Dry weather can cause cracks in an earthen pond dam that can become serious leaks when heavy rain returns. Inspecting your pond dam during drought and addressing accessible cracks with granular bentonite before the pond refills can help keep a manageable maintenance problem from becoming a much more serious one.
If your pond is dropping during extreme summer heat, don't just watch the water level.
Walk your pond dam.
Long periods of hot, dry weather expose clay soils that may have been wet or underwater for months or even years. As that soil loses moisture, it shrinks. In clay-heavy soils especially, that shrinkage can produce cracks that range from small surface checks to openings several inches deep—or deeper than you can actually see.
Those pond dam cracks may not look particularly threatening while everything is dry. In fact, they're easy to walk right past.
The problem often doesn't reveal itself until the rain comes back.
The Problem Isn't Necessarily the Crack. It's What Happens When the Water Returns.
When sustained rainfall returns, a pond can refill surprisingly quickly. Water begins moving back across ground that may have spent weeks baking in summer heat, and eventually the rising pond reaches those cracks.
Water naturally seeks the easiest path available through soil. Cracks, voids, animal burrows, poorly compacted areas and old penetrations can provide those pathways through an earthen pond dam.
Penn State Extension specifically warns that when pond levels remain low during drought, exposed pond soils can dry and crack, resulting in leaks when the pond refills.
Learn more about leaking ponds from Penn State Extension
That's the part we worry about.
Once water begins moving through a weakness in an earthen dam, it can begin carrying fine soil particles with it. Over time, that process of internal erosion, or piping, can enlarge the pathway. A crack that didn't seem particularly impressive while the dam was dry can become something very different once it has water pressure behind it.
Oklahoma State University Extension warns that fast leakage or flowing water through or beneath a pond dam is a serious condition because internal erosion can progress toward dam failure.
Read Oklahoma State University Extension's guidance on leaking farm ponds
That's why we would much rather find a crack in August than discover a leak after several days of rain.
This Is Part of Fish Farming That Doesn't Usually Make the Pictures
People understandably associate fish farming with fish.
And obviously, we spend a tremendous amount of time working with fish. But keeping fish alive and growing also means maintaining the infrastructure that holds their water. That means ponds, dams, berms, spillways, pipes, drains, valves and a whole lot of dirt.
Walking our pond dams is simply part of what we do.
During periods of extreme heat and drought, we're paying particular attention to exposed soil. When pond levels drop, we're looking at areas that aren't normally visible and checking for cracking, erosion, animal activity, settlement and anything else that could eventually become a water-management problem.
The photographs in this article came from one of those inspections. There wasn't a catastrophe. The dam hadn't failed. We weren't responding to water pouring through it.
We were trying to make sure it never got that far.
That's an important distinction because pond maintenance is generally a lot cheaper and easier than pond repair.
We Use Bentonite All the Time Around Ponds
Bentonite isn't something we discovered because we wanted another product to put on a shelf. It's one of the basic materials we use ourselves every day.
Any time we're plumbing in and around ponds and outdoor tanks, working around water-retaining soil, sealing around appropriate penetrations or dealing with areas where we don't want water finding an easy path, bentonite is one of the tools available to us.
We also use it preventively.
When we're walking a dam, berm or other supporting earth around water and find accessible shrink cracks like the ones in these photographs, we don't like leaving an open pathway there and hoping everything closes back up when it rains. We work granular bentonite into the accessible voids while they're exposed. That's also representative of how we decide what pond products to carry at Newalla Fish Company.
We try to sell the things we actually use.
There are thousands of pond management products we could put on our website. That's not particularly interesting to us. We'd rather stock products that solve problems we encounter ourselves and that we understand from actually using them. Granular bentonite is one of those products.
Why Bentonite?
Bentonite is a naturally occurring, highly expansive clay.
When sodium bentonite becomes hydrated, it absorbs water and swells dramatically. In the right application, that expansion allows the clay to occupy pore spaces and voids that otherwise provide pathways for water.
USDA Natural Resources Conservation Service technical guidance discusses bentonite as a pond-sealing material and notes its substantial expansion when hydrated.
Read USDA-NRCS technical guidance on ponds and bentonite sealing
Penn State Extension similarly identifies bentonite as one method used to address pond leakage and explains that wet bentonite expands to fill cracks and pore spaces in soil.
Read Penn State Extension's explanation of bentonite for pond leaks
It's a relatively simple material. There isn't a complicated chemical reaction we're trying to create. We're taking advantage of the physical properties of an expansive clay to make it more difficult for water to travel through an unwanted pathway.
Why We Use Granular Bentonite for This Kind of Work
Bentonite comes in different forms, and the form matters. Powdered bentonite can be extremely useful when building or renovating a pond because it can be incorporated into soil and compacted as part of the pond bottom or dam construction.
Granular bentonite gives us another option. The granules are heavier and sink rather than immediately dispersing across the water surface. That's particularly useful when we're trying to put bentonite into a specific location instead of treating a broad area.
Oklahoma State University Extension makes this same distinction when discussing leaking ponds, noting that powdered bentonite is generally used when it can be incorporated into exposed soil, while granular bentonite is needed when applying the material through standing water.
Read OSU Extension's recommendations for bentonite and pond leaks
For the cracks shown here, however, we had an even better situation, with lack of rain, drought had exposed the problem and given us direct access to it.
A Small Crack Can Take a Surprising Amount of Bentonite
This is something photographs don't convey particularly well. You see a crack in the ground and think you're looking at the entire problem. Then you start pouring granular bentonite into it.
