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What Nebraskans need to know about groundwaterBy David Ostdiek Panhandle Research and Extension Center, Communications Specialist Nebraska When Nebraskans gather to talk these days, the topic is almost as likely to be ground water as football. For half a century ground water development and use has been mostly unregulated in Nebraska. But drought, conflicting demands for scarcer water, new laws, and demands to comply with interstate river-basin compacts have spurred policy makers at the local, regional and state levels to begin drafting and enacting new ground rules to govern future water use. In both the Platte and Republican River basins, Nebraskans are drafting and adopting management plans and rules. The bottom line for irrigators in both basins will be limits on, and in some cases reductions to, the amount they may pump. One result of all the attention given to water is that Steve Sibray has found his expertise more in demand. Sibray, UNL's research hydrogeologist for the Panhandle, frequently finds himself speaking to local audiences, explaining the physical realities of one of Nebraska's most vital natural resources. In fact, "Ground Water: What Nebraskans Need to Know" was the title of a presentation that Sibray recently made to a Women in Agriculture conference sponsored by UNL. Sibray's basic message is that there are certain physical realities about ground water systems that Nebraskans should understand when they make rules or policies, including: Ground water is a limited resource. For this reason, it is important to conserve water. The hydrologic cycle describes how water moves and changes form. Most groundwater originates as precipitation. (One exception is the North Platte Valley, where most of the groundwater originates as seepage from the large irrigation canals constructed a century ago). In many areas, most of the precipitation that falls on a given area is used by plants or else runs off the land until it collects in ponds or streams. But a small percentage infiltrates below the root zone, enters an aquifer and becomes ground water. This depends on the soil and plant communities. In the Sandhills, with lighter soils, nearly half the precipitation might end up as ground water. Ground water is distributed unevenly, particularly in the Panhandle. Some areas have a lot of ground water, some have none. Aquifers vary widely in the amount of water they can store, how fast water travels through them, and how readily the water can be pumped. This all depends on the local geology. Ground water does not exist in huge underground lakes and streams. Sibray advises someone buying property to first check with a local driller or a geologist to find out if there is groundwater beneath it. Ground water and surface water are connected. Recall the hydrologic cycle. Water that falls as precipitation moves above and below ground, quickly or slowly, moving downhill. The nature and degree of the connection vary from one location to another, and, again, depend heavily on local geology and other factors. Groundwater pumping always impacts water levels, even if the impacts are limited to the local area surrounding the pump. Buckets and bath tubs are frequently used as analogies for how aquifers behave, but in real life, aquifers do not behave like buckets or bath tubs; as the water is removed, the water table does not decline everywhere at a uniform rate. The effects of pumping depend on numerous factors, including the proximity to the nearest stream; geology of the aquifer; the amount of water in the aquifer, and the spacing of pumps. Ground water pumping impacts surface water supplies. How much a stream is affected by ground water pumping depends on factors such as the distance between the well and the stream, as well as the geology. In irrigation, the amount of water pumped does not equal the amount of water used. The amount of water consumptively used is the evapotranspiration attributed to the plants. "If you really want to control water use," Sibray says, "control ET. Controlling pumping is an indirect way of controlling the amount of water used." Defining "safe yield" or "sustainability" can be tricky business in the real world. It is a misconception about water that there's a magic pumping level equal to recharge, Sibray says. A sustainable level of ground water use is defined by laws and economic constraints, not by physical constraints such as recharge. At the other extreme, it's impossible to predict when or if an aquifer will dry up from overpumping. Sibray says he's often asked when an aquifer will go dry. Before the aquifer dries up completely, its shallower areas will be depleted. Wells drilled into the shallower areas will stop pumping, leaving fewer wells pumping only from the deeper areas. As water levels decline, pumping in some locations will either become economically unfeasible or physically impossible. Remember, aquifers are not like bath tubs. Science can be used to better understand the physical situation, but cannot resolve legal questions. The bottom line, according to Sibray, is that "until we get our legal framework figured out--who gets water in certain circumstances"--there will be the potential for conflicts. For more information about the Panhandle Research and Extension Center visit www.panhandle.unl.edu. 4/7/08 Date: 3/28/08 Advertisement
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