This project aims to develop an instrument used to answer river morphological questions. With regard to the Dutch rivers, these issues arise as a result of management questions related to navigability during low flows, morphological developments after flood-plain restoration and morphology near constructions. Apart from the last subject, for which a lack of knowledge still exists with respect to hydrodynamics, these problems are translated into research-questions with respect to transport of sediment and related morphological developments.
Within this project, river morphological issues are studied in relation to the theme ' dynamics of river bifurcations ' of the Morphological Triangle (which is a knowledge platform for river-morphological research in the Netherlands). Questions which are treated include: how does the interaction of several sediment fractions contribute to large-scale morphological development, how does this coincide with the large observed dynamics of the bed forms, and how may these effects be modelled efficiently for practical applications.
Also related questions regarding large-scale water movement relevant to morphology (such as spiral flow in bends), the interaction between morphology and vegetation, and processes such as bank erosion, belonging to a more natural planning of the river area (secondary channels) are some of the subjects being considered within this project.
Over the past several years, the development of more extensive boundary conditions, input options, alluvial and vegetation roughness formulations, bank erosion, graded-sediment modelling, and modelling of spiral flow effects in sharp bends have been important topics involved in this project. The modelling system Delft3D is used as the foundation for these developments, where it is applied in 2-D (depth averaged) flow mode. In 2004 a connection was also made with Baseline, which is a GIS-based datamanagement system used for the Dutch rivers. In addition, the activities for integrating the gradedsediment approach into a new Delft3D morphology module were started up in 2004. The objective of this integration is to allow for combined modelling of gravel, sand and (cohesive) silt mixtures while returning the effect of grain-sorting processes and dune development on bed roughness.
The application of the newly developed 2-D graded-sediment functionality for the Pannerdensche Kop river bifurcation (in cooperation with the Morphological Triangle) and for several rivers in Japan (in co-operation with J-Power, Japan) has demonstrated both the benefits and limitations of this new approach. Also, new developments for bank erosion are now being tested for field cases, aiming at validation and setting the program for further improvements. The outcomes of this research meet the demand for more detailed and accurate modelling approaches, and the regular Delft3D-software users are expected to benefit from these improvements. |
