Water storage and groundwater

The quays in De Onlanden are being raised so that extra water can be temporarily stored during extreme weather conditions — on average once every 25 years, for around 5 to 10 days. The water will then flow off in a controlled manner towards the sea.

Research shows that this will have no lasting effect on the groundwater level. In some areas, the water level may rise slightly for a short period, but the water authority measures to prevent any nuisance. 

When the extra balancing lake is used balancing lake only in the event of extreme rainfall), the soil is already saturated due to the extreme rainfall.The water levelthen riseseverywhere, including outside De Onlanden. In the event of drought, it actually falls. A geohydrological analysis shows that the changes in water levels are limited and temporary, with no structural consequences for surrounding residential areas.

A higher groundwater level can be caused by:

• A lot of rain
• Poor drainage
• Soil that allows little water to pass through (such as loam)
• Subsidence due to peat.

Drainage is the removal of water via ditches and trenches. Dehydration takes place underground, for example with drainage pipes. Both are important for proper water drainage.

The owner of the plot is responsible for drainage on their own property. The water authority for the larger water system. In the event of flooding in villages or towns, the municipality is the point of contact. 

Drainage is the removal of water via ditches and trenches. In villages, water first flows into ditches or ponds, then into the main water system. In the past, sometimes too little surface water was constructed for new buildings, which meant that water could not drain away during prolonged rainfall. Since the mandatory water assessment was introduced in 2003, more attention has been paid to the construction of water systems in new building projects. 

 

Groundwater is found in the soil and changes due to rain and evaporation. Surface water is water that you can see, such as in ditches and rivers. Sometimes the water in ditches can affect the groundwater, depending on the soil.

The Noorderzijlvest Water Authority measures groundwater levels using monitoring wells. Anyone can view information about water levels online:

• WAM Portal:up-to-date data on groundwater, surface water, pumping stations weirs.
• Geoweb:map showing watercourses, pumping stations, weirs water level areas.
• AHN viewer: elevation map of the entire Netherlands.

This information is public and accessible to everyone.

In areas where the water level may temporarily rise slightly, the water authority is taking water authority . These have been discussed with residents during home visits. Examples of measures include:

• Additional pumps to remove water
• Building quays around houses
• Raise the ground level and drain water differently
• Drain water to another area
• Widen ditches and dig deeper

No. The current network of monitoring wells is sufficient to measure groundwater in the area.