Wadi damming and its impacts in an arid region of Algeria: Case of M'Zab Wadi basin

Most dams have been built to maximize short-term economic benefits, often with little or no understanding of their long-term hydrological and ecological consequences. Historically, the downstream region of the M'Zab wadi basin (MWB) has experienced recurring flood events, resulting in significant economic losses and fatalities. In response, three flood-retention dams were constructed upstream of the MWB to mitigate future flood risk. While these dams have effectively reduced the magnitude of downstream floods, they have also led to unintended environmental consequences, including soil salinization, degradation of shallow groundwater quality, and the decline of oasis ecosystems. This paper aims to highlight the environmental impacts of flood-retention dams on downstream areas of MWB, using an integrated approach that combines remote sensing and geographical information systems (GIS). A Landsat time series (2005–2023), spanning both pre- and post-dam construction periods, was analysed to track changes in downstream vegetation cover. Results show a decline in spate-irrigated palm groves downstream after dam construction, with an overall 12% reduction in area across the study region and a 23% decline specifically within the old groves of Ghardaïa. The results point to the need for a holistic flood risk management strategy that balances flood mitigation with the long-term sustainability of fragile ecosystems. The methodology used can help decision-makers evaluate dam-related impacts and inform future dam planning and monitoring in regions with similar environmental conditions.