Laserfiche WebLink
CHAPTER 8. DAM FAILURE <br />8-12 <br />8.5.4 Environment <br />Reservoirs held behind dams affect many ecological aspects of a river. River topography and dynamics <br />depend on a wide range of flows, but rivers below dams often experience long periods of very stable flow <br />conditions or saw-tooth flow patterns caused by releases followed by no releases. Water releases from dams <br />usually contain very little suspended sediment; this can lead to scouring of river beds and banks. <br />The environment would be exposed to a number of risks in the event of dam failure. The inundation could <br />introduce many foreign elements into local waterways. This could result in destruction of downstream <br />habitat and could have detrimental effects on many species of animals, especially endangered species such <br />as salmon. <br />8.6. VULNERABILITY <br />8.6.1 Population <br />Vulnerable populations are all populations downstream from dam failures that are incapable of escaping <br />the area within the allowable time frame. This population includes the elderly and young who may be unable <br />to get themselves out of the inundation area. The vulnerable population also includes those who would not <br />have adequate warning from a television or radio emergency warning system. The potential for loss of life <br />is also affected by the capacity and number of evacuation routes available to populations living in areas of <br />potential inundation. <br />8.6.2 Property <br />Vulnerable properties are those closest to the dam within the inundation area. These properties would <br />experience the largest, most destructive surge of water. Low-lying areas are also vulnerable since they are <br />where the dam waters would collect. Transportation routes are vulnerable to dam inundation and have the <br />potential to be wiped out, creating isolation issues. This includes all roads, railroads and bridges in the path <br />of the dam inundation. Those that are most vulnerable are those that are already in poor condition and would <br />not be able to withstand a large water surge. Utilities such as overhead power, cable, and phone lines could <br />also be vulnerable. Loss of these utilities could create additional isolation issues for the inundation areas. <br />Vulnerability numbers are provided for each mapped dam inundation area, as summarized in Table 8-6 <br />through Table 8-8: <br />– The estimated loss from the Cle Elum dam failure scenario is $234 million. This represents <br />five percent of the total assessed value of Cle Elum. <br />– The estimated loss from the Easton Diversion dam failure scenario is $82 million. This <br />represents two percent of the total assessed value of the planning area. <br />– The estimated loss from the Keechelus and Kachess dam failure scenario is $276 million. This <br />represents six percent of the total assessed value of the planning area. <br />Table 8-6. Loss Estimates for Cle Elum Dam Failure <br />Jurisdiction Number of Buildings <br />Exposed <br />Exposed Building <br />Value <br />% of Total Assessed <br />Value <br />Cle Elum 474 $54,106,855 61% <br />Ellensburg 311 $48,097,160 5% <br />Kittitas 0 $0 0% <br />Roslyn 0 $0 0% <br />South Cle Elum 224 $8,549,880 98%