ANALYSIS OF THE WINTER LOW-FLOW BALANCE OF THE SEMIARID WHITE RIVER, NEBRASKA AND SOUTH-DAKOTA

Low-flow studies are needed to quantify the effects of water consumpti on on streamflow, water quality, groundwater resources, and contaminan t transport. The low-flow water balance of a river in a cold region is simplified in winter because evapotranspiration is negligible, irriga tion water withdrawals and diversions are halted, and precipitation oc curs largely as snow, minimizing the spatial and temporal variability of runoff. We investigated the monthly low-flow water balance of White River reaches over seven consecutive winters. Water going into or out of storage as ice or melt, obtained with an air temperature index mod el, can be a dominant component of the water balance. The point estima te method is used to account for parameter uncertainty and variability , providing the mean, variance, and limits of dependent variables such as water storage as ice and inflow from a subbasin. Negative surface water yield from several-thousand-square-kilometer subbasins occurred regularly through the period, indicating a significant flow from the r iver to the alluvial aquifers. The winter water balance results sugges t either a perched river or a coupled surface water-groundwater hydrol ogic system in particular subbasins, consistent with the field investi gations of Rothrock (1942). The winter flow exchange between the surfa ce and subsurface can be used to estimate the annual exchange for both hydrologic conditions.