In November 2019 ARA Sul discovered remarkable groundwater fluctuations in the Maputo - Incomanti River Basin. The data may indicate depletion of the groundwater system. Lizete Dias (ARA Sul) reacted: “We never knew there was such a large groundwater extraction in that area. Systematic analysis provides a lot of insight.””.
"Scenario study needed"“
In November 2019, a delegation of Dutch Water Authorities travelled to Maputo, Mozambique. They were invited to assist ARA Sul with the development of a strategic groundwater plan. Hydrologist Robert Broekhuis: “Since we don’t have a crystal ball, the development of the growth in water demand is unpredictable. A scenario study is needed to provide insight into the effects of the actual groundwater use and the different water demands.”. ”
Groundwater modelling
To be able to interpret the observations in a validated manner, a groundwater model is required. This model should approach reality as near as possible. The base of this model has been developed by experts Pieter Filius and Marijke Jaarsma. “To validate and calibrate the model, we needed monitoring data. ARA Sul has a groundwater monitoring network, from where multiple-year monitoring data can be extracted and made available for the model” – Said Robert.
Remarkable ground water fluctuations
The Mozambican and Dutch experts executed a time series analysis of the available groundwater level data. In certain monitoring series, they observed eventual abnormal groundwater fluctuations: strange ‘peaks and drops’.
Indicated depletion
On a larger scale, these new insights may indicate the depletion of the groundwater system. Lizete Dias from ARA Sul replied: “We never knew there was such a large groundwater extraction in that area. Systematic analysis provides a lot of insight.”“.
Hereunder in the left graph fluctuations in groundwater level appear twice a day. In this case, it means, the groundwater level is influenced by the tide. The right graph shows a groundwater decline at approximately 7 AM, lasting till 12 PM (only once a day). Which suggests that it’s caused by an "on-off" groundwater extraction. In addition, the water level never becomes a flat line (groundwater level at rest).
