‘God created the world, but the Dutch created Holland’. Dutch people like to explain how their country has been shaped by the struggle against the water. The construction of dikes is one of the key factors in this heroic story. Without dikes, half of the Netherlands would be regularly flooded by the sea and the rivers.
Dike networks are not isolated, but form part of their environment. In such an environment, there are certain similarities between the different dikes: they share the same landscape, the same flood defence role, or the same history. The dikes in the coastal areas, for example, were specifically designed and constructed to withstand storms and wave run-up: the sea dikes. Sea dikes are one dike group.
Overview of all dike groups, systems and types
Each of the dike groups has its own types of dike. These types differ in how they came about, in their structure, and in their use. Some of the dikes in the dike groups only work in combination with each other: two or more types of dike that only hold back the water when working in unison, as a dike system.
Sea dikes can usually be spotted at a single glance. From the dike crest, there is often a distant view across the whole area. Sea dikes are stony on the flood defence side; sometimes they resemble a highway due to their asphalt revetment. There is a good reason why these materials are used: sea dikes defend against the tide, which can reach up to the top of the dike twice a day, and whose waves can cause huge impacts. There are regional differences between the sea dikes of the dune area between Hoek van Holland and Den Helder, and the sea dikes of the marine clay areas in the north and southwest of the Netherlands.
Example of dike system and dike type from the sea dikes
If you look carefully at the dike map, you will see the winding, elongated dikes that follow the rivers of the Netherlands. The winter dikes are the most recognizable kind of river dikes, and they have been regularly moved and raised over the course of time. They are often the main local routes through the countryside. Seen from the dike, the winding river is always visible from one side, sometimes at a distance, and sometimes directly next to the dike. The dike winds through dike villages, past former breach holes, orchards, and agricultural areas. On the inner side, the river dikes are often reinforced by a support berm, meant to offer counter-pressure against the prolonged flooding.
Example of a dike type from the river dikes
The low-lying Netherlands consists largely of polders: contiguous areas where the water is artificially managed. If the water is not pumped out, then the polder will be flooded. Dikes play a crucial role in water management in the polder. The origin of polders may lie in the exploitation of the peat lands, the reclaiming of lakes, or the revetment and diking of individual parcels of land or groups of these, with more and dikes being dug and connected. Polder formation occurred in the coastal landscape, the river landscape, and the peat land; many current polder dikes were originally river dikes or sea dikes.
Example polder dike.
The dike group known as ‘meerdijken’ (lake dikes) consists of two dike types: lake dikes of the old land, and lake dikes of the new land. The lake dike group owes its existence to the closing of former inlets by means of the Zuiderzee Works and the Delta Works. The lake dike separates the land from a lake, in places where a lake was formed by the closing off of the sea. In many cases, these are former sea dikes that now hold back water from a lake, instead of water from the sea. Yet in the former Zuiderzee, which is today’s IJsselmeer, large land reclamation projects were undertaken. New lake dikes were built around these areas, and these new dikes protect reclaimed land areas such as the Noordoostpolder from the lake water.
Example lake dikes.
Canal dikes lie along canals: constructed waterways with a controlled water level. These canals and canal dikes are often upright, and cross through different landscapes. In order to regulate the water in the canal, interesting flood defence artificial structures have often been built at the intersections with rivers or polders.
Example canal dike.
Defence Line Dikes
In the Netherlands, a number of unique military defence systems have been built, in which the water was the ally: the weapon that would bring the enemy to a standstill. With the waterlines, use was consistently made of the specific local terrain conditions, and the existing watercourses and dikes. For this reason, not every waterline was the same, but there are certainly similarities.
Example of dike system and dike type from the Defence Line Dikes group
Dams and storm surge barriers
Dams and storm surge barriers form a special group within the dike systems. Dams protect and dike the hinterland from water, but with an important difference: a dam lies between two bodies of water. Unlike dikes, dams therefore have a two-sided flood defence profile. Because of dams’ similarity to conventional dikes, they are often still called dikes, as is the case with the Afsluitdijk< and the Houtribdijk.
Example closed dam
After having temporarily served as flood defence barriers, emergency dikes are removed. Traditionally, emergency dikes were constructed from material that is locally available. This consisted mainly of sediment and vegetation residues, meaning that emergency dikes in different areas could have different forms and different construction methods. Later, emergency dikes were built in a modular and demountable way: they consisted of stackable and reusable parts, such as sandbags. Modern emergency dikes do not need to be stacked, but are put into position mechanically.