River Basins

Major river catchments are referred to as River Basins, and include many distinct landscapes from mountains to foothills to flat river plains. The boundary of the catchment follows the ridge line of mountains and hills surrounding the river system.

Victorian Streams
Victorian watercourses range from small, turbulent streams in the steeply graded rocky gullies of the uplands to the broad, meandering rivers of the low hills and plains.

Perennial or permanent streams, which flow for most of the year, are fed largely by interflow or groundwater flow. These rise mainly in the East Victorian Uplands and the western half of the South Victorian Uplands. (see landform map)

Intermittent or seasonal streams, which cease to flow in dry seasons, are fed mostly by interflow. These rise mostly in the West Victorian Uplands, where summer drought is more pronounced.

Ephemeral streams in the north-west of the state usually flow only from surface runoff after heavy rain. Flows are often short-lived and may not occur for years at a time.

Rainfall and Streamflow
During and immediately following rainfall, runoff contributes directly to streamflow, causing sharp peaks in flows. During and immediately following rainfall, runoff contributes directly to streamflow, causing sharp peaks in flows. Monthly streamflow reports across Victoria are available on DSEs Our Water Our Future website (external link).

Water that infiltrates the soil becomes interflow, or groundwater flow, taking days or weeks to reach the streams. This provides the regular, or baseflow, of streams.

• Streamflows closely follow the pattern of rainfall distribution.
• The major source of streamflows is from rain and snowfalls in the Victorian Alps. The only other areas generating substantial flows are the Grampian and Otway Ranges.

• For planning and management of water resources, streamflow variability is as important as the mean volume of flow.
• Annual streamflows in Victorian streams, like Australian streams, are more variable than streams in North America and Europe.
• Victorian streamflows are less variable than those in most other Australian states.
• 80% of streamflows come from the high rainfall areas in the east (40% of the state’s area) and only 20% from the drier western part of the state (60% of the area).

• There is a general trend from high streamflow variability in streams in the west of the state to low variability in streams in the east.

• Streamflows in Victoria vary widely between seasons.
• Most of the annual stream discharge occurs in July, August, September and October. These months provide about 60% of streamflows Victoria-wide, and 75% of flows in the western streams.
• Streamflows decrease during the summer and autumn months.

• Streamflows in Victoria also vary widely between years.
• Dry years and wet years occur almost at random.
• Lengthy runs of dry or wet years can occur.