Intermittent Flow Events - Salinity Loading Relationships in the Lower Colorado River Basin, Southern Nevada

Abstract

The Bureau of Land Management (BLM), in recognition of the need to identify the mechanisms and significance of salinity loading from arid ephemeral drainages in the Lower Colorado River Basin, sponsored this reconnaissance effort. The principal project objectives were to sample the water quality of flash flood events over a two year period in selected drainage basins and relate field data to the probable type and magnitude of salinity loading that ungaged arid basins could contribute to the Colorado River. Remote water samplers were placed in four tributary basins along the north shore of Lake Mead. Calculated average TDS values for flows ranged from 1,270 to 2,000 mg/l. Water was generally a calcium sulfate type. TDS generally increased down -channel during an event. Estimates of peak discharges and volumes showed that the largest events occurred in the two largest drainage basins. Results of analyses based on a series of conservative assumptions showed that 2,700 and 1,200 metric tons of salt entered Lake Mead from the study area in 1978 and 1979, respectively. This influx of salt would have increased the total dissolved solids (TDS) of the Colorado River at Hoover Dam by .08 mg/l in 1978 and .04 mg/l in 1979. Extrapolation of generalized study results to include similar drainage basins associated with both Lake Mead and Lake Mohave showed that a total annual increase in TDS of .50 mg/l could be attributed to ephemeral basin runoff.