World Water Quality Assessment Use Case Study – Cape Town Aquifers: Deliverable 5 – Summary Report

United Nations Environment Programme ; World Water Quality Alliance (2021)

The central aim for all three initial use cases is the integration of in-situ measurements, remote sensing based Earth Observation and water quality modelling data to derive the best possible current state of water quality combined with a multi-stakeholder driven process defining demand for water quality services. The ultimate objective was to provide an evidence base that links water quality hotspots to solutions and investment priorities. The results emanating from this approach are due to be shared widely with the World Water Quality Alliance partners for further consideration and illustration of the approach. The Cape Town aquifer use case comprises various aquifers in and around Cape Town that are earmarked for water supply to the city. The Cape Flats aquifer underlying most of the city is highly vulnerable to pollution from land-use activities, including small-scale agriculture and sand mining, and from landfill sites, cemeteries, industrial areas and informal settlements without proper sanitation. This has led to salinization of the groundwater and contamination with nutrients, microbiological and industrial contaminants, hydrocarbons and, possibly, contaminants of emerging concern. Extensive in situ monitoring data, remote sensing (Earth Observation) data, detailing land use and identifying pollution sources, and vulnerability and flow modelling were used in the assessment. Feeding into stakeholder engagement, groundwater protection zones were proposed as a potential assessment product. The high variability of natural groundwater quality and the lack of historic water quality data had prevented assessments of the current state of deterioration. Nonetheless, the findings can be extrapolated to other urban centres with similar geological settings. The full report of the Cape Town Aquifer summarises the stakeholder engagement process, data assessment and hotspot identification, associated with each of the three aquifer systems investigated, and includes a description of the products developed as part of the study and as discussed with stakeholders and the water quality actions taken or planned by the City of Cape Town. It concludes with recommendations regarding the way forward.

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