In cooperation with the U.S. Air Force, Air Logistics Center, Kelly Air Force Base, Environmental Management Office
Gain-Loss Study of Lower San Pedro Creek and the San Antonio River, San Antonio, Texas, May–October 1999
By D.J. Ockerman
U.S. Geological Survey
Open-File Report 02–023
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Contents
Abstract
Introduction
Purpose and Scope
Description of Study Area
Hydrologic Conditions Before and During Study
Approach
Streamflow Gain-Loss Measurements
Estimation of Ground-Water Inflow and Outflow
Gain-Loss Determinations and Estimation of Ground-Water Inflow
Tributary Inflow
Diversions
Measurement Summaries and Ground-Water Inflow Estimates
Summary
References
Figures
| 1. | Map showing location of study area and selected data-collection sites | |
| 2. | Photograph showing USGS streamflow-gaging station San Antonio River at Theo Avenue (08178505) | |
| 3. | Graph showing cumulative rainfall, daily mean streamflow, and days of streamflow-measurement surveys, San Pedro Creek and San Antonio River, May–October 1999 | |
| 4. | Photograph showing streamflow measurement at San Antonio River dam spillway near Padre Park, July 1999 | |
| 5. | Schematic diagram of subreaches showing streamflow-measurement sites, streamflow-gaging stations, inflows, diversions, and return flows | |
| 6–10. | Photographs showing: | |
| 6. | Confluence of San Pedro Creek and the San Antonio River, July 1999 | |
| 7. | Seepage inflow along Concepcion Creek channel, July 1999 | |
| 8. | Riverside Creek at San Antonio River, July 1999 | |
| 9. | Seepage along west bank of San Antonio River, above Mission Road, July 1999 | |
| 10. | San Antonio River diversion to Padre Park Acequia, July 1999 | |
Tables
| 1. | Monthly rainfall and departure from normal, January–October 1999 |
| 2. | Location of streamflow-measurement sites and streamflow-gaging stations, San Pedro Creek and San Antonio River |
| 3. | Subreaches for gain-loss estimates, San Pedro Creek and San Antonio River |
| 4. | Summary of gain-loss determinations for subreaches along San Pedro Creek and the San Antonio River during streamflow-measurement surveys, May–October 1999 |
| 5. | Summary of tributary discharges (attributed to shallow ground-water inflow) to subreaches along SanPedro Creek and the San Antonio River during streamflow-measurement surveys, May–October 1999 |
| 6. | Summary of estimated shallow ground-water inflow for subreaches along San Pedro Creek and the San Antonio River during streamflow-measurement surveys, May–October 1999 |
Abstract
Five streamflow gain-loss measurement surveys were made along lower San Pedro Creek and the San Antonio River from Mitchell Street to South Loop 410 east of Kelly Air Force Base in San Antonio, Texas, during May–October 1999. All of the measurements were made during dry periods, when stormwater runoff was not occurring and effects of possible bank storage were minimized. San Pedro Creek and the San Antonio River were divided into six subreaches, and streamflow measurements were made simultaneously at the boundaries of these subreaches so that streamflow gains or losses and estimates of inflow from or outflow to shallow ground water could be quantified for each subreach. There are two possible sources of ground-water inflow to lower San Pedro Creek and the San Antonio River east of Kelly Air Force Base. One source is direct inflow of shallow ground water into the streams. The other source is ground water that enters tributaries that flow into the San Antonio River. The estimated mean direct inflow of ground water to the combined San Pedro Creek and San Antonio River study reach was 3.0 cubic feet per second or 1.9 million gallons per day. The mean tributary inflow of ground water was estimated to be 1.9 cubic feet per second or 1.2 million gallons per day. The total estimated inflow of shallow ground water was 4.9 cubic feet per second or 3.2 million gallons per day. The amount of inflow from springs and seeps (estimated by observation) is much less than the amount of direct ground-water inflow estimated from the gain-loss measurements. Therefore, the presence of springs and seeps might not be a reliable indicator of the source of shallow ground water entering the river. Most of the shallow ground water that enters the San Antonio River from tributary inflow enters from the west side, through Concepcion Creek, inflows near Riverside Golf Course, and Six-Mile Creek.