Enschede: Rainwater as a resource

In 1994, the planning and development of the residential area Ruwenbos in Enschede began. The municipality wanted to create a sustainable district in all aspects, especially in water and greenery, which were fully involved in the property development and which had to follow sustainable DUBO-keur® building principles.

The integrated planning approach was a new thing for the municipality of Enschede. Because of this, there was total plan freedom for the water and urban development experts in charge of the process. The result was a ‘finger plan’ with blue-green fingers (ecological zones) folding into grey fingers (streets). The 400 new houses in Ruwenbos were designed as a garden city with respect to existing trees and slopes.

All runoff water from paved areas and roofs in Ruwenbos is transported via open gutters to a separated system of three ‘wadis’ traversing the area. A wadi is a u-shaped green ditch with a drainage element underneath that holds rainwater and allows it to seep into the ground. The water in the wadis is stored to a level of approximately 0,25 metres, a level designed to be exceeded only every two years. Overflow is discharged to a retention pond south of the area, which is used for recreational purposes by the residents.

The wadis of Ruwenbos were the first to be constructed in the Netherlands. Consequently, at the time of construction, there was little experience with the design and performance of wadis. This resulted in over-sizing by 300 %. However, the system functions well and is appreciated by the residents. The only problem experienced is clogging due to the presence of leaves in the wadis, which delay the infiltration process. So from time to time, the residents have to remove leaves manually.

Involvement of residents

A sustainable water system with ecological functions like the one in Ruwenbos is sensitive to pollution. This means it is undesirable for inhabitants to wash their cars on the street or use herbicides that pollute the wadis by means of runoff water. As the municipality cannot pass legislation about behaviour, involvement of local residents has been important.
Information meetings in small groups have occurred to answer questions about the wadi system and encourage dialogue about acceptable behaviour. The stimulation of social cohesion was important to the district designers as the maximum performance of the system requires that residents act sustainably. A municipal water manager puts it this way: “Only if sustainability is a personal conviction, will it succeed.”

Organisation

During the planning, development, construction and maintenance of Ruwenbos, the municipality of Enschede has gained a lot of valuable experience. Construction of the landscape based stormwater drainage system along with the building of a new housing estate demanded special attention. As did the issues of drainage during the construction phase, loss of infiltration capacity due to construction activities, the policy for gritting icy roads, maintenance of the drainpipes, etc. The costs for the construction of the wadi system per square metre are less than the costs of a traditional sewer system. However, costs for maintenance are higher than a normal system.