FLOOD WARNING SYSTEM
for the
JOHNSTONE RIVER

Johnstone River in flood at Innisfail February 1999 (Cyclone Rona) Photo: Brian Cassey

Contained in this document is information about: (Last updated November 2017) Flood Risk Previous Flooding Flood Forecasting Local Information Johnstone ALERT System Flood Warnings and Bulletins Interpreting Flood Warnings and River Height Bulletins Flood Classifications Other Links

Flood Risk

The North and South Johnstone Rivers rise in the tablelands of the north tropical coast and flow through steep narrow gorges to their junction on the coastal plain at Innisfail. The headwaters of the catchments are located in high rainfall areas and the rivers are capable of producing severe flooding, especially in the Innisfail area. The North and South Johnstone Rivers have a combined catchment area of about 1,600 square kilometres at Innisfail.

There is a strong rainfall gradient across the catchment with the heaviest rain generally falling along the eastern side of the catchment around Topaz, Crawfords Lookout and Innisfail.  In the western area of the catchment, rainfall totals tend to be significantly less. Heavy localised rainfall along the coastal strip to Crawfords Lookout can cause rapid river rises in the lower Johnstone Rivers around Innisfail and Mourilyan, although larger floods tend to be associated with catchment wide heavy rainfalls.

The Johnstone River delta area can be subject to severe flooding with low lying areas being susceptible. Large areas of agricultural areas can be inundated and residential areas affected.  

Previous Flooding

Severe flooding of the Johnstone River is often associated with tropical cyclones. The two highest floods at Innisfail in recent years occurred in February 1986 and February 1999. The flood records for Innisfail indicate that the highest recorded flood occurred in 1913 and was about 1.7 metres higher than the 1999 flood. Historical evidence indicates that the floods in 1893 and 1894 were even higher.

Flood Forecasting

The Cassowary Coast Regional Council, in conjunction with the Bureau of Meteorology operates a flood warning system for the Johnstone River catchment. The ALERT network consists of automatic rainfall and river height stations which regularly forward data via radio telemetry to a base station located at the Council office in Innisfail and the Bureau's Flood Warning Centre in Brisbane. The system provides early warning of heavy rainfall and river rises in the catchment and enables more accurate and timely flood warnings and forecasts. The balance of the network consists of volunteer rainfall and river height observers, who forward observations by telephone when the initial flood height has been exceeded at their station. The Department of Environment and Resources Management also has automatic telephone telemetry stations in the catchment.

The Bureau's Flood Warning Centre issues Flood Warnings and River Height Bulletins for the Johnstone River catchment during flood events. Quantitative flood forecasts are issued when moderate flood levels are likely to be exceeded at Innisfail, with an objective to provide between 3 and 9 hours warning of flood levels and forecasts updated every 3 hours during the flood event.

Local Information

The Cassowary Coast and Tablelands Regional Councils are able to provide further information on flooding in your area of the Johnstone River catchment.

Johnstone River ALERT System

The Johnstone River ALERT flood warning system was completed in 1989 as a co-operative project between the Bureau of Meteorology and the previous Johnstone Shire Council. The system comprises a network of rainfall and river height field stations located on the Tablelands as well as the coastal plain which report via VHF radio to a base station computer located in the Council office in Innisfail. The field stations send reports for every 1 millimetre of rainfall and every 50 millimetre change in river height. 

The base station computer located in the Council office collects the data and has software that displays it in graphical and tabular form. The data is also received by the Bureau's Flood Warning Centre where it is used in hydrologic models to produce river height predictions. 

Flood Warnings and Bulletins

The Bureau of Meteorology issues Flood Warnings and River Height Bulletins for the Johnstone River catchment regularly during floods. They are sent to radio stations for broadcast, and to local Councils, emergency services and a large number of other agencies involved in managing flood response activities. Flood Warnings and River Height Bulletins are available via :

Local response organisations
These include the Councils, Police, and State Emergency Services in the local area. 

Internet/World Wide Web
Flood Warnings, River Height Bulletins and other weather related data are available on the Bureau's Web page at http://www.bom.gov.au . The Queensland Flood Warning Centre website is http://www.bom.gov.au/qld/flood/ .

Telephone Weather
Flood Warnings are available through a recorded voice retrieval system, along with a wide range of other weather related and climate information.

Interpreting Flood Warnings and River Height Bulletins

Flood Warnings and River Height Bulletins contain observed river heights for a selection of the river height monitoring locations. The time at which the river reading has been taken is given together with its tendency (e.g. rising, falling, steady or at its peak). The Flood Warnings may also contain predictions in the form of minor, moderate or major flooding for a period in the future. River Height Bulletins also give the height above or below the road bridge or causeway for each river station located near a road crossing. 

One of the simplest ways of understanding what the actual or predicted river height means is to compare the height given in the Warning or Bulletin with the height of previous floods at that location. 

The table below summarises the flood history of the Johnstone River catchment - it contains the flood gauge heights of the more significant recent floods.

Historical flood heights for all river stations in the Johnstone River Floodwarning network, as shown on the map, are available from the Bureau of Meteorology upon request.

Flood Classifications

At each flood warning river height station, the severity of flooding is described as minor, moderate or major according to the effects caused in the local area or in nearby downstream areas. Terms used in Flood Warnings are based on the following definitions.

Minor Flooding : Causes inconvenience. Low-lying areas next to watercourses are inundated. Minor roads may be closed and low-level bridges submerged. In urban areas inundation may affect some backyards and buildings below the floor level as well as bicycle and pedestrian paths. In rural areas removal of stock and equipment may be required. Moderate Flooding : In addition to the above, the area of inundation is more substantial. Main traffic routes may be affected. Some buildings may be affected above the floor level. Evacuation of flood affected areas may be required. In rural areas removal of stock is required. Major Flooding : In addition to the above, extensive rural areas and/or urban areas are inundated. Many buildings may be affected above the floor level. Properties and towns are likely to be isolated and major rail and traffic routes closed. Evacuation of flood affected areas may be required. Utility services may be impacted.

Each river height station has a pre-determined flood classification which details heights on gauges at which minor, moderate and major flooding commences. Other flood heights may also be defined which indicate at what height the local road crossing or town becomes affected by floodwaters. 

The table below shows the flood classifications for selected river height stations in the Johnstone River catchment. 

The above details are correct at the time of preparing this document. Up-to-date flood classifications and other details for all flood warning stations in the network are at: