Program of the USGS in Texas
Estimation of Volume and Quality of Stormwater Runoff and Associated Recharge Within the Edwards Aquifer Recharge Zone
PROBLEM
The Edwards aquifer is the major source of water for more than one million people in the San Antonio/Bexar County area and provides nearly all of the water used for industrial, military, irrigation, and public supplies. Most recharge to the Edwards aquifer occurs west of Bexar County and is from direct infiltration of precipitation and streamflow loss in the recharge zone. After entering the aquifer, the water moves from west to east to points of discharge in Bexar County (mostly public supply wells) and then northeast, parallel or almost parallel, to the northeast-trending Balcones faults into Comal and Hays Counties, where it is discharged by withdrawals (wells) and springs. Additional recharge to the Edwards aquifer occurs in the recharge zone in northern Bexar County and southern Comal and Hays Counties.
OBJECTIVE
- To determine the quantity of stormwater runoff at stream sites within selected subbasins of the recharge zone representing specific land usage.
- To characterize stormwater quality at these stream sites.
- With the aid of a predictive model, estimate (a) runoff quantity and constituent loadings entering from above, originating from, and exiting the recharge zone and (b) recharge volume to the Edwards aquifer in Bexar County.
APPROACH
Objectives 1 and 2 will be accomplished through the following tasks:
A network of streamgaging/water-quality sampling stations will be established at five stream sites within the EARZ. Each of the five sites will be located within a subbasin having specific land-usage. The land-use categories of the sites are typical of land-use within the EARZ of Bexar county.
Rain gages operated by the Edwards Underground Water District (EUWD) and located within the Bexar County EARZ will provide rainfall data to be used for the calibration of the predictive model (objective 3).
For selected runoff events, the quantity and quality of stormwater runoff will bedetermined at the five stations. Water-quality samples will be collected and compositedas flow-weighted samples, providing data representing event-mean concentrations (EMCs).
The mean and median of the set of EMC values determined for each single land use,subbasin station will be used to characterize stormwater runoff from the various land-use categories.
Objective 3 will be accomplished through the following task:
The Hydrologic Simulation Program - Fortran (HSPF) model will be used to estimate thequantity and quality of stormwater runoff entering the EARZ, recharging the aquifer, and exiting the EARZ in Bexar County.
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U.S. Department of the Interior |
U.S. Geological Survey