FLOW OF WATER IN CHANNELS AND PIPES. 55 



and w = 62^ Ib. per cubic foot ( = weight of water as 

 taken in practice). Therefore the ihrust=p = wh 

 = 9 x 62*5 = 562*5 Ib. Say the distance between the 

 posts is 10 ft., calculate the pressure at 8 ft. from top 

 water level = 8 x 62*5 = 500 Ib., and on a layer of the 

 bottom of the gauge i ft. deep we have a total pres- 

 sure of 



500 x 562*5 



x 10 = 47*4 cwt. = P 

 2 x 1 12 



SHI 



12'* 16 



Posts /6x/6 

 W-O'CtoC. 



FIG. 45- 



From this we require to find how thick the bottom 

 boarding will have to be. This will be equal to 



IPX 



= say 6 in., which would be provided by two layers 

 of 1 1 in. x 3 in. stock size boarding, which need only 

 be continued 4 ft. 6 in. upwards, a single thickness 

 of the same boarding sufficing thereafter. The 

 boards would be tongued and grooved, The iron tie 



