NEEDLE DAMS. 



221 



Needle Dams in Europe. The most complete system of needle dams is to be 

 found on the Meuse in Belgium, their construction having been completed about 1878. 



The first dams on this river were closed entirely by needles, and in 1866 the sys- 

 tem was continued by the construction of three Chanoine wicket dams. As these did 

 not prove entirely suitable, the work was completed with nine dams using needles 

 for the passes and wickets for the weirs. In these latest works the locks are 39 feet 

 wide, with an available length of 328 feet, and a depth of 6.9 feet on the lower miter- 

 sill, the upper and lower sills being on the same level. The passes are 150 feet in length, 



SECTION OP NEEDLE DAM ON THE LOWER SEINE, PRIOR TO 1880. 



with weirs 179 feet in length, and in some cases a fixed weir is provided also. The 

 pass trestles are spaced about 4 feet apart, and weigh about noo Ibs. apiece with all 

 attachments, being raised by the method of separate chains and a portable winch. 

 The needles, which support a head of 8.2 feet with about 10.2 feet on the sill, are 12.3 

 feet long and 3}^ inches wide, with a maximum thickness of 4^ inches, and weigh- 

 ing about 55 Ibs. They are supported by escape-bars on the Kummer system, and 

 are removed by releasing the bar, allowing the needles to pass down stream. 



The weirs are provided with wickets 4 feet 3 inches wide, and 7 feet 4 inches high, 

 with a space of 4 inches between each, and are provided with butterfly valves in the 

 upper parts, for the easier regulation of the pools. They are raised and maneuvered 

 from a trestle bridge, and lowered by tripping-bars. 



