92 IRRIGATION FARMING. 



tion, if properly put up, will stand any natural pressure 

 that may come upon it from the impounded waters. 



In storing water for irrigation it is advisable to 

 make the slopes, particularly the inner one, more flat, 

 and to prote(5l them, where they are likely to be washed, 

 by riprapping with rock, or slag, or lining with lum- 

 ber. In works of lesser magnitude pebble-stones placed 

 along the water-line will serve the purpose just as well. 



Masonry Work. — In constru(5ling a dam entirely 

 of solid masonry no definite rules can be given, as the 

 circumstances governing all cases will in no two 

 instances be alike, and we can only give the method by 

 which a substantial dam of this sort has been con- 

 struc5led. Let us take for example the Bear valley reser- 

 voir in Southern California. Into the solid rocks of a 

 gorge the dam is abutted and is built in a curve arching 

 inward, forming the arc of a circle, with a diameter of 

 335 feet, illustrated very graphically in Fig. i8. Its 

 dimensions are, on the top, 300 feet from the abut- 

 ments, 60 feet from the bed-rock of the creek in the 

 highest point, and conforming to the mountain slope 

 on either side. The foundation is 17 feet in width, 

 running up to 3 feet on the top, which is covered with 

 huge blocks for coping. The whole is built of vast 

 granite blocks, which were quarried near the margin 

 of the lake and floated to the wall on scows, while a 

 derrick built on a raft placed them in position. The 

 best quality of Portland cement was used for laying 

 them, and all the interstices were filled with beton, 

 which was thoroughly tamped into place, until the 

 whole strucflure is one homogeneous mass. There are 

 3,304 yards of rock work, on which 1,300 barrels of 



