Multi-Scale Risk and Impact Assessment of Potential Dam Failure in the United States
Aging water infrastructure in the United States (U.S.) is a growing concern. According to the 2018 National Inventory of Dams (NID) database, there are more than 90,000 dams registered in the U.S, and their average age is 57 years. The compounding impact of climate change with aging dams has increased the potential for and exposure risk of dam failure-driven floods. At the national level, dam failure with an absence of a state dam safety program and Emergency Action Plans (EAPs) trigger local-economic collapse causing malfunction of flood control, economic paralysis, and fatalities with property losses. Since the 1950s, which is known as the Dam nation period, dams have been providing sustainable water resources for the entire continental United States (CONUS). Dams are considered a vital infrastructure providing water and water ways to communities and industries, therefore, a dam safety program is required along with increasing economics. At the state level, dams play a significant role as well (e.g., agriculture, navigation, and recreation) to increase the quality of life. Therefore, a scheduled inspection of dams inevitably leans on dam management agencies and private owners for protecting benefits from the existing dams. However, due to the various regional characteristics and legislations by the states, such as topography, privacy, and security issues, systematic administrating of dams is poorly conducted. Dams in the Black Belt areas of Alabama, home to some of the most socioeconomic vulnerable communities in Alabama, indicate an extremely low level of regular dam inspection based on the NID. At the site level, hyper-resolution inundation floodplain mapping for dam breach is crucial to improve EAPs and to minimize adverse impacts of the dam failure. However, hyper-resolution 2D modeling for hydrodynamics and costly bathymetric surveys limit understanding of the impact of antecedent flow conditions on flood mapping at the site level.This dissertation proposes a multiple-scale risk and impact assessment of potential dam failure in the United States with a focus on the state of Alabama, the only state in the CONUS with no formal dam safety legislation, in order to better understand 1) how the risk and preparedness of potential dam failure in the United States vary at a range of spatial scales (site-level to national-level), 2) how the economic benefits of the existing dams vary across the U.S. states in terms of the marginal cost of water use, and 3) what are the values of cutting-edge technologies are beneficial in better describing the flood inundated areas due to potential dam failure. This dissertation consists of five main chapters. In Chapter 1, the objectives and goals of this dissertation are addressed. In Chapter 2, the spatiotemporal patterns of the growth of dams and their potential hazard and economic benefit are assessed, using more than 70,000 NID-registered dams in the CONUS. In Chapter 3, the state-level risk of dam failure is assessed using more than 2,000 dams in the state of Alabama. The vulnerability of communities to dam failure is high in populated counties with high incomes while less populated counties with lower incomes show a low vulnerability to dam failure due to the relatively small storage capacities of the existing dams. In Chapter 4, the sensitivity test of inundation flood mapping to initial river depth with antecedent flow condition is also conducted using the experimental simulations of the two-dimensional hydrodynamic model with a Remotely Operated Vehicle (ROV). Applying the NID database which is updated with EAP data for the entire dams in the U.S, the results of the dissertation provide quantified data on potential economic values and hazards of dams. Therefore, the results of the dissertation are useful to not only estimate the total cost of recovery but also assess potential losses of the water cost due to dam failures. In addition, providing calculated cost of flood damage restoration would be a valuable index for flood insurances and increasing public awareness as a beginning step of dam safety. Furthermore, using an underwater drone has been successfully applied to acquire precise Digital Elevation Model (DEM) data and flood maps. If fully autonomous underwater drones are available later, the drones would play a key role in floodplain research areas as well as not only river streams, but also river basins are accessible to measure the bathymetric survey. The findings of this study can be useful data for reconsideration of the dam safety programs and EAPs, and it further emphasizes the need for careful design of EAPs accounting for antecedent flow conditions and accurate river channel depths for places that are required to establish safety programs.