Flow into submerged Grate Inlet
Flow into submerged Grate Inlet
(OP)
Hello,
I was wondering if anyone had any advice on calculating the flow into a submerged grate inlet. I'll be contacting the vendor shortly because I know the flowrate will be highly dependent on the grate geometry.
Basically, we're using a submerged grate inlet to act as a flow control for a detention basin. The initial detention basin outfall was constructed incorrectly and instead of tearing it out and constructing a new one, we're just going to add a grate inlet where the detention basin outfalls.
This grate will be submerged by about 1"-2" of water. I don't have the exact WSE yet. My goal is to limit the flow to 5 cfs for the water surface elevation that is generated by the 10 year - 72 hour storm. I'm assuming that flow into the grate would be orifice flow since it's entirely submerged. I don't really know where it transitions from weir flow to orifice flow. I'm hoping that the vendor will have some design information that will help me.
Does anyone have any advice on how one would go about designing this grate inlet to limit flow to 5 cfs with a given head (WSE)? I was just going to use the orifice flow equation:
Q = Cd*A*(2*g*d)^0.5, where
Cd = orifice coefficient
A = clear opening of grate
g = g (duh)
d = depth of flow or WSE elevation above grate (head)
Would this be the right way to go about it? Any help would be greatly appreciated.
Peace,
Stoddardvilla
I was wondering if anyone had any advice on calculating the flow into a submerged grate inlet. I'll be contacting the vendor shortly because I know the flowrate will be highly dependent on the grate geometry.
Basically, we're using a submerged grate inlet to act as a flow control for a detention basin. The initial detention basin outfall was constructed incorrectly and instead of tearing it out and constructing a new one, we're just going to add a grate inlet where the detention basin outfalls.
This grate will be submerged by about 1"-2" of water. I don't have the exact WSE yet. My goal is to limit the flow to 5 cfs for the water surface elevation that is generated by the 10 year - 72 hour storm. I'm assuming that flow into the grate would be orifice flow since it's entirely submerged. I don't really know where it transitions from weir flow to orifice flow. I'm hoping that the vendor will have some design information that will help me.
Does anyone have any advice on how one would go about designing this grate inlet to limit flow to 5 cfs with a given head (WSE)? I was just going to use the orifice flow equation:
Q = Cd*A*(2*g*d)^0.5, where
Cd = orifice coefficient
A = clear opening of grate
g = g (duh)
d = depth of flow or WSE elevation above grate (head)
Would this be the right way to go about it? Any help would be greatly appreciated.
Peace,
Stoddardvilla





RE: Flow into submerged Grate Inlet
RE: Flow into submerged Grate Inlet
It seems like there's no established method of determining whether the flow into a grate inlet is orifice or weir flow.
Peace,
Stoddardvilla
RE: Flow into submerged Grate Inlet
Peace,
Stoddard
RE: Flow into submerged Grate Inlet
RE: Flow into submerged Grate Inlet
RE: Flow into submerged Grate Inlet
I found an awesome reference for Neenah grate inlets....exactly what I was looking for. Check it out:
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Click on the link to the right for "Sag or Ponding Conditions". It looks like it calculates using a combination of the two equations AND it does it for specific actual products. I haven't messed around with it yet, but it looks like it does the trick. If it works right, it's going to be a lifesaver for me. Check it out, let me know what you think or how it compares to FHWA HEC22 Urban Drainage Design Manual.
Peace,
Stoddard
RE: Flow into submerged Grate Inlet
RE: Flow into submerged Grate Inlet
http://www.udfcd.org/downloads/down_critmanual.htm
RE: Flow into submerged Grate Inlet
RE: Flow into submerged Grate Inlet
RE: Flow into submerged Grate Inlet
But, as the graph indicates, if you calc Q for both, the lower Q (or the higher H) always controls. That automatically determines your control.
Engineering is the practice of the art of science - Steve
RE: Flow into submerged Grate Inlet
Engineering is the practice of the art of science - Steve