Model-Based Analysis of Macrophytes Role in the Flow Distribution in the Anastomosing River System

Abstract

The impact of vegetation on the hydrology and geomorphology of aquatic ecosystems has been studied intensively in recent years. Numerous hydraulic models developed to date help to understand and quantitatively assess the influence of in-stream macrophytes on a channel’s hydraulic conditions. However, special focus is placed on single-thread rivers, leaving anastomosing rivers practically uninvestigated. To fill this gap, the objective of this study was to investigate the impact of vegetation on flow distribution in a complex anastomosing river system situated in northeastern Poland. The newly designed, one-dimensional, steady-flow model, dedicated for anastomosing rivers used in this study indicated high influence of vegetation on water flow distribution during the whole year in general, but—as expected—significantly higher in the summer season. Simulations of in-stream vegetation removal in selected channels reflected in Manning’s coefficient alterations caused relatively high discharge transitions during the growing season. This proved the significance of feedback between process of plants growth and distribution of flow in anabranches. The results are unique and relevant and could be successfully considered for the protection of semi-natural anabranching rivers.