Tuesday, May 26, 2015

The Creeping Terror!

Lake Corangamite - as I mentioned in my previous post - is not considered part of the Barwon Basin. This does not mean however, that water from the Lake Corangamite system can't make its way to the Barwon, a fact which was highlighted with disastrous consequences in the 1950s. By the beginning of 1953, 60,000 acres of the best farming land in the country had disappeared beneath an inexorable tide of salt water and the financial cost in lost revenue and land value ran into the millions of pounds. Not only could the surface water remain for years after the flooding took place, but once dry, the high salinity of much of the water meant that the land was now so salty as to be useless for agricultural purposes.
Farmland in the Western District
The reason: record rainfall which had seen water levels in the lakes and swampy, low-lying areas rise in a way which had not occurred for a century. Lake Colac which normally had a circumference of 90 miles, now measured 150 miles around and had overflowed into Lough Calvert, Lake Gnarpurt was threatening to overflow into Lake Corangamite, taking the small spit of land which separated them with it, thereby elevating water levels and flooding even more of the surrounding countryside. Eventually, the water reached Lake Murdeduke where it overflowed into the Barwon Basin, ultimately draining into the Barwon river.
In the normal, geological scheme of things, this is how rivers and creeks form. Major flooding events such as those which occurred along the Barwon and across the Western District of Victoria in 1852, 1951-1953 and 1995, cause significant change over thousands, even millions of years, to the way in which water drains from a region. Whilst geologically older areas have more established drainage patterns, the Western District is relatively young geologically speaking, with the most recent volcanic eruptions occurring a mere 7,000 years ago. As a result, drainage patterns are still ill-defined, which of course accounts for the large number of lakes and swamps in the region.
All this was scant consolation to the farmers and graziers of the Western District during the 19th and 20th centuries whose livelihood was at risk every time water levels rose, and by mid-January, 1953 they were at crisis point. Something had to be done, as the Colac Shire President declared, to stop the "creeping terror"!
The issue had been discussed for decades, even as far back as the 1870s so of course they had a plan - a plan which involved the Barwon. As a matter of urgency, it was decided by the state government, the relevant shire councils and the State Rivers and Water Supply Commission, that immediate action was required. The Colac Shire President declared that the township was prepared to close for a week if necessary, in order to provide the labour to complete the works.
The plan was a simple, open drainage channel controlled by flood gates which, when complete, would carry water from Lake Colac north via low-lying ground to Lough Calvert from where it would again be diverted via a channel south to Sanctuary Lake (aka Salt Lake) and from there, via a third section of channel to Birregurra Creek near Warncoort from whence it would flow into the Barwon at its confluence near Conn's Lane.
Low-lying land at the northern end of Lough Calvert
On Friday, 24th April, the Argus proudly reported that after nine weeks of hard work, the first stage of the scheme had been opened with due ceremony, the previous day when the flood gates were opened near the Warrowie Estate, allowing water to flow from Sanctuary Lake into Birregurra Creek. It was planned that over the following three months, four feet of water would be drained from Lough Calvert and surrounding land before the second phase of the project which would see water from Lake Colac and other local lakes directed into Lough Calvert via an extension of the channel. The scheme was to be overseen by the specially commissioned Lough Calvert Drainage Trust.
This second stage did not come into action however, until August, 1954 when permission was granted for a foot of water to be drained from Lake Colac. So far so good. This however, did nothing to alleviate the same issues faced by those property owners threatened by the flooding of Lake Corangamite, Lake Murdeduke and areas in between.
Another solution was required for them. In April, 1954 affected locals were pushing for Lake Corangamite to be drained, however then premier John Cain declared this to be unfeasible as the Barwon could not cope with the volume of water which would need to be diverted. Instead, it was postulated that a weir constructed on the Woady Yaloak River near Cressy could then divert water to the Barwon via a channel which would reduce flooding in the area. This was not a new idea. It had first been postulated as early as 1876, but it was not until the inundation of the 1950s that action was finally taken.
Low-lying land on the shores of Lake Martin. Water from Woady Yaloak River
drains into the lake before entering the Cundare Pool and eventually, Lake Corangamite
