Coastal Dynamics

Abstract

This book deals on "Coastal Dynamics", which will be defined in a narrow sense as a mathematical theory, which starts from given equations of motion for the sediment, which leads with the continuity equation and given boundary conditions to a calculated (eventually schematized) coastal topography, which is generally a function of time. This is clearly analogous to aero- and hydrodynamics, thermo-dynamics, hydrology and other related fields. The subject of this book, however, covers only a specific part of the Coastal Dynamics. It is based upon the notion of old masters, that for a manager the back-side of a cigar-box should be large enough to evaluate all the information and anti-information which is poured over him. For instance: statements, based upon high-tech number-crunching can find a sad end when those do not match large-scale continuity. Think for instance of tidal computations, in which time-varying boundary conditions (shoals which emerge above water level during a part of the tide) are not reproduced accurately enough. The positive role of refined numerical techniques on solving problems in coastal dynamics should be stressed. However, one will not find much about it in this book. Emphasis is on physics, rather than on mathematics. It is meant for coastal managers, to inspire them, to enable them to put sensible questions and, if necessary, to say: "Oh, no sir". The theory would be sterile without a consideration about the validity of the equation of motion, so much the more, while these equations of motion are not as evident, straightforward and single- valued as for instance the Euler - equations in hydrodynamics. The Newtonian laws are not quite sufficient for the computation of the sediment motion, because the motion of grains is subject to stochastic processes as the shape of the grains, the shape of the granular bed surface, turbulence, irregular wave motion etc. In modern sophisticated computer models a physical approach going far into details is possible, this includes the consideration of water and sand apart from each other, investigation of turbulent and viscous forces on the grains, and calculation of the sediment motion.