ACCORDING to Australian aboriginal mythology Bunyips are monsters that live in rivers. According to Ron Pike, an Australian who has spent his life working with water from the Murrumbidgee River, much of what is being claimed about Australian rivers is as unreasonable as a belief in Bunyips:
“The lack of flow volumes in the rivers of the Murray Darling Basin (MDBC) in recent years is not due to irrigation and over extraction. The facts are that without the storages and the irrigation industries, conditions would have been considerably worse. Throughout the MDB there is presently more wetland habitat than there would have been had there been no irrigation for the last several years. It is also wrong to suggest that increasing stream flows by releasing extra water from storages, somehow benefits the environment. It makes no appreciable difference to the environment whether the Murrumbidgee at say Narrandera is running at 3,500 megalitres per day or 25,000 megalitres per day. The flows in both cases remain within the banks and do not, and cannot, water the floodplain or most wetlands.
Reading the journal notes of the men who were the first explorers of the rivers of the Murray Darling Basin (MDBC) gives us a number of facts which are still relevant if we care to understand the system and wish to maintain it for the good of future generations.
The explorers note that once the rivers of the MDB leave the hills and commence their meandering journey across the plains, the stream flow is twenty to forty feet below the surrounding flood plain. Only at the Macquarie Marshes, the wetlands of the lower Lachlan and to a lesser extent above the Bahmar Choke in the Murray do the rivers flow above their bank, other than in large floods.
Most of the other rivers in the MDB, including the Murray have the same characteristics; once they reach the flood plain (it is on the flood plain that the wonderful River Red Gums grow and also the vast but irregularly watered wetlands preside); they flow well below the surrounding plains. Therefore these wetlands are only ever flooded in periods of excessive catchment rainfall which causes the river to flow above its banks. When this happens the wetlands explode in a volcano of abundant life across all species natural to this environment.
A magnificent, spontaneous and symbiotic food chain develops only limited by the environment in which it exists, and sadly it seems, not understood by many present day commentators.
In order to understand the system it is necessary to have some understanding of water volumes.
A megalitre is 1 million litres or 1000 cubic meters. It is the measure that is used for all sales and purchases of water throughout the MDB. It is also used by all Municipal authorities. For those who want a comparative picture, an Olympic Pool is around 1.7 megalitres, depending on depth and width.
In the case of the Murrumbidgee, the photograph shows the river running at around 2,400 megalitres per day. If a release from both Burrinjuck Dam (full capacity 1.03 M megalitres) and Blowering Dam (full capacity 1.6 M megalitres) of 20,000 megalitres per day were to be made in this situation, it will not put water onto the flood plain. A flow of 40,000 M/d will put some water into a few low lying Billabongs and backwaters, but will not put water on the floodplain. All that would be achieved is a high river flow for a few days. Most of which would run to the sea and to waste. The same applies to most other valleys in the MDB.
To put water onto the Murrumbidgee floodplain and fill the wetlands requires volumes in excess of 150,000 megalitres per day. This is far beyond what is possible from existing storages. It will only ever be achieved by Mother Nature and man has no influence on its recurrence and little on its magnitude. As an example of what is required to flood any of the MDB river valleys, the Murrumbidgee flood of September 1974 is enlightening. Following heavy rain in the area of the ACT, Burrinjuck dam quickly filled and a day later there was almost 400,000 megalitres per day going over the spillway, plus the outlets were fully open. There was sufficient water going down the Murrumbidgee Valley to fill Burrinjuck from empty every two days.
While this flood reached a height of 9.19 meters at Wagga Wagga it was not an exceptionally large flood historically. This and greater volumes are required in most of the river valleys of the MDB to water the wetlands.
Our early explorers and settlers recognized the huge flow changes that occur in our river systems. They were also aware that this old river system was very unpredictable. It moved from abundance of flow to completely dry at irregular intervals.
While a vocal minority of modern man seems unable to accept these historical and present facts, we are prone to make bad decisions on behalf of future generations. From the 1840s to present time we do have sufficient records to support the variability of stream flows within the MDB. One of these is at Wagga Wagga where records have been kept since 1844 and show that there have been 77 floods over 8.23M. Note a flow of 3,000 mgs. /day is a river reading of approximately 1 metre at this site.
To stress the point, the Murrumbidgee at Wagga has to rise 7 metres above normal flow to reach flood level and water the floodplain. This requires volumes far in excess of any storage on the system.
Ron Pike now lives at Coff Harbour on the NSW Central Coast in Australia. Read Part 1 here. Photograph of the Murrumbidgee River at Gogeldrie taken on September 3, 2008.