orvault).Thepresettlingisintendedtoremovelargersolids,butnotexpectedtomeetwaterqualitytreatmentgoalsorsizingguidelinesforpretreatmentfacilities.Ifconcentratedflowsareenteringthecell,engineeredflowenergydissipation(e.g.,rockpadorflowdispersionweir)mustbeincorporated.Aminimumoneinchgradechangebetweentheedgeofacontributingimpervioussurfaceandthevegetatedflowentranceisrequired.Untiltheupstreamcatchmentareaisthoroughlystabilized,flowdiversionanderosioncontrolmeasuresmustbeinstalledtoprotectthebioretentionareafromsedimentation.Bioretentionfacilitiesarenotpermittedwithinfive(5)feetofpropertylines(excludingthepropertylineabuttingtheright-of-way)withoutagreementfromtheneighboringpropertyowner.CityofCamas—StormwaterDesignStandardsManual6-2
Chapter 6:Low Impact Development
Continued
6.03 Permeable Pavements
Permeable pavement in City of Camas rights-of-way requires prior approval from the City.
Permeable pavement systems may be applied to driveways,parking areas,sidewalks,and roads
that are privately owned and maintained.
Modeling of runoff from areas of permeable pavement surfaces must conform to requirements in
Volume III,Appendix III-C of the Stormwater Manual.
Permeable pavements installed on slopes have an increased potential for lateral flows through the
storage reservoir aggregate.This reduces the storage and infiltration capacity of the pavement
system.For longitudinal slopes greater than two percent,the subbase must be designed to create
subsurface ponding to detain subsurface flow and increase infiltration.Ponding may be provided
using design features such as terracing berms (check dams).The berms must not extend to the
elevation of the surrounding ground.They must be designed to provide sufficient space to pass
water from upgradient to lower gradient basins without causing flows to surface.
A minimum separation of 2.0 feet from the seasonal high water mark to the bottom of the base
course is required.
Permeable pavement surfaces shall not be used to manage runoff from adjacent impervious
surfaces without supporting design calculations showing adequate infiltration rates to
accommodate flows.Otherwise,permeable pavements shall be solely for the purpose of
infiltrating rainfall that falls directly upon them.
Pervious surfaces shall not drain to permeable pavement surfaces at any time.Debris,sediment,
or any particulate material shall be prevented from migrating from pervious areas onto
permeable pavement surfaces.
Permeable pavement surfaces shall not be used in areas subject to sanding for traction during
snow and ice accumulation.
Permeable pavement surfaces shall not be used to mitigate runoff for the following land uses:
•An area of a commercial or industrial site subject to an expected average daily traffic
(ADT)count equal or greater than 100 vehicles per 1,000 square feet of gross building
area.
•An area of a commercial or industrial site subject to petroleum storage and transfer in
excess of 1,500 gallons per year,not including routinely delivered heating oil.
•An area of a commercial or industrial site subject to parking,storage,or maintenance of
25 or more vehicles that are over 10 tons gross weight (trucks,buses,trains,heavy
equipment,etc.).
City of Camas —Stormwater Design Standards Manual 6-3
Chapter6:LowImpactDevelopmentContinued•Aroadintersectionwitha20-yearprojectedADTcountof25,000vehiclesormoreonthemainroadwayand15,000vehiclesormoreonanyintersectingroadway,excludingprojectsproposingprimarilypedestrianorbicycleuseimprovements.ThetrafficcountcanbeestimatedusinginformationfromTripGeneration,publishedbytheInstituteofTrafficEngineers(ITE2003),orfromatrafficstudyperformedbyaprofessionalengineerortransportationspecialistwithexperienceintrafficestimation.•Areasofsiteswithindustrialmachineryandequipment.•Railroadyardsandareaswhererailroadequipmentmaintenanceisperformed.•Logstorageandsortingyards.•Aircraftmaintenanceareas.•Fuelingstations.•Vehiclemaintenanceandrepairareas.CityofCamas—StormwaterDesignStandardsManual6-4
Chapter 7:Conveyance Systems
7.01 Introduction
This chapter presents design requirements for open channel and closed conduit stormwater
conveyance systems.
7.02 Design and Construction Standards
The following design standards shall be followed:
•Culverts shall be designed in accordance with the Washington State Department of
Transportation’s Hydraulics Manual.
•Fish passage culverts shall meet the design criteria specified in WDFW’s Fish Passage
Design at Road Culverts.
•All pipe materials,joints,manholes,and other products associated with conveyance
systems shall be designed and constructed in accordance with the most current city-
adopted edition of Washington State Department of Transportation’s Standard
Specifications for Road,Bridge,and Municipal Construction,except as revised in this
manual or the City’s standard details.
•Conveyance systems shall be designed to meet the standards shown on City of Camas
Stormwater details.
•All storm mains shall be located within the proposed or existing street rights-of-way
unless otherwise approved.
•French drains may be required along proposed roadways depending on location and site
conditions.
Minimum Pipe Diameter
®Public mainline storm sewers shall be a minimum of twelve (12)inches inside diameter.
Downstream pipe diameters shall not be reduced except when approved by the City.
•Public storm sewer laterals shall be ten (10)inches inside diameter.Larger pipe diameter
may be used with large capacity catch basins and when approved by the City.
Approved Pipe Materials
The following table lists approved pipe materials and their specifications for public storm
sewers.
