18 



removed when the water level has fallen to a depth that 

 the operator can wade. 



In small impoundments which are to be drained 

 infrequently, one of a number of outlets may be used. 

 The Canfield outlet is the most commonly used. It 

 consists merely of a pipe cut to the proper length so 

 that it will act as an overflow and control the pond 

 level. This pipe is inserted in a 90° ell attached to 

 the drainline and can be tipped to the desired level 

 to drain the pond. This outlet and a modification are 

 shown in figure 5. 



Another outlet is merely a cement block laid around 

 the outlet pipe, attached to which is one of a number of 

 gates (fig. 6). Themost common is the usual irrigation 

 gate, which may be purchased for about $15. A homemade 

 gate may be made by bolting a channel iron to the block 

 on either side of the opening and insej-ting a piece of 

 boiler plate which fits over the opening and has a 

 handle welded on it. This may be made by a blacksmith. 



Research workers at Auburn University (Ala.) have 

 designed an inexpensive gate which is attached to the 

 bell of a piece of soil-pipe. This costs from $8 to 

 $12. At present, they are experimenting with an 

 adaptation which is attached to a 45 ell so that it 

 can be opened by pulling a wire on shore. This elimi- 

 nates the need for a platform to the outlet, which 

 must be located in the pond beyond the toe of the levee 

 and at the lowest point in the bottom. If the pond is 

 to be drained frequently, one of the standard outlets 

 for hatchery ponds should be used. 



Hatchery ponds should be equipped with an outlet 

 which will readily permit drainage and removal of fish 

 that have beenpropagated. There are two general types 

 which may be adapted to conditions. One type has the 

 outlet and water-control structure inside the pond and 

 the catch basin for collecting fish outside. The other 

 has the outlet kettle and catch basin inside the pond. 



The conventional catch basin cuid outlet are shown 

 in figure 7. Built of concrete, this structure makes 

 it possible to control the water level and to drain the 

 pond. The outlet is at the low point in the back of a 

 concrete chimney or outlet box. It should extend about 

 10 inches above the pond level. 



The chimney usually has two sets of slots. The 

 outer slots are provided for a screen, which prevents 

 fish from leaving the pond and debris from entering the 

 pipeline. The screen is made of hardware cloth on a 



