by commercial shipping or larger pleasure boats. For further details on
transients in constricted waterways, see also Blaauw and Verhey (1983),
Fuehrer (1985), Kolkman (1978) and Schofield and Martin (1988).
11.8 Locks
11.8.1 GeneralConcentrated heads on canalized rivers and canals are usually overcome by
navigation locks. The main components of locks are the lock gates, the lock
chamber, and the lock valves and filling (emptying) systems (Novak, 1994).
Lock gates are of different types: mitre, hinged, sliding, vertical lift,
submerged Tainter (horizontal axis), sector (vertical axis), reversed Tainter,
etc. Valves in the lock-filling system are usually vertical lift, butterfly or cylin-
drical valves. Stop logs or vertical lift gates are used as emergency closure
gates (for further details of gates and valves, see Chapter 6). Lock chambers
must be designed with sufficient stability against surface- and groundwater
and earth pressures, and must have sufficient resistance against ship impact.
Clearances of up to 1.0 m are usually allowed on either side of the
largest vessel, with the effective length of a lock usually being 1–5 m greater
than the longest vessel the lock is intended to accommodate. Because of
the difference in elevation of gate sills, the upstream gate is nearly always
smaller (lower) than the downstream one. The gate sill elevation controls
the draft of tows that can use the lock; usually, 1–2 m is added to the
required design depth as a provision for future development of the water-
way. The lock sizes (length L, width Band particularly their head H),
together with the selected system of lock filling and emptying, determine
the design of the lock as well as the type and function of its gates.
In the course of the filling and emptying of the lock, a complicated
unsteady flow occurs, not only in the lock itself but also in its approach basins.
This flow exerts considerable forces on the barges; these forces must not
exceed a permissible limit, and their effect must be eliminated by the tying of
the vessels with mooring ropes in the lock or in its approach basin. During
emptying of the locks the vessels are usually affected by smaller forces than
during filling, because of the greater initial depth of water in the lock.
According to the size and type of filling we can divide locks into four
categories:
- locks with direct filling and emptying through their gates, this
method being used mainly for small and medium lock sizes; - locks with indirect filling by means of short or long culverts situated
either in the lateral lock walls or in its bottom, and connected with
the lock chamber by means of suitably designed outlets;