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 consumption on streamflow, water quality, groundwater resources, and contaminant transport. The low-flow water balance of a river in a cold region is simplified in winter because evapotranspiration is negligible, irrigation water withdrawals and diversions are halted, and precipitation occurs 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 model, can be a dominant component of the water balance. The point estimate 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 river to the alluvial aquifers. The winter water balance results suggest either a perched river or a coupled surface water-groundwater hydrologic system in particular subbasins, consistent with the field investigations of Rothrock (1942). The winter flow exchange between the surface and subsurface can be used to estimate the annual exchange for both hydrologic conditions.