Warragamba Dam

In 1910, Ernest de Burgh, Chief Engineer for Water Supply and Sewerage, in the NSW Public Works Department prepared a proposal for a dam on the Warragamba River and followed it up in 1918 with more detailed plans. His proposals were passed onto the newly formed Metropolitan Water and Sewerage and Drainage Board in 1925 when it took over from the P.W.D. The completion of the Warragamba Emergency Scheme required during its peak 1,000 waged employees at the Headworks, and a further 1,000 on the Pipeline. All buildings used in the construction of the Emergency Scheme were designed for later re-use as cottages for the future maintenance and operations personnel. Some of these buildings were relocated from elsewhere. The main works office was the original police station at the Nepean Dam site.[1]

In 1940, a weir and water pumping station, known as the Warragamba Emergency Scheme, reached completion, just downstream of the main dam site,[2] located on the east bank of the Warragamba River. Access to the site was along the road currently known as Weir Road. Major elements of the construction works still extant include the weir, a 10-cable cableway, shads, batching plants, roads, electrical substation, chlorination plant, maintenance staff accommodation, balance reservoir, Megarritys Bridge, water pumping station, tunnels, and associated pipelines.[1]

In 1943 the Metropolitan Water, Sewerage and Drainage Board invited the geologist William Browne to investigate a proposed site. Browne found a more suitable site and continued as geological adviser until completion.[4] The site was reviewed and approved by Dr John Savage, considered the pre-eminent expert in this field, and formally accepted by the Metropolitan Water, Sewerage and Drainage Board on 2 October 1946.[2] The Board appointed Thomas Upton as the engineer.

The Warragamba River flows through a gorge that varies in width from 300 to 600 metres (980 to 1,970 ft), and is 100 metres (330 ft) in depth. This gorge opens at its upper end into a large valley, the Burragorang Valley. This river configuration allows for a relatively short but high dam wall, in the gorge, to impound a vast quantity of water.[2]

Dam construction began in 1948 and was completed in 1960. The resulting dam of the Warragamba River formed Lake Burragorang, which is one of the largest reservoirs for urban water supply in the world.

The dam wall comprises 1,612,000 cubic yards (1,232,000 m³) of concrete. It was laid as interlocking blocks roughly 17 metres (56 ft) on each side, which were later grouted together to form a continuous, monolithic wall. It is so large that engineers had to use two techniques to prevent the temperature from becoming too hot as the concrete set. One was to add ice to the wet concrete, the first application of this technique in Australia. The other was to embed cooling pipes into the concrete and circulate chilled water through the pipes. As a result, the dam wall was cooled in a few months instead of the estimated 100 years it would have taken to cool naturally.[2]

Warragamba Dam

The main spillway has five crest gates: A central drum gate with a 27 metres (89 ft) clear span with a pair of radial gates on each side. Each radial gate has a 12 metres (39 ft) clear span. The drum gate is hinged along the upstream edge to the upstream crest and lowers into the dam wall to allow water to flow over it. When fully open, it forms a continuation of the crest profile.[2] All gates open automatically as the dam passes full water level, or can be manually opened.[2][6] The auxiliary spillway is normally closed by a series of fuse plugs that are designed to be washed away in the event of an extreme flood event.[7]

As originally designed, the dam could safely withstand a peak inflow of 500,000 cubic feet per second (14,000 m³/s), leading to a peak discharge of 354,000 cubic feet per second (10,000 m³/s) down the spillway.[2] Following a 1987 and 1989 re-evaluation of the potential rainfall and flood risks, the New South Wales Government authorised for the dam wall to be raised by 5 metres (16 ft) and constructed an auxiliary spillway on the east bank of the dam.[6]

There is also a hydroelectric power station at the dam that can generate 50 megawatts (67,000 hp)[8] which is currently disconnected from the electricity grid.[9] Water levels became very rarely high enough to allow operation of the power generators. It had rarely been used by 2012.[10]

In 2006, the Warragamba Deep Water Storage Recovery Project, part of the Metropolitan Water Plan, penetrated the base of the dam wall to allow the previously inaccessible lowest water in the reservoir to be available. This new outlet was below the minimum level required for gravity flow, which delivered water from the existing outlets. The project constructed a new pumping station downstream of the dam. The new pumping station is within the Emergency Scheme pumping station chamber. This project provided access to eight per cent more water or approximately six months of extra supply. On 15 April 2006, the project reached a major milestone when it increased the available storage from 1,857 gigalitres (6.56×10¹⁰ cu ft) to 2,027 gigalitres (7.16×10¹⁰ cu ft).[5]

Enhancements to the dam were completed in 2009, including the addition of an auxiliary spillway to manage extreme flood events.[7]

Other recent major work includes a complete upgrade of the three passenger lifts within the dam wall, an upgrade of the travelling crest crane and a complete upgrade of the four water supply outlets in the valve house, which includes the replacement of