Pond Boss Forums GENERAL QUESTIONS Help Silt Build Up

Common problem with all water impoundments, silt. Do not know how old my pond is but I now have cleared out most, if not all the black "pond muck" and am left with 6-10" of silt before I hit solid ground. This is the case from shore to middle of lake (tested with long pole).

Is there a way to remove/reduce this silt without draining the pond?

If I reduce the silt will it just turn the solid base into silt immediately or will it build up over time (as I expect).

Pond is 1/8th an acre and max 6' deep, so not huge. I was just hoping to have a section or two where I could wade out without sinking?

I am going to have to "generalize" since I am not at your pond site, but what I say will probably be mostly true.

Usually the "muck" in a pond is decaying organic matter, and the "silt" in a pond is from particles that were transported into the pond by moving water, or even sometimes the air.

Both muck and silt can rob your pond of valuable depth.

Excellent job clearing out your muck. That is a good start!

Do you have a groundwater pond or a pond filled by surface run off?

If a run off pond, then most of your silt probably came in during heavy rain events. The most cost-effective solution for that problem is prevention. Do you have good ground cover throughout the watershed that drains into your pond? If not, improve it where you can.

Is there a plowed agricultural field that drains into your pond when rains hit that bare ground? If so, you could install a silt fence (ugly, but cheap) to slow the surface flows so the silt will drop out of the water flow and be stabilized in place by your groundcover. If that is too ugly, then perhaps you could put in a low berm that exactly follows a contour line on your property to achieve the same goal.

There is even a chance that much of your silt came in when the pond was initially constructed. There are a few horror stories on Pond Boss where someone finished their pond and immediately had a frog-strangler rain that eroded the banks and filled in 1-2 feet of silt on a single day.

Moving from prevention to cure, you can probably improve your pond by removing some or all of the existing silt. The hard-packed or solid base at the BOTTOM of the pond should not turn into soft silt as a result of your operations. However, there are two problems to be aware of. There is a chance that the solid base is a compacted clay liner to seal your pond. If you punch through that layer, or even just thin it enough, then your pond might start leaking. You can run equipment over that layer and even scrape and remove silt, but be very careful!

The second problem is the SIDES of your pond. For piled, loose materials there is a concept called "angle of repose". You have observed it when you see sand piles at construction sites, etc. When you start removing material from the base of the pile, the top of the pile will eventually have to collapse to re-establish a stable angle of repose.

I am mentioning this because as you remove silt, it may affect your submerged banks in the pond. If your sides are loose silt over a solid packed base, then you should be just fine clearing the silt. If you have loose silt over barely compacted silt, then you may have some slumps around your pond edges after your project due to wave action loosening up your newly exposed "base". If that is the case, then your best solutions are keep the pond full as much as possible, and plant some beneficial submerged plants at your pond edges to stabilize the slope.

Finally, everything I said above may not be applicable, if you have a groundwater pond that feeds through a layer of unconsolidated (loose) sand and gravel. I tried to deepen one of my groundwater ponds two summers ago during the drought. After I got through the muck, I discovered a sand layer that was two feet thick. I kept stepping back the excavator from that exposed layer and tried to deepen the pond. Instead, the water-saturated sand just flowed right into any hole I excavated. I finally had to move back about 40 feet to where there was a big, natural clay plug. I excavated out the center portion of that plug about 8' deep and was able to make steep sides. The reason for that story is that if you have a groundwater pond, you may be able to deepen your pond in some areas and not be able to remove silt in other areas.

The above was all theoretical, now to the more practical. Can you easily drain your pond, and then soon have enough water that it re-fills? If so, that is the best situation for removing silt. Do you own (or rent) equipment for that task? With very little practice, you can scrape exactly the depth you want with a mini-excavator or back hoe.

If none of that is feasible, then you might even be able to try a "poor boy" solution. If you laid out a strip of landscape fabric and hand-placed concrete pavers on that, you might be able to easily create some wading sections where you desire. I would just purchase the cheapest pavers you can find, since you will never see them. I would go with the largest size possible that you can easily manipulate by hand. If 16x24 pavers give you panic when your head goes underwater on the deeper portions, then definitely go to a smaller size.

Good luck on your pond project! If you list the goals for your pond, you can probably get some additional advice on ways to achieve those goals.