Floodplain Mapping Using HEC-RAS and ArcView GIS

A significant deficiency of most computer models used for stream floodplain analysis, is that the locations of structures impacted by floodwaters, such as bridges, roads, and buildings, cannot be effectively compared to the floodplain location. This research presents a straightforward approach for processing output of the HEC-RAS hydraulic model, to enable two- and three-dimensional floodplain mapping and analysis in the ArcView geographic information system. The methodology is applied to a reach of Waller Creek, located in Austin, Texas. A planimetric floodplain view is developed using digital orthophotography as a base map. A digital terrain model is synthesized from HEC-RAS cross-sectional coordinate data and a digital elevation model of the study area. The resulting surface model provides a good representation of the general landscape and contains additional detail within the stream channel. Overall, the results of the research indicate that GIS is an effective environment for floodplain mapping and analysis.