City of Camas —Stormwater Design Standards Manual 7-1
Chapter7:ConveyanceSystemContinuedTable7-1:AllowableStormSewerPipesSpecificationsApprovedTypeofPipeAASHTOM252orM294TypeSCorrugatedPolyethylene(CPE)PolyvinylChlorideASTMD3034ANSIA21.51orAWWAC151DuctileIronPipe(DIP)ASTMC14ClassIIorIIIConcretePipe(CP)ASTMC76ClassIVorVReinforcedConcretePipe(RCP)HighDensityPolyethylene(HDPE)AWWAC906Notes:•CPandRCPareconsideredrigidpipe.Seerigidpipebeddingdetails.•PVC,CPE,HDPEandDIPareconsideredflexiblepipe.Seeflexiblepipebeddingdetails.•Transitionsinpipesizesareonlyallowedatstructures.PipeSlopeMinimumdesignandas-builtslopesarelistedinTable7-2.As-builtslopesshallproduceameanvelocity(whenflowingfullorhalffull)ofatleasttwo(2)feetpersecond(fps),baseduponaManning's"n"of0.013.Lateralstoinletsandcatchbasinsshallhaveaminimumslopeof0.01ft./ftSeparationStormsewersshallbedesignedtoprovidesix(6)inchesminimumverticalandthree(3)feetminimumhorizontalclearance(outsidesurfaces)betweenstormdrainpipesandotherutilitypipesandconduits.Forcrossingsofsanitarysewerslines,WashingtonStateDepartmentofEcologycriteriaapply.PipelineAlignmentsWhereaminimalfallisnecessarybetweentheinletandoutletpipesinastructure,pipesshallbealignedverticallybyoneofthefollowing,inorderofpreference:•Matchpipecrowns.•Match80percentdiametersofpipes.•Matchpipeinverts.Pipedirectionchangesorsizeincreasesordecreasesareallowedonlyatmanholesandcatchbasins.CityofCamas—StormwaterDesignStandardsManual7-2
Chapter 7:Conveyance System
Continued
City of Camas —Stormwater Design Standards Manual 7-3
Chapter7:ConveyanceSystemContinued7.03ManholesManholesarerequiredatthefollowinglocations:Ateverychangeingradeoralignmentofsewer.Ateverypointofchangeinsizeofsewerorpipematerial.Ateachintersectionorjunctionofsewermains(SeeSection8.03forcatchbasinconnections).Atintervalsof400feetorlessindevelopedareas,unlessotherwiseapprovedbytheCity.Attheendofamainpipesystem,unlessanotherstructureisapprovedbytheCity.1.2.3.4.5.Manholespacingmaybeincreasedto600feetforsewersinexcessof36-inchesdiameter,subjecttoapprovalbytheCity.Wheneverfeasible,permanentvehicularaccessshallbeprovidedtomanholeslocatedineasements.Manholesoutsideofpublicright-of-wayshallhavelockingframeandcovers(i.e.,Camlock).Thisrequirementmaybewaivedformanholeslocatedinpavedeasementsorfencedinareas.Manholesoutsideofpublicright-of-wayshallbedesignedtostandatleastsix(6)inchesabovefinishedgrade.Theminimumrequiredinsidediameterforamanholeis48-inches.Manholesbuiltoverlargediameterpipes,thosegreaterthan24-inches,requireaspecialconstructiondetail.Forconstructionofthemainline,providea0.2footminimumand0.4footmaximumdropinflowlineelevationthroughmanholes.Wheregradeconsiderationsareconsideredcritical,thedesignengineermayrequestawaiver.Insuchcases,thedropmaybereducedto0.1footforstraightthroughmanholesortonodropifthepipeislaidthroughthemanhole.7.04DesignStormFrequencyTheSantaBarbaraUrbanHydrograph(SBUH)methodortheRationalMethodshallbeusedtodeterminepeakflowratesforsizingconveyancesystems.Thepeakrunoffratefromthedesignstormstobeusedfordesignofstormwaterconveyancesystemsshallbeasfollows:•The10-yearstorm:Contributingdrainageareaslessthan40acres.•The25-yearstorm:Contributingdrainageareasof40acresormore.•The100-yearstorm:-Culvertswithcontributingdrainageareasgreaterthan200acres.—Culvertsinareasofspecialfloodhazard,asdescribedinFEMAFloodInsuranceRateMaps(FIRM)andreportsforClarkCounty.CityofCamas—StormwaterDesignStandardsManual7-4
Chapter 7:Conveyance System
Continued
The design storm shall be applied to the entire contributing drainage area projected under full
build-out conditions.
For sites that discharge to a Flow Control-Exempt Surface Water (see Appendix I-E of the
Stormwater Manual and Chapter 1 of this manual)via a closed channel conveyance,the engineer
shall demonstrate that sufficient downstream conveyance capacity exists to accommodate the
increased flows from the project.
7.05 Hydraulic Methods
Two hydraulic methods can be used for the design of pipelines.The first method is a gravity
flow or open channel design,which is most commonly performed using Manning’s equation.
This method assumes that flow is steady (does not change with time)and uniform (the depth and
velocity remain constant throughout the pipe for a given flow).Manning’s equation can be found
in standard hydraulic textbooks and in the WSDOT Hydraulics Manual (WSDOT 2007).
The second method is a pressure flow design,where the water surface elevation rises above the
crown of the pipe.A backwater analysis is performed to determine the level of the water surface
(the hydraulic grade line)for a pipeline system with a given diameter,slope,and flow rate.This
method also assumes steady flow,but the flow is not necessarily uniform (the slope of the
hydraulic grade line differs from the slope of the pipe).
New pipes shall be designed to operate in an open-channel regime during the design storm and
shall be sized using open channel design methods.Under certain hydrologic and hydraulic
conditions,however,flow can rise above the pipe,creating a pressurized pipeline.For those
situations,it is important to determine the hydraulic grade line to ensure that water does not
overtop manholes and catch basins.A backwater analysis shall be calculated under any of the
following conditions:
•Pipes with slopes less than 0.50 percent.
•Pipes with velocities over 6.5 feet per second (fps)(for subcritical flow only).
•Inlet and outlet pipes forming a sharp angle (45 degrees or greater)at junctions.
•Pipe inverts less than three (3)feet deep when entering and leaving junctions.
When using Manning’s equation for the design,each pipe within the system shall be sized and
sloped such that its barrel capacity at normal full flow is equal to or greater than the required
conveyance capacity for the peak runoff of the design storm.A Manning’s “N”of 0.013 shall be
used for all pipes in Table 7-1.Table 7-2 provides the allowable minimum pipe slope and
associated design capacity.
City of Camas —Stormwater Design Standards Manual 7-5
Chapter7:ConveyanceSystemContinuedCityofCamas—StormwaterDesignStandardsManual7-6
Chapter 7:Conveyance System
Continued
Table 7-2:Storm Sewer Pipe Capacity and Minimum Slopes
Inside Pipe
Diameter
(inches)
Minimum Pipe Slope Design Capacity
(cfs)
n=0.013DesignAs-Built
8 0.0039 0.0034 0.70
10 0.0030 0.0025 1.10
12 0.0025 0.0020 1.59
15 0.0020 0.0015 2.50
18 0.0017 0.0012 3.64
24 0.0011 0.0008 6.40
30 0.00088 0.00058 9.88
36 0.00065 0.00045 14.15
42 0.0005 0.00037 19.35
48 0.00045 0.00031 25.29
Allowable Velocities and Slopes
Table 7-3 lists maximum slopes,velocities,and anchor spacing.If velocities exceed 15 feet per
second for the conveyance system design event,anchors shall be provided at bends and
junctions.
Table 7-3:Maximum Pipe Slopes and Velocities
Maximum
Slope
Allowed
Maximum
Velocity
Allowed
Pipe Slope Above Which Pipe
Anchors RequiredTypeofPipeMaterial
20%(1 anchor per 100 L.F.of
pipe)CPE 30%30 fps
Concrete or smooth-lined
CPE 10%(1 anchor per 50 L.F.of pipe)20%30 fps
Ductile Iron*20%(1 anchor per pipe section )None None
40%(1 anchor per 100 L.F.ofHDPE**None Nonepipe)
*Flanged joints required.
