|Better Farming Series 35 - Better Freshwater Fish Farming: Further Improvement (FAO, 1986, 61 p.)|
21. If the new ponds that you build are less than 500 square metres (a 20 x 20 metre pond = 400 square metres), you can use pipes with screens for the inlet, outlet and overflow, just as you did in Booklet No. 29 for your 15 x 15 metre ponds.
Inlet pipe with screen
22. For the 15 x 15 metre pond you learned how to build in Booklet No. 29, you made the inlet and the outlet about 10 centimetres in diameter and the overflow about 6 centimetres in diameter. With an inlet or outlet of 10 centimetres, it will take about half a day to fill or empty a pond of this size.
23. If you have built a pond of 20 x 20 metres, your inlet, outlet and overflow should be a little bigger. You can make the inlet and the outlet about 15 centimetres in diameter and the overflow about 10 centimetres in diameter. With an inlet or outlet of 15 centimetres, it will take about one day to fill or empty a pond of this size.
24. You can further improve a pipe outlet by placing a collar of cement around the centre of the pipe.
Collar in centre of pipe
25. The collar will hold the pipe in place in the bank and keep water from seeping through the bank outside the pipe.
26. The drawings below show you how to build a wooden form to make a cement collar.
A collar should be about 10 cm thick and at least 15 cm from the pipe to each edge of the collar
2 build a wooden form to mould the cement around the pipe
3 place the pipe in the form and fill the form with a mixture of one part cement to two parts sand, and some water
4 remove the form after the cement has completely dried
Note: you can make a form using nails; however, if you use wooden screws, you can take the form apart and use it again