Defaulting to critical depth through a bridge

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Defaulting to critical depth through a bridge

Yair Simonson
Recently I have been struggling with a steady 1D model with a bridge crossing for a while because I could not resolve/justify the program of defaulting to critical depth at the upstream and downstream ends of the bridge.

I tweaked every  aspect of the model in an effort to identify the cause. Nothing I did made a big difference.
Today I finally discovered that when you reduce the steepness within the bridge cross sections it no longer encounters this issue.

In this particular case i discovered that the lidar surface i was using is slightly higher at the upstream side of the bridge as compared to the received survey. So I am going to correct the model by using the surveyed data for sections near the bridge and lidar only for sections far from the bridge. The reduced gradient within the bridge will solve my issue. Basically, I had "bad" geometry.

However, if this were not the case and my Lidar surface were accurate. Would there be any way to get around the defaulting to critical depth warning? It seems to me that there might exist a context in which the program is incapable of running to completion without hitting one of these default to critical depth situations. Is this the case? Or am i missing something?