This study investigates the distribution of macrozoobenthos in relation to meso-scale bedforms in the southern North Sea. Three sites on the Dutch Continental Shelf were sampled that are representative of large areas of the North Sea and show diverse morphological settings. These sites are (i) part of a shoreface-connected ridge, (ii) the lower part of a concave shoreface and (iii) a sandwave area. Within these sites, two or three different morphological units were distinguished. Sampling was undertaken in two seasons for two consec utive years. The species composition was analysed for differences in benthic assemblage within sites, based on the meso-scale morphology, and between sites and seasons. In addition, the benthic assemblage was correlated to water depth, median grain size (D50) and sorting (D60/D10). Results show that significant differences in the benthic assemblage can be found related to meso-scale bedforms, but macro-scale morphological setting and seasonal effects are more important.@en

Geophysical Research Abstracts, Vol. 8, 02516, 2006 SRef-ID: 1607-7962/gra/EGU06-A-02516 © European Geosciences Union 2006 Modelling the influence of vegetation on the morphodynamics of a flood event in the Allier, France M.J. Baptist Delft University of Technology, Faculty of Civil Engineering and Geosciences, Water Resources Section, Delft, The Netherlands ([email protected]) Understanding the interactions between vegetation and the morphology of rivers is becoming increasingly important in view of modern river management and climate change. There is a need for predictive models for the natural response of rivers to river rehabilitation. One way to study the effects of river rehabilitation is to study natural reference rivers. The Allier in France is considered as a landscape reference for the to-be-restored Border Meuse in the Netherlands. The Allier is highly dynamic, large amounts of sand and gravel are transported during floods and its morphology changes considerably from year to year. The riparian vegetation is characterised by pioneer species on the low-lying dynamic point-bars, herbaceous vegetation and grass on the higher parts and extensive softwood floodplain forests, mainly consisting of poplars, on the older and higher floodplains. Due to the river dynamics, this river shows natural rejuvenation of vegetation such that older forests are removed by erosion and young pioneer vegetation can start growing on the point-bars. This model study investigates the role of vegetation on the morphological changes of a single flood event that took place in December 2003. A state-of-the-art 2-DH morphodynamic model was applied in a 6 Mm2 study area. This model accounts for the effects of vegetation on the hydraulic resistance and on the reduction of bed shear stress and subsequent bed load sediment transport. The model results show that vegetation has a pronounced effect on the hydrodynamics and morphodynamics. The results also reveal that this model has only limited success in simulating the observed morphological changes. Recommendations for further model development will be made. It can be concluded that vegetation is an important factor for the morphodynamics of gravel bed rivers, but our knowledge is at present insufficiently advanced to accurately predict the morphological changes in this section of the Allier.@en

The construction or designation of detention areas along lowland rivers is considered along many European rivers. Since Croatia accommodates large detention areas, both natural (e.g., Mokro Polje) and controlled (Lonjsko Polje), it serves as an excellent example for planned detention areas elsewhere in Europe. This modelling study focuses on the controlled detention area of Lonjsko Polje. The flooding characteristics of the area are assessed in combination with the vegetation development and the transport and storage of sediment and phosphorus. Results of the modelling show that it is not so much the intake capacity that determines the flood duration time of a detention area, but the drainage capacity. A too long inundation duration following a flood event is shown to lead to major shifts in the vegetation composition. The results further indicate that about 30% of the sediment and adsorbed phosphorus that enters the detention area during an extreme (1:100 years) flood is retained within the area; this is about 10% of the total sediment and adsorbed phosphorus load of the Sava. Results of this study can be used to properly design and manage detention areas along lowland rivers.@en

The paper describes the process of induction of equations for the description of vegetation-induced roughness from several angles. Firstly, it describes two approaches for obtaining theoretically well-founded analytical expressions for vegetation resistance. The first of the two is based on simplified assumptions for the vertical flow profile through and over vegetation, whereas the second is based on an analytical solution to the momentum balance for flow through and over vegetation. In addition to analytical expressions the paper also outlines a numerical 1-DV k-¿ turbulence model which includes several important features related to influence plants exhibit on the flow. Last but not least, the paper presents a novel way of applying genetic programming to the results of the 1-DV model, in order to obtain an expression for roughness based on synthetic data. The resulting expressions are evaluated and compared with an independent data set of flume experiments.@en

Numerical simulations of the effects of vegetation on flow and morphology are helpful to understand the behaviour of natural rivers and to predict the developments of rehabilitated rivers. However, some fundamental problems remain in modelling these interactions. This paper describes the application of two-dimensional and three-dimensional numerical models to natural and rehabilitated river systems, i.e. the Rhine (the Netherlands), Allier (France) and Volga (Russia). The results show that vegetation has a pronounced effect on flow patterns and morphological developments in rivers. This can be subdivided in remote effects and local effects. Further analysis of the model results shows a fundamental shortcoming in the mathematical modelling of the effects of vegetation on the local sediment transport capacity. Traditional approaches to modelling vegetation roughness yield erroneous results in combination with common sediment transport equations. Therefore, research focuses on the development of new model approaches to accurately simulate the influence of vegetation on flow and morphology.@en

GECCO-2005 A joint meeting of the fourteenth international conference on genetic algorithms ICGA-2005) and the tenth annual genetic programming conference (GP-2005). ACM Order Number 910052 7. CONCLUSIONS Four formulations for waterdepth-related resistance induced by vegetation are studied and compared. Two have been explicitly derived by a scientist building upon the extensive literature on this subject. One expression was derived by dimensionally aware genetic programming, and finally one expression was created by manually analysing and improving the genetic programming equation. It was found that the genetic programming equations were superior to the manually derived equations, both on their performance on synthetic training and laboratory testing data, and in the economy of detail that needs to be modelled. The manually found expression was found to be in good agreement with previous expressions found in the literature, and performed competitive with the detailed model that was used to generate the training data.@en