Pond Boss Forums INTRO Questions & Observations How to Stabilize Wet Sand in the Shoreline?

My lowest groundwater pond has finally gone dry. However, I was able to dig deeper into the sandy bottom with a shovel and reach the current level of the groundwater by getting down another 18".

I would like to deepen the pond bottom, so I once again have a small pond. Or more importantly, create a useable source of water (especially during normal conditions).

I believe this little 0.1 acre pond was built with a dragline in the '20s or '30s.

Two of the banks are very steep (greater than 45 degrees) because they were piling up topsoil and then clay-loam subsoil that was pretty sticky.

I dug a test pit with a mini-excavator a few years ago. The bottom of the pond consists of a layer of coarse sand. There is a creek just over the fence line past the bank of my pond that keeps the sand layer recharged with water.

When I was digging the test pit, the saturated sand was just flowing back into the hole I had just created with the bucket.

Does anyone have any suggestions on deepening this pond when I will essentially be digging a sand pit pond?

One idea was to lay down ground fabric and truck in some rock and try to build a stabilized bank that I gradually extended downwards whenever I was able to make a little extra depth.

Another idea, was to brute force it with a big excavator and just take out large amounts of sand until the banks reached some stable equilibrium.

Another idea was to build a crib by driving some steel pipes and working logs down to stop the sand flow. Then tack some ground fabric to the inside. Hopefully, water would come in through the seams between the logs but the fabric would screen the sand out.

My final idea was to try to bury some flexible, perforated 6" drain tile pipe and run that into a small sump with a pond liner. This is probably the best idea if I can figure out how to work the pipe down 2-4' through the sand.

Obviously, I am mostly giving up on this pond with the last two ideas. However, I think excavating a new 1/2-acre pond a few hundred feet away and sealing it with the clay at that location would give me a viable pond. I just need to use the little groundwater pond as the water source for the larger pond.

Anyone have any wiser suggestions for this type of problem?

No suggestions. Sand is porous and can run a long way in each direction.

The ONLY way to stabilize the sand banks is to make them no steeper than 3:1 slope. Any steeper than that and you will constantly be fighting a battle to keep the sand from sloughing off and falling into the pond.

Have not worked much with sand but pond inlet and spillway were a clay/silt mix that flowed easily when wet. I put down some inches of gravel, #2 stone, and mixed it in so that the gravel was the continuous phase in the top layer. Then put geo-textile on top of that and then gravel on top of that. Water still found a way to flow through this but the structure seems stable after a year. My guess is that deep sand would require coarse stone (#3?) mixed in a few inches, enough so that there is stone-to-stone contact. As you know, sand is dilatent but flows like water when diluted, so I don't think you want it to be rocks in sand soup, but rock on rock. Don't know how well just stabilizing the top layer will work in your case and this would be a lot of gravel. Sand is hard to keep in place. Empirical estimation of beach-face slope and its use for warning of berm erosion

Just a thought.

Thanks for the advice.

The sand that is below the water table will not even stabilize at a 3:1 slope. I may have to try Retired's advice and see if I can get some stabilization with fabric and stone.

The good news is that there is 100 years of muck and loess mixed in with the sand at the bottom of the pond. Every time the water level goes down, I get an explosion of terrestrial plants inside the pond boundaries. The deer have to do some work to make a trail to reach the usual water pools in the middle. I believe if I can get the sand semi-stabilized, then the plants will quickly come to my assistance.

Good news, the project worked and we once again have a pond with water despite the long-term drought.

I did forget the first rule of pond projects: You must design your project to match what the actual soil conditions give you!

I rented an excavator and started digging out the corner of the pond adjacent to the dry stream. Water started filling my hole once I got below the current groundwater level. However, I could not deepen the hole because the wet sand just kept flowing in. I tried cutting shallow banks, but they were very unstable.

I then conceded defeat and went back to my old test pit that was in the middle of the pond. I kept deepening and widening the hole, but I couldn't access the nice sand that held the groundwater aquifer. I was worried any newly constructed pond at this location would not be a viable water source since my "re-fill rate" would be too slow without a lot of connection to the aquifer.

Finally, the little light bulb went off over my head and I realized this soil distribution was a good thing!

The solid clay portion gave me the ability to excavate a stable hole that could act as a water storage sump for the new "down-sized" pond. I therefore dug out to a depth 8' below the old pond bottom. I then worked my way back over to the sand layer, which I eventually encountered about half way between my two test pits.

The new pond filled up in a few hours and I have 5' deep water in the clay sump and about 6" of water covering the sand bank and keeping it stable.

I have not run a pumping rate test yet. However, I should be able to take out significant amounts of water and then maybe rest a day to let the pond re-fill.