Samenwerking met vrije vismigratie als leidraad

Johan Coeck, Peter Paul Schollema, Koen Martens & Niels Brevé

viswaterbeleid, connectiviteit, rivier, vismigratie, waterbeheer

De internationale stroomgebieden van Rijn, Eems, Maas, Schelde en IJzer zijn volgebouwd met tienduizenden stuwen, sluizen, gemalen en waterkrachtcentrales. Deze kunstwerken zijn belangrijk voor scheepvaart, hoogwaterveiligheid, landbouw en energieproductie. Ze hebben echter een negatieve impact op trekvissen, zoals zalm, zeeforel of aal, zelfs tot op het niveau van populaties. De Beneluxbeschikking M (2009) 1 ‘Vrije Vismigratie’ biedt een richtlijn voor herstel. Navolging liet lang op zich wachten, maar toch zit er anno 2019 schot in de zaak: ongeveer 4.000 vismigratiebarrières in Vlaanderen en Nederland zullen op termijn worden opgeheven.

Restoration of longitudinal connectivity in river catchments

Johan Coeck, Peter Paul Schollema, Koen Martens & Niels Brevé

Water policy, connectivity, river, fish migration, water management

In Europe, the catchments of the Rhine, Eems, Meuse, Scheldt and IJzer contain tens of thousands of weirs, locks, pumping stations and hydropower plants. These engineered constructions are built for shipping, land drainage, f lood control, water abstraction or energy production, however, they have a negative impact on the populations of migratory fish, such as salmon, sea trout or eels, but are also an obstacle in the life cycle of potamodromous fish populations in the rivers. The Benelux decision M (2009) 1 ‘Free fish migration’ offers a guideline for recovery of the longitudinal connectivity in the rivers of Belgium, the Netherlands and Luxemburg. In Flanders and the Netherlands about 4.000 priority obstacles for fish migration must be solved before 2027. In general, there are three types of fish migration barriers: pumping stations, weirs & locks and hydroelectric power stations. Each of these barriers requires specific solutions. Regulated river trajectories should become more natural by dam removal and ecological restoration. Where complete removal of the obstacles is not possible, the most natural solution is considered. The construction of larger natural diversions can, under certain
circumstances, provide compensation for the river habitat loss. Pumping stations must be made passable in two directions to let fish be able to leave the polder safely as well as to return from the sea. Extensive measures have been taken and are planned in various rivers to keep fish migrating downstream away from the turbines and to divert them to a safe passage. At the first evaluation period of the decision in 2015, about 30 to 40% of these ‘fish migration barriers’ were ‘solved’, mainly by building all kind of fish passes. Serious catching up will be necessary to reach the 2027 goal of the decision. Thorough evaluation of the functionality of the fish passes is also essential. When several fish passes in line only function partly, the population that reaches the spawning grounds in the upper part of the catchment might be too small to be self-sustainable. Where possible, partly or full removal of the barriers must be the first option to restore the longitudinal connectivity of the rivers as this option assures 100% efficiency in terms of fish passage and also restores the negative effects of the barriers on the riverine habitat.

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