Iron Trunk Aqueducton the Grand Union Canal

Cosgrove Aqueduct or the Iron Trunk Aqueduct

Length - 101 feet
Width - 15 feet
Height - 60 feet
Water Depth - 6 feet 6 inches

The Iron Trunk Aqueduct is one of the most unusual and historically significant structures on the Grand Union Canal. Located near Wolverton in Buckinghamshire, this striking cast-iron trough carries the canal across the River Ouse, replacing an earlier masonry aqueduct. Its construction marked a major step forward in canal engineering, demonstrating how new industrial materials could solve long-standing structural problems.

Today, the Iron Trunk Aqueduct remains a fascinating example of early 19th-century innovation on Britain’s inland waterways.

Location and Purpose
The aqueduct carries the Grand Union Canal (formerly the Grand Junction Canal) over the River Great Ouse floodplain near Wolverton. This crossing was essential to maintain a level canal route between London and the Midlands, avoiding the need for locks and ensuring efficient movement of goods.

However, the river’s tendency to flood created serious challenges for early canal engineers.

What Was There Before the Iron Trunk Aqueduct

When the Grand Junction Canal first opened through this area in 1800, the crossing was made using a conventional brick and stone aqueduct. This structure proved problematic almost immediately:

• The River Ouse frequently flooded
• Water pressure undermined the masonry foundations
• Repeated damage caused leaks and structural instability

Despite repairs, the original aqueduct could not withstand the river’s conditions. A completely new solution was needed.

Engineers Involved
The replacement aqueduct was designed by Benjamin Bevan, a highly respected civil engineer and surveyor of the early 19th century. Bevan was a strong advocate of using cast iron for canal structures, recognising its strength, durability, and resistance to water damage. Bevan was highly impressed and influenced by Thomas Telford's aqueducts on the Llangollen Canal.

His work on the Iron Trunk Aqueduct helped establish iron trough aqueducts as a practical alternative to masonry designs.

Dates of Construction
Original masonry aqueduct: circa 1800
Iron Trunk Aqueduct constructed: 1811
Opened to navigation: 1811
The new structure was built alongside the canal with minimal disruption to traffic, a notable achievement for the period.

Special Construction Methods and Design
The Iron Trunk Aqueduct was revolutionary for its time and incorporated several advanced engineering techniques:

• Cast Iron Trough Design
  The canal channel is carried in a large cast iron trough, rather than stone or brick
  The trough is made from prefabricated iron plates bolted together
  Joints were carefully sealed to ensure watertight integrity
• Support Structure
  The iron trough is supported on brick piers, lifting it safely above flood levels
  The reduced weight compared to masonry lessened stress on the foundations
• Advantages Over Masonry
  Far more resistant to flood damage
  Less prone to cracking and leakage
  Easier to repair and maintain
  Allowed for a slimmer, more elegant structure

This design avoided direct contact between canal water and the river below, greatly improving long-term reliability.

Why the Iron Trunk Aqueduct Was Important

The aqueduct represented a major shift in canal construction philosophy:

• It proved cast iron could outperform traditional materials
• It solved a long-standing flooding problem on a key trade route
• It influenced later aqueduct designs across the canal network
• It helped keep the Grand Junction Canal commercially viable

At a time when canals were vital to Britain’s industrial economy, maintaining uninterrupted navigation was essential.

Modern-Day Use and Significance

Today, the Iron Trunk Aqueduct continues to carry canal traffic as part of the Grand Union Canal, now used almost entirely for leisure boating.

on the Grand Union Canal

• Its distinctive industrial appearance
• Its historical importance
• Its role as an early example of iron canal engineering

Interpretation boards nearby help explain its history, making it a popular stop for walkers, cyclists, and canal enthusiasts.

Why the Iron Trunk Aqueduct Stands Out

• One of the earliest iron trough aqueducts in Britain
• Built in 1811 to replace a failed masonry structure
• Designed by Benjamin Bevan
• Demonstrates innovative use of cast iron in civil engineering
• Still in use over 200 years later

Few canal structures illustrate the transition from traditional to industrial engineering as clearly as this aqueduct.

Conclusion
The Iron Trunk Aqueduct on the Grand Union Canal is a remarkable piece of early industrial engineering. Built in 1811 to overcome persistent flooding issues, its cast-iron trough design represented a bold departure from conventional canal construction. More than two centuries later, it continues to carry boats safely across the River Ouse, standing as a lasting testament to ingenuity, adaptation, and the evolving science of canal engineering.