FLOATING AND RAFTING 
397 
a crowbar or a lever. They are especially serviceable for dams 
a<r storage reservoirs through which logs are not sluiced, but 
where it is necessary to suddenly release large quantities of water 
in order to carry logs over very rough stretches. The needles 
may be liberated by breaking the bottom beam by a charge of 
dynamite. 
Barn-door Gate. — This has one or two heavy gates or doors 
hung vertically on bearings attached to the sides of the sluice. 
Fig. 137. — An Upstream View of a Rafter Dam having a Needle Gate. 
Appalachian Mountains. 
Double gates are held in place, when closed, by an upright beam 
in the center of the sluiceway, and single gates by a similar 
beam placed on one side of the sluiceway. A horizontal pole 
is sometimes used instead of an upright one to hold the gate 
shut. These gates have been used in Pennsylvania and in some 
parts of the Appalachian mountains, but they are not popular 
because the force of the water throws them open so violently that 
they are often damaged. A light drop gate often is built to shut 
off the flow of water while the large gates are being closed. 
