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CIVIL ENGINEERING SOLUTIONS, INC. 1325 Howe Avenue Suite 202 Sacramento, CA 95825 The status of this report is PRELIMINARY unless the appropriate signature is provided to the left. Signature will not be provided until review is complete. © 2005- Civil Solutions STORMWATER MANAGEMENT GUIDE STORMWATER QUALITY BEST MANAGEMENT PRACTICES Tehama County, California A Guide to Be Used for Designing Permanent Phase II Stormwater Quality Elements of the Project OCTOBER 2005 Prepared By: JOB # 2005.05
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Page 1: STORMWATER MANAGEMENT GUIDE STORMWATER … BMP Design... · APPENDIX A: Managing Mosquitoes in Stormwater Treatment Devices ... Bioretention Vortex Separator ... Stormwater BMP Design

CIVIL ENGINEERINGSOLUTIONS, INC.

1325 Howe Avenue Suite 202Sacramento, CA 95825

The status of this report isPRELIMINARY unless theappropriate signature is provided tothe left. Signature will not beprovided until review is complete.

© 2005- Civil Solutions

STORMWATER MANAGEMENT GUIDE

STORMWATER QUALITY BEST MANAGEMENT PRACTICES

Tehama County, California

A Guide to Be Used for Designing Permanent Phase II Stormwater Quality Elements of the Project

OCTOBER 2005

Prepared By:

JOB # 2005.05

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TABLE OF CONTENTS

SECTION 1 INTRODUCTION ............................................................................................................ 11.1 BACKGROUND ............................................................................................................... 11.2 NPDES PHASE II .............................................................................................................. 21.3 DOCUMENT ORGANIZATION ...................................................................................... 4

SECTION 2 APPLICABLE STANDARDS AND METHODS OF DESIGN .................................. 52.1 POLLUTANT CONSTITUENTS OF CONCERN ........................................................... 52.2 POLLUTION REDUCTION STRATEGIES .................................................................... 5

2.2.1 Reducing Runoff That Requires Treatment ........................................................... 62.2.2 Controlling Sources of Pollutants .......................................................................... 62.2.3 Treatment Control BMPs ....................................................................................... 7

2.3 EROSION .......................................................................................................................... 82.3.1 Sheet Erosion ......................................................................................................... 82.3.2 Gully Erosion and Channel Erosion ...................................................................... 82.3.3 Policies and Design Criteria .................................................................................. 9

2.3.3.1 Reservoir Trap Efficiency .......................................................................... 92.3.3.2 Particle Size Distribution ........................................................................... 92.3.3.3 Minimum Basin Storage ............................................................................ 92.3.3.4 Storage Area and Depth of Ponding .......................................................... 92.3.3.5 Sediment Delivery Ratio and Total Sediment Yield ................................. 92.3.3.6 Basin Clean Out Interval ............................................................................ 9

2.4 VOLUMETRIC DESIGN CRITERIA ............................................................................ 112.4.1 Design Volume Percentile ................................................................................... 112.4.2 Volumetric Design Criteria .................................................................................. 122.4.3 Maintenance Storage Reserve .............................................................................. 132.4.4 Example Outlet Design ........................................................................................ 14

SECTION 3 SOURCE CONTROL BMPs ........................................................................................ 153.1 QUALITATIVE BMPs .................................................................................................... 153.2 SOURCE CONTROL BMPs ........................................................................................... 153.3 ADDITIONAL SOURCE CONTROL MEASURES ...................................................... 16

SECTION 4 CHOOSING AND DESIGNING TREATMENT CONTROL BMPs ....................... 174.1 GENERAL DESIGN CRITERIA/INFORMATION NEEDS ......................................... 18

4.1.1 Soils ..................................................................................................................... 184.1.2 Climate ................................................................................................................. 194.1.3 Topography .......................................................................................................... 204.1.4 Site Design ........................................................................................................... 20

4.2 VOLUME BASED DESIGN ........................................................................................... 214.3 FLOW-BASED BMP DESIGN ....................................................................................... 22

4.3.1 General Flow-Based Design Criteria ................................................................... 224.4 DESIGN OF SPECIFIC BMPS ....................................................................................... 23

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SECTION 5 BMP FACT SHEETS .................................................................................................... 35SECTION 5.1 SOURCE CONTROL BMP FACT SHEETS .......................................................... 36

SECTION 5.2 VOLUMETRIC BMP FACT SHEETS .................................................................... 37

SECTION 5.3 FLOW BASED BMP FACT SHEETS ...................................................................... 38

LIST OF TABLES

Table 1 - Acronyms and Abbreviations Used in this GuideTable 2 - Treatment Control BMPSTable 3 - Targeted Water Quality ConstituentsTable 4 - Source Control BMPsTable 5 - Sun City Tehama SoilsTable 6 - Volumetric BMPs Specified for the Sun City Tehama ProjectTable 7 - Flow-based BMPs Specified for the Sun City Tehama Project

LIST OF FIGURES

Figure 1 - 48-hour Percentage of Runoff Capture vs Unit Basin StorageFigure 2 - Isohyetal Map of Tehama CountyFigure 3 - Climate Data for Tehama County from Rusle2 DatabaseFigure 4 - Cumulative Frequency Hourly Rainfall Intensity

APPENDICES

APPENDIX A: Managing Mosquitoes in Stormwater Treatment Devices

APPENDIX B: Managing Mosquitoes in Surface-Flow Constructed Treatment Wetlands

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TABLE 1

ACRONYMS and ABBREVIATIONS USED IN THIS GUIDE

Acronym orAbbreviation

Reference

CS Civil Engineering Solutions, Inc. (a.k.a. Civil Solutions)

GW GW Consulting Engineers

TC Tehama County

CASQA California Stormwater Quality Association

NPDES National Pollutant Discharge Elimination System

SWQ Storm Water Quality

BMP Best Management Practice

WOUS Waters of the United States

MUSLE Modified Universal Soil Loss Equation

MS4 Municipally (Owned) Separate Storm Sewer Systems

WQV Water Quality Volume

The Handbook California Stormwater BMP Handbook (CASQA, 2002)

The Guide This document, A Guide to Be Used for Designing PermanentPhase II Stormwater Quality Elements (Civil Solutions, 2004)

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SECTION 1INTRODUCTION

Civil Solutions has prepared this document to provide guidance in choosing and designing Phase IIcompliant permanent BMPS for the proposed Sun City Tehama development.

There are two types of treatment BMPS distinguished by the hydrologic criteria used to design them;volumetric design and flow-based design. Examples of each are given in Table 2 below.

