Ideally, where your earthen pond is located should be a swampy area such that you don’t dig too deeply before reaching water source. Earthen pond is not supposed to be deeper than 4feet.
The deeper the pond is, the more difficult it is to manage the pond, for example: if it is deeper than 4feet before you can get sufficient water, the pond is not likely to supply enough water for your fish farm.
Therefore how deep you will dig before getting water must be known before deciding on the fish farming site.
This involves digging the soil usually clay (25 %clay) to a depth ranging from 0.5- 1.0 m at shallow end and 1.5- 2.0 m at the drain end to raise fish. Pond can be of any shape as long as it is well constructed. However rectangular or square shapes are considered the best.
This is usually practicable in swamping environment. This rule away the problem of water maintenance as there is natural flow in and out of water in the pond.
Construction of Earthen Bottom Ponds
Earthen bottom ponds have several advantages. They are relatively simple to build, inexpensive per unit of surface area, and if well constructed, of low maintenance and usually long lasting.
However, there are many drawbacks to these ponds that make them a less advisable choice. Earthen bottom ponds require a great deal of land as small earthen ponds do not maintain themselves well.
Small natural ponds never clear properly due to the slow but invariable dissolution of soil into the water and the difficulty of underwater shelf construction with clay soils. In addition, any of the natural occurrences such as moles and insects digging into the pond will have a greater effect on smaller ponds.
Most plants in earthen ponds are planted directly into the soil, as plant roots often creep over the edge of pots and escape. Once out of the pot, most aquatic plants become very aggressive with their spread being checked only by water depth.
For these reasons, earthen bottom ponds, especially small ones, are not recommended.
If the decision is made to build an earthen pond, the soil must have a relatively high clay content which makes the soil more difficult to work. Due to the required size and land needed, they are more expensive per pond.
Plants in them are prone to grow more vegetatively and flower less. Plants, fish, and other wildlife are harder to maintain. Unwanted guests to the pond will be more common and much harder to control.
The water may often be muddy in appearance. If fish are included in the pond, they will keep the water muddied as they forage on the bottom.
The basic construction of earthen bottom ponds starts with size and shape designs. Once these factors are determined, remove the soil plus 6 inches for relining.
Bring back onto the site enough of the heaviest (highest clay content) soil that you have and line the bottom and sides with a 6 inch layer.
This soil must be wetted as it is returned and rolled until all of the structure is broken down and the soil becomes slick. This is called “puddling” the soil and creates a layer almost impervious to water. Then wait for enough rain to fill the pond before planting.
Steps involve in earthen pond construction
The following steps are required:
• Clearing of proposed site
• Setting‐out which involves pegging and lining with the rope
• Mark‐out the areas inlet and outlet
• Topsoil removal and storage
• Construction of embankment
• Construction of inlet drainage pipes/ water control structures
• Construction of screen at both inlet and outlet.
(i) Excavated Pond
An excavated pond is often built on level terrain and its depth is achieved solely by excavation. An excavated pond is relatively safe from flood damage, is low maintenance and can be built to expose a minimum water surface area in relation to volume.
This is beneficial in areas of high evaporation losses and a limited amount of water supply. Ponds should have gentle slopes on dikes as depicted in the Figure below
(ii) Embankment Pond
This type of pond is built by creating an embankment or dam used to impound water and is usually constructed in a valley or on gently sloping land. It is not recommended to build an embankment pond on greater than a 4% slope. Less excavation may be needed to build this type of pond.