Kenneth J. Dalgarno BE, FIE Aust.,
|No.||Make||No. of Stages||Type||Motor(Kw)||Speed(RPM)||Capacity(M3/s)||Head(m)||Date in stalled|
|1 & 2||Gwynne||4||Turbine||485||1500||0.13||268||1912|
|3||Kelly & Lewis||5||Turbine||1120||1000||0.25||275||1935|
|5 & 6||Thompson||3||Volute||1120||1500||0.33||229||1955|
|7 & 8||Thompson||3||Volute||1044||1500||0.34||225||1963|
During the 1920s, the water supply needs of Canberra’s small population (5000) could be met by pumping on only one or two days per month. Rather than maintain skilled technicians in Canberra for such infrequent occasions, it became the practice to have one or two technicians travel up from Melbourne for the pumping operation. Old hands said that the Melbourne men looked forward to the monthly trip to Canberra. However, after the novelty of this excursion wore off, a simpler pump, driven hydraulically by a “Pelton Wheel”, was installed in a nearby small pump house. This used 0.27 cub. metres/sec. to pump 0.01 cub. metres/sec. But despite this inefficiency, the continuous operation was sufficient to provide for the population of that time — and there was plenty of water from the Cotter.
A series of mechanical failures over its first three years of use led to the abandoning of this practice and to the resumption of the excursions from Melbourne. Most of the Pelton Wheel installation is still intact and could be fairly easily restored as part of a total Cotter Pumping Station Working Museum. In the meantime, when the full Canberra water supply system approaches the need for a further storage, or if work needs to be done on the Bendora Gravity Main, the availability of the Cotter pumping
The review of this part of our heritage in water engineering led to the study of a report by William Corin after whom Corin Dam is named. In a paper to the Electrical Association of Australia in 1914—15, Corin spoke ,of a proposal first put forward by that well known engineer E.M. de Burgh for “a combined water supply and hydro electric power scheme from the Cotter River for the Federal Capital”.
This was to have a dam well up the Cotter River with a “race or flume to a balancing reservoir on the top of Mt McDonald whence a fall of 268 metres is available to the Murrumbidgee River”. Staging was feasible, and the scheme was claimed to be “sufficient to provide all the power and domestic water necessary for a population of at least 80,000 people”.
Even in those early days, at the beginning of the century, investigations were made of city water supply schemes on the Naas, Gudgenby and Paddys’ rivers. Indeed, the Gudgenby scheme investigated by Pridham and Weedom in 1901—06 with a dam opposite Mt Tennent should be the next storage for the ACT.
Until after World War II, Canberra’s water supply system consisted simply of the original Cotter Dam and Pumping Station, the rising main to Mt Stromlo and the service reservoirs at Red Hill, Ainslie and Black Mountain from which all reticulated water was drawn.
In 1947—48, a decision was made to raise the 18.3 metre high Cotter Dam to the originally proposed height of 30.5 metres but a subsequent review of the quality of the original design and workmanship, led to a more con- servative decision.
There were several reasons for these reservations. Firstly, there was evidence of cracking in the old structure, arising from an alkali-aggregate reaction. Next, the specific gravity of some concrete was found to be only 2.16 rather than the design assumption of 2.40. Also, at the time the original structure was designed, there was insufficient understanding around the world of the effect of uplift pressures on large dams. Many old structures were subsequently strengthened, and the Cotter Dam also needed revised uplift assessments.
For all these reasons, a decision was made to build a new and larger dam downstream of the present structure. However, the rapid post war expansion demanded more urgent action, so the existing structure was raised only to a height of 25.8 metres.
This work involved:• Tents near the Cotter Reserve for workmen;
Flashboards were used on the spillway crest to provide extra storage, yet fail and hence lower the crest in times of flood.
Apart from the hydro-electric plant itself this work was all completed satisfactorily and remained as the sole storage for Canberra’s water supply until Bendora was completed in 1961. Indeed Cotter still has a reserve function even though its capacity is now only 2.2 per cent of Canberra’s total storage and 8 per cent of the current total Canberra safe draft.
During the raising of the Cotter Dam (1949—51), a second 600 mm dia. main was laid from the dam through a second tunnel to the pumping station, crossing the river on the high level road bridge.
This gave a greater positive pressure on the “suction” side of the pumps, and a more secure inlet which could function independently in the event of a failure of the old tunnel constructed about 1915 below the river bed.
To further increase the efficiency of the pumps, one of the twin 600 mm diameter suction mains from the dam was replaced in 1956 by a 900 mm diameter main as far as the old tunnel entrance. In 1965, a pump-in-line booster was put into that 900 mm main near the tunnel mouth, being a Pomona (Fairbanks Morse) 4-stage propellor type of 890 Kw delivering at 590 RPM, 0.21 cubic metres per second against a head of 34 metres.
Like Cotter Dam and many other engineering projects, the Cotter Pumping Station had its share of interesting stories. Two can be told here.
