Desired Future Conditions
A Report by the Barton Springs/Edwards Aquifer Conservation District
The rains that returned to Central Texas in the fall of 2009 continued intermittently through most of 2010, ending the most serious drought to grip the Barton Springs Aquifer since the creation of the Barton Springs Edwards Aquifer Conservation District in 1987. The District regulates the pumping of groundwater from the Aquifer, which is the drinking water source for more than 50,000 people, a critical resource for many industries and employers, and the origin of Barton Springs and its ecosystem.
With the drought as a prelude, the District undertook to carry out the assignment to determine the “desired future conditions” (DFC) of the Aquifer during the next 50 years. Based on the DFC’s adopted by the groundwater conservation districts in each groundwater management area across Texas, the Texas Water Development Board will issue the amount of “managed available groundwater” (MAG) that each district may permit for withdrawal. The MAG will be, in effect, a cap on nonexempt pumping (and maybe also a floor.)
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Blanco River Recharges Barton Springs During Drought
Nico Hauwerta, Brian Huntb, Marcus Garyc, Steve Johnsond
Click images to view full size figures
The Blanco River appears to be an important source of recharge for Barton Springs during times of drought, as demonstrated by recent groundwater tracing. This exciting new finding gives scientists a better understanding of how flows at Barton Springs are sustained during drought conditions.
Between May 2008 and February 2009, fluorescent dye injected in the Blanco River watershed was detected at Barton Springs. The tracers also showed up in wells in the Mountain City and Ruby Ranch areas, in addition to wells south of the Blanco River toward San Marcos Springs (Figure 1). These tracer injections targeted lower-flow drought conditions, ie., below average flow rate for Barton Springs of about 50 cubic feet per second (cfs). During low-flow conditions in 2009, groundwater flow rates through the Edwards Aquifer to Barton Springs decreased substantially compared to the 3-day travel time from nearby Onion Creek measured in 2005, under high-flow conditions. Tracers from the Blanco River generally took about three months to arrive at Barton Springs during the 2008 to 2009 traces (Figures 2 and 3). The Edwards Aquifer Authority is preparing a report in conjunction with the Barton Springs/Edwards Aquifer Conservation District, Zara Environmental, and the City of Austin to describe the Blanco River groundwater tracing study and its results in detail.