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

The estuary of the Oued Massa, southern Morocco, has experienced alternatin g phases of tidal and lagoon conditions. Using field surveys, aerial photog raphs and rainfall-runoff records the dominant processes and recent evoluti on of the estuary are described. These data suggest that the character of t he estuary has changed since the upstream impoundment of the river by the Y oussef Ben Tachfine reservoir. The frequency of low-flows has been signific antly increased by river regulation, as has the mean interval between flood events. Using reconstructed flow series it is speculated that lagoon condi tions have become more common in the post-impoundment era than at any time since the 1920s. Although increases in winter precipitation projected by th e global climate model HadCM2 for 2030-2049 imply a higher frequency of flo od 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. Co pyright (C) 2001 John Wiley & Sons, Ltd.