| OCR Text |
Show CEA Report Dam Safety P TUDIES COMMISSIONED by the Bureau of Reclamation i^ J indicate that the probable maximum flood would result in a maximum water surface elevation 5 feet below the crest of the dam. 32 This outcome, however, relies on careful management of reservoir levels during the snowmelt and storm seasons. While it appears that catastrophic dam failure is highly unlikely, unexpected floods can cause severe damage at enormous expense. Catastrophic spillway failure is significantly more likely, and almost occurred in 1983 during a relatively low flood. • The reservoir must remain nearly full to operate the hydropower plant economically. However, a full reservoir does not allow room for floodwaters. • Flooding during the 1983 spring snowmelt season severely damaged the spillways of Glen Canyon Dam. Repairs cost $ 130 million. This flood had maximum inflows to Powell reservoir of only 120,000 CFS. A slightly larger flood, or one of longer duration, could have resulted in catastrophic failure of the spillways. • July of 1884 delivered an estimated flood of 300,000 CFS past the mouth of the Paria River, 15 miles downstream of Glen Canyon Dam. Geological evidence indicates floods of much greater magnitude. 38 • The probable maximum flood, based on meteorological models, would result in inflows to Powell reservoir of nearly 700,000 CFS. 32 Figure 9 Photographs showing damage to spillway after 1983 flood ( BOR). page 12 |
