The Zuiderzee and Delta Works of the Netherlands

The Eastern Scheldt Surge Barrier, part of the Delta Works, protects the land from flooding during storms. (Credit Vladimír Šiman licenced through Creative Commons Attribution 3.0 Unported)

When people think of the Netherlands two things often come to mind: Tulips and windmills. Both of these have been symbols of this European country for centuries. The tulip was introduced from Asia in the 17th century and has been a source of income for Dutch farmers ever since. The windmills date from the 1400's and though they are picturesque, they are actually symbols of a serious life and death struggle that has raged in the Netherlands for years: The Dutch people and their land against the sea.

The most recent of these battles took place in the 20th century when the Dutch engaged in two massive projects to enlarge and secure their land against the ocean. The Zuiderzee Works and the Delta Works took most of the century to complete and together are considered one of the Seven Wonders of the Modern World.


The Netherlands is one of the most low-lying countries in the world. Today about a quarter of the land area is actually below sea level. Because of this when a large storm raises the water level along the coast much of the country is subject to heavy flooding. In the first century A.D. people began building artificial hills, called terps, and locating their villages and towns on top of them so that when floods came their homes would be safe. After a while it occurred to the people that if they connected the terps together with long walls, called dikes, they could keep the water out of their farmlands also. Eventually the Dutch started eyeing areas that had been unusable because they were flood zones or were underwater like marshes and lakes. Dikes were built around these and they were given the name polders. For a polder to be made dry enough for framing or building they had to be drained of water. The earliest pumps were connected to windmills and driven by the wind. As more and more land was added to the Netherlands through polders more and more windmills were needed. Soon the Netherlands became known as the land of windmills.

Seven Quick Facts
Size: Created 895 square miles of land. (2318 square km)
Length: Afsluitdijk dam - 20 miles (32 km)
Cost: Afsluitdijk $710 million, Delta Works $7 billion
Started: Zuiderzee - 1918, Delta - 1950.
Completed: Zuiderzee - 1967, Delta - 1997
Location: Netherlands, Europe.
Other: Turned the Zuiderzee from a bay into a lake.

Taming the Zuiderzee

One of most notable features of the Netherlands was the Zuiderzee. The name meant "Southern Sea" in Dutch, but it was actually a shallow bay of the North Sea that ran 60 miles (100km) inland and was about 30 miles (50km) wide. Despite its great size covering almost 2000 square miles it was only about 15 feet deep.

While the Zuiderzee was a resource for fishing and allowed access for trade, it could become dangerous whenever one of the frequent North Sea storms would push water through the bay's inlet. Dikes would fail and the resulting floods would kill hundreds or even thousands of people. In 1421 a seawall on the Zuiderzee dike broke during a storm and flooded 72 villages killing about 10,000 people.

In the 17th century the first plans to address this problem were drawn up. It wasn't until the 19th century, however, that the technology to actually do the job was developed. Cornelis Lely, a Dutch civil engineer, came up with a plan that proposed building a long dam that would close off the Zuiderzee and turn it into a lake. The plan also included building four polders in the lake that would be drained and used mainly for agriculture.

Lely became Minister of Transport and Public Works in 1913 and tried to push his plan forward. Not everybody agreed with his ideas, however. Fishermen along the Zuiderzee were concerned that they would lose their livelihood. Others were worried that such a project might create higher water levels at other places along the coast. The government was also alarmed about the enormous price tag of the project.

In 1916 during a winter storm, however, several dikes gave way along the Zuiderzee and the result was more damaging floods. After this disaster Lely's bold plan gained much public support. On June 14, 1918 the Zuiderzee Act was passed and the project was officially started. Its goals were to protect the region against floods from the North Sea, increase the country's food supply by creating polders that could be turned into farmland and use what remained of the Zuiderzee to improve water management.

Construction on the Afsluitdijk in 1931

The Afsluitdijk

The first step in the plan was to enclose the Zuiderzee by building a 20 mile long dam across the bay. Something like this had never been done before, so the Dutch engineers made the wise decision to start by building a much shorter dam out to the island of Wieringen which would form the first part of the enclosure of the bay. The experience gained in the exercise was valuable when the longer dam, the Afsluitdijk, was built from the other side of Wieringen across the bay to the village of Zurich in 1927.

