Is there a practical way to determine the maximum hydraulic capacity of a river in HEC-RAS?

I would like to know for each cross section of my 1D model what the maximum flow rate will be before overflow occurs (from the main channel to the left/right overbanks).

I know two possibilities to get this info, but they are not really practical:

  1. For each cross section open the corresponding rating curve and determine at what discharge the water level reaches the LOB or ROB
  2. Run a steady state plan with increasing flow, then check for each cross section profile at what flow the water level reaches the LOB or ROB

I seek a simpler solution.

1 Answer 1


To determine the maximum flow rate before overflow, we need to know the maximum water surface elevation beyond which the overflow will occur. Once we know the WSEL, we can use the Perform design hydraulic computation option in HEC-RAS to compute the discharge by selecting the type as Uniform Flow. To compute the discharge we need to enter the slope which satisfies the uniform flow equations for the given cross section and the corresponding WSEL at which the discharge needs to be computed. This process has become a lot easier since my organization has adopted GeoHECRAS.

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