TABLE 2TREATMENT CONTROL BMPS

Volumetric Criteria Flow-Based CriteriaWet Ponds Vegetated SwaleDry Extended Detention Vegetated Buffer StripConstructed Wetlands Multiple SystemsBioretention Vortex SeparatorWater Quality Inlet WQ Vault/SeparatorsMultiple System Biofilters

1.1 BACKGROUND

In 1992 the “Stormwater Task Force” produced four handbooks of stormwater quality Best ManagementPractices (BMPS); “New Development and Redevelopment”, “Construction”, “Industrial andCommercial” and “Municipal”. Subsequently, the group reformed under the name “CaliforniaStormwater Quality Association” (CASQA) and in 2003 released updated versions of the handbooks. The updated handbooks provided additional guidance regarding design methodology andimplementation of BMPS. The handbooks were also brought up to speed with the current state of the artin BMP devices, and NPDES Phase II criteria. The CASQA New Development and RedevelopmentHandbook will be referred to in this report. The Handbook defines a Best Management Practice as,

“any program, technology, process, siting criteria, operating method, measure or device,which controls, prevents, removes or reduces pollution.”

Although not officially a State agency, the Stormwater Task Force was comprised of representativesfrom State agencies, local agencies and the private sector, and the State of California recognized thehandbooks it published as compliant with the State’s requirements for Phase II BMPS.

Some project areas which are to remain undisturbed following construction will be bypassed through theproject without treatment (“source separation” BMP). Most permanent discharge locations will includetreatment upstream of the connection point to a Water of the State, swale, or other water way.

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1.2 NPDES PHASE II

There are three significant differences between the Phase I and Phase II requirements that apply to thisproject:

1. Re-suspension of Constituents. The Phase II handbooks make it clear that runoff events inexcess of the stormwater quality (SWQ) design runoff event should not result in the re-suspension of constituents previously collected within a BMP. Therefore, it will be necessaryto demonstrate that for all storm events (through the 100-year event) re-suspension will notoccur, or high flow bypass facilities will be required. At this time, it will be assumed that re-suspension occurs when the average flow velocity exceeds the “scour velocity” (as definedbelow). In addition, maintenance practices will be required to remove from grassy swales,biofiltration facilities, etc., any dead vegetation, cut grasses or other detritus that could bemobilized by subsequent runoff events.

Determination of the “scour velocity” will be done by one of two methods:

a) The CASQA methodology provides some guidance for evaluating potential sheet, gullyand channel erosion, and is most appropriately used for sizing rip rap. CASQA Table 8-2lists maximum “Permissible Velocities” for earth lined sections and guidance fordetermining when channel lining is indicated.

b) This criteria comes from the “Erosion and Sediment Control Handbook” by Goldman,Jackson and Bursztynsky. Section 8.2f of this manual notes that the SWQ facilityresuspension issue is very similar to the problem which can occur in grit-settlingchambers at sewage treatment plants. The equation that describes that process is:

Vs = (1.486 / n ) * r(1/6) * [ k * (Sg - 1) * (d / 304.8) ] (½)

Where, Vs is the “horizontal water velocity that would just resuspend sediment (ft/sec)”

n = Manning’s ‘n’ value.r = Hydraulic Radius (ft)k = Shape Coefficient (0.04 for granular materials)Sg = Specific Gravity (2.65 for mineral particles)d = design particle diameter (mm), 0.02 for most sediment basins.

Simplifying the equation with the suggested values :

Vs = 0.0031 * [ r(1/6) / n ] for the 0.02 mm particle size (20 micron).

Solving this equation shows that even velocities of less than 1 fps have the potential toresuspend sediments. Values range from 0.13 fps for a r=4 and n=0.03 (deep and smooth)basin to 0.017 for r=0.25, n=0.10 (shallow and rough) basin. Probably the biggest impact inthe solution of this equation is the selection of a targeted particle size to not be re-suspended.

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2. Treatment of the Entire Tributary Areas. It has been clarified in Section 5.5.1 of the updatedHandbook that in order for a BMP to function properly, it must be designed for the entirecontributing flow area, including offsite areas. Some previous methodologies may have onlyconsidered treating runoff from the newly created impervious surfaces within the contributingwatershed. Where conditions permit, clean runoff from some undisturbed areas of this projectmay be passed through separate drainage ways and not mixed with untreated runoff fromdeveloped areas. This is known as “source separation”, and allows BMPs to be sized for onlythe developed areas.

3. No Treatment in WOUS. The updated Handbook emphasizes that the intent of the CleanWater Act is to reduce the potential for discharging polluted runoff to the protected waters ofthe United States (WOUS). While the definition of WOUS seems to be evolving, it generallyincludes wetlands, vernal pools, year round flow locations, areas with special vegetation, andsome swales and channels. Civil Solutions interprets this to mean that when stormwater runofffrom the proposed development flows to identified WOUS, BMPs are to be installed upstreamof the WOUS.

While it may seem that the Phase II updates are additional requirements, the additional informationprovided in the Handbook also allows for more flexibility in design, as we will present in Appendix A,and throughout this guide.

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1.3 DOCUMENT ORGANIZATION

This guide divided into four sections and appendices:

Section 1: This introductory information

Section 2: The standards and methodologies for choosing and sizing BMPs for the proposed SunCity Tehama Development site.

Section 3: Source Control BMPs.

Section 4: Descriptions of the BMPs which are applicable and likely to be used on this project. Calculation sheets and summary design guidelines are included for each BMP type,where appropriate.

Section 5: The FACT sheets from the CASQA Handbook for the BMPs described in Section 3 andspecified for this project.

Appendix A: Revised Universal Soil Loss Equation Version 2 (RUSLE2)

Appendix B: Excerpts from the Sun City Tehama Covenants, Conditions and Restrictions andEasements That Help Protect Water Quality

Appendix C: “Lawn Care for the Homeowners of the Sun City Tehama Community”

Appendix D: “The Integrated Golf Course Management Plan and Chemical Application ManagementPlan for the Heritage Ridge Golf Course on Sun City Tehama”

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SECTION 2APPLICABLE STANDARDS AND METHODS OF DESIGN

2.1 POLLUTANT CONSTITUENTS OF CONCERN

While there is no official documentation, there is general agreement that natural conditions and historicactivities in the watershed have led to an excess of fine sediments and total suspended solids (TSS) inAuburn Ravine downstream of the proposed project site. These constituents of degraded water qualityare a primary focus of the BMPs proposed for Sun City Tehama.

Other water quality constituents introduced by residential construction include those associated withroadways and automobiles, lawns, gardens and golf courses, and other normal human activities. TheCASQA Handbook identifies targeted constituents and rate the qualitative removal efficiency for eachBMP. Table 3 lists targeted constituents identified by CASQA. The table of relative removal efficiencyis included with the fact sheet for each BMP in Section 4.

