There are several ways to create these features. The left and right bank features are optional. Press Open.įigure 4: Stream.ter stream channel, cross sections and bank features Notice the terrain file contains 3D features for the stream channel, cross sections and left and right banks. If there isn’t, you will have to create a new IO specification.ġ. Examine the list to see if there is an export specification for a HEC-RAS *.geo file. If you are not sure if this option is enabled, choose menu Module | Setup | Export. In order to do this example you will also need to have the HEC-RAS export option enabled. To run this example you will need Terrain Tools ® or RoadEng ® Version 5.1163 or higher. The Terrain Module will calculate reach lengths and bank positions automatically from left, right and main channel features.įigure 2: Bank positions and reach lengths Creating a Hec-Ras File Reach lengths are considered for the left overbank, main channel, and right overbank areas and indicate the path of flow between cross sections. Reach lengths are used to define the distance between cross sections and are used for energy loss calculations in HEC-RAS. Bank stations separate the main channel area from the adjacent floodplain (termed the left and right overbank areas). Cross sections are taken perpendicular the direction of flow both in the main channel and in the overbank areas. Station-elevation data represent the ground surface at designated locations in a river reach. Cross-section data includes station-elevation coordinates, main channel bank stations, downstream and reach lengths. In Terrain each reach a terrain feature.įigure 1: River Network and Cross SectionsĬhannel cross-section data is used in HEC-RAS to characterize the flow capacity of the river and floodplain. A river may be composed of one or more reaches. A reach is defined in HEC-RAS as starting or ending at junctions - locations where two or more streams join together or split apart. A river system is a collection of reaches, all oriented downstream. River networks define the connectivity of the river system. HEC-RAS can be used to model a single river reach or an entire river network. The geometric and flow data are used to calculate steady, water surface profiles based on energy loss computations. HEC-RAS requires definition of the land topography and flow information for hydrologic events. HEC-RAS is a one-dimensional, steady-flow, water surface profiling program (U.S. Generally, this study discovered that flooded areas in the upstream and middle parts of Fetam River are high as related to the downstream parts.Download the files associated with this example: Exporting to HEC-RAS.zip These flooded areas along the side of the Fetam River are 27.31, 24.85, 20.47, 17.34, and 13.78 km 2 for 100, 50, 25, 10, and 5 years return periods, respectively. The inundated areas were particularly high from Abaya Kalo, Achigi, and Denbun kebeles for all return periods. Built-up areas and agricultural fields are located along the river banks and are highly susceptible to flooding. These critical floods were damaging the areas around Fetam River, which is hazardous to social and economic growth due to loss of lives and destruction of properties. The flooded areas on Fetam River have been represented depending on 5% incidence peak flows for different reoccurrence eras using the HEC-RAS model, GIS for spatial data handling, and HEC-GeoRAS for interfacing among HEC-RAS and GIS. Using the past data on river banks and the release of earlier floods besides topographic data, maps were made to illustrate areas predictable to be covered with the flood for different releases. Flood inundation mapping is used to define the zones which are more susceptible to flood along the river when the release of a stream surpasses the bank-full stage along the river. Therefore, this study was conducted to map flood inundation areas along the Fetam River using GIS and HEC_RAS. One of these measures is inundating flood hazard areas. This can be minimized by giving attention to flood risk measures. Flood occurs due to rapid population growth, land degradation, and climate change, and causes harmful damages to human beings and properties.
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