Technically Speaking

Looking into Nebraska’s Water Supply Crystal Ball

By Jim Goeke

    Nebraska is in a unique historic position, similar to where Nebraska was in the 1880s when barbed wire and windmills combined to “close” the open range, except today easy, unlimited access to the state’s water is closing. In Nebraska, we have been fortunate to have experienced above-normal precipitation during the 1980s and 1990s, only to embark on a drought in 2000 that persists to the present and may extend into the future.

   Droughts are common in Nebraska and the High Plains, and in the past have prompted the building of reservoirs to store and deliver water for irrigation while protecting against floods. For those without access to surface water for irrigation, drilling wells became the solution to drought. By 2000 we had almost 100,000 irrigation wells in Nebraska. In some areas of imported surface water, water levels have risen and in other areas of intensive irrigation development, water levels have dropped. Declining water levels create immediate and far-reaching problems.

   Surface water regulation in Nebraska began in the mid 1890s, probably driven by the drought of the early 1890s. Surface water is administered through the Department of Natural Resources (DNR) under the Doctrine of Prior Appropriation – first in time, first in right. It wasn’t until 1975 and the passage of the Groundwater Management Act that groundwater was regulated under the Doctrine of Correlative Rights whereby everyone would have access to beneficial use of groundwater and would share and share alike in times of shortage.

   The fact of the matter is that surface and groundwater are connected and yet in Nebraska we have treated them as though they aren’t. LB 108, the Conjunctive Use Bill passed in 1996, formally recognized the connection between surface water and groundwater. LB 962, passed in 2004, provided for the effective management of hydrologically connected waters by the designation of over-appropriated and fully appropriated areas and the development of integrated management plans formulated by the DNR and appropriate Natural Resources Districts working together.

   While surface water is easily accessible to experience and use, groundwater is an act of faith, below the ground, out of sight and experience. We can think of groundwater as a massive, inexorably moving conveyor belt, moving groundwater to where it meets the land surface and becomes surface water. If we drill an irrigation well, the water that is pumped and consumptively used (not to return to the conveyor belt) is that amount of water that will not eventually make it to the stream. Due to the very slow movement of groundwater, usually 100 to 300 feet per year, it may be decades or centuries before the impact of the water consumptively used today isn’t available as stream flow. Therefore it is apparent that our water use today can have far-reaching impacts on stream flow and the populations of endangered species and humans that depend on it.

   We are fortunate in Nebraska that our farsighted forefathers had the wisdom to initiate programs to inventory, measure and monitor our water resources. We are also fortunate that for the last 35 million years, sediments shed from the eroding Rocky Mountains have built up our enviable groundwater reservoirs or aquifers. In the early 1930s the University of Nebraska Conservation and Survey Division (C&SD), in cooperation with the United States Geological Survey (USGS), initiated a test-drilling program to characterize the aquifers of Nebraska and explain the geologic history of the state. Over the same period, the C&SD worked closely with the Nebraska Well Drillers Association to help the drillers keep accurate and detailed logs of the wells they drilled. The result of this collaboration is a network of almost 5,000 C&SD/USGS test holes and logs for many of the 100,000 or so wells drilled in Nebraska.

   In addition, water levels have been measured in wells across the state since the 1960s to track water level variations or essentially keep the pulse of the groundwater resources of the state and answer the questions “How much water do we have?”, “What’s happening to our groundwater?” and more recently “What’s happening to our water quality?” 

   As our administrative and legal systems have developed, we have concerned ourselves with running out of water, with degrading our water quality and, most recently, with the effects of groundwater pumpage on surface water flows.

   Surveys of our water resources indicate how fortunate we are in Nebraska. It seems ironic that as the home of the “Great American Desert” Nebraska is a virtual water machine. On average, 1.7 million acre feet of surface water flow into the state and 8.9 million acre feet flow out. Actually the “Great American Desert” or the Sand Hills, with its high infiltration over more than 20,000 square miles, absorbs, stores and transmits vast amounts of water. The streams issuing from the Sand Hills, in fact, are among the most constant flowing streams in the world, in contrast to the Platte east of Columbus that depends greatly on snowmelt runoff from the Rocky Mountains. So connected are much of the surface water and groundwaters in Nebraska that Richard Harnsberger noted, “If you dyed all the groundwater in Nebraska red, all the streams in Nebraska would flow pink.”

