High nutrient loads to lowland rivers has resulted in an increased growth of macrophytes. To garanty the discharge capacity managers of waterways remove all vegetation. This management has a lot of negative ecological consequences and leads to high economical costs.This project has the aim to develop mowing patterns which garanty the discharge and has a low ecological impact. Besides this we shall investigate the impact of this management on bottom morfology. In short we try to get insight in the relation between macrophytes, fysical parameters and different mowing patterns.The project is divided in 4 parts : mapping out of the vegetation, ex situ and in situ experiments, sediment dynamics. The results of the mapping out shall form the basis of the ex situ experiments. Together with the results of the in situ experiments and the sediment dynamics this has to lead in a proper management of waterways. In the ex situ experiments we test the following hypthesis : emergents have a greater influence on the efficiency of the mowing patterns than submergents. The ex situ experiments shall take place in a flume which gives us the chance to control biological and fysical parameters. Altogether this has to lead to optimal dates and frequencies of mowing.