Model Study Using SNTEMP for 2000 and 2001 Clause Samples

Model Study Using SNTEMP for 2000 and 2001. (One-Dimensional Model) Parametrix and TRPA (2002) estimated the effect of the Reservoir on water temperature during the 2001 drought year, using the Stream Network Temperature Model (SNTEMP). Data available prior to model selection and for 2000, which was for years with normal summer flows, indicated little vertical or lateral stratification of the Reservoir (which supported the use of SNTEMP). However, 2001 was a year of extreme low summer flows and significant longitudinal stratification, a difference in temperature from upstream to downstream, was observed in the data. A problem encountered in applying SNTEMP to the Project was related to model reliance on daily time steps with no “carry-over” of heat transport across days. During the low flows in 2001, the daily time step did not adequately represent the transfer of water through the Reservoir. For low flow years, such as 2001, different models such as CE-QUAL-W2, MASS 1 or MASS 2 (Modular Aquatic Simulation System 1D and 2D) were determined to be better predictors of quantitative temperature changes as a result of the project. To compensate for the low flows in 2001, the SNTEMP model was adapted to these conditions by treating the Reservoir as three separate stream segments. In the process of calibrating the SNTEMP model, the simulated temperatures under the measured climatological and hydrological conditions in 2001 were as expected for the upper portion of the Reservoir (▇▇▇▇▇ Bridge), but time lags of one day in the middle of the Reservoir (Daroga Park) and two days at Rocky Reach Dam were observed. To determine the cause of this time lag, Chelan PUD applied the FloodWav model to Reservoir in 2001 to determine water travel times. FloodWav, maintained by the National Weather Service, computes water travel times in a depth and width- averaged manner (i.e., one-dimensional, plus-time scale), and predicted travel time from ▇▇▇▇▇ Dam under the average 2001 study period flow of 60,000 cfs (extreme drought conditions). The predicted water travel times from ▇▇▇▇▇ Dam were 0.44 days to ▇▇▇▇▇ Bridge, 1.56 days to Daroga Park, and 3.51 days to Rocky Reach Dam. This simulated delay in water movement within the Reservoir generally matched the downstream temperature data recorded by the installed thermographs. This water travel time information was used to modify the study by segmenting the Reservoir into three sections. This effort partially compensated for the one-dimensional limitations of the SNTEMP model. ...