About the Dender basin

With resp. 32.830 and 18.448 inhabitants, Geraardsbergen and Lessines are two small cities along the Dender river. In 2010, both communes were severely hit by an extreme weather event, which affected larger parts of Belgium. Since Geraardsbergen is situated in the Flemish Region and Lessines in Wallonia, they form an interesting case for cross-regional comparison.

The Dender is part of the international Scheldt basin, but the catchment has its own distinctive features. The river has a length of 69 km, half of its basin lies on Flemish territory and the other half in Wallonia (CIW, 2008). Below is an image of the Dender basin.[1]


Figure 1 Dender basin with indication of Geraardsbergen and Lessines (source: Grenzeloze Schelde, 2014)

The main part of the basin is merely accessible for small, recreational vessels (max. 300 ton), but between Aalst and Dendermonde the river can be used for freight transport. As a consequence, the river is categorised as navigable and managed by navigable watercourse managers Waterwegen & Zeekanaal (Flanders) and DGO2 (Wallonia). Its tributary rivers, on the other hand, are controlled by several non-navigable water managers.

The Dender is known as an erratic river and is very sensitive to flooding. The river is highly influenced by precipitation; in dry periods its flow discharge can be very low but once a period of continuous rainfall occurs, it turns into Flanders’ fastest waterway (Milieuboot, 2010).

Since the floods of November 2010, actions have been taken in both parts of the basin in the form of immediate protection measures and longer-term prevention.


About the city Lessines and its flooding problems

Lessines is a municipality in the Province of Hainaut with approximately 18.000 inhabitants. It is located along the Dender and between the municipalities Ath and Geraardsbergen, at about 38 kilometres from the Capital.


Figure 1: Picture of Lessines during 2010 flood. Source: Le Soir.

Lessines is a municipality that is particularly vulnerable to floods. Lessines has been severely hit by the floods of 2010, when more than 1.5 million cubic metres of rain fell in the Lessines area and the Dender left its embankments. The floods of 2010 resulted in severe material damage, approximately 19 million euro in Lessines alone and 95 million euro in the Walloon Region as a whole; one person died during the 2010 floods. In retrospect, the general feeling within the municipality of Lessines with regard to the 2010 event was that Lessines was neither adequately protected from nor prepared to cope with these floods.

 LessinesFigure 1: map of Belgium with indication of Lessines. Source: www.gilkain.be

Changes after the 2010 floods

Following this event, floods were put high on the political agenda. For example, at the level of the city, a working group has been created, which consists of personnel of the city administration, members of the city council and delegates from an organisation of flooded citizens. However, the restricted interest and capacity at city level constitutes a barrier for the effectiveness of this working group.

Furthermore, specific infrastructural measures were taken, such as the dredging of the watercourses, and studies were ordered to examine the creation of a retention basin and dike infrastructure. It is however generally assumed that these measures will not suffice to protect against every future flood.

One of the issues identified during the 2010 floods was the response time for evacuation, that proved to be slow and inadequate. This resulted, amongst others, from the absence of an emergency plan or coordinating body at the level of the City at the time. One point of criticism in this regard, often heard during our interviews, is that the competent authority of the City had not called in the emergency phase, resulting in e.g. delays in response time of the army intervention team and a lack of multidisciplinary coordination.

Thus, a safety cell and emergency planning official have been installed in the years following the flood event. Also, the General Emergency and Intervention Plan is expected to enter into force in 2015, and a Specific Emergency and Intervention Plan for floods is under construction.

Lessines is, to some extent, undertaking efforts for flood prevention. Following the floods of 2010, the City council decided to strictly forbid any type of construction in flood-prone areas, without having made a distinction between low, moderate or high risks. That restriction, however, turned out to be economically unfeasible, and was therefore relaxed. At this point in time, all projects and houses that are being developed in areas with a high flood risk are being refused. In the areas with a moderate to low risk, case-to-case analyses are made by the competent authorities. If deemed necessary, conditions can be laid down in the permit. In this regard, analogue bottlenecks as those identified within the other case studies, e.g. the City of Antwerp, have been found in the Lessines case. For example, there is insufficient follow-up in the field of the implementation of the conditions following the issuance of the permit.

In sum, the floods of 2010 have truly shaken up the quaint City of Lessines. In the wake of the event, several measures along the array of the different strategies set forth by STAR-FLOOD have been adopted and are being implemented. However, as is also confirmed by our respondents, several obstacles still need to be overcome before the FRGA in Lessines can be considered as being truly resilient and appropriate.


[1] Source: Integrated Water Policy Flemish Region, http://www.integraalwaterbeleid.be/nl/bekkens/denderbekken.

Assuralia, ‘Meest getroffen gemeenten overstromingen 2010’, http://www.assuralia.be/fileadmin/content/documents/persberichten/111110_NL_Bijlage-overstromingen-nov2010.pdf, 2011 (accessed at 12/11/2014).

CIW (2008). Het bekkenbeheerplan van het Denderbekken (2008-2013). Integraal waterbeleid in de praktijk. Erembodegem.

Milieuboot (2010). De Dender tussen Ath, Geraardsbergen en Aalst nader bekeken. Nieuwsbrief De Milieuboot 60. Aalst.