368 



WATKII-TIIANSruHT. 



It is evident tbat when the confined water of the reservoir 

 presses with all its weiglit on the whole sluice-<:rate, on open- 

 ing the latter, the violent rush of water would damage the 

 banks below ; such gates can therefore be used only where 

 the watercourse below has steep rocky banks. They have 

 also the disadvantage, that the sudden rush of water may not be 

 able to carry downstream all the wood which is lying on the 



Vu;. -200. 



X'Nj^i^wui^^?^ 



bed of the water-course, so that much of its effect is lost. In 

 the Tyrol, self-opening sluice-gates are used, which open when 

 the reservoir is full. 



(t)) Sluice-valves. — Sluice-valves are used in well-constructed 

 floating-channels and wherever the banks need protection against 

 the downward rush of water, so that the amount of water 

 passing through the passage in the dam may be regulated at 

 will. These valves are opened by means of a lever fitting into 

 cogs, a ratchet preventing the descent of the valve (fig. 210). 

 In the Absdach sluice, the so-called ladder sluice-gates are 

 adopted, the construction of which may be seen in fig. 204. In 

 order to avoid the use of heavy valves, two smaller ones side-by- 

 side may be used, or several, each of which works in its own 



