I was looking for any ideas, directions, recommendations or sympathy lol regarding silt washing into a 2 acre pond from a large rain. Location: I am in Northeast Georgia and we get 4-5 inch rain events about 2 or 3 times a year. The creek in question is a spring but drains about 25 acres of mature timber. This creek drainage is not flat as the terrain is somewhat hilly and accumulates a lot of rain despite there being a riparian buffer. During these big rain events the creek turns into a massive river.
The soil for the last 200 feet or so is fairly boggy. There is a pinch point between 2 tree. Beyond this pinch point the creek just seems to dump silt as the land flattens out and it is getting hard to define the ponds edge. I tried using t-posts and cedar logs to make a V funnel but the water just demolished it.
I am considering a steel culvert at the pinch point and use concrete blocks, poured mason for weight and secure them with T post. I am not sure what this accomplishes. There isn't a lot of "room" as the creek approaches the pond because of edges become steeper.
Any ideas for what I could do besides restoration by removing silt from the mouth to just reset the clock?
I'll express sympathy. Sorry that your pond is getting filled with silt!
Looking at your pics, it appears that the forest soil is probably a clay-silt. I believe that means you are going to have to undertake a fairly large endeavor to solve the problem. For any temporary obstruction that you create, the running water is going to erode a path through your soft soil and send the muddy rain water right back to your pond.
How large of a pipe or culvert would it take to convey all of the water in that creek due to a 4-5" rain? I think that will be the factor that controls your solution.
One solution is to build an actual dam for that creek that will NOT be overtopped during a big rain event. However, if you are building a dam, then you might as well build a pond. It would be nice to have an upper pond, but that tree-covered slope does not look like a great place to build a pond.
Another solution that might be relatively cheap, would be to rent a little excavator and create a bypass for the creek. It would go around your pond and deliver the water to the same place your current pond outlet delivers water. However, in your pictures, it appears you have a high bank around your pond. Excavating a long trench 3' deep is relatively easy, but doing one 10' deep is a whole different job, and the sides will cave during fast water flows.
Can you intercept the creek higher up the slope and build a diversion ditch around your pond? That might work if you have a good route.
If the maximum water flow is only the amount of two 6" pipes, then you could make a small diversion dam at a higher elevation for the creek and run two lengths of corrugated 6" drain pipe around your pond and deliver the storm water below your main dam. (However, I suspect your stream flow is larger than that.)
Do you want to clear some timber in your woods? If you created some clearings and uniformly graded the slope, then you might be able to establish a few bands of thick grass. That would not be a 100% solution, but you might be able to significantly reduced the silt load going into your pond.
Finally, I guess you could build a "clean out peninsula" in your pond and an underwater berm to contain the delta of silt that builds from your creek entry point. If you keep the silt in place, you could clean it out every few years with an excavator.
Sorry for not having any good solutions. Just throwing out some ideas so you can see if you can fashion a solution that fits the actual conditions that you can observe on the ground. Hopefully, someone else drops in with some better ideas.
Good luck on your project. A 2-acre pond in the woods is a beauty that you need to take good care of!
Unfortunately the only thing I can see that would help would be to cut down a bunch of trees, dig a deep silt catching pond that allows the velocity of water to slow down so the silt drops out of the water. Once there is some dwell time for the water in the silt pond to catch the silt, the water would then go to the main pond. You'd have to have access for heavy equipment to that smaller pond, and clean it out every year during the dry period.
I have a smaller 1.25 acre pond with 25+ acre watershed. I have a ditch that runs from above the pond down past the dam and a concrete weir/board gate to control how much water goes into the pond through a 12" conduit (oversized for me). Most of the water stays in the ditch but your could reverse this and have most of the water go into the culvert. It looks like the left side of the pond is steep and quite wooded. If the right side is less steep or less wooded, I would think that a conduit or pipe (as FishinRod describes) combined with a poured concrete structure could work. Some pictures might be found in this previous post.
Another thought, similar to the upstream settling pond would be to employ a series of settling check dams. The idea is that the check dams are spaced so that, when filled, each dam backs up water to just below the previous dam. This is shown by NY state in the figure. I have used these structures to control the flow in my main drainage ditch.
I used to have a stand pipe but converted it to a 6" siphon. The siphon is just a gravity drain until about a 4 or 5" rain puts it into full siphon mode. The shut off air valve that runs back into the pond is below full pool, therefore the siphon mode stays on until the pond comes down to this level. The siphon is capable of pulling down below this valve even during major events or soon after.
I think the creek in question is a bit more than half of the inflow during peak events.
I bet you could build a little dam with clay in your small creek. Build it higher on the slope in a sunny spot so you can grow grass on the dam face. Give it LOTS of freeboard and run a 6" pipe around your current pond.
If you have a little rock available, maybe make an emergency spillway around your new creek dam. That way, when you get a 6" rain you will get a little silt in your main pond and not have your creek dam get overtopped and blown out.
In hindsight, I think I am wrong. Also your pics suggest more water going down your little timber creek than a 6" pipe could convey.
While your 2-acre pond is surviving big rain events with a 6" outlet, it has a large storage area. For every foot the water level rises, your pond has accumulated 652,000 gallons of water. The main outlet then passes that water over several hours or days.
If you build a tiny dam on the hill slope, your new pond will have very little storage area for rising water.
I believe your trade-offs would then be building a higher dam with more freeboard and more storage space, or adding a second 6" outlet pipe for the tiny pond.
Your distances and local conditions will control your final solution.
(Hope that makes sense, you have a slightly complicated problem that I have not answered well.)
