Existing seasonal pond, want to hold water in summer. Problem solving :)

Hi all, I have an existing pond site on my property that fills seasonally and flows out through a culvert into a perimeter drain (i.e., it never overfills and is very full and mobile in winter) but dries out totally in summer. I'm not sure if the img tag is working but the picture is here: https://imgur.com/a/MfkRHDb

I am trying to find a method to retain water in summer and am working with a friend to come up with some solutions. A EPDM liner is out of budget and also not viable for a few reasons.

Last week, my friend came out with his machine and scraped all the mud from the bottom to expose the clay layer at the very bottom (which holds water) but the layers of aggregate material on the other (gently sloped side) and higher up in the wall are very sandy and likely the reason all the water dries up in summer.

From the picture, you can see that the sides are VERY steep at the back. It's a vertical drop on the back side and a gradual slop on the access side. It is approximately 15 feet deep on the steep side.

On the steep side, water seeps in all year round. Since my friend came and scraped, it's been refilling very slowly from the sides (where the dark patch is on the right hand side of the back wall in the picture) and it's accumulated about 5 inches of water at the bottom in a few days (he dug on Sunday and it was dry).

In the winter, water runs heavily into the pond from the rest of my property through a series of ditches. When it rains in a month or two it will fill quickly and stay full.

Reducing the slope on the steep side is not viable because of the big cedar trees as well as just the general cost and amount of work required.

We are considering digging the bowl out further to the clay layer to catch more of that seep water and then seeing about getting a truck load of blue clay from nearby excavation projects and using it to line the access (not so steep) side and reducing the grade as far as possible around the front 2/3 (just not touching the vertical back side where the water is seeping in).

Legend for the picture: the white line shows the current shape of the base, the orange line is where we'd smooth out the grade and deepen the base. The whole orange area would be lined with clay as well as similarly along the access slope. We'd leave the water seepage wall alone. The blue circle is where water is currently pooling after a few days.

Thoughts? Ideas? Many thanks for any ideas.

That layer of sand and aggregate will always allow water to seep away.
Lining of the dam site, with clay or a plastic dam liner covered with soil is probably the only way to hold water

Suggest looking up gleying a pond here and also google.  Might help.

Second part is if you added a floating island can you shelter it from sun and wind?

John C Daley wrote:Rhat layer of sand and aggregate will always allow water to seep away.
Lining of the dam site, with clay or a plastic dam liner covered with soil is probably the only way to hold water

Yes that’s what I’m assuming as well. We are going to try to increase the bowl size and depth where it’s holding and line the sides with clay and hope it fills up to the sand layer which would be plenty for my needs.

We just need to correct the slope as much as possible for the clay to adhere. I’m assuming clay won’t stay on a slope that steep. The plastic liner is a no go because there’s trees all along the top and I’m also worried that with the amount of water seeping IN right now and the in flowing ditch, I will end up with water behind and under the liner which would be a disaster.

Clay is the way to go. If it can be sourced locally, so much the better.  I also remember reading about how small dams were created on limestone in the UK in prehistoric times, by scooping out the shape and then spreading straw and leaving it to rot.
https://ruralhistoria.com/2024/05/16/capturing-the-clouds-the-history-of-britains-ancient-dew-ponds/
this is the best reference I could find, but I'm sure there are more.

Can you give us some details of size, slope angle etc
Bentonite is a particular type of clay, sold in bags which can be purchased and used to seal the ground, rather than digging around for a suitable material.

In the part of Texas I live in folks use a timer on their water well to keep their ponds filled with water,

I do not feel that this is sustainable so my pond is empty.

We went with bentonite and that did not work.

Some folks say gleying a pond with pigs works though my soil is so rocky that I don't feel that would work here.

I hope is that you will find a solution ...

C. Letellier wrote:Suggest looking up gleying a pond here and also google.  Might help.

Second part is if you added a floating island can you shelter it from sun and wind?

I have done a lot of research via google already - had ducks on it for a decade for gleying purposes and the bottom is very well sealed. My question is about the steep vertical sides and the shape of the bowl at the bottom. How would gleying be possible on a side that steep? I'm not sure I follow.

Why would I add a floating island? What is the purpose?

John C Daley wrote:Can you give us some details of size, slope angle etc
Bentonite is a particular type of clay, sold in bags which can be purchased and used to seal the ground, rather than digging around for a suitable material.

It's about 30 feet by 30 feet, 15 feet deep at the deepest point and only 6-7 feet deep at the shallow access end. The angle of the back wall is basically vertical while the slope around the other 2/3s varies from about 45 degrees to 30 degrees or so. Our plan is to correct the slope on the 2/3 to about 20-30 degrees (to make it flat enough to hold the clay) and leave the vertical side but dig out the bottom below the natural clay line so there's more of a holding space for the water. Where the blue circle is in the photo is refilling and I'd like to expand that area to the left at the same depth where the base clay will hold it from the bottom. Then clay up the 20-30 degree slopes as well.

I've been trying to source dried bentonite around here but haven't had much luck. The blue clay we have around here is frequently used for pond bases and nearly free if you get lucky with a trucking company needing to get rid of some big loads. So I'm going to try that first and if no luck, will try harder to get some bentonite for next year.

