Improved Process for Floodplain Delineation from Digital Terrain Models

Flooding is a hazard with serious socioeconomic consequences for all activities and infrastructure within an affected floodplain. Accurate delineation of flood extents and depths within the floodplain is essential for flood management officials to make sensible and fair decisions regarding construction, insurance, and other regulated practices on land and property potentially affected by flooding. Traditional methods for manually delineating flood extents from computed hydraulic models are tedious, subjective, and prone to mistakes. With the advent of high-powered computers and accurate digital terrain models, the possibility of automating floodplain delineation is achievable. An improved process is presented for delineating floodplains accurately from a digital terrain model (DTM) and hydraulic model in an automatic environment and providing the flexibility of incorporating professional judgment in the process. The most significant improvements are (1) use of georeferenced water levels from different sources; (2) a refined water levels selection procedure for interpolation such as the use of quadrant, flow path, and flow distance; and (3) incorporating user-defined flood barriers. The outcome of these improvements is a flexible, easy-to-use floodplain delineation process that is independent of hydraulic modeling systems, water-level sources, and DTM data structures and maintains hydraulic connectivity over the floodplain. The use of georeferenced water levels also makes the process capable of integrating 1D and 2D model results in floodplain delineation.