**Butt-fused joints required.
CPE =corrugated polyethylene;HDPE =high density polyethylene;L.F.=linear feet;fps =feet per second;
City of Camas —Stormwater Design Standards Manual 7-7
Chapter7:ConveyanceSystemContinuedHigh-densitypolyethylene(HDPE)pipesystemslongerthan100feetshallbeanchoredattheupstreamendiftheslopeexceeds25percent,andthedownstreamendshallbeplacedinaminimumfour(4)footlongsectionofthenextlargerpipesize.Thisslidingsleeveconnectionallowsforthehighthermalexpansion/contractioncoefficientofthepipematerial.7.06OpenChannelsOpenconveyancesshallbedesignedbyoneofthefollowingmethods:•Manning’sequation(foruniformflowdepth,flowvelocity,andconstantchannelcross-section).•Directstepbackwatermethod(usingtheenergyequationforvaryingstreamchannelcross-section).•Standardstepbackwatermethod(usingacomputerprogram).Manning’sequationmaybeusedwhereuniformflowconditionsexist(i.e.,theflowdepthandvelocityremainconstantthroughoutthechannelreach).However,ifaflowrestriction(suchasaculvertorbridge)causesflowstoriseabovenormaldepthwithinachannelreach,abackwateranalysisshallbeperformed,usingeitherthedirectsteporstandardstepbackwatermethods.Directstepmethodsmaybecalculatedusingaspreadsheetorcomputerprogram(seethe2005KingCountySurfaceWaterDesignManualforanexample).Thestandardstepmethodisavariationofthedirectstepmethodandiscommonlyperformedusingacomputerprogrambecauseoftheiterativeprocessinvolved.ThemostcommonprogramusingthestandardstepmethodistheU.S.ArmyCorpsofEngineersHEC-RASprogram.AllowableVelocitiesVelocitiesmustbelowenoughtopreventchannelerosion,basedonthenativesoilcharacteristicsorthecompactedfillmaterial.Forvelocitiesabove5fps,channelsshallhavean8-inch-thickrock-linedbottomandsideslopetothetopoftheroadwayshoulderorshallbestabilizedinafashionacceptabletothecounty.Waterqualityshallnotbedegradedbypassagethroughanopenconveyance.Table7-4providesspecificguidanceonchannelprotectionmeasures.CityofCamas—StormwaterDesignStandardsManual7-8
Chapter 7:Conveyance System
Continued
Table 7-4:Open Conveyance Protection
Velocity at
Design
Flow (fps)
Min.Height Required Above
Water SurfaceProtectionThickness
0-5 Grass lining**N/A 0.5 feet
5-10 Light loose riprap*1 foot 1.5 feet
10-20 Heavy loose riprap*2 feet 1.5 feet
20+Engineered dissipater
required Varies 2.0 feet
*Riprap shall be in accordance with WSDOT/APWA Standard Specifications (WSDOT 2008).
Note:Riprap sizing governed by side slopes on channel,assumed ~3.1.
Bioengineered lining allowed for design flow up to 8 fps.**
Channels with a slope of less than 6 percent and peak velocities of less than 5 fps shall be lined
with vegetation.Other conveyance protection systems may be allowed if submitted through the
appropriate variance process.
Side Slopes and Minimum Freeboard
Channel side slopes shall not exceed 2:1 for undisturbed ground (cuts)as well as for disturbed
ground (embankments).All constructed channels shall be compacted to a minimum 95 percent
compaction,as verified by a modified Proctor test (ASTM D1557 /AASHTO T180).
Channels shall be designed with a minimum freeboard of 0.5 feet when the design flow is 10 cfs
or less and 1 foot when the design discharge is greater than 10 cfs.
7.07 Outfalls
All pipes and culverts that discharge to streams,rivers,ponds,lakes,or other open bodies of
water are designated as outfalls.The design and installation of proper energy dissipaters is
critical to prevent erosion at or downstream of the point of discharge.Energy dissipater systems
include rock splash pads,flow dispersal trenches,and gabion mattresses.
All energy dissipation at outfalls shall be designed for peak flows from a 100-year,24-hour
storm event.Table 7-5 summarizes the rock requirements for rock splash pad outfalls.
City of Camas —Stormwater Design Standards Manual 7-9
Chapter7:ConveyanceSystemContinuedTable7-5:RockRequirementsforRockSplashPadOutfallsDischargevelocity(fps)1ThicknessLengthHeightTypeWidthQuarryspalls1foot8feetor4xdiameter,whicheverisgreaterDiameter+6feetCrown+1foot0-5Lightlooseriprap2feetDiameter+6feetor2xdiameter,whicheverisgreater12feetor4xdiameter,whicheverisgreater5-10Crown+1footAsrequiredHeavylooseriprapAsrequiredAsrequired10-20Crown+1footEngineereddissipaterrequired20+1.RiprapandquarryspallsshallmeetWSDOTspecifications(2008)fortheclassesnoted.Otherenergydissipationsystemsmaybeallowedthroughtheplanreviewprocess.7.08OutfallstoDetentionPondsInvertelevationsforconveyanceoutfallsintodetentionpondsshallbesetatanelevationwherethewatersurfaceelevationinthedetentionpondhasa10percentorsmallerchanceofbeingequaledorexceededinanygivenyear.ThisisdeterminedinWWHMbyperformingastage-frequencyanalysis.Afterperformingthedurationanalysisanddeterminingthefinaldetentionpondsize,gotothe“Analysis”sectionofWWHM,selectthe“STAGEMitigated”dataset,andclickon“runanalysis”.Thestagefrequencysummaryistabulatedintheupperrightcomer.Selectthe10-yearstageandsettheinvertelevationoftheoutfallpipeatorabovethiselevation.7.09ConveyanceSystemEasementsPubliclyOwnedSystemsEasementsshallbeprovidedtotheCityforaccessandmaintenanceofallconveyancesystemswithinthesitethatwillbemaintainedbytheCity(includingstreams,ifused).EasementsshallbeasshownonDetailG6intheCamasDesignStandardsManual.CityofCamas—StormwaterDesignStandardsManual7-10
Chapter 7:Conveyance System
Continued
City of Camas —Stormwater Design Standards Manual 7-11
Chapter 8:Drainage of Roadway Pavements
8.01 General Requirements
Drainage design for roadways shall be in accordance with "Hydraulic Engineering Circular No.
22,Urban Drainage Design Manual"(FHWA and NHI 2001).
The Santa Barbara Urban Hydrograph (SBUH)method or the Rational Method shall be used to
determine peak flow rates for sizing collection systems (catch basins and inlets).
Roadway drainage shall not exceed the capacity of the inlet or produce a flow depth of greater
than 0.12 feet at the edge of the travel lane for the ten-year storm.The travel lane shall remain
open to emergency vehicles and the flow depth of any storm event,up to the 100-year storm
event,will not exceed 0.5 feet.Flooding in parking lots shall not exceed 1.0 feet.
8.02 Catch Basin Locations
Catch basins and inlets are required at the following locations:
At any low point in the roadway or curb returns at intersections.1 .
Where any roadway transitions from a crown section to a shed section to prevent gutter
flow from flowing across the roadway.
Such that a maximum of 400 linear feet of paved street is collected by a single catch
2 .
3.
basin.
