Blauwe Aderplan Baarle-Nassau

As a result of climate change, existing sewer systems are often overburdened by heavier rainfall, causing flooding and damage. Water needs to be treated, buffered and discharged as efficiently as possible. Iv has, therefore, drawn up a rainwater management plan for the municipalities of Baarle-Nassau and Baarle-Hertog. The plan will serve as a blueprint for all future sewerage system projects, redesigns and building plans.

Iv conducted various field inventories and identified specific area characteristics, opportunities and risks for incorporating the future rainwater management system. Following the inventory phase, Iv prepared a draft design for optimising and redistributing rainwater using a ‘blauwe ader’ pipeline (part of the ‘blauwe aderplan’ that entails spatial modifications to surface water and associated watercourses) . The results of this approach can be found in the news item below: Baarle-Nassau and Baarle-Hertog to achieve a future-proof rainwater management system.

The location of the municipality is unique. The Belgian part consists of dozens of exclaves, which in turn surround Dutch territory. The exclaves often cross roads and even buildings. Although the two municipalities work closely together on sewerage and water management, laws and regulations differ. The Dutch municipality of Baarle Nassau and the Belgian municipality of Baarle Hertog were closely involved in the project from the beginning. When drawing up the rainwater management plan, water buffering on private land in the Belgian parts was taken into account. In particular, the central area of both municipalities has a high concentration of paved surfaces and relatively few options for collecting or draining water. The current system cannot cope adequately with heavy rainfall.

Another challenge is that groundwater is relatively low, averaging about 1.5 to 2 metres below ground level. Only in the Loveren area do water levels rise to just below ground level. This low water level can lead to drought during dry periods (in the summer months) but also provides opportunities to buffer water during peak rainfall periods.

The plan drawn up by Iv ensures a balance between draining extreme rainfall and tackling drought in the summer months. Disconnection prevents the mixing of rainwater with dirty water, reducing the load on treatment. The ‘blauwe ader’ pipeline drains water from flooded locations towards the outlying area, mainly using watercourses. Due to the low groundwater level, these watercourses are dry for much of the year. There is room here to store water on a large scale and allow it to infiltrate slowly. The ‘blauwe ader’ is partly executed as an infiltration pipe so that during average rainfall, most rainwater infiltrates locally into the soil. This also combats desiccation within the existing built-up areas. The rainwater management plan considers future building plans and development projects, among other things, and sizing rainwater pipes to the expected coverage of paved surfaces in the future. Besides the primary system (blauwe ader), the plan also consists of marked areas where local measures are taken, such as wadis and smaller measures on private property. By designating some smaller areas with a drainage location, rainwater can be managed efficiently, taking local conditions into account.