Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? Need to Improve Pond Overflow

The overflow on my 2 acre pond needs improvement. I have owned the property since 2012 and it has overwhelmed the single 4” corrugated overflow pipe and flooded the back yard for the third time. I’m sure they didn’t plan for the back yard to be the emergency overflow but that’s what nature dictates. It does no harm except for a little erosion down the driveway and it makes a mess. Due to location I think my options are limited to adding another pipe(s) in the same location with outflow to the same ditch. I’m thinking a 6” corrugated pipe or perhaps multiple pipes in the same trench running to the same ditch. By running at an angle across the front yard I’ll get another 12-18” in grade, allowing me to place the pipe lower on the pond bank where it will pick up water sooner than the existing 4” pipe does. I’ll shoot that grade on my next trip down. Please take a look at the attached pix and tell me what you think of this plan and if you see a better plan.

I'm not an expert by any means but, based on the picture I would think that a 4" and 6" pipe would still be a bit undersized. Any way to go bigger? 10 or 12"? I have a single 6" on my 2 acre pond and it does not keep up well at all. If I add another or bigger pipe it would be at least 12"

Also is there an inlet pipe on the pond or where does the water flow in from? Depending on this it may be more practical to reduce the amount of water coming in.

I do some excavating and small pond building, in your situation I would consult an engineer to run a few numbers and find out what size overflow pipe you need, there are a bunch of variables such as how big an acreage are you collecting in your pond,
A 4" corrugated drain tile is not big enough to drain anything, and is more then likely crushed to half capacity or less at anyplace along its length, just from stepping on it wrong.

Let me ask this...

Does the water over flow the dam when this happens (or elsewhere for that matter)? OR jsut back up?

I ask ,becuase, if it does flow out you can get an idea of the amount of water flow you would need to accomodate. This is a bare rule of thumb for laymen estimates only. The actual watershed estimates should be made so that an expert can reccomend the proper size taking into consideration the run off, legth of drain pipe, and slope.

For example, my pond has over taken the emergency overflow a time or two prior to it's renovation. It had an 18 or 20 inch diameter pipe and too much watershed. I witnessed the over flow once and the span of water was 20 feet wide and about 4 inches deep. That's over 6 square feet of cross sectional water (plus the flooded existing pipe. That would have translated to an additional 36" diameter overflow pipe at a minimum to of handled that event.

I say "at a minimum" because the slope of the pipe and the length play a role in the pipe size as well. The more flat the slope and the longer it is means you need a larger diameter pipe.

It looks like you have a long way to go to the ditch and pretty flat ground. If your pond is merely backing up and not overflowing the dam, an expert should be consulted to evaluate what I mentioned earlier.

Thanx for the responses. This is a ground water pond so the only inflow is from the watershed. I have never calculated the watershed, I'll do that. There is no dam per se, just a big clay lined bowl; The 4" overflow was added as an afterthought. My initial thought was to use a trencher that cuts 5 1/2" wide trench and finesse the 6" pipe into place. For a little more money I can rent a mini excavator with a 25" wide bucket and lay a larger pipe or 2 or 3 6" pipes side by side. the distance on the existing pipe is about 225' and the proposed route is 250'.

It looks like you have a well manicured, rather flat, piece of ground. Any chance you would consider excavating a low path from the pond to the road ditch to act as an actual emergency overflow? No pipes needed and if you make it wide enough it would carry a lot of water.

Just a thought as a mildly sloped swell would not be much of an issue regarding erosion so long as it's got grass growing in it.

I'm with Quarter Acre on this. Simple, High capacity. You can make it as wide as you need. Be sure to get some bermuda grass turf growing on it asap.

Consider a siphon

A swale to the ditch would make the most sense to me. That being said, I would investigate the ability of the ditch to flow and handle the overflow before any ground sculpting. Is there a possibility the ditch won’t have the capacity to hold overflow and normal ditch flow when high volume rain events occur?

Based on your description, you have a watershed pond, rather than a ground-water pond. Installing the recommended drains will likely be the cheapest alternative long-term. Most critical is a well designed emergency spillway that is wide enough to handle heavy rain events that might occur every 2-5 years. The slope of the emergency spillway should be as shallow as possible, and along with the the right width, should keep the water velocity low enough to prevent the soil from washing out. It should be planted in grass ASAP after construction, and should be constructed in virgin soil, not fill. The primary drain should handle most rain events and should be designed based on your watershed area and local rainfall history (like the emergency spillway). Both the size of the pipe, its length, and drop effect its capacity to carry water, along with the free-board of the dam before the emergency spillway kicks in. This all can be complicated, but your local NRCS or DNR may be able to help. For me, I still go bigger to be safe. Good luck!

I'm moving the emergency spillway on our hatchery pond to a flatter area as we speak. Narrow emergency spillways increase water velocity and depth, and that's a bad thing because of erosion. My experience has also been that there is far less fish loss during heavy rain events when the overflow is widened.