EPA Temperature TMDL Model Sample Clauses

EPA Temperature TMDL Model. Analysis with RB10 (One-Dimensional Model) EPA water temperature modeling, using a one-dimensional model and 30 years of data (RB10 model; Xxxxxxxx, 1999), indicated that generally the Columbia River increases in temperature through spring and summer at about the same rate as before construction of the hydroelectric projects. However, the river without reservoirs had much lower flow rates in late summer and water temperature was much more variable in response to changes in climatic conditions. Peak temperatures during hot weather were often higher than today, but on average the river exceeded 18.0°C for a shorter duration before the hydroelectric project dams were constructed (EPA, 2001). EPA has issued a review draft TMDL for temperature on the Columbia River. Supporting data presented by EPA at public workshops and in the draft TMDL’s appendices show that most of the temperature changes due to human effects are the result of large storage reservoirs. Smaller run-of-river projects, including Rocky Reach Hydroelectric Project, have much less of an effect on water temperatures. The results of comparing the 30-year average temperature shows that the individual temperature effects of Rocky Reach and other small run-of-river projects is quite small compared to the projects with larger reservoirs (Figure 2-14). The EPA modeling results also show that the Reservoir, when compared to a theoretical river segment with the Reservoir removed and all upstream dams removed, has the tendency to increase the cooling of water temperatures from October-June, and increase the heating of water from July- September (Figure 2-15). As seen in Figure 2-15, the Project’s effect on water temperature, averaged over 30 years and assuming that Xxxxx and Chief Xxxxxx dams were removed, is generally less than 0.2°C. As demonstrated by the jagged appearance of the line in Figure 2-15, the RB10 model’s precision is insufficient to predict if the Reservoir’s effects on water temperature are always within 0.3°C of water temperatures that would occur if the Project did not exist. The RB10 model does have sufficient precision to predict trends and long-term averages, thus the prediction that the Rocky Reach Project would, on average, have less than a 0.2°C effect of increasing local water temperatures if there were no dams below Grand Coulee Dam is statistically valid. (Acronyms for individual dams are GC (Grand Coulee), CJ (Chief Xxxxxx), We (Xxxxx), RRH (Rocky Reach), RIS (Rock Island), Wa...