The Yallock Outfall Scheme and the construction of the Spillway at Cora Lynn were the last major engineering works undertaken on the drainage of the Koo Wee Rup Swamp. This work was the subject of an article, Yallock Outfall Scheme Completed written by W.T. Griffiths, Dip. C.E., E.W.S., Executive Engineer, in the January 1966 edition of AQUA, the official journal of the State Rivers and Water Supply Commission. I have transcribed it, below. The article appeared on pages 114-119 and included two photographs (one reproduced) and two plans (both reproduced).
In February, 1963 the issuing of the final certificate to
the contractors who constructed the spillway ford between Koo Wee Rup Main
Canal and the Yallock Outfall signified the effective completion of the Yallock
Outfall Scheme.
This project was conceived after the disastrous 1934 floods
to protect both the township of Koo Wee Rup and the areas of rural land along
the Koo Wee Rup Main Canal from occasional flooding following heavy rain.
The Commissioners Koo Wee Rup Flood Protection District contains
about 100,000 acres of land and extends from the head of Western Port Bay to
the Main Gippsland Railway line. It is situated about 35 miles south-east of
Melbourne.
Once known as the “Great Swamp” this area was so frequently
inundated that it was practically useless. It was a hindrance to the development
of Gippsland as it acted as a barrier to communication.
Reclamation works first started in 1885 (1) under the direction
of the Swamp Board and later under the Public Works Department.
In 1912, following floods which demonstrated the inadequacy of
the works, the Government directed the State Rivers and Water Supply Commission
to prepare plans and estimates for improving the scheme, and this led to the Lower
Koo Wee Rup Flood Protection District of 56,500 acres being constituted by the
commission in 1917.
For a more comprehensive history of the Koo Wee Rup Flood
Protection District up to the end of 1934, readers are referred to “Swamp
Reclamation in Victoria, 1935” by L.R. East, C.B.E, M.C. E., M.I.C. E.,
F.ASCE., M.I.E. Aust. At this stage, State reclamation works had converted these
swamp lands into a highly productive farming community with a population of 3,
500 persons.
In November, 1934 the Commission submitted a Schedule of
Works for Government approval among which was a item of $200,000 (2) for flood protection
in the Lower Koo Wee Rup and Cardinia Flood Protection Districts, as they were
known before amalgamation into the Koo Wee Rup Flood Protection District in
1962.
Only a few days after the submission of this schedule, a disastrous
flood swept through the area causing very severe losses the 40,000 cusec flood
discharge from the Bunyip River being nearly four times as great as any flow
previously recorded.
The Commission, realising the need for further protective
works, secured grants from Unemployment Relief and Commonwealth funds to begin
carrying out the most urgent works affecting the Cardinia area.
The preparation of a scheme of flood relief for the Yallock end of the lower Koo Wee Rup District presented a much more difficult problem, but after extensive investigations, a detailed proposal was prepared and estimated to cost $295, 000.
It was emphasised by the Commission that, even with an
expenditure of this order, complete protection could not be provided to all
lands in the District in the event of a flood of similar dimensions to that of
1934.
These protective works for the Lower Koo Wee Rup District –
known as the Yallock Outfall Scheme – provided for levee banks to form a narrow
floodway alongside the main canal in which overflows from the canal would be
contained in all but the most exceptional floods. From this floodway water
would be led to the Yallock Creek and thence to Western Port Bay.
Because of the complex flood problem in this area and the contentious nature of the works the Commission recommended to the Royal Commission on Water Supply, then sitting, that its proposals should be examined by an independent expert. The Royal Commission agreed to this and Mr. E.G. Lupson, M.I.C.E., was appointed for this purpose. In his report of July, 1937, he substantially concurred with the Commission’s proposals. In a joint report submitted to the Government, the Commission, the Victorian Railways and Mr Ritchie recommended the construction of the Yallock Outfall Scheme at the estimated cost of $400, 000 and that the scheme should be considered as a State project.
