RAS Terrain DevelopmentĪ new Terrain Layer is created by selecting one or many raster (gridded) datasets and importing them into a single layer.

To use a Terrain Layer in RAS Mapper it must first be “created” and then “associated” with the geometry and plans of interest. It is also used for preprocessing geometric data for 2D Flow Areas, computing flood depths, and inundation boundaries from simulation results. Terrain data can be used in RAS to visualize the floodplain geometry. In the event that sufficient detail is not provided in the terrain model (such as at a levee), the hydraulic structure option is available in RAS to override elevation data. When used for developing 2D Flow Area information, RAS will allow the placement of breakline locations (to align cell faces) where elevation data will be extracted for cell faces elevation profiles. If the model is intended to capture the detailed hydrodynamics through a bridge opening, the grid-cell size must be small enough to capture and represent the piers (or high ground) that will significantly direct flow. For instance, even though a larger cell size may appropriately capture the ground surface definition in the overbank areas, the cell size must be small enough to capture the more abrupt changes in elevation that tend to occur in the main channel.

Further, if a detailed 2D model is being developed, bridge piers, training walls, and buildings should be included in the terrain such that they can eventually be included in the 2D Flow Area mesh.īecause RAS supports a DTM as a gridded model, the grid-cell size used to represent the terrain must be small enough that it captures the features of the terrain. The definition of linear features that direct the movement of water such as levees, floodwalls, and roadways should be captured in the terrain model while such features as bridges should not be included. In other words, a good terrain model is comprised with accurate bathymetric information to supplement the more readily acquired overbank information. In order to properly represent the floodplain area and develop an accurate geometry for the river analysis, the DTM must have representative data in the main channel and the overbank areas. The RAS Terrain support is for raster data of many formats, but once processed, the data will be stored in the GeoTiff format. HEC-RAS supports the use of a digital terrain model (DTM) for representing the bare earth ground surface. HEC-RAS supports the use of terrain data in a raster format - once terrain data has been imported to HEC-RAS it is referred to as a RAS Terrain. A good terrain model represents the ground surface well in locations that affect the movement of water through the floodplain. The first step in creating a good hydraulic model is having good terrain data.

Run a flt file on hec ras