Prediction of Transmission Losses in Ephemeral Streams, Western U.S.A

Abstract

Transmission losses (TL) are complicated phenomena that characterize the processes of evapotranspiration and infiltration as water moves down a stream. This analysis focuses on transmission losses that occur within the stream and can be computed with data from tandem stream gauges. Data from Walnut Gulch Experimental Watershed (WGEW), in southeast Arizona, are the primary source. The WGEW is a typical watershed in the region where a network of alluvium- filled stream represents a range of widths and slopes. TL results were compared with those from other U.S. streams as re- ported in several published papers. TL per kilometer (TL/km) were calculated by dividing the difference between flow volumes at the upstream and downstream gages by the distance between gages. Only storms that occurred above the up- stream gage were considered. TL/km for several storms and stream reaches were plotted against the inflow volume and peak inflow discharge and a consistent pattern emerged. These plots yielded parameterized equations that were used to compare published TL for Queen Creek, AZ and several Plains States streams. The sediment characteristics of the streams were also incorporated into the model by using their hydraulic conductivity. The objective of this study was to develop a simple, rapid method requiring only a minimum of pre-existing data to determine transmission losses in ephemeral streams in arid climates that can be used easily by regulators and planners. Furthermore, the models can contribute to the determination of significant nexus of the US Clean Water Act (CWA), Section 404 jurisdiction.