The rise of the swale

In the past, clean rainwater usually mixed with dirty waste water in the sewers. As a result, relatively clean rainwater was transported unnecessarily to a water treatment plant via pipes. Currently, systems that separate the rainwater from the sewer system are increasingly being considered. Allowing the rainwater to infiltrate into the ground not only prevents the waste of relatively clean water and overloading of the sewer, but it is also good for the groundwater level.

Allowing water to infiltrate instead of discharging it into the sewer system is possible using a swale: a ditch or trench with a water-permeable bottom. Nevertheless, a traditional swale appears not always to work in practice as might be expected from its construction.