Fluviatile sediment fluxes to the Mediterranean Sea: a quantitative approach and the influence of dams

Abstract

AbstractThe Mediterranean drainage basin incorporates more than 160 rivers with a catchment >200 km2, of which only a few are larger than 50 × 103 km2: this observation emphasizes the role of the smaller rivers. The present investigation, incorporating the analysis of data sets from 69 rivers, has estimated a total sediment flux of some 1 × 109 tonnes (t) year−1; of this, suspended sediment contributes some two-thirds of the load, with the remaining third supplied by the combined dissolved and bed-load components. The magnitude of the sediment supply is best demonstrated by various observations: (i) some 46% of the total length of the Mediterranean coastline (46 133 km) has been formed by sediment deposition; (ii) many Mediterranean deltas have prograded in recent times by, at least, several metres per year; and (iii) Holocene coastal (inner shelf) deposits are some tens of metres in thickness. The construction of hundreds of dams around the Mediterranean Sea, especially over the last 50 years, has led to a dramatic reduction in the sediment supply- to approximately 50% of the potential (natural) sediment supply. Such a reduction is considered to be the primary factor responsible for the loss of coastal (mainly deltaic) land, with annual rates of erosion ranging from tens (Ebro, Po) to hundreds of metres (Nile).