Next step is to add cross sections.Written by Chris Goodell, P.E., D.
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You should now have 5 parallel lines in RAS Mapper, as seen in Figure 15. Right click Flow Paths, start editing, and remember to stop editing and save changes when finished. These represent the center of the conveyance area in the floodplain on the left overbank and the right. įigure 14: RAS Mapper with centerline and bank linesĤ. Refer to Figure 14 to see what this looks like. Define the right and left banks, stop editing, and save your changes. Bank lines help distinguish between overbank roughness areas and the channel roughness areas. Your work should resemble Figure 13 at this point.ģ. Right click the Rivers layer, click "Stop Editing" and then answer yes to save your work. When done, name the river "ME-23" and name the reach "Conveyance". Hold down the shift button to pan around. Click with the left mouse button to place a node, and double click to finish. It may be helpful to refer to the map (in the tab above). It will extend from White Lake to the project area. Toggle between the terrain layer and the map layer to determine where the centerline of our channel should go. Name the new geometry "Pecan Island Conveyance Channel"2. Within RAS Mapper, right click Geometries and click "Add new Geometries". In such cases the channel location may be better identified with the terrain layer toggled off.The results from this activity will include:One geometry file, "Pecan Island Conveyance Channel"Results TemplateFigure 2.2.1: Screenshot of entire river schematic (50 points)Figure 2.2.2: Close-up shot of channel under HWY 82 (50 points)ResourceAccess LinkResults TemplateTemplate_Activity_2.2_HD.docxInstructions1. This often occurs in low lying marsh areas like that seen in coastal Louisiana. Sometimes when viewing LiDAR data uncertainties in channel location occurs because of overtopping of channel banks when the data was obtained. When doing this it may be necessary to toggle the terrain layer on when the location of the channel is unclear due to obstructions such as vegetation, shadows, etc. Require(, function () ).call(this, require || RequireJS.require) Ĭreating a 1D Geometry FileWe will create 1D geometry files by tracing over the aerial background in our HEC-RAS project. Learning ObjectivesAt the end of this section, the following is expected:Using HEC-RAS, the student will be able to create georeferenced polylines for project application.Using HEC-RAS, the student will be able to express georeferenced polylines in terms of terrain elevation.Using HEC-RAS, the student will be able to modify existing cross sections in terms of terrain elevation.ABET outcomesThere are no specified ABET outcomes for these objectives. (measured along the centerline)Bank stations – Distinguishes the main channel segment of the cross section from the floodplain segments.ROB and LOB – The right and left overbank or floodplain, respectively.Center station - The station located in the center of the main channel in a cross section.Invert elevation – lowest elevation of the main channel in a cross section. (measured along the centerline)Downstream reach length – The distance between the current cross section and the adjacent downstream cross section. Listed below are terms that are necessary to define the geometry and location of cross sections in HEC-RAS.River station – The distance from the most downstream end of the channel. Cross sections should be situated perpendicular to the flow of the channel and extend across the entire floodplain. Cross sections define the roughness, slope, shape, and flow capacity of the channel and adjacent floodplains.
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A new cross section is necessary each time the channel geometry varies. A ground surface profile that transverses a channel is commonly called a cross section. The positive sign convention for flow is developed by drawing each reach from upstream to downstream.While the River System Schematic identifies the location and connectivity of a channel, the geometry of a channel is portrayed by the ground surface profiles that transverses it. The River System Schematic for this module is created using RAS Mapper. Only one river and reach identifier is necessary in this module because there are no junctions. A junction is the convergence or divergence of two streams.
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The reach identifier specifies a specific section of the river located upstream or downstream of junctions. The river identifier specifies the actual name of the river. Each reach has a river identifier and a reach identifier. The River System Schematic consists of reaches, junctions, storage areas, storage area connections, and pump stations. The River System Schematic develops how the river system is connected and establishes the positive sign convention for flow.
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The geometric data for any HEC-RAS project begins with the River System Schematic.