MODEL WatErshED MastEr pLan anD pLanning tOOL – WatEr ...pacewater.com/wp-content/uploads/2012/10/Watershed...characteristics. This will assist in the planning process to support

MODEL WatErshED MastEr pLan anD pLanning tOOL –WatEr QuaLity anD npDEs rEguLatiOns iMpLEMEntatiOnPACE performed a watershed-wide analysis of the San Gabriel/Coyote Creek watersheds (and is currently preparing plans for the remaining watersheds located in Orange County) to illustrate how to implement new various control measure re-quirements to mitigate hydromodification on new developments. These measures include low impact development (LID), hydromodification control, and treatment control to address hydrologic conditions of concern (HCOC), and support long-term watershed masterplanning goals. The planning process involved a multi-step process of characterizing and analyzing the wa-tershed and sub-surface conditions utilizing sophisticated GIS mapping tools. The project effort resulted in a dynamic planning tool that is accessible by County staff and property owners and provides watershed-specific support for integrating water quality, hydromodification, water supply and habitat protection issues as part of selecting and designing BMPs to meet the requirements of the County’s Model Water Quality Management Plan (WQMP). Specifically, this planning tool provides information related to infiltration feasibility and hydromodification susceptibility at the watershed and sub-watershed scale that will help inform BMP selection and design for a proposed project. Infiltration feasibil-ity and hydromodification susceptibility are fundamental factors in the selection and sizing of BMPs to meet the requirements of the MWQMP and TGD.

Specific features of the watershed management planning tool include:• Regional watershed application of new MS4 criteria• Watershed information mapping database characteristics and constraints to assist site specific user• Identification of areas with Hydrologic Conditions of Concern (HCOC) for default basis• Technical foundation for site assessment screening using infiltration LID• Identification of areas with ability to participate in regional / subregional BMPs opportunities• Subwatershed plans and strategies planning /process•Technical guidance for demonstrating equivalent water quality benefits compared to onsite facilities

WatErshED CharaCtEriZatiOn / Mapping tOOLs

A GIS database will help to characterize the physical resources that provide the foundation for an understanding of watershed characteristics. This will assist in the planning process to support identification of project opportunities and constraints, while guiding effective watershed planning implementation.

Topographic Relief

Hydrologic Soil Types Depth to Groundwater

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Anaheim Bay-Huntington HarborWatershed

Newport BayWatershed

Santa Ana River Watershed

Los Angeles County

San BernardinoCounty

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Watershed inventory / Characterization• Technical foundation for site assessments• Identification of opportunity / constraints

– Hydrologic Characteristics– Drainage Facilities Inventory– Water Supply– Geologic Constraints

Data sources• Multiple Agencies

Limitations• Funding Resources/Level of Accuracy/Availability

Regional Channel Types

Santa Ana RiverWatershed




Los Angeles County


CHANNEL TYPES

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FIGURE 4.1COYOTE CREEK/SAN GABRIEL CREEKWATERSHED INFILTRATION HYDROMODIFICATION MANAGEMENT PLAN

Nikki "Hoopz" Alexande

LegendEarth (Unstable)Earth (Stabilized)Stabilized

WatErshED DELinEatiOn DrainagE FaCiLitiEs / Mapping tOOLs

Urban Drainage Facilities Regional Database

Urban Drainage Facilities Regional Database





Los Angeles County


E03

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A06

A01

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REGIONAL FLOOD FACILITIES

8,500 0 8,5004,250

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Legend

Regional Flood Facilities

Local Storm Drains

Urban Drainage Facilities Mapping Database

Urban Drainage Facilities Mapping Database

COnstraint CharaCtEristiCs FOr hyDrOMODiFiCatiOn anD LiD

Watershed hydromodification mapping characterizes all major channels or reaches within a given watershed as “susceptible” or “not susceptible” to hydromodification and includes delineations of the tributary area to each susceptible channel reach. Hydro-modification is defined as the physical response of stream channels to changes in catchment runoff and sediment yield caused by land use modifications. The maps are intended to be used as the default basis for determining whether a susceptible channel segment exists downstream of the project a part of determining whether HCOCs exist.

hydromodification susceptibility Mapping tool

Channel Erodibility Data• Watershed mapping / subareas• 100-year floodplains• Hydrography• Lakes / reservoirs / basins• Storm drains• Channel locations / types / materials

– Verification with aerial photographs– Extent of digital channel data

• In-stream structures

Watershed Erosion• Erosion potential

Data issues• Quality of data• Conflicts / inconsistencies

Limitations• Verification required in downstream

Hydromodification Susceptibility – Erosion Potential

Watershed Surface Soils – Erosion Potential

Hydromodification

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Los Angeles County


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Potential Areas of Erosion, Habitat, &Physical Structure Susceptibility

Channel TypeEarth (Unstable)

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COnstraint CharaCtEristiCs FOr hyDrOMODiFiCatiOn anD LiD

Infiltration feasibility maps are intended to provide a preliminary planning level assessment of those infeasibility criteria that can be mapped meaningfully at a watershed or sub-watershed scale. The maps identify areas where infiltration is clearly infeasible to avoid the need for small projects to conduct site-specific testing that is unlikely to be necessary.

infiltration Feasibility assessment Mapping tool

infiltration Limitations / Constraints• Soil permeability• Depth to shallow groundwater• Groundwater protection / Contamination• Landslides• Sewer systems high I/I zones• Liquefaction hazard zones

