This paper assesses the critical analysis of the design process of Dartmouth Dam by majorly focusing on its conceptual design phase of the dam. The conceptual design of the Dartmouth Dam basically consider the requirement analysis of the dam during its construction, system planning, functional analysis, system operation requirements, performance measurement, feasibility study, maintenance and support concept, and also needs identification. The Dartmouth Dam is a large rock-fill embankment dam with a chute spillway that is uncontrolled across the Dart, Gibbo, and Mitta Mitta rivers, a number of other minute distributaries as well as the Morass Creek. The dam is situated North-East of Victoria States, Australia, near Mount Bogong.
Some of the purposes of the Dartmouth Dam include water conservation, water supply for both industrial and domestic purposes, Hydro-electric power generation, and also for irrigation purposes. The reservoir impounded is referred to as Dartmouth Reservoir and is normally known as Lake Dartmouth. The Dartmouth Generation Power Station produces power to the grid of the nation and is situated near the walls of the dam. The major supplier of water to the Dartmouth Dam is River Murray which is 2500km long, rising in the Alps of Australia and discharging into the sea in South Australia (Allan, 2010).
The major reason for designing the Dartmouth Dam by the River Murray Commission was to catch the flows during winter and release water during the season of irrigation. South Australia was specifically keen in maintaining the flow of the river during dry seasons since the place is located far downstream and is supplied last by the flow of water hence proposed the construction of the dam. Other reasons for the construction and design of the Dartmouth Dam include the water conservation, water supply for both industrial and domestic purposes, Hydro-electric power generation, and also for irrigation purposes. These reasons lead to the construction for the dam and a 150MW power station at the toe of the Dartmouth dam to produce power from the releases of irrigation and also absorbing the fluctuations discharge on the demand of power before releasing the water to the downstream river (Association, 2010).
This section analyses a high-level and early life cycle activity on the Dartmouth Dam with an aim of predetermining, committing, and establishing the development schedule, cost, form, and function of the dam and its products. The conceptual design of the Dartmouth Dam basically consider the requirement analysis of the dam during its construction, system planning, functional analysis, system operation requirements, performance measurement, feasibility study, maintenance and support concept, and also needs identification. The construction of the Dartmouth Dam which was expected to have a capacity of 6.25 million megaliter storage would have provided South Australia with extra control over its portion of water (Golzé, 2009).
The proposed plan or method for the design and construction of the Dartmouth Dam was an earth core rockfill which is composed of a middle earth core as the elements that is impervious, supported both downstream and upstream by compressed rockfill shoulders. In the middle of the downstream rockfill and earth core, there are thin zones of fine materials to avert any particles from earth from being washed into the spaces of the rockfill resulting into the development of a leak. Similar upstream zones prevent erosion of the core elements when there are changes in the level of the reservoir. The external slopes were expected to be steep since he rockfill is free-draining and strong, hence reducing the cost of the construction of the dam as well as the number of materials in the embankment (Guyer, 2018). The figure below shows the proposed plan for the Dartmouth Dam design:
Figure 1: Proposed Design of the Dartmouth Dam (Hanna, 2012)
The initial earth core rockfill dam in Australia was Bradys Dam which was approximately 20m and was completed in 1953. The rockfill was not compacted but rather dumped. The application of the compacted rockfill started in 1965 and became adopted globally in the same year. In Australia, the three highest dams are all earth core rockfill dams since it has been proven that this dam design is the most economical type in case there is need of a very high embankment (IPC, 2010).
The new Commonwealth government brought together all the States in Australia and ultimately established the River Murray Commission during the historic agreement in 1914 and would be supported financially by all the four governments of Australia. In the agreement, the storage in Lake Victoria was to be raised, and 26 locks and weirs were to be constructed between Echuca in Victoria and Blanchetown in Australia. The weirs were expected to establish extra ponds from which water would be diverted or pumped to the regions of irrigation adjacent. South Australia was specifically keen is maintaining the flow of the river during dry seasons since the place is situated downstream and get to use the water after others and hence they proposed the erection of Chowilla Dam which was approximately within the border state (Jackson, 2011).
