In Belgium, the case study site is the Scheldt river basin. It has a total area of 36,416 sq. km. The Scheldt river, which is 350 km long, originates in northern France and flows through the Walloon region (Belgium), the Flemish region (Belgium), and the Netherlands. The Scheldt basin is a highly urbanized and heavily built-up area, which covers 13% of the total area (Scaldit report). In the MERLIN project, we only focused on the upper Scheldt which is located in the province of East Flanders and in particular the Zwalm river basin.
The Zwalm river basin is situated in the south-western part of Flanders (Belgium), has a total catchment area of 117 sq. km (Dedecker, Goethals, & De Pauw, 2002), and is dominated by sandy-loam (Pauwels, Verhoest, & De Troch, 2002). Annual rainfall ranges between 700-1000 mm (Huygens, Verhoeven, & De Sutter, 2000). Climatic conditions can be categorized as humid temperate (Pauwels et al., 2002; Troch, De Troch, & Brutsaert, 1993). Despite the Flanders region being generally flat, the topography of the basin is best described as rolling hills, mild slopes and altitudinal differences of up to 150 m (Goethals, Dedecker, Gabriels, & de Pauw, 2003; Pauwels et al., 2002). These attributes have strong amenity values and offer opportunities for recreation and tourism. The land use within the basin is mainly agriculture (arable crops and pasture) with about 10% urban land cover (Goethals et al., 2003; Pauwels et al., 2002). The Zwalm river forms the main stem of the catchment and has a length of 22 km before flowing into the larger river Scheldt (Dedecker et al., 2005; Huygens et al., 2000). At the confluence, the Zwalm river has an average discharge of about 1 m3.s-1 with a very irregular regime (i.e. minimum and maximum flows ranging from below 0.3 m3.s-1 during summer to 4.7 m3.s-1 during the rainy periods, respectively) (Dedecker et al., 2002).
Despite the recognition of the Zwalm basin as a biodiverse region in Flanders, stream conditions within the basin are not without issues. For instance, soil erosion is one of the most significant processes which results in considerable transport of sediments throughout the river system (Goethals et al., 2003). The presence of a weir impedes migration of several organisms (e.g. eel). Many parts of the river are still contaminated by diffuse pollution from agricultural land and urban wastewater in which about 40% of the untreated wastewaters are directly discharged into the streams (Boets et al., 2021; Goethals et al., 2003).
Text obtained from Forio et al., 2020
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