Measurements of coastal currents in the assessment of environmental impact

Pollutants ejected into the ocean environment are dispersed and transported by the water movements induced by wind forces, tides bottom topography and shoreline configuration. Whether the pollutants have an impact on the environment depends primarily upon where they are carried and how much they are diluted along the way. We expect current measurements to tell us not only the trajectories followed by a given pollutant, but also the variations in the trajectories and the variations in the currents that affect the dilution of a pollutant. This information is provided by techniques that follow the movement of water (Lagrangian) and ones that measure water movement past a given point (Eulerian). This paper focuses on the latter, primarily because instrumentation measuring currents at fixed points can provide the required length of records over many months. This yields information on seasonal changes in circulation as well as detailed data on variations occurring over several seconds or minutes. Current measurements must provide data on variations over seconds to hours to properly assess the dilution characteristics of circulation. These must also be made under a wide range of conditions to provide information on the changes in the characteristics from day-to-day and season-to-season. Basic current regimes that govern transport and dispersion of material repeat themselves at a given location. Unattended current meters that record rapidly over periods of several months are required to determine the frequency of occurrence as well as the energy associated with such regimes.