2oi6 The Cornell Reading Courses 



due to frost may not be low enough to cause a leak. If more soil is 

 removed from the pond area than is needed for the dike, such excess 

 may be dumped profitably on the outside of the dike and used to 

 increase its breadth. 



Inlet 



From the intake box at the dam (Fig. 170, page 2012), water may be 

 conducted to the pond either through a pipe or through an open ditch, 

 the bed and the banks of which should be protected against erosion. 

 The bed may be protected by paving it with stones, the banks by planting 

 willow cuttings close together along them. It is well to insert a screen 

 at some point along the ditch or at its entrance to the pond, in order 

 to prevent fish from migrating upstream. 



Outlets 



The outlet is a very important part of the pond. It must be so con- 

 structed as to permit a free passage of excess water without endangering 



the dike and a complete draining of 

 the pond whenever desired. It 

 should also maintain a fairly con- 

 stant water level and should be 

 ,1^. *:^' ''f^X ^-^Wi. ^ properly screened to prevent the 

 M^l-I-Q'^-<rr^\!' / ''^''' escape of fish. Three tvpes of 

 ">---.>|£!;^:^. «rV-,.?^v'i^r~^- dependable outlets are illustrated 



Fig. 176.— Outlet for pond. A, flash- m figures 176, 177, and 178. 



boards; B, apron; C, core; D, embank- A box of wood or concrete, which 



ment; E, screen ^^^ several flashboards (A) that 



slide up and down in grooves and can be removed when it is desired to 

 drain the pond, is shown in figure 176. When in position, these flashboards 

 regulate the depth of water in the fishpond. A screen (E), inserted in 

 grooves, can be pulled out whenever it becomes clogged. Undermining 

 of the embankment is prevented by an apron of concrete or planking 

 at B . The cores (C) extending well into the dike are generally necessary 

 to prevent seepage at the jimction of dike and outlet box. This type 

 of outlet is a convenient one, for almost any water level may 'be main- 

 tained by regulating the number and the size of the flashboards. An 

 additional advantage lies in the possibility of quick draining. It is difficult, 

 however, to prevent leakage at the junctions of the flashboards; therefore 

 this form of outlet can be recommended only for ponds having an abundant 

 water supply in simimer. 



For ponds having a small water supply in summer, the form of outlet 

 illustrated in figure 177 is recommended. Here drainage is accomplished 

 by means of an iron pipe (F) with a gate valve (G) on the upstream end. 