Inlets shall be used at intersections to prevent street cross-flow,which could cause
pedestrian or vehicular hazards.It is desirable to intercept 100 percent of any potential street
cross-flow under these conditions.Intersection inlets should be placed on tangent curb
sections near comers.Catch basins and inlets shall be placed so that water will not
accumulate on walking surfaces per ADA guidelines.
In sag vertical curves,where significant ponding may occur,flanking inlets shall be
placed to limit spread on low gradient approaches to the level point.The flanking inlets are
intended to provide relief if the inlet at the low point becomes clogged or if the design spread
is exceeded.
Combination inlets or curb opening inlets shall be used in sag locations.Grate inlets are
not allowed because of their tendency to become clogged.
Combination curb inlets are required on slopes greater than 10 percent or when necessary
to prevent bypass flow from crossing an ADA ramp.Curb ramps and their approaches shall
be designed so that water will not accumulate on walking surfaces per ADA guidelines.
4.
5.
6 .
7.
City of Camas —Stormwater Design Standards Manual 8-1
Chapter8:DrainageofRoadwayPavementsContinued8.03CatchBasinConstructionStandardsAllpipematerials,joints,manholes,andotherproductsassociatedwithconveyancesystemsshallbedesignedandconstructedinaccordancewiththelatestCity-adoptededitionoftheWashingtonStateDepartmentofTransportation’s“StandardSpecificationsforRoad,Bridge,andMunicipalConstruction"(WSDOT).ConveyancesystemsshallbedesignedtomeetthestandardsshownonCityofCamasStormwaterdetails.Publiclateralsshallbeconnectedtoamanholeorotheraccessiblestructure.Catchbasinlateralsshallnotbeconnectedtothestormmainbyteeorwye,unlessspecificallyapprovedbytheCity.Allconnectionstocatchbasinsshallbewatertight.CityofCamas—StormwaterDesignStandardsManual8-2
Chapter 9:Offsite Analysis and Mitigation
9.01 Introduction
This chapter provides requirements for offsite analysis and mitigation.These requirements are in
addition to the minimum requirements.
The offsite analysis is a field investigation of downstream impacts on water quality and surface
water conditions resulting from a development,redevelopment,or other land-disturbing activity.
An offsite analysis must be performed for all development and redevelopment activities that
meet the applicability thresholds identified under Minimum Requirement 7,except those that
meet one of the exemptions identified in Section 9.2 of this chapter.
The information in this chapter is supplementary to Volume I,Section 3.3 of the SMMWW,
Optional Guidance 2:Off Site Analysis and Mitigation.
9.02 Exemptions
A project is exempt from performing an offsite analysis if any of the following three conditions
apply:
1.Based on information provided by the developer and included in the final technical
information report (TIR),the City determines that there is sufficient evidence to conclude
that the project will not have a significant adverse impact on the downstream and\or upstream
drainage system.
The project:
a.Adds less than 2,000 square feet of new impervious surface;and
b.Adds less than 35,000 square feet of new pervious surface;and
c.Does not construct or modify a drainage pipe/ditch that is 12-inches or more in
size/depth or that receives runoff from a drainage pipe/ditch that is 12-inches or more in
size/depth;and
d.Does not contain or lie adjacent to a landslide,steep slope,or erosion hazard area.
The project does not increase the rate,volume,duration,or location of discharges to and
from the project site for storms greater than V the 2-year event (e.g.,where existing
impervious surface is replaced with other impervious surface having similar runoff-
generating characteristics or where pipe/ditch modifications do not change existing discharge
characteristics).
2.
3.
City of Camas —Stormwater Design Standards Manual 9-1
Chapter9:OffsiteAnalysisandMitigationContinued9.03OffsiteAnalysisTheoffsiteanalysisshallextenddownstreamfortheentireflowpath,fromthedevelopmentsitetothereceivingwateroruptoone(1)mile,whicheverisless.Ifthereceivingwateriswithin!4mile,theanalysisshallextendwithinthereceivingwaterto!4milefromthedevelopmentsite.Theanalysisshallextendupstreamtoapointwhereanybackwatereffectscreatedbytheprojectcease.Theapplicantshallusebesteffortstoobtainthesedata,whilerespectingprivateproperty.Existingoffsiteimpactsthatarenotaffectedbytheprojectsitedonotrequiremitigation.However,incaseswheretheprojectsitewasthecauseoftheexistingimpact,itistheresponsibilityoftheapplicanttomitigateforthoseimpacts.Theoffsiteanalysisshoulddocumentanyapparentexistingdeficiencies.QualitativeAnalysisThefollowingsubsectionsdescribecomponents(ortasks)ofthequalitativeanalysis.Task1:MapoftheStudyAreaAsitemapshallbesubmittedshowingpropertylines,topography(ataminimum,aUSGS1:24000quadrangletopographicmap),siteboundaries,studyareaboundaries,downstreamflowpath,andpotential/existingproblems.Task2:ReviewofAllAvailableInformationontheStudyAreaThistaskshallincludeallavailablebasinplans,groundwatermanagementareaplans,drainagestudies,floodplain/floodwayFEMAmaps;wetlandsinventorymaps,criticalareasmaps,streamhabitatreports,salmondistributionreports,andotherapplicablestudies.Task3:FieldInspectionoftheStudyAreaThedesignengineershallphysicallyinspecttheexistingonsiteandoffsitedrainagesystemsofthestudyareaforeachdischargelocationforexistingorpotentialproblemsanddrainagefeatures.Aninitialinspectionandinvestigationshallincludethefollowing:Investigateproblemsreportedorobservedduringthereviewofavailableinformation.Locateexisting/potentialconstrictionsorcapacitydeficienciesinthedrainagesystem.Identifyexisting/potentialfloodingproblems.Identifyexisting/potentialovertopping,scouring,banksloughing,orsedimentation.Identifysignificantdestructionofaquatichabitat(e.g.,siltation,streamincision).Collectqualitativedataonfeaturessuchaslanduse,impervioussurface,topography,1.2.3.4.5.6.CityofCamas—StormwaterDesignStandardsManual9-2
Chapter 9:Offsite Analysis and Mitigation
Continued
soils,presence of streams,and wetlands.
Collect information on pipe sizes,channel characteristics,and drainage structures.
Verify tributary drainage areas identified in Task 1.
Contact City of Camas Public Works,neighboring property owners,and residents about
drainage problems.
Note date and weather at time of inspection.
7.
8 .
9.
10 .
Task 4:Description of the Drainage System and Its Existing and Predicted Problems
For each drainage system component (e.g.,pipes,culverts,bridges,outfalls,ponds,vaults),the
analysis shall include the location,physical description,problems,and field observations.
All existing or potential problems (e.g.,ponding water,erosion)identified in Tasks 2 and 3 shall
be described.The descriptions shall be used to determine whether adequate mitigation can be
identified or whether more detailed quantitative analysis is necessary.The following information
shall be provided for each existing or potential problem:
Magnitude of or damage caused by the problem.
