Application of SWAT for Water Quality Modeling of the Caddo Lake Watershed, TX

Transcription

1 Application of SWAT for Water Quality Modeling of the Caddo Lake Watershed, TX Kendra Riebschleager, M.S., E.I.T. August 5, 2009 Espey Consultants, Inc S. 2 nd Street, B-300 Austin, TX

2 Outline Description of Study Area Scope of Work Methodology Project Setup/Watershed Delineation Edit Inputs Initial Results Calibration Procedures Manual Sensitivity Analysis Auto-Calibration Next Steps Coordinate with Lake Model Alternatives Analysis 2

3 Description of Study Area 3

4 Description of Study Area Population ~570,000 (10 counties, 1 parish) Employment Services, wholesale/retail, and manufacturing Agriculture Livestock 64%, crop sales 22.5% Natural Resources oil and gas industry, lignite 4

5 Description of Study Area Topography Gently rolling to hilly dissected by flat floodplains and terraces Avg. Elevation 200 to 500 ft msl Major Drainages Big Cypress Creek Little Cypress Creek Black Cypress Bayou James Bayou Frazier Creek 5 Soils Bowie-Cuthbert-Kirvin Associations gently sloping to steep, well drained to moderately well drained, loamy and gravelly Darco Association gently sloping to moderately steep, well drained, sandy soils Cuthbert-Redsprings Association Strongly sloping to steep, well drained, gravelly soils.

6 Description of Study Area Vegetative Cover Pine and mixed Pine-hardwood Forests Cultivated or Pasture land Bottomland hardwood forest and Cypress Swamp Climatology Avg. Annual Air Temperature 64-67ºF Precipitation Storm events 60 days/yr ~33 inches Evaporation Monthly Range ~10 in summer, 3 in winter 6

7 Description of Study Area Photo: Bruce Moring, USGS 7

8 Scope of Work Model the watershed influences on Caddo Lake Extent of Study: Cypress Basin downstream of Lake O Pines Parameters of Interest: Nutrients, DO, Bacteria Develop hydrodynamic and water quality model for Caddo Lake Perform Alternatives Analysis in support of WPP 8

9 Watershed Modeling Methodology

10 Watershed Modeling Cypress Creek Basin encompasses 110 mi 2 over two-thirds rural significant amount of agricultural lands SWAT provides a wide variety of agricultural surface treatments enabling simulation of structural and non-structural BMP's for evaluation of alternative strategies for runoff control from agricultural areas. Currently not including bacteria in SWAT model SELECT approach Load Duration Curves 10

11 Watershed - SWAT Model Setup Watershed Delineation Hydrologic Response Unit (HRU) Definition Unique areas with similar hydrologic characteristics to lump model runs Input Data Files Weather data (precip, temp) PS and NPS Pollutant Loadings Permitted Discharges Fertilizer/Pesticide Applications Land Practices Ponds and Reservoirs 11

12 SWAT - Watershed Delineation Digital Elevation Model NED 30-m NHD Plus Streams Define Points of Interest 12

13 SWAT Watershed Delineation Things to Consider Calibration data Water Quality Station Locations USGS Flow Gage Locations Point Sources Direct discharges from WWTP Expected Loading from CAFOs Reservoirs and Large Ponds Lake O Pines controlled discharge National Inventory of Dams (storage > 15,000 ac-ft) Lake Gilmer

14 SWAT Delineated Watersheds Lake O Pines Watershed 14

15 SWAT - HRU Definition Inputs Include: Land use Soils Slope NLCD 2001 verified by aerial photography NRCS SSURGO SWAT derives from the DEM Four Classes 0-1%, 1-3%, 3-9%, >9% 15

16 SWAT Edit Input Data Files Weather data (precip, temp, etc.) Is data sufficient to spatially and temporally describe watershed? SWAT assigns weather data from nearest station location to sub-watershed How can we improve the data? Interpolation Techniques Point Source and Non-Point Source Pollutant Loadings Permitted Discharges Fertilizer Applications Livestock Grazing Septic Systems Land Practices Pond data storage > 15,000 ac-ft Along stream network Reservoir data Volume Construction date 16

17 Run the SWAT Model Route watershed surface pollutants through catchments Rainfall/Runoff Mechanisms Simulated Weather Events SCS Curve Number Method Growth and Decay Plant Uptake Route pollutants from catchments to streams Incorporates QUAL-2E model for routing and predicting stream concentrations 17

18 SWAT Initial Run 80 Average Monthly Flow at USGS Black Cypress Bayou SWAT Subbasin 89 SWAT Flow USGS Gauge Flow Flow (cms) /1997 7/ /1999 4/2001 9/2002 1/2004 5/ /2006 2/2008 7/2009 Date 18

19 SWAT Calibration Process 1. Hydrology Daily Predicted vs. Measured at gauged locations 2. Sediments Total amounts (tons/acre) TSS concentrations LOADEST for monthly load predictions 3. Water Quality Depends on reliable hydrology/sediment predictions Available SWQM data Nitrogen (Total N, TKN, NH4, NO3, NO2) Phosphorus (Total P, Ortho-P) 19

