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An analysis of surface water level and quality using real-time, high-resolution sensors to inform stormwater management

Fahad Aziz is a new addition to the team at Umvoto! Fahad Aziz (Junior Water and Environmental Scientist) passed his MSc in Environmental and Geographical Sciences from the University of Cape Town in 2020. His MSc was titled “An analysis of discharge and water quality of an urban river and implications for stormwater harvesting”. In his study Fahad monitored and analysed surface water level and quality from the Liesbeek River (Cape Town, South Africa) using real-time, high-resolution sensors.

About the Study

The study examined the potential to augment groundwater supplies and aquifer recharge from stormwater harvesting to alleviate the increasing demand for water in water stressed cities. The research analysed the discharge of an urban river and associated water quality fluxes during rainfall events to determine the suitability for stormwater harvesting. This was done by simultaneously monitoring water level and quality using real-time, high-resolution sensors to generate continuous data. Water quality parameters monitored in the study included Electrical Conductivity, Dissolved Oxygen, pH and Temperature.

The study area indicating the Liesbeek Catchment, river, three monitoring sites and suburbs.

Rationale

While modified urban rivers and streams become efficient stormwater canals, they have a reduced capacity for removing pollutants during low flow periods resulting in a general decline in water quality. Despite the stormwater harvesting potential of urban rivers, they continue to degrade due to the drainage system being viewed as drains or sewers for waste products instead of functioning rivers. Stormwater harvesting has a number of benefits such as improving water security, preventing, or reducing flooding and improving the condition of urban waterways through flow modulation.

Findings

The study found that rainfall resulted in significant responses in all variables with significant levels of dilution. Rainfall ultimately resulted in an increase in discharge and Dissolved Oxygen, whilst lowering the Electrical Conductivity. The dilution factor of rainfall was intensified during high rainfall events. Hydrographs and pollutographs produced by the sensors indicated that the peak flow and highest dilution levels do not coincide during rainfall events. The best water quality during a rainfall event was found immediately after the peak flow and therefore indicated the suitable range for stormwater harvesting in terms of water quality.

Hydro and pollutograph showing changes in discharge and water quality in response to a rainfall event. The graph shows the improved water quality occurring immediately after the peak flow.

Work at Umvoto

Since joining Umvoto, Fahad has been involved in surface water quality analysis in the Cape Flats Aquifer to better understand surface and groundwater interactions. He is also involved in The Umvoto Foundation, assisting with the Khayelitsha Pavement Improvement Project which aims at establishing a vegetable garden at a primary school in Khayelistha.

8 Beach Road
Muizenberg
Cape Town

+27 21 709 6700 amanzi@umvoto.com