Sediment deposits in North African catchments contribute to around 2%–5% of the yearly loss in the water storage capacity of dams. Despite its semi-arid climate, the Tafna River plays an important role in Algeria’s water self-sufficiency. There is continuous pressure on the Tafna’s dams to respond to the demand for water. The Soil and Water Assessment Tool (SWAT) was used to evaluate the contribution of different compartments in the basin to surface water and the dams’ impact on water and sediment storage and its flux to the sea in order to develop reservoir management. The hydrological modelling fitted well with the observed data (Nash varying between 0.42 and 0.75 and R² varying between 0.25 and 0.84). A large proportion of the surface water came from surface runoff (59%) and lateral flow (40%), while the contribution of groundwater was insignificant (1%). SWAT was used to predict sediments in all the gauging stations. Tafna River carries an average annual quantity of 2942 t·yr⁻¹ to the Mediterranean Sea. A large amount of water was stored in reservoirs (49%), which affected the irrigated agricultural zone downstream of the basin. As the dams contain a large amount of sediment, in excess of 27,000 t·yr⁻¹ (90% of the sediment transported by Tafna), storage of sediment reduces the lifetime of reservoirs.

The objective of this study is to propose a modelling approach to quantify the contribution of mains coastal catchments of North Africa in sediment and nitrate fluxes to the Mediterranean Sea. We use the Soil and Water Assessment Tool (SWAT) on the biggest coastal rivers, Moulouya (55 860 km²), Tafna (7200 km²), Chelif (44 694 km²) Oued el Kebir (8 824 km²) and Medjerda (23 213 km²). Simulation was performed monthly from 2003 to 2013. The model represents correctly the dynamics of water, sediment and nitrate flux. Rivers carry between 22 .10³ to 390 10³t yr^-1 of sediments and Oued el Kebir contributes with 55% of the total amount, while nitrate fluxes vary from 182 to 1715 t yr^-1 and Moulouya contributes with 32% of the total quantity. The simulations show us that the North African dams stocked a large amount of sediment (98%) and nitrates (39%) transported by rivers.