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Agua Hedionda Flood Study
GIS Applications
City of Vista, San Diego County
Southern California
The project consisted of performing hydrologic and hydraulic analyses and floodplain mapping, integrated with GIS application for Agua Hedionda Creek within the City of Vista, San Diego County, California. The HEC-RAS data used for the analysis was based on an aerial topographic map prepared for this study and field survey data at the faces of bridges within the study reach. Cross-sections were located at selected distances along the stream channel and at the faces of the bridges.
In developing the HEC-RAS model, the ArcView ver. 3x software along with the 3D Analyst, Spatial Analyst, and HEC-GeoRAS extensions were used. The HEC-GeoRAS extension was used to generate HEC-RAS geometric data consisting of: 1) Cross-section geometry, 2) Flow lengths (channel and overbanks), and 3) bank stations. The process involved in the hydraulic analysis included the following steps: 1) Creation of Terrain Triangulated Irregular Network (TIN), 2) Creation of 2-D lines, 3) Generation of HEC-RAS import file, 4) HEC-RAS Modeling, 5) Generation of HEC-RAS GIS export file, and 6) Floodplain Delineation.
The terrain TIN was developed from the topographic mapping. The map consisted of 2-foot contours in MicroStation format as 3-D lines. In ArcView, a terrain theme was created from the contours. A TIN was then created from the terrain theme. Sets of 2-D lines were required in the generation of a HEC-RAS GIS import file: channel centerline, bank locations, flow path lines, and cross-section locations.
Each set of lines was created as a separate ArcView shape file. After the 2-D lines were created, the lines and the terrain TIN were identified in a theme set-up dialog box. The HEC-RAS import file was then created. This ASCII file consisted of three parts: the header, the centerline coordinate listing, and the cross-section data. The HEC-RAS GIS import file was read into the HEC-RAS project using the geometry data editor. The roadway bridges that existed along Agua Hedionda Creek within the study reach were inserted into the HEC-RAS model.
After the HEC-RAS model was created, and the output deemed acceptable, the GIS export function in HEC-RAS was applied. The export file was an ASCII text file containing a header that included file names, number of profiles, reaches, cross-sections, etc. With the HEC-RAS GIS export file created, HEC-GeoRAS was used to assist in mapping the floodplain. In ArcView, a theme set-up dialog box under HEC-GeoRAS extension was activated. The HEC-RAS GIS export file, the terrain TIN, and the name of the output directory, where the floodplain themes were to be stored, were specified. Water surface TIN and the terrain TIN were them meshed to produce the 100- and 500-year floodplain.
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