This is generally a matter of choice and also the design of your consultant. Meanwhile being on the floor of the fish pond / tank is good especially in a situation where the farmer doesn’t want to see any plumbing work on the surface only that it involves the perforation of the inlet pipe which may be blocked over time but it definitely serves the same purpose for which it was made.
Therefore, whether it is on the top or floor of the fish pond, the main thing is that it supplies water into the fish pond.
POND OUTLET STRUCTURES
1) Outlet Structures
1. Outlet structures are built for two main reasons:
- to keep the water surface in the pond at its optimum level, which usually coincides with the maximum water level designed for the pond;
- to allow for the complete draining of the pond and harvesting of the fish whenever necessary.
2. In addition to these major functions, a good outlet should also ensure as far as possible that:
- the amount of time necessary to drain the pond completely is reasonable;
- the flow of the draining water is as uniform as possible to avoid disturbing the fish excessively;
- there is no loss of fish, especially during the draining period;
- water can be drained from the top, bottom or intermediate levels of the pond;
- any reasonable excess of water is carried away;
- the outlet can be easily cleaned and serviced;
- the construction cost and maintenance are relatively low.
3. In most cases, outlets have three main elements:
- a collecting area on the inside of the pond, from which the water drains and into which the stock is collected for harvest;
- the water control itself, including any drain plugs, valves, control boards, screens and gates;
- a means for getting the water to the outside of the pond such as a pipe or a cut through the wall, and/or an overflow structure. In both cases, a protected area on the outside of the wall must prevent the drain water from scouring the walls or drainage channel.
4. Pond outlets can be built in various ways, using different materials such as bamboo, wood, bricks, cement blocks or concrete. There are four main types, which will be discussed in turn:
- simple cuts through the dike;
- simple pipelines and siphons;
- sluices; and
5. The main principles of design, including pipes and overflows, are discussed first in the next section.
Read Also: Importance of a Fish Net on a Concrete Pond
Important points when designing outlets in a Fish Pond
1. When designing and constructing an outlet structure, you should pay particular attention to the following points:
(a) Design a water discharge capacity large enough so that the pond can be drained within a reasonable amount of time, from a few hours for a small pond to one to two days for a large pond. (To select the right size of pipes see later in this section.)
(b) Design the elevation of the bottom of the outlet structure low enough to ensure complete drainage of the pond, so that:
- on the pond side, it is at least 10 cm lower than the lowest point in the pond;
- it slopes away from the pond, preferably with a slope equal to or greater than 1 percent;
- at its end, it is at least 20 cm higher than the bottom of the drainage canal.
(c) Design its total length so that the water will be discharged well away from the outside toe of the dike to avoid damaging it by erosion.
(d) For a barrage pond, the outlet should be built away from the streambed if possible and dug in lower than the lowest point of the pond bottom.
(e) Plan for the outlet to be built before or right after the beginning of the dike construction, depending on the type of pond.
(f) If the outlet structure is heavy, be sure to build it on very well compacted soil only. You may also need to support it with simple piling.
(g) If there is an outlet pipe through the dike, it is always best to build at least one antiseepage concrete collar around it:
- place it so that it will be integrated with the dike;
- build it perpendicular to the pipe;
- extend it at least 15 cm from all sides of the pipe;
- make it at least 10 cm thick.
(h) When building the dike above the pipes, be sure to compact the earth well around them.
(i) Remember that small pipes can become easily blocked, particularly inside the pond. Therefore:
- avoid using pipes with a very small diameter;
- protect the entrance of all pipes with a screen, and keep this screen clean through regular checks.
Note: you should try to standardize the type of outlet to be built on your fish farm, to make them easier and more economical to use.
2. To assist you in selecting the right type of outlet, you should also take into account how much you can invest and which kind of materials are locally available.
Characteristics of various pond outlets
Here are some amazing fish farming books to guide you and help you get started: