Water Quality Modeling Using SWMM to Validate Lake Tahoe TMDL - - PowerPoint PPT Presentation

Catchment-scale Hydrologic and Water Quality Modeling Using SWMM to Validate Lake Tahoe TMDL Implementation Pollutant Load Estimates

Will Anderson, Tahoe RCD May 24, 2012 Measured data courtesy of Russell Wigart, El Dorado Co. DOT, Tahoe Engineering Division

Introduction

• Watershed modeling plays a central role in

water quality assessment & TMDL

• Model provides concise estimates of pollutant

loads

– e.g., annual average Fine Sediment Particle Load

Introduction

• Need for closer look into model results vs.

measured data

• Modeling and monitoring data require analysis

– Grab sample reveals snapshot in time – Instant concentration vs. annual load – Need for long-term flow data and meteorology

TMDL Context

• Mandate: % reduction in fine sediment runoff
• Jurisdiction responsibilities:

– New stormwater general permit – Delineate stormwater catchments (2009) – Estimate pollutant loads and report to Water Board – Earn “credits” for reducing loads

• Pollutant Load Reduction Model (PLRM) is basis

for estimating pollutant loads

– Developed by nhc for Lahontan RWQCB

PLRM: How does it work?

SFR Impervious 17% SFR Pervious 42% Vegetated 3 22% Secondary Roads 19%

LAND USE ROAD & PARCEL CONDITIONS SOIL TYPE SLOPE

PLRM: How does it work?

SFR Impervious 17% SFR Pervious 42% Vegetated 3 22% Secondary Roads 19%

LAND USE ROAD & PARCEL CONDITIONS SOIL TYPE SLOPE

PLRM: How does it work?

SFR Impervious 17% SFR Pervious 42% Vegetated 3 22% Secondary Roads 19%

LAND USE ROAD & PARCEL CONDITIONS SOIL TYPE SLOPE

METEOROLOGI C DATASET: 18 years

PLRM: How does it work?

SFR Impervious 17% SFR Pervious 42% Vegetated 3 22% Secondary Roads 19%

LAND USE ROAD & PARCEL CONDITIONS SOIL TYPE SLOPE

METEOROLOGI C DATASET: 18 years

PLRM: How does it work?

SFR Impervious 17% SFR Pervious 42% Vegetated 3 22% Secondary Roads 19%

LAND USE ROAD & PARCEL CONDITIONS SOIL TYPE SLOPE

METEOROLOGI C DATASET: 18 years Annual Average Load!!

PLRM Refinement Process

1) Set up catchment in PLRM interface 2) Run SWMM5 for event basis

Calibrate / reduce errors

3) Run revised parameters in PLRM for catchment load crediting

Catchment in Montgomery Estates

Catchment characterization

• 18.5 acres
• 11.3 % slope
• Residential/

secondary roads

• Fast-draining soils
• Curb and gutter:

– All stable shoulders – Moderate to high risk due to slope – Conveys stormwater flows directly to Trout Creek

Marshall Trail: rolled curb and cut slope

SFR Impervious 17% SFR Pervious 42% Vegetated 3 22% Secondary Roads 19%

Catchment Land Use Distribution:

Single Family Residential & Secondary Roads

PLRM Land Use Configuration

PLRM Land Use Configuration

(Vegetated)

BMP Driveway Survey

• 70 total parcels
• 5.7 % BMP certificate/working
• 20 % need maintenance (i.e. source control only)

PLRM Drainage Conditions

%BMP

Each Land Use Becomes Subcatchment in SWMM5

Single Family Residential

• w/BMP
• non-BMP

Secondary Roads Other (Veg)

BMP

(infiltration area)

Each Land Use Becomes Subcatchment in SWMM5

Russ Wigart, El Dorado Co. DOT-TED installing field equipment— Sigma flow-weighted auto sampler

June 28, 2011 Storm Event

• El Dorado Co. DOT-TED fieldwork by

Russ Wigart

• Flow gage and water quality sampler in

storm drain manhole, 5-minute rainfall

• Forecast: ~1 inch total precipitation

–Known runoff yield interval to set Sigma

• Recorded: 0.93 inch rain, 9905 cu. ft.

runoff over 13 hours

June 28, 2011 Storm Event

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 6/28/11 19:12 6/28/11 21:36 6/29/11 0:00 6/29/11 2:24 6/29/11 4:48 6/29/11 7:12 6/29/11 9:36

Runoff (cfs)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18

Precipitation (in/5 min)

Measured flow Precipitation

SWMM5 runoff vs. measured

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 6/28/11 19:12 6/28/11 21:36 6/29/11 0:00 6/29/11 2:24 6/29/11 4:48 6/29/11 7:12 6/29/11 9:36

Runoff (cfs)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18

Precipitation (in/5 min)

Measured flow SWMMtest Precipitation

Flow-duration curve

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Runoff (cfs) Percentile (flow)

Measured flow SWMMtest

“OK, so now what?”

