From monitoring network to near real time groundwater forecast. A case study in Cape Town Table Mountain Aquifer, South-Africa
Résumé
Groundwater level monitoring is essential for assessing the availability, behaviour and trend of groundwater. Associated with a modelling tool, groundwater level fluctuations can be predicted at short to middle term using precipitation probabilities or meteorological forecast. This is the purpose of the MétéEAU Nappes tool implemented by BRGM for the City of Cape Town (CoCT) in the Table Mountain Group Aquifer (TMGA). This case study shows how near real time groundwater level monitoring can be used to support the municipality in managing its future groundwater withdrawals.
The TMGA is an important source of groundwater in the Western Cape region of South Africa. It is an unconfined aquifer that is recharged by rainfall. It has been monitored in the Steenbras area for more than 10 years before CoCT started groundwater production from the Steenbras wellfield in 2021, providing approximately 7% of the city's water supply.
The MétéEAU Nappes forecasting tool is already implemented on many observation wells of the French national piezometric network where it is used for decision making by the French administration. It allows in particular to anticipate several threshold levels of drought and take appropriate measures. It combines real time water cycle measurement data with a groundwater level lumped model (e.g. Gardenia model), extrapolates observations for the next 6 months and compares it to statistical occurrences. This tool can help to protect the Steenbras wellfield as a critical source of water for CoCT in the TMGA.
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