7886 - Laserfiche WebLink

Home Browse Search

Reservoir Operating Studies Studies to Define an Environmental Baseline at Maybell In 1986, the U.S. Fish and Wildlife Service applied the HYDROSS modeling methodology to the Yampa and Green River basins to assist in assessing the cumulative impacts on streamflows of water developments for irrigation, power, municipal, and recreation. The Service's HYDROSS application was aimed primarily at identifying the impacts associated with the Stagecoach Reservoir Project near Steamboat Springs. From this modeling analysis, the Service defined a "Section 7 Baseline" condition for the Stagecoach project and Interim Flow Recommendations at Deerlodge Park. A detailed review of the HYDROSS application was conducted as part of the Phase I Study. As the current study progressed, it became apparent that there was a need to have the flow recommendations defined at Maybell and it was decided that the Yampa River basin model could be used to help define preliminary flow recommendations Maybell. This was accomplished by defining a model scenario that represented current potential demand conditions plus additional depletions that had already undergone Section 7 consultation or which had otherwise been reflected in the HYDROSS Environmental Baseline. The "current potential conditions with consulted depletions" model scenario was defined to correspond as closely as possible with the previous modeling work done by the Service in connection with the Stagecoach Reservoir Project (SRP) Section 7 consultation. In particular, this scenario is meant to provide the "Environmental Baseline" required for conducting preliminary Section 7 consultations for the proposed enlargement of Elkhead Reservoir. It was necessary to "re-create" the Environmental Baseline using the Yampa River basin model since the differences between the modeling approach used in the present study and the HYDROSS approach used by the Service made direct comparisons of current model results to the original HYDROSS-based Environmental Baseline difficult. Table 2-3 presents a statistical summary of flow conditions at Maybell resulting from the "current potential conditions plus consulted depletions" model scenario. Average monthly flows are presented for three exceedance levels, the 25th percentile, the 50th percentile (or median), and the 75th percentile. The 25th percentile flows are flows which are exceeded in 25 % of years, i.e., they correspond to wet year conditions; the 75th percentile flows are exceeded in 75 % of years and correspond to dry year conditions. More detailed results of this model scenario can be found in Appendix D. Preliminary Flow Recommendations at Maybell The preliminary flow recommendations at Maybell are basically the median flows which result from this "current potential conditions with consulted depletions" model run. The preliminary flow recommendations are presented in Table 2-4. 2-10