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* Spring 2002 *
Over 75% of the water supplied by the Truckee Meadows Water Authority (TMWA) to its 78,000 customers comes from surface water sources and storage, with the remainder coming from groundwater sources. Almost all of the surface water sources are linked to the Truckee River, which originates in the pristine Lake Tahoe area, flowing 100 miles through the mountains and metropolitan areas of Reno and Sparks to its terminus at Pyramid Lake. Surface water supplies from the Truckee River are treated at the Chalk Bluff (75 million gallons per day (MGD) capacity) and Glendale (25 MGD capacity) Water Treatment Plants. One of the concerns for efficient management of drinking water treatment is the fate and behavior of contaminants that may be spilled or discharged into the Truckee River. In particular, the TMWA would like to be able to estimate when a contaminant would arrive at each of the treatment plants to prepare for either diverting the contaminated flow or treating it appropriately. A one-dimensional FORTRAN-based spill model was developed by Dr. John Warwick at the University of Nevada-Reno (UNR) in 1996. This model, called spillm, was combined with a geographic information system (GIS) interface that allowed the user to model a contaminant spill at different locations along the river under fixed flow scenarios measured at Farad, California. Subsequent to the development of the model, a large flood occurred on the Truckee River in 1997, which may have altered the geomorphology of the river. The research involved an investigation of the appropriateness of re-calibrating the developed spillm. model, or calibrating an HSPF model, or another spill model to evaluate spills in the Truckee River system. We evaluated the spillm model, tried to incorporate additional available hydrologic data for the Truckee River, and tried to calibrate the model for current hydraulic conditions in the river. The current model took into account the whole Truckee River Watershed from Tahoe City (Lake Tahoe), California, to Derby Dam (Pyramid Lake), Nevada. The Truckee Watershed is topographically an enclosed basin with the slopes of the Sierra Nevada’s to the east along the California-Nevada border. The drainage area basin is approximately 3120 square miles with 1940 square miles contributing to stream flow, with the Truckee River extending more than 115 miles. We suspected that we were unable to obtain acceptable predictions with the spillm. model because changes in the cross-section geometry due to a flood in 1997 were significant enough to affect the hydraulics of the river, and/or the hydraulics were incorrect. We therefore developed a new spill model based on the US Geological Survey (USGS) OTIS model. The new model was calibrated with data collected during a dye study on the Truckee River in 1999 for flows in the river at about 500 cfs at Farad. We combined the calibrated reaches into one model and set up spreadsheets to enable the user to quickly plot the results of model runs for spills at different sites. Thus, the model can be used to investigate the timing and concentrations of a contaminant spilled at different sites along the river for flow conditions of about 500 cfs at Farad. In its current form, however, the model should not be used to predict contaminant fate and behavior due to spills in the river for river flows of greater or less than 500 cfs. We then used the calibrated model to evaluate threshold low flows and time to critical concentration at the Chalk Bluff Water Treatment Plant and the Glendale Water Treatment Plant resulting from spills of selected constituents of concern. For further information contact Dr. Saito, lsaito@cabnr.unr.edu
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