The water system in de Grotestraat is attuned to the naturally present considerable relief of more than thirty metres between the Sallandse Heuvelrug and the Reggedal. On the high part of the street, the water is disconnected from the pavement at the growing places of the trees. This water is buffered in rainwater crates underneath the plants, where it eventually evaporates through the foliage of the trees. On the low part of the street is a twelve-meter-wide wadi (bioswale) designed with a length of 120 meters and a storage capacity of 750 m3. In extreme downpours, the wadi captures the run-off from the water. Rainwater from the mountain is slowed down and drained into the stream course of the river Regge. By linking attractive living space to the climate wadi, double use is created for both the water system and users of the public space.

The redevelopment of the Grotestraat has resulted in a friendly and hospitable city centre on the border of the Sallandse Heuvelrug and the Reggedal. Existing restaurants and cafes along the new wadi have been given space in addition to existing terraces directly adjacent to the wadi. Nijverdal is back on the map with its green oasis in the heart of the city centre. The recent measurements of visitors to Nijverdal in the high season show a sharp increase.

OKRA has won the Water Resilient Cities Award 2019 for ‘The best sustainable drainage system for rainwater in an urban environment’ for the redevelopment of the Grotestraat. The annual Water Resilient Cities (WRC) award recognises the best projects using Sustainable Drainage Systems (SuDS) in Belgium, France, the Netherlands and the United Kingdom. Sustainable technical solutions for water management, water collection and drainage make the city centre of Nijverdal area climateadaptive, thus resistant to recent climate developments with periods of extreme precipitation and periods of extreme drought and heat in summer.

The landscape qualities of the area on the Sallandse Heuvelrug are visible and experienceable right to the core of Nijverdal, which contributes to an attractive, healthy and liveable city centre. The substantial decrease in motorised traffic has led to more space for pedestrians and cyclists and good facilities for bicycle parking. Existing cafes and restaurants along the climate wadi have been given space for terraces directly adjacent to the wadi. Between the trees, there is also room for public (free) seating and a groundwater controlled water playground has been created in the centre of the wadi. The wadi forms both a spatial centre of gravity and a relaxed and shady place to stay. During the summer period, the Grotestraat is closed to car traffic for a number of days to provide extra space for events and festivities.

Key points were the reuse of high-quality materials and smart design within the framework of the existing underground infrastructure. We did not work with concrete materials, but with natural stone, because it ages better and also because it fits better with the history of Nijverdal. A diverse assortment of plane trees, lime trees, fly pines and larches naturally represent species in the area: ornamental grasses, ferns, perennials and shrubs form the picture. Some ten existing plane trees have been replanted elsewhere in the city.

The redevelopment of the 800-metre-long Grotestraat is distinctive because of its green-blue structure with a climate-adaptive wadi and water-bearing plant pockets around the trees. The revitalisation of the city centre and dealing with climate change go hand in hand in this project. The landscaping qualities of the surrounding area are now visible and experienceable right to the core of Nijverdal. The area covered by the project is 19,200 m2. The street is 800 meters long and 24 meters wide. The surface of the planting areas is 6.000 m2; the storage capacity is 600 m2. The surface of the climate wadi is 1500 m2. The wadi has a storage capacity of approx. 750 m3.

The redevelopment of the Grotestraat has resulted in a friendly and hospitable city centre. Most importantly, the asphalt has been removed from the street, and the area has been set up as a residential area. The substantial decrease in motorised traffic has led to more space for pedestrians and cyclists and excellent facilities for bicycle parking. By linking attractive living space to the climate wadi, double use is created for both the water system and users of the public space.

Sustainable technical solutions for water management, water collection and drainage make the city centre of Nijverdal area climate-adaptive, thus resistant to recent climate developments with periods of extreme precipitation and periods of severe drought and heat in summer. No other place in the Netherlands takes extreme rainfall, drought and heat into account in this way. Nijverdal will soon be used as a textbook example when it comes to storing rainwater in the city.