I’m working on a 1D hydraulic model of an open channel with a downstream culvert. The culvert is represented as an open orthogonal section. I’m trying to understand why the upstream water surface elevation increases in the channel even though I widened the cross-section upstream of the culvert entrance. My current assumption is that the increase in water level is caused by contraction losses associated with the transition from a wider channel section into the narrower culvert. What are the recommended practices for modelling these transitions in a 1D environment?
Without the specifics of your model, I’d suggest opening to the first chapter of an open channel hydraulics text. It sounds like by widening the channel you’ve reduced the unit discharge. It is conservation of energy. There is less velocity head, so you end up with more elevation head.