Bio-morphodynamics of the Lower Volga river - a reference for river rehabilitation in The Netherlands.

Abstract

In recent years, the concept of 'Cyclic Floodplain Rejuvenation' (CFR) has been adopted as a guiding principle for ecological rehabilitation in combination with flood protection of the lower Rhine and Meuse rivers in The Netherlands. This concept is based on erosion and sedimentation processes in natural fluvial systems that periodically reset the morphological and vegetation succession of the river floodplain. In regulated and harnessed river systems, controlled and artificial rejuvenation of floodplain habitats could be an interesting approach to solve the nature-flood protection dilemma. This, however, requires thorough understanding of the natural dynamics of lowland rivers and the bio-geomorphologic interactions on floodplains. These have been studied in a joint project of Dutch and Russian research institutes along the Allier River (France) and the Lower Volga (Russian Federation), which are considered semi-natural references for the lower Meuse and Rhine rivers. The present study focused on the Lower Volga, a large low-gradient sand-bed river with a bank-full discharge of about 10.000 m 3 s -1 . It is a 300-km long single to multi-channel system characterized by natural morphology of meandering alluvial rivers. The flood plain is about 30 km wide, with mostly natural vegetation and some extensive land use. Morphological changes over the past decennia were reconstructed, and succession schemes of morphology and associated vegetation types were established. This was achieved using aerial photographs, old river maps, satellite images, and morphological mapping and vegetation surveys in the field. The results revealed different rejuvenation cycles for different morphological units, each with a characteristic vegetation succession scheme. From these, guidelines for artificial CFR of the lower Rhine were derived.