A river basin or river catchment is an area of land where all water that falls on that land, flows into one river. It can flow directly into the river or go through smaller rivers or streams that flow into the larger river. A river basin can be divided in sub-basins.
A delta or delta system is part of a river basin. Deltas are geographically well-defined flat sediment plains, subject to frequent inundation by river and sea.
Integrated Water Resources Management (IWRM) is defined as a process that promotes the coordinated development and management of water, land and related resources in the river basin in order to maximise the resultant economic and social welfare in an equitable manner, without compromising the sustainability of vital ecosystems.