Step3: Post-Processing of Hydraulic Results and Floodplain Mapping
The post-processing of hydraulic analysis results is developed new maps with the same TIN map. Visualization of final results should be performed on ArcMap to create a flood inundation map.
Data import from HEC-RAS
Formatting
The process begins with converting the proprietary spatial data format (.RASExport.sdf) file into the XML file format which is a readable format for the ArcGIS software. By selecting the “Convert RAS Export RAS SDF to XML” feature in HEC-GeoRAS toolbar of ArcMap can easily achieve that purpose.
Layer setup
Setting up the Layer is a crucial step for the processing the HEC-RAS results. The figure below shows a typical set of Layer Setup of HEC-RAS Post-processing. For this post-processing analyses, the Rasterization Cell size is set to 2 map units. Generally, setting of less cell size represents a better resolution of the results of floodplain visualization. 1 map unit is beyond the processing capacity of the program, so 2 map units can be considered the best possible rasterization cell size.
Layer Setup for HEC-RAS PostProcessing
Import RAS Data
Execution of importing RAS data into GIS should be performed when the Layer Setup is done in order to continue the post-processing steps. That can be run by selecting the function “Import RAS Data” in “RAS Mapping” option. This selection developed a new data frame with the following feature classes: River2D, XS Cut Lines, and Bounding Polygon. The figure below shows the operation of the Import RAS Data function.
Import RAS Data Window
Floodplain mapping
Floodplain mapping basically involves two steps, which are explained in following sections.
Water TIN
The first step of floodplain mapping is to generate a water surface TIN form the cross section water surface elevations. The following computational procedure is selected from the HEC-GeoRAS toolbar: “RAS Mapping” —> “Inundation Mapping” —> “Water Surface Generation”. Figure 19 shows the water surface TIN.
Water Surface TIN of Chilliwack River
Floodplain Delineation
The following computational step is selected from the HEC-GeoRAS toolbar: “RAS Mapping” —> “Inundation Mapping” —> “Floodplain Delineation Using Rasters”. Selecting the water surface profile (100-year, 200-year) can delineate corresponding floodplain map. The water surface TIN was converted into a depth grid file (e.g., d PF 2), and a floodplain boundary feature class (e.g, b PF2).
The figure above shows floodplain results form the HEC-GeoRAS model at on section of Lower Reach of the Chilliwack River under 200-year flood. Yellow lines represent the floodplain boundary. The inundation depth grid is represented with different hues of blue. A dark blue represents a high value of water depth. On the contrary, a light blue represents a low value. By utilizing the “Identify tool” button, water depth at any point can be simply identified. For instance, in the figure above, the water depth of the arrow points is 8.333 m. More flood plain results are attached in the next section of the report.