In the early days, there was a standing order to the pumping station that, when Parliament was in session, the condition of the pumps would not be varied without approval of the Power Station Superintendent, regardless of the state of the reservoirs. It had been found that starting or stopping of the pumps resulted in a variation of line voltage, and this caused a dimming or brightening of lights in the Houses of Parliament, to the distraction of the sitting members. It was also feared that this voltage drop might cause the passenger lifts to malfunction which in turn could cause the Government to fall during a division!
On one occasion, a major burst of the 600 mm rising main from the Cotter pumping station to Stromlo, was caused by a cat belonging to the officer-in-charge of the station. During the early 1950s, in the small hours of the morning, a longitudinal weld of the main, just above the pumping station, tore apart some 1.5 metres long and 130 mm wide. Investigations revealed that the cat had strayed into the station, wandered behind the switch- board, and shorted out the 11,000 volt circuit. The protective circuit breaker opened and power went off the pump. A station attendant in a panic, slammed the Lamer Johnson valve shut and the water hammer did the rest.
It is to the credit of the Department of Works mechanical maintenance fitters that the burst main was back in service the following day.
In a separate chapter, Clive Price records the choice between Bendora and Googong for the late 1950s addition to the storage capacity of the water supply system. The thin concrete arch of Bendora, 47.2 metres high was chosen, anticipating a subsequent gravity main to Mt Stromlo to avoid the high cost of pumping through the Cotter Pumping Station. Several sites had been examined near Bendora but the one shown to be best was that identified 45 years earlier by William Corin.
Whilst a double curvature arch dam can be made very thin and hence much more economical in concrete, it is essential that it be built against strong abutment rock. After the designs were finalised, some concern was expressed about the abutment rock and the possibility of nappe vibration exacerbating the stresses in some doubtful areas. A second opinion suggested that, where some doubt existed, the conservative attitude would be to adopt a concrete gravity design. However this would have cost very much more money and would create a serious delay at a time of exploding population growth. Bearing in mind the opportunity to control nappe vibration with flow splitters, and to reinforce abutments with rock bolts and stressing cables, the decision was made to implement the double curvature arch design as already finalised.
The extent of excavation and grouting of the foundations and abutments was reviewed very carefully during construction but was further reviewed as the dam neared completion when a similar dam in France failed with a loss of about 300 lives in a village downstream. Bendora’s design was shown to be very sound. Indeed the authors would pay tribute to Ken Harding who was the Supervising Engineer in the Department of Works responsible for the design. In addition, to his acknowledged skills in complex engineering analysis, Harding, like his fellow engineer, Ar Fokkema, had an invaluable intuitive feeling for design, enabling him to detect a poor assessment by an interstate authority and later two different errors by a long established overseas organisation.
Even while Bendora Dam was being completed, growth rates had risen to 12 per cent and were predicted to stay high. In the early sixties the case for the gravity main was established, detailed route investigations proceeded down the precipitous slopes, designs were completed and construction took place.
This fully welded steel pipeline starts at the 900 and 1050 mm outlets previously built into Bendora Dam, then at 1600 and 1450 mm diameter, it passes down the very steep and rugged country a distance of 19.3 km to be concreted into a trench under the Murrumbidgee River nearly 300 metres below the dam. It then connects to the 1050 mm rising main adjacent to the Cotter Pumping Station and leading to Mt Stromlo.
With the exception of four elevated creek crossings, the pipeline is entirely buried, protected internally with coal- tar enamel and externally with coal-tar enamel reinforced with fibreglass and felt wrap.
Pipeline stability was achieved with reinforced concrete anchors together with compacted backfilling. Full trench~ section cut off walls were spaced to suit the grade and a minimum of 0.6 m of top cover was protected by lateral and longitudinal drains. The pipeline route includes ten river crossings, all submerged, with reinforced concrete anchorage and protection. The main was commissioned on January 1968 during the serious drought that had commenced in January 1965.
While Corin Dam also was completed in January 1968, nine months ahead of schedule, there were negligible inflows to start filling the storage. Severe water restrictions were imposed, and arrangements were made with the Snowy Mountains Council to release water from Tantangara Dam to flow down the Murrumbidgee to Canberra where it would be pumped into the Cotter Dam using an existing suction line for the Cotter Pumping Station.
The water was released from Tantangara but little arrived in Canberra. Apart from the water table being so low and the river a succession of water holes, most land holders along the river felt entitled to any water available, and presumably pumped accordingly. However, the drought finally broke in May 1968.
Until the early 1950s, Canberra enjoyed a clear water supply. Logging in the lower catchment, and clearing of the Cotter Reservoir, required for the raising of the Cotter Dam, led in 1955 to consumer complaints regarding the level of turbidity in the water supply. Consumer dissatisfaction appeared to have been exacerbated by the addition of chlorination at the Cotter Pump Station in 1955.
