MAPPING REGIONAL GROUNDWATER RECHARGE

Long-term, spatially variable, mean annual recharge to groundwater in Nebraska was estimated by a water-balance approach. This approach uses Geographic Information Systems (GIS) layers of land cover, elevation of land and groundwater surfaces, base recharge and the recharge potential in combination with monthly climatic data. The method uses novel techniques (automated baseflow separation, a new evaporation estimation method, and GIS) that became available only in the past decades. A recharge map for Nebraska with this resolution has never been produced before. The novelty of our approach is that it circumvents the need of applying a regional groundwater-flow model that has traditionally been the workhorse of this type of recharge estimations. The problem with the traditional approach of groundwater flow modeling has always been the high uncertainty associated with obtaining permeability values representative of the watershed-to-regional scale. Because the possible range for this parameter is very wide, so has always been the potential for errors in the recharge estimates, which at the regional scale are hard to verify.