General frequency and duration.
Return frequency of storm or flow when the problem occurs (may require quantitative
analysis).
Water elevation when the problem occurs.
Names and concerns of the parties involved.
Current mitigation of the problem.
Possible cause of the problem.
Whether the project is likely to aggravate the problem or create a new one.
1.
2.
3.
4.
5.
6.
7.
8.
Quantitative Analysis
Upon review of the qualitative analysis,the City of Camas may require a quantitative analysis,
depending on the presence of existing or predicted flooding,erosion,or water quality problems
and on the proposed design of the onsite drainage facilities.The analysis shall repeat Tasks 3 and
4 above,using quantitative field data,including profiles and cross-sections.
The quantitative analysis shall provide information on the severity and frequency of an existing
problem or the likelihood of creating a new problem.It shall evaluate proposed mitigation
intended to avoid aggravation of the existing problem and creation of a new problem.
City of Camas —Stormwater Design Standards Manual 9-3
Chapter9:OffsiteAnalysisandMitigationContinued9.04MitigationTheCitymayrequiremitigationmeasures,dependingontheresultsoftheaboveanalyses.MitigationmeasuresshalltaketheformofacceptableBMPsfordownstreamerosioncontrol.ThepublicationentitledIntegratedStreambankProtectionGuidelines(WDFWetal.2003)shallbeusedtoguidedesignandinstallationofstreambankerosionBMPswithinandadjacenttostreams.WheretheoffsiteanalysisrevealsimpactsotherthanthetypeslistedinTask4above,theCitymayrequiremitigationofatypetobedeterminedbytheDirector.CityofCamas—StormwaterDesignStandardsManual9-4
Chapter 10:Definitions
“Basin”means a topographic region in which all water drains to a common point.
"Basin plan"means a plan that assesses,evaluates,and proposes solutions to existing and
potential future impacts to the beneficial uses of,and the physical,chemical,and biological
properties of waters of the state within a basin.
"Best management practices"or "BMPs"means the schedules of activities,prohibitions of
practices,maintenance procedures,and structural and/or managerial practices approved by the
Washington State Department of Ecology that,when used singly or in combination,control,
prevent or reduce the release of pollutants and other adverse impacts to waters of Washington
State.
“City”means the City of Camas.
"Collection and conveyance system"means the drainage facilities,both natural and man-made,
which collect,contain,and provide for the flow of surface and stormwater to a receiving water or
infiltration facility.The natural elements of the conveyance system include,but are not limited
to,small drainage courses,streams,rivers,lakes,and wetlands.The human-made elements of the
collection and conveyance system include,but are not limited to,gutters,inlets,ditches,pipes,
channels,and retention/detention facilities.
“Continuous Runoff Model”means the most current version of the Western Washington
Hydrology Model (WWHM)or any other equivalent model approved by the Department of
Ecology.
“Contributing drainage area”means the subject property together with the basin contributing
water runoff to the subject property.
“Design storm”means the rainfall from a storm of 24-hour duration.For example,two-year
storm means the two-year,24-hour storm event.
“Development”means land disturbing activities,construction,installation or expansion of a
building or other structure,creation or replacement of impervious surfaces,associated with
residential,commercial,or industrial land use improvements.
"Director"means the director of the City of Camas public works department or designee.
“Downstream analysis”means an analysis of the stormwater impacts of proposed development
activity including the effects on existing upstream and downstream drainage systems and
property,and the ability of the natural drainage ways to pass additional flow created by the
development.
City of Camas —Stormwater Design Standards Manual 10-1
Chapter10:DefinitionsContinued“Drainageproject”meanstheexcavationorconstructionofpipes,culverts,channels,embankmentsorotherflowalteringstructuresinanystream,stormwaterfacility,orwetland."Flowcontrolfacility"meansadrainagefacilitydesignedtomitigatetheimpactsofincreasedsurfaceandstormwaterrunoffflowratesgeneratedbydevelopment.Flowcontrolfacilitiesaredesignedtoeithertoholdwaterforaconsiderablelengthoftimeandthenreleaseitbyevaporation,planttranspiration,and/orinfiltrationintotheground,ortoholdrunoffforashortperiodoftime,releasingittotheconveyancesystematacontrolledrate."Groundwater"meanswaterinasaturatedzoneorstratumbeneaththesurfaceoflandorbelowasurfacewaterbody.“HydrophyticVegetation”meansthesumtotalofmacrophyticplantlifethatoccursinareaswherethefrequencyanddurationofinundationorsoilsaturationproducepermanentlyorperiodicallysaturatedsoilsofsufficientdurationtoexertacontrollinginfluenceontheplantspeciespresent.“Impervioussurface”meansahardsurfaceareawhicheitherpreventsorretardstheentryofwaterintothesoil.Examplesinclude,butarenotlimitedto,structures,walkways,patios,driveways,carports,parkinglotsorstorageareas,concreteorasphaltpaving,gravelroads,packedearthenmaterials,haulroadsandsoilsurfaceareascompactedbyconstructionoperations,andoiledormacadamsurfaces.“InfiltrationFacility”meansadrainagefacilitydesignedtousethehydrologicprocessofsurfaceandstormwaterrunoffsoakingintotheground,commonlyreferredtoasapercolation,todisposeofsurfaceandstormwaterrunoff."Land-disturbingactivity"meansanyactivitythatresultsinamovementofearthorachangeintheexistingsoilcover(bothvegetativeandnonvegetative)and/orexistingsoiltopography.Land-disturbingactivitiesinclude,butarenotlimitedto,clearing,grading,fillingandexcavation.Compactionthatisassociatedwithstabilizationofstructuresandroadconstructionshallalsobeconsideredalanddisturbingactivity.Vegetationmaintenancepracticesarenotconsideredland-disturbingactivity.“LowImpactDevelopment”or“LID”meansastormwatermanagementandlanddevelopmentstrategyappliedattheparcelandsubdivisionscalethatemphasizesconservationanduseofon-sitenaturalfeaturesintegratedwithengineered,small-scalehydrologiccontrolstomorecloselymimicpre-developmenthydrologicfunctions.“LowImpactDevelopmentManual”or“LIDManual”meanstheLowImpactDevelopmentTechnicalGuidanceManualforPugetSounddatedJanuary2005andupdatederratasheetsCityofCamas—StormwaterDesignStandardsManual10-2
Chapter 10:Definitions
Continued
issued or approved by the Director as may be necessary to correct clear and obvious
mathematical and technical errors in manual criteria.
“National Pollutant Discharge Elimination System”or “NPDES”means the national program for
issuing,modifying,revoking,and reissuing,terminating,monitoring and enforcing permits,and
imposing and enforcing pretreatment requirements,under sections 307,402,318,and 405 of the
Federal Clean Water Act,for the discharge of pollutants to surface waters of the state from point
sources.These permits are referred to as NPDES permits and,in Washington State,are
administered by the Washington State Department of Ecology.