There was a recurrance of consumer complaints in the mid-1960s following renewed forestry activities in the lower Cotter catchment. Public attitudes perhaps were best summed up by a correspondent who wrote to The Canberra Times asking why people were complaining about the water supply since he had found that, after hosing, there was no need to apply either fertiliser or topsoil to his lawn.
Despite the foreseen activity for Corin Dam and the Bendora Gravity Main, NCDC and the Department of Works engineers believed that the unoccupied Cotter Catchment was sufficiently protected not to need the expense of water treatment — a charge that would have to be conveyed to the ratepayers. To decide whether logging activity in the pine forests of the catchment could be made compatible with the maintenance of an adequate quality of water without the expense of treatment, NCDC engaged Professor Teakle, a specialist in agricultural science from the University of Queensland. The late Professor Teakle compiled a set of guidelines which provided for the harvesting of logs in a manner consistent with the protection of water supply.
Ultimately, a decision was taken to provide limited treatment of lower Cotter water as an additional safeguard. At that time, the daily consumption varied between 45 megalitres in mid-winter and 230 megalitres in mid- summer. A capacity of 90 megalitres/day was chosen. By utilising the old 13.6 megalitre water reservoir on Mt Stromlo, a low cost design was evolved consisting of flow splitter, sedimentation bays, clear water storage, waste- water recovery tanks, sludge lagoons, control building including chemical storage and dispensing equipment, and a mixing length of 1350 mm diameter steel main. Facilities for chlorination and addition of fluoride were transferred from the Cotter and Stromlo.
This plant was commissioned on 21 June 1967. Having regard for the protection provided by the unoccupied catchment, this plant was considered adequate to achieve reductions in most water quality parameters to acceptable levels.
Considerable public debate had taken place on the proposal to add fluoride to the water supply. The argument against this was perhaps best summed up by the person who wrote to The Canberra Times calling fluoride a poison and not wanting to have the very best teeth in the cemetery.
The arguments in favour of having a water supply with the optimum content of fluoride were appreciated in the early 1960s by dentists, the public health engineers of NCDC and the Department of Works, and by the medical officers at the Department of Health. The Department of the Interior supported these views which have been confirmed over succeeding years by the major drop in dental caries, particularly among children born in the ACT.
The chapter on Lakes and Dams describes events leading to the decision to build Googong. While the Commonwealth had paramount rights to the use of the waters of the Queanbeyan and Molonglo rivers, special legislation was required to be enacted in the Commonwealth and NSW Parliaments to enable the project to proceed. The legislation fell victim to the 1974 double dissolution of the Commonwealth Parliament, delaying the commencement of the project by 12 months.
The project was also the first to come under the Commonwealth Environmental Protection (Impact of Proposals) Act, necessitating the drafting of the first Environmental Impact Statement under the terms of the Act.
An essential component of the project put forward for approval, was a sophisticated water treatment plant required because this terminal city water supply reservoir would collect water running off a partially occupied catchment.
From the multiple level dry outlet tower, the water passes through the plug in the construction river diversion tunnel to a pumping station one kilometre downstream of the dam. Details of the pumps are:
|Type:||single stage, centrifugal 800 Kw.|
|Number:||currently four(later to seven).|
|Operating Head:||79 metres.|
|Pump Supply Contract:||all Pumps Pty Ltd(Pumps were made in USSR)|
The Googong Water Treatment Plant was designed to safeguard the quality of water supply for a wide range of raw water conditions. The treatment process adopted comprises coagulation by liquid alum and a cationic polymer coagulant aid, flocculation, sedimentation, filtration, pH adjustment and stabilisation with lime, recarbonation and fluoridation by sodium silica fluoride. Filters have dual media beds of sand and activated carbon which also adsorbs taste and odour-causing compounds. A non-ionic polymer is used as a filter aid. In addition special treatment processes are required occasionally to deal with excessive colour and abnormally high manganese content. Auxiliary liquid and dry chemical feeding systems can feed chemicals such as hydrochloric or sulphuric acid, sodium hydroxide, iron salts and potassium permanganate.
The first stage of the plant was completed in 1978, with an installed capacity of 180 Ml/d. The plant was designed by the Department of Construction in association with Caldwell Engineers, and was constructed by John Holland.
From the treatment plant, water is conveyed 26 km to Campbell reservoir by a pipeline varying in outside diameter from 1050 mm to 1800 mm. Branch mains convey some water also to Mugga and Red Hill Reservoirs.
The work was put into service at the end of 1978.
The first four reservoirs constructed were at Mt Stromlo (1914), Upper Red Hill (1914), Russell (1926) and Black Mountain (1933), all of which were rectangular in shape and unroofed. After these followed Lower Red Hill (1939) and Ainslie (1940). These were circular and of the old conventional design in reinforced concrete.
The first prestressed reservoir was built at Narrabundah in 1959 (18.2 megalitres). This was followed by many more of similar design and capacity. Larger reservoirs to the order of 45 and up to 68 megalitres were generally rectangular, of cut and fill construction with concrete lining.
