New Maassluis street is entirely rain-proof
Gijsbert Dirkzwagerstraat is a new street amidst other houses in the small blue-collar neighbourhood called ’t Stort, located in Maassluis city centre. In this street, 27 energy-efficient social rental homes have been constructed, specifically intended for young families. The outdoor area is the first street in Maassluis to be entirely “rain-proof”: the entire street is aimed at retaining water and capable of coping with 60-mm torrential rain.
What has prompted the construction of this new street?
’t Stort is a densely developed, pre-war blue-collar neighbourhood in the Kapelpolder industrial estate, adjacent to the Maassluis historic city centre. Because of its dense development, the neighbourhood is prone to waterlogging during torrential rain. In addition, the expansive black roofs of the industrial buildings exacerbate heat stress in the area. Gijsbert Dirkzwagerstraat used to accommodate industrial facilities. The municipal plan to re-develop this area into a residential street opened up opportunities to rain-proof the street.
How has the municipality set about the project?
In 2018, Maassluis joined Rainproof. This network intends to rain-proof cities in order to cope with the severe downpours that are occurring increasingly frequently. One of the measures used to this end is increasing the sponge effect of the soil. This boosts the rainwater retention capacity of the soil, similar to a sponge absorbing water. Maassluis wants to implement such measures and has set about the development of Gijsbert Dirkzwagerstraat as follows:
- The authorities have expanded and adapted the rainwater sewer underneath the new street. Now, rainwater only enters the sewer once the greenery and the soil can no longer absorb any water. The sewer has been adapted to have water flow in two directions. This enables larger volumes of water to be drained simultaneously to various buffers for temporary storage. The rainwater sewer is also connected to a large water buffer in the port outside the plan area.
- The authorities are encouraging the residents of the new street to contribute to rain-proofing the city. They can do so by keeping their gardens green and by collecting and reusing water. For example, the municipal executive has presented the residents with a beautiful plant for their gardens, and the terms of their tenancy agreements stipulate that a minimum of two-thirds of the garden must be green.
Furthermore, the municipality is investing additional sums in greening the city, and aims to interconnect different water buffers wherever possible.
What results have been achieved?
This approach has turned Gijsbert Dirkzwagerstraat into a green street capable of infiltrating some 7 mm of water during rainfall. At least two-thirds of every garden is green, and all the sheds have a green rooftop and a rain barrel. The street is designed in such a way as to easily cope with downpours up to 60 mm. The street has already seen several heavy showers and coped well with all of them.
A special feature of this project is the combination of public and private. The municipality is investing in greening and rain-proofing the street, whilst concurrently encouraging residents to rain-proof their gardens. As a matter of fact, this is not entirely non-committal: the tenancy agreement stipulates that gardens may be paved up to a maximum of one-third.
Lessons to be learned from the project
Maassluis has learned a great deal from this project. These are the main lessons to be learned:
- In many rainwater sewers, water flows in only one direction, which is a shame. A bi-directional sewer can drain twice as much water.
- Greenery is cheaper than sewers. Sewers are quite expensive, especially if the soil is polluted. For that reason, a multi-disciplinary approach to the outdoors, based on natural cycles, would be preferable: focus attention on the maintenance of greenery and save on the construction of sewers.
- Inform residents at the earliest stage possible on how they can green their gardens. Most residents are willing to green, but many do not know how.
- Lay out a section of the garden beforehand and provide good-quality garden mould. Contractors often supply soil that is unsuitable for gardens, which later on needs to be replaced at great cost. This extends to both pavement subsoil and planting subsoil.
- Ensure that rules and regulations are properly set down and pre-arrange their enforcement.
- Provide additional supervision of outdoor areas when residents have just moved in and are laying out their gardens. For example, prevent residents from depositing heaps of sand in lower-level green spaces. The sand will compact the soil and compromise its water-permeability. Other infiltrating facilities, such as porous pavement, are also prone to clogging and silting up if covered or bordered by heaps of sand.