Introduction

Motion in the coastal ocean is largely driven by both wind and the tidal oscillation of the adjacent ocean. The complicated shape of the coastal boundary and the irregular bathymetry of estuaries and continental shelves often make the circulation resulting from the interactions between these mechanisms difficult to measure and to understand. When terrestrial runoff intrudes into this dynamic melee, it is unlikely that a simple theory will provide us with quantitative predictability for the motion of particles. Numerical simulations are, therefore, central to practical problems involving the transport of materials in the coastal ocean. Nevertheless, simple and elegant theories for important aspects of buoyancy-influenced coastal currents have been developed and evaluated with careful laboratory and field campaigns. These have become central to a broad understanding of coastal physics and are the focus of this chapter.

Phenomenology

There are many published reports describing the distribution of salinity at the mouths of rivers and estuaries. A few examples are listed inTable 8.1 to illustrate the diverse range of physical scales that have been examined. Figure 8.1 shows the near-surface salinity distributions from three plumes chosen to illustrate the complexity of behavior that must be understood. The first example, Fig. 8.1a,b, shows the salinity in Long Island Sound at the mouth of the Connecticut River reported by Garvine (1975). The measurements were acquired from a small boat survey in a few hours surrounding low slack water during the spring freshet.