Canberra now has 42 reservoirs located as inconspicuously as possible on hills and saddles throughout the metropolitan area.
In the early 1960s, the NCDC and the Department of Works agreed to implement the policy that treated water should not be exposed to daylight until it emerged from the consumer’s tap. Hence all existing and subsequently constructed service reservoirs were roofed.
With the exception of the 450 mm diameter unlined cast iron water main built in 1915 from Cotter Pumping Station to Mt Stromlo (and cement lined in situ in 1967) all mains in Canberra are built with welded steel, cement lined pipes.
A zoning system of up to three zones avoids excessive pressures in low areas and insufficient pressure in high areas.
In addition to distributing water to all the urban areas of Canberra, the system also supplies water to Queanbeyan (as from 1925), Oaks Estate (as from 1938) and Hall (as from 1967).
The existing Cotter River systems can supply water on an unrestricted basis to a population of up to 225,000 persons.
When the second stages of the Googong pumping station and treatment plant are constructed to match the capacity of the Googong Dam, the total system will be able to serve a population of 450,000 persons, including provision for riparian rights, minor irrigation of nearby parklands and topping up of lakes in time of drought.
In this inland part of the world’s driest habitable continent, the disposal of wastewater and water borne wastes is a considerable challenge to public health engineers — a challenge made worse by the complexity of the biological and chemical processes that take place when even the treated wastes are injected into the natural water courses, particularly as these sometimes cease to flow. In the early days, when Canberra’s population was small, the natural water courses were able to absorb reasonably treated wastewater but not since Canberra began to develop into Australia’s largest inland city.
A review of most of the early records discloses a variety of
treatment proposals with the inevitable evidence of conflict
between Griffin and the Department. These schemes
(a) The one favoured by the Department of Home Affairs. This was a Septic Tank Process, followed by filter beds, with effluent to be spread over some 1200 hectares in the Weston Creek area. The scheme was said to have an ultimate capacity for 125,000 persons.
(b) A modified version of the above scheme. This would provide for only 15,000 persons, which it was estimated would be adequate for the first 10 years. The plant was to be located, as an interim measure, at Yarralumla Creek.
(c) A third scheme put forward by the City Designer, Walter Burley Griffin, would not have required a Main Outfall Sewer, having an unspecified number of Emscher or Imhoff Tanks in the city area, with treatment at an early stage and effluent being discharged into the proposed ornamental lakes in the Molonglo River.
(d) The Oliver proposal for eight Emscher or Imhoff tanks each serving a specific area of the Federal City and suburbs.
(e) The Langley schemes from Colonel F.F. Langley, advisory expert in Sanitary Engineering from the Inter- national Health Board of the Rockefeller Foundation. In a report dated 1 November 1922, Colonel Langley offered four choices of treatment:
• Simple sedimentation, with separate digestion of solids, and treatment of liquids on land.
• As above, but with treatment of liquids by trickling filters for better oxidation.
• The activated sludge system.
• A complex version of the first involving sedimentation, activated sludge, clarification, then trickling filters or other equivalent oxidising device.
Col. Langley did not strongly recommend the activated sludge process because of the high cost of the process as then carried out and the fact that the population using the water downstream did not demand at that time nor did it expect to demand the higher degree of purification accomplished by the activated sludge process.
Because of the nature of the soil at Weston Creek, he would not consider any land treatment for the effluent on a longterm basis, but proposed simple sedimentation and sludge digestion of solids, with land treatment of the effluent. He regarded the adoption of the activated sludge system as an auxiliary feature rather than as the sole feature of the plant.
For the small quantity of sewage to be treated during the first few years, the above arrangement would assure a reasonable freedom from offensive odours and the preservation of reasonable purity in the stream below and would be about as economical a treatment as could be arranged.
In the long range, Langley considered that the land
dispersion of the effluent, even if adopted at the outset,
would ultimately be abandoned. “There are certain old
established devices for oxidising sewage liquids and there
are other promising features which have been given trial,
but which are not yet supported by long experiences.”
(f) The Chief Engineer, Works and Railways (Mr T. Hill) 6 December 1923, put forward four schemes for investigation, developing in stages as suitable for from 6,000 to 20,000 persons. • Sedimentation plus sprinkling filters discharging into the Molonglo River. Incineration of solids and an option for humus tanks.
• A pumping version of the above gravity scheme.
• A scheme pumping even higher than the last so that the final effluent could be discharged over prepared ground.
• An alternative site for the last scheme higher up the Weston Creek Valley.
The scheme favoured by the Department involved pumping the effluent another 30 to 60 metres higher for distribution in the Weston Creek area, but this was strongly criticised by the Engineer-in-Chief of the Melbourne and Metropolitan Board of Works, Dr Calder E. Oliver.
Finally, at the Federal Capital Advisory Committee on 28 January 1924, it was moved by Mr de Burgh that an extensive scheme for disposal into the Weston Creek area be adopted and this was agreed to.
