Hydrodynamic and pollutant transport models applied to coastal seas

Role of mathematical models and of field measurements in solving water quality problems is described. When simulating phenomena in different space and time scales there are some important differences, regarding forcing factors, time averaging and measuring technique. Two case studies are presented: (a) Modelling of mercury cycling in Trieste Bay. 2D Hydrodynamic model Is used together with a sedimentation model and with a mercury mass transport model. Simulation of several bio-chemical processes as methylation, demethylation, reduction and sedimentation is included, (b) Long term simulations of transport-dispersion of radioactive pollutants in Japan sea is described. Thermohaline forcing, wind forcing, and inflow currents are taken into account. Results are in good agreement with measurements. 1 Modelling in Different Space and Time Scales It is well known, that mathematical models are an extremely efficient tool when saving environmental problems related to water quality. The models aim at understanding the basic processes involved and the response of the system to different forcing. With simulations of different possible solutions the models can finally be used as a management tool. Cheng and Smith [1] state that for a fixed cost, the computing power increases five to ten times every five years. This promises that in the near future sophisticated 2D and 3D water quality models will be widely used on personal computers like today zeroand one-dimensional models are used. Water quality modelling is needed in environments with very different space scales from small bays and marinas with dimensions of several hundreds of meters, through larger coastal seas to global ocean areas of the dimensions of several thousands of kilometers. Time scale is usually connected with space scale, although it also depends on the type of pollutant and its biological and chemical growth/decay characteristics. Fig 1. presents the space time diagram with six cases of model applications and Table I. gives some details of the cases. All these six cases, so different in their space and time scales, were simulated by the same model. This model named LMT3D, developed at the University of Ljubljana, has already been described, (Rajar [6], Rajar et al [8]) so only some basic characteristics are given here. Transactions on Ecology and the Environment vol 9, © 1996 WIT Press, www.witpress.com, ISSN 1743-3541