Johnstone River in flood at Innisfail February 1999 (Cyclone Rona)
Photo: Brian Cassey
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. Tides can have a
significant impact on the smaller floods but little effect in larger
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 March 1967. The flood records for Innisfail indicate
that the highest recorded flood occurred in 1913 and that it was about 1.5
metres higher than the 1986 flood. Historical evidence indicates that the
floods in 1893 and 1894 were even higher.
The Johnstone Shire 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 offices 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 warning
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
Natural Resources also operate a number of automatic telephone telemetry
stations throughout 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.
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
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.
In consultation with the Johnstone Shire Council, the Bureau issues
Flood Warnings for the Johnstone River.
The base station computer located in the Johnstone Shire 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
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 :
Radio stations, particularly the local ABC, and local commercial
stations, broadcast Flood Warnings and River Height Bulletins soon
Local response organisations
These include the Councils, Police, and State Emergency Services in the
Internet/World Wide Web
Flood Warnings, River Height Bulletins and other weather related data is
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/hydro/flood/qld
Flood Warnings are available through a recorded voice retrieval system,
along with a wide range of other weather related and climate
1900 955 360
1300 659 219
Telephone Weather Services Call Charges:
1900 numbers: 77c per minute incl. GST; 1300 numbers: Low call cost
- around 27.5c incl. GST. (More from international, satellite, mobile or
Weather by Fax
Flood Warnings and River Height Bulletins are also available through a
facsimile information retrieval system, along with a wide range of other
weather related and climate information.
Main Directory (Free call)
1800 630 100
1902 935 065
River Height Bulletins
1902 935 057
Weather by Fax Call Charges: 1902 numbers: 66c per minute, incl. GST;
1800 numbers: Free (More from international, satellite, mobile or public
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 highest know
floods recorded at selected river height locations, together with
heights of recent floods.
Highest Recorded Flood (in metres)
All heights are in metres on flood gauges.
[*] These heights are taken at old gauge sites and may not relate to
flood levels from existing gauges sites.
Assessment of Flood
Major flooding requires a large scale rainfall situation over the
Johnstone River catchment. The following can be used as a rough guide
to the likelihood of flooding in the catchment:
Average catchment rainfalls of in excess of 200mm in 24 hours may
cause stream rises with moderate to major flooding and traffic
disabilities to develop, particularly in the lower reaches downstream
of Nerada on the North Johnstone River and Corsis on the South
Johnstone River extending to the coastal plain around the
Innisfail township and the mouth of the Johnstone River.
Average catchment rainfalls of in excess of 300mm in 24 hours may
cause significant stream rises with major flooding and traffic
disabilities to develop, particularly in the lower reaches
downstream of Nerada on the North Johnstone River and Corsis on the
South Johnstone River extending to the coastal plain around the
Innisfail township and the mouth of the Johnstone River.
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.