How locks work

Lock gate on River Barrow

A typical lock gate on the River Barrow navigation at Graiguecullen near Carlow town. The lock gate is a feature on the River Barrow in the control of ideal water levels for easy navigation.

Carlow County Library

Lock gate on River Barrow
Carlow County Library

Lock gate on River Barrow

A typical lock gate on the River Barrow navigation at Graiguecullen near Carlow town. The lock gate is a feature on the River Barrow in the control of ideal water levels for easy navigation.

Carlow County Library

Enlarge image

Navigation on a canal is made possible by means of locks. They are essential when the canal flows through territory which changes in elevation i.e. when there are heights and hollows along its course. When a canal boat enters a lock the water level rises or falls, so that the boat can proceed on its journey. Changes in the water level come about by directing the water to flow into or out of the lock, after the sluice gates have been closed.

A canal boat moving "upstream" enters the lock through one gate, which is then closed behind it. The sluice gate on the other end is then opened. Water enters the lock chamber and it raises the boat up. When the water level reaches the correct height i.e. when it reaches the same level as the higher portion of the canal, the second gate is opened. The boat then passes through. The process is reversed on the downstream journey.