• Modeled flow shows good response to

precipitation

• Peak flows and timing look good
• Total volume predicted by PLRM 26% higher

than measured

• Parameter adjustment?

– Measured flows do not respond to 0.01 inch /5min events (seems to be loss from surface or pipes) – Initial peak flow over-estimated (initial storage)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 6/28/11 19:12 6/28/11 21:36 6/29/11 0:00 6/29/11 2:24 6/29/11 4:48 6/29/11 7:12 6/29/11 9:36

Runoff (cfs)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18

Precipitation (in/5 min)

Measured flow SWMMtest Precipitation

SWMM5 runoff vs. measured (adjusted parameters)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Runoff (cfs) Percentile (flow)

Measured flow SWMMtest

Flow-duration curve (adjusted parameters)

Water Quality Results: Measured TSS, n=19

flow-weighted EMC TSS = 202 mg/L

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 6/28/11 19:12 6/28/11 21:36 6/29/11 0:00 6/29/11 2:24 6/29/11 4:48 6/29/11 7:12 6/29/11 9:36

Runoff (cfs)

100 200 300 400 500 600 700 800 900 1000

TSS (mg/L)

Measured flow TSS samples

EMC EMC TS TSS S = = 20 202 mg/L 2 mg/L

SWMM5 Water Quality – TSS mean = 207 mg/L

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 6/28/11 19:12 6/28/11 21:36 6/29/11 0:00 6/29/11 2:24 6/29/11 4:48 6/29/11 7:12 6/29/11 9:36

Runoff (cfs)

100 200 300 400 500 600 700 800 900 1000

TSS (mg/L)

Measured flow TSS samples TSS-SWMM

Pollution reduction strategies

• Pollutant source control treatments

– Parcel-scale BMPs – Road maintenance and sweeping – Site-specific conditions, e.g. eroding cut slopes

• Catchment-scale treatments

– Dry basin, infiltration basin, wet basin, storm filters, etc.

• El Dorado Co. DOT-TED example

– Infiltration basin design in catchment – How big?? 33% of runoff volume typical

2 4 6 8 10 12 14 WS_73 3783CF 5675CF 11350CF

Catchment size alternatives

Runoff Volume (ac-ft/yr) 800 1600 2400 3200 4000 4800 5600 TSS and FSP (lb/yr) Runoff Vol(ac-ft/yr) TSS(lbs/yr) FSP(lbs/yr)

PLRM Infiltration Basin Results:

Size alternatives—Based on flow yield from 1-inch storm

2 4 6 8 10 12 14 WS_73 3783CF 5675CF 11350CF

Catchment size alternatives

Runoff Volume (ac-ft/yr) 800 1600 2400 3200 4000 4800 5600 TSS and FSP (lb/yr) Runoff Vol(ac-ft/yr) TSS(lbs/yr) FSP(lbs/yr)

PLRM Infiltration Basin Results:

Size alternatives—Based on flow yield from 1-inch storm

Sized for 33% Sized for 100% Sized for 50% Baseline

2 4 6 8 10 12 14 WS_73 3783CF 5675CF 11350CF

Catchment size alternatives

Runoff Volume (ac-ft/yr) 800 1600 2400 3200 4000 4800 5600 TSS and FSP (lb/yr) Runoff Vol(ac-ft/yr) TSS(lbs/yr) FSP(lbs/yr)

PLRM Infiltration Basin Results:

Size alternatives—Based on flow yield from 1-inch storm

Sized for 33% Sized for 100% Sized for 50% Baseline

• 55% flow
• 72% FSP
• 71% flow
• 83% FSP

PLRM Refinement Process

1) Set up catchment in PLRM interface 2) Run SWMM5 for event basis

Calibrate / reduce errors

3) Run revised parameters in PLRM for catchment load crediting