TABLE 3TARGETED WATER QUALITY CONSTITUENTS

Targeted Constituents

Sediment

Nutrients

Trash

Metals

Bacteria

Oil and Grease

Organic

2.2 POLLUTION REDUCTION STRATEGIES

Projects similar to the Sun City Tehama project have typically been conditioned for SWQ improvementssimilar to the following items:

“The (drainage) report shall address storm drainage during construction and thereafterand shall propose “Best Management Practice (BMP) measures to reduce erosion, waterquality degradation, etc. Said BMP measures for this project shall include: Minimizingdrainage concentration from impervious surfaces, construction management techniques,and erosion protection at culvert outfall locations.”

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“Storm drainage from on-site impervious surfaces shall be collected an routed throughspecially designed catch basins, vaults, filters, etc. for entrapment of sediment, debrisand oils/greases as approved by DPW.”

Section 2.3.4 of the CASQA Handbook indicates there are three strategies by which “Pollutants ofConcern” can be reduced:

1. Reducing runoff that needs to be captured, infiltrated or treated.

2. Controlling sources of pollutants

3. Implementation of treatment control BMPs

The following sections describe the measures being taken by the proposed Sun City Tehama project toimplement these strategies and comply with the conditions of approval.

2.2.1 Reducing Runoff That Requires Treatment

Methods that will be employed to reduce the amount of runoff that requires treatment include designstrategies that:

• Reduce the amount of impervious surface. The use of porous paving for private drives,walkways, patios etc. will be encouraged.

• Disconnect impervious surfaces from the stormdrain. Directly connected impervious surfacesare those that drain directly to the stormdrain system through pipes, curb and gutter streets, orconcrete lined channels. Runoff from relatively clean areas, such as rooftops, can bedisconnected from the stormdrain system by directing it over pervious areas, such as lawns andother landscaping, prior to collection in the treatment system. This greatly reduces the relativeincrease in runoff and the amount of runoff that must be treated.

• Provide separate flow pathways for runoff from the developed portion of the project and naturalareas in the same watershed. Treat the runoff from the developed area before combining it withflow from the natural areas, rather than treating the combined runoff further downstream. Thisapproach, called “source separation”.

2.2.2 Controlling Sources of Pollutants

Public education on sources of water pollution that can be easily controlled by responsible individualbehavior, restrictions on activities that are inappropriate for residential areas, and proper management ofpublic and private facilities, such as the golf course, are effective means of controlling the sources ofwater pollution. The Sun City Tehama project has taken several steps to accomplish these goals,including developing an education program for homeowners, landscape professionals and golf courseoperators. The recommendations for homeowners and landscape professionals are summarized below.

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Excess nutrients and herbicides are some of the most damaging pollutants in natural waterways and themost difficult to remove with BMPs, therefore:

• Use all fertilizers and pesticides in the amounts and for the purposes specified by the product’smanufacturer. Read the label and head the warnings. Don’t over use. More is not better.

• Be aware of the weather conditions. Don’t apply spray or broadcast fertilizers or herbicideswhen wind is high or rain is expected that day.

• Be aware where you apply. Keep lawn care products on the lawn and not on the sidewalk,walkways or streets. Be extra careful when applying lawn care products near natural areas.

• Don’t over water when applying lawn care products. If water is running from the lawn into thestreet or yard drainage system it is carrying some of the lawn care products you just applied(and paid for) with it.

• Mechanical controls are good alternatives. However, mechanical controls can also be overdone,breaking up soil and exposing it to erosion at the next watering. Over watering can be a realproblem after mechanical weed removal as well.

• Granular products are more stable, easier to apply, less likely to go where they are not wantedand easier to clean up than powders or liquids.

• Organic approaches can be much safer for the water and environment, but can also be a problemis not handled correctly.

• Clean up spills of lawn care products and dispose of properly, don’t wash spilled chemicalsdown the drain or into the street.

• Dispose of surplus liquid chemicals properly, don’t pour them down the drain!

• Don’t put lawn and garden clippings in the street, “over the fence” into natural areas or downdrainage channel banks, etc. Mulch them or dispose of them as “green waste” wheneverpossible.

2.2.3 Treatment Control BMPs

Section 4 is devoted to Treatment Control BMPs

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1George R. Foster, Research Hydraulic Engineer (retired) National Sedimentation Laboratory USDA-AgriculturalResearch Service Oxford, Mississippi Prepared for USDA-Agricultural Research Service Washington, D.C. July 1, 2003

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2.3 EROSION

2.3.1 Sheet Erosion

Sheet erosion is the relatively uniform loss of soil over a large area, and is directly related to the generalcharacteristics of the soil, the type of ground cover, and specific “management” measures taken tominimize erosion. Historically, the Universal Soil Loss Equation (USLE) was used to estimate sheeterosion. However, the USLE was created for agricultural applications, and is of limited use in estimatingsoil loss from urbanizing areas. The Revised Universal Soil Loss Equation, Version 2 (RUSLE2)1 hasbeen developed by the USDA to,

“...evaluate potential erosion rates at specific sites, guide conservation and erosioncontrol planning, inventory erosion rates over large geographic areas, and estimatesediment production on upland areas that might become sediment yield in watersheds.RUSLE2 is land use independent. It can be used on cropland, pastureland, rangeland,disturbed forestland, construction sites, mined land, reclaimed land, landfills, militarylands, and other areas where mineral soil is exposed to raindrop impact and surfaceoverland flow produced by rainfall intensity exceeding infiltration rate (Hortonianoverland flow).”

The RUSLE2 program is relatively easy to use and can be obtained free from the USDA. The RUSLE2Database contains information for Tehama County Soils and climate. RUSLE2 can be used to comparethe impact of different grading methods and erosion control practices during construction, to evaluatechanges in sediment yield over time as disturbed soils recover, and to compare the erosion potential ofdifferent soils and different slopes. More information on RUSLE2, including how to obtain RUSLE2free from the USDA is available in Appendix A. Civil Solutions recommends using RUSLE2 tocalculate sediment removal from a watershed.

2.3.2 Gully Erosion and Channel Erosion

The potential for gully erosion is related to soil characteristics and the slope of the terrain. Gully erosioncan produce very large quantities of soil loss (and therefore sediment supply) from a relatively smallarea due to the three dimensional characteristics of a gully. Deep gullies can form quickly, progressrapidly, and are extremely difficult to remediate.

Channel erosion potential is also related to the soil characteristics of the channel banks and bed,steepness of the channel and extent of changes in the watershed hydrologic characteristics. The potentialfor gully and channel erosion on the site is evaluated in more detail in the project drainage study.

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2.3.3 Policies and Design Criteria

Tehama County currently has no specific policies or design criteria for sediment retention structures,including trap efficiency, particle size, minimum basin storage capacity, storage area and depth ofponding, sediment delivery ratio and clean out interval. The following recommendations are based onCASQA, Phase II MS4 criteria and other local jurisdictions.

