What Are Canal Locks And How Do They Work?

A canal lock is a watertight chamber with gates at both ends that raises or lowers boats between two stretches of water at different heights. The boat enters the chamber, the gate behind it closes, water is let in (to raise it) or let out (to lower it) through sluices, and the next gate opens onto the new water level - in effect, a hydraulic staircase. The concept dates back to a Chinese pound lock built around AD 984 by the engineer Qiao Weiyo.

Geographical disparity across the globe has been the greatest hindrance to trade and movement by sea. Given that the sea is the most popular avenue for bulk transport, even to this day, engineers are perpetually seeking solutions to reduce the costs associated with lengthy sea travels.

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Why Are Canals Needed?

Canals are artificial waterways constructed mainly for transportation or irrigation purposes. The use of watercraft on irrigation canals is mostly prohibited. Similarly, water used in transportation canals is deemed hazardous for irrigation purposes.

Transportation canals usually connect two natural water bodies, such as oceans or rivers. They are typically constructed in regions where landmasses ‘pinch’, so this connection can be made with a minimal amount of construction work. This enables the ships to bypass several thousand kilometers by passing through a much smaller distance (100-200km).

That said, it’s not practical to dig consistently through land for several hundred kilometers. Therefore, canals can’t be dug too deeply and do not have a uniform depth through their entire length. This can make canals hazardous for larger ships.

What Are Canal Locks?

Oceangoing container vessels are huge by any stretch of the imagination. When fully loaded, the largest of them have a draft (the depth of hull below the waterline) of around 14 to 16 metres (45 to 52 feet), making them susceptible to any obstruction in the beds of shallow waters.

To overcome this problem, watertight cabins were designed to elevate the surface of the water, and along with it, the ship. This would clear the hull of any obstruction in the canal bed and help them pass more easily.

These cabins are known as canal locks. While the pound lock has been around since around AD 984, when the Chinese engineer Qiao Weiyo built one on the Grand Canal, the design has been refined over the years. Today, canal locks are automated to make them more efficient and safer to operate. They are not only restricted to the maritime industry, but have also been domesticated to a certain degree, finding use in theme parks and local waterways.

Construction Of A Canal Lock

Canals have watertight gates built into them at various levels. Between them, the gates enclose a chamber of water called a ‘lock’.

The level of water is the highest in the central-most lock and decreases as one moves towards either side. A canal lock is comprised of the following components:

1. Watertight Chambers

Canal beds and walls are lined with concrete to prevent the seepage of water into the ground. These chambers are supplied and emptied to raise and lower boats that enter the locks.

2. Flood Gates

These simultaneously activated split doors enable a ship to enter the lock. They close against the direction of water flow, enabling the lock to remain watertight.

3. Sluices / Paddles

Sluices are channels of water that connect two locks. They supply water to and from the watertight chambers.

4. Lock Gear

Lock gears are responsible for lock operation, such as the opening or closing of flood gates and water sluices that fill up or empty the lock. In locks that see heavy use, these are either automated or manned by a crew dedicated to this purpose.

Working Of A Canal Lock

This brings us to our main question: “Can boats really climb staircases?”

In order to clear the ever-changing canal bed, locks are arranged in succession so that the boat may ‘ascend’ into the canal and ‘descend’ out of it, much like a staircase.

A vessel going through a canal encounters the following steps:

1. Entry

The vessel enters the first lock and the floodgates close behind it, forming a watertight system

2. Elevation

The boat is then moored to the canal walls while the sluices open, bringing in water from the lock in front. This inflow of water raises the ship, while bringing the water in equilibrium with the ‘donor’ lock. The floodgates between the two locks can now open and the ship can sail through to the next lock.

3. Descent

Descent is the exact opposite of elevation, wherein the lock with the ship empties into the ‘recipient’ lock. The water level decreases in the donor lock and becomes equal to that of the recipient lock, descending the ship along with it. The floodgates can now open and allow the ship to pass through to the next lock.

4. Exit

The entry and exit locks have water levels that are in equilibrium with the rest of the canal. This enables the ship to continue its journey in the rest of the canal with relatively uniform beds.

Here is a video showing canal locks in operation.

Advantages And Disadvantages Of A Canal Lock

The inherent advantages of canal locks are that they make traversing through water bodies quite easy. They also eliminate the prohibitive expenses of maintaining a consistent depth for the entire stretch of a canal.

However, there are also some disadvantages to canal locks. Water to canals, and consequently their locks, must be supplied from nearby waterbodies, such as rivers or oceans.

Repetitive flooding and depletion of water during canal operation can upset the pH values of soil in regions near the canal. This makes the soil unsuitable for any type of cultivation and promotes land erosion.

At the same time, the sluices that carry water to and from the lock always lose water. While it is an insignificant percentage of the volume of water contained within the lock, it can amount to a substantial amount, given that several million liters of water are moved around during a single lock operation. This can lead to acute water shortage problems.

Examples Of Canal Locks

Canal locks are not only deployed on significant water bodies, but can also be found on small streams and rivers. However, some of the most prominent canal locks are found on transportation canals. Notable for their size and the amount of traffic handled daily, these locks are not only engineering marvels, but also epicenters of global commercial activity.

Some of these famous canals are explained below:

1. Panama Canal Locks, Panama

• Number of lock chambers: 12 in the original 1914 set (six chambers per direction) plus another 6 in the new Cocoli and Agua Clara locks opened in 2016 to handle Post-Panamax ships

• Elevation: ships are lifted about 26 m up to Gatun Lake and back down to sea level on the other side

• Total length of canal: 82 km (51 miles)

2. Grand Canal Locks, China

• Number of locks: 24

• Elevation: Up to 42m from the canal bed level

• Total length of canal: 1776 km

3. Caen Hill Locks, England

• Number of locks in the Caen Hill flight: 29

• Elevation: a 72 m rise in just 3.2 km (a 1-in-44 gradient), one of the steepest in the UK

• Total length of the Kennet and Avon Canal: 87 miles (140 km), of which the famous straight flight is around 2 miles long

Recent Challenge: The Panama Canal Drought

One contemporary illustration of the disadvantage of canal locks came in 2023–2024. Each transit of the Panama Canal pours roughly 200 million litres of fresh water from Lake Gatun out into the sea, and a strong El Niño plus record warming dropped the lake to its lowest January level on record. The Panama Canal Authority had to cut daily transits from 38 down to about 24 in late 2023 and as low as 18 a day by February 2024, a stark reminder that canal locks are only as reliable as the watershed that feeds them. Normal capacity returned by mid-2024 as rainfall recovered.