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.