In September of that year, the House of Representatives referred to the Parliamentary Standing Committee on Public Works, the question of the sewage treatment works, so that an innocuous effluent might be obtained for discharge into the Molonglo River at Weston Creek.
The proposal subsequently adopted, provided for a first unit of four Imhoff sedimentation tanks (the four most northerly) and three trickling filters, 21 metres diameter by 1.83 metres deep, to deal with 2.28 Ml daily, being the sewage from 5,000 persons, plus flushing water for scouring the sewers in the initial stage. The proposal also included a small experimental activated sludge unit to treat sewage from 500 people. The scheme provided for augmentation to treat sewage from, as a first extension, 10,000 people and later from 25,000 people. In 1925, the Parliamentary Standing Committee on Public Works accepted these recommendations.
The Committee was at pains to point out that, whilst the Commonwealth was taking great care to prevent any possible pollution of the Molonglo River below the City, the river above the City still received surface drainage and septic tank effluent from the town of Queanbeyan, where, at that time, there was no attempt to provide a town sewerage system.
The Canberra plant came into operation in 1927.
About 1939, six additional Imhoff tanks and another group of three filters were added. About 1948-49, when the population of Canberra was about 19,000, sludge lagoons were added to take the load from the Imhoff tanks. The hydraulic capacity of the filters was also increased. This enabled the plant to handle sewage from a population in excess of 30,000, but the effluent was not quite up to the usually accepted British Royal Commission standard of 20 mg/1 of biological oxygen demand and 30 mg/1 of suspended solids. However, having regard to detention time and loading, the performance was much better than would have been expected.
Subsequent augmentations of the plant took place in 1956—57 to 25,000 persons; in 1960—61 to 60,000 persons; in 1967-69 to 120,000 persons and in 1973 to 130,000 persons. The plant had started with a capacity of 5,000 persons.
In its final form, the plant was using primary and secondary sedimentation, high and low rate trickling filters, sludge digestion and some activated sludge.
The original Imhoffs and some of the earlier low rate trickling filters were abandoned. In the late 1960s odour problems associated with Canberra’s air temperature inversions were being encountered in the nearby towns of Woden-Weston Creek and then at Government House, Yarralumla. In addition to several refinements this led to the abandoning of sludge drying beds. The plant was finally closed in August 1978 when the new Lower Molonglo Water Quality Control Centre achieved practical completion.
In 1914, even before a decision was made on the original method of treatment, the Department of Home Affairs had proceeded to design the main outfall sewer westbound from the Canberra Hotel. Along its length of 4.8 km the tunnel was to pass under what is now Stirling Park, the Royal Canberra Golf Club, Lady Denman Drive and Cotter Road. (Brick ventilation shafts from the completed tunnel can be seen today from these roads). The depth of the tunnel varies between 1.5 m and 24 m.
In 1915 the Parliamentary Standing Committee on Public Works accepted the proposal for the deep egg- shaped sewer tunnel 1.68 m high by 1.12 m wide on a concrete invert with sides either concrete or brick depending on the ground encountered.
Construction of the sewer proceeded until April 1917 when it was held up following a report of the Royal Commission investigating Canberra’s administration. Work recommenced in 1922 after a report by Mr E.M. de Burgh, Chief Engineer for Water Supply and Sewerage, Department of Works, NSW.
No record seems to be available as to any brick construction adopted, nor are there records of the mix or quality of concrete used — an important factor in a sewer tunnel. The current regular inspections show that after a life of 55 to 65 years and despite regular surcharging over the last 15 years, there is little evidence of any serious deterioration. This tunnel is still a vital component of Canberra’s sewerage system.
In 1960, Minty was told by the late Doug Vest, the foreman in charge of driving the tunnel, that they struck so much cavernous limestone during the driving that he seriously believed that the Canberra lake would never hold water!
As the westbound tunnel nears the periphery of the Treatment Works area, it makes a sharp right angle turn into the works — evidence, it has been claimed, that the tunnel was originally intended to go beyond Weston Creek to a site at Stoney Creek, also discharging into the Molonglo. No records could be found to support this, and it seems possible that the tunnel was kept to the South simply for better cover or better driving conditions. The tunnel was completed in 1924.
The original Weston Creek Treatment Works and the main outfall sewer tunnel had to be complemented of course with a system of intercepting sewers of which two deserve a mention. The first was built to collect waste water from north of the Molonglo River. It was an inverted syphon built under the river and on an alignment just upstream of the present Commonwealth Avenue Bridge.
This was in the form of a tunnel designed for two, 450 mm diameter pipes, but initially having one cast iron pipe 230 mm in diameter. When Lake Burley Griffin was being built, the tunnel carried one 450 mm and one 230 mm pipe, but having regard for the age of the tunnel, the possibility of collapse under the pressure of the lake in flood and the difficulty of coping with a collapse, the decision was made to abandon this system. A replacement was provided by 500 and 450 mm pipes through the superstructure of the new Commonwealth Avenue Bridge, with a vent through the south-east decorative pylon of the bridge and a storm tank in Commonwealth Park. Foradded security, the 500 mm main is on the eastern side of the southbound bridge and the standby 450 mm main on the eastern side of the northbound bridge.
In 1953, Parliament approved a change in Canberra’s plan so that in lieu of the lake as now built, there was to be a dam at Acton Peninsula with a mere “ribbon of water” downstream of the hospital. Hence, when soon after this, expansion of the Northern Suburbs called for further sewer capacity across the Molonglo, the decision was made to built another inverted syphon in the form of two 380 mm diameter pipes and one 225 mm diameter pipe just downstream of the expected Acton Dam, near the Royal Canberra Hospital.
Unlike the Commonwealth Avenue inverted syphon in tunnel, these pipes were laid across the river in a rock trench and encased in concrete. North of the river, pile supports were added when the lake was built. These syphons are nevertheless regarded as susceptible to sedimentation and possible blockage.
The construction of Lake Burley Griffin in the early sixties precipitated the rationalisation of the plethora of minor sewerage systems that had accumulated over the years, upstream of the Lake at places like Fairbairn, Pialligo, Duntroon, Harman, Fyshwick and Narrabundah. Interim rationalisation minimised pollution of the lake in the early years and in 1967, the Fyshwick Sewage Treatment Works was completed, collecting wastes from all these areas except Queanbeyan for which the cost was considered too high.
The plant has a capacity equivalent to 20,000 persons, and the treatment consists of coarse screening, grit removal and primary sedimentation, followed by low rate trickling filters, secondary sedimentation in humus tanks and sludge digestion. Four-stage lagoon treatment is followed by chlorination.
The Fyshwick plant was designed in a new era of emphasis on re-use of water. After final treatment in large maturation ponds, and chlorination, the emerging effluent was to be used for irrigation upstream of the lake. This has been done very successfully on the playing fields of Duntroon Military College but the quantity used is less than that available. Further areas should be established for such irrigation.
By 1964, NCDC had decided to move into the Belconnen Valley, and proposed a trunk sewer through the valley leading to a new Water Pollution Control Centre at the western end of the valley.
NCDC engaged the Australian consultants, Scott and Furphy to design both the trunk sewer and the Treatment Works.
The Trunk sewer was a 1500 mm diameter concrete pipe laid in a trench adjacent to the Ginninderra Creek, except for a short length tunnelled through a ridge.
In the very early stages of the development of this valley, sewage was led into a temporary timber septic tank just north of the town centre site. When the permanent sewer down the valley to the proposed treatment plant was completed in 1968, the population was still small and the sewage was led into an Imhoff tank.
When the first stage of the treatment works (50,000 persons) was completed in 1970, the Imhoff tank then served as a stormwater tank. The treatment plant known as the Belconnen Control Centre was later enlarged to serve 100,000 persons.
In addition to the usual components in a modern treatment plant, activated sludge was used, followed by maturation ponds. The plant was designed to produce a 15/15 final effluent but in fact, achieved the high standard of less than 10mg/i of both biological oxygen demand and suspended solids.
In 1967, Alan M. Vorhees & Associates submitted to NCDC their report responding to the Commission’s brief for a Land Use Transportation Study on a metropolitan scale. The consultant’s General Plan Concept provided for a series of self-contained towns in each of the main ACT valleys with peripheral parkways flanking the urban areas giving a metropolitan structure in the shape of a Y. This became known as the “Y” Plan.
The study called for a new Town of Gungahlin, north of Mitchell, part of which drained not to the new Belconnen plant, but back to the Sullivans Creek Valley. Despite an NCDC decision not to develop urban areas in the Majura Valley, the Gungahlin proposal and other aspects of the “Y” Plan called for a review of metropolitan sewerage strategies.
One possibility was to tunnel from Clunies Ross Street, under Black Mountain to a new treatment plant to the west, hence allowing relief to, or replacement of, the sixty year old main outfall sewer tunnel on the south side. Thus began some prolonged discussions between NCDC and Works Department on sewerage strategies referred to as the “North versus South” discussions.
Associated with these in-house studies, NCDC engaged Camp, Dresser and McKee, a firm of leading hydraulic consulting engineers from USA to review the existing system and future expansion, from which they were asked to prepare a metropolitan sewerage strategy plan. These consultants, working closely with NCDC and Works Department engineers recommended that the individual treatment plants in individual valleys be phased out and that one large plant having the economy of scale be built well downstream, capable of staged development to cope with all expected expansion, and treating the wastewater to a high standard that minimised biological growth. These consultants forecast the possible need to reduce the nutrients, nitrogen and phosphorus, to very low figures.
At the time, considerable concern had been expressed around the world for the need to maintain the quality of the environment. Algal blooms were continuing to appear in the Murrumbidgee and Burrinjuck Dam, and reports from senior engineers visiting other countries, all led to acceptance of the consultants’ recommendations.
