Comparisons of remotely sensed observations with modelling predictions for the behaviour of wastewater plumes from coastal discharges

Abstract. Thermal infrared data collected from overflights of a number of power plant cooling water discharges are presented and compared with the predictions of theoretical model studies. The sites in question are characterized by rather complex discharge conditions and irregular topography. These factors are seen to assert significant controls on the spreading of the plumes in the marine receiving waters. Semi-empirical theoretical models are applied to these cases, and the comparisons with the remotely-sensed data are shown to be qualitatively good. The consequences of inadequate and incomplete source data are shown to be serious for quantitative comparisons between field (i.e., remotely-sensed) data and model predictions and examples are presented to show that very good quantitative agreement is obtained when water depths, discharge geometries, source excess temperatures, and crossflow velocities are known with even moderate precision. In contrast, cases are discussed where information on these observables is either not available or of questionable quality; for such cases, quantitative agreement between predicted and observed temperatures is poor, even when plausible estimates are made for the values of missing input data. It is demonstrated that under certain tidal conditions for these sites, the surrounding topography plays a significant role in the dynamics of the cooling water discharge fields, by steering the resulting effluent field, and hence affecting the level of mixing of the effluent with the receiving ambient water. The study has also confirmed the usefulness of the length scale parameterisation approach for the analysis and interpretation of cooling water plume trajectories.