期刊名称：Journal of Environmental Hydrology (ältere Jahrgänge)
印刷版ISSN：1058-3912
电子版ISSN：1996-7918
出版年度：2010
卷号：18
出版社：IAEH
摘要：A study was made to determine the locations and rates of groundwater gains and losses (seepage) in the roughly 350-mile lower reach of the Niobrara River in northern Nebraska, United States, including the 76 miles designated as a National Scenic River, using synoptic main-channel and tributary discharge measurements. Results were compared to those from a 1980 study, to groundwater and surface-water head measurements, and to alluvial thickness estimates along the main channel. For 2009, most tributary reaches west of Valentine had gains of about 0�2 cubic feet per second per mile (cfs/mi), but upper Minnechaduza Creek had losses of 5 cfs/mi. Eagle Creek, Long Pine Creek, Verdigre Creek, and the Snake River showed the largest tributary gains of >3 cfs/mi. The remainder of the study region showed a mix of gains and losses along tributaries. For the main stem, results from the 1980 and 2009 seepage studies indicated similar patterns of total flow, cumulative tributary inflow, and cumulative main-stem seepage gain/loss. Upstream from the confluence with the Snake River, Niobrara River flow increases were almost entirely from main-stem seepage gains; downstream from the confluence, the number of contributing tributaries increased substantially, and tributary inflows were the largest source of main-stem flow increases below Norden. For many individual main-stem reaches, seepage rates for this study did not agree with the results obtained during the 1980 study; but, for four longer reaches classified by their differing geology, there were increasing gains in the upper two reaches followed by losses in the third reach - rates were 1.8, 4.1, and -5.5 cfs/mi for 1980; and 2.6, 3.4, and -2.3 cfs/mi for 2009, respectively. In the fourth geologic reach, there were no data for 1980, but the 2009 results indicated that this reach had the largest rate of main-stem seepage gain, 8.5 cfs/mi. The broad-scale spatial patterns of main-stem flow gains and losses were coincident with similarly scaled patterns of bedrock and unconsolidated alluvial-aquifer thickness, and with reach-scale measurements of head differences between groundwater and surface water.
