Timber-Pass Structures

hydraulic engineering structures designed to pass floating timber (in rafts or loose) through dams and other structures on rivers.

Ship locks are often used on navigable rivers to pass rafts. However, in order to reduce water consumption and achieve maximum use of the handling capacity of the locks, special timber-pass structures are constructed—log booms, which are inclined chutes made of wood, concrete, or reinforced concrete with rectangular cross section. A fast hydraulic flood gate, usually segmented, is installed at the head part of the chute. Floating bollards that are articulated with the chute are installed to reduce the shock when the raft emerges from the chute into the lower water. Water flows through the chute at 2–4 m per sec. The water rate and raft speed in log booms can be reduced by artificially increasing the roughness of the chute bed or by building in zigzag-shaped outcrops (cutoffs) or brushwood barriers. Much water can be saved by installing a second gate in the chute to form a sluice chamber in the head part of the boom to hold the raft; the raft will float with the chamber’s water after the second gate is opened.

Timber slides (or log slides), which are chutes of triangular or trapezoidal cross section that usually are made of wood, are used to pass loose-floating timber. Depending on the water fed into the timber chutes, the slides are called floating, semifloating, or wet. Floating timber slides are used to float timber (when the water level is within 0.7-0.9 the diameter of the logs), and their slopes usually lie within the range 0.001-0.01. In semifloating timber slides the timber is transported in a semisuspended state, sliding along the bottom. This greatly reduces water consumption for passage of the logs (the water level is within 0.2-0.6 the diameter of the logs). Wet timber slides have steep slopes, and the little water they use serves only as a lubricant to move the logs along the chute (water depth, 0.5-1.5 cm).