3GG 



W ATE K-TKANSPORT. 



at Herrenwies in the Black Forest, with two sluice-gates (b b) ; 

 (a a) are smaller ^Mtes which are opened first to relieve the 

 pressure on h l>. 



(6) Dams of combined masonry and earth. — These are the most 

 highly perfectiouetl of all, and are used in the Bavarian forest, 

 as shown in transverse section in fig. 20G. The masonry rests 

 on a foundation of piles, and the reservoir side of the dam is 

 faced with hewn stones resting on cemented rubble-masonry 

 containing a thin layer of concrete. A wall of cement and clay 



Fig. 207. 



bounds this structure, and a well-stamped earth-dam is continued 

 towards the valley. This mode of construction, and a liberal use 

 of cement and concrete to a considerable depth in the foundations 

 of the dam, make it in the highest possible degree watertight. 



(e) Sluice-gates. — The gates for the chief outlet of water from 

 the reservoir are usually in the middle of the dam, but some- 

 times at its base. The sluice-gates usually open into a channel 

 which conveys the rush of water at some distance from the dam 

 into the natural bed of the stream. This protects the lower 

 side of the dam from being undermined by the water, and is 

 specially important in the case of wooden sluices and earth-dams, 

 as in iig. 203, )n l> n. The sluice-gates are closed by various 

 contrivances, and they may be distinguished, according as they 

 open with a rush, as in ordinary sluice-gates, or are raised 

 gradually, as in the case of vertical! \ opening valves. 



(0 Sluice-gates opening in the ordinary way. — This is effected 



