ESTABLISHING THE HATCHERY 



FiGURK 9. — Catch basin constructed outside the pond. 



usually made of 2-inch by 8- or 

 10-inch treated, finished lumber, 

 and beveled on either end to fit. 

 The boards are placed one over the 

 other up to the desired water level 

 in the pond, and they serve as aji 

 overflow where rainfall or other 

 water may raise the pond above the 

 desired level. These boards may 

 be kept ti<j:ht by snuill wedges in- 

 serted at either end of the upper 

 board. 



The type of construction used is 

 a matter of |)reference. The solid 

 wall i)rovides a tight outlet with 

 an ea.sily manijmlated outlet gate. 

 On the other hand, the dam boards. 



or stoplogs, can be removed at will 

 and the water level kept at any de- 

 sired point in the pond. Also, if 

 an irrigation or other gate is used, 

 the total pressure of the water is 

 against the screen when the pond 

 is being drained, a.nd should the 

 gate become blocked with debris 

 (as is generally the case) , the screen 

 may be broken. If dam boards 

 are used, they are removed one at 

 a time and the pressure is only tht 

 depth of the flow over the board; 

 c()nse(iuently, the screens seldom be- 

 come entirely blocked and are never 

 broken by pressure; also, there is 



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