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W Beck posted a topic in Hydraulics and Floodplain ModelingHello, I am attempting to use WMS / HEC-RAS to determine the threshold discharge for overbank flow in a third-order watershed. This is part of a floodplain sediment storage study. I am running a series of flows through the model and trying to determine the minimum discharge required to initiate overbank flow. I am assessing the overbank threshold visually, using flood depth contours (generated within the _fd dataset). I assume the presence of any flood depth contour ≥0 represents overbank flow in my WMS model (see attached image 1). I also assume that stream reaches without contours present are not exhibiting overbank flow. I should note that I inserted field-measured cross sections into my model. I have three questions: 1.) Can you offer any advice regarding visual (or non-visual) methods of determining the incipient point of overbank flow? I assume if there was a way to indicate top of banks in relation to flow depth, this would be helpful (e.g., a non-planform view of the cross section and associated flood depths). For image 1, the contour range is 0 (min) to 1 (max), with 5 intervals. 2.) The flood depth contour polygons often exhibit a width that is nearly equal to the channel width in my watershed model (Image 1) - so, how can I be sure the flood depth is not being calculated within-channel? Again, I'd like to know if the flood depth is occurring in the floodplain and not in-channel. 3.) I have noticed that many "isolated" flood depth contours appear around cross sections, even at flows that I would not expect to be out of bank. Any thoughts on this? See image 2. Again, I am interested in determining the minimum discharge needed for overbank flow. Any advice on this non-traditional use would be greatly appreciated!!! Thank you.