Monday, September 24, 2018

Drought in the Barton Springs segment of the Edwards Aquifer: Are we in or out?

Alarm Stage II Drought
Lovelady well height: 475 ft-msl
Barton Springs: approximately 90+ cfs 10-day average (USGS gauge is currently under maintenance)


September 23, 2018
Since early September we’ve received more than 10 inches of rainfall that has ultimately produced runoff and recharge to the aquifer. Present the streams are flowing (Onion Creek > 100cfs), water levels are rising, and Barton Springs is flowing > 60 cfs). So how can we still be in drought?

In fact, I received a call late last week from a groundwater user pointing out that the local news declared the end of the drought last week, and they asked why is it that the BSEACD is still under official Stage II Alarm drought declarations since July 12th. Indeed, for our area the US drought monitor maps show drought conditions in early September and then non-drought conditions by mid-September after the rains (https://droughtmonitor.unl.edu/).

The primary reason is that changes in the amount of groundwater in an aquifers generally lag behind the effects of weather for a variety of reasons. Drought is defined as “a period of drier-than-normal conditions that result in water-related problems.” However, there are several varieties of drought, with what most people consider drought actually classified as 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, but Barton Springs can be highly sensitive to relatively minor and localized rainfall events. We’re seeing this right now with Barton Springs responding to these 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 drought and are rising, but are below their trigger level for now.

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.

The good news about the current groundwater drought is that the Lovelady water-level trends are currently rising upward at a rate of about (0.3 ft/day) and if they continue rising, we may be out of drought by early October 2018. The short-term and long-term forecasts are calling for more rain, so the outlook is very good that we may exit groundwater drought conditions soon.
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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