Low Permeability Soils

Potential Landslide Areas

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Los Angeles County


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Potential Landslide Areas

rEgiOnaL WatErshED OppOrtunitiEs anD pLanning stratEgiEs

A key role to watershed planning is to identify potential opportunities for regional and subregional stormwater management facilities that can play a critical role in meeting water quality, hydromodification, water supply, and/or habitat goals within the watershed rather than relying on individual site-specific treatment. Future subwatershed analysis can tier off this regional facility planning effort to develop subwatershed control strategies in compliance with the MS4 Permit. Subwatershed BMP facilities identified as part of this initial screening process are intended to serve as the planning and implementation tool for developing a subwatershed control approach, demonstrating that stormwater requirements and watershed objectives are still met based on scientifically based and technically sound analysis.

process for implementing subregional /regional Facility strategies

Generalized Steps1. Select opportunity locations2. Develop subwatershed plans and supporting analysis3. Implement regional/subregional facilities and administer participation

Facility implementation and prioritization also depends on variety of factors including (1) maximizing water quality benefits, and (2) timing opportunities of projects (i.e. development forecasts).

Site Factors• Physical characteristics• Ownership considerations• Receiving water conditions• Watershed characteristics• Development forecasts• Stakeholder input

subwatershed plan Minimum Elements1. Develop Subwatershed control strategy2. Conceptual facility plans and design criteria3. Estimate facility capacity and expected performance4. Establish criteria for project participation5. Describe implementation plan

– Funding mechanism– Schedule– Monitoring / Operations /Maintenance

Open Space Areas with ExistingRetarding Basins

Resulting Potential Regional Sites

Contributing Watershed - Regional Sites

Infiltration Constraints Physiographic Constraints

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Los Angeles County


0 8,500 17,000Feet

LegendSubbasin OutlinesPotential BMP Opportunities

REGIONAL/SUBREGIONAL BMP OPPORTUNITIESWATERSHED INFLUENCE ZONES


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Los Angeles County


B01-08

B01-04 B01-11B01-19

B01-17

B01-22 B01-31 B01-46

B01-54

B01-58

B01-62

B02-02B01-15

B01-13 B01-20

B01-25B01-47

B01-45

B01-50B01-52

B01-57

A03-19

A03-21

A03-23

A03-25

A04-01

A03-16

A03-15

B01-34

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A03-09A03-08

A03-07

A03-14

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A03-03

B02-05

B01-26B01-05

B01-39

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B01-12

B01B03

B01B06

B01B07

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B01-48

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A03-10

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B01B04

LegendSubbasin Outlines

B01-57

Potential BMPBMP Contributing Area

REGIONAL/SUBREGIONAL BMP OPPORTUNITIESWATERSHED INFLUENCE ZONES


0 8,500 17,000Feet!I

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Newport Bay-Newport Coastal

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LEGENDPotential BMP Locations

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Open Area



Los Angeles County


CypressRetarding

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Potential BMP LocationsExisting Retarding Basin

Open Area

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Los Angeles County


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LEGENDPotential BMP Locations

Existing Retarding Basin

Open Area

Potential BMP Location Removed

ORANGE COUNTYORANGE COUNTY

LOS ANGELES COUNTYLOS ANGELES COUNTY

LOS

ANGELES

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LOS

ANGELES

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FULLERTON

ANAHEIM

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BUENA PARK

PLACENTIA

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LA PALMA

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PCPI Results0 - 1011 - 2021 - 3031 - 4041 - 50

ORANGE COUNTYORANGE COUNTY

LOS ANGELES COUNTYLOS ANGELES COUNTY

LOS

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Subbasins

PCPI Results0 - 1010 - 20 20 - 3030 - 4040 - 50

Implementation planning should also emphasize the strategic location of BMPs that have been chosen to maximize the pollutant reduction within a watershed. An approach using a GIS-based tool can provide guidance for the systematic prioritizing of BMP projects to optimize pollutant reduction in a cost effective manner. The tool employs different weighting factors to assess high pollutant loading based on pollutant generation and watershed impairments. The methodology will generate a numerical scoring system to determine the subwatershed priority index based on the annual commutative pollutant loading tributary to a specific facility and weighted based on watershed specific impairments for the different pollutants to provide a relative importance within the watershed.

rEgiOnaL BMp iMpLEMEntatiOn priOritiZatiOn

Methodology for analysis of Determination of regional BMp prioritization

• Analysis similar to Geosyntec SBPAT• Smaller subwatershed parcels of 40 acres• Computation of annualized area weighted pollutant load for different constituents landuse based

– Runoff Coefficients– Pollutant EMCs– 85th percentile 24-hour depth

• Normalize between high to low valueCopper

Zinc

Overall Pollutant Loading Results

Subbasin Pollutant Loading Results

17520 nEWhOpE strEEt, suitE 200 | FOuntain VaLLEy, CaLiFOrnia 92708 • 714.481.7300 | WWW.paCEWatEr.COMAdditional Offices: Scottsdale • Beijing • Moscow

gis WatErshED sitE pLanning tOOL

Identify Site

1

2

3

4

6

Regional Facility & Drainage Facilities

Site BMP InformationSite Subwatershed Location

Regional Infiltration Constraints

Receiving Waters Flowpath

An interactive GIS mapping tool was developed to assist general public located within the watershed to be able to utilize the information database about their specific site and readily provide information in a format that would (1) answer specific questions about their site related to MS4 permit requirements and applying the WQMP, (2) assist in providing the required design information for BMP facilities, and (3) identifying the regional BMP which could be uti-lized to mitigate their particular site.

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MODEL WatErshED MastEr pLan anD pLanning tOOL – WatEr ...pacewater.com/wp-content/uploads/2012/10/Watershed...characteristics. This will assist in the planning process to support

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