How to keep sandy soil from caving in to pond

[joesandy1822]

We finished digging our pond today (for the most part). I'm hoping to get the liner in tomorrow, as it will be delivered in the afternoon and we're looking at more rain tomorrow night. I've lost a lot of time lately because every time we get heavy rains, which has been a lot lately, the sandy soil was caving back into the hole. Our soil is VERY sandy.

I have a huge concern now. The top edge of the pond (where you would walk) is especially sandy and crumbly no matter how much I tamp it down. This is, in part, because we had an above ground pool there until about a week ago, and when they removed the pool, there was sand underneath. When we dug and tossed the soil, the top edge ended up being even more sandy than normal.

My question is how to prevent the edge from caving in when we walk on it. We made the typical first ledge about 8-10" deep to put the rocks on to secure the liner. Those rocks won't be walked on. The top edge, however, I would like to be able to walk on. I hope I'm describing this right. I will attach a simple drawing that will hopefully help. Maybe all the rocks on the first "rock ledge" will be enough support? I'm not sure yet what we will edge the very top with. Maybe flagstone would be a good choice to add stability, and we could use the rounder "boulders" on the rock ledge.

Any suggestions would be appreciated. Thanks!

Sandy

 

[capewind]

We have the same issue here, we live on a sandbar ... you have two choices ... either line your walls with concrete block or pour support walls, or work WITH the weather. Until your pond is full, the liner is COMPLETELY secure (including your top rocks), you will keep fighting this issue. We own a landscape company (term used loosely ... we do many aspects of the trade) and since ponds are a personal hobby, do pond installs as well. We've been getting slammed with rain, hubby is well behind schedule (over booked) and had no choice but to "take on the weather" to get a pond in. Like you, he had the hole ready, but then stayed late one night to get the liner in, and partially filled .. then hoped for the best ... it rained ... only a small area of shelf collapsed, which meant draining the pond, pulling the liner back, sneak a big sheet of cardboard in, and rebuilt the wall/shelf (then remove the cardboard and get the liner back in place) ... it's a headache you want to avoid if you can. My best advice is to NOT put the liner in tomorrow, let it rain, and as soon as you have 3-5 days of GOOD weather, clean up any cave ins, and get that liner in, and well secured ASAP. The walking area you are concerned about will be fine once everything is done, and you can put grass, mulch or pavers on that area.

 

[gardengimp]

The walking area you are concerned about will be fine once everything is done, and you can put grass, mulch or pavers on that area.

CW is right about the building part, at least so far as my humble experience digging a single pond in sugar sand.

However, so far as after the pond is in, and walking along the sides? It depends on your soil type. I've seen pictures of your sand Cape, and it sure looks like it has a lot of clay content in it. Our sand is sugar sand, the super fine stuff like you imagine on a nice sandy beach. There is zero clay content to our sand. It will not hold up to traffic. The solution for sugar sand is to build the side walls with concrete block. How many rows of concrete block I expect depends on how disturbed your sand is. The more clay content in the sand, the more stable it will be. Sand and loam are both wiggly around and collapse kind of stuff. Not good building material.

Here is a portal to the online soil survey database. Its interesting looking up your soil types, and reading up on just how rich or poor your soil is!

 

[capewind]

I wish we had a good amount of clay mixed it. We have "pockets" where the "dirt" has a good mix, but most of the area is "beach sand" (no place here is more than a mile from the ocean or an inlet, as the crow flies) .. some areas are all beach sand (closer to ocean), and others are more of a sandy loam mix (closer to an inlet) ... we DO have good top soil though I will however say that our beach sand (literally at the beach) is not the powdery soft sand of the tropics. The floor of our basement sits TWO feet above sea level, although the town average (at street level) is 24 feet above sea level.