It can be found on FHWA webiste here: Ĭowan’s Equation yielded a value of 0.062, which was substainally larger than my initial value of 0.040. Cowan Equation is a simple equation that was developed after studying 40-50 streams. Therefore, he suggested that I use Cowan’s Equation to determine the channel’s Manning’s “n” value. The creek that I modeled was windy, had sloughed channel walls, and even some random obstructions. After talking with some co-workers, one asked if I had the correct Manning’s “n” value. This caused the water surface at one of the cross sections to still default to critical depth. I recommend reading through this 4 page write up and see if his suggestions apply to your model: Īfter reading his Notes on Critical Depth, I realized that I need to add interpolated cross sections between two sections. Knipe, PE, CFM of the Indiana DNR wrote a concise explanation & offered some suggestions for this scenario.
Therefore, I knew that I needed to revise my model.ĭavid B.
There are scenarios where critical depth may be an valid solution, however, they are rare in the state I practice. This is a serious problem, because the water surface profile is not actually being calculated instead, HEC-RAS assumes the water surface to be at critical depth.
#FIXING HEC RAS ERRORS SOFTWARE#
I modeled a bridge with HEC-RAS and the software gave me a warning message stating that it could not find a solution, so it assumed critical depth. I’ve seen this problem twice now, so I thought I’d put up on the blog.
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