Hydraulic Jump in Sequential Check Dam Modelling
2

Question

Hydraulic Jump in Sequential Check Dam Modelling

Twinkie (Civil/Environmental)

(OP)

13 Apr 16 13:38

I would like to model a trapezoidal channel with three sequential check dams.

I am using this BMP for peak rate and volume control.

Channel Slope = 0.06 ft/ft (average of the three)
Width= 2 ft
Sides = 4:1
Depth = 2 ft
Height of Check Dam = 1.50 ft

Section L = 90 ft; 180 ft; 180 ft (upstream to downstream)

I have this routed in HydroCAD: Reach > Pond > Reach > Pond > Reach > Pond with each reach having it's own drainage inflow.

I have the check dams modeled as a broad-crested weir in each pond. Flow overtops each of the check dams, and flows to the downstream reach.

My question: Is there a way to see the elevation of the hydraulic jump in the downstream channel to ensure the elevation remains within the section?

Thanks in advance, file is attached if that helps.

http://files.engineering.com/getfile.aspx?folder=6fa42515-844a-4b03-955e-96

psmart (Civil) · Answer 1 · 2016-04-13 14:29:10

A HydroCAD reach is only intended to model normal Manning's flow. If you have more complex reach flow conditions, including tailwater or a hydraulic jump, you should use a different modeling approach.

In many cases you can simply omit the reach and model pond-to-pond, which will preserve the tailwater capabilities of each pond and it's associated outlet devices. (All pond outlets are tailwater-sensitive)

For additional details please see www.hydrocad.net/checkdams.htm

Peter Smart
HydroCAD Software
www.hydrocad.net

beej67 (Civil/Environmental) · Answer 2 · 2016-04-13 21:07:37

Modeling hydraulic jumps (if that's indeed what you're trying to model) requires software that can calculate gradually varied flow profiles. HEC-RAS, really. I'm not convinced that's what you have, though. It sounds more like you just have three weirs, backwatering each other.

If you're not worried about the gradually varied flow profile through your ditches, model all three as ponds.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

Twinkie (Civil/Environmental) · Answer 3 · 2016-04-14 12:09:28

Thank you, gentlemen for the replies. This was to satisfy a reviewer. I ultimately just modeled the ponds in series, and did the math by hand. The "jumps" were negligible.

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Hydraulic Jump in Sequential Check Dam Modelling
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