In addition to earlier overseas studies by W.C. Andrews and C.J. Price, NCDC sent its water supply and waste- water specialist Charles Speldewinde on a three-month study tour looking at modern wastewater plants and the consultants who had designed them. About the same time the Commonwealth Department of Works sent their Chief Hydraulic Engineer, Howard Jones on a similar overseas assignment.
Both came back convinced that the Commission had to build a plant capable of removing the nutrients and producing a final effluent which could be released into the Murrumbidgee River at a standard suitable for body contact sports. The consultant chosen to design this plant, the Lower Molonglo Water Quality Control Centre, was the American, David Caldwell, who associated his firm with the large Australian firm of structural consultants, John Connell and partners.
The consultants proposed a physical/chemical/biological plant using ammonia stripping for the nitrogen side such as planned to accommodate up to three more similar stages. NCDC and Works’ engineers acknowledged the very high standards achieved there, but were concerned about such issues as the environmental effect of the towers and the effect of Canberra’s winter climate on the processes.
Accordingly Caldwell proposed the use of nitrification/ denitrification using anoxic stripping towers with methanol. Pilot studies were carried out at a similar plant being developed at Contra Costa, north-east of San Francisco, where similar very high final effluent quality was being demanded.
The design adopted is illustrated in the adjacent diagram. It has a potential capacity to treat 109 megalitres/day currently equivalent to 400,000 persons. The site is planned to accommodate up to three more similar stages.
Due to scale and the latest design techniques, the capital cost of the plant was comparable with conventional plants, but the methanol process and the oil burning sludge furnaces were conceived before the petroleum products crisis of the mid-seventies. However, the flexibility of the plant is now allowing new techniques to make major reductions in the need for petroleum products.
It was found to be economical to use a temporary local sewage treatment works (Pasveer ditches) in the Tuggeranong Valley for the first residents in 1974, but in the meantime a concrete lined tunnel 1.9 m diameter was driven from the lower (northern) end of the valley 9.1 kilometres to the periphery of the Weston Creek works. This was complemented by the Molongo Outfall Sewer from the Weston Creek plant 15 km to the Lower Molonglo plant. Most of this latter sewer is a 2.6 metre diameter concrete pipe laid in a trench along the contour and backfilled. However, there are two tunnels and several large creek crossings using steel pipe on piers.
Once the Lower Molonglo plant came on line, another tunnel was completed from the Belconnen Water Pollution Control Centre, thus allowing that plant to be phased out. The tunnel is 5.3 km long, has a circular section of 2130 internal diameter lined with a minimum of 240 mm of concrete with two vortex drops at the Belconnen end. It was completed in 1979, thus bringing close to completion the majority of the master wastewater strategy plan. Most wastes were then draining to one major plant discharging a final effluent ranking amongst the best in the world.
Unlike so many Australian towns and cities often built on or near rich river flats, Canberra is fortunate in being planned and developed having regard to long term floods. But it has not been immune from the property damage and even loss of life arising from deluges.
Lake Burley Griffin has been designed to pass major floods. In the surrounding area no significant buildings are vulnerable to anything smaller than a flood with a return frequency of one hundred years.
In urban areas, stormwater pipes carry five year discharges, with twenty year capacities in town centres. Routes are identified for acceptable depths of overland flow in excess of these discharges.
There are still some areas in old Canberra, in particular, where these standards have not been applied, but in the new areas, a deluge some years ago in Aranda emphasised the importance of adequate standards and allowed easier access to finance for such work.
No attempt has been made to research the lives lost in the pioneer years of the ACT due to floods and downpours, but over the past quarter of a century, the one outstanding tragedy occurred in January 1971.
Yarra Glen had been extended into the Woden Valley taking over from Kent Street as the primary access. Inter- changes on Yarra Glen were being built progressively and had been completed at Hopetoun Circuit, Kent Street and Carruthers Street. Pending the construction of the inter- change just north of the Phillip Town Centre, a typical low-level crossing in the form of a multi-pipe culvert was in use to cross the large stormwater channel passing down the spine of the valley. Other parts of the valley’s bridge and stormwater infrastructure were also yet to be completed.
On the night of 26 January 1971, starting at between 7.30 and 7.50 pm, a coalescing of two intense storm centres produced more than 100 mm of rain over 270 hectares in one hour in the Farrer, Torrens, Mawson area. This tremendous deluge moved down the valley over a two hour period. Seven lives were lost, all from motor vehicles, including those of a nineteen-year-old girl and four young children from one car. The loss of these seven lives in one night was a deeply felt tragedy.
Reports were prepared “on a full and searching basis”. The subsequent enquiry revealed the following figures for the return frequency of rainfall of one hour duration.
|Once in 2 years||20mm|
|Once in 10 years||28mm|
|Once in 50 years||36mm|
|Woden Valley Storm||90mm|
The flood had substantially passed through the valley in a period of two hours.
