Water Quality Decision Support Tool

An increasingly high fraction of people live near the coast or in a community of coastal users. Increased impervious surfaces near the coast, discharges from waste-water treatment facilities, direct discharge from industrial pipelines, as well as intensive farming practices in inland areas, from which there is run-off during rainfall events, all affect the quality of the water flowing into the ocean at the coast.

The purpose of the Water Quality Decision Support Tool (DeST) is to provide support to coastal managers’ decision making processes by providing a consolidated view of various remote-sensed and in-situ sources of water quality data.  It is also expected that scientists and researchers will need access to consolidated and integrated datasets that allow for understanding of historical conditions and comparison with other, relevant datasets.

In-situ data is typically gathered by government, municipalities, Non-Government Organisations (NGOs) and research organisations in support of various objectives.  For example: the Department of Environment Affairs (DEA) monitors water quality at or near outfall points for compliance with permitted conditions; Wildlife and Environment Society of South Africa (WESSA) monitors beaches to see if they comply with Blue Flag requirements; local municipalities monitor beaches, bays and harbours to ensure water is safe for usage; NGOs monitor areas of interest to ensure that their environment is being safeguarded for the public.

Over the past few years, ocean colour satellites have become available with appropriate resolution for near coastal observations.  These satellites can provide remote sensed data every few days applicable to a wide range of coastal phenomena, including gross water quality parameters.  They can therefore support the detection of substantial changes to aspects of coastal ecoystems over time and space.

Processed satellite imagery is used in the Water Quality DeST to provide information on: the concentration of phytoplankton as given by the pigment chlorophyll a; the turbidity of the water due to suspended sediment or discharged particles; and the presence of any unusual discharge material causing surface discolouration e.g. industrial effluent.  Satellites are not able to directly detect bacterial pathogens, heavy metals or other water quality parameters that do not cause a colour change.

The two satellite constellations relevant to water quality are: the Sentinel 2 series, providing products at 10 m to 60 m resolution every five days; and the Sentinel 3 series, providing products at ±300 m resolution every day.  The satellite data, acquired from the European Space Agency (ESA) and the European Organisation for Meteorological Satellites (EUMETSAT), are processed by the Council for Scientific and Industrial Research (CSIR) using regionally appropriate algorithms.  The focus is on sites important for aquaculture, urban and industrial extraction and discharge, desalination infrastructure, estuarine conservation and fisheries management, and recreational use.