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A spectral evolution model is implemented of the extended Boussinesq equation which can be used for varying bathymetry even in deep water region. In this model, a contribution of the triad nonlinear interaction can be segregated from that of the bottom shoaling effect. For a simple onedimensional case, an attempt to express the triad interaction as a source function term in the energy balance equation is shown. Numerical sensitivities for different initial phases and different frequency band widths are investigated. It is observed that the numerical results are dependent on the initial phases. An ensemble mean of many realizations or a frequency averaged estimation of a single realization with a very fine frequency resolution provides convergent results. These numerical estimations of the spectral model agree well with experimental data for finite-amplitude waves propagating over a bar in shallow water.

This literature review is part of the ongoing research on sand transport in oscillatory sheet-flow, as taking place at the coast during storms. Because sheet-flow corresponds to conditions of high shear stress, large amounts of sand are transported. Therefore it is an important part of the total sand transport (sheet-flow and suspended load). Sand transport is a very important phenomenon in almost all coastal engineering problems. When a harbour is to be developed it is important to know how much sand is transported and in what direction, in order to prevent sedimentation problems in the entrance channel or in the harbour itself. Another example deals with coastal defence measures to prevent erosion of a beach. Either the use of coastal structures, like breakwaters, groynes etc., or a beach nourishment scheme requires information about the magnitude and direction of the general and local sand transport. Unlike the sand transport in rivers, which can be assumed to occur in a merely one- dimensional, steady uniform flow, the sand transport at the coast is the result of a complex interaction of steady currents and a wave-induced unsteady oscillatory flow at an arbitrary angle to the current. In order to predict the resulting sand transport, many different models have been developed. The aim of this literature study is to present an overview of the models, that predict the unsteady sand transport in sheet-flow conditions. Some of the models are specifically derived for sand transport under sheet-flow conditions, while others have a more general basis. A comparison is made between the capability of the different existing models in predicting the sand transport in sheet-flow conditions. Moreover also the different experimental studies on sand transport in oscillatory flow are presented. As a result of the comparison the most encouraging direction for the ongoing research is determined.

This report focusses on discontinuous behaviour of hydraulics and morphology in rivers. The varying widths, slopes and bed levels that can be observed in mountain rivers can induce rapid, or discontinuous changes at a short lengthscale. When present, these discontinuities have a major impact on changes in water and bed levels during floods. In this study, existing theories on discontinuous solutions are applied to river flows with mobile beds. The propagation rate and stability of a discontinuity are analysed with the Lax shock-wave criterion. Effects of transitions in flow regime are described qualitatively by solving the Rankine-Hugoniot relations. Attention is paid to the effect of river bed mobility on discontinuous flows.

This report evaluates the B009 data of the back-ward facing step experiment which was one of a series of the experiments that were designed and conducted by Hofland and Booij (2004) and De Ruijter (2004). In this experiment, the flow field and the pressure field were measured (by PIV and pressure sensors) during the displacement of a single stone from a granular bed. This measurement shows similarities to the results from previous experiments. At the time the stone started to move, two flow structures were found to be responsible for the entrainment: a large-scale sweep (u'>0 and v'>0), causing increased quasi-steady forces, and an embedded small-scale structure with vertical velocity fluctuations, sigma(v'), causing turbulence wall pressure fluctuation (TWP). In the four entrainments, these structures were present simultaneously in the instantaneous flow fields.

In this report the analytical and numerical formulations, testing and calibration of the third generation wave hindcast model WAVEWATCH are presented. WAVEWATCH is specially designed to operate in a combined wave-current model. The main attention is focussed on numerical aspects of the model, including academic test cases and comparison with other third generation wave models (which do not include current effects). Furthermore, preliminary results of calculations for a south westerly storm in the southern North Sea are presented to illustrate the effects of wave-current interactions in the southern North Sea in such conditions

