Hydrologic setting of two interdunal valleys in the central Sand Hills of Nebraska

The Sand Hills of Nebraska, one of the largest grass-stabilized dune region s in the world, has nearly 5000 km(2) of wetland environments and is one of the most productive waterfowl regions of the United States, Yet, the hydro logy of the region is not well defined. This paper presents the results of a two-and-a-half-year study to characterize the hydrology of two distinctly different interdunal valleys within the Sand Hills. The valleys, located a t the Gudmundsen Sand Hills Laboratory in the central Sand Hills, reflect t he two major types of interdunal environments: dry,short grass valleys (the east valley) and subirrigated wet meadows (the west valley), In the west v alley, ground water flows from west to east and there are significant, upwa rd vertical gradients (0.005 to 0.045), In contrast, ground water in the ea st valley predominantly flows from west-southwest to east-northeast. Where vertical gradients exist, they are downward (0.0025 to 0.07), Therefore, th e east valley is a "recharge" or flow-through valley. Seasonal ground water table fluctuations indicate that net recharge is greatest between growing seasons. The relatively high topographic relief of the water table on the f lanks of the west valley, resulting from higher topographic relief of the a djacent dunes, drives ground water discharge into the valley wetland, devel oping a local how system, In contrast, the topography of the water table in the east valley, which is flanked by dunes with lower relief, is insuffici ent to generate a distinct local ground water flow system.