Truckee River Restoration Modeling

Abstract

The Truckee River is a vital resource to Nevadans in the northwest region of the state, providing water for public water supplies, irrigation, recreation, and industrial uses. The river and its terminus, Pyramid Lake, provide valuable water and habitat for endangered Lahontan cutthroat trout and cui ui species. Increased urbanization and the prevalence of water diversions have caused a decline in water quality, and the resulting detrimental effects on habitat have brought about the need to restore the river to a more natural condition to improve habitat and the river's overall health. In an effort to improve water quality and enhance habitat for fish, birds, and other wildlife, a restoration project on the Truckee River is underway. Restoration completed thus far includes modifying a meander, narrowing the channel from 200 to 120 feet, raising the river about two feet to reconnect it to its natural floodplain, raising two existing riffle sections, excavating two oxbow wetlands, and revegetating the floodplain with native species. In this investigation, we will modify and use the previously calibrated model TRHSPF (Truckee River Hydrologic Simulation Program-Fortran) to model the restoration of the river in the McCarran Ranch restored area, and to test the hypothesis that restoration of the Truckee River from McCarran Ranch downstream will improve the nitrogen assimilative capacity of the river. In this study, assimilative capacity is defined as the allowable load that meets the current (2003) water quality standards for total nitrogen on the lower Truckee River. Nitrogen is a nutrient of concern because high concentrations lead to excessive plant growth and oxygen depletion, detrimentally affecting habitat and water quality. Changes in the nitrogen assimilative capacity of the Truckee River will be calculated under different restoration management scenarios. The TRHSPF model uses information such as time history of rainfall, temperature and solar radiation, land surface characteristics and land management practices to predict flow rate, sediment load, and nutrient concentrations. The successful application of this model will aid in future management decisions regarding further restoration activities, increased loading on the river, and the ongoing reassessment of TMDLs for the Truckee River.