![]() ![]() Because the tributary is relatively flat along its longitudinal slope, flow ends up going both directions (upstream and downstream). Here’s what the results look like in this example:Īs shown above, where the connection alignment crosses the tributary on the right, the weir embankment elevation is set at the existing ground elevation. Essentially we’ve added an internal boundary condition (similar to SA boundary conditions in TUFLOW). As with the dam outlet works example, it requires a few iterations to match the desired hydrograph (which would have been provided from HMS, RORB, or other rainfall-runoff model) but it gets the job done in the end. When I run the model, flow that is stored in my artificial reservoir in the left tributary is then introduced into the tributary on the right. Because there is no other flow crossing the connection line, I could just as well raise the elevation of the entire weir embankment, but in this example I have only raised the weir elevations within the left tributary to function as a dam and block the flow (raising the head sufficiently to push water through the culvert). I add a culvert with the upstream station in the left channel and the downstream station in the right channel. I then edit the SA/2D Area Connection and click on the Weir/Embankment editor and copy/paste the terrain profile data into the weir/embankment profile. I then add an SA/2D Area Connection that crosses each of the tributaries as shown here: In the schematic below, I’ve assumed the tributary on the left is outside of my area of interest and that I want to bring some flow into the tributary on the right without moving the external boundary around that tributary. You can see what I mean by the “Pac-Man” method here (in case that designation isn’t as self-explanatory as I might think as a retro fan). Keep in mind, though, that the 500-point limitation on weir embankments still holds, and the weir elevations cannot be set below the ground level. The cross section points filter can be used to reduce the number of points for a long connection, but then some of the weir elevations will also need to be raised, so the process gets very awkward if you move the inflow and outflow locations too far apart.Īlthough the Wormhole Method is a bit cumbersome for this purpose (because it requires some trial and error to adjust the culvert outflow hydrograph to match the desired inflow hydrograph at the internal boundary condition location), it can be used in a pinch.īelow is an example that shows how to use a wormhole culvert (essentially a SA/2D Area Connection with upstream and downstream culvert centerline stations located some distance apart) to introduce an internal boundary condition. Wormhole culverts then essentially become a workaround for allowing internal boundary condition lines. By introducing an artificial upstream storage area outside of my area of interest (but inside of the 2D Area) and connecting it to my desired inflow location with a wormhole culvert, however, I can add inflows anywhere I’d like. This becomes problematic when there is flow on both sides of the inflow, however. When a tributary’s headwaters are located completely within the 2D area, for example, I’ve had to use the “Pac-man Method” (putting a slice into my external boundary) just to introduce the inflow. In the current version of HEC-RAS, inflows can only be introduced along the external 2D Area boundary, and I frequently run up against this limitation. Wormhole Culverts Part 5: What’s the best shape for a wormhole culvert?.Wormhole Culverts Part 4: Sensitivity analyses for wormhole culverts.Wormhole Culverts Part 3: Comparing wormhole culverts to 1D/2D bridges and culverts.Wormhole Culverts Part 2: Using wormhole culverts for internal boundary conditions.Wormhole Culverts Part 1: Introducing the wormhole concept.Wormhole Island: Using a wormhole culvert to introduce internal boundary conditions into HEC-RAS 2D models ![]()
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