8 



the pond level or are located high enough on the drain- 

 age basin so that the level is maintained by run-off 

 from surrounding land. 



In sections of the country where rainfall is rel- 

 atively high, as in the Gulf States as far west as 

 Louisiana, the drainage area should be about 5 acres 

 for each acre-foot of water in the pond. In those 

 sections where rainfall is lower — this includes south- 

 eastern Wisconsin, and southern, central, and western 

 Minnesota — the proportion of drainage area should be 

 greater. It is particularly desirable that drainage 

 be from good pasture land, a stable forest area, or 

 other well-covered land. Eroded or improperly tilled 

 soils allow rapid run-off, which results in silty 

 waters and gradual filling of the pond. Some operators 

 who must take waters from tilled land, construct a 

 small settling pond or silt basin above the regular 

 pond. The lower end of the pond site should be of 

 sufficient width to provide an adequate auxiliary 

 spillvjay to carry off occasional flood waters. 



Pond Construction 



Small impoundments are generally constructed by 

 building a dam across a narrow gully where the banks 

 are of sufficient height to provide water deep enough 

 for fish during the winter. The depth at the dam should 

 be from 5 to 15 feet, depending upon the severity of 

 winter weather and the topography of the pond bottom. 

 In northern Illinois the depth should be at least 10 

 feet; the farther north the pond, the more this figure 

 should be increased. 



First consideration is given to laying out the dam 

 and outlining the confines of the water level in the 

 pond. Because of the acreages of water impounded, 

 earthen dams are used almost exclusively. Determination 

 of a desirable top width is the first step in the design 

 of the dam. Generally, the top of the dam is 6 or 7 

 feet wide; but if it is to be used as a road for auto- 

 mobile travel, the dam should be at least 11 feet wide. 

 The equipment to be used in constructing the dam may 

 also affect the width of the top, If teams are used, 

 the top of the dam should be 5 feet wide; tractors 

 require a width of at least 10 feet. When the height 

 of the dam and width of the top are known, the base can 

 be laid out. 



Ordinarily, the upstream or pond side of the dam 

 is sloped at the rate of 3 feet for each l foot of 



