Just as a pretty addition to your property, or as a water storage facility, or as a home for waterfowl and fish, a small dam or oversized pond on your smallholding is sure to add value if it is constructed properly.

There are, however, some considerations which could make or break the idea.

Firstly, before building a dam, be sure you have access to sufficient water to keep it relatively full. Will it be used as a storage for rainwater, in which case the run-off will need to be channeled into it, or will it be fed by a borehole? Those, really, are your two options, even if your property is on the banks of a river, because tampering with the flow of a river or watercourse requires a permit and if you neglect to obtain one, and stick to its provisions, you will be fined.

Building a dam floor

If the ground you dig the hole in is not porous you may be able to get away with filling the dam and sealing any obvious fissures with a substance such as bentonite or one of the artificial leak sealers.

Bentonite is a mineral which, in powder form, expands many times on contact with water, sinks to the bottom (or sides if applied correctly) and remains there by hydrological action, effectively slowing or preventing the leaking of water into the soil.

In some cases bentonite is mixed with soil loosened from the banks of the dam before filling so that it expands and provides a uniform seal as the dam fills.

The same principle applies to artificial dam sealers.

The problem with both bentonite and the artificial sealers is that they might need regular re-application if new fissures and leaks are detected.

Dam liners

If you don’t intend to allow livestock to wade into the water, a flexible dam liner is an excellent option. These can be shaped exactly to the dimensions and contours of your proposed design and welded from PVC-coated fabric. Once the hole is prepared the lining is simply rolled out and smoothed, before filling takes place. Damage to the edge can be prevented by laying paving stones or rocks to make an attractive “shoreline” to your water feature.

There are a couple of considerations to laying a flexible liner. The first is that preparation of the hole must be immaculate. This means that the surface is absolutely smooth and free of any protrusions such as stones or tree roots.

The second is that the liner must lie in close contact with the surface, and not be pulled taut in any way. If this happens you can be sure that it will, in time split where there is added tension caused by the pulling. Another consideration for long life is that the dam should remain as full as possible, as ultra-violet rays from the run will degrade the liner.

building a dam
Using a dam liner. Image: Tata Ma Tarps & Linings.

The final solution to building a dam is also the most expensive, and that’s to build it with a mesh reinforcing layer contoured to the shape of the pond, covered with a strong concrete.

Keeping your dam clean

Finally, any expanse of open water will, in time, become stagnant, turn a sludgy green, and become toxic to any form of wildlife if the water is not aerated and passed through some form of filter. This is particularly true if the dam is to support the keeping of fish, whose waste needs to be removed.

In some form or another, therefore, a pump will be required to circulate the water through a filter. This need not be a mechanically-constructed device, but can be an attractive addition to the pond itself in the form of a plant-filled “rockery” at one end. This will aerate the water as it cascades over the rocks, and filter it, as it passes through the gravel and sand used to hold the plants.

The plants themselves provide the filtration, removing and using the nutrients contained in the water as it passes through.

This is part one of a series on Dams and Fish. To ensure you don’t miss out on future articles, click here to subscribe for free to receive our newsletter at the end of the series.

Part Two: Fish Farming Takes Many Forms

Part Three: Is A Trout Farm A Viable Option For You?

Part Four: Getting Started With Aquaponics

Part Five: Building An Affordable Round Dam

Main Image: Tata Ma Tarps & Linings

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