Modeling converging channel

[thatdamengineer]

Probably a very elementary question for many of you. I have a spillway channel concrete lined, 80ft wide bottom width 5:1 s/s. transitioning to a 20 ft wide channel w/1:1 s/s elevation deop from 80ft width to 20ft width is 24ft. How to model using Hydrocad... I have tried the reach node using a vee channel and entered the exit section and used the elevation profile.

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[psmart]

You said you "tried" to use a reach. Did you have a problem?

You should be able to describe that geometry with a trapezoidal reach.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[thatdamengineer]

Peter, Thanks for the reply... I have a spillway with a cross section of 80ft bottom width and 5:1S/S at elev 1106. It has to transition down to elev. 1082 and an approximate 20ft wide channel w/ 1:1 S/S. When I said I tried, I got an answer, but should I use multiple reaches say at 2 ft elevations and incrementally transistioning from the 5:1 s/s and 80ft wide to the 1:1 s/s and 20ft bottom width? Is one reach section adequate? or should I be modeling with 12 more reaches as I have 2ft Lidar contours?
Cecil Bearden

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[psmart]

You could use multiple reaches in series, but a reach is intended only for modeling normal flow with a constant cross section. Frankly, it sounds like you may need to use HEC-RAS or similar software that is specifically intended to model water surface profiles with a variable cross section. .

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[thatdamengineer]

ok Thanks

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[psmart]

Of course, it all depends on the exact goals of your model. For further details please see

http://www.hydrocad.net/reach.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[beej67]

Spillway design is a pretty deep and complicated field. You need to consider hydraulic jumps, energy dissipation, cavitation, etc. I might consider using HydroCAD (or similar) to do the reservoir routing, with the first section of spillway channel as a broad crested weir, use that to determine your peak flowrates out of the reservoir, and then stick that in HEC-RAS as a steady state flow condition and see what happens.



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