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Groundwater districts seek to predict future aquifer levels

Monday, September 8, 2008 by Jacob Cottingham

Officials with Central Texas groundwater management districts may be fighting an uphill battle to preserve their aquifers in the face of some dire predictions on what a growing population will do to the water table in the Hill Country over the next 50 years, including a drop of 33 feet in the next half century – and that is with very limited population growth.


Declining aquifer levels are a problem across much of the southwest, including Priority Groundwater Management Area No. 9, whose members met in Kerrville last month.


Skipping discussions on population growth, the managers began talking about how to preserve groundwater supplies through conservation and other means. The Priority Groundwater Management Area – or PGMA, pronounced “pig-ma” – is one of a series of groundwater agencies organized by the Texas Commission on Environmental Quality to take a regional approach to groundwater conservation.


Nine Central Texas districts — including the Barton Springs Edwards Aquifer Conservation District and the Hays Trinity Groundwater Conservation District – – met Aug. 29 for a PGMA 9 voting session to determine future conditions for the region’s aquifers for the next 50 years. While some measures on smaller aquifers did pass, the agencies did not vote on a controversial drawdown level for major features such as the Middle Trinity Aquifer in Hays County.


In the days leading up to the meeting,  local citizens  — spurred by activist groups like the Hill Country Alliance — flooded email inboxes and phone lines with concerns about the proposed drawdown level and the methodology by which the PGMA was establishing the level.. According to Andrew Backus, president of Hays Trinity district, at least 80 citizens made the trek to Kerrville to watch and for some, to voice an opinion.


Primarily, the object of attention was computer modeling of the aquifer’s future condition that did not appear to factor in the Drought of Record. That event is often used as a baseline worst-case scenario in water management. In order for water levels to be considered sustainable, pumping would theoretically be able to continue under such a drought. For PGMA 9, the record event was a seven-year dry spell that lasted from early 1950 through December of 1956.


Modeling for the region is a complex task that takes into account projected population growth, recharge rates, and current levels of pumping. The mapped area is then divided into one-square-mile cells that make up a grid. The grid is then run through an algorithm that takes into account water availability under the record drought conditions.


According to Backus, when a certain number of grids run dry, the model “doesn’t converge” and essentially crashes. Unfortunately for citizens of the region, if the model uses drought of record conditions it crashes at the current levels of pumping. That means that without any additional pumping in the nine-county region, should a similar drought reoccur, water quantity would be substantially affected.


Backus told In Fact Daily, “part of what is driving this is that some counties’ population projections would suggest that they’re going to put a tremendous pressure on the groundwater system. So they’re experimenting with larger numbers [of drawdown] that they felt the population would allot. I feel that’s somewhat of a backward process…” He said that some conservation districts have turned this exercise into “desired future groundwater availability, not desired future condition of the aquifer.”


Kirk Holland, general manager of the Barton Springs district said “recognizing additional pumpage that may occur in the future is not a sustainable yield amount… is a risk that GMA 9 has indicated that its elected representatives want to run.”


Backus cautioned that this does “not necessarily (mean) that the aquifer is going to completely dry up, but it will substantially drop water levels in places. The point of this exercise is to drag people to the table and make them aware of the consequences of what’s happening here. If you’re OK with drying up the spring and rivers and streams go for it, but do it in the open and do it consciously and decisively. The science exists so we don’t in 10 years go ‘Gosh, the Blanco doesn’t flow six months of the year, what happened?’”


Holland says that options do exist for alternative water sources, although he conceded that political will for such options – aquifer storage, desalinating brackish water, rainwater harvesting or support for additional surface water supplies – often requires a substantial drought affecting the lifestyles of citizens. “What we can do is manage it in a scientifically sound, rational and equitable fashion and under a groundwater management plan that stretches out a scarce resource for as long as possible,” he explained.


For now, it seems that both local districts will be struggling to provide leadership on this crucial issue. Backus said that his conservation district has “been the most vocal” about reducing the average draw down to 15 feet. Holland said that another option would be segmented areas of the aquifer, which would give different geographic areas more or less available drawdown.


“We need to be conservative with resources because if 33 feet (of drawdown) is acceptable, it becomes self-fulfilling and it’s better to move slowly,” Holland said. “GMA 9 understands that.”

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