The Watermachine: multifunctional area for flood protection and improved water quality - Kristalbad, Enschede

Enschede and Hengelo face flood/drought risk, water-quality challenges and biodiversity-conservation needs, all intensifying with climate change. Floods in 2010 and 2013 flooded tunnels, forced highway/road detours and caused major basement damage. Historically flood water was discharged rapidly via the Twente canal, but rising summer drought, harming farmers and natural areas, now favours retention. The area must also meet Water Framework Directive water-quality requirements, and Kristalbad, one of the last green corridors between the two cities and part of the Dutch ecological network, is important for species migration.

Redevelop Kristalbad multi-functionally: provide water storage capacity for cloudbursts and intense rainfall to protect nearby cities and transport infrastructure, ecologically purify stored water (enabling agricultural reuse to address drought), develop the area's ecological connecting-zone role, and add recreational use while improving landscape quality.

The Swedish-developed 'Watermachine' concept was applied: Kristalbad is divided into interconnected compartments periodically filled from the Elsebeek River, rainfall and a wastewater treatment plant, holding a total storage capacity of 187,000 m3 to keep floodwater out of Hengelo and Enschede during extreme rainfall while also buffering drought impacts on crops, farmland and habitats. Water flows through the compartments, which use varying elevations, over about four hours back to the Elsebeek River, purified naturally via light, air and vegetation processes before reuse for groundwater recharge and recreation. Ecological corridors and habitat-improvement measures (e.g. breeding sites) support the Dutch ecological network's connectivity and local biodiversity.

Total redevelopment cost was about 6 million EUR (research, planning, design, communication and Watermachine/recreation-facility construction, excluding land-purchase costs), funded by national, provincial and local government plus national subsidies. Benefits include avoided flood-damage costs and avoided costs of alternative technological water-purification solutions, good-quality water availability in dry periods, recreational use by citizens and tourists, and biodiversity gains -- more than 150 different water-bird species have been recorded in the area.

Success stemmed from sustained involvement of local, regional and national policymakers from the outset, which secured formal approval and permissions, and from strong social support driven by recreational benefits for residents and tourists. A limiting factor was that subsidy applications carried very strict deadlines, forcing the planning process to move much faster than ideal.