FLOOD06904 - Laserfiche WebLink

Home Browse Search

14 LAWN LAKE DAM AND CASCADE LAKE DAM FAILURES, COLORADO FIGURE 9.-A, Water overtopping Cascade Lake dam. B, Cascade Lake Dam in the initial stages of failure. C, Cascade Lake Dam taken a few seconds after photograph B. D. The location of Cascade Lake Dam immediately after total failure. Photos A-D courtesy of Grace Davis George and Jennifer D. George. E, The location of Cascade Lake Dam following the failure and draining of Cascade Lake. Top of the large boulder on the reservoir floor is shown in D and in figure 8. Modeling," the flood could have had greater peak dis- charges with more damage for different breach develop- ment and hydraulic conditions. The flood occurred during daylight hours in clear weather, and with suffi- cient numbers of witnesses to photograph and relate their experiences, good documentation of the flood was made. The important hydrologic elements of a flood are peak discharges and depths of flow, traveltimes, vol- umes, frequency, and flooded areas; these elements are discussed in this section of the report. It is important to document dam-break floods since limited information is available for assessment and hazard mitigation of possible future dam-break floods. FLOOD DATA STATION DESCRIPTIONS AND STREAMFLOW DATA Flood data obtained at two gaging stations and five miscellaneous sites in the affected area are tabulated in downstream order in the section entitled "Gaging Sta- tion and Miscellaneous-Site Data." Station descriptions give the location of each site, the method of discharge determination, and peak discharge or peak stage dur- ing the flood. Where available, information also is given on gage datum, nature of gage-height records obtained during the flood, and maximum stage and discharge known prior to this flood. PEAK STAGES AND DISCHARGES Peak stages and discharges are important in assess. ing the magnitude of a flood and its associated damages. For the most part, this was true for this flood. Damages were compounded because of the high flow velocities and because of the debris load transported by the flood. As the flood far exceeded the magnitude of previous flows at the two streamflow-gaging stations, and since it peaked very rapidly, direct-discharge measurements could not be made. Peak-flow rates can be computed indirectly using existing methodology with reasonable accuracy following a flood. Flood discharges were computed at seven locations along the flood path (fig. 1). Several different methods