Water Level Monitoring
Water level data are critical for EAA’s management of the San Antonio Pool and the Uvalde Pool of the Edwards Aquifer. Water levels are measured around the clock using different devices in monitoring wells throughout the aquifer. Water level data are used for many purposes, including as criteria for determining when to impose groundwater withdrawal reductions on aquifer users during droughts and understanding and appreciating our shared natural resource.
Water levels at the J-17 Index Well are provided here as raw data in 15-minute intervals. These are provisional readings and are subject to further qualitative review by the EAA.
This data may be is subject to change due to instrument issues or physical changes at the measurement site, which may result in significant revisions to the data. Data displayed here are subject to revision until they have been thoroughly reviewed and receive final approval. Questions? Contact us at email@example.com
How Does it Work?
To ensure accuracy, the EAA uses three different devices to measure water level. The elevation of the water in the well—the potentiometric surface—is created by artesian pressure in the aquifer and is measured in feet above mean sea level (msl). For example, since the ground level at J-17 measures 730.8 feet above msl, when the water rises to 70 below the ground’s surface, subtracting 70 from 730.8 gives us an aquifer level reading in the San Antonio Pool of 660.8 feet above msl.
Every day, the highest water level recorded between the hours of 12 a.m. and 8 a.m. is reported as the daily high. However, during periods of heavy rain, water levels in the well may rise throughout the day so the highest water level would then be recorded in the late evening and a correction would be made to the previous reading. The EAA uses this information for official historical reporting and for determining and enforcing groundwater reductions during periods of high aquifer demand and/or drought.
Well J-27 is the official Edwards Aquifer water level index well for Uvalde County. Automated equipment in J-27 collects water level data which is reported to the EAA. To ensure that the public can view representative water level data, the daily high-water level will be reported on the EAA website. These are provisional readings and are subject to further qualitative review.
The EAA is solely responsible for obtaining and reporting water level readings from J-27. The EAA uses this information to determine when critical period management (drought management) pumping reductions are required for the Edwards Aquifer in Uvalde County.
Comal Springs/San Marcos Springs Data
Average daily springflow measurement is conducted by the United States Geological Survey (USGS). For more information on how springflow is calculated, please visit the USGS Streamflow and Springflow at Comal and San Marcos Rivers page. Because these measurements reflect daily averages, they are reported for the previous day. Measurements are in cubic feet per second (cfs).
Visit the Historical Data page to view statistics and download data.