FLOATING AND RAFTING 395 
being closed while that with th(> lower pool is opened. The 
gate may be made to assume any intermediate position by reg- 
ulating the extent to which the two valves controlling the 
inlet and outlet of the chamber under the gate are opened. 
The objections to this form of gate are: (1) the overlap of the 
upper leaf over the lower one necessitates lifting a considerable 
amount of water when the gate is raised; (2) the head of water 
obtainable is only about one-third of the total width of the 
leaves: (3) the friction between the two leaves, even when re- 
duced by rollers makes it difficult to operate the gate smoothly; 
(4) the gate must be made in one section and if the gate is wide 
one side is apt to go up faster than the other causing twisting 
strains; (5) any driftwood or stones which may lodge between 
the leaves make the lowering of the gate impossible until the 
obstruction is removed. However, water can be let out of the 
reservoir very rapidly and the gate can be raised and lowered by 
one man as no special effort is required, both of which are ad- 
vantages. 
Logging dams with "bear-trap" gates 80 feet wide have been 
built and operated in Wisconsin 
Half-moon Gates. — A dam constructed to store water for log 
sluices often has a gate called the "half-moon." It is not used 
for wide sluiceways nor for large heads of water. The gate, which 
is slightly curved, fits tightly into the sluiceway with the convex 
face upstream. It is supported by four arms from 16 to 24 feet 
long, which are attached to a beam hung on bearings placed on 
either side of the top of the sluiceway. A platform erected over 
the gate supports a drum actuated by a hand wheel with gearing, 
or by a hand lever. Chains are attached to either side of the 
gate head and are passed up over the drum. The gate, which 
swings through an arc of a circle with a radius equal to the length 
of the supporting braces, is raised by winding in the chain. 
Needle or Bracket Gate. — Splash dams, especially in the Appa- 
lachian mountain and Pennsylvania regions, are often provided 
with needle gates which are made of hewed or sawed 3- by 5-inch, 
or 3- by 6-inch scantlings placed vertically across the opening, 
thus forming a solid front. The needles are supported at the 
lower ends by a cross-beam or groove cut in the base sill. The 
tops rest against a cross-beam to which the needles are attached 
by short chains. The needles are raised either by a windlass, 
