The set of rivers and other temporary or permanent watercourses and reservoirs in a given territory. 

The structure of the hydrographic network - its density, lakes, wetlands - is determined by the whole complex of physical and geographical conditions, and above all by climate (sum of annual precipitation, evaporation), topography, geological structure of the area. In the process of erosion, new areas are added to the river catchment area that previously did not flow into the river system, eliminating areas without drainage, depressions, etc. 

The reduction in flow leads to the isolation of individual parts of the hydrographic network. When only a system of watercourses is considered, the term "river network" is used. However, the terms hydrographic network and river network are often used interchangeably.