This guide suggests using RUSLE2 to estimate average annual sediment yield for proposed sedimentbasin locations. This method was used to determine the reserve capacity required to obtain satisfactory“cleanout intervals”. However, the requirements listed below related to settling time, particle capturesize and trap efficiencies may be superceded in this guide by Phase II design methodologies as indicatedin the 2003 CASQA Handbook.

2.3.3.1 Reservoir Trap Efficiency

The percentage of the sediment yield which should be captured with a BMP. Phase II MS4Attachment 4 criteria specifies 80% TSS removal rates.

2.3.3.2 Particle Size Distribution

To be determined by laboratory tests for use in trap efficiency and settling time computation.

2.3.3.3 Minimum Basin Storage For the site’s soil qualities, the volume required to achieve the minimum trap efficiency given

the estimated annual inflow.

2.3.3.4 Storage Area and Depth of Ponding

Basin travel time must be equal to or greater than the particle settling time to achieve trapefficiency.

2.3.3.5 Sediment Delivery Ratio and Total Sediment Yield

The total sediment yield is the mass of sediment that is estimated to leave the project site inrunoff. Gross erosion is defined as the sum of the three contributing sources, and total sedimentyield is defined as the gross erosion times the “sediment delivery ratio” (DR). The sedimentdelivery ratio is a function of the drainage area and ranges from 0.60 for the smallest basins to0.05 for basins of 500 sq mi.

2.3.3.6 Basin Clean Out Interval

A calculation which is useful in structuring a maintenance program. Determined from thecapacity of the basin and the volume of water needed to produce the required settling time. Thesediment storage volume can be determined by assuming a clean out interval and adding thevolume of solids estimated to be captured during that time to the required water storage volume.

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FIGURE 1

48-HOUR PERCENTAGE OF RUNOFF CAPTURE VS UNIT BASIN STORAGE

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2.4 VOLUMETRIC DESIGN CRITERIA

Section 5.5.1 of the CASQA Handbook specifies that,

“Typically, a volume-based BMP design criteria calls for the capture and infiltration ortreatment of a certain percentage of the runoff from the project site, usually in the rangeof the 75th to 85th percentile average annual runoff volume. The 75th to 85th percentilecapture range corresponds to the “knee of the curve” for many sites in California forsites whose composite runoff coefficient is in the 0.50 to 0.95 range.”

The Attachment 4 to the MS4 permit specifies in Methodology “b”:

“The volume of annual runoff based on unit basin storage water quality volume, to achieve 80percent or more volume treatment by the method recommended in California Best ManagementPractices Handbook - Industrial/Commercial (2003)”.

The runoff volume curves are illustrated by Figure 1 for the Redding gage location in Tehama County,California, for the 48-hour event. These curves are recommended for use in the region that includes theSun City Tehama project site.

The handbooks make provisions for local jurisdictions to develop their own criteria. Tehama Countyhas not yet determined the exact criteria it will require for sizing water quality facilities within theCounty, and has indicated that it will consider long-term maintenance costs when balancing watershedprotection and overall improvement costs.

For this project, the charts provided in the Handbook for the gaging station at Redding CA will be mostapplicable. Copies of the complete graphs for this station are included in the CASQA New DevelopmentHandbook.

2.4.1 Design Volume Percentile

Section 5 of the CASQA Handbook discusses the choice of average annual runoff volume percentile touse for WQV design. Based on the Redding Gage data, the approximate increase in design storage from a75th percentile event to an 85th percentile event is 33% of the 75th percentile event volume. Events largerthan the design event would receive some treatment, but events smaller than the design event may notreceive full treatment. A complete breakdown of the impact of alternate design criteria is presented inAppendix A of this guide. Based on the significant increase in basin size for a marginal gain in eventcapture, and the relatively low value in treating higher runoff events vs improved treatment efficiencyfor more frequent runoff events, Civil Solutions recommends the 80th percentile event criteria as thebasis for volumetric design BMPs on this project, per the minimum requirements of the MS4 permit.

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2.4.2 Volumetric Design Criteria

Volumetric design for this project will be based on the appropriate drawdown criteria of the BMPdevice. For devices such as extended detention, a 48-hour drawdown is applicable. Generally, thismeans that for the design water quality volume (WQV) no more than 50% of the WQV is to be releasedduring first 24 hours, and total release of all waters in the basin should be complete within 72 hours.

For devices such as Wet Ponds, the 24-hour drawdown criteria is applicable. The designer should verifythe design requirements listed in the Fact sheets for each BMP included with this document.

It may not be possible to design all basins to meet the 50% drawdown and 100% drawdown timingcriteria, using standard construction methods and materials. Since the 72-hour criterion is critical forvector abatement efforts, which are now itemized as an MS4 requirement, it takes precedence andcannot be compromised. After assuring complete drawdown in 72-hours, the design should come asclose to the 50% criteria as possible. Note that the total drawdown time of 72 hours applies to the totalstormwater quality basin volume, including the maintenance reserve volume as described below.

WQV (in3/ft2) = a * C * P6, where,

a is a constant of 1.582 for the 24-hour design eventC is the weighted average Runoff Coefficient “C” valueP6 is the mean annual runoff event in inches (.55 inches for the Redding Gage)

Since, “a” and P6 are constants for this location the equation is more easily solved as follows:

WQv (in3/ft2) = 0.8701 * COr, the total unit storage volume in cubic feet per contributing acre:

WQV (ft3/acre) = 3158 *C or

WQV (ac-ft/ac) = 0.0725 * CSo for any 80th percentile stormwater quality volumetric device, the design peak 48-hourdrawdown storage volume can be computed by the following equation:

WQV (ft3) = 3158 * 3(Ci * Ai)Where,

Ci is the runoff coefficient for an individual landuse within the total tributary watershed, andAi is the tributary area in acres for that landuse.

