Development and applications of an integrated one- and two-dimensional, numerical, urban rainfall-flood simulation model

The rainfall and stormwater-produced flood is one of the most severe natural disasters, especially for urban areas. Rainstorm can generate a large amount of surface stormwater (runoff) in a short period of time due to the high-intensity rainfall. This may lead to local flooding in a urban area including flooding of streets/roads, residential houses, and commercial districts when stormwater cannot be drained out quickly enough due to an inadequate drainage system. Stormwater flooding is a complex flow process, which starts initially from shallow overland surface flow on the earth surface, then converges into channel or pipe flow and finally enters ditches and rivers. Flooding occurs when runoff exceeds capacity of receiving and drainage facilities, e.g., underground stormwater pipes and drainage ditches/channels. In this study, an integrated one-dimensional (1-D) and two-dimensional (2-D), numerical model is developed to simulate a local rainfall produced flooding process over an urban area. This study does not deal with the flood from upstream watersheds and flowing over levees/banks of a river into urban areas.; The rainfall distributions over time and space are the driven force and source for this type of urban floods and are treated as the model input parameters. The model simulates flooding and recession processes starting from rainfall on initial dry land including simulations of rainfall loss, 2-D overland flow, 1-D channel flow, and 1-D stormwater pipe flow. The model results provide us with the spatial flood risk information, e.g., water depth, inundation time, and flow velocity over a whole study area during flooding. Such spatial flood risk information from the model can be very useful in the decision making of flood prevention and evacuation for many agencies, e.g., the Federal Emergency Management Agency (FEMA), other state and county emergency management agencies, and local drainage districts. The model can also provide us the flood risk mapping for the National Flood Insurance Program of FEMA.; The model is applied to simulate the flooding event in the City of Beaumont during tropical storm Alison in June 2001. The model is calibrated with recorded water depths and water levels at five alert stations during the Alison rainstorm in good agreement. Tropical storm Kenna is used to check the performance of a planned detention pond. Two hypothetical storms are also used to simulate potential flooding in Beaumont area during these extreme severe rainfall conditions. Many theoretical and technical problems, such as the irregular mesh adoption and division, 1-D and 2-D integration techniques, stormwater pipe flow simulation; GIS application and data preprocessing are developed for the model application.; The model is also applied to estimate the traveling time for very flat basins with comparison to laboratory and field experimental data. A formula to estimate the traveling time for a mild slope in a flat basin is developed. Suggestions for future model improvement are developed.