· · · Repository Hydraulic Engineering Reports

Background report on how to make realistic waves in laboratory flumes, including the method of splitting wave signals into incoming and reflecting waves

Schaalregels dynamisch onderzoek aan droge en met water verzadigde grond, schaalregels bij verweekte grond

Het project betreft het beproeven van teenconstructies met een horizontale kracht. De gedachte daarbij is dat deze kracht de belasting representeert die de bekleding uitoefent op de teenconstructie indien deze naar beneden glijdt en tegen de teen gaat rusten. Er zijn twee locaties beproefd. Op één locatie bestaat de teenconstructie uit een rij perkoenpalen en op de andere uit een doorgaande houten damwand. In beide gevallen is de teen voorzien van een kreukelbrem met steenbestorting. De doelstelling van de proeven is het verkrijgen van inzicht in het mechanisch gedrag van de teenconstructie voor wat betreft zijn functie als laterale steun van de steenbekleding. Dit bij variatie van de steunkracht en variatie van de waterstand.

A least squares method to separate the incident and reflected spectra from the measured co-existing spectra is presented. This method requires a simultaneous measurement of the waves at three positions in the flume which are in reasonable proximity to each other and are on a line parallel to the direction of wave propagation. Experimental investigations have shown that there is qood agreement between the incident spectra calculated by the least squares method and the incident spectra measured concurrently in a side channel.

Laboratory experiments to provide calibration data for numerical and empirical models of flow, morphodynamics, functionality and sustainability of low crested structures. Output of the tests are flow velocities and drag forces. This document describes the set-up of the tests.

The present report, produced within the framework of the EU funded project DELOS, attempts to recognise and analyse main scale effects in the physical modeHing of rubble mound breakwaters used in offshore and coastal engineering. Scale effects appear in physical modeHing because the ratios between the farces of interest, as present in prototype, cannot be maintained in a scaled model. The report is by no means intended to resolve the problems associated with scale effects, given the complexity of this issue. However this discussion provides a preliminary understanding of these effects. Respect to the aforementioned objectives, the present report is structured as foHows. The properties of sea water are summarised in Section 2. Section 3 provides a brief overview of sealing rules used in hydraulic physical modeHing. Section 4 is dedicated to surface tension effects on breakers. Section 5 deals with the complex problem of sealing air content from prototype sea water to model fresh water. A general overview of main scale effects in relation to the different processes associated to the interaction between waves and rubble mound breakwaters is presented in Section 6. Sealing of movable-bed models are addressed in Section 7. The effects of marine organisms on water and mound units are described in Section 8. In Section 9 conclusions are drawn, which summarise the main points worth consiclering when addressing the problem of scale effects in wave-related models with rubble mound breakwaters. Selected issues are further discussed in the attached appendices. Example of the Hydrodynamics at Pellestrina. Example of the sediment budget at Lido de Pellestrina.

Considerations on fluid motion in and around closure gaps, two-dimensional local scour in loose sediments, local scour caused by vortex streets, behaviour of dumping material when exposed to currents, results of model tests applied to an actual project *** The closure of the final gaps is the most difficult part of the construction of the dams in the 'Delta plan' of the Netherlands. In this contribution various factors concerning the water motion in closure gaps are discussed in general terms. These factors are: the tidal motion in the region, the changes of velocities in and near the closure gap during the closure period, and the way in which they can be computed. Remarks are made about the interaction of water motion and soil mechanics. ** The conformity and time scale of local scour is studied from model experiments. A description of the flow pattern in the scouring hole and the development of the scouring process with time is given. A time-scale relationship is derived from experiments with a wide range of scales. The int1uence of the velocity profile and turbulence intensity on the scouring process is demonstrated with some examples. ** In this article considerations are given about three-dimensional local scour caused by vortices, in -~10n-cohesive bed-material. After a general characterization of the scour-patterns for different closing-methods and a description of the flow-pattern, the process of local scour is described more in detail. As the development of the scouring process with time is very important for practical purposes, estimates of the time-scale are given based on reproduction in models and on a systematic research program as well. ** After an introduction, the results are discussed of a series of laboratory model tests, performed in view of establishing a criterion of stability for the various dumping materials exposed to current-action. In working out the test results it has appeared that the critical flow velocities for a certain material could be expressed as a linear function of log h, h being the difference between the downstream water-level and the dam's crest-level. ** The paper deals with the way in which the Hydraulics Division of the Delta Directorate uses the results obtained from model tests in the Hydraulics Laboratory when designing the dams with which the various tidal channels are to be closed. The hydraulic problems that have to be overcome are described in general. as well as the manner in which they are tackled. The final plans for an actual project as treated in this paper are a compromise, since a great number of factors, particularly technical planning and economic considerations are involved.

In January 2002 HR Wallingford published the results of work undertaken on behalf of P&O Ports Limited and the Port of London Authority to investigate the effects of dispersion of fine material arising from dredging and reclamation activities associated with the proposed London Gateway Port (Reference 1). Further plume modelling results, produced for P&O Ports Limited, were published in March 2003 (References 2 and 3). As an aid to understanding the sensitivity of the plume model used for these studies a series of sensitivity tests were undertaken. These sensitivity analysis tests have not been previously published and a selection of test results are presented in this report to provide additional confidence in the results published in References 1, 2 and 3.