The background images will assist the user in figuring out where to draw the 2D flow area boundaries in order to capture the tops of levees, floodwalls, and any high ground that will act as a barrier to flow. Additionally, the user may want to bring in a shapefile that represents the protected area, if they are working with a leveed system. Once you have terrain data and various Map Layers in RAS Mapper, they can be displayed as background images in the HEC-RAS Geometry editor. The best way to do this in HEC-RAS is to first bring in terrain data and aerial imagery into HEC-RAS Mapper. The user must add a 2D flow area polygon to represent the boundary of the 2D area using the 2D flow area drawing tool in the Geometric Data editor (just as the user would create a Storage Area). Note: for a more detailed description of how to use the HEC-RAS two-dimensional modeling capabilities, please see the separate User's manual that comes with HEC-RAS called " 2D Modeling User's Manual".Ī 2D Flow Area, and computational mesh, is developed in the HEC-RAS Geometry editor by doing the following: Draw a Polygon Boundary for the 2D Flow Area 200 X 200 ft cells), and the automated tools within HEC-RAS will build the computational mesh. However, the user will most likely select a nominal grid resolution to use (e.g. This means that the computational mesh can be a mixture of 3-sided, 4-sided, 5-sided, etc… computational cells (up to 8 sided cells). This algorithm was developed to allow for the use of a structured or unstructured computational mesh. The HEC-RAS 2D modeling capability uses a Finite-Volume solution scheme. ![]() 2D Flow Areas can be connected to another 2D Flow area or a Storage Area by using a SA/2D Area Connection (this is described later in this chapter). 2D Flow Areas can be connected to a river reach by using a lateral structure connection. Then the user must define the computational mesh.ĢD Flow Area can be located at the beginning of a reach (as an upstream boundary to a reach), at the end of a reach (as a downstream boundary to a reach), or they can be located laterally to a reach. 2D Flow Areas are defined by laying out a polygon that represents the outer boundary of the 2D Flow Area. Two Dimensional Flow Areas (2D Flow Areas) are regions of a model in which the flow through that region will be computed with the HEC-RAS two dimensional flow computation algorithms.
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