Pond engineering: A few more questions

I've just had two excavators out to get estimates on repairing my 1-acre pond. Their suggestions differed on several key points.

1) One suggested a single L-shaped pipe of 18-in diameter, with a valve. This is the traditional "down-and-through-the dam" shape, and what I have in there now.

The other suggested multiple culverts running straight through. For instance, a pair of 15-inchers. His opinion was that multi-15s would handle more flow than a single 18, that a valve is never used, and that the L-shape provides no advantages.

2) Both galvanized and PVC materials are available in either configuration. Both seemed to prefer galvanized for its strength (harder to crush), although PVC would last longer (resist metal eroding/rusting). One mentioned that the deeper "grooving" which adds strength to the PVC creates more places for dirt, etc to get caught.

3) The job will involve draining the pond / cutting through the dam, letting the bed dry, dredging out the silt (I am hoping to restore it to its original depth of 30 years ago), the reconstructing the earthen dam with new drainage pipes in place.

One contractor indicated he can do this during the winter (Northern Virginia here), and that the bed will dry / freeze enough in a few weeks for work to proceed. The other indicated that it will be a spring / summer project?

4) I don't have the estimates yet, but one guy seemed to think that removing 4 ft of silt covering an acre would be a month's work, which would be prohibutive. Does this sound within the realm of reason?

Your problems/proposed repairs aren't quite clear to me from your post - maybe more info? Or maybe I'm just being a bit dull at my end...

One thing springs quickly to mind however. Locally there is a small farm with a pond about your size. Like you they have seen the pond silt in over the last few decades, and were interested in renovating the pond. Upon investigating the issue they discovered that simply getting the required permit to DRAIN the pond is virtually impossible. Apparently once a pond has become established the areas arond it are considered wetlands, and as such fall under the authority of the federal government. In addition, a survey and approval by the Army Corps of Engineers is required before any attempt is made to drain the pond. There were other issues as well, which I don't quite remember, but none of it was good.

I would be sure to check carefully before you proceed - you might find yourself in hot water right quick.


Gregg

DaRube,
I think this link has been posted before, but I would suggest that you go here http://www.pondboss.com/ and ask your question. From the home page, click on Ask the Boss and it will take you to the discussion forum. I think you'll discover a lot of valuable information there.

Cross section of the drain pipes places two 15 inch pipes way ahead of a single 18. Do you need a valve? Why?

You need an overflow drainage path in case for whatever reason the drains don't and the water would flow over the dam. NEVER let water flow over an earthen dam! The overflow path needs to be wide and relatively flat to discourage erosion should it ever be used.

There are alternatives that son't require draining the pond to remove silt. These include suction dredging which could require DIY equip and labor, rental equip and DIY labor, or a pro job.

Then comes the queston of what to do with the sucked out mud. I have considered ditches and terraces with straw to filter the removed water. In this approach you filter the water through straw and let the water run back into the pond. Another method does similar but deposits the mud on the backside of the dam. Hauling really thin mud away is NOT MY FIRST CHOICE.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

Thanks for the replies, guys!! [img]/forums/images/icons/smile.gif[/img]

Autotech, I think I'm going to be OK with the regulatory folks. I've had a guy from the county extension service and another from the NRCS out here, and I asked the second guy explicitly if I had any wedlands concerns. Both were OK with me proceeding with the work. But it sure was good to have that reassurance.

CowboyDoc, thanks for the pointer to PondBoss. I think someone actually mentioned it to me in my prior post, but I neglected to check back there before I posted this one. Some days I'm more "efficient" than others. [img]/forums/images/icons/blush.gif[/img] [img]/forums/images/icons/tongue.gif[/img] PondBoss has a great specialist forum. I've posted a few there, and I'm happy to report back.

Interestingly, at PondBoss they were talking about an entirely different design for drainage which has really captured my interest ... namely the self syphoning drainage system. If I can resolve my few remaining questions regarding freeze management and "sizing", it may very well be the way I go.

And, Pat, thanks for pointing out the cross-section as the operative factor for capacity. Even if I go with the syphon method for the pond drainage, there is another conduit project I'm gonna need worked where the same principle applies.

Alas, my pond is so silted in and shallow that sunction drainage would not be an option ... except for the deepest parts. I'm mulling whether a combined approach (with suction dredging in the deep areas prior to bursting the dam, and traditional dredging the shallows afterwards) might speed up the project and/or be cost effective. One thing is for sure ... no matter what approach I take, "mud management" is gonna be a BIG job. [img]/forums/images/icons/crazy.gif[/img]