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? LAND USE SOIL TYPE Secondary SFR Roads Impervious 17% 19% SLOPE ROAD & PARCEL Vegetated 3 CONDITIONS 22% SFR Pervious 42%
PLRM: How does it work? LAND USE SOIL TYPE Secondary SFR Roads Impervious 17% 19% SLOPE ROAD & PARCEL Vegetated 3 CONDITIONS 22% SFR Pervious 42%
PLRM: How does it work? LAND USE METEOROLOGI SOIL TYPE Secondary SFR C DATASET: Roads Impervious 17% 19% SLOPE 18 years ROAD & PARCEL Vegetated 3 CONDITIONS 22% SFR Pervious 42%
PLRM: How does it work? LAND USE METEOROLOGI SOIL TYPE Secondary SFR C DATASET: Roads Impervious 17% 19% SLOPE 18 years ROAD & PARCEL Vegetated 3 CONDITIONS 22% SFR Pervious 42%
PLRM: How does it work? LAND USE METEOROLOGI SOIL TYPE Secondary SFR C DATASET: Roads Impervious 17% 19% SLOPE 18 years ROAD & PARCEL Vegetated 3 CONDITIONS 22% SFR Pervious 42% 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
Catchment Land Use Distribution: Single Family Residential & Secondary Roads SFR Secondary Impervious Roads 17% 19% Vegetated 3 22% SFR Pervious 42%
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
Each Land Use Becomes Subcatchment in SWMM5 Single Family Residential -w/BMP -non-BMP Secondary Roads BMP (infiltration area) Other (Veg)
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 1.6 0.00 0.02 1.4 0.04 Measured flow 1.2 Precipitation (in/5 min) 0.06 Precipitation 1.0 Runoff (cfs) 0.08 0.8 0.10 0.6 0.12 0.4 0.14 0.2 0.16 0.0 0.18 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
SWMM5 runoff vs. measured 1.8 0.00 1.6 0.02 1.4 0.04 Precipitation (in/5 min) 1.2 0.06 Measured flow Runoff (cfs) SWMMtest 1.0 0.08 Precipitation 0.8 0.10 0.6 0.12 0.4 0.14 0.2 0.16 0.0 0.18 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
Flow-duration curve 1.0 0.9 0.8 Percentile (flow) 0.7 0.6 0.5 0.4 0.3 0.2 Measured flow 0.1 SWMMtest 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Runoff (cfs)
“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)
SWMM5 runoff vs. measured (adjusted parameters) 1.6 0.00 0.02 1.4 0.04 1.2 Precipitation (in/5 min) Measured flow 0.06 1.0 Runoff (cfs) SWMMtest 0.08 Precipitation 0.8 0.10 0.6 0.12 0.4 0.14 0.2 0.16 0.0 0.18 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
Flow-duration curve (adjusted parameters) 1.0 0.9 0.8 Percentile (flow) 0.7 0.6 0.5 0.4 0.3 0.2 Measured flow 0.1 SWMMtest 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Runoff (cfs)
Water Quality Results: Measured TSS, n=19 flow-weighted EMC TSS = 202 mg/L 5.0 1000 Measured flow 4.5 900 TSS samples 4.0 800 3.5 700 Runoff (cfs) TSS (mg/L) 3.0 600 2.5 500 2.0 400 1.5 300 EMC EMC TS TSS S = = 20 202 mg/L 2 mg/L 1.0 200 0.5 100 0.0 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
SWMM5 Water Quality – TSS mean = 207 mg/L 5.0 1000 Measured flow 4.5 900 TSS samples TSS-SWMM 4.0 800 3.5 700 Runoff (cfs) TSS (mg/L) 3.0 600 2.5 500 2.0 400 1.5 300 1.0 200 0.5 100 0.0 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
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
PLRM Infiltration Basin Results: Size alternatives — Based on flow yield from 1-inch storm 14 5600 Runoff Vol(ac-ft/yr) Runoff Volume (ac-ft/yr) 12 4800 TSS(lbs/yr) TSS and FSP (lb/yr) 10 4000 FSP(lbs/yr) 8 3200 6 2400 4 1600 2 800 0 0 WS_73 3783CF 5675CF 11350CF Catchment size alternatives
PLRM Infiltration Basin Results: Size alternatives — Based on flow yield from 1-inch storm 14 5600 Runoff Vol(ac-ft/yr) Runoff Volume (ac-ft/yr) 12 4800 TSS(lbs/yr) TSS and FSP (lb/yr) 10 4000 FSP(lbs/yr) 8 3200 6 2400 4 1600 2 800 0 0 WS_73 3783CF 5675CF 11350CF Catchment size alternatives Baseline Sized for Sized for Sized for 33% 50% 100%
PLRM Infiltration Basin Results: Size alternatives — Based on flow yield from 1-inch storm 14 5600 Runoff Vol(ac-ft/yr) Runoff Volume (ac-ft/yr) 12 4800 TSS(lbs/yr) TSS and FSP (lb/yr) 10 4000 FSP(lbs/yr) -55% flow -72% FSP 8 3200 -71% flow -83% FSP 6 2400 4 1600 2 800 0 0 WS_73 3783CF 5675CF 11350CF Catchment size alternatives Baseline Sized for Sized for Sized for 33% 50% 100%
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
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