The scheme however, was not without its opponents. Mr J.M. MacIntyre, Engineer-in-Chief of the Geelong Waterworks and Sewerage Trust (and namesake of the MacIntyre Bridge over the Barwon in Geelong) warned the State Parliamentary Public Works Committee that diverting such a large amount of water during periods of high flow in the Barwon would result in catastrophic flooding in the flats downstream towards Geelong, rendering surrounding land useless and seriously affecting the operation of the mills along the river in town. The Trust felt that the diversion should not be implemented unless steps were first taken to prevent flooding downstream.
Regardless, the scheme, including a channel of around 38km was finally commissioned in May 1959. Precautions in the form of seasonally variable salinity limits were placed on the operation of the channel and works were undertaken on the Barwon floodplain in the region of Breakwater and Marshall to mitigate the effects of any downstream flooding resulting from the increased flow from the Woady Yaloak diversion. Operation of the diversion is also dependent upon a maximum downstream water level in the Barwon.
The Blackpool Regulator on the Colac-Ballarat Road south of Cressy, near
the start of the Woady Yaloak diversion
Both the Woady Yaloak and Loch Calvert diversion schemes are controlled by a series of regulators which allow water flow to be reduced or increased according to salinity levels in the Barwon, water levels in each of the lakes and other factors including a mandatory period of no flow for two weeks during May and June which allows for better quality dam water for landowners in the district. This latter however, is dependent upon a minimum flow of 250Ml/day in the Barwon.
Looking east along the channel from the Colac-Ballarat Road
 The system was given its first real test in 1960 when flooding occurred across the district. No disastrous flooding occurred downstream in Geelong.
In 1966 a different approach to flood-control in the region was taken when provisions were made via the Lake Corangamite Act, for landholders whose properties were directly adjacent to Lake Corangamite, to surrender their land nearest to the lake to the government in return for compensation.
A similar process was put in place for those who owned land around Lake Colac which saw the government either buy or lease back flood-prone land near the lake.
In 1975, the diversion scheme was again tested with significant flooding in the region and along the Barwon. Even with the diversion in operation, Lake Colac overflowed and out of season releases of water were made in 1975 and 1976 in order to reduce flooding. This procedure was used a number of times over subsequent years, with Lake Colac again overflowing in 1991. The authorities ordered that control of the facility be tightened in 1981 after an unauthorised release of water occurred from the Lough Calvert system during the summer months.
On 1st July, 1998, the administration of both channels was transferred from their respective regulatory bodies to the Corangamite Catchment Management Authority. In recent years, both drainage schemes have been underutilised. The Woady Yaloak Diversion was last used in 2000 and in the decade following flooding in 1995, rainfall is estimated to have fallen by 12% in the region.
A very dry channel at the Poorneet Road crossing, south of Lake Weering
Also dry. Cressy Road
Not surprisingly, water levels in Lake Colac, Lake Corangamite, Lake Murdeduke and other lakes and wetlands around the region have decreased and the health of these water bodies has declined. Numbers of fish and invertebrates have decreased and bird numbers also fluctuate with changes in salinity which in Lake Corangamite currently stand at somewhere near 4 times greater than seawater. It has been suggested that these adverse changes in Lake Corangamite's ecological health are in large part due to to the Woady Yaloak Diversion Scheme.
Much of the infrastructure appears to date back to its initial construction in 1959.
Road crossing, Cressy Road
Some newer infrastructure alongside the old on McIntyre's Road
As recently as 2010, catchment management rules required the automatic diversion of water from Woady Yaloak River via the drainage system when water levels in the river reached a particular height, regardless of water levels in the lake, meaning that extra water from Woady Yaloak River could not be diverted to help maintain water levels and address salinity issues in Lake Corangamite.
It has been suggested that these rules be reviewed and changed if necessary to improve the health of the lake and surrounding wetlands.

The rock-lined channel, McIntyre's Road
Whilst low water levels in the lake are not unheard of (in the 1860s the lake dried out completely, with low water levels also recorded in 1914 and the 1930s), without significant flooding events and a return to higher average rainfall, it is anticipated that much of the biodiversity for which the region is listed under the RAMSAR agreement will disappear.
For further information, the following report here by the Corangamite Catchment Management Authority includes more details of both diversion schemes as well as maps indicating the main features of each channel.