NewsDrop-October-2024

AQUIFER SCIENCE

By: Mark Hamilton Executive Director of Aquifer Management Services

AQUIFER CONDITIONS DATA FROM INDEX WELLS & SPRINGS HOW WE COLLECT

Figure 5. The J-17 Index Well in 2006.

Figure 4. Comal Springs, Landa Park News Braunfels, Texas.

Figure 6. The J-17 Index Well in 2022.

Comal Springs 12/19/1927 – present

J-17 Index Well 11/12/1932 – present

High: 534 on 10/14/1973 Low: 0 (no flow) between 6/13/1956 and 11/3/1956 These readings are measured in cubic feet per second.

High: 703.31 on 6/14/1992 Low: 612.51 on 8/17/1956 These readings are measured in feet below mean sea level.

Scan this QR code to watch a video captured at the J-17 Index Well in San Antonio, Texas. Hear from Bryan Anderson, EAA Director of Data Management, and Charles Crawford, EAA Data Collections Superviso r, as they explain EAA data collection efforts for aquifer conditions. https://youtu.be/EtTQkEqjV5c?si=mYLFaqEYn4WP-bof

J-27 Index Well 10/24/1940 – present

Figure 7. Chart reading from the J-17 Index Well for an earthquake event that occurred in 2009.

San Marcos Springs 5/26/1956 – present

High: 889.05 on 6/15/1987

High: 451 on 3/12/1992 Low: 46 on 8/15/1956 These readings are measured in cubic feet per second.

To learn about how the USGS calculates springflow, please scan this QR code. https://webapps.usgs.gov/ spring_calc/

Low: 810.95 on 4/13/1957 These readings are measured in feet above mean sea level.

Figure 2. Shows the EAA jurisdiction with markers indicating the aquifer conditions area indexes.

Figure 3. San Marcos Springs, Spring Lake San Marcos, Texas.

Figure 1. Example of Edwards Aquifer Conditions Table from September 4, 2024.

managing the aquifer to the benefit of all who rely on it. The period of record for these sites as well as their respective locations are primary factors in both their selection as index locations and their usefulness as key modeling points in the EAA groundwater model. The EAA groundwa ter model is designed to mimic system behavior and function as a tool for developing manage ment methods designed to ensure continuous springflows in a repeat of the drought of record. Management methods, such as CPM, ensure compliance with the terms of the Edwards Aqui fer Habitat Conservation Plan (EAHCP) and the Incidental Take Permit (ITP) associated with it, by bringing added certainty to the region regard ing the Edwards Aquifer.

measurements to ensure data accuracy. One added difficulty in measuring springflow is the influence of surface runoff during rain events. USGS staff have a well-established process for separating the runoff from the springflow such that estimates are as accurate as possible, even after rainfall events. The Index Wells and two spring groups discussed herein are statutorily designated as measurement points for determining CPM. Importantly, each of these locations have significant data histories. For example, the continuous data record for J-27 goes back to 1940, for J-17 that record goes back to 1932, and for springflow the earliest record goes back to 1927 for the Comal Springs. These long periods of record are essential to

The two spring groups, Comal and San Mar cos Springs, are measured in similar fashion to the index wells, using a pressure transducer and telemetry equipment. Springflow at each system is estimated using methodology that involves calculating flow across a known chan nel cross section, in the streams just down stream of the springs. The height of water, combined with a known area of stream cross section provides a basis for making accurate spring discharge estimates. Much like the index wells, data are transmitted at 15-minute intervals to the USGS data servers, in units of cubic feet per second (cfs). USGS staff make calibration and reference measurements at the springs in similar fashion to the way that EAA staff conduct calibration and reference

equipment to minimize the risk of data loss in these wells. Data integrity is maintained by regular calibration checks at the Index Wells to always ensure the accuracy of the equipment. If water levels meet criteria for a change in EAA Critical Period Management (CPM) Plan stages, staff visit the well in question (i.e. J-17 Index Well or J-27 Index Well) to make confirmatory measurements prior to issuance of notice to make a change in CPM stage. The CPM is a groundwater reduction initiative implemented during periods of drought, when water levels and springflows are low.

The table in figure 1, showcases these data for both the San Antonio and Uvalde Pools. The San Antonio Pool is comprised of readings from the J-17 Index Well, Comal Springs, and San Marcos Springs. The Uvalde Pool is comprised of water level data from only the J-27 Index Well. Water level data are collected from the Index Wells in 15-minute intervals using a pres sure transducer paired with a telemetry device. Water level data are then automatically trans mitted to the EAA in near real time and reported in units of feet above mean sea level (ft msl). For added data security, each index well is equipped with redundant measurement

Our agency collects water levels from the J-17 Index Well, and J-27 Index Well, while the United States Geological Sur vey (USGS) measures flow rates from Comal Springs, and San Marcos Springs. Collectively, these data are considered the aquifer condi tions, which are displayed on the front page of our website in a table that is updated daily.

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