CANAL CONS'TRUCTION. 75 



at the headworks without flowing into and filling up 

 the bottom of the canal proper. Many devices have 

 been invented in the hope of diverting sand from a 

 ditch, and the best of these no doubt is Gordon Land's 

 sand gate, se<5lional plans of which are presented in 

 Figs. 13, 14, and 15. 



In the Land Invention, the flume contains both 

 the headgates occupying the full width, and the sand 

 gates, which are on the lower side of the canal. There 

 are two floors above the headgates, and the flume is 

 set so that the upper floor is on the proper grade of the 

 canal. Just at the flume and for a short distance above, 

 the bottom of the canal is about two feet below the 

 grade. The sand gates, which may vary in number, 

 according to the width of the canal, are on the lower 

 side, and each of these gates is connedted with the 

 canal by a separate channel until it reaches the side 

 nearest to the discharge. These channels are curved 

 and properly fitted. Each one of these forms sc sepa- 

 rate funnel, and the gates are kept constantly raised 

 because, as in the case of nearly all canals, the natural 

 stream under riparian rights is entitled to the flow of 

 some of its full tide at least. The sand is pulled from 

 the far side of the canal, which is the chief advantage. 

 The planks forming the sand funnels are set edgewise 

 and thus support the floor of the main watercourse 

 above. 



Waste Gates. — The safety-valve of a canal is its 

 waste gate, and there are many styles in use. That 

 which we will describe herewith is known as Nelson's 

 automatic waste gate, and is described as follows, as 

 well as shown by se<5lional drawing. Fig. 16. 



