Increasing resilience to floods in the city of Leuven The flooding of the Dyle River in the city of Leuven has always been an issue as the naturally-occurring steep slopes and historical deforestation upstream of Leuven easily lead to rapid increases in flow rate and water level during high precipitation. These floods occurred after heavy rainfall or after sudden thaws following cold winters, resulting in the rivers overflowing. The most extreme flooding event in its recorded history took place in 1891, which led to a third of the city being flooded, and it remains a reference point for the river’s destructive potential. Since then, flooding events (e.g. in March 1947 leading to extensive flooding in the upstream municipality) have remained a regular occurrence and prompted a number of interventions. In the 1970s, the idea to protect the city of Leuven began with the design of traditional hydraulic solutions, in particular a large flood reservoir in Neerijse valley upstream of Leuven. The poor water quality and the agricultural land use (still very important in that period) made it a requirement that the flood reservoir would not take up more space than was absolutely necessary. During the design period of this traditional hydraulic solution, growing environmental awareness led Leuven to explore more nature-based solutions that take the ecological health and landscape value of the river valley into consideration (La Rivière 2014). Using new modelling software and taking into account the ecological requirements, the protection measures were tested, yielding successful results. The tested measures included a controlled flood reservoir in Egenhoven and natural, uncontrolled flood zones in the Neerijse valley (La Rivière 2014.). In this new approach, instead implementing a hard engineered solution with artificial flood reservoirs, the natural processes has been restored resulting in “wet” valley floors along the River Dyle upstream of Leuven. Infrastructure works are kept to a minimum and are intended to 'guide' the river rather than contain it (La Rivière 2014). In addition to the provision of areas to store water upstream of Leuven, it may be possible to slowly enhance the capacity of the channel network within the city over the years, providing that there is sufficient support within Leuven. Although the capacity enhancements will be relatively small, when these are coupled with flood resistant and resilient constructions, they will help to reduce the amount of storage required upstream. In the EU project Flood Resilient City (FRC), the Flanders Environment Agency implemented a number of measures to enhance the capacity of the channel network within the city. The existing quay-walls were improved to maintain the discharge capacity in the city centre. This was done in close contact with the riparian owners. In that way they became more aware of the river flowing next to or close to their houses. At one location it was possible to build a terrace alongside the river and a small park for people to enjoy. During high water the steps can flood. This increases the capacity for the river in the city centre. Additionally the terrace helps to make more people in Leuven aware that the Dijle is a living river, and that there is an ongoing threat of flooding (Source: http://www.floodresiliencity.eu). Terraces alongside the River Dyle in the city of Leuven. Photo: @Flemish Environment Agency |
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Flemish Environment Agency should be Flanders Environment Agency