Earthen pond - meaning and illustration

Many people prefer to begin with extensive aquaculture when venturing into the aquacultural sector for many reasons. Some, because of its lower cost of operation, some because it is less complicated to manage, unlike the semi-intensive or intensive aquacultural system. Obviously,  extensive aquaculture is generally recommended for those starting a business with insufficient funds or aquacultural know-how. Earthen ponds have proven to be the cheapest and most practical rearing structures for extensive aquaculture especially in rural areas where land and natural water supply is cheap and accessible. However, some factors have to be considered when choosing a site to dig earthen ponds. Let us take a look at some of these vital factors first.

Criteria to consider when selecting a good site for earthen ponds

A certain number of factors should be considered when selecting a good site for earthen pond construction. Below is a detailed description of the six major factors needed.

1. Good quality water which is available all year round: the medium in which fish are grown is water. Thus, good quality water, free from all forms of pollution, must be available all year round to fill the ponds either canalised from a water source via an inlet pipe or flowing from beneath the pond bottom. The water input is needed to continuously refresh the polluted water and replace water loss due to evaporation and seepage through the bottom or walls, without which the fish will die of pollution and dryness. Water sources can be streams, springs, rivers, groundwater wells, boreholes and lakes.

Good quality water is the most important criterion to consider when choosing a site. Water quality for fish farming is mostly the physicochemical characteristics such as pH, conductivity, dissolved oxygen, dissolved CO2, temperature, iron levels, nitrite, ammonia levels, Suspended solids etc.

2.  Nature of soil: In earthen pond construction, the required soil must be that which will retain water preferably clay or silt-clay. Sandy and rocky soils are not suitable for the construction of ponds. It must therefore contain a minimum of 20% clay and a maximum of 60% clay. To test the soil, take a handful of wet topsoil, mould it into a ball and throw the ball into the air. Allow it to drop, if the ball does not break up, the clay content is good for water retention in the proposed site.

3. Topography: A site with a gentle slope is ideal for ponds. This is to enable canalised water to flow from the water source into the ponds by gravity, without using pumps. The essence of the slope is to ease the construction and drainage of the pond when impounded with water. The more porous the soil, the higher the slope needed, since porous soils lose water more rapidly than tight clay soils, and will need a fast water replacement. A slope of 2.5: 1 for tight soil and 4.1 for loose soil is required.

4. Environmental consideration: The site must be where drainage from domestic sewage, polluted water from industrial waste and chemicals used for agricultural purposes will not drain into the earthen ponds. The fishpond must not constitute a nuisance to inhabitants if it is close to a residential area. Seek approval from the local environmental safety body, to make sure your business is rated environment friendly before constructing the fishponds, to avoid fines from the Government.

5. Accessibility of the fishpond site: A fishpond should be constructed where there is easy access to good roads for easy transportation of farm inputs and transportation of produce for delivery. It should be easily accessible to markets for farmers to make adequate profit by selling directly to consumers, processing plants and fishmongers.

6. Vegetation of fishpond site. The site selected for pond construction should not be heavily shaded or wooded to reduce land deforestation costs. Furthermore, heavily wooded land around the pond will imply more water leakage via the growing roots of the surrounding trees when they penetrate the pond dikes. This will also increase pond pollution from falling leaves, branches, or fruits. For extensive fish farming which requires some sunlight for the production of phytoplankton for fish fries, the presence of many trees may shade the sunlight needed for primary production in the earthen fishpond.

Earthen pond types and designs:

There are three major types of earthen ponds notably:

• Dug-out(or dugout) pond, which is constructed by excavating the soil to hold water;
• Embankment pond, which is constructed by building a wall across a sloppy valley to create a reservoir to hold the descending water; and
• Cut-and-fill pond, a hybrid which is formed by constructing both a dug-out and embankment pond.

Materials, equipment and machines required for the construction of an earthen pond

If you have studied the site and it passes the test on the above criteria, you can then move on to build the fishpond. The following materials are required for this stage:  

 (A) Large fishponds: the following major equipment and materials will be needed when constructing large ponds, say, of more than 100m².

1. Land with a C of 0 (Certified Ownership) with survey plan;
2. Bulldozer: for removal of vegetation and levelling;
3. Payloader: a piece of heavy-duty construction equipment that lifts and carries materials using an articulated arm. Used to dig out the earthen pond and fill the earth on the dykes;
4. Tape rule for measurements;
5. Twine: for tying and ensuring straightness of surfaces;
6. Pegs: to delimit the pond;
7. Wheelbarrow: for transporting small weights;
8. Shovel: for shaping and levelling pond surfaces;
9. Roller: a heavy-duty machine that will be used to compact and smooth surfaces during pond construction.
10. Digger: for light digging. It is used for digging fond water canals, storms, stones, etc., in the pond area.

Other minor materials needed are sand, iron rods, planks, cement, nails, gravel, granite, planks, measuring tape, rope carpenter's level and head pans. Read this post for aquaculture construction machinery

(B) Small-sized earthen ponds. The following are required:

• Land with Certified Ownership, with survey plan
• Shovel
• Wheelbarrow
• Head pans
• Diggers
• Machete
• Ropes
• Stakes
• Spades
• Hammer/mallet

Other materials include sand, gravel, planks, measuring tape, granite, iron rods, planks, cement, nails, rope carpenter's level and head pans.

Constructing an earthen fishpond