Book SectionsTable of Contents
The Problem Puddle Power Frog-Friendly Backyard Why are we concerned about amphibians?
Wetlands - function/type Wetland issues
How to help amphibians
Community Green Plans
Concrete, Fiberglass or Clay Ponds?Concrete and Fiberglass Ponds
We recommended that flexible pond liners be used as opposed to concrete and fiberglass. Concrete ponds are expensive requiring footings, reinforcements and several solid inches of concrete. Although concrete ponds should have a long lifespan, it is not uncommon to find cracking within a few years. Construction of a large concrete pond often presents technical problems best handled by professionals.
A fiberglass pond is expensive costing approximately three times that of a PVC flexible liner. When placing a fiberglass pond into the ground you must not use the original soil that was dug out to pack around the liner. Brick sand which is free of stone should be used because it has excellent drainage, and will not hold water like soil will. This will prevent water from becoming trapped below the fiberglass pond causing it to cork or come up out of the ground. Check the top of the pool with a spirit level at intervals so that when filling is complete the top is level in all directions. Several small fiberglass pools can be placed side by side around a central land area that is heavily planted to create one wetland. Remember to place rocks or logs in deep or steep sided pools so that toadlets and froglets can climb out.
If your soil particle size is small (sandy, silty soils) with a clay content of at least 10% then soil compaction is the easiest way of sealing the bottom of your pond. Alternatively, soils with a clay content of more than 20% can be imported for compaction. Alternatively, bentonite clay can be purchased.
Although clay lined ponds are the most natural looking, clay is not the best choice of impermeable barriers for backyard ponds. The clay itself is very heavy and can leak if not installed correctly. Bentonite clay is applied at the rate of 1 to 3 pounds per square foot, tilled in, and then rolled to compact the particles. Use a sprinkler to wet the bentonite before compacting. Bentonite swells when wet but if complete drying occurs bentonite shrinks and may compromise the seal. Add water immediately, otherwise the clay will dry out and crack. If you empty the pool it must not be allowed to dry out. A mixture of sand and earth is placed on top to protect the water-resistant clay liner from mechanical damage.
Geotextile clay liner is a product that sandwiches bentonite clay between two layers of felt. The felt is sewn so that the clay cannot move and collect anywhere along the width or length of the roll. Geotextile clay liners are generally used for large farm ponds, and are expensive.
Consult your bentonite supplier for alternative methods of application (including adding bags of clay directly to the pond to achieve a water barrier as the clay particles settle out on the pond bottom).
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