The weighted C value is simply:

( * )C AA

i i

i

∑∑

For the 24-hour Drawdown Design, the Water Quality Volume is calculated as:

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WQV (ft3/acre) = 2584 *C 2.4.3 Maintenance Storage Reserve

Most volumetric based facilities will require that a some of the design volume be set aside for thestorage of collected sediment between maintenance cycles. For example, take a watershed that yields 4tons per acre per year (E) in the ultimate permanent operation cycle of the volumetric device (postconstruction and plantings). Assuming an average delivery ratio of 60%, the sediment yield to thevolumetric BMP would be approximately 2.4 tons per acre per year. For soils with a density of 120lbs/ft3, this equals roughly 40 cubic feet per acre per year. Assuming that the minimum desiredpermanent maintenance cycle would be no less than every 2 years, the net reserve storage volumerequired would be 80 ft3 per contributing acre. Notice that for the assumptions of 60% delivery ratio anda density of 120 lbs/cu ft, the annual reserve volume in cubic feet is 10 times the soil loss rate in t/ac/yr.Therefore,

TOTAL SWQ BASIN STORAGE (ft3) = WQV + RESERVE = 3158 * 3(Ci * Ai) + (10*E*AT*M)

Where: AT = Total contributing Area (3Ai)E = Annual soil loss (t/ac/yr), andM = maintenance cycle (years)

Civil Solutions used RUSLE2 to estimate sediment yields from the developed and undeveloped areas ofthe project site. For the developed area we assumed 150 feet of flow path and slopes of 2 percent, withtypical landscaping vegetation cover. Sediment yield from the developed areas of the site is estimatedto be approximately 1.0 t/a/y for all soil types. The required maintenance reserve for those volumetricfacilities that only receive runoff from the developed areas of the project site is quite small. A reservevolume of 5% of the WQV will have a maintenance cycle of longer than 3 years.

The RUSLE2 analysis predicts sediment yields from the undeveloped areas of the project site to rangefrom 14 to 54 tons/acre/year, depending upon the soil type, length and slope of the overland flow path.The analysis assumes that the ground cover for the undisturbed areas of the site is mature range grass.Based on these much higher sediment loads, volumetric water quality facilities that receive a significantamount of runoff from undeveloped areas will require significantly greater reserve volumes. Thedeveloped areas only require 10 cubic feet /acre of reserve storage, while the undeveloped areas wouldrequire from approximately 140 to 540 cubic feet/acre of reserve storage. Civil Solutions recommendsmore detailed analysis for those volumetric facilities that receive a significant proportion of their waterquality volume from undeveloped areas with steep slopes and erodible soils.

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2.4.4 Example Outlet Design for 48-hour drawdown

Storage facility outlet design must meet three criteria:

1. The capacity to pass the maximum flow required to draw down the storage facility in thedesign period of 48 hours,

2. The ability to control the rate of outflow so that no more than 50% of the design WQV isreleased in the first 24 hours

3. The ability to assure that the entire volume is released within the maximum time period of72-hours.

The maximum average flow rate of the discharge pipe or structure is found by dividing the WQV by 48hours, or with appropriate unit conversion:

Qavg = 0.25 (cfs/af) * WQV (af)

Where, The WQV is the design peak 48-hour drawdown storage volume for SWQ treatment anddoes not include maintenance reserves.

Note: Storage is converted to acre feet in the above equation.

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SECTION 3SOURCE CONTROL BMPs

A key element to better water quality in downstream facilities, is to reduce the amount of constituentswhich runoff from the development areas. Source Control is often the most effective Best ManagementPractice tools which can be implemented. They are usually very cost effective as well. However, theycan sometimes be difficult to implement as they may require educating a large population.

Section 3 and 4 of the CASQA “New Development and Redevelopment” handbook focuses on SourceControl BMPs.

3.1 QUALITATIVE BMPs

Directly Connected Impervious Area (DCIA): Impervious areas which connect directly to a stormdrainage system without passing over a pervious area such as landscaping will contribute more runoffand require larger treatment facilities. Streets and parking lots are large contributors to this impact.

For this project, the street standards have already been selected, so the opportunity to reduce directlyconnected areas within them has passed. However, where private roads are constructed in the future,this should be considered in the design. One solution, which this project will utilize, is to limit theamount of curb and gutter and/or AC dike placement. Curb and gutter and/or AC dike should only beused to prevent erosion, and where the project improvement standards require its use. For example,Main collector roadways with adjacent landscaping could drain to a buffer strip along the roadway(within the landscaping) which would treat the runoff without it ever being placed in a storm drainsystem.

The opportunity to reduce directly connected impervious areas at parking lots within the project maystill exist. Section 3.2.2 of the CASQA “New Development and Redevelopment” handbook should beconsulted for methods in which the DCIA can be reduced.

Other contributors to high DCIA values are potentially, driveways, maintenance areas, and roof draincollection systems

3.2 SOURCE CONTROL BMPs

At the direction of the County we have included Fact Sheets for Source Control BMPs in Section 5.1 ofthis report. We recommend that the developer provide the fact sheets for SD-10 to SD-21 to homebuyers, and SD-20 to SD-36 to purchasers of large parcels for residential, multifamily and commercialuses. SD-20 to SD-36 would also be applicable to the project Golf course facilities.

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TABLE 4 SOURCE CONTROL BMPs

Design BMPs

SD-10 Site Design and Landscaping

SD-11 Roof Runoff Controls

SD-12 Efficient Irrigation

SD-13 Storm Drain System Signs

Materials BMPs

SD-20 Pervious Pavements

SD-21 Alternative Building Materials

Areas BMPs

SD-30 Fueling Areas

SD-31 Maintenance Bays and Docks

SD-32 Trash Enclosures

SD-33 Vehicle Washing Areas

SD-34 Outdoor Material Storage Areas

SD-35 Outdoor Work Areas

SD-36 Outdoor Processing Areas

3.3 ADDITIONAL SOURCE CONTROL MEASURES

Additional items regarding the proposed source control related facilities of this project will bedeveloped, including a guide to lawn care for the homeowners of Sun City Tehama, and an integratedgolf course management plan and chemical application management plan for the golf course at Sun CityTehama.

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SECTION 4CHOOSING AND DESIGNING TREATMENT CONTROL BMPs

Treatment control BMPs are chosen based on site conditions, constituents of concern, and project designrequirements. Site conditions include soil characteristics, topography, and climate. Constituents ofconcern include fine sediments, oil/grease/hydrocarbons, and excess nutrients. Site conditions includethe geometry of the project layout and the size and shape of available land area. Every project will havea different combination of these factors to consider when choosing appropriate BMPs.

There are two categories of treatment control BMPs, those designed on volumetric criteria and thosedesigned on flow rate criteria. The design water quality volume (WQV) is typically 75% to 85% of theaverage annual runoff from the area served by the BMP. The WQV is determined from charts of rainfalldata for region, similar to the one in Figure 1. Flow-based design criteria can be either a continuous flowrate or peak flow rate calculated for the specified return period design event.

TABLE 5.1 of the CASQA Handbook specifies 5 types of Treatment Control BMPs:

1. Infiltration: The infiltration potential of the Type C and Type D soils on the site make this typeof BMP unsuitable for this project, and we have not included examples of these devices in thisdocument.

2. Detention and Settling: We have proposed extensive use of these facilities for this project.

3. Biofiltration: We have proposed extensive use of these facilities for this project, usually inconjunction with another BMP type.

