"Schemes for diverting the Clarence have been put forward at regular intervals for close to 100 years, and all have been rejected as being economically unviable, and environmentally devastating, and socially unacceptable."

 

Clarence Valley Independent, 5 December 2020:

Investigating Potential River Diversions

It’s on again! Another plan to solve all inland Australia’s drought problems, by taking supposedly inexhaustible quantities of water from the Clarence River.

The latest scheme comes via a NSW Government draft Regional Water Supply Strategy which at this stage is only listed as an option, suggesting a: “Comprehensive investigation of potential diversion of flows from the east of the Great Dividing Range”.

We really have to ask, how many comprehensive investigations do we need? Schemes for diverting the Clarence have been put forward at regular intervals for close to 100 years, and all have been rejected as being economically unviable, and environmentally devastating, and socially unacceptable.

The Clarence diversion idea has been supported by a mythical 5 million megalitre average annual flow figure and perpetuated by the propensity for modern day consultants to rely on desk-top reviews.

The reality is, Clarence River flows, measured at the Lilydale gauge, have averaged barely 2 million megalitres since it was installed in 1970. So where did the 5 million figure come from?

The last report to quote that amount was by the Snowy Mountains Engineering Corporation in 2007, referencing a NSW Water Resources report from 1981, That report in turn referenced a seminar by the Department of Water Resources, which claimed to have “relied on readily available information…”.

Undoubtedly, that ‘readily available’ information’ came from a June 1975 report promoting “The Jackadgery Multi-purpose Dam Project”, which claimed the Clarence “has a long-term average annual runoff of some 5 million megalitres”, but provided no reference.

My guess is that they simply took the readings from the Lilydale gauge which had been installed 4 years earlier and used that 4-year average. However, 1972 recorded the highest ever flows, over 9.5 million megalitres, thus inflating the 4-year average to 5 million.

It’s hard to believe consultants would not check readily available on-line figures from gauges, but I suppose, if you are proposing to pump 1 million megalitres across the range, 5 million looks a lot better than 2 million!

– John Edwards

From 10 November to 6 December 2020 the Clarence River at Lilydale was less than 1 metre in height and, as readers will probably have guessed, the automatic gauge reading on the summer morning of 6 December was 220.4 megalitres. In fact daily water flow had been below 250 megalitres for the previous 12 days.

As for longer period records derived from rainfall, stream water level and discharge rate - the Lilydale gauge has shown monthly water flow rates from1971 to 2020 which do not support the idea that there is 'surplus to needs' water flowing down the Clarence River and into the estuary.

Clarence River at Lilydale, Clarence Valley NSW
IMAGE: realtimedata.waternsw.com.au