220 IRRIGATION. 



frames should be thoroughly well cased in with planking, 

 which should extend some distance into the bank, and 

 be well protected with puddled clay, tightly rammed in 

 around it. The outer slope, and top of the dam, should 

 be of plank or timber, with an apron upon which the 

 overflow is received and carried off. The bed of the 

 river at the foundation should be well searched for sunken 

 logs, or brush, which should be removed before any earth 

 is thrown in. These points should be looked to whether 

 the work be large, or small. 



For small streams, dams of very simple construction 

 will be sufficient. Cribs of timber, consisting of a sill, 

 an upright post mortised in the center of the sill, and two 

 timbers placed like the rafters of a house but one at a 

 greater angle than the other from the ends of the sill 

 to the top of the post, are placed lengthwise in the 

 bed of the stream for the framework of the dam. The 

 timber which slopes at the greater angle is placed at 

 the front of the dam. The cribs should be placed 

 from 6 to 12 feet apart, as the stream is smaller or larger. 

 They are joined together by planks or timbers, spiked or 

 bolted to them, and the rear of the dam is covered with 

 plank jointed and fitted together very closely. Stone or 

 gravel may then be thrown in, until the cribs are filled, 

 care being taken to pack clay closely at the bottom, 

 so that no water will escape. The front of the dam 

 may then be planked over, and an apron, or floor of 

 plank, laid to protect the bed of the stream from the 

 waste water. The earth-dam upon the banks of the 

 stream must be carefully joined to the crib-dam, and 

 should be supported in the center by posts driven in the 

 ground, to which three or four planks in hight are spiked. 

 A dam of this kind may be made to serve for streams of 

 any size, as it admits of expansion in length, hight, and 

 width, and increase of strength, indefinitely. "Where 

 the hight required is not more than four feet, a dam of 