4. Filtration: We do not anticipate using filtration devices on this project. However, they may berecommended by a proprietary device manufacturer for site-specific applications.

5. Flow Through Separation: These vaults and inlets will likely be used within the project wheresuitable area for an alternate device is not available. These devices may also be more costeffective for areas of less than 30 acres.

The BMPs recommended for the Sun City Tehama project are listed by design criteria in Tables 6 and 7.

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4.1 GENERAL DESIGN CRITERIA/INFORMATION NEEDS

4.1.1 Soils

The Sun City Tehama project site includes several different types of soils, falling into three of the fourhydrologic soil groups (HSG). Type B soils are present in the intermittent stream channels, Type C andType D soils are distributed throughout the site.

TABLE 5SUN CITY TEHAMA SOILS

Soil

Name Infiltration Rate(in/hr)

HSG

Aw 0.16 B

Ay 0.16 B

CxB2 0.07 D

DxD 0.09 C

NrD 0.07 D

NrE 0.07 D

NvD 0.09 C

NwD 0.09 C

NwE 0.07 D

Rr 0.07 D

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2Source: California Department of Water Resources Bulletin No. 195, Rainfall Analysis for Drainage Design Vol. 1:Short-Duration Precipitation Frequency Data, 1976

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4.1.2 Climate

The Sun City Tehama area receives an average of approximately 25 inches of rainfall per year, as shownon Figure 2.2 The rainfall distribution, average temperature and erosivity R values from RUSLE2 arepresented in Figure 3 below.

FIGURE 2ISOHYETAL MAP OF TEHAMA COUNTY

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FIGURE 3CLIMATE DATA FOR TEHAMA COUNTY FROM RUSLE2 DATABASE

4.1.3 Topography

Slopes for the developing areas of the project protected by BMPs range from 1% to 8% and overlandflow lengths generally vary from 150 feet to 1000 feet in length. Slope and overland flow lengthsignificantly effect the amount of sediment removed from the watershed and captured by a BMP.

4.1.4 Site Design

The Sun City Tehama project is concentrated on a relatively small area of the entire site. The site islarge enough to accommodate detention ponds, swales and other larger scale BMPs.

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4.2 VOLUME BASED DESIGN

Table 6 lists BMPs selected for this project which would be sized based on the volumetric criteria, alongwith a brief description of the locations or situations where they will be used. The numbering refers tothe number on the BMP Fact Sheets from the Handbook that are included in Section 5.

TABLE 6VOLUMETRIC BMPs SPECIFIED FOR THE SUN CITY TEHAMA PROJECT

BMP Description/Location

TC-20: Wet Ponds Used at locations where newly constructed year-round lakeimprovements are proposed.

TC-21: Constructed Wetlands Use is similar to TC-20, but include enhanced biological facilitiesand reduced maintenance options.

TC-22: Dry Extended Detention Used where BMPs are located within detention facilities and/orat pipe discharge locations.

TC-32: Bioretention Bioretention is not planned for use in the major projectimprovements, but is included as they may be used in the futureby individual lot builders.

TC-50: Water Quality Inlet May be used where other BMPs cannot be installed due to siteconstraints

TC-60: Multiple System The combination of features available with multiple BMPs maybe necessary to meet permit requirements and site constraints.

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4.3 FLOW-BASED BMP DESIGN

4.3.1 General Flow-Based Design Criteria

BMPs selected for this project which would be sized on flow-based criteria are listed in Table 7 below:

TABLE 7FLOW-BASED BMPs SPECIFIED FOR THE SUN CITY TEHAMA PROJECT

BMP Description

TC-30: Vegetated Swale To be used for small areas of disturbance or where smallareas of impervious surface are created.

TC-31: Vegetated Buffer Strip To be used for areas where roadway runoff would not becollected by a roadway gutter or dike system, and roadwaydrainage would be discharged to adjacent slopes.

MP-51: Vortex Separator To be used only where the contributing runoff is entirelyfrom streets and other constructed impervious surfaces, andno other BMPs are suitable. May be used in vehicle serviceyards and chemical storage areas for spill control.

TC-60/TC-8: Multiple Systems The combination of multiple BMP features at a single BMPlocation may be proposed.

TC-4: Biofilters Biofilters will be proposed extensively in combination withother BMPs.

TC-7: WQ Vault/Separators To be used only where the contributing runoff is entirelyfrom streets and other constructed impervious surfaces, andno other BMPs are suitable.

This project proposes to make use of Flow-based BMPs. Flow-based BMP design standards apply to,

“BMPs whose primary mode of pollutant removal depends on rate of flow of runoff throughthe BMP… Typically a flow-based BMP design criteria calls for the capture and infiltrationor treatment of the flow runoff produced by rain events of a specified magnitude.”

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The CASQA Handbook cites three alternative methods for calculating the design flow rates for Flow-based BMPs:

1. Factored Flow Approach: Typically 10% of the 50-year peak flow rate.

2. California Stormwater BMP Handbook Approach: Typically twice the 85th percentile hourlyrainfall intensity.

3. Uniform Intensity Approach: The magnitude of runoff resulting from a rain event equal to atleast 0.2 in/hour in rainfall intensity.

The first approach will not be used for this project.

The second approach simply requires reading the 85th% rainfall intensity from the appropriate CASQAcumulative frequency hourly rainfall intensity curve. The 85th percentile rainfall intensity for theRedding gage is 0.132 in/hour (Figure 4), and twice this value is 0.264 in/hour.

The Uniform Intensity Approach is even simpler as it specifies the design intensity of 0.20 in/hr. CivilSolutions recommends using The Uniform Intensity Approach.

The chosen design intensity is used in the Rational Method to calculate the design flow rate. TheRational Method should only be used for areas less than 25 to 50 acres, depending on composite CValue. See design parameters for each BMP for actual sizing criteria based on the computed flow rate.

4.4 DESIGN OF SPECIFIC BMPS

Failure of some BMPs is to be expected, which is why it is important to use a diverse selection orcombination of BMPs to reduce the potential for complete system failure. Before getting into the detailsof design it is important to note that BMP siting and design is not an exact science. Many factorsincluding soils conditions, project conditions, watershed size and runoff potential should all beconsidered when selecting appropriate BMPs.

The following pages contain worksheets and summary design criteria for volumetric and flow-basedBMPs. This information would be useful in assisting with design calculations. Civil Solutions has alsoprepared summary spreadsheets for the volumetric device sizing which is based on the samemethodology. Most calculations submitted by Civil Solutions would be provided in summaryspreadsheet format. The reader is referred to the BMP Factsheets in Section 4 for more detailedselection and design criteria.