The construction of the Dartmouth Dam which was expected to have a capacity of 6.25 million megaliter storage would have provided South Australia with extra control over its portion of water. The dam was designed to be 5.6km long earth embankment, spanning two creeks and River Murray, and grounded on a depth of sand. Nevertheless, the concerns about rising salinity, evaporation losses, and the cost resulted in the desertion of the site in the year 1967. The Mitta Mitta River was the primary tributary which flows on the Victorian section in Lake Hume (Jansen, 2012). An appropriate site for the dam construction was noted to be 110 km upstream of the river, at the junction of Dart River. The proposed dam has to be 180m high in order to store 4 million megalitres of water making the dam to be the highest dam in Australia. The design of the proposed Dartmouth Dam was done by the Snowy Mountains Engineering Corporation and the construction authority was the State Rivers and Water Supply Commission of Victoria which was appointed by the River Murray Commission (Leslie, 2013).
After the appointment of the State Rivers and Water Supply Commission of Victoria as the construction authorized by the River Murray Commission, the construction and design of the Dartmouth Dam started in 1973 and was later completed by Thiess Bros. Pty Limited in 1979 having cost the Australia government a lump sum of A$139 million. The Dartmouth Dam stores water during summer from Victorian snowfields and then discharges the water into River Mitta Mitta and afterwards into the Murray River for the purposes of irrigation. The crest of the spillway that is uncontrolled is 486 meters and is about 92 meters in length. When full, flood flows over the crest and then water return to the river through a cascade of open rock which slowly opens to 300 meters at the level of the river (Martin, 2014).
After the Dartmouth reservoir has attained its capacity of 99%, it is deliberated to be fully operational and releases are then positioned to permit downstream inflows to preclude the water level from further rising. Releases are permitted through the power station and outlet works when possible and water will specifically flow over the spillway if substantial flood inflows get in from upstream and the storage is almost full. This method protects the spillway, maximizes operating flexibility for the hydro-power generation, and minimizes the chance of flooding downstream. The Dartmouth Dam is also a common recreational trout fishery, being restocked regularly by the Department of Primary Industries of Victoria. The Dartmouth Power Station has a generating capacity of 180 megawatts with a single Francis turbine-generator. This being the largest hydroelectric turbine single installed in entire Australia (Pedro, 2009).
The Dartmouth Dam is composed of a dam itself, a hydro-electric power station, low-level and high-level outlets, spillway, cofferdam and a river diversion tunnel. The dam is 670m in length, 180m in height, and possesses 14 million m3 of material. The spillway crest length is 91m, surface area at full supply level is 63 km2 and catchment area is 3600 km2. The height of the dam is a very important dimension since it denotes the optimum hydraulic pressure which the water tightness of the foundation and embankment must resist. The cofferdam of height m was designed to divert the flows of summer through the tunnel diversion tunnel of the diameter of 6m during the construction of the embankment (Society, 2013).
The rockfill on the downstream face of the cofferdam was protected using steel mesh to prevent it from washing away in case the floods overtop it. The rockfill quarry on the left bank was intended to both dissipate the energy of the water flowing over the spillway on the way to the river level and also supply the huge quantity of rock for embankment. The quarry was established in a sequence of benches approximately 15m high which acts as a waterfall cascade during discharge of flood. During the processing of embankment construction, it was significant that the earth core was free from settle under its specific weight, for the maintenance of its water tightness (Stephens, 2010).
Figure 2: High-level outlet of the Dartmouth Dam (Thomas, 2010)
The comparison of the zones of the filter was reduced progressively until similar measurement rates of settlement so as to encounter this effect undesired. The low-level outlet is available for releases when the reservoir is low since it operates under a much higher head. This outlet has two discharge-regulating gates on either of its sides as shown in the figure below:
Figure 3: Low-level outlet of Dartmouth Dam (Thomas, 2010)
They are situated inside the tunnel and the huge energy of the water discharged is dissipated within an enlarged tunnel length lines with reinforced concrete.
