Influencia del complejo de embalses Mequinenza-Ribarroja-Flix (río Ebro) en la morfología del cauce situado aguas abajo

Resumo

Impounded channels suffer frequently a series of changes due to water regulation and sediment starvation. In this paper, the effects of impoundment are analysed along a 40 km reach of the Ebro River, located downstream of the Mequinenza-Ribarroja-Flix reservoir complex. The main changes recognized in this channel are: lack of sedimentation, bar scouring close to the dam, encroachment of vegetation into bars and banks, and wash out of fine sediments leading to channel armouring. Such alterations produced a quick channel stabilization. Two factors were responsible for these alterations, namely the previous presence of abundant gravels and a high rate of vegetation colonisation in the section. The morphosedimentary evolution of the reach since 1927 until the sixties, when reservoirs were built is also assessed in the paper. Such evolution was dominated by the effects of rare catastrophic events. Throughout the study period two events fulfilling these characteristics were recorded. The effects of each flood together with the role of the River Ciurana confluence during them are also emphasized. The River Ebro Delta is developed close to the study reach, so that these results also throw light on the sedimentary processes operating in it, both before and after dam closure.