Nearly 275,000 addresses in the Netherlands lie in unprotected areas
A new national map (PDF) developed by HKV in cooperation with the Dutch Association of Insurers shows where flood defences, such as dykes, do not safeguard buildings against high water. The map calls these places unprotected areas. This does not mean naturally high-lying land, which does not need a defence. Nearly 275,000 homes and other units lie in unprotected areas, and standard building and contents insurance does not cover flood damage there. The map also shows how deep the water could get during floods of different severity.
What is an unprotected area?
An unprotected area is the strip of land between a flood defence and the water that the defence holds back. The land behind the defence is a protected area. Naturally high-lying land along the main water system lies above the water levels that flood defences are designed for, so the map does not count it. Areas without any flood defence, such as parts of the Limburg hills, are also left out. Standard policies already cover overflowing water there.
How many units are affected?
The map counts 274,685 units in unprotected areas. A unit is a home or other space with its own address in the national register, and one building can hold several units. Along the large rivers, lakes and coast, 125,375 units lie in unprotected areas. Along regional canals, rivers and streams, the number is 149,540. A total of 230 units fall in both groups. Most units are homes.
How deep could the water get?
Along the large rivers, lakes and coast, depths vary strongly depending on how rare the flood is. In a flood that happens once every 10 years, about 89 percent of units stay dry. In a flood once every 10,000 years, just over half are flooded, and more than 11 percent face water deeper than one metre. Along regional waterways, depths are much smaller. The scenarios there only go up to a flood once every 1,000 years, and even then 98 percent of units stay dry. In most cases the water stays below 0.2 metres. The depths show water at ground level and do not include measures on buildings.
How does climate change play a role?
Climate change is expected to make flooding in unprotected areas worse, mainly in the long term. Along the large rivers, lakes and coast, rising sea levels and higher river discharges raise water levels. In the coming decades the change stays limited. In the second half of this century, the rise can reach several decimetres to more than one metre, depending on the climate scenario. Along regional waterways, extreme rainfall is the main driver. Water boards, the regional authorities that manage water, actively control levels in canals, so depths are expected to stay limited, although floods may become more frequent. Regional rivers and streams may flood both more often and deeper. The map itself shows the current situation, not future climate scenarios.
How can the map be used?
The map gives a first indication at national scale, for example to determine cover options and to estimate the size of the area. It has no legal status and relies on public data of varying detail. For decisions on a single property, the official records of the water board remain leading. In a web viewer, users can click a location to see its status and expected water depths. The authors also ask whether it is logical, purely from a flood risk view, to exclude unprotected areas along regional waterways from cover, given their limited depths.