Basics
Surface Water and the Water Cycle
Water is one of the important and life giving natural resources.
Water is endlessly circulating between the oceans, the atmosphere and the land. Water that is seen on the surface, either flowing or stored in natural depressions (lakes, waterholes etc.) is called Surface Water.
Surface water can be:
- permanent (perennial) - flowing or held in natural depressions throughout the year
- semi-permanent (ephemeral) - flowing or held for only part of the year
- man-made - held in structures ranging from dams to a water tank that catches rain.
Climatic Zones
The abundance of surface water is controlled mainly by climate. The NT has two climatic zones, humid and arid.
Humid
- Mean annual rainfall 600mm to 1500mm
- Streamflow 2 megalitres per hectare per annum
- All the streams flow north into the Timor Sea or the Gulf of Carpenteria.
- Streamflow shows huge variability. Most streams have recorded nil flow over the dry season months but maximum monthly stream flows up to 10 times the average during the wet.
Arid
- Mean annual rainfall 100mm to 550mm.
- Stream flow 0.2 megalitres per hectare per annum
- All streams flow inland and do drain into the sea.
Drainage Divisions
River basins are the catchment areas of major rivers of which there are 39. They are grouped to form drainage divisions based on rivers flowing into a particular sea, or inland.
The NT is covered by four drainage divisions, the Timor Sea, the Gulf of Carpentaria, the Western Plateau and Lake Eyre.
