RAS will then determine the number of interpolated cross sections necessary between each set of original cross sections so that the main channel reach lengths never exceed that maximum distance. Here you can see there’s a single input box for the Maximum Distance between XS’s. You can choose to interpolate over an entire river/reach, or a segment of a reach, based on your selection of the Upstream River Station and Downstream River Station. This method is good for testing whether the spacing of cross sections will help produce a more numerically stable simulation. They are interpolated based on the internal interpolation scheme, with no user interaction, except for entering a maximum spacing value. This is also called “blind” interpolation, because you cannot see nor control how HEC-RAS interpolates new cross sections. The first interpolation method, Option A, is called Interpolation “Within a Reach…”. Interpolating cross sections is a quick and convenient way to satisfy this relationship. Finally, in unsteady flow modeling, there’s a relationship between cross section spacing, wave speed, and computational time step that minimizes errors and numerical instabilities (Courant Condition). There’s also that pesky warning message that seems to always pop up:Įach of these warning messages suggest that more cross sections will provide a better solution. Additional cross sections are needed in areas of rapidly varying flow and/or significant grade breaks to avoid overestimation of energy loss ( ). Also, cross sections are needed to properly define the expansion and contraction zones around bridges, culverts, and inline structures. Cross Sections should be selected early on in your project to adequately define changes in geometry, roughness, bed slope, and discharge. First, let’s briefly review why you may need to interpolate cross sections in HEC-RAS. There are two options for interpolating cross sections in HEC-RAS: “Within a Reach…”, let’s call this Option A, and “Between 2 XS’s…”, Option B. Today’s topic is “XS Interpolation Within a Reach”. Each post will discuss a feature in the menu items, starting with the Tools menu item in the Geometry Schematic.
Interpolate add onin excel for mac series#
I’m starting a new series called “Exploring HEC-RAS”. Exploring HEC-RAS: XS Interpolation Within a Reach
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