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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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pdf (19.6 MB)


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.

 


U.S. Department of the Interior, U.S. Geological Survey
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