RIVER WIDENING OF OVERDIEPSE POLDER

During periods of extremely high water, the river Bergsche Maas could threaten villages and cities located along the river. Widening the river at the Overdiepse Polder near Waspik allows more water to flow through the river during periods of high water. As part of the Room for the River programme, the dyke has been lowered so that it will not present a barrier to the drainage of excess water. At the same time, the constructed so-called ‘terps’ (dwelling mounds) help maintain the important functions for housing, work, agriculture and livestock farming.

From marshland to terp plan

For more than 750 years, the Overdiepse Polder consisted largely of marshland and peat bogs. During the St. Elisabeth flood in 1421, the area was completely inundated. Around 1900, the Bergsche Maas was excavated to deal with the constant flooding in the region around the city of Den Bosch. This gave the area its current form, with the Bergsche Maas in the north and the Oude Maasje river in the south. The area had always been inundated during wintertime, until a safety lock was built in the Oude Maasje during World War II. This safety-lock ensured that the polder remained dry year-round. In the 1970s, the first farms were built in the polder.  

The floods of 1993 and 1995 showed, however, that the Bergsche Maas did not have enough capacity to drain extreme high water levels. In order to make more room for the river, the dyke at the Overdiepse Polder was lowered to allow the area to store water during high water situations. The project was completed in 2015.

Layout of the Overdiepse Polder

Three interrelated measures have been implemented to make the Overdiepse Polder suitable for the drainage of river water:

  1. The dyke on the north bank of the Bergsche Maas has been lowered. This allows river water to flow into the polder during high peak water
  2. On the south side, a new winter dyke has been built to hold back the water flowing in from the river and protect the hinterland
  3. Eight dwelling mounds (terps) have been built against the new dyke, so farmers living in the Overdiepse Polder can stay high and dry

Extra space is provided for nature and recreation, in addition to the river and agriculture. The sand dredged to build the terps and the new dyke left a 5.5 hectare pond called the Westplas, which has an ecological function.

 

Terp plan for future-proof housing and employment

By removing a polder's flood barriers usually the area is no longer suitable for human activities such as housing or farming. But in the case of the Overdiepse Polder, farmers are still able to live and work due to the plan created by the Overdiepse Polder Interests Association, in which the farmers designed a proposal for the construction of dwelling mounts (so called terps). This terp plan was elaborated together with the Province of North Brabant, and as such included in the Room for the River programme. As part of the project the original farms have all been demolished, and consequently some of the families had to move out of polder due to the project. New terp farms were built in collaboration with the eight farmers who chose to continue working in the polder. These terps will keep the families and their animals safe and dry during high water situations. All eight terps have been completed between 2013 and 2015.   

Water innovation prize and international attention.

In 2012, the terp plan submitted by the Overdiepse Polder Interests Association has won the Water Innovation Prize for the category Special Interest Groups & Private Initiatives. The jury praised the innovative application of a centuries-old idea, as well as the good cooperation between the local governments (regional water authorities, municipalities and provincies). “The project shows that the inventiveness inherent in society can be utilised to a good end, and that citizen participation led to this breakthrough.” The approach used for the Overdiepse Polder has also drawn considerable attention from abroad. Delegations from around the world come to see how citizens’ ideas are applied in this far-reaching partnership. Without the farmers, the Overdiepse Polder would have become a nature reserve, and all families of the area would have had to find a new place to live. Thanks to their own idea, eight families could continue their agricultural activities in the polder. 

Safety for more than four million people

Statistics indicate that the river will flood the Overdiepse Polder once every 25 years. The water catchment created by the Room for the River measure will lower the flood levels in the Bergsche Maas by 27 centimetres, which will protect the residents of cities upstream such as the cities Waalwijk and Den Bosch from flooding.

RIVER WIDENING OF OVERDIEPSE POLDER IN FACTS AND FIGURES

The measures to widen the river in the Overdiepse Polder gave the Bergsche Maas more space and lowered the level of the river by 27 centimetres. They also preserved the area for agriculture, both today and in the future, thanks to a terp plan created by the residents and entrepreneurs themselves. Old farms and agricultural buildings are demolished. Several of the farmers have continued their activities on eight new terps.

 

Activities

  • construction of eight new terps
  • dredging 5.5 hectares of sand for the Westplas
  • excavating 500.000 m3 of sand to lower a 6-km stretch of the dyke.

Effect

  • lower the water level by 27 cm at Waspik

Partners