A stable isotope study of bank storage mechanisms in the Truckee river basin

River, ground water, and snow samples were collected in the Truckee river drainage basin in northern California and Nevada to determine the mechanisms of bank storage. Lake Tahoe, the source for the Truckee river, has a σD of −57 and σ 18 O of −5.5. These compositions are more enriched than the average local precipitation, calculated to be −117 in σD and −15.8 in σ 18 O , due to continued evaporation during the long residence time of the water in the lake. Thus, Lake Tahoe water can be easily recognized allowing for easy tracing as bank storage. An enrichment threshold value was developed to explain the stable isotopic ratios observed in the Truckee river. The σD value of −85 was determined as being the threshold value, below which evaporation can explain the isotopic composition observed in the Truckee river, and above which the presence of Lake Tahoe water is required. There does not appear to be a direct relationship between the σD value of the Truckee river and the discharge to the river from Lake Tahoe, at least in the upper reaches of the basin. The rise in σD of the river to a value similar to that of the lake appears to move progressively upstream and is thought to be related to the discharge of the bank-stored Lake Tahoe water.