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FIGURE 4CUMULATIVE FREQUENCY HOURLY RAINFALL INTENSITY

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TC-20: WET PONDSBMP DESIGN WORKSHEET

5. TOTAL WETPOND VOLUME: Total Wetpond Volume (VOLT ) (ft3) = (WQV + PPV + MSRV)WHERE:

WQV = Water Quality Volume (ft3) = 2584 * 3(Ci *Ai) PPV = Minimum Permanent Pool Volume (ft3) = 2 * WQV andMSRV = Maintenance Storage Reserve Volume (ft3) = (10*E*AT*M)

AND: Ci is the runoff coefficient for each subarea of the tributary watershedAi is the tributary subarea in acres, AT = 3Ai = total tributary area (ac)2584 = units conversion factor E = Estimated Average Annual soil loss (t/ac/yr)M = maintenance cycle (years)

WATER QUALITY VOLUME (FT3)

Area (Ai) (acres) Landuse (Ci) Ci*Ai

3Ai = 3(Ci*Ai) =

WQV (ft3) = 2584 * 3(Ci*Ai) =

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TC-20: WET PONDSBMP DESIGN WORKSHEET

(cont)

6. CALCULATE DESIGN VOLUMES IN CUBIC FEET AND ACRE-FEET3(Ci*Ai) = AT = 3Ai = total tributary area (ac) = E = Estimated Average Annual soil loss (t/ac/yr) = M = maintenance cycle (years) =

Design Volume Formula (ft3) Cubic Feet Acre-feetWater Quality Volume WQV 2584 * 3(Ci*Ai)Minimum Permanent Pool Volume (PPV) PPV = 2 * WQV

Maintenance Storage Reserve Volume (MSRV) (10*E*AT*M)Total Stormwater Quality Volume (SWQv) (WQV + (MSRV)Total Wetpond Volume (VOLT ) (WQV + PPV + (MSRV)

Design volumes in cubic feet are useful for excavation quantities, flow rate calculations, etc. Volumes inacre-feet are useful for site layout, checking depth and other pond geometry constraints.

7. WETPOND OUTLET DESIGN

Target Release Rate = ½ of Water Quality Volume (WQV) over 24 hoursQ24 (cfs) = 0.125 * WQV (ac-ft) = cfs

Limiting Release Rate = Total Stormwater Quality Volume (SWQV) within 72 hoursQ72 (cfs) = 0.17 * SWQV (af) = cfs

8. WETPOND GEOMETRY

Feature Limit ValueLength/width ratio minimum 1.5 to 1Maximum depth less than 8 feetAverage depth no than greater than settling velocity * residence timeShore side slopes (z) no steeper than 3 (for grass protection)Aquatic vegetation cover less than 1/4 of pond surface areaProvide access to pond whendistance from shore

greater than 20 feet

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TC-21: CONSTRUCTED WETLANDSBMP DESIGN WORKSHEET

1. TOTAL WETLAND VOLUME: Total Wetland Volume (VOLT ) (ft3) = (WQV + PPV)WHERE:

WQV = Water Quality Volume (ft3) = 2584 * 3(Ci *Ai) PPV = Minimum Permanent Pool Volume (ft3) = 2 * WQV and

AND: Ci is the runoff coefficient for each subarea of the tributary watershedAi is the tributary subarea in acres, 2584 = units conversion factor

WATER QUALITY VOLUME (FT3)

Area (Ai) (acres) Landuse (Ci) Ci*Ai

3Ai = 3(Ci*Ai) =

WQV (ft3) = 2584 * 3(Ci*Ai) =

2. CALCULATE DESIGN VOLUMES IN CUBIC FEET AND ACRE-FEET

Design Volume Formula (ft3) Cubic Feet Acre-feetWater Quality Volume WQV 2584 * 3(Ci*Ai)Minimum Permanent Pool Volume (PPV) PPV = 2 * WQV

Total Wetland Volume (VOLT ) (WQV + PPV + (MSRV)Design volumes in cubic feet are useful for excavation quantities, flow rate calculations, etc. Volumes inacre-feet are useful for site layout, checking depth and other pond geometry constraints.

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TC-21: CONSTRUCTED WETLANDSBMP DESIGN WORKSHEET

(cont)

3. WETLAND OUTLET DESIGN

Target Release Rate = ½ Water Quality Volume (WQV) over 24 hoursQ24 (cfs) = 0.125 * WQV (ac-ft) = cfs

Limiting Release Rate = Total Stormwater Quality Volume (SWQV) within 72 hoursQ72 (cfs) = 0.17 * SWQV (af) = cfs

4. Wetland GEOMETRY

Feature Limit ValueLength/width ratio minimum 1.5 to 1Maximum depth less than 4 feetAverage depth highly variable create complex microtopographyShore side slopes (z) no steeper than 3 (for grass protection)Aquatic vegetation cover less than ½ of pond surface areaProvide access to pond whendistance from shore

greater than 20 feet

Forebay equal to 15 - 25% of permanent poolvolume

The forebay replaces the Maintenance Storage Reserve Volume (MSRV) of a wetpond. See theFactsheets for more detailed information.

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TC-22 EXTENDED DETENTION BASIN

BMP DESIGN WORKSHEET

1. TOTAL EXTENDED DETENTION BASIN VOLUME: Total Extended Detention Basin Volume (VOLT ) (ft3) = (WQV + MSRV)

WHERE:WQV = Water Quality Volume (ft3) = 3158 * 3(Ci *Ai) MSRV = Maintenance Storage Reserve Volume (ft3) = (10*E*AT*M)

AND: Ci is the runoff coefficient for each subarea of the tributary watershedAi is the tributary subarea in acres, AT = 3Ai = total tributary area (ac)3518 = “C=1.0 Unit basin design volume”E = Estimated Average Annual soil loss (t/ac/yr)M = maintenance cycle (years)

WATER QUALITY VOLUME (FT3)

Area (Ai) (acres) Landuse (Ci) Ci*Ai

3Ai = 3(Ci*Ai) =

WQV (ft3) = 3518 * 3(Ci*Ai) =

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TC-22: Extended Detention BasinBMP DESIGN WORKSHEET

(cont)

2. CALCULATE DESIGN VOLUMES IN CUBIC FEET AND ACRE-FEET3(Ci*Ai) = AT = 3Ai = total tributary area (ac) = E = Estimated Average Annual soil loss (t/ac/yr) = M = maintenance cycle (years) =

Design Volume Formula (ft3) Cubic Feet Acre-feetWater Quality Volume WQV 3518 * 3(Ci*Ai)Maintenance Storage Reserve Volume (MSRV) (10*E*AT*M)Total Stormwater Quality Volume (SWQv) (WQV + (MSRV)Total Extended Detention Basin Volume (VOLT ) (WQV + PPV + (MSRV)

Design volumes in cubic feet are useful for excavation quantities, flow rate calculations, etc. Volumes inacre-feet are useful for site layout, checking depth and other pond geometry constraints.