The engineers found that a type of material called till (or boulder clay) made an excellent base for the dam. As the name suggests it is a mixture of small boulders and clay that was deposited during the Glacial Period. Fortunately it was readily available as it could be obtained by simply dredging it up from the bottom of the Zuiderzee. The till was loaded into ships which hauled it out to the mouth of the bay and dropped it onto two parallel lines along what would be the course of the dam. The space between the two rows of till was filled with regular sand, and then a layer of till was placed on top. To complete the base of the dam a coating of basalt rock and willow branches was laid down. The dam's design called for it to rise 25 feet above sea level, so another layer of sand was placed to top of that, which was covered with another deposit of till. The surface was then planted with grass to help guard against erosion. The project proceeded faster than planned and was two years ahead of schedule when on May 28, 1932 the last connection to the sea was closed that the Zuiderzee became a lake named Ijsselmeer. Then dam took another year to fully complete as a road was built along the top and 25 sluices were constructed to allow excess water in the lake to be discharged to the sea. Two sets of locks were also created to allow ships to move in and out of the Ijsselmeer to the ocean. It is estimated the dam cost the equivalent of $710 million in 2004 United States dollars.

Making Land

Even before the Afsluitdijk was complete, the Dutch started working on the first of the polders, the Wieringermeer. It's dikes were completed in 1929 and by 1930 it had been pumped dry, not by windmills, but by one modern diesel powered pumping station and one electrically powered pumping station. Both used large Archimedes screw type pumps to move the water. Additional work took another four years before the land could be used for agriculture and construction. The polder added a total of 75 square miles of area to the country.

The second polder, the Noordoostpolder, was started in 1936 and draining it wasn't finished until 1942. The area turned out to be a good resource for the Dutch Underground resistance in World War II as it provided almost 230 square miles of undeveloped land to hide from the Nazi occupation force.

World War II also brought some setbacks to the project, however. In April 1945, the retreating German forces blew up the dike of the Wieringermeer, flooding the land again. Fortunately the Dutch managed to reclaim the polder by the end of the year, though much of the infrastructure was destroyed and had to be rebuilt.

In 1950 work on the the Oostelijk Flevoland, the third polder, was started and by 1957 it had added 208 square miles of territory to the Netherlands. Two years later work on the fourth polder, Zuidelijk Flevoland, was started and finished in 1967.

The Dutch considered building a fifth polder in the Ijsselmeer, but after several false starts, it was never completed. Even so the territory created by the project totaled over 895 square miles.

The Delta Works

The Delta Works were a series of construction projects started in 1950 designed to limit flooding. Just south of the Netherlands city of Rotterdam the Rhine, Meuse and Scheldt rivers meet the North Sea. This estuary area was extremely low lying and had been subject to heavy floods for centuries. Shortly after the completion of the Afsluitdijk, the Dutch decided they could limit the damage to this area by using dams to effectively shorten the coastline. No work was started until the 1950's however.

The Zuiderzee plan drawn up by Lely in 1891.

A major flood in the region during January 1953 killed more than 1,800 people when a storm surge caused 89 dikes to fail. Over 72,000 residents had to be evacuated and 10,000 houses and buildings were destroyed. Repair and reconstruction cost nearly a billion dollars. This prompted the government move forward with the project as quickly as it could. Originally the plan called for estuaries Oosterschelde, Haringvliet and Grevelingen to be dammed and turned into lakes, just like the Ijsselmeer. Because of environmental concerns, however, it was decided to protect the Oosterschelde from storm surges by a barrier instead. The storm surge barrier is a series of massive values that are normally open so that water can move in and out of the estuary. This helps preserve the natural environment. However the valves can be closed to create a dam during a storm so no high water enters the area. Another storm surge barrier was also built to protect the river Nieuwe Waterweg when raising the existing levees along the waterway proved too difficult.

Though officially completed in 1997 at the cost of $7 billion, the Netherlands continues to add infrastructure to the Delta works as needed. It is estimated that it will continue to need construction to protect the area against the rising water levels caused by global warming.

Copyright 2011 Lee Krystek. All Rights Reserved.