Conclusions in the report by the Department of Works said:
“a) Analysis of the above data supports a conclusion that
the storm and flood in the Woden Valley on the night of
26 January 1971 was an event which must be considered
of rare occurrence with an average return period most
probably in excess and even well in excess of 100 years
for the Woden Valley in its past and present condition”.
“b) When compared with subsequent relatively large floods in the Woden Valley on 5 February 1971 and 10 February 1971, the flood of 26 January 1971 was more hazardous not only in its far greater peak flow rate but also in the rapidity of the rise rate of the flood which caused areas to change from safe to unsafe within a relatively few minutes”.
Despite the rare nature of this occurrence, extensive reviews were made of physical situations and organisational procedures to minimise the possibility of another such occurrence.
In an NCDC technical paper, details are provided of various designs used for large stormwater channels. In other papers, advantages and details are given of storm- water retarding basins such as have been built at Southwell Park and Manuka.
The final point that must be made on stormwater developments over the last twenty-five years, is the increasing emphasis on water quality. The techniques used to minimise deterioration in standards were prevention of pollution, erosion control, screening, ponding and use of biological filters.
In the above sections of this chapter, developments in water supply, wastewater and stormwater have been discussed cussed separately but each is closely interrelated in terms of both quantity and quality. This becomes particularly apparent in periods such as the current prolonged drought associated with hot weather. Indeed, the lakes and rivers as well as the dams are a vital part of the total water quality system. To maintain our river, lake and dam system at the highest level of quality, it is necessary to make a very detailed scientific study of all the important parameters at a large number of sampling points throughout the region. Such readings need to be taken regularly, and the values of each parameter assessed to understand what controls are necessary.
Until the nineteen seventies, the water quality studies
tended to be associated with specific projects like Lake
Burley Griffin and the discharge points from each of the
sewage treatment works. In 1975, however, NCDC issued
a brief for a study of the rivers and lakes of the Murrumbidgee
River basin upstream of Burrinjuck Dam with
particular reference to the ACT region and the effect of
events within the ACT on the quality of these waters. The
objectives of the study were:
“a) To provide a bench mark data base describing the present physical chemical and biological characteristics of lakes and streams of the basin.
“b) To develop the means for predicting the effect of changing land-use and of alternative land and water resource planning and management strategies on water quality and aquatic ecology of lakes and streams of the basin.
“c) To establish water quality objectives and criteria necessary for the preservation and enhancement of aquatic ecology and present and future beneficial uses of lakes and streams of the basin.
“d) To develop and evaluate water quality management control methods and criteria providing for the efficient utilisation of resources consistent with water quality objectives and criteria.
“e) To identify ongoing studies required to improve and consolidate the data and to provide the information required for continual re-assessment of effects of urban development.”
The work involved a large number of engineers and scientists from many Commonwealth and State organisations, private consultants and Australian and overseas specialists. Their two-volume report was presented in July 1978 and laid a solid foundation for continuing water quality monitoring and management in the region. Complementary specialist reports have followed, thus providing for this sensitive inland region one of the best possible bases for regional environmental control.
To close this chapter on water supply, wastewater, stormwater and regional water quality control, the authors would stress the close relationship between these four facets, and the importance of monitoring and controlling the potential eutrophication processes in the lakes and streams of the region.
The interrelated physical, chemical and biological processes are very complex. When the Lower Molonglo Water Quality Control Centre was being conceived, it was not clear whether it was necessary or desirable to extract the biostimulant, nitrogren. Provision was made for this but ten years later as this book goes to print, this is still a debatable issue, emphasising the importance of continuing monitoring and analysis.
Progressive urban development must be kept compatible with the preservation of as much as possible of our natural heritage.
The close partnership and personal warmth that existed between the engineers of NCDC and the Department of Works over twenty-five years tempts the authors to record names with some succinct words on their skills and idiosynchrasies. However, we will content ourselves by recording the name of the late Don Stockdill who, for about 20 years, led the team of engineers in the Department of Works and who did so much of the planning design and construction work for NCDC. His engineering skills and personal qualities won the respect of all his associates. His name has been perpetuated in the road that leads from Belconnen down to the Lower Molonglo Water Quality Control Centre.
The authors express their appreciation to Australian Archives, the National Library of Australia, the National Capital Development Commission and the Department of Transport and Construction (formerly the Department of Works).
Special thanks are due to Ross McIntyre, Director of the Canberra Region of the Department of Transport and Construction, not only for the resources he made available for this chapter, but also for the leading role he played for some twenty years in the close partnership between his department’s engineers and those of NCDC.
Charles Speldewinde and Ian Lawrence from NCDC made constructive comments on the text as did Ron Lewis, past Director-General of Works and Frank Waitt, past Chief Hydraulic Engineer of that Department.
The following engineers from the Department of Works also provided technical comments — Tim Richardson, Ar Fokkema, Trevor Daniel, Kevin Payne and Mark de Plater.
Professor Neale, Director General of Australian Archives, took a personal interest in this work and offered old photographs from his family collection, some of which have been used in this chapter.
To all of these we express our thanks.
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