Resolution No. 4814 - Laserfiche WebLink

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Creek Dam, an extremely unlikely event, could require the evacuation of over 250,000 people with damages in excess of $10 billion. Adjusting these 1987 estimates for inflation and for population growth suggests that damages could easily exceed $20 billion. Detailed casualty estimates have not been made for catastrophic dam failures affecting Lane County. However, given the large inundation areas, high water depths, and the logistical difficulties in evacuating 250,000 people to safe ground, it is not difficult to imagine that a truly catastrophic dam failure could potentially result in 1,000 or more deaths. The probability of catastrophic failure of these dams is impossible to estimate with any accuracy, from present data. Most likely, the probability is less than 0.1% per year (less than once in 1,000 years, on average) and perhaps substantially less. However, the consequences of failure are so high that careful evaluation is certainly warranted. The potential impacts of dam failures on the Eugene/Springfield Metro Area are summarized below in Table 12.6 Table 12.6 Potential Impacts of Dam Failures on the Eugene/Springfield Metro Area Inventory Probable Impacts Portion of Eugene/Springfield Metro Direct ~mpacts limited to mapped inundation areas for dam Area affected failures, or to smaller areas for more t~kely partial failures Buildings Heavy damage in inundation areas Streets within Metro Area Damage and closures in inundabon areas Roads to/from Metro Area Damage and closures in inundation areas E~ectdc power Damage and loss of service in inundation areas Damage and loss of service ~n ~nundation areas. Potenbal for Other Utilities major damage to water and wastewater treatment plants in extreme events Potential for high casualbes (deaths and injuries) in extremely Casualties unlikely major dam failures, depending on warmng time avadable and effectiveness of evacuabons 12,6 IVlitigation Strategies Possible dam failures affecting the Eugene/Springfield Metro Area are Iow probability events, but the potential casualties and economic consequences are extremely high. The combination of Iow probability but large consequences makes analysis of such situations difficult from both a technical and a public policy perspective. The evaluation is difficult technically because it requires detailed engineering analysis of each dam and careful probabilistic risk analysis. As always, communication with the public must be non-alarmist, but factual, realistic and informative. Recommendations 1. Because of the age of these dams, the seismic design basis of all of the dams potentially affecting the Eugene/Springfield Metro Area is significantly below current seismic design requirements. Preliminary seismic evaluations have been done but without sufficient detai~ to evaluate the probabilities of dam failures. Because of the Public Review Draft: August 6, 2004 12-9