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Gary Conley

gary@2ndnaturellc.com831-426-9119

www.2ndnaturellc.com

Aligning Stormwater Model Specification with

Management Needs: a Practical Tool for

Estimating Load Reductions (TELR)

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Clean water through sustainable land management decisions, using transparent

science to communicate priorities and track accountability.

2NFORM

www.2NFORM.com

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The Problem

• Natural variability of urban catchments make measuring changes difficult

• Monitoring data are limited in spatial extent and utility of short timeframes

• Stormwater managers require tools that operate on scales relevant to decision making reporting requirements (NPDES, MS4)

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Modeling philosophy

All models are wrong, but some

are useful-George Box, 1976

Complex Simple

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Modeling Philosophy

Models used in the regulatory process should be no more complicated

than is necessary to inform regulatory decision and that it is often

preferable to omit capabilities that do not substantially improve model

performance (NRC, 2007)

Adapted from Hanna (1988) and EPA (2009)

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Development Objectives

• Well tested algorithms from USDATechnically robust

Easy to use

Aligns with stormwater information needs

• Standardized inputs + clear guidance• Purpose built for stormwater managers

• Objective, transparent prioritization• Track progress towards WQ goals• Test heuristic management scenarios

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1 TELR Structure

• USDA SCS curve number

runoff generation

• LU characteristic runoff

concentrations

• USDA TR-55 method for

peak inflow/outflow

• Routing is by NRCS lag

method with urban

adjustments

• Annual time step

• Structural + non-structural

BMPs

HTR

IND

SFR

IND land use (% imp)

land use type

decentralized BMPs

centralized BMPs

runoff/loads

URBAN CATCHMENT

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http://www.2ndnaturellc.com/reports/

TELR Inputs

• Publicly available

data

• Precipitation

• Soils

• Land use

• Impervious area

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TELR Catchment Delineation

• Urban catchments ~ 100 acres

• Catchments are have

either diffuse or discrete

outlets

• Connectivity to receiving

waters

• Urban hydrography dataset

utility beyond modeling

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TELR vs SWMM based Model Results

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TELR vs SWMM based Model Results

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Land Use

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BMPs + Condition

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Parcel Condition

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City of Watsonville, CA

DEMO

NameLoad Rate

(ac-ft/yr) (ft/yr)

3050 3050 3578 3578 35783578

ac-ft/yr

305

2745

665

2395

932

2626

1180

2398

1550

2028

Rate (ft/yr)

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City of Watsonville, CA

Name Load Rate (ton/yr) (ton/ac/yr)

400 400 427 427427

Ton/yr

40

360

85

315

119

308

150

277

178

249

Rate ton/ac/yr)

DEMO

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Receiving

Water

Runoff

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Catchment Reductions

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Phase II MS4 requirement satisfaction

Post-construction

requirements

Public outreach and

educationWeb-based spatial outputs

Parcel runoff neutrality estimates

Runoff and particulate pollutant

load reduction estimates

Pollution prevention

and good

housekeeping

Seamless integration with BMP

inventory and condition trackingBMP Asset tracking

MS4 requirement TELR output

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Support

Regulators

EPA Region 9 (CA, NV, AZ, NM, HI) support and tight contacts Recent CWA contracting mechanism

CA Regional Board Funding and SupportRegion 3; Funded BMP RAMv3 and TELR in partRegion 6; Funded BMP RAM v1 and v2 , Road RAM v1, v2Collaborative relationship, encourage expansion of use

Regulated entities

Over 40 municipal partners across California

CommunityProvides the accountability and transparency

NGOsAlignment with a widespread call for a shift towards quantified environmental outcomes

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Gary Conley

2NDNATUREp 831.426.9119

gary@2ndnaturellc.com

www.2NFORM.com

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Modeling Philosophy

Sto

rmw

ater

Run

off

Time

Uncertainty envelope