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4 Fish Pond Construction
IMPORTANT:
Stress that the "right" way in any situation is the way which:
* the owner can afford
* the owner can manage easily
* fits the owner's needs most completely
Construction should begin only after careful planning such as that outlined in the preceding sections on "Planning."

A fish pond has three main parts: the walls, the water inlet, and thedrainage system. Walls are also called dams, dikes, levees, or bunds. This manual uses "walls." Whatever they are called, walls hold the water in the pond. They can be built using soil taken from inside the pond, or they can be built with soil taken from another place. They must be strong enough to withstand the pressure of all the water inside the pond: water constantly pushes against the walls. Theymust also be water-tight (impermeable), so the pond does not leak.
The water inlet, located above the pond water level, is used to let water into the pond and is closed off after the pond is filled.
The drainage system is used to empty the water from the pond when the farmer is ready to harvest the fish.
There are many ways of making inlet and drainage systems: the most important criterionis that they work. But the walls are especially important: they are all that keep the fish inside the pond. The walls must be built carefully.
Pond construction follows the same principles whether the pond is a single backyard pond or part of a large fish hatchery. These are the steps in pond construction:
* Survey the land
* Mark out the area of the pond
* Measure and mark out the walls* Excavate the pond bottom, if necessary
* Build the drainage system
* Build the water inlet
* Build the walls
* Seal the pond bottom and walls
Each of these steps will be discussed in detail in the following pages.
Mark out the Pond Site
Measure, the Walls
Now that the slope is known, the place of the main wall is known. The main wall is at the end of the pond which will bedeepest, and is the wall where the drainage system will go.
Mark out the main wall, and any other walls that will be built, with stakes. The walls, when finished, will be wide: it does not matter so much where the stakes are placed within the width of the planned walls, for they are to be used as height markers.

The farmer has to plan the depth of his pond and the height of his wall. If the pondis going to be 2m deep at the deepest end, for example, the walls should always be at least 30cm higher than the water level for a small pond, and at least 50cm higher for a large pond. Also, the walls will settle after they are finished, so it is best to make the wall 10% higher than the desired final height of the wall. A 2m deep pond, therefore, would have walls with a total height at thedeepest point of 2.5 or 2.6m [height of wall before it settles = depth of pond + 30cm (for small pond) or 50cm (for large pond) + 10% of depth and 30 or 50cm].
Tie strings to the stakes along the main wall line, at a height of 2.5 or 2.6m for a pond whose deepest end will be 2m. Use a levelling device to connect strings to the stakes marking the other walls, if the pond has other walls, at the samelevel as the string marking the height of the main wall. The strings are the building markers. When the walls reach the strings, they are the right height.
Dig the Pond Bottom
As stated before, the pond bottom must slope downward from the shallow end to the deep end to help drainage. The pond bottom usually has a slope of from 2 to 5%. (A slope of 2% would mean that for every 100cm change inlength there is a 2cm change in height.)

The pond bottom must be clear of rocks, roots, trees, and stumps so that later, when a net is used to harvest the fish, the net will not get caught and tear. If the pond bottom is already smooth and slopes well, it can be left alone. Or, if the pond bottom only has grass on it, the grass does not need to be removed before the pond is filled. In fact, once...