Its basis is the watershed line of the catchment. The Thames River Basin District, including the Medway catchment, covers an area of . It is most saline on the Iranian shore, where the catchment basin contributes little flow. The Ganges Basin alone has a catchment of about . ZINWA is subdivided into different areas of water catchment. Slow-rising floods most commonly occur in large rivers with large catchment areas. Kaitaia lies within the Awanui River catchment. There are also baseflow contributions from the major aquifers in the catchment. Above this point is the extensive catchment of the headwaters of the Rhine. The Tawau Hills National Park established as a natural water catchment area. Water is gathered from roof catchment systems. There is hardly any arable land in the catchment. The catchment area of the lake is . Launceston's water comes from the Launceston Water Catchment. Flooding of the Yarrowee catchment occurs occasionally.