In terms of surface water, the most important hydrological basin is that of Sakia El Hamra, which covers an area of 81,000 km².
The rest consists of poorly individualized diffuse networks, due to the almost horizontal topography, infrequent precipitation, and high evaporation.
The important features that characterize the flows are:
- The very low number of days of flow in the year, caused by the scarcity of precipitation.
- The strong floods during significant rainy episodes;
- The weak parts (in terms of basin area) are active, contributing to the flows.
