Edwards Aquifer Urban Hydrology Network

Continuous Monitoring Tracks Local Surface-Water and Groundwater Connections

Summary of findings from Opsahl and others, 2020

Continuous monitoring of surface water, groundwater, and springs in the San Antonio segment of the Edwards aquifer is a central component of the USGS Urban Hydrology Network in San Antonio. This next generation of hydrologic monitoring technology serves a variety of information needs specific to local communities, including real-time information about water quality and hydrologic conditions for the karstic Edwards aquifer, which is the primary water supply for the city of San Antonio.

USGS "super sites" examine the dynamic connection between urban stormwater runoff and recharge to shallow groundwater of the Edwards aquifer. These sites monitor both streamflow and groundwater levels and are sites of water-quality sample collection during periods of groundwater recharge.

Muddy water rushing out of culverts beneath road.

Flood event at the West Elm Creek at Encino Rio site.

Site locations shown on the interactive map

Rainfall at the San Antonio International Airport and continuous water-level altitude, stage data, and sampling dates for the West Elm Creek and Encino Rio well site pair.

  • Continuous monitoring of streamflow at West Elm Creek, an ephemeral recharge stream in an urbanized area in northern San Antonio, captures the timing and magnitude of runoff events.
  • Relatively large flow events on West Elm Creek and other similar streams in the area provide recharge to the aquifer that is observed and recorded in shallow groundwater wells. The response to such flow events is often immediate, with substantial amounts of urban recharge entering the aquifer.
Hydrographers pouring water into sampling equipment on a table.

U.S. Geological Survey hydrographers processing a groundwater sample for pesticide analysis at the Encino Rio site.

Water-level altitude and the number of detections of herbicides, insecticides plus fungicides, and the total number of detections in samples collected from the Encino Rio well.

  • Continuous monitoring also is used to determine the timing of water-quality sample collection. Samples for contaminants, such as pesticides, can be strategically collected before, during, and after groundwater recharge events from stormwater-runoff sites and shallow groundwater wells.
  • Water-quality results associated with groundwater recharge events provide insight into sources of contaminants to the aquifer.