Slide 23 of 33
Notes:
- This chart (similar to the first two) shows the elevation probability at Libby Dam for the end of August in 2003. About 44 percent of the time, Libby will be lower in the “no new resource” scenario. In years when it is lower, it will be 17 feet lower on average. In the worst case, Libby is 45 feet lower.
- The biological opinion draft limit for flow augmentation for anadromous fish at Libby is 2,440 feet (or 20 feet down from full). As can be seen in the chart above, the solid black line is on or above 2,440 feet about 80 percent of the time. The remaining 20 percent of the time, Libby is drafted below this limit to help maintain flows for sturgeon or for power needs.
- In the “no new resource” scenario (red dashed line), Libby is below the biological opinion draft limit nearly 40 percent of the time. It is safe to assume that in each case where the red dashed line is below the solid black line, that Libby was used for power needs and not for flow augmentation.
- Remember that impacts at other reservoirs are similar to those presented here for Libby.
- In conclusion, relying too heavily on the hydro system for reliability concerns results in a higher probability that reservoirs will be at undesirably lower elevations in the winter months and that less volume of flow augmentation water will be available by mid-April. Flows are not affected as much as one might think because reservoirs are likely to be drafted deeper than the biological opinion limits in the summer for power needs.
