I am trying to have our survey stations be the same in HEC-RAS but our stationing has a few station equation adjustments along it (our stationing is adjusted 90-95 feet depending on its location).
The first problem that I am trying to rectify is the stationing that appears within HEC-RAS. I am currently having issues with generating geometry from inroads into hec-ras and am looking for some assistance. I don't know if my last post went through so sorry if this seems repetitive. I'll use contour maps to help guide me, but in the absence of good terrain information, I'll usually measure about 1/3 the distance from the main channel to the waters edge. The instructions for measuring the LOB and ROB reach lengths is to follow the perceived "center of mass of flow" of the respective overbank. I that case the main channel will have longer reach lenghths than the overbanks. Sometimes you have a fairly straight floodplain, while the main channel meanders around within that floodplain. For example, if you have a river bending to the left, the LOB reach length will be the shortest and the ROB reach length will be the longest. Now.how does HEC-RAS know the meandering characteristics of the river? The ONLY effects of meandering that HEC-RAS accounts for in the computations is the varying reach lengths (LOB, Channel, and ROB) for a given cross section. Some people like to call the "0" point the channel centerline, and so all station points to the left the centerline will have negative stationing and all points the right will have positive stationing. Most people will start their stationing at 0, but you don't have to. One cross section could start its stationing at 500, and the very next one can start its stationing at -200. No.the cross sections do not have to always begin their stationing the same distance from the imaginary centerline. The following RAS Bloggery article will help with junctions. Where it can get tricky is at a junction.
OVERBANKS LENGTHS HEC RAS SOLUTIN TRIAL
It takes a little bit of practice to do this correctly, and most of the time some trial and error, but as long as you remain perpendicular to the flow lines and don’t intersect, you’ll have a good set of cross sections. It can be very helpful to draw these flow lines before cutting cross sections. Notice that the cross sections are drawn so that they are not only perpendicular to the main channel, but also to my perception of the flow lines in the floodplain. The light blue lines are my impression of the flow lines through this terrain, if water were flowing appreciably in the floodplain. The brown lines represent the edge of the flood plain. In the figure below, the dark blue line represents the main channel. The trick is to keep them from intersecting, while also staying perpendicular to flow lines. That is why it is common to see cross sections snap at different angles outside the main channel (we call this doglegging). And they cannot intersect with each other. All rights reserved.Ĭross sections must be perpendicular to the flow lines at all locations.
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