“Native vegetation”means vegetation comprised of plant species,other than noxious weeds,that
are indigenous to the Pacific Northwest and which reasonably could have been expected to
naturally occur on the site.Examples include trees such as Douglas Fir,Western Hemlock,
Western Red Cedar,Alder,Big-leaf Maple,and Vine Maple;shrubs such as Willow,Elderberry,
Salmonberry,and Salal;and herbaceous plants such as Sword Fern,Foam Flower,and Fireweed.
“Natural location”means the location and elevation of those channels,swales,and other non-
man-made conveyance systems as defined by the first documented topographic contours existing
for the site,either from maps or photographs.
“New development”means land disturbing activities,including Class IV-general forest practices
that are conversions from timber land to other uses;structural development,including
construction or installation of a building or other structure;creation of impervious surfaces;and
subdivision,short subdivision and binding site plans,as defined and applied in Chapter 58.17
RCW.Projects meeting the definition of redevelopment shall not be considered new
development.
“Peak discharge”means the maximum stormwater runoff rate in cubic feet per second
determined for the design storm.
“Pollution”or “pollutants”means such contamination,or other alteration of the physical,
chemical or biological properties,of any waters of the state,including change in temperature,
taste,color,turbidity,or odor of the waters,or such discharge of any liquid,gaseous,solid,
radioactive,or other substance into any waters of the state as will or is likely to create a nuisance
or render such waters harmful,detrimental or injurious to the public health,safety or welfare,or
to domestic,commercial,industrial,agricultural,recreational,or other legitimate beneficial uses,
or to livestock,wild animals,birds,fish or other aquatic life.
“Pollution-Generating Impervious Surface”or “PGIS”means those impervious surfaces
considered to be a significant source of pollutants in stormwater runoff.Such surfaces include
those which are subject to :vehicular use,industrial activities or storage of erodible or leachable
City of Camas —Stormwater Design Standards Manual 10-3
Chapter10:DefinitionsContinuedmaterials,wastes,orchemicals,andwhichreceivedirectrainfallortherun-onorblow-inofrainfall.Metalroofsarealsoconsideredtobepollution-generatingunlesstheyarecoatedwithaninert,non-leachablematerial(e.g.,baked-onenamelcoating).“Pollution-GeneratingPerviousSurface”or“PGPS”meansanynon-impervioussurfacesubjecttouseofpesticidesandfertilizersorlossofsoil.“Pre-developedcondition”meansthelandcoverthatexistedatasitepriortoDevelopmentorRedevelopment.ForprojectsrequiredtocomplywithMinimumRequirement#7forflowcontrolasdefinedinBGMC18.250.050(G)thepre-developedconditionshallbeassumedtobeaforestedlandcoverunlessreasonable,historicinformationisprovidedthatindicatesthesitewasprairiepriortosettlement.“Projectsite”meansthatportionofaproperty,properties,orrightofwaysubjecttolanddisturbingactivities,newimpervioussurfacesorreplacedimpervioussurfaces.“Redevelopment”means,onasitethatisalreadysubstantiallydeveloped(i.e.,has35%ormoreofexistingimpervioussurfacecoverage),thecreationoradditionofimpervioussurfaces;theexpansionofabuildingfootprintoradditionorreplacementofastructure;structuraldevelopmentincludingconstruction,installationorexpansionofabuildingorotherstructure;replacementofimpervioussurfacethatisnotpartofaroutinemaintenanceactivity;andlanddisturbingactivities.“Regionalfacility”meansafacilitydesignedtotreatandcontrolstormwaterrunofffrommultipleprojectsites."Registeredsoilscientist"meansapersonwhoisqualifiedtoevaluateandinterpretsoilsandsoil-relateddataforthepurposeofunderstandingsoilresourcesastheyaffectenvironmentalqualityandwhoiscertifiedwiththeAmericanRegistryforCertifiedProfessionalsinSoilScience.“Replacedimpervioussurface”meanstheremovalandreplacementofanyexteriorimpervioussurfacesorfoundationforstructures,ortheremovaldowntobaresoilorbasecourseandreplacementforotherimpervioussurfaces.“Roofdownspoutsystem”meansinfiltrationordispersionsystemsthatmeettherequirementsstatedinChapterThreeofVolumeIIIoftheWesternWashingtonManual.“Runoff’meanswaterthattravelsacrossthelandsurfaceanddischargestowaterbodieseitherdirectlyorthroughacollectionandconveyancesystem.CityofCamas—StormwaterDesignStandardsManual10-4
Chapter 10:Definitions
Continued
“Site”means the area defined by the legal boundaries of a parcel or parcels of land that is (are)
subject to development.For road projects,the length of the project site and the right-of-way
boundaries defining the site.
“Source control BMP”means a structure or operation that is intended to prevent pollutants from
coming into contact with stormwater through physical separation of areas or careful management
of activities that are sources of pollutants.The Stormwater Manual separates source control
BMPs into two types.Structural Source Control BMPs are physical,structural,or mechanical
devices,or facilities that are intended to prevent pollutants from entering stormwater.
Operational BMPs are non-structural practices that prevent or reduce pollutants from entering
stormwater.See Volume IV of the 2005 Stormwater Management Manual for Western
Washington for details.
“Stormwater”means runoff during and following precipitation and snowmelt events,including
surface runoff and drainage.
"Stormwater facility"means a constructed component of a stormwater drainage system,designed
and constructed to perform a particular function,or multiple functions.Stormwater facilities
include,but are not limited to:pipes,swales,ditches,open channels,culverts,street gutters,
detention ponds,retention ponds,constructed wetlands,storage basins,infiltration devices,catch
basins,manholes,dry wells,oil/water separators,biofiltration swales,and sediment basins.
“Stormwater Manual”means the 2005 Stormwater Management Manual for Western
Washington,which is the 5-volume technical manual (Publication Nos.05-10-29 through 05-10-
33)prepared by the Washington State Department of Ecology for use by local governments that
contains BMPs to prevent,control,or treat pollution in stormwater.
“Stormwater site plan”means the comprehensive report containing all of the technical
information and analysis necessary for regulatory agencies to evaluate a proposed new
development or redevelopment project for compliance with stormwater requirements.Contents
of the Stormwater Site Plan will vary with the type and size of the project,and individual site
characteristics.It includes a Construction Stormwater Pollution Prevention Plan (Construction
SWPPP)that must be submitted to and approved by the Washington Department of Ecology,and
a Permanent Stormwater Control Plan (PSC Plan).Guidance on preparing a Stormwater Site
Plan is contained in the Stormwater Manual,Chapter 3 of Volume I.Modified submittals of
stormwater site plans are permitted as specified in the General Requirements.
“Threshold Discharge Area”means an onsite area draining to a single natural discharge location
or multiple natural discharge locations that combine within one-quarter mile downstream as
determined by the shortest flow path.
