The use of ecological information in the selection of quality objectives for river conservation and restoration in Flanders (Belgium)

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Abstract
Due to the intensive use of freshwater resources, the ecological quality of catchments and watercourses in Flanders has been considerably lowered. Watercourses with natural stream characteristics and/or vulnerable species are rare and are quite often isolated headwaters. To restore the natural variety of river types and vulnerable species within Flanders and to restore the network within the catchments, there is an urgent need for river restoration programmes. To work efficiently, priority levels for catchment areas and quality objectives for watercourses should be designated. Our task was to develop a policy map based on objective ecological knowledge, taking into account the legal land designation and nature conservation. Based on a large field survey, which consisted of gathering ecological information of watercourses throughout Flanders, a typology of rivers with reference framework was devised. Secondly, a priority map at a catchment level for integrated water management planning was developed. Three priority levels were distinguished based on the current ecological quality, the (legal) land designation, and the occurring river types within each catchment area. Thirdly, quality objectives were assigned to the priority zone watercourses. Four classes are selected: class I, in which nature conservation is the principal objective; class II, in which nature conservation should become the principal objective; class III, where nature conservation is an important subsidiary function; and class IV, in which most watercourses have a connecting function allowing migration of vulnerable species. The goals for the four classes were linked to different quality requirements. The methodology developed for construction of a priority map and for assignment of water quality objectives to priority watercourses is explained in detail. An ecological evaluation of the sub-catchments of the river Nete and the river Dyle is used to discuss the selection of priority zones. Five sub-catchments are described in more detail to illustrate the assignment of quality objectives to priority zone watercourses.