Pond Boss Forums POND CONSTRUCTION Building a dam Bar guard flow restriction

Does anyone have an idea of how much a bar guard restricts water flow? I have a 24" Agri-drain heavy duty bar guard which has a total of 16 bars spaced a little over 3" apart. I haven't measured the bar widths but they look like 3/8". So do you just add the width of those up and then subtract it from the total pipe diameter? If so, this would reduce the flow of my pipe down from a 24" to an 18".... I just replaced a 15" overflow pipe with this 24" pipe and added about 4-5 feet of headboard on the dam b/c I had the dam topped this spring. I hate to reduce the 24" pipe to an 18" with the bar guard. But..If that is the case, would it be better to build something 4-5 feet out in front of the pipe so as not to restrict the total flow?

Their ad says "Provides maximum flow rates". I don't think it restricts like you are speculating. I wouldn't worry much about it, unless you are in a hurricane region, then it could overtop regardless, in a storm like last year near Houston.

Yes, I called them to see if they had done any testing and they said they had not.... so hopefully you're right and I am overcompensating for what I think the restriction would be. I know when I researched the flow rate on a 15" pipe vs a 24" pipe it was like 7,000 GPM vs 21,000 GPM...possible flow rates if all things were optimal.

Figure up all the open area in your guard, and then compare it to the cross sectional area of the pipe. The longer the guard, the greater the open area.

If the guard went straight across, flat to the end of the pipe, your assumption would be correct. The guard is cone-shaped, so I suspect the total area of the openings exceeds the cross sectional area of the pipe.

The guard may modify the way the water goes in by creating vortices at full flow. Those calculations could be approximated with a hydraulic study, which the company said it did not do. Personally, I would leave the guard in place, otherwise some sticks could get across the opening, trap other debris, and block a large portion of the flow.

Ok, that makes sense. I won't be back out at the property until tomorrow but I will figure that up and see what I come up with. Thx!

Well, If my "seat of the pants" calculations are correct, then you are correct. I came up with 452.44" for the cross sectional area of the pipe, and 615.83" for the total area of the openings on the pipe when figured one way, and 464" figured in another way...so if those are correct then they would both be larger than the cross sectional area of the pipe. Thanks.

I can tell you one thing. If you do not have a bar guard and two turtles just the right size get stuck in the pipe, the flow restriction will be a lot greater than what the bar guard would have been.

Don't ask me how I know.

John, I know how you know.

I've got 2 rat guards because of grass carp, and there has never been any noticeable difference in flow before or after the guards. Several of us here use the Agri Drain Bar Guards on our pipes.

John, that would be some BIG turtles to plug a 24" pipe...

Thanks AL, that is good to know!