I would try and get a more accurate picture of the sediment/soil profile before investing in a laborious or costly solution. That would probably mean digging one or two deep test pits or cuts with a machine so that you can look at undisturbed soil layering down several feet or until you reach clay or bedrock. In and immediately around the pond itself was likely heavily disturbed during original excavation, so do your investigating a little ways away from there. The clay layer may be shallower than you think, and something you could bed into with another cheap barrier material if clay isn't available. But you might also explore the thickness and consistency of clay layer and find out if there's plenty of it that moving some from the bottom to the sides won't compromise water holding there.

Anne Miller wrote:In the part of Texas I live in folks use a timer on their water well to keep their ponds filled with water,

I do not feel that this is sustainable so my pond is empty.

We went with bentonite and that did not work.

Some folks say gleying a pond with pigs works though my soil is so rocky that I don't feel that would work here.

I hope is that you will find a solution ...

Thanks very much. I actually had pigs in there a few years ago and you're exactly right, the big potato sized rocks prevented any meaningful sealing as well as the sandiness of the soil (it's essentially sandstone that hasn't finished hardening. you can bust it up with a shovel and a hoe but it's undiggable otherwise).

What happened when you tried bentonite?

Ben Brownell wrote:I would try and get a more accurate picture of the sediment/soil profile before investing in a laborious or costly solution. That would probably mean digging one or two deep test pits or cuts with a machine so that you can look at undisturbed soil layering down several feet or until you reach clay or bedrock. In and immediately around the pond itself was likely heavily disturbed during original excavation, so do your investigating a little ways away from there. The clay layer may be shallower than you think, and something you could bed into with another cheap barrier material if clay isn't available. But you might also explore the thickness and consistency of clay layer and find out if there's plenty of it that moving some from the bottom to the sides won't compromise water holding there.

We are at the clay layer with the digging we did last week. If you look at the picture, you can see where the grey/blue line is in the base of the pond. We are planning to expand that bowl in the clay layer and then use additional clay to try to firm up the sandy banks after correcting the slope.

You're right that it's possible there's enough down there to do the sides. I'll know more next week when we keep digging.

ETA, just heard from a local gravel yard that they'll send me a truck of blue clay for the cost of the trucking which is great news.

Jill Dyer wrote:Clay is the way to go. If it can be sourced locally, so much the better.  I also remember reading about how small dams were created on limestone in the UK in prehistoric times, by scooping out the shape and then spreading straw and leaving it to rot.
https://ruralhistoria.com/2024/05/16/capturing-the-clouds-the-history-of-britains-ancient-dew-ponds/
this is the best reference I could find, but I'm sure there are more.

This was a fascinating read, thank you for sharing!

James Freska wrote:We are at the clay layer with the digging we did last week. If you look at the picture, you can see where the grey/blue line is in the base of the pond. We are planning to expand that bowl in the clay layer and then use additional clay to try to firm up the sandy banks after correcting the slope.

The clay layer likely begins higher up, where water is seeping in (due to running downhill across the top of said clay, below porous layer). The question is where that porous/clay boundary is along the lower, shallow slope, and how you can most readily create a retention barrier from that point upward to desired grade or overflow lip. Moving clay up from the bottom into a ~foot thick layer across that lower slope down a little past the boundary point might work well.

Ben Brownell wrote:

James Freska wrote:We are at the clay layer with the digging we did last week. If you look at the picture, you can see where the grey/blue line is in the base of the pond. We are planning to expand that bowl in the clay layer and then use additional clay to try to firm up the sandy banks after correcting the slope.

The clay layer likely begins higher up, where water is seeping in (due to running downhill across the top of said clay, below porous layer). The question is where that porous/clay boundary is along the lower, shallow slope, and how you can most readily create a retention barrier from that point upward to desired grade or overflow lip. Moving clay up from the bottom into a ~foot thick layer across that lower slope down a little past the boundary point might work well.

Thank you, yes, this seems like it might work. I just found out I'll be able to easily and cheaply get a truckload or two of clay from nearby excavation sites so we should have lots to work with. We will dig down and expose the base clay and work up from there on the shallow end and create a barrier like you're suggesting.

Would you recommend mixing the clay with the existing soil for the top layer? Like for instance, say we build it up a foot or so for the barrier of pure clay and then lay a mixture of the sandy soil and clay over top to provide some traction?

Folks where I live use pond liners to keep water in their ponds as well as what I mentioned about using a timer to keep the pond filled.

Anne Miller wrote:Folks where I live use pond liners to keep water in their ponds as well as what I mentioned about using a timer to keep the pond filled.

Thanks, an artificial liner is not viable here due to cost and the steep slopes with water running/seeping as well as mature cedar trees at the top of it.

I could not justify using water from my well to keep the pond full, we have enough water for what we need but not a lot of excess and this is a bit of a luxury exercise and if it doesn't work, I will be fine to live without

James Freska wrote:I could not justify using water from my well to keep the pond full

My sentiments exactly, that is why my pond is empty.