Operational forecast methodology for submarine outfall management: application to a Portuguese case study

Abstract

Coastal waters are an integral part of the natural environment. Careful planning and management is needed to protect and conserve them, and to ensure that the water supply is useful for a variety of uses. Submarine outfalls for effluent disposal are used to ensure that the water quality is maintained and that the environmental values and water uses are protected. Decision on treatment and disposal is based on objectives set by national and international legislation and on coastal and maritime uses identification. An operational forecast methodology is proposed for the management of submarine outfalls providing information to deal with the marine environment problems and to satisfy needs at different levels for coastal communities. From a management perspective the forecast methodology will support decision making by predicting where a discharged plume is likely to be transported over a few days from its last known location. Short-term forecasts of maritime climate and hydrological conditions along with foreseen effluent characteristics (depending on seasons and population equivalent) of the studied region are used for an accurate estimation of the effluent plume advection and diffusion processes near the coastline. The operational forecast methodology, continuously evaluating the plume behavior and its relation with the protection perimeter (identified through a coastal usage map), allows the implementation of a precautionary and adjustable management of the submarine outfall. Corrective measures (e.g. increase dilution, increase the number of outlets, increase outflow speed) may avoid possible operational disruptions and minimize potential water quality impacts. To illustrate the application of the procedure, a submarine outfall case study located in the Portuguese coast is analysed.