Present knowledge on fluvial processes in mountain rivers should be expanded to enable the development of projects dealing with mountain rivers or mountain-river catchment areas. This study reviews research on hydraulic and morphological features of mountain rivers. A major characteristic of mountain rivers is the variability of the hydraulic and morphological parameters. Flows can change from extremely non-uniform flow over large roughness elements at low stages to relatively uniform flow at high stages. The irregularity of geometry complicates the modelling of the turbulent, non-uniform and/or unsteady behaviour of water and sediment. It can be concluded that, due to the complexity of the conditions observed, a proper, general description of sediment movements in mountain rivers is not possible yet. Description or prediction of morphological developments at present is limited to exceptionally isolated phenomena. Morphological responses of a river to a flood depend on (i) the size-distribution of the bed material and (ii) the distribution in time and place of hydrographs and sediment supply. The effects and relevancy of extreme hydraulic conditions have to be investigated, to enable description and prediction of long-term morphological evolution. Considering the importance of extreme, and subsequently low-frequency variables, the prospect of theoretical simulation models of morphological processes in mountain rivers seems rather remote.

In this report, transport problems are solved with a particle method that takes into account the Eulerian background flow field. Dispersion and other transport problems can be solved applying this model, as long as the corresponding transport process is formulated with a flux gradient relation, i.e., the advection-diffusion equation. The particle method has been made consistent with such a transport process. Since many 3D flow models are formulated in general coordinates, the 3D particle displacements are also given with respect to such a coordinate system. Analytical and numerical aspects of this particle method have been studied. The effectiveness of the method has been demonstrated with two academic test cases including streamlines in a recirculation zone and grid dependency in a discharge problem.

Previous research (e.g., Jongeling et al 2003; Hofland 2005) has shown that turbulence has an important influence on stone stability and in non-uniform flow it should be modeled explicitly. The dimensionless entrainment rate should be used to describe the bed response because of its complete dependence on local hydrodynamic conditions and independencies on time and bed material. In all studies where entrainment rate data are available, the correlation between the flow forces and the bed response still shows a high scatter level (e.g. the data of Jongeling et al (2003) and De Gunst (1999). Therefore, more experiments are needed to increase understanding of this cause-and-effect relation and to verify the available stability parameters for non-uniform flow. In this research, experiments were carried out in which both the bed response (quantified by a dimensionless entrainment rate) and the flow field (velocity and turbulence intensity distributions) are measured. The flow in a gradual expansion ope nchannel and its influence on stone stability were chosen to study as in such a flow the turbulence intensity is high. Three experimental set-ups with different expansion dimensions were used to create different combinations of velocity and turbulence. The nine-month experiment1 has resulted in a huge amount of data available. In this report the experiment arrangement and data processing methods that are employed are described and the measured data and some calculated variables are presented. The report is structured as follows. In Section 2 the experimental set-ups are described in additional to the instrumentation, hydraulic conditions and experimental procedures. Data processing methods is briefly described in Section 3. In Section 4 the measured data to determine stone parameters are presented. Finally in Section 5 the measured data and calculated variables are presented in detail.

The ability of describing and predicting hydraulic and morphological phenomena in mountain rivers is limited, partially due to the limits of deterministic approaches where stochastic effects in sediment supply and water inflow are extremely significant, and partially due to the very specific conditions that can be observed in mountain rivers, that complicate the modelling. The dynamics of morphology and hydraulics of mountain rivers must be known when applying numerical modelling procedures to mountain rivers. Simplifying a complex, nonuniform geometry significantly affects the behaviour of the model at high values of the Froude number. The number and type of boundary conditions to be prescribed at a boundary can change with flow regime. Hydraulic and morphological changes in supercritical flows are coupled and transversal effects are significant. The mathematical models discussed are a single-layer model and a double layer model conform Ribberink (1987). With the help of the characteristics, the models are analysed and compared. Analysing the characteristic surface yields indispensible insight in the twodimensional behaviour of the mathematical models. To prevent the mathematical model from being elliptical, the thickness of the mixing layer has a maximum. This value is investigated, approximated and evaluated. It appears that the behaviour of the model can be significantly affected by the model parameters (hydraulic as well as morphological). Regarding the selection between onedimensional and two-dimensional modelling, it can be concluded that transverse effects have a significant influcence on the behaviour of the model for Froude near unity. Conclusions in this report stress the need for research on the modelling of complex geometry for flow with higher values of Froude and the prediction of the model parameters used (such as mixing-layer thickness and sediment fluxes) at varying flow conditions.