Dried up dune valleys recovering

24/01/2006 14:00

In the last ten years, water companies that obtain their water from the dunes have been taking measures to prevent the drying up of dune areas by the extraction of drinking water. The policy to restore these dried up areas seems to have had an effect: in areas where these measures were implemented the variety of species has increased and more plant species can be found which are characteristic of wet dune valleys.

Water extraction and evaporation drying up dunes

Dutch water companies starting pumping up drinking water from the dunes in the second half of the nineteenth century. This led to a fall in groundwater levels in these areas. In many places vegetation and the corresponding plant species of the originally wet dune valleys disappeared. The planting of wooded areas in the dunes also resulted in the drying up process, as this led to an increase in evaporation.

Share of wet dune species
Share of wet dune species

Bringing water to the dunes

To compensate for the deficiency of groundwater, in 1940 water was transported from elsewhere to the dunes for the first time. This process is called surface infiltration. In the dune area Berkheide near Katwijk on the North Sea Coast, polder drainage water (boezemwater) was used to infiltrate the dunes for the first time. Other areas were later infiltrated with river water. Around 1960 this method was being used on a wide scale. 
The purpose of these measures was not to rewet the dune areas, but to use the dunes as a filter to make drinking water. This infiltration only led to local rewetting.

Anti-drying up measures

Since 1995 dune water companies have been taking special measures to stop the dunes from  drying up, among other things by extracting less water, levelling dunes to the level of the groundwater and filling in extraction canals and infiltration lakes. In dune areas where these measures have been implemented the share of plant species that are characteristic for wet dune valleys has increased. Examples are floating pennywort and water mint.
Because the weather has been wetter than average in recent years, the number of species of plants characteristic for wet dunes has also increased in areas where restoration measures have not been implemented, though to a lesser extent.

Variety of species
Variety of species

Increase in species

In areas where the measures have been taken to restore groundwater levels the average number of species has increased. Outside these areas the variety of species remains constant. A larger variety of species usually means a higher natural value.

Lodewijk van Duuren and Mark van Veen