20 SWAT - Model Calibration Sensitivity Analysis Determine which input parameters have greatest influence on model results Use both measured and literature values for fine tuning model inputs Incorporate Stakeholder Suggestions based on their knowledge of the watershed 20

21 SWAT Calibration - Hydrology Key Considerations Water Balance Overall Amount Distribution among hydrologic components Storm Sequence Time lag or shifts Time of concentration, travel time Shape of Hydrograph Peak Recession Consider antecedent conditions 21

22 SWAT Calibration - Hydrology Initial Run Graphically compare prediction to flow data at gauged locations Manual Calibration Adjust model parameters to more appropriately describe watershed Primarily Graphical Exercise Sensitivity Analysis Which parameters have the greatest influence on the model predictions? Auto-Calibration Based on manual adjustment and modifying most sensitive parameters to meet model objectives Saves time, increases efficiency Statistical Optimization Techniques 22

23 SWAT Initial Run 80 Average Monthly Flow at USGS Black Cypress Bayou SWAT Subbasin 89 SWAT Flow USGS Gauge Flow Flow (cms) /1997 7/ /1999 4/2001 9/2002 1/2004 5/ /2006 2/2008 7/2009 Date 23

24 Manual Calibration Procedure Peak Flows CN, canopy cover, soil available water capacity, soil evaporation Groundwater (baseflows) Minimum flow, revap => Increase Deep Aquifer Recharge Time of Peak Overland and Channel Roughness (n values) Surface lag coefficient 24

25 Manual Calibration Daily Flow at USGS / Subbasin 89 Black Cypress Bayou USGS Gauge Flow SWAT Daily Flow Sim 16 SWAT Daily Flow Sim Precip at Jefferson Flow (cms) /1/2000 2/20/2000 4/10/2000 5/30/2000 7/19/2000 9/7/ /27/ /16/2000 Date

26 Manual Calibration Flow (cms) Flow Duration Curve SWAT Sim 16 Black Cypress Bayou Gauge 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percent Exceedance 26

27 Sensitivity Analysis Estimate the rate of change in the output of a model with respect to changes in model inputs Parameters important to have more accurate values Understand the behavior of the system being modeled Evaluate applicability of the model Rank Name Description Location 1 ESCO Soil evaporation compensation factor *.hru 2 ALPHA_BF Baseflow alpha factor [days] *.gw 3 GWQMN Threshold water depth in the shallow aquifer for flow (mm) *.gw 4 CN2 Initial SCS CNII value *.mgt 5 CH_N2 Manning s n value for main channel *.rte 6 CH_K2 Channel effective hydraulic conductivity [mm/hr] *.rte 7 SURLAG Surface runoff lag time [days] *.bsn 8 SOL_AWC Available soil water capacity [mm H 2 O/mm soil] *.sol 9 CANMX Maximum canopy storage [mm] *.hru 27

28 Auto-Calibration In Progress Automation of calibration requires the formulation of closeness measures (objective functions) Automatic Optimization Algorithms that optimize an objective function by systematically searching the parameter space according to a fixed set of rules Simplified by Sensitivity Analysis determine parameters to optimize Manual Calibration narrow optimization space for parameters SWAT-CUP SUFI-2 Local Optimization Nash-Sutcliffe Objective Function 28

29 Next Steps

30 Calibration Re-run model with calibrated hydrology parameters Begin Sediment Calibration Nutrient Calibration 30

31 Lake Modeling Watershed model output (SWAT results) will be input to the lake model Pollutant loadings reaching the lake based on watershed characteristics and practices Special Considerations for Caddo Lake Lack of temperature stratification Off-channel wetland areas Shallow depths Invasive Species (Macrophytes) Giant Salvinia Hyacinth 31

32 Lake Modeling EC Determined the Appropriate Model based on Caddo Lake s Unique Environment WASP7 (Water Quality Analysis Simulation Program) Determine through scenario analysis the impact of watershed NPS load Percent Reduction Goal Relative to other sources of pollutants (resuspension, lake discharges, etc.) 32

33 SWAT - Alternatives Analysis Modify Watershed Practices Fertilizer Application CAFO waste management Structural BMPs Wastewater Treatment Options Consolidate or Replace septic systems Additional Regionalized Collection Systems Resultant Change in Pollutant Loadings Feed to lake model 33

34 Questions or Comments Phone Kendra Riebschleager David Harkins Tim Osting Ernest To 34 Espey Consultants, Inc S. 2 nd Street, B-300 Austin, TX 78704

35 Extra Slides 35

36 SELECT Potential Bacteria Loading Spatially Explicit Load Enrichment Calculation Tool Distributes Sources of Bacteria Livestock, Wildlife, Septic Systems, WWTPs Within the appropriate habitat Livestock in pastures/grassland Wildlife in forested and non-developed lands Septic Systems in residential areas without municipal services Considering other factors Magnitude of fecal production and bacteria concentration Soil type Distance to streams and waterbodies 36

37 Lake Modeling - WASP 37