Flood-Prone Area Delineation Using DEMs and DOQs

Author: Josh Lear
Organization: Nebraska Natural Resources Commission

P.O. Box 94876
301 Centennial Mall South
Lincoln, NE 68509-4876
USA

Phone: 402-471-3954
Fax: 402-471-3132
lear@nrcdec.nrc.state.ne.us

The single-most important element of any comprehensive hazard mitigation program is hazard identification. Flooding continues to be Nebraska's most costly natural hazard. The Nebraska Natural Resources Commission (NNRC), the state agency responsible for all matters pertaining to floodplain management, has been tasked by the Legislature with accelerating flood hazard identification. In an environment of shrinking state and federal budgets, traditional detailed floodplain studies have become prohibitively expensive in terms of time and money.
NNRC has developed an interactive process that takes advantage of Arc's GRID, ARCEDIT, and ARCPLOT modules, integrated with watershed and river modeling software, to develop flood-prone area maps. The process allows for rapid and efficient, limited-detail floodplain mapping over large rural areas where there is limited existing development and little potential for future development. NNRC's interactive process extracts critical hydrologic information from digital elevation data using GRID. Discharges are calculated at user-specified locations using regional regression equations. Flood depths are calculated in watershed modeling software using the calculated discharge. The flood depths are converted to a flood surface in GRID, which is compared to the digital elevation data to determine the flood-prone areas. Arcedit is used to review and edit these boundaries. The resulting flood-prone area coverage is published with a DOQ background. This process provides a cost-effective method of identifying and mapping flood-prone areas.