Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? Drainage and duckweed

I’ve got a smaller pond, 1/4-1/2 acre, that is tormenting me. It’s fed by a natural spring of modest flow. There is an spillover pipe of 6” that limits drainage due to a thick blanket of duckweed. The pond is probably 30 or more years old as is the metal piping. The pond was created in a V of a spring branch where the lower section was created by building a levee at the lower side of that V. I’m considering trenching and installing a 12”-18” double wall culvert pipe hoping it will aid in draining off much of the duckweed. I’d have to continually pump the pond down to excavate and replace the original spillover. So, I’m I wasting time and money on the culvert pipe? Would I be better off with a new and larger spillover including a valve at the elbow to drain the pond for cleanup? Also, duckweed, how do I address this formidable problem most effectively? I’m open to any ideas short of mortgaging the farm to fix it. Thanks in advance.

Duckweed and Watermeal are problematic as you have found out. Flumioxazin is the active ingredient in Clipper or it's generic counterparts. Use that to spray it and spray any new plants that show up in 30 days. 6-12 ounces per surface acre in enough water to cover the area that you want to spray. 1/2 acre would be 3-6 ounces. etc. If the plant isn't sprayed, it won't die. I like to mix in a bit of pond dye to be able to see where I sprayed and to monitor the plant coverage.

To drain the pond for cleanup, if you have the fall, you could use a siphon system. If the original 6" pipe was made of galvanized steel it might rust through shortly and you would have to dig it up to replace it anyway.

Wizbang,

I am a little confused by these two statements.

What exactly do you mean by: the 6" pipe "that limits drainage due to a thick blanket of duckweed"?

Is the pipe clogging with duckweed and the spring inflow is filling your pond above the normal pool level?

I am also confused by your statement that you want to install the large culvert pipe "hoping it will aid in draining off much of the duckweed."

I am unfamiliar with the concept of draining off the duckweed.

One common option for people that need to periodically pull down the water level in their pond is to install a bottom-drain siphon system.

Siphon Diagram

If you installed that type of system, then the cut through the dam DOES NOT have to be at the bottom!

You could even simplify the system and install the siphon above ground with no trenching at all. You would need a way to seal the outlet of the siphon system and a way to fill it with water. Then you close the valve at the high point of the siphon (where you were adding water) and open the seal at the outlet. (The seal at the bottom could be as simple (and cheap) as wrapped plastic sealed with duct tape.)

The siphon would then drain your pond down to the desired level. You just stop it by letting air in again at the top.

Hope that helps! Or came back with some more info, and we will try again.

Essie, The old steel pipe spillover is certainly rotting away but water continues to drain through it. I’m guessing it is a simple L shaped pipe considering where the pipe exits about 10’ below the water level on the downside of the levee. Yes, the duckweed is so thick it builds up around the inlet of the spillover restricting flow. There is a low spot further down the levee where water is draining over the levee and onwards towards a creek. Because the natural spring fills the pond rather quickly any chemicals are thinned and washed away. The siphon system is intriguing.

FishingRod, Yes, the duckweed is restricting flow and it isn’t being carried away with the spillover. I thought I would trench across the top of the levee and install a double wall culvert pipe of substantial size such the the duckweed could be carried away as an aid to chemical treatment. I do want to install a fountain to help with oxygenation too but that won’t happen soon as funds are diverted elsewhere. The link to the siphon system is helpful and I could recess it in the levee so not to impede the tractor or off-road toys.

Wizbang,

Having a spring that flows so much water that it goes over the "dam" is a good problem to have. There are many people on Pond Boss with very low ponds that are jealous of you right now!

Does your spillway pipe ALSO have to serve as the emergency outlet for big rain events? Or does your pond only have a small watershed that feeds surface runoff into it?

If you are NOT worried about flooding due to a big rain cutting out your levee, then adding a siphon to pull down your water level might be an easy and inexpensive solution. (As opposed to removing the old culvert and adding a much larger size.)

A siphon running in "full siphon mode" will expel more water than the same size pipe only flowing due to gravity feed. Would a 4" siphon be able to stay ahead of the flow from your spring and allow you to lower the water level? (It gets more difficult to work with and more expensive to move up in size on PVC pipe.)

If your spring flow varies during the year, then you may want to utilize the "automatic" siphon as shown in the previous diagram. If you get it set up correctly, then that should help prevent water from overfilling your pond and flowing over your levee.

Good luck on getting your pond fixed!

That's why you need to use a contact herbicide and not a systemic herbicide.