Culvert Modeling in HEC-HMS

[OKPE]

I am having trouble modeling a culvert in HEC-HMS. I am using version 3.01. I tried version 3.4 but it had several bugs.

I have a watershed broken into two sections, seperated by a canal. There is a culvert under the canal. Basically, I want to model the contribution from the upper watershed as a truncated, flat top hydrograph, with the flat portion the peak culvert capacity. I thought this might be easiest to do as a Source (in which case I would run the upper watershed model seperately, and get data for a hydrograph and input it into the source), but I am having trouble linking the source upstream of the other watershed. I also want to do some channel routing, probably just using the Lag method.

Any suggestions on the best way to do this?

 

[SMIAH]

I would probably use another program as Hydro Culv or HY-8.
Keeping HMS to estimate the peak flow at the culvert inlet.
You could use HEC RAS to model the reach with the culvert on it.

lower watershed? A sketch maybe?

 

[Drew08]

Route the watershed entering the culvert to a diversion element. The diversion element can be defined with a Qin per Qout table that may look like:

Qin Qout
0 0
X X
99999 X

Where X is the maximum culvert capacity and 99999 is some number larger than the expected peak runoff rate. Outflow from the diversion element will match the runoff hydrograph up to a maximum discharge of X. Everything else will be diverted. From the diversion element, both the outflow and diverted flow can be routed downstream separately.