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.

Water quality research of the Colorado River corridor of Grand Canyon examines important relationships between densities of fecal coliform bacteria in surface water and underlying bottom sediments. Surface water sampling alone does not accurately reflect baseline water quality status of natural recreational waters, as sediments often harbor microbial densities in several orders of magnitude of overlying waters. Water-based recreation activities and natural wave and current processes can resuspend sediment and associated microbial populations, including enteric pathogens. Data show significant associations between surface water and bottom sediment microbial populations, demonstrating the importance of a combined sampling approach to water quality analyses.

The Tucson Water Department has developed a long-range water master plan utilizing a computerized hydraulic modeling system from which to determine size and phasing of major water capital improvements. Alternative water sources and amounts were modeled under a fifty-year peak demand condition. Nodal pressure, pipeline headloss, and reservoir drawdown results were evaluated against pre -set standards to determine the optimal solution to the supply- demand balance. A mid-range demand condition for 1990 was modeled subsequent to the modeling of the 2030 planning horizon to incorporate a major domestic water source change. Sizing of new facilities will he based upon the long-range solution. Phasing of capital improvements will he based upon existing system deficiencies, rate and spatial distribution of growth, delivery date of new imported surface supply, and the availability of funds for water project construction.

Major events during the summer of 1974 led to the beginning of a new, progressive program of water resources management for the City of Tucson. Critical supply shortages during the 1974 peak demand period brought into sharp community focus the need to reassess the previously existing philosophy of meeting continually increasing demand for water with extensive capital construction. An analysis of the impacts resultant from unmanaged peak demands, increased water level declines, potential land surface subsidence, projected increased operational costs and changes in water quality led staff and consultants to formulate and recommend the "Beat the Peak" program. A new philosophy on basin -wide groundwater withdrawals was implemented along with additional programs designed to evaluate the effect of our continued dependence on local groundwater sources. The results of this new management approach have been impressive. Per capita water consumption has been voluntarily reduced, total groundwater pumpage has been reduced and the potential for land surface subsidence is being actively evaluated resulting in direct benefits to Tucson Water and the customers it serves.