WETTING AND DRYING IN TWO-DIMENSIONAL TIDAL NUMERICAL MODELS

The purpose of this research is to adapt and improve existing two-dimensional numerical tidal models so that they can cope with regions where the tide falls and rises to uncover and cover inter-tidal banks without incurring numerical shocks which may be caused by the discretization of time and space. This thesis presents a review of current practices in the numerical modelling of flooding and drying banks in two dimensions. A two-dimensional depth-averaged numerical model has been written and is presented. It is used as a tool with which to investigate various existing algorithms which represent the physical process of the wetting and drying of intertidal zones. An alternative method with which to represent the moving boundary has been developed. This method is free from disturbances usually caused by the implementation of a moving boundary in such a numerical scheme. A 2NM numerical model of the Wash, U.K., is run to provide hind-cast tidal data pertaining to a particular site and period. A field programme is established to provide validation data for the model. Finally, conclusions from the programme of research are drawn

Regional-scale probabilistic shoreline evolution modelling for flood-risk assessment

Rapid deterministic modelling of shoreline evolution at regional and coastal-scheme scale enables Monte-Carlo simulations by which long-term shoreline statistics can be estimated. This paper describes UnaLinea, a fast, accurate finite difference solver of the one-line sediment continuity equation. The model is verified for the evolution of an initially straight shoreline of a plane beach subject to regular breaking waves at constant angle of incidence in the presence of either a groyne or a continuous single-point feed of sediment. Grid convergence and stability tests are used to obtain accurate, stable results, with satisfactory computational efficiency. Influences of wave input filtering and event-based sediment loading are considered. The rapid deterministic model is applied to Monte-Carlo simulations of the evolution of the west coast of Calabria, Italy for different scenarios including increased sediment load from a river and selected beach nourishment. The potential role of probabilistic shoreline evolution in regional coastal flood-risk assessment is explored through application to an idealised stretch of the Holderness coastline, U.K., where flood depths and expected damage are estimated for a 1000 year return period event

Effect of the current-wave angle on the local scour around circular piles

This paper studies the effect of the wave front-current angle on the scour around a circular pile. An experimental study was carried out in the Coastal, Ocean and Sediment Transport (COAST) laboratory at the University of Plymouth (UK) using a single monopile of 0.125 m in diameter and an 8 m long by 1.5 m wide by 0.2 m high sand pit. The results obtained during the test campaign show the influence of the angle between waves and currents on both the maximum scour depth and the time scale of the process. Wave fronts partially aligned with current (65°) produce deeper scour holes than perpendicular forcing conditions (90°). Wave fronts partially against the current (115°) produce less scour than any of the two previous scenarios. The addition of waves reduced the maximum scour depth, compared with the current-only case. The development of the scour hole was found to be more rapid when waves are added to the current, with 50% of the final scour achieved in half the time. The results show that wave direction relative to the current is an important component in scour prediction.The authors would like to thank the contribution of Dr. Kieran Monk, Mr. Gregory Nash, Mr. Peter Arber, Mr. Alastair Reynolds, and Mr. Andrew Oxenham during the test setup and the whole experimental campaign. The research was supported by Intelligent Community Energy (ICE) project, INTERREG V FCE, European Commission (Contract No. 5025).Peer ReviewedPostprint (author's final draft