ILEE Lunch seminar

Camille Carpentier & Liévin Castelain (Biology): Evaluation of the effectiveness of hydromorphological restoration work carried out 10 years ago on the Bocq (Wallonia, Belgium)

SUMMARY: Thanks to the European LIFE+ Walphy project (2009-2013), three water bodies were restored and its effectiveness was scientifically monitored before and after restoration. In the Bocq basin, the longitudinal continuity was improved through removal or building of 23 obstacles. The transversal continuity was enhanced through rehabilitation of 3.7 km of watercourse using different techniques. Since then, five stations have been subject to hydromorphological and biological surveys. The comparison of before and after restauration demonstrated the short-term effectiveness of the improvements. Ten years later, the question of the sustainability of the improvements and their ecological benefits arose, both on a stationary scale and on the scale of the water body. The current assessment (2021) was carried out according to these two scales, based on geomorphological and ecological monitoring of the restored and control stations, as well as analysis of data from stations of the EU Water Framework Directive (WFD). The durability of the developments was variable, depending on the type of work. Hydromorphologically, the analysis of restored sites generally shows a slight decrease in the gains obtained a few years after the works. This could be attributed to the filling in of the hydraulic annexes or to a dispersion of the injected pebbles. Biologically, the balance is positive, but the time and intensity of the response of the indicators differ, depending on the type of development and the scale considered. At the scale of the water body, certain fish parameters show changes along with the increase in longitudinal continuity.

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