The impact of river regulation and climate change on the barred estuary of the Oued Massa, southern Morocco

The estuary of the Oued Massa, southern Morocco, has experienced alternating phases of tidal and lagoon conditions. Using field surveys, aerial photographs and rainfall–runoff records the dominant processes and recent evolution of the estuary are described. These data suggest that the character of the estuary has changed since the upstream impoundment of the river by the Youssef Ben Tachfine reservoir. The frequency of low-flows has been significantly increased by river regulation, as has the mean interval between flood events. Using reconstructed flow series it is speculated that lagoon conditions have become more common in the post-impoundment era than at any time since the 1920s. Although increases in winter precipitation projected by the global climate model HadCM2 for 2030–2049 imply a higher frequency of flood flows entering the reservoir in the future, the magnitude and frequency of such inflows are still within historic variability. Nonetheless, higher inflows may produce more frequent spills with concomitant bar breaching and termination of lagoon phases. Despite this, it is argued that the presence of the dam is ultimately of greater consequence to the functioning of the estuary–lagoon system than future precipitation changes over the region. Copyright © 2001 John Wiley & Sons, Ltd.