Arid and semi-arid areas are characterised by differentiation in meteorological conditions. Sometimes the rains are rare and not very intense and at other times they are dense and very intense, resulting in torrents that often lead to strong soil erosion. Most of the time, the losses occur at the solids level because the erosion effect is too high. In this study, we want to evaluate the transfer of solid sediments as a function of liquid transport in the basin of Wadi Zeddine at Ain Defla in Algeria. To understand this phenomenon, we used the data of liquid flows ( Q_l, m ³∙s ^–1) and concentration of suspended sediments ( C, g∙dm ^–3), transported in the river, the data collected by the NWRA (National Water Resources Agency), over 24 years have been used to find a relationship between these two quantities, to estimate the quantity of solid transport Q_s (kg∙s ^–1) in the watercourse of the catchment area studied. The results obtained show a good correlation between solid and liquid flows, with a correlation coefficient estimated at 90%, and the average annual sediment supply recorded at the outlet of the Wadi Zeddine watershed is estimated at around 88,048 Mg, which corresponds to 202 Mg∙km ^–2∙y ^–1/ erosion rate. This value is comparable to those found in other regions with similar hydrological regimes.

The pressure on the use of water and climate change has caused a decreased availability of water resources in semi-arid areas in the last decades. The Setif Province is one of the semi-arid zones of Algeria as it receives an average less than 400 mm∙year–1. The question of the evolution of demographic pressures and their impacts on water resources arise. By applying WEAP software (water evaluation and planning), the aim is to develop a model of water resources management and its uti-lization, assess the proportion of the resource-needs balance and analyse the future situation of water according to different scenarios. This approach allows to identify the most vulnerable sites to climatic and anthropogenic pressures. The estima-tion of the needs for drinking water and wastewater in the Setif Province has shown that these needs increase over time and happening when the offer is not able to cover the demand in a suitable way. It is acknowledged that there is a poor exploita-tion of water resources including underground resources, which translates into unmet demand in all sites of demand.