Measures

What measures are needed to store extra water termporarily in De Onlanden in the future, so that flooding can be prevented in extreme weather conditions? We have mapped this out. 

Planning area and measures map

What measures are needed to store extra water temporarily in De Onlanden in the future? How can flooding be prevented in extreme weather conditions? We have mapped this out. 

A number of important decisions were made during the expansion of the balancing lake De Onlanden: 

  • More space for water
    The water level at peak load will rise from +0.15 metres to +0.18 metres NAP. This is because the planning area has become slightly smaller. As a result, the water level may rise by 3 centimetres.
  • Relocation to Hooiweg
    The boundary of the area will be relocated to Hooiweg. This means that no new embankment will be needed along lake Leekstermeer. This is better for the tranquility of the nature reserve.
  • New and modified weirs 
    There will be two new weirs will at Hooiweg. The existing Doolhof weir will also be modified. The fixed thresholds at lake Leekstermeer will remain as they are.
  • Raising embankments
    The existing embankments in the area will be raised. This will keep the area safe during high water levels. 

Nature conservation measures

Measures are also taken to improve nature as part of the expansion of the balancing lake. This is good for plants, animals, and the landscape.

  • More marshland
    Turfing is carried out and ditches are widened.
    This will create more marshland, which is good for bird species such as the bittern.
  • Higher water level
    A higher water level will result in more waterlogging, which is good for marsh plants and animals. A separate decision will be made on raising the water level.
  • Safety for animals
    Refuge mounds will be created. Animals can go there when the water is high.
  • Keeping more water in the area
    Some ditches are being filled in (closed). This helps to raise the groundwater level and keep more seepage water in the area. 

Additional measures

  • The Zanddijk pumping station will have increased pumping capacity. Other pumping stations are also modified.
  • Buildings on Roderwolderweg, Moleneind, and De Bommelier are protected against flooding.
  • Roads such as Woudrustlaan, Roderwolderdijk, Drentsedijk, and access roads to TenneT and Gasunie will be raised.
  • The concrete path on the Weeringse dyke will be raised to NAP +0.50 m and will function as an embankment.
  • The Sandebuur pumping station is located outside the project area, but will also be modified because it drains water to De Onlanden.