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GIS FOR FLOODPLAIN MAPPING IN DESIGN OF HIGHWAY DRAINAGE FACILITIES

Since the 1960s, civil engineers have employed a variety of computer models for stream floodplain analysis. HEC-2 and its Windows counterpart, HEC-RAS, have been the principal models used for such analyses. A significant deficiency of these programs is that the location of structures impacted by floodwaters, such as roads, homes, and businesses, cannot be effectively compared to the floodplain location. This report presents straightforward approaches to processing HEC-RAS output to enable two- and three-dimensional floodplain mapping in a geographic information system (GIS). The methodology was applied to a segment of Waller Creek in Austin, Texas. The HEC-RAS stream geometry and flood elevation data were imported into ArcView GIS, in which the cross sections were mapped along a digital representation of the stream. A planimetric view of the floodplain was developed using a digital orthophotograph as a base map. An approach to three-dimensional floodplain visualization through the integration of HEC-RAS stream cross-section data into a digital terrain model of the study area is under development. The results indicate that GIS is an effective environment for floodplain visualization and analysis.