Lock (water transport)

The word sluice is derived from the Middle Latin sclusa ("weir"), which has its origin in the Latin excludere ("to exclude"). The term stands for the closure of an opening within a transverse structure that dams a body of water. For this reason, the first locks were called barrage locks. In a broader sense, a sluice limits the "flowing" in its discharge by time and quantity. ^{(p. 1)} In French it became écluse, and in Spain esclusa is common. Dutch calls these technical devices sluizen as the plural of sluis, and in English the sluices are called locks (English lock).

In addition to ship lifts, inclined planes and boat lanes (for smaller pleasure craft), locks are among the descent structures in transport hydraulic engineering. Generally, locks are used for drop heights of up to about 25 metres, and ship lifts are usually built for greater heights. The first exception in Germany will be the new Lüneburg lock, which will have a lifting height of 38 metres.

In general, locks can be divided into sea locks and inland locks. Due to the size of seagoing vessels, sea locks are significantly larger than inland locks, which are divided into river locks and canal locks. Port locks are often part of a port or are located at its entrance, regardless of whether it is a sea or inland port. Sometimes port locks are called such only because they are located near a port.

The different designs or types of chamber sluices are further developments and adaptations to take account of the different operational, topographical and water management requirements. The special forms are, for example, those for large lifting heights, busy waterways or areas with little water.

In addition to their function for navigation as a connecting element of waterways, locks are also used within the framework of water management as barrage locks to regulate water levels and flow.

For details see section: Locking gates

Locks are located at barrages, canal stages, waterway crossings, barrage facilities or port facilities. If two or more locks are constructed independently of each other, they are referred to as a group of locks. Otherwise, the terms lock system or lock complex are commonly used for several locks.

The process of passing through a lock is a lockage. Depending on the direction, a distinction is made between upstream lock (upstream lock) and downstream lock (downstream lock). The area in front of the lock with the higher water level is called headwater (also upper current) and the other is called tailwater (also lower current). In these two areas are the outer harbours, where the ships can moor to wait for the lock.

The ships enter the lock chamber from the outer harbours. It is bounded on both sides by the head and the tail, in which the lock gates are located. The draught at the lock heads determines the maximum possible draught of the ships for the lock passage. The position of the jetties may be marked by yellow lines on the chamber wall, which determines the useful length of the chamber. During lockage, the closing devices remain closed so that the chamber water level can be changed independently of the external water levels.

The filling of the lock chamber is usually done by taking water from the headwater and emptying it by letting it down into the tailwater. In the simplest case, this is done via closable openings in the gate or by opening it gently and carefully. In any case, filling and emptying should always be done gently so as not to create strong ship movements inside and outside the chamber. In most cases, lockable circulation channels are arranged on both sides of the lock heads for this purpose, the construction of which is relatively complex. It is very helpful to have a sufficiently dimensioned bottom run under the chamber bottom, from which the filling and emptying takes place very evenly.

The lock gates must seal off the lock chamber as tightly as possible from the adjoining canal stops. For safety reasons, they must extend approx. one metre above the water level in the headwater or tailwater. Depending on the application, different types of sluice gates are used. The most important are: Mortise gate, lift gate, flap gate, segment gate and sliding gate. ^{(p. 54)} A fully functional sluice gate is a prerequisite for controlled sluice operation. Therefore, the gates must be specially protected against damage. The greatest danger arises when a ship enters the lock if it can no longer be stopped in front of the gate. Special impact protection equipment with damping elements can prevent or at least mitigate this. For ram gates, there are gate niches in the sides of the lock heads into which the gate swings when it opens, so that the ships have completely free passage. The same applies to flap gates and segment gates, which are placed in a recess in the floor.