Relation between resistance characteristics due to aquatic weed growth and the hydraulic capacity of the river Aa

Vegetation growth drastically influences water levels and flow patterns in lowland rivers. As soon as plants start to grow in spring, the flow resistance increases to reach a maximum in early summer. The universities of Ghent and Antwerp are conducting scientific research in the river Aa in Belgium in order to better understand the relation between aquatic weed growth and the hydraulic capacity of the river and to come to a more accurate determination of the different influencing parameters. Velocity measurements are performed in multiple cross‐sections on a regular basis and studied. Discharge calculations are based on velocity measurements, which deliver important information about structural characteristics of the river, presence of vegetation, etc. Removing the vegetation allows for determining species and vegetation density as well as for studying the influence of plants on flow distribution and patterns. It is shown that the resistance coefficient, influenced by the amount of biomass, is an important parameter for the hydraulic characteristics of the river. The presence of macrophytes and their blockage characteristics are studied and a relation between discharge, biomass and resistance coefficient is set up. This leads to more reliable results in the application of hydraulic models for river management and river restoration purposes. Copyright © 2009 John Wiley & Sons, Ltd.