Could We Dredge the Netherlands Without Fossil Fuels?

For centuries, the Dutch landscape was maintained through dredging powered by humans, animals, wind, and the tides.

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Date: August 5, 2018 | Authors: Kris De Decker & Melle Smets

A 1699 scale model of a sail-rigged scratcher. Image: Maritiem Digitaal

The Vital Arteries of the Dutch Economy

The dredging industry has served as the fundamental support system for the Netherlands for generations. If the maintenance of rivers, harbors, and canals were to cease for even a few years, the nation's logistics and commerce would continue as normal grind to a complete halt.

While modern operations rely on massive ships burning up to 3,000 litres of fuel every hour, the past offered a different approach: ingenious, low-tech tools and natural energy sources.

The Challenge of Siltation

Because the Netherlands is situated in a river delta, it faces a constant influx of clay and silt. Maintaining navigable depths is critical for trade, especially for the Port of Rotterdam, the largest in Europe.

Current Maintenance Requirements:

• Remove $\approx 30$ to $35 \text{ million m}^3$ of mud annually.
• Manage $20 \text{ million m}^3$ specifically within the Rotterdam port.
• Dispose of $3.5$ to $5 \text{ million m}^3$ of toxic sediments in landfills.
• Adapt to larger vessels resulting from "modal shift" policies (moving freight from road to water).

"The drive for sustainability via water transport ironically increases the need for dredging, as ships grow larger and require deeper channels."

Modern Industrial Power

Today's dredging is a feat of high-energy engineering. The scale of power required is immense:

# Estimated fuel consumption for a large dredger
fuel_per_hour = 3000 # litres
hours_per_day = 24
total_daily_consumption = fuel_per_hour * hours_per_day
print(f"Daily fuel use: {total_daily_consumption} litres")

A History of Low-Tech Dredging

Before the era of internal combustion, the Dutch utilized a variety of manual and mechanical methods to keep their waters clear.

1. Manual Labor and the Baggerbeugel

The most basic method involved workers standing on small boats or wooden planks supported by the shore and a floating container. They used a tool called the baggerbeugel (dredge bag).

• The Tool: A pole up to 6 meters long, featuring a metal annular scraper and a net.
• The Technique: The worker rested the handle on their shoulder, using both hands to drag the net across the floor.
• The Scale: For massive projects, such as the Northern Holland Canal (1822-1825), thousands of these laborers were employed. This manual method remained in use for shallow ditches until roughly 1960.

Dredging by hand. Image: Maritiem Digitaal

The baggerbeugel tool. Image: Maritiem Digitaal

2. The Evolution of Dredge Mills

To reduce the grueling nature of manual labor, the Dutch developed the dredge mill in the late 16th century.

• Human-Powered Mills: These could reach depths of 2 meters. However, as merchant ships grew to depths of 3.5–5 meters, human power became insufficient.
• Animal-Powered Mills: By 1829, teams of 3 to 6 horses operated bucket chains, allowing for depths of 5–7 meters.

Efficiency Comparison: At a depth of $3.2 \text{ m}$, a horse-powered mill could collect $\approx 20 \text{ m}^3$ of mud per hour.

$\text{Modern Suction Dredger} \approx 300 \times \text{Horse-Powered Mills}$

Prisoners operating a dredge mill. Image: Beeldarchief Rijkswaterstaat

3. Mechanical Innovations

Other refinements included:

• Winch-driven bags: Introduced in the 16th century, these used ropes and winches on pontoons to pull the dredge bags.
• Valve Barges: Invented in the early 19th century, these boats featured bottoms that could be opened to release sediment without sinking the vessel.

Mechanical bags on a pontoon.

A valve barge. Image: Maritiem Digitaal

Human powered scratcher. Source: Maritiem Digitaal