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Recharge Dams Water enters the Aquifer easily in the recharge zone, but the subsurface drainage is generally inadequate to hold all the water that falls in large rain events. Recharge conduits and sinkholes quickly become filled and the remaining water has to flow over the surface and on past the recharge zone. The idea behind recharge dams is that by slowing water down, more can be forced to go into the Aquifer during wet times which will sustain flows at Comal Springs above critical levels and keep the J17 index well at a higher level during dry times. There are actually two types of recharge dams that have been proposed and considered. Type I dams would be constructed on the creeks and rivers of the Edwards Plateau, the catchment area for the Aquifer, where they would catch storm runoff and release it slowly toward the recharge zone. Several studies have determined that Type I dams would have to be very large and expensive and would inundate large areas during rainy times and leave large mud-crusted areas during dry times, so authorities consider them generally not feasible. Type II dams would be constructed on the recharge zone itself and would slow down water as it runs off the plateau, allowing more time for it to go into the ground.
Some of the best sites for Type II dams already have dams on them, such as Medina Lake. Some other sites that have good potential to recharge large amounts of water have been identified, but they have unfortunate side effects such as inundating Garner State Park! Also, landowners may not be willing to give up their property for such projects, and there is concern that land on the recharge zone is environmentally sensitive and would be impacted by such structures. Further, it is unclear who would pay and who would benefit. For example, if people in San Antonio pay to build a dam, water that goes into the Aquifer as a result will instantaneously increase springflows in New Braunfels, which mainly benefits people other than those who paid. On the other hand, maintaining springflows also benefits people in San Antonio because the periods of time that restrictions have to be imposed would be shorter. Still, users who paid for the structure would probably expect to get some "credit" or benefit in terms of actual water as some percentage of the additional water that went in the Aquifer. There would also have to be provisions made to ensure protection or mitigation for downstream water rights holders who may be impacted by such projects. To make recharge dams a success and part of an overall solution, complicated issues like these will have to be worked out. Though many questions and issues exist, there is indeed some potential to build additional Type II recharge dams. They would not be a magic-bullet type of solution and could only supply a small percentage of overall projected water needs. The draft plan of the South Central Texas Regional Water Planning Group estimates an average of 21,000 acre-feet per year could be added to the Aquifer. In short term droughts additional recharge could get us over the hump, but recharge dams probably can't help in a long term drought because there will be no water to recharge. The Edwards is not a good storage aquifer where water stays put for use tomorrow. As long as enough hydraulic pressure exists to force water up of the level of springs, significant amounts of water will flow out. In a 3-5 year drought, all the water that was recharged during wet times will have left the Aquifer. To be most effective and cost-efficient, recharge enhancement initiatives will probably have to be developed on a large and comprehensive scale with the cooperation and involvement of many agencies such as the Edward Aquifer Authority, SAWS, and numerous area cities and purveyors.
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