Leiden must become a better “sponge” against floods

To make Leiden climate resilient, space for water is needed. (Photo: Louis Smit)

As one of the most densely built cities, the sponge effect of Leiden must improve so that the city can absorb enough rainwater. It is essential that the water sinks into the ground and does not immediately disappear into the ditch or sewer and thus cause inconvenience. Permeable paving, more greenery, and fewer tiles in the garden enhance this sponge effect.

In the coming years, an area equivalent to about eighty football fields in the city will be prepared for wetter winters and extreme rainfall.

These are the answers of the Rhineland Water Board and the municipality of Leiden to Omrup Slotelstad’s questions about how to arm Leiden against the consequences of climate change. As we showed recently Climate scenarios From KNMI and in international forecasts, the Netherlands will increasingly experience warmer and drier summers and wetter winters. Extreme rainfall events also occur regularly and these extreme weather events are increasing.

fossil
Due to the great challenge of housing construction, Leiden is becoming more dense and compact. This means that there is a risk of not having space for water. “We are looking for ways to store additional water, which can also be done by collecting rainwater on roofs or through ditches, for example. In addition, we are looking for space to add trees and greenery for infiltration, but also for cooling on summer days.” Al-Hara,” says the water board and the municipality, which are working together to create a water space in Leiden.

According to them, we should mainly look at opportunities to design public spaces smarter and better using less stone, more green space and additional open water. Public space includes sidewalks, streets, squares, and parks. An example of a completed redevelopment project mentioned is Lakenpark, and an example of a future redevelopment project is Jan van Houtkade.

Eighty football fields
Activities are combined during design. “In conjunction with the planned sanitation works, the streets are being renovated and made greener. In the coming years, an area equivalent to about eighty city football fields will be prepared for the future in this way. The first neighborhoods have now been created or are under construction: Houtkwartier, Noorderkwartier East and Gasthuiswijk “, according to the municipality of Leiden and the Rhineland Water Board.

This year, a separate two-pipe sewerage system was installed in Gasthuiswijk. The second pipe drains rainwater into the newly dug water. In addition, parking spaces have been grouped, providing more space for green spaces.

Green road
The so-called green-blue framework also plays a role in the city’s adaptation to a changing climate. “This spatial concept consists of the Single Park and the second green ring, with links between them. This means that everyone has a green path a short distance from their home to walk, exercise, go to the park or to one of the countryside surrounding Leiden. On a day In hot summer, these green places provide cooling,” according to the Water Board and the municipality.

Individuals can also do a lot. This way they can green their roofs. There is a support system for this. They can also remove tiles from their gardens. According to the sustainability index of energy supplier Vattenfall, more than half of the total park area in the province of South Holland is covered with tiles.

Flood risks
To what extent can or should a city like Leiden arm itself against the surplus of water that comes not from above but from the sides, from rivers, canals or the sea? Answer: “It is good for the municipality to be aware of the flood risk. The vast majority of Leiden is above the NAP level (Normal Amsterdam Level). Some reclaimed areas, such as Merenwijk, are at a fairly low level and are protected by barriers which are strongly maintained by the Water Board .

Leiden Sustainability Community Policy Area