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7. Controlling the water in the pond
Overflow
Controlling trash and fish: Screens
169 If there is too much water in your pond, some of the water may flow over the banks. This may wash the banks away and some of your fish may get out.
170 You can use an overflow to keep the water in your pond from rising over the banks.
171 The better outlets you learned about in items 107 to 119 will act as an overflow.
172 If you use a straight pipe outlet or a siphon to let water out of your pond, you will need another kind of overflow.
173 This kind of overflow can be made from a piece of bamboo or a pipe of plastic or metal. The overflow pipe should be about 6 centimetres in diameter.
174 The overflow pipe should be long enough to reach through the top of the bank from the inside of the pond to a place far enough on the outside to keep overflow water from washing away the bank. You will need a pipe about 4.5 metres long to do this.
175 If you cannot get a pipe that is long enough, join short pieces of pipe or bamboo together (see items 100 and 101).
176 It is best to place your overflow in the bank at the lower end of your pond right above the outlet so that the water that overflows can run off in the outlet ditch.
177 If you are going to put the overflow over the outlet, you can put it in the same gap that you dug for the outlet in item 96. The water line should be about 50 centimetres below the top of the bank, so put your overflow there as you rebuild the bank.
178 If you are going to put the overflow in another place, you will have to dig another gap in the bank about 50 centimetres deep.
179 When the pond is full, the overflow will keep the water about 60 centimetres deep at the shallow upper end and about 90 centimetres deep at the deepest part.
Controlling trash and fish: Screens
180 Your inlet should have a screen to keep out wild fish, dirt and trash when you fill the pond.
181 If you fill your pond with an inlet trench, it should have a screen, too.
182 A siphon, which is very small, usually does not have a screen.
183 Your outlet should have a screen to keep your fish from getting away when you empty your pond.
184 Your overflow should have a screen to keep your fish from getting away when the pond is too full and the water begins to overflow.
185 You can easily make screens for your inlet, outlet and overflow from fine-mesh plastic or metal or from a tin with holes in the end.
186 Screens should be placed outside the pond on the inlet pipe and inside the pond on the outlet and overflow pipes.
187 This will keep the pipes from filling with trash which could stop the flow of water.
188 Lash the screens tightly in place on the pipes, using heavy cord or light wire.
189 If you fill your pond by cutting a trench through the bank, you can screen the opening using a fish trap, split and woven bamboo, a clay pot with holes in the bottom or a piece of metal roofing with holes.
190 When you are filling or emptying your pond, clean the screens often. If you do not do this, dirt and leaves will cover them up and the water will not flow.
Summary
YOU HAVE LEARNED HOW TO CONTROL THE WATER IN THE POND
Provide an overflow for each pond to control its water level:
Use screens to prevent
