Effects of the construction of dams on the water and sediment fluxes of the Moulouya and the Sebou Rivers, Morocco

The sediment fluxes of the Moulouya and the Sebou Rivers – the two largest rivers in Morocco – were estimated on the basis of suspended sediment loads carried by these rivers towards the coastal zone. The high rate of the specific sediment yield of the Sebou (995 t km year), which is one of the highest in Africa, is probably due to the fact that the drainage basin is characterized by young mountains, extended erodible sedimentary rocks, irregular and often stormy precipitation and scarce vegetation. Recently, the construction of dams and changes in rainfall have drastically reduced these sediment load and water discharges. It is estimated that the construction of dams has reduced the water discharge of the Sebou and the Moulouya rivers by 70 and 47% respectively, and their sediment fluxes by nearly 95 and 93%. The damming of rivers has also had a profound effect on the coastal zones, which reacted by reaching a new sedimentary equilibrium. The forcing induced by the estuarine behavior of the lower stretches of both rivers downstream of the dams has greatly disturbed the mouth topography and coastal stability.