The clearing of land for agriculture in the Cann Valley commenced in the 1870s. On the fertile floodplains, trees were ringbarked or felled, and vegetation was removed and burnt. Paddocks were ploughed, pasture sown and stock introduced.
River banks were cleared to provide stock access to water, for river crossings and by stock grazing.
A major flood in February 1919 commenced a process of bank erosion, channel widening and the stripping of topsoil from the floodplain. Photographs in the 1930s, 1940s and 1950s show a massive widening of the river channel with high, eroding banks following major flood events.
Flood damage 1978
Extensive works were undertaken in an attempt to manage these channel changes by private landholders, the Cann River Improvement Trust (1963-1990) and the East Gippsland River Management Board (1990-1997). These works included desnagging, the clearing of vegetation and channel straightening.
Unfortunately, these works increased flow velocity and stream power which significantly reduced the capacity of the channel to withstand erosion.
Following the 1978 floods, the Cann River Improvement Trust embraced the view of the Trust engineer Ian Drummond to hold the alignment of the river through retard fields and bank protection works, and to stabilise the channel with bank vegetation. Other works included eradication of willows and wattles growing in the channel, erection of stock exclusion fencing, and revegetation using native species.
After 1990, these works were continued by the East Gippsland River Management Board.
A 1997 report also identified bed degradation in the floodplain reach since 1983 as a major contributing factor to the instability of the river. The report considered that without bed stability, the banks were prone to erosion due to loss of support at the ‘toe’ of the bank and an increase in bank height. And without bank stability, the conditions would not be right for indigenous vegetation to become re-established and provide natural defences against further erosion.
Rock chute, Cann River
The report also recommended the construction of rock structures to stabilise the river bed.
The June 1998 flood on the Cann River upstream of the floodplain reach was estimated to be a 30 to 40 year
The Flood Response Program (FRP) consisted of three components - grade control structures, intermediate structures and revegetation.
The FRP proposed that seven grade control structures (rock chutes) be built to increase the stability of the bed and banks, and reduce the risk of ongoing stream bed deepening. In the end, four grade control structures were built above the Princes Highway Bridge.
‘Intermediate structures’ (pile fields) between the grade control structures were also proposed to reduce the potential for the fluidisation of the stream bed and assist with the re-establishment of vegetation. Twenty structures were proposed. In the end, nine structures were built (8 above the Princes Highway Bridge).
Pile field, Cann River
Revegetation was designed to support and compliment the immediate and long term stabilisation of the rock structures. Extensive plantings of native vegetation, including sedges and rushes in the sand bed of the river were completed in 1999 and following years.
These works have been continued in recent years by the East Gippsland CMA. These works have included the maintenance of fencing to prevent stock access to the river, weed control including willows, revegetation, rock chutes and pile fields. Additional pile fields were constructed below the Princes Highway Bridge in late 2012.
These works are designed to support a ‘natural healing approach’ to the rehabilitation of the river which is expected to take some years to occur. As the vegetation becomes established it will provide natural defences against erosion, although some damage is expected to occur during major flood events.
Over time, the river channel will reduce in size. During major floods, the river is expected to ‘break its banks’ and flow onto the floodplain, releasing the destructive force of the water that was previously retained within the river channel and caused so much damage in the past.