City of Camas —Stormwater Design Standards Manual 10-5
Chapter10:DefinitionsContinued“TotalMaximumDailyLoad”or“TMDL”meansawatercleanupplan.ATMDLisacalculationofthemaximumamountofapollutantthatawaterbodycanreceiveandstillmeetwaterqualitystandards,andanallocationofthatamounttothepollutant’ssources.ATMDListhesumoftheallowableloadsofasinglepollutantfromallcontributingpointandnonpointsources.Thecalculationmustincludeamarginofsafetytoensurethatthewaterbodycanbeusedforthepurposesthestatehasdesignated.Thecalculationmustalsoaccountforseasonablevariationinwaterquality.Waterqualitystandardsaresetbystates,territories,andtribes.Theyidentifytheusesforeachwaterbody,forexample,drinkingwatersupply,contactrecreation(swimming),andaquaticlifesupport(fishing),andthescientificcriteriatosupportthatuse.TheCleanWaterAct,section303,establishesthewaterqualitystandardsandTMDLprograms."TreatmentBMP"meansaBMPthatisintendedtoremovepollutantsfromstormwater.AfewexamplesoftreatmentBMPsinclude,butarenotlimitedto,wetponds,oil/waterseparators,biofiltrationswales,andconstructedwetlands.“UndergroundInjectionControl”or“UIC”wellmeansamanmadesubsurfacefluiddistributionsystemdesignedtodischargefluidsintotheground,consistingofanassemblageofperforatedpipes,draintiles,orothersimilarmechanisms,oradugholethatisdeeperthanthelargestsurfacedimension.Subsurfaceinfiltrationsystemsincludedrywells,pipeorfrenchdrains,drainfields,andothersimilardevices.“Wetlands”meansthoseareasdefinedaswetlandsunderChapter16.53CMC.AnytermsnotdefinedinthischaptershallbeasdefinedintheStormwaterManual.CityofCamas—StormwaterDesignStandardsManual10-6
Appendix A:Hydrology Data
City of Camas —Stormwater Design Standards Manual A-1
CityofCamas—StormwaterDesignStandardsManualA-2
Table A-1:Sheet flow “n”Values and “k”Values Used in Time Calculations for Hydrographs
“n,”Sheet Flow Equation Manning's Values (for the initial 300 feet of travel)n *
Smooth surfaces (concrete,asphalt,gravel,or bare hand packed soil)
Fallow fields or loose soil surface (no residue)
Cultivated soil with residue cover (s<0.20 ft/ft)
Cultivated soils with residue cover (s>0.20 ft/ft)
Short prairie grass and lawns
Dense grasses
Bermuda grass
Range (natural)
Woods or forest with light underbrush
Woods or forest with dense underbrush
0.011
0.05
0.06
0.17
0.15
0.24
0.41
0.13
0.40
0.80
*Manning values for sheet flow only,from Overton and Meadows 1976 (See TR-55,1986)
“k”Values Used in Travel Time/Time of Concentration Calculations
Shallow Concentrated Flow (After the initial 300 feet of sheet flow,R =0.1 )ks
1.Forest with heavy ground litter and meadows (n =0.10)
2.Brushy ground with some trees (n =0.060)
3.Fallow or minimum tillage cultivation (n =0.040)
4.High grass (n =0.035 )
5.Short grass,pasture and lawns (n =0.030 )
6 .Nearly bare ground (n =0.25)
7.Paved and gravel areas (n =0.012)
3
5
8
9
11
13
27
Channel Flow (intermittent)(At the beginning of visible channels R =0.2)k
1.Forested swale with heavy ground litter (n =0.10)
2 .Forested drainage course/ravine with defined channel bed (n =0.050)
3.Rock-lined waterway (n =0.035)
4.Grassed waterway (n =0.030)
5.Earth-lined waterway (n =0.025)
6.CMP pipe (n =0.024)
7.Concrete pipe (0.012 )
8.Other waterways and pipe
5
10
15
17
20
21
42
0.508/n
Channel Flow (Continuous stream.R =0.4)kc
9.Meandering stream with some pools (n =0.040)
10.Rock-lined stream (n =0.035)
11.Grass-lined stream (n =0.030)
12.Other Stream,man-made channels and pipe
20
23
27
0.807/n
Reference:DOE Stormwater Management Manual for the Puget Sound Basin,February 1992.
City of Camas —Stormwater Design Standards Manual A-3
TableA-2:Type1ARainfallDistributionCumulativePercentRainfallCumulativePercentRainfallTime(minutes)PercentRainfallTime(minutes)PercentRainfallTime(hours)Time(hours)1.328.10.00.07.04200.001.329.40.40.44301031.20.84401.8200.41.833.0300.41.24501.64603.436.4400.441.82.04705.4500.42.744.52.48.04801.0600.41.846.32.8490700.43.25001.347.7800.41.349.03.6510900.41.350.40.44.05201005300.951.21100.54.50.952.15.09.05402.01200.553.05500.91300.55.50.953.96.05601400.50.954.86.55701500.50.955.67.05801600.55900.956.50.67.617057.48.210.06000.93.01800.658.38.86100.91900.659.26200.92000.69.46300.960.02100.610.00.960.910.66402200.60.761.611.36502300.76600.762.412.011.02400.74.00.763.112.76702500.763.813.46800.72600.76900.764.514.12700.765.214.87000.72800.766.07100.72900.815.666.712.07200.73000.816.45.00.767.40.817.37303100.768.118.17403200.868.818.97500.73300.869.619.77600.73400.80.670.120.77703501.070.713.07800.63601.021.66.071.322.67900.63701.071.80.61.023.58003808100.672.41.024.539073.025.48200.64001.073.626.88300.64101.3CityofCamas—StormwaterDesignStandardsManualA-4
Table A-2:Type IA Rainfall Distribution (continued)
Cumulative
Percent
Rainfall
Cumulative
Percent
Rainfall
Time
(hours)
Time
(minutes)
Percent
Rainfall
Time
(hours)
Time
(minutes)
Percent
Rainfall
14.0 840 0.6 74.1 21.0 1260.0 0.4 92.8
850 0.6 74.7 1270.0 0.4 93.2
860 0.6 75.3 1280.0 0.4 93.6
870 0.6 75.8 1290.0 0.4 94.0
880 0.6 76.4 1300.0 0.4 94.4
890 0.5 76.9 1310.0 0.4 94.8
15.0 900 0.5 77.4 22.0 1320.0 0.4 95.2
910 0.5 77.9 1330.0 0.4 95.6
920 0.5 78.4 1340.0 0.4 96.0
930 0.5 78.9 1350.0 0.4 96.4
940 0.5 79.4 1360.0 0.4 96.8
950 0.5 79.9 1370.0 0.4 97.2
16.0 960 0.5 80.4 23.0 1380.0 0.4 97.6
970 0.5 80.9 1390.0 0.4 98.0
980 0.5 81.4 1400.0 0.4 98.4
990 0.5 81.9 1410.0 0.4 98.8
1000 0.5 82.4 1420.0 0.4 99.2
1010 0.4 82.8 1430.0 0.4 99.6
17.0 1020 0.4 83.2 24.0 1440.0 0.4 100.0
1030 0.4 83.6
1040 0.4 84.0
1050 0.4 84.4
1060 0.4 84.8
1070 0.4 85.2
18.0 1080 0.4 85.6
1090 0.4 86.0
1100 0.4 86.4
1110 0.4 86.8
1120 0.4 87.2
1130 0.4 87.6
19.0 1140 0.4 88.0
1150 0.4 88.4
1160 0.4 88.8
1170 0.4 89.2
1180 0.4 89.6
1190 0.4 90.0
20.0 1200 0.4 90.4
1210 0.4 90.8
1220 0.4 91.2
1230 0.4 91.6
1240 0.4 92.0
1250 0.4 92.4
City of Camas —Stormwater Design Standards Manual A-5
CityofCamas—StormwaterDesignStandardsManualA-6
FigureA-1:TypeIARainfallDistributioni6.0oMHW!5.0U4>ua.4-*o4.0-ioICui—#a.3.0-!;!2.0!1.0i!\\l0.0Time{minutes}0200400800100012001400!CityofCamas—StormwaterDesignStandardsManualA-7
CityofCamas—StormwaterDesignStandardsManualA-8a.
