Rating Curve of a Grass-Lined, Open-Channel Spillway

[Drew08]

Hi all,

I'm trying to get a feel for what methods engineers typically used to determine the stage-discharge rating curve of a grass-lined, open-channel spillway. Something you might see functioning as an emergency spillway at an earthfill dam or retention pond.

Please share what you normally use, not necessarily what can be used.

Thanks.

 

[RWF7437]

Manning's Equation.

 

[cvg]

Manning's may be ok at some flow rates, but also check weir flow.

n-value may be dependant on velocity - will the high velocity flow water rip out the grass? If so, what happens to your n-value?

Also depends on the approach conditions - will the flow be controlled by the spillway inlet control section? Is there a spillway training wall? How deep is the water upstream of the inlet control section?

Steepness - is the spillway channel steep, or will it flow subcritical? under all flow conditions?

 

[chicopee]

cvg, I don't do spillways and dams, however, for curiosity sake, what is a spillway training wall?

 

[SMIAH]

Q=CLH^3/2 ?

Using Effective Length and an appropriate C.

 

[cvg]

as water moves from reservoir towards the spillway, it comes in from all directions and increases from essentially zero velocity. When it gets to the control section, it has to turn in the direction of spillway. It has considerable momentum and it is difficult to turn the flow towards the spillway. This will reduce the effective weir coefficient at the spillway control section. A training wall extends from the edge of the spillway towards the reservoir and guides the water straight towards the spillway.