   Estimates from the USGS High Plains Regional Aquifer Systems Analysis (RASA) in 1980 indicated Nebraska  had 66 percent of the 3.25 billion acre feet of drainable water available in the High Plains aquifer, or 2.145 billion acre feet of water. By 1980, water levels had been declining over much of the eight-state aquifer area. While Texas had 70 percent of the depletions, Nebraska had 0 percent due to rises in south central Nebraska offsetting declines in the southwestern, southeastern and northwestern parts of the state.

   The indications of the early RASA model indicated that much of Nebraska and the rest of the High Plains aquifer would experience substantial declines from 1980 to 2020. The abundant rainfall in the 1980s and 1990s wasn’t considered in the model and, as a result, water levels actually came up in eastern and southeastern Nebraska, but have resumed declining since the drought of 2000. Estimates in 2002 indicated that available groundwater in Nebraska had only been reduced by a little over one .5 percent.

   So what’s the big deal? The big deal is that surface water and groundwater are connected. Even a small reduction of our groundwater reserves can affect surface water flows, thereby imperiling endangered species dependent on those flows for habitat and imperiling human beings dependent on those flows for irrigation or municipal well field supplies.

   In 1997, Nebraska became part of the Co-Operative Agreement with Colorado and Wyoming and agreed to deal with the status of surface and groundwater in the Platte Basin. The COHYST model was developed to assess in great detail the surface and groundwater systems in the Platte basin. Stream depletion factors were calculated and plotted to designate over-appropriated and fully appropriated areas. Over-appropriated areas are defined by the 28-40 line, which refers to the area in which pumping a well for 40 years would directly or indirectly affect baseflow to a stream by  28 percent or more of what the well pumped over the 40-year period. Fully appropriated areas were defined by a 10-50 line that refers to a line defining an area with which pumping a well for 50 years would directly or indirectly affect baseflow to a stream by 10 percent or more of what the well pumped over a 50-year period. Much of Nebraska is included within these definitions and will be required to develop an Integrated Management Plan through the cooperative efforts of the NRDs and the DNR

   In addition to the Cooperative Agreement on the Platte, in 2004 Nebraska, Kansas, and Colorado signed an agreement resolving differences pertaining to the Republican River Compact, originally signed in 1943. The Republican River Settlement also included a model of the Republican Basin to be used primarily as an accounting tool. Similar to the Cooperative Agreement, the Republican Settlement has led to the imposition of a moratorium on new wells in the Republican Basin in Nebraska, the requirement of meters and allocations, and obligated Nebraska to provide quantifiable volumes of water to Kansas.

   In both the Platte and Republican Basins, the issue of finding the finances necessary to return to 1997 levels of development and to provide Kansas with their allotment of water has not been resolved and is a looming problem to be dealt with.

   As modeling efforts similar to COHYST include the other drainages in the state, stream depletion factor lines of similar scientific rigor will designate over-appropriated and fully appropriated areas. In addition, these models, like the COHYST model, will be able to focus on very specific local areas to answer questions about the impacts on our water resources as we develop new municipal supplies, construct ethanol plants, cool power plants and develop confined animal feeding operations.

   The entire future management and regulation of Nebraska’s hydrologically connected waters will be based on the models generating these stream depletion factor lines. The essential data sets, so long in development, make these models possible. These data sets make possible detailed maps of depth to water, water table contours, saturated thickness, aquifer hydraulic characteristics, geologic materials and bedrock contours. While the models based on these data sets don’t provide all the answers, they do provide the necessary starting point to preserve a future for Nebraska’s water resources and mandate continued dedication to improving our data sets to improve the quality of our predictive and management models. Y Jim Goeke is a research hydrogeologist with the Conservation and Survey Division/School of Natural Resources, University of Nebraska-Lincoln.