Surface water
Water that appears on the surface, either flowing or stored in lakes and waterholes, is called surface water.
Surface waters are essential for human, plant and animal life.
Most surface water comes from rainfall runoff from the surrounding land area or catchment.
Types
The 3 types of surface water are:
- permanent or perennial - presents as rivers, lakes, springs and swamps - these are supported by groundwater when there's little or no rain
- semi-permanent - holds water for part of the year and are usually small creeks, lagoons, waterholes or low lying areas in the arid zone
- man-made - held in man-made structures ranging from lakes, dams and turkey nests to artificial swamps and sewage treatment ponds.
Climate and zones
Wet and dry seasons cause great changes in surface water.
This makes the amount of water on the ground go up and down.
In some parts where it's really hot and dry, it’s normal to have little water on the ground. But when it rains, the water can fill up rivers and other places for a short time.
This happens a lot in the Top End, which gets plenty of rain.
The Northern Territory (NT) has 2 main climatic zones:
- Top End - covering the northern one-third of the NT. It has a noticeable wet and dry season.
- Arid zone - covering the southern two-thirds of the NT. It has no clear wet season.
Read more about the climactic zones on the Territory Stories website.
The following helps to decide which zone a resource belongs to.
Top End
- Distinct wet and dry season, with over 95% of rainfall happening between October to April.
- Rainfall of more than 600mm in most years.
- Seasonal runoff of more than 0.5ML per hectare in most years.
- Streamflow with daily peak flows more than 10 times the average wet season flows.
- Seasonal (wet season) groundwater recharge happens in most years.
Arid zone
- No distinct wet season, less than 95% of rainfall happening between October to April.
- Variable and episodic rainfall, with less than 600mm occurring in most years.
- Runoff of less than 0.5ML per hectare per year, commonly with consecutive years of no streamflow
- Groundwater recharge happens rarely or not at all.
Taking surface water
There are rules and conditions for taking surface water in the Top End during the wet season.
Find out more about taking surface water.
Data and monitoring
Surface water is monitored in the NT, especially in areas of development where water extraction needs to be managed to prevent negative environmental impact.
Surface water data on streams and rivers can be collected as one-off (discrete) measurements. They can also be collected continuously by gauging stations.
Gauging stations collect water level, flow and rainfall data. They can also collect discrete water quality data.
You can get data from current and historic water gauging sites on the NT water data portal.