FLOW 0V WATER IN CHANNELS AND PIPES. 51 



notches cut in them, so as the small flow may be 

 accurately registered. The building of such a gauge 

 to give good results requires a little care. In the 

 first place, the water has to be altogether diverted 

 by a temporary channel. If this is impracticable, 

 coffer-dams must be formed taking half the stream at 

 a time. 



The conditions to be specially observed in con- 

 struction are as follows : 



1. The ends must tail into the banks at least 3 ft., 

 and puddled with clay. 



2. The gauge must be set truly level, and well 

 puddled at the bottom. 



'Pile 



FIG. 40. 



3. On the downstream side of the gauge there 

 must be a stone apron of 18 in. of stones, set at least 

 6 in. below the lowest notch. 



4. End walls of masonry are preferable to mere 

 puddle. 



5. It must be very strongly strutted. 



6. In loose ground it should be founded upon 

 piles, and sheet piles driven at the upstream side to 

 prevent the puddling blowing out under pressure. 

 The bearing piles would be 4 in. to 6 in. square. 



Now bearing in mind the conditions set forth, a 

 very suitable form of gauge is given in figs. 40, 41, 