And pouring. ...and pouring more.
A crack that looks relatively insignificant from the surface can accept a surprising amount of material because you're only seeing the opening. The void may continue downward, branch underneath the surface or connect with shrinkage that isn't visible from above.
That's one of the reasons we don't simply scatter a little bentonite over the top and call it done. When we're dealing with an exposed crack, we want the granules down in the accessible void.
In the photographs accompanying this article, you can see exactly what that looks like. The white material isn't decorative marking or fertilizer. It's granular bentonite being put directly where we've found cracking.
We're trying to occupy that space before water does. This allows the bentonite granules to settle and expand as they absorb underground moisture, seeling offthe crack from becoming a future pond failure.
How to Inspect Your Own Pond Dam During Drought
Drought creates a rare maintenance opportunity for a pond owner.
As the pond recedes, or rain becomes more scarce, portions of the shoreline and upstream face of the dam that may normally be underwater become accessible. If you've owned the pond for years, you may literally be looking at soil you haven't seen since the pond was originally filled.
Take advantage of that opportunity. Walk the upstream or water-facing side of the dam. Walk the crown. Walk the downstream face. Inspect the spillway and look closely along both the current waterline and the old waterline.
You're looking for things that have changed:
- Open cracks in exposed clay
- Deep or widening cracks
- Animal burrows
- Holes or cavities
- Depressions or settlement
- Slumping or movement
- Eroded areas
- Damage around pipes or penetrations
- Unusual wet areas on the downstream face
Oklahoma State University Extension recommends routinely walking pond dams and inspecting them for these kinds of problems.
See OSU Extension's pond dam inspection and maintenance recommendations
One inspection isn't enough forever, either. Soil moves. Animals dig. Vegetation changes. Water levels change. A pond dam is infrastructure, and infrastructure needs inspection.
What We Did With the Cracks in These Photos
The process shown here was straightforward.
We walked the dam during a drought, identified accessible dry-weather shrink cracks and filled those voids with sinking granular sodium bentonite. We continued adding material where the crack would accept it rather than assuming the visible surface opening represented the entire void.
Before
Dry-weather shrink cracks exposed in the clay of an earthen pond dam after prolonged summer heat and falling water levels.
IMAGE: Cracks in earthen pond dam caused by drought and extreme summer heat
During Treatment
Granular sodium bentonite being worked directly into exposed cracks while the pond level is low.
Image text: Granular bentonite pond leak sealant filling cracks in an earthen pond dam
After
The accessible cracks and voids have been filled with granular bentonite before sustained rainfall and rising pond levels return.
Image: Pond dam cracks filled with granular bentonite before heavy rain
This is not particularly glamorous work, but neither is rebuilding a pond dam. We'll take the bentonite.
The Bentonite We Use Is the Bentonite We Sell
If you've followed Newalla Fish Company for very long, you've probably noticed that a lot of what we sell comes directly from problems we've had to solve ourselves.
That's intentional.
We're fish farmers first. We maintain ponds and water systems because that's part of keeping fish. When something earns a permanent place in our own shop, truck or pond-management routine, that's when it becomes interesting to us as a product.
Our Granular Bentonite Pond Leak Sealant comes in 50-lb bags and is a sinking granular bentonite intended for targeted applications around ponds. We use this product for the same reasons our customers do: water has an incredible ability to find places we'd rather it didn't go.
If you've got an exposed crack, known seep or another appropriate targeted application, granular bentonite gives you a relatively simple tool for dealing with it.
Shop Newalla Fish Company 50-lb Granular Bentonite Pond Leak Sealant
Sometimes the Right Answer Isn't Bentonite
Not every pond leak is a bentonite problem. And not every damaged dam should be repaired by a pond owner.
If a dam is experiencing significant structural movement, bentonite isn't going to magically turn it back into a sound dam. Likewise, if water is actively piping through an embankment, muddy water is emerging from the downstream face, a hole is enlarging, a substantial portion of the dam is slumping or something simply looks seriously wrong, we would not tell you to buy a pallet of bentonite and hope for the best.
That's beyond preventive maintenance.
USDA-NRCS provides engineering standards for pond construction and maintenance, and local NRCS offices can be an excellent starting point when a pond owner encounters a potentially significant structural problem.
Find your local USDA Service Center
We sell bentonite. That doesn't mean bentonite is always the answer. Knowing the difference is part of managing a pond responsibly.
Don't Waste a Drought
Nobody who owns a pond likes watching the water disappear during a drought. But low water gives you an opportunity.
You can see shoreline that normally isn't visible. You can inspect the upstream face of your dam. You can find animal burrows, erosion, cracks and other potential problems while they're exposed and accessible. So when the summer gets brutally hot and your pond starts dropping, don't just stand on the bank and look at the water.
Walk the bank like we do. It's part of our routine because we'd much rather spend an hour inspecting a dam and filling a few cracks than spend thousands dealing with a problem after the water returns. Mother Nature will eventually bring the rain back. The objective is to have the pond ready when she does.
Granular Bentonite for Pond Leaks and Dam Cracks
The granular bentonite shown in these photographs is the same type of product we use in our own pond work. We only sell product that we use - check out 50-lb bags of sinking granular bentonite pond leak sealant for targeted pond leaks, exposed cracks, pond edges, dams, leaks and spillway plumbing.
Order Granular Bentonite Pond Leak Sealant from Newalla Fish Company
Newalla Fish Company
The Experts in Pond Sportfish
