In cooperation with the San Antonio Water System
Simulation of Streamflow and Estimation of Streamflow Constituent Loads in the San Antonio River Watershed, Bexar County, Texas, 1997–2001
By Darwin J. Ockerman and Kenna C. McNamara
U.S. Geological Survey
Water-Resources Investigations Report 03–4030
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Contents
Abstract
Introduction
Purpose and Scope
Description of Study Area
Description of Simulation Model, Modeling Process, and Loads Estimation Method
Simulation of Streamflow
Model Calibration and Testing
Lower Medina River Basin
Leon Creek Basin
Upper San Antonio River Basin
Salado Creek Basin
Lower San Antonio River Basin
Error Analysis
Sensitivity Analysis
Simulation of Streamflow by Basin and Source Category
Estimation of Streamflow Constituent Loads
Source Concentrations Used for San Antonio River Constituent Loads Estimation
Estimation of Streamflow Constituent Loads Using Source Concentrations With HSPF-Simulated Flow
Summary
References
Figures
| 1–4. | Maps showing: | |
| 1. | San Antonio River watershed, Bexar County, Texas | |
| 2. | Data-collection sites used for Hydrological Simulation Program—FORTRAN model calibration, testing, simulations, and estimation of streamflow water-quality constituent loads | |
| 3. | Study area land use, Bexar County, Texas | |
| 4. | Lower Medina River Basin stream and reservoir (RCHRES) segments | |
| 5. | Graphs showing measured and simulated 7-day mean streamflow at Medina River at San Antonio, Texas (08181500), 1997–2001 | |
| 6. | Map showing Leon Creek Basin stream and reservoir (RCHRES) segments | |
| 7. | Graphs showing measured and simulated 7-day mean streamflow at Leon Creek at IH–35 at San Antonio, Texas (08181480), 1997–2001 | |
| 8. | Map showing upper San Antonio River Basin stream and reservoir (RCHRES) segments | |
| 9. | Graphs showing measured and simulated 7-day mean streamflow at San Antonio River at Loop 410 at San Antonio, Texas (08178565), 1997–2001 | |
| 10. | Map showing Salado Creek Basin stream and reservoir (RCHRES) segments | |
| 11. | Graphs showing measured and simulated 7-day mean streamflow at Salado Creek at Loop 13 at San Antonio, Texas (08178800), 1997–2001 | |
| 12. | Map showing lower San Antonio River Basin stream and reservoir (RCHRES) segments | |
| 13. | Graphs showing measured and simulated 7-day mean streamflow at San Antonio River near Elmendorf,Texas (08181800), 1997–2001 | |
| 14. | Pie diagram showing contribution to streamflow, in percent, at San Antonio River at Elmendorf, Texas (08181800), 1997–2001 | |
| 15. | Pie diagram showing sources of simulated streamflow, in percent, at San Antonio River near Elmendorf, Texas (08181800), 1997–2001 | |
| 16. | Graphs showing comparison of streamflow loads estimated from Hydrological Simulation Program—FORTRAN-simulated flow and source concentrations with loads computed from actual samples at San Antonio River near Elmendorf, Texas (08181800), 1997–2001 | |
| 17. | Pie diagrams showing sources of selected streamflow constituent loads, in percent, San Antonio River near Elmendorf, Texas (08181800), 1997–2001 | |
Tables
| 1. | Selected characteristics of basins in the San Antonio River watershed, Bexar County, Texas |
| 2. | Data-collection sites used for Hydrological Simulation Program—FORTRAN model calibration, testing, and simulations and estimation of water-quality constituent loads |
| 3. | Major recycled wastewater discharges, Bexar County, Texas |
| 4. | Basin-related model parameters for the Hydrological Simulation Program—FORTRAN |
| 5. | Process-related model parameters for the Hydrological Simulation Program—FORTRAN |
| 6. | Pervious and impervious land segment areas for basins in the San Antonio River watershed, Bexar County, Texas |
| 7. | Selected annual PERLND and IMPLND process-related parameters for flow, San Antonio River watershed models, Bexar County, Texas |
| 8. | Annual measured and simulated streamflow for basins in the San Antonio River watershed, Bexar County, Texas, 1997–2001 |
| 9. | Sensitivity of selected annual process-related parameters, Salado Creek Basin, 1997–2001 |
| 10. | Sources of simulated streamflow at San Antonio River near Elmendorf, Texas (08181800), 1997–2001 |
| 11. | Water-quality concentrations used for estimation of streamflow constituent loads |
| 12. | Estimates of selected annual streamflow constituent loads, by source, San Antonio River watershed, Bexar County, Texas, 1997–2000 |
| 13. | Sources of selected streamflow constituent loads, San Antonio River near Elmendorf, Texas (08181800), 1997–2001 |
Abstract
The U.S. Geological Survey developed watershed models (Hydrological Simulation Program—FORTRAN) to simulate streamflow and estimate streamflow constituent loads from five basins that compose the San Antonio River watershed in Bexar County, Texas. Rainfall and streamflow data collected during 1997–2001 were used to calibrate and test the model. The model was configured so that runoff from various land uses and discharges from other sources (such as wastewater recycling facilities) could be accounted for to indicate sources of streamflow. Simulated streamflow volumes were used with land-use-specific, water-quality data to compute streamflow loads of selected constituents from the various streamflow sources.
Model simulations for 1997–2001 indicate that inflow from the upper Medina River (originating outside Bexar County) represents about 22 percent of total streamflow. Recycled wastewater discharges account for about 20 percent and base flow (ground-water inflow to streams) about 18 percent. Storm runoff from various land uses represents about 33 percent.
Estimates of sources of streamflow constituent loads indicate recycled wastewater as the largest source of dissolved solids and nitrate plus nitrite nitrogen (about 38 and 66 percent, respectively, of the total loads) during 1997–2001. Stormwater runoff from urban land produced about 49 percent of the 1997–2001 total suspended solids load. Stormwater runoff from residential and commercial land (about 23 percent of the land area) produced about 70 percent of the total lead streamflow load during 1997–2001.
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