Tuesday, April 7, 2020

Welcomed Rain Holding Off Drought

Lovelady well height: 481 ft-msl
Barton Springs: approximately 57 cfs 10-day average

April 23, 2020
Since the beginning of 2020, the Barton Springs/Edwards Aquifer region has received a little over 10 inches of rainfall, producing some runoff and recharge to the aquifer. After about 3.5 inches of rain between April 3rd-4th, area streams are flowing (Onion Creek > 40 cfs) as well as Barton Springs ( > 60 cfs).  For the moment, we are not in drought.

It often takes time for groundwater levels to reflect changes in the weather. Drought is defined as “a period of drier-than-normal conditions that result in water-related problems.” However, there are several varieties of drought.  Generally, people are most familiar with a meteorological drought—a rainfall deficit effecting the landscape. However, over time, the lack of rain produces agricultural and ultimately hydrological droughts. Droughts that affect the Barton Springs segment of the Aquifer can be best characterized as hydrological, but more specifically a groundwater drought. 

Groundwater droughts, by the very nature of the hydrologic cycle, often have a time-lag response to high rainfall, or lack of rainfall, conditions. The District utilizes flow from Barton Springs and water levels in the Lovelady monitor well to indicate overall storage and drought status of the aquifer. Barton Springs is the primary natural discharge point and is a good measure of the overall health of the aquifer system. However, like a stream, Barton Springs can be highly sensitive to relatively minor and localized rainfall events. We’re seeing this right now with Barton Springs responding to recent rains and flow well above its drought trigger. Conversely, the Lovelady well has a muted response to minor rainfall, but is a good measure of overall storage in the aquifer. Water levels have responded to the recent rains, but continue a downward trend towards Alarm Stage Drought II.

For the District to declare drought conditions, either spring flow or the Lovelady water levels need to be below their respective drought thresholds. However, to exit a drought stage, both spring flow and water level must rise above their respective drought trigger values. This latter requirement keeps the District from making multiple declarations about drought over short periods of time. A good example occurred in 2014 when the District officially remained in Alarm Drought Stage II from July 2014 through January 2015 (Figure 1). However, during that period Barton Springs temporarily responded to two large rain events that did not result in significant increases in recharge and storage to the aquifer as indicated by water levels in the Lovelady well.

Without more rain, groundwater levels could dip beneath the Drought threshold as soon as mid-May to June. The good news is we are entering the wettest months of the year in Central Texas.
More information on District’s drought trigger methodologies:

Figure 1. Period of Stage II Alarm Drought from 2014.  The BSEACD declared drought in July 2014 and then exited drought conditions in early 2015. This illustrates that Barton Springs responded to rainfall events, but did not result in significant increases in storage within the aquifer as represented by the Lovelady Well.  

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