The major requirements for the operation of the Dartmouth Dam include the reservoir which is sometimes known as Lake Dartmouth, water supply from Mitta Mitta Rivers, Banimboola Hydroelectric Power Station, and Banimboola Pondage or Dartmouth Dam Regulating Pond. The major supplier of water to the Dartmouth Dam is River Murray which is 2500km long, rising in the Alps of Australia and discharging into the sea in South Australia. The reservoir impounded is referred to as Dartmouth Reservoir and is normally known as Lake Dartmouth. The Dartmouth Generation Power Station produces power to the grid of the nation and is situated near the walls of the dam. The Dartmouth Dam is composed of a dam itself, a hydro-electric power station, low-level and high-level outlets, spillway, cofferdam and a river diversion tunnel (Victoria, 2009).
The 180MW Francis turbine-generator operating at full velocity was stopped instantaneously by unknown body left in the penstock after maintenance. After initial dismay concerning the wall integrity, the hydro-electric plant installation was replaced and repaired but was not operational for numerous years. A crack of the wall would have demolished only on few occasions in the sparsely settled agricultural area and small town in a relatively narrow 120 km Mitta Mitta valley beneath the dam, but more importantly, would have led to the probable failure of the earthen walls and over-topping. This is directly upstream of the regional cities of Wodonga and Albury and more densely settled areas of irrigation, and results would have been catastrophic (Weaver, 2012).
The performance measurement of the Dartmouth Dam can be determined by its significance in the regions such as in water conservation, water supply for both industrial and domestic purposes, Hydro-electric power generation, and also for irrigation purposes, as well as disadvantages such as then negative ecological impact the dam possess in the region. The Dartmouth Power Station has a generating capacity of 180 megawatts with a single Francis turbine-generator. This being the largest hydroelectric turbine single installed in entire Australia. The operation and construction of the Dartmouth Dam have resulted in significant variations in the ecology and the flow patterns of the Murray and Mitta Mitta rivers. Specifically, the unnatural cold water released from the Dartmouth dam has led to the disappearance of the Macquarie Perth, Trout cod, and Murray Cod from River Mitta Mitta within just a few years of operation (Guyer, 2018).
The technical performance measures are the quantitative values measured, predicted, and estimated which describes the performance of the Dartmouth Dam. The figure below shows the technical performance measure of the Dartmouth Dam:
|
Technical Performance Measure |
Quantitative Requirement |
Current Benchmark |
Relative Importance (%) |
|
Components |
*Embankment dam *Dartmouth Reservoir *Dartmouth Power Station (Guyer, 2018) |
Spillage Capacity 2,750 m3/s Total Capacity of 3,856 GL Installed capacity 150 MW |
42 |
|
Capacity |
*Embankment dam (Spillage Capacity 2,750 m3/s) *Dartmouth Reservoir (3,856 GL) *Dartmouth Power Station (150 MW) (Victoria, 2009) |
Dam volume 14.1×106 m3 Total capacity 3,856 GL Annual generation 310 GWh |
28 |
|
Human Factors |
Less than 8% error rate per year |
Less than 12% error rate per year |
4 |
|
Process Time |
Commenced in 1973 to 1976 |
Timeline of 3 years |
10 |
|
Maintainability |
Minimum of 3 times per month |
Monthly |
16 |
|
100 |
Conclusion
This paper assesses the critical analysis of the design process of Dartmouth Dam by majorly focusing on its conceptual design phase of the dam. The Dartmouth Dam is a large rock-fill embankment dam with a chute spillway that is uncontrolled across the Dart, Gibbo, and Mitta Mitta rivers, a number of other minute distributaries as well as the Morass Creek. Some of the purposes of the Dartmouth Dam include water conservation, water supply for both industrial and domestic purposes, Hydro-electric power generation, and also for irrigation purposes. The major reason for designing the Dartmouth Dam by the River Murray Commission was to catch the flows during winter and release water during the season of irrigation.
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