Figure A-2:2-Year,24-Hour Clark County Isopluvial Map
City of Camas —Stormwater Design Standards Manual
FigureA-3:10-Year,24-HourClarkCountyIsopluvialMapCityofCamas—StormwaterDesignStandardsManualA-10
Figure A-4:25-Year,24-Hour Clark County Isopluvial Map
ii
v ’8.0”
'ft
A-11CityofCamas—Stormwater Design Standards Manual
FigureA-5:100-Year,24-HourClarkCountyIsopluvialMapCityofCamas—StormwaterDesignStandardsManual
Table A-3:Runoff Curve Numbers
LAND USE DESCRIPTION CURVE NUMBERS BY
HYDROLOGIC SOIL GROUP
CAB D
Cultivated land (1):winter condition 86 91 94 95
Mountain open areas:
grasslands
low growing brush and 74 82 89 92
Meadow or pastures:65 78 85 89
Wood or forest land:undisturbed 42 64 76 81
Wood or forest land:young second growth or brush 55 72 81 86
Orchard :with cover crop 88 92 9481
Open spaces,lawns,parks,golf courses,cemeteries,landscaping:
Good condition:
area
grass cover on over 75%of the 68 80 86 90
77 85 90 92
Fair condition:grass cover on 50-75%of the area
Gravel roads &parking lots:76 85 89 91
Dirt roads &parking lots:72 82 87 89
Impervious surfaces,pavement,roofs etc.98 98 98 98
Open water bodies:100 100 100 100
Single family residential (2 ):
Dwelling Unit/Gross Acre
1.0 DU/GA
1.5 DU/GA
2.0 DU/GA
2.5 DU/GA
3.0 DU/GA
3.5 DU/GA
4.0 DU/GA
4.5 DU/GA
5.0 DU/GA
5.5 DU/GA
6.0 DU/GA
6.5 DU/GA
7.0 DU/GA
%Impervious (3)Separate curve number shall be
selected for pervious &impervious
portions of the site or basin
15
20
25
30
34
38
42
46
48
50
52
54
56
PUD’s,condos,apartments,
commercial businesses &
industrial areas
%impervious
must be
computed
City of Camas —Stormwater Design Standards Manual A-13
TableA-4:HydrologicSoilsGroupsMapSymbolSoilNameHydrologicGroupiiiisiBpBBEARPRARIEBBBpCBEARPRARIEBCnBCINEBARBCnDCINEBARBCnECINEBARCINEBARBCnGBCINEBARCrEBCrGCINEBARCISPUSBCsFCLOQUATOBCtADCvACOVECOVEDCwACDoBDOLLARIn-situFILLLANDFnCGEEGeBCGEEGeDGEECGeECGEEGeFDGuBGUMBOOTHESSONCHcBCHELLSONHcDCHESSONHcECHESSONHcFCHESSONHgBCHESSONHgDCHESSONHhEBHILLSBOROHIABHILLSBOROHJBBHILLSBOROHICBHILLSBOROHIDBHILLSBOROHIEBHILLSBOROHIFBHILLSBOROHoABHILLSBOROHoBBHILLSBOROHoCBHILLSBOROHoDBHILLSBOROHoEBHILLSBOROHoGBHILLSBOROHsBCityofCamas—StormwaterDesignStandardsManualA-14
Table A-4:Hydrologic Soils Groups (cont.)
Map Symbol Soil Name Hydrologic Group
HtA HOCKINSON D
HuB HOCKINSON D
HvA HOCKINSON D
KeC KINNEY B
KeE KINNEY B
KeF KINNEY B
KnF KINNEY B
LaE LARCHMOUNT B
LaG LARCHMOUNT B
LcG LARCHMOUNT B
LeB LAUREN B
LgB LAUREN B
LgD LAUREN B
LgF BLAUREN
LIB BLAUREN
LrC LAUREN C
LrF CLAUREN
McB McBEE C
MeA CMcBEE
MIA CMcBEE
MnA MINNIECE D
MnD MINNIECE D
MoA MINNIECE VARIANT D
MsB MOSSYROCK B
NbA BNEWBERG
NbB NEWBERG B
OdB ODNE D
OeD OLEQUA B
OeE OLEQUA B
OeF BOLEQUA
OhD OLEQUA VARIANT C
OhF OLEQUA VARIANT C
OIB OLYMPIC B
OID OLYMPIC B
OIE OLYMPIC B
OIF OLYMPIC B
OmE OLYMPIC B
OmF OLYMPIC B
OpC OLYMPIC VARIANT C
City of Camas —Stormwater Design Standards Manual A-15
TableA-4:HydrologicSoilsGroups(cont.)HydrologicGroupSoilNamemMapSymbolmmmOLYMPICVARIANTOpECOLYMPICVARIANTCOpGOLYMPICVARIANTCOrCPhBPILCHUCKCPOWELLCPoBPOWELLCPoDPOWELLCPoEPuAPITYAT,TUPBRIVERWASHDRaRIVERWASHDRcROCKLANDRkDROUGHBROKENLANDARoSALKUMBSaCSARADSIBSARADSIDSARADSIFSAUVIEBSmASAUVIEBSmBSAUVIESnADSAUVIEBSpBSEMIAHMOOCSrSEMIAHMOOVARIANTDSuBSvASIFTONTLATISCHDVADERBVaBVADERBVaCWASHOUGALWaABWASHOUGALBWgBWASHOUGALBWgEWASHOUGALBWhFWINDRIVERVARIANTBWnBWINDRIVERVARIANTBWnDWINDRIVERVARIANTBWnGWINDRIVERVARIANTBWrBWINDRIVERVARIANTBWrFYACOLTBYaAYACOLTBYaCYACOLTBYcBCityofCamas—StormwaterDesignStandardsManualA-16