Sediment behaviour in overland flow over grassed areas
Grassed areas, such as grass filter strips (GFS), and grassed swales, have been used extensively for the surface water protection against erosion and polluted runoffs. In order to use grass properly for water purification, it is important to understand and model sediment behaviour in runoff over grassed areas. This project was concerned with sediment transport in non-submerged overland flow through grass. The work contains several distinctive parts, as discussed below. A broad based literature study was carried out. It was found that the literature on sediment transport in shallow non-submerged flow through grass is very restricted, although a lot has been published on GFS performance in rural environment. Usually, the published field works have not been focused on the processes involved, but rather on the overall GFS performance. Therefore, the methods currently used for modelling of sediment transport through grass are very poor. To overcome these problems the literature on related subjects was also incorporated in the study. A laboratory investigation was carried out in a flume at the Aberdeen University Fluids Laboratory, aimed at development of a new method for assessment of sediment transport in non-submerged, steady, and uniform flow through grass. A field study was conducted in order to verify the findings of the laboratory study and provide data for verification of a complex dynamic model developed in the next stage of the project. A grassed channel was formed at a well established and maintained lawn at the University campus. Three experiments were carried out with clean water (no sediment present) in order to investigate infiltration and overland flow through grass. Using similar equipment to that used in the laboratory study, six experiments were carried out in the same way as the laboratory deposition experiments. They confirmed the findings of the laboratory study. The data already gathered during both laboratory and field study may be used for various improvements of TRAVA, but new studies are needed for its further verification and development.