154 IRRIGATION FARMING. 



depth of water passing over the notch, because if meas- 

 ured direcflly on the notch the curvature of water in 

 passing would reduce the depth. The Une D isa level 

 from the bottom of the notch (B) to the top of the 

 stake (£), while the dotted line C represents the top 

 of the water, and the distance between the lines from 

 the top of stake gives the true depth or spill over 

 the weir-board. The lines in the sketch have the 

 appearance of running over the top of the board, when 

 in fad; they pass behind it, but for the purpose of illus- 

 tration the reader is supposed to look through the board 

 and the post. The surface of the water below the 

 board should not be nearer the notch (B) than ten 

 inches, that the flow will not be impeded. Neither 

 should the nature of the channel above the board be 

 such as to force or hurry the water to the board, but 

 should be of ample width and depth to allow the water 

 to approach the board quietly. If the water passes the 

 channel rapidly it will be forced over the weir and a 

 larger quantity will pass than if allowed to spill from a 

 large body moving slowly. 



Weir Table. — The table on the opposite page 

 may be of service where the delivery is such that it 

 can be measured over a rec5langular weir, as described 

 under the foregoing caption. 



To use the table, measure the depth of water in 

 inches over the weir. From the depth so measured find 

 in the table the miner's inches flowing for each inch of 

 width in the weir opening. The width of the weir 

 opening in inches multiplied by miner's inches in the 

 table gives the miner's inches flowing over the weir. 

 Multiply the miner's inches by .02 to obtain the cubic 