3. EXTENDED DETENTION BASIN OUTLET DESIGN

Target Release Rate = ½ of Water Quality Volume (WQV) over 24 hoursQ24 (cfs) = 0.125 * WQV (ac-ft) = cfs

Limiting Release Rate = Total Stormwater Quality Volume (SWQV) within 72 hoursQ72 (cfs) = 0.17 * SWQV (af) = cfs

4. EXTENDED DETENTION BASIN GEOMETRY

Feature Limit ValueLength/width ratio minimum 1.5 to 1Typical depth between 2 to 5 feetAverage depth no than greater than settling velocity * residence timeShore side slopes (z) no steeper than 3 (for grass protection)Aquatic vegetation cover none

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TC-30 VEGETATED SWALE

BMP DESIGN WORKSHEET

1. DESIGN FLOW

Design flow is the peak flow rate from a storm with an intensity equal to twice the 85th percentileintensity or 2.0 in/hr.

2. VEGETATED SWALE GEOMETRY

For the calculated peak flow rate, the geometry of the swale is dictated by the following limitations.Based on the slope of the site and the available flow path length, determine the depth of flow andresidence time for a single channel width of 10 feet. If the residence time is too short or the depth offlow is too great, split the flow among additional baffled flow paths.

Feature Limit ValueMinimum Length no less than 100 feetWidth between baffles no greater than 10 feetResidence time no less than 10 minutesDepth of flow no greater than 4" or 2/3 height of grassLongitudinal slope no greater than 2.5%Manning’s N for width calculation equal 0.25

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TC-30 VEGETATED SWALE BMP DESIGN WORKSHEET

(Cont)

The following figure can assist in assessing the suitability of a site for installing a vegetated swale.Based on the minimum residence time of 10 minutes, maximum depth of flow of 4 inches, minimumflow length of 100 feet and the maximum longitudinal slope of 2.5%, for any peak flow rate, the limitsin the graph apply. For example, the graph can be used to determine the minimum flow length requiredfor a site with steeper slopes, or the maximum slope that can be tolerated for a site with limited length offlow pathways.

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TC-31 VEGETATED BUFFER STRIP BMP DESIGN WORKSHEET

1. DESIGN FLOW

Vegetated swales are not designed for a specific flow rate or return period storm. Their design is based on creating the physical features in the table below to assure shallow sheet flow conditions and to reducethe potential for channelization and erosion.

Feature Limit ValueMinimum Length no less than 15 feet in direction of flowTypical Length approximately 2 times the length of tributary areaWidth equal to tributary area to be treatedMaximum Length of tributary area (indirection of flow toward buffer strip)

no greater than 60 feet

Depth of flow well below average height of vegetationMaximum Longitudinal slope no greater than 15%Minimum Longitudinal slope no less than 1.0%Minimum depth to groundwater between 2.0 feet and 4.0 feetMaximum flow velocity no greater than 1.0 fps

Additional Design Guidelines

• Buffer area should be densely vegetated with a mixture of erosion-resistant plants.

• Buffer area should be contiguous with tributary area.

• Top of the buffer area should be 2-5" below adjacent pavement to prevent buildup of vegetationand sediment at the edge of the strip that could prevent water from entering buffer.

• While toe and top of slope should be as flat as possible, buffer strip design must prevent pondingthat could lead to vector control problems.

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TC-32 BIORETENTION BMP DESIGN WORKSHEET

Bioretention is most applicable for very small tributary areas, probably only one or two landuses(pervious and impervious). Designed to drain or infiltrate within 72 hours. No permanent pool ormaintenance reserve volume are required.

1. WATER QUALITY VOLUMEWQV = Water Quality Volume (ft3) = 3158 * 3(Ci *Ai)

WATER QUALITY VOLUME (FT3)

Area (Ai) (acres) Landuse (Ci) Ci*Ai

3Ai = 3(Ci*Ai) =

WQV (ft3) = 3158 * 3(Ci*Ai) =

2. BIORETENTION FEATURE GEOMETRY

Feature Limit ValueLength no less than 15 feet (25 ft preferred)Width no less than 40 feetSoil permeability no less than 0.50 in/hr (or install subdrains)Depth excavation no less than 4 feetLongitudinal slope no greater than 20%Depth to water table no less than 6 feetTree or shrub density no less than 1 per 50 sq ft

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Sun City Tehama BMP Guidelines - Design Worksheets Oct 2004

Civil Engineering Solutions, Inc.

SECTION 5BMP FACT SHEETS

Page 41: STORMWATER MANAGEMENT GUIDE STORMWATER … BMP Design... · APPENDIX A: Managing Mosquitoes in Stormwater Treatment Devices ... Bioretention Vortex Separator ... Stormwater BMP Design

Sun City Tehama BMP Guidelines - Design Worksheets Oct 2004

Civil Engineering Solutions, Inc.

SECTION 5.1SOURCE CONTROL BMP FACT SHEETS

Page 42: STORMWATER MANAGEMENT GUIDE STORMWATER … BMP Design... · APPENDIX A: Managing Mosquitoes in Stormwater Treatment Devices ... Bioretention Vortex Separator ... Stormwater BMP Design

Sun City Tehama BMP Guidelines - Design Worksheets Oct 2004

Civil Engineering Solutions, Inc.

SECTION 5.2VOLUMETRIC BMP FACT SHEETS

Page 43: STORMWATER MANAGEMENT GUIDE STORMWATER … BMP Design... · APPENDIX A: Managing Mosquitoes in Stormwater Treatment Devices ... Bioretention Vortex Separator ... Stormwater BMP Design

Sun City Tehama BMP Guidelines - Design Worksheets Oct 2004

Civil Engineering Solutions, Inc.

SECTION 5.3FLOW BASED BMP FACT SHEETS

Page 44: STORMWATER MANAGEMENT GUIDE STORMWATER … BMP Design... · APPENDIX A: Managing Mosquitoes in Stormwater Treatment Devices ... Bioretention Vortex Separator ... Stormwater BMP Design

Sun City Tehama BMP Guidelines - Design Worksheets Oct 2004

Civil Engineering Solutions, Inc.

APPENDIX A: Managing Mosquitoes inStormwater Treatment Devices

Page 45: STORMWATER MANAGEMENT GUIDE STORMWATER … BMP Design... · APPENDIX A: Managing Mosquitoes in Stormwater Treatment Devices ... Bioretention Vortex Separator ... Stormwater BMP Design

Sun City Tehama BMP Guidelines - Design Worksheets Oct 2004

Civil Engineering Solutions, Inc.

APPENDIX B: Managing Mosquitoes inSurface-Flow Constructed Treatment Wetlands