17 



Weir board 011 a ditch. 



The method of placing a trapezoidal weir board across a ditch is shown 

 by Fig 5. The measurement of depth of water is taken from the top of a 

 stake driven level with the crest of the weir. Fig. 6 shows a trapezoidal 

 weir board placed in a ditch with an apron and side wings to prevent cut- 

 ting of the earth sides and bottom of the canal. 



. BOX FOR 



3 TO 4O MfNER.5 INCHES. 

 Weir box. 



Fig. 7 is a drawing of a trapezoidal weir box. The weir crest is 12 

 inches long, the depth of the notch is 7 inches. It is designed for a capa- 

 city of 5 to 40 British Columbia miners' inches. It can be used for as little 

 as 3 miners' inches. For 40 miners' inches it requires a depth of water on 

 the crest of 5 % inches which is a little large for that width of notch, and 

 for very accurate results a larger weir would be preferable. 



Wings and cut off aprons are provided on the upstream and downstream 

 end of the box to prevent the water from washing around or under the box. 

 A wooden strip is nailed on one side of the box with its top level with the 

 weir crest, from which the measurements of depth of water will be taken. 



Fig. 8 is a photograph of a similar weir box installed to measure the flow 

 from a pumping plant. 



The method of installing a rectangular weir in a concrete lined canal is 

 shown by Fig. 9. In this case the weir board is made of metal plates. 



