3 Retention ponds in series 2

[jesspo]

Ok, this might be a retarded question because well, I like dealing with refineries, not ponds.

In the sketch I've provided there shows a series of 3 ponds. Ponds A and B are slightly above pond C. They all currently drain by gravity, there are butterfly valves between B and C and on the outlet of C which goes to the stream.

The Structure in the upper right is what our current discharge culverts look like 24" Plastic with a grate that feed 8" plastic pipe which drains to the next pond/stream.

THE PROBLEM: Pond C must be almost completely drained before we are able to get A&B to flow into it. Once A/B drain into C the level is too low. So without redoing the entire grading/piping, is there a way in which we could get A/B to flow into C while the level is higher.

PROPOSED SOLUTION: I suggested we put a sump pump near the exit of B which is piped directly into the 24" Plastic pipe and close the openings so the pressure from pump could over come the back pressure. Would this be ok? Obviously the Openings at the bottom of the drain would need to be closed, so the back flow isn't faster than the pump.

I realize i've probably left out some important details, please just inform me what else we need to know before we can come to a solution.

Thank you.

 

[cvg]

draw me a good hydraulic profile and maybe I could be convinced. So far, your sketch leaves a lot to my imagination. As long as the valve between the two ponds is open, they will equalize to the same level. You don't need a pump to do that.

 

[TerryScan]

cvg - correct but he is not looking for the same level. He is looking for A & B to be dry and C to have a pool.

jesspo - it would be a lot simpler and less maintenance and problems to simply over excavate Pond C below the outlet elevation in order to acheive a pool for asthetics. Then, let everything equalize and drain by gravity.

 

[jesspo]

a lot simpler to excavate? that's like 30k of work and engineering, my ponds are already setup as described.

How is the riser closed off to pond B EXCEPT by pump inlet, not going to work? You say Ponds B&C will equalize if i leave the valve open, so if Pond C is connected to that riser drawn, with the only outlet the top and i pump water into the bottom, won't that work as well?

 

[gbam]

jesspo - you mention the 30k of cost for the over excavation. How much will the installation of a pump be plus the operational and maintenance costs? Typically, a gravity system will be cheaper in the long run.

 

[jesspo]

running a <3 hp pump doesn't add up very fast especially when we'd only have to run it every other day or less.

Gbam, are you saying the setup would work? I understand that there are alternative solutions, but i was told low cost, and easy installation/maintenance.

I have come to the conclusion that it will work, although not as well as excavation or just burying a dedicated line for a pump.

 

[cvg]

see attached sketch for some thoughts.

 

[gbam]

For the pump alternative, my thought is to block the Pond B outlet pipe at the inlet or as close to it as possible to minimize excavation like in your concept drawing. Use CVG's idea and discharge pump near top of riser.

I think you still need to look at the Pump cost, initial dewatering and O&M costs for the pump alternative and compare that to the excavation alternative to find the most cost effective alternative. Simulate wet and dry cycles with your pump alternative to see if there is increased costs during certain times of the year. What is the ground water level and will these ponds continue to fill during the dry times?

Also make sure that you can continuously discharge to the stream with out fines etc...

 

[DFrancke]

Late comment as I just got into this thread:
You mentioned a max allowable flow rate which suggests you have a permit for these ponds and their discharge. If you have a permit you want to find out if any of the ponds are allowed by permit to retain water beyond 48-72 hours after rainfall. If there are detention ponds then they are probably meant to be dry except with rain fall. If they are permitted as such you need to be sure you will not be in violation of your permit before you start keeping water in any of the ponds beyond the permitted time.

Just a thought.