Hec ras cross section spacing

Written by Chris Goodell December 2, Written by Chris Goodell, P. All rights reserved. So the question was, which depth do you use?

Boundary geometry for the analysis of flow in natural streams is specified in terms of ground surface profiles cross sections and the measured distances between them reach lengths. Cross sections are located at intervals along a stream to characterize the flow carrying capability of the stream and its adjacent floodplain. They should extend across the entire floodplain and should be perpendicular to the anticipated flow lines. Occasionally it is necessary to layout cross-sections in a curved or dogleg alignment to meet this requirement. Every effort should be made to obtain cross sections that accurately represent the stream and floodplain geometry. An example of laying out cross sections is shown below in the figure below.

Hec ras cross section spacing

Written by Chris Goodell October 8, Either way, approaching an unsteady HEC-RAS model especially a dynamic one as a beginner with little experience and understanding of how to stabilize it can cause significant delays in your project and worse, completely blow up your budget. Although the model ran to completion without crashing, it had unacceptably high errors. The following lists out the courses of action taken to stabilize the model. The links following some of these items will take you to more information about that particular technique. Cross Section Spacing. The initial spacing was way too coarse. A visual check alone of the geometry schematic and profile plot should encourage you to investigate a finer cross section spacing. Geometry Schematic. Profile Plot Samuels equation suggests anywhere from 15 ft to 50 ft spacing depending on what bed slope you use. I interpolated to 50 ft for the entire reach.

The general approach to laying out cross sections is to ensure that the cross sections are perpendicular to the flow lines.

Cross-sectional cut lines should be created to capture the entire extent of flooding anticipated by the dam break scenario. As in any hydraulic modeling study, cross sections must be laid out to accurately describe the channel and floodplain geometry. Cross sections are laid out perpendicular to the anticipated flow lines of both the channel and the floodplain, during high flow conditions. Cross sections also need to be added immediately upstream and downstream of: tributary inflow locations; dams and other inline structures weirs, drop structures, or natural drops in the bed profile ; bridge and culvert crossings; levees and other types of lateral hydraulic structures. An example of a cross section layout is shown in the figure below. In addition to describing the physical changes and hydraulic structures within the channel and floodplain, there are also numerical considerations for adding or removing cross sections.

Cross sections are developed based on the location layout of cross section lines and properties from other layers such as the River, Bank Lines, and Terrain layers. Cross sections should be laid out perpendicular to where water will flow in the channel and overbank areas. Therefore, most cross section lines should be created from a minimum of four points the end points and points at the edge of the main channel. Cross sections will also be visualized when looking in the downstream direction; therefore, they should be created from left to right when looking downstream RAS Mapper will automatically flip the line to have the correct orientation. There are many considerations when developing cross section data for orientation, locating, and spacing, but keeping in mind that the cross sections should represent a smooth transition in geometry elevation and area and properties conveyance, surface roughness, etc is paramount. Use the terrain, river centerline, bank lines, flow path lines, inundation mapping, and other data to properly place cross section lines. Elevation data will also be automatically extracted.

Hec ras cross section spacing

Written by Chris Goodell December 2, Written by Chris Goodell, P. All rights reserved. So the question was, which depth do you use?

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So the question was, which depth do you use? Especially if you are running in unsteady flow. You might also try a computer reboot too, if the first suggestion doesn't work. Thanks-Chris Jennifer Morreale on April 14, For many years I struggled with these seemingly arbitrary model selections…primarily how far to extend a model upstream and downstream of a structure of interest, and interval spacing of the cross-sections. Anonymous on January 19, Dear Chris, Apologies for the delayed response! Try smoothing out your curve. Already a member? Fread's equation implies smaller streams and steeper hydrographs will require tighter cross sections. You do that in the Htab parameter windows. I used the initial conditions as the first point of the hydrograph even tried changing the ranges and it still gave me the errors.

Written by Chris Goodell October 8, Either way, approaching an unsteady HEC-RAS model especially a dynamic one as a beginner with little experience and understanding of how to stabilize it can cause significant delays in your project and worse, completely blow up your budget. Although the model ran to completion without crashing, it had unacceptably high errors.

Hi Chris. Solution solver went unstable, iteration 2 at 15JAN Dam 1 Load More. The thing to understand here is that you've got a complicated system, that's only really model-able "correctly" with some kind of finite element analysis of the navier stokes equations in 3d, which is more of a doctoral thesis than an engineering project. Thank you all for your help, however I don't think I did a good job in explaining my problem If you ever do get a chance to test the threshold of application about the equation's results, I'd love to see the results and get that up on the blog. Todd 1 R. Registration is open for the October 11th - November 15th webinar series. The only correct visualization is the "in memory" ras 5. How can I fix this? Hope this helps. The general approach to laying out cross sections is to ensure that the cross sections are perpendicular to the flow lines.