Stream Temperature Simulation of Forested Riparian Areas: II. Model Application

The SHADE-HSPF modeling system described in a companion paper has been tested and applied to the Upper Grande Ronde (UGR) watershed in northeast Oregon. Sensitivities of stream temperature to the heat balance parameters in Hydrologic Simulation Program-FORTRAN (HSPF) and the riparian shading parameters in SHADE were analyzed for stream temperature calibration. Solar radiation factors (SRF), as well as diurnal, seasonal, and longitudinal variations, were evaluated to verify the accuracy and reliability of SHADE computations. Simulated maximum values of stream temperature, on which the riparian restoration forecasts are based, are accurate to 2.6–3.0°C compared with 8–10°C exceedances over stream temperature goals for salmon habitat restoration under the present riparian vegetation conditions. Hourly simulations have approximately the same accuracy and precision. Stream temperature regimes were simulated for different hydroclimatic conditions and hypothetical restoration scenarios of riparian vegetation. Regardless of natural weather cycles, the restoration of riparian vegetation is needed along many headwater streams to significantly alleviate the lethal and sublethal stream temperatures currently associated with salmon habitat in the UGR basin.