Earthworks for the banks of the Yallock Outfall commenced
late in 1939, but due to the war and its aftermath, progress was slow and they
were not completed from Western Port Bay to the Main Canal at Cora Lynn until
the 1956-57 financial year.
Meanwhile, at the request of landowners, whose properties
would be affected by the proposed floodway alongside the Main Canal, the
Commission attended a meeting of these landowners at Cora Lynn on December 4,
1953. In addition to requesting the Commission expediate the scheme, the
landowners suggested the construction of a short spillway just upstream of Cora
Lynn to divert floodwaters, in excess of the Main Canal’s capacity below that
point, to the Yallock Outfall. Such a spillway would remove the necessity of
using approximately 275 acres of farmland for the floodway.
The Commission examined this suggestion in detail and,
having found it to be practicable adopted it as part of the proposed work in July 1960 (3).
Model tests were carried out at the Commission’s Hydraulic Experimental Station at Werribee to determine the type and size of spillway which would be required to split the flow accurately in the Main Canal at Cora Lynn, leaving only the safe flow of 4,000 cusecs to continue on down the Main Canal to Western Port Bay.
The design was thus based on diverting, to the Yallock
Outfall, 10,000 cusecs out of a possible 14,000 cusecs flood in the Main Canal,
and continuing to provide road access along the south-eastern bank of the Main
Canal.
Consideration was given to enlarging the Main Canal above Cora Lynn to 14,000 cusecs but no further action was taken because it was found that the Canal was enlarging itself by erosion. Arising from this, the short section of channel connecting the Main Canal to the Yallock Outfall has been excavated to take only 6, 000 cusecs although there is enough room between its banks for excavation to the ultimate 10, 000 cusecs capacity. (See Fig. 2, above.) An interesting fact noticed during the model tests for the side spillway was that, for lengths of spillway exceeding 200 feet, there was no significant increase in discharge.
Some way had to be found to divert the surplus flow in the
Main Canal over the spillway. This problem was solved by providing an earthen hump
in the opposite bank [which would direct the] water (4) over the spillway. The final overall length of the
spillway – which was also designed as a ford – was approximately 400 feet, the
extra length being due in part to the approach grades and to an increase in
effective length as a result of the hump mentioned above.
On May 16, 1962 the contract for the construction of the ford between the Yallock Outfall and the Koo Wee Rup Main Canal was sealed, Janus Constructions Pty Ltd being the contractor
Protracted wet weather, together with unsatisfactory blue
clay which was encountered made it necessary to excavate 3 to 5 feet extra
depth of cut to enable a satisfactory subgrade to be constructed.
During compaction of the ford bank, some of the sand filling
from one sandpit caused considerable trouble because it had a high moisture
content and contained sufficient fine particles of clay to make the fill spongy
under compaction. This material had to be removed and replaced with an evenly
graded sand fill. (See Fig 1., above.) The ford was surfaced with a high quality asphalt pavement as concrete
would have been too costly and inflexible.
Following competition of the contract for the ford, the
Commission awarded a contract for the installation of flashing warning lights
at the approaches to the ford to Glorad Engineering Services Pty. Ltd. These
lights, designed after liaison with the Shire of Berwick and the Traffic Commission,
commence operation when the Main Canal rises to 3 inches below ford level.
Shortly after the lights commence operating, the District
staff close the gates at each end of the ford and traffic is thus detoured.
From the completion of these works to the present time there
has been no major flood flow in the Main Canal. There have been only 11
occasions when small flows passed over the ford, and on each occasion the
warning light system worked satisfactorily.
In conclusion, it is interesting to note that the granite
beaching used on the downstream apron of the ford and which was obtained from a
quarry at Tynong North, is reputed to be the same granite as that used in the
Shrine of Remembrance.
This photo (which was a slide) was taken by my Dad, Frank Rouse, in November 1971, during a flood. You can clearly see the grantite beaching, as described above. This is my brother Michael, he's in the Yallock Outfall and we are looking towards the Main Drain or Main Canal as Mr Griffiths calls it in his article.
