EVALUATING EVAPOTRANSPIRATION, GROUNDWATER AND SURFACE WATER INFLUENCES AT A NEBRASKA SAND HILLS WETLAND MITIGATION SITE

Successful compensatory mitigation is based largely on the ability of investigators to determine the quality of mitigation as supported by functional assessment techniques contradicting the traditional standard of quantity in replacing lost wetland area. In doing so, certain hydrologic conditions must be met and are better understood when proper identification of water sources and sinks are assessed. The development of a water budget for a wetland mitigation site for purposes of addressing performance standards outlined by the United States Army Corps of Engineers is an essential task to determine viability of the site to, within reason, maintain functions replaced due to Section 404 procedures of The Clean Water Act. The history of compensatory mitigation within the Sand Hills region of north-central Nebraska is poorly-defined and nearly non-existent. Aside from the well studied 5000 km² of area possessing wetland characteristics within mostly interdunal valleys, studies focusing primarily on the enhancement and/or restoration within mitigation are lacking, but necessary and essential in maintaining regionally-specific aquatic resources. A 14 month field study was conducted on a semi-arid wetland mitigation site located within the Sand Hills region of Nebraska. The primary objective of this study was to develop a crude representation of the water balance for the site in order to meet regulatory performance standard specifications. Utilizing on-site meteorological instrumentation and data analysis via the Bowen-ratio energy budget approach, surface energy balance ET measurements were correlated with the influence of the highly variable water table depth and on-site surface water retention and flow. Groundwater and surface water flux were assessed via subsurface monitoring wells and an adjust-a-flume series flume. A secondary objective was to make use of measured estimates in order to meet credit certification of the site for further use as a banking instrument for future crediting of Nebraska Department of Roads (NDOR) projects. It is believed such information would benefit NDOR for reasons of monitoring and possible acquisition of additional land leading to potential mitigation within similar geographic service areas.