SECTION 4: RISK ASSESSMENT
minutes for upstream locations. Flash floods occur within six hours of the beginning of heavy rainfall, and dam failure may occur within hours of the first signs of breaching. Other failures and breaches can take much longer to occur, from days to weeks, as a result of debris jams or the accumulation of melting snow. Dam failures are of particular concern because the failure of a large dam has the potential to cause more death and destruction than the failure of any other manmade structure. This is because of the destructive power of the flood wave that would be released by the sudden collapse of a large dam. Dams are innately hazardous structures. Failure or poor operation can result in the release of the reservoir contents — this can include water, mine wastes, or agricultural refuse – causing negative impacts upstream or downstream or at locations far from the dam. Negative impacts of primary concern are loss of human life, property damage, lifeline disruption, and environmental damage.
Warning Time: 4 – Less than 6 hours
Duration: 3 – Less than 1 week LOCATION
The North Carolina Dam Inventory, maintained by North Carolina Department of Environmental Quality, provides a detailed inventory of all dams in the state. Wake County worked with the state dam safety agency to compile information on all dams in an upstream of the planning area and to identify high hazard dams in poor condition which may be in need of mitigation. As of February 2024, there are 577 dams in Wake County, of which 312 are rated low hazard, 59 are rated intermediate hazard, and 206 are rated high hazard. Additionally, there are 8 dams that are rated high hazard that are located within five miles of the Wake County jurisdictional boundary. Figure 4.9 shows the location of all dams in Wake County. Table 4.14 lists all dams with high hazard potential in the county and Table 4.15 lists all dams with high hazard potential that are located within the five-mile buffer of Wake County. Dams are listed by jurisdiction according to the nearest downstream location listed in the North Carolina Dam Inventory.
Wake County, NC Multi-Jurisdictional Hazard Mitigation Plan
WSP June 2024 Page 87
Made with FlippingBook interactive PDF creator