Morphological effects of spatially varying grain size and bed roughness in rivers

Many morphological models that are in use today, make use of spatially constant grain sizes and bed roughness. Application of this spatially constant grain size and bed roughness is not a correct representation of reality. When making use of actually measured grain sizes, the prediction of the morphological changes does not necessarily improve. Linear analyses of the application of spatially varying grain sizes show that the spatial variation of grain sizes can have much impact on the bed topography in rivers. Two different linear analyses have been conducted by Mosselman & Sloff (1998) and Sieben (2000). One shows a difference in the length and dampening of the bed perturbations due to free excitation. The other shows the existence of a response in the bed topography like a superimposed waveform, due to forced excitation. Implementation of the spatially varying grain size resulted for Olesen's experiment (1985) in effects according to free and forced excitation. For the models of the Waal bend at Nijmegen and Pannerdense Kop, the effects were according to forced excitation. Both linear analyses show morphological effects due to the spatially varying grain size as well as due to spatially varying bed roughness. The spatial variation of the bed roughness should, according to the analyses, have a counteracting morphological effect in regard to the morphological effects of the spatially variation of the grain size. Application of spatially varying bed roughness resulted for Olesen's experiment in effects according to free and forced excitation. For the other two models the implementation of spatially varying bed roughness resulted in effects according to forced excitation. Implementation of a grain size distribution which has reached an equilibrium state leads to a bed level response according to free excitation. While the implementation of a grain size distribution which has not reached an equilibrium, like in rivers with variable discharge, leads to a bed level response according to forced excitation. Implementation of an alluvial bed roughness predictor led to no satisfactory results for Olesen's experiment and the Waal bend at Nijmegen. However, for the model of Pannerdense Kop the results of the computation matched the prototype better than the computation with uniform grain sizes and bed roughness. This was caused by two main effects. The first was a forced excitation due to the spatially varying bed roughness. The second was a change in the sediment distribution at the bifurcation.Civil Engineering and Geoscience

Synthesis of SBW belastingen

The Dutch Water Act (in Dutch: 'Waterwet 2009') stipulates that water boards must assess the quality of their primary water defences every six years. The Statutory Safety Assessment Suite (in Dutch: 'Wettelijk Toetsinstrumentarium', or shortly WTI) prescribes the rules to be applied. The WTI mainly comprises of the Safety Test Regulations (VTV), the Hydraulic Boundary Conditions (HBC) and the underlying Technical Reports and Guidelines. The HBC must be determined and established by the Minister of Transport, Public Works and Water Management every six years. The scope of the SBW-Belastingen project concerns the filling in of the main knowledge gaps in the determination of the HBC, insofar as they fall under one of the four pillars of SBWBelastingen: statistics, physics, probabilistics, uncertainty analysis. This new knowledge is obtained by means of site measurements, laboratory research, models and desk studies. A significant amount of research, covering all four pillars of SBW-Belastingen, has been performed in the period 2008-2010. This synthesis report summarises the main results from the research performed within the framework of SBW-Belastingen during the years 2008-2010. The report will give a general overview of all research topics addressed before the start of SBW-Belastingen as well as a more detailed description of the progress: conclusions and recommendations of the research topics addressed within the framework of SBW-Belastingen in the period 2008-2011. The result of this synthesis is a statement of the performed research so far and a recommendation for research to be performed in the period 2011-2016.SB

Zoekkaart kwelders en waterveiligheid Waddengebied: Een verkenning naar locaties in het Waddengebied waar bestaande kwelders of kwelderontwikkeling mogelijk kunnen bijdragen aan waterveiligheid

In dit rapport wordt een \u91Zoekkaart Kwelders en Waterveiligheid Waddengebied\u92 gepresenteerd. Deze zoekkaart geeft een beeld van locaties in het Waddengebied waar kwelders mogelijk kunnen bijdragen aan de waterveiligheid. Dit gaat zowel om bestaande kwelders als om het stimuleren van nieuwe kweldervorming. De zoekkaart is gebaseerd op de huidige en toekomstige waterveiligheidsopgave, de abiotische randvoorwaarden en de natuurwaarden langs de Waddenkust. Het Deltaprogramma Waddengebied wil de zoekkaart gebruiken in gebiedsbijeenkomsten, waarin samen met lokale stakeholders wordt gezocht naar geschikte waterveiligheidsstrategieën in het Waddengebied. Deze strategieën richten zich naast waterveiligheid op doelstellingen voor de natuur en de ruimtelijke kwaliteit