Balancing lake and groundwater
Questions and Answers on Frequently Asked Questions: Balancing lake and Groundwater – additional balancing lake De Onlanden.
Why does the groundwater sometimes rise near houses and farmland?
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. Dewatering takes place underground, for example with drainage pipes. Both are important to proper water drainage.
The owner of a plot is responsible for drainage on their own property. The water authority is responsible for the larger water system. In the event of flooding in villages or towns, the local council is the point of contact.
Why are there sometimes problems with drainage?
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.
What is the difference between groundwater and surface water?
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.
Where can I find information about water levels?
The Noorderzijlvest Water Authority measures groundwater levels with monitoring wells. Anyone can view information about water levels online:
- WAM Portal (Dutch only)0: up-to-date data on groundwater, surface water, pumping stations, and weirs.
- Geoweb (Dutch only):map showing watercourses, pumping stations, weirs, and water-level regulation areas.
- AHN Viewer (Dutch only): elevation map of the entire Netherlands.
This information is public and accessible to everyone.
What measures are taken to prevent problems?
In areas where the water level may rise slightly temporarily, the water authority is taking measures. These have been discussed with residents during home visits. Examples of measures include:
- Additional pumps to remove water
- Build embankments around houses
- Raise the ground level and drain water differently
- Drain water to another area
- Widen ditches and dig deeper
Will there be more groundwater measuring points?
No. The current network of monitoring wells is sufficient to measure groundwater in the area.
Is your question not listed?
Please let us know at optimalisatieonlanden@noorderzijlvest.nl
No rights can be derived from the answers.
Does the additional space in the balancing lake impact groundwater?
The flood embankments in De Onlanden are being raised so that extra water can be stored temporarily during extreme weater, on average once every 25 years for about 5 to 10 days. Afterwards, the water will flow in a controlled manner toward the sea.
Studies have demonstrated that this has no lasting effect on the groundwater level. In some areas, the water level may rise slightly for a short time, but the water authority takes measures in those areas to prevent any inconvenience.
When the additional balancing lake is used, which only occurs during extreme rainfall, the ground is already saturated from the heavy rain. In that case, the water level rises everywhere, including outside De Onlanden. During droughts, it actually drops. A hydrogeological analysis shows that changes in water levels are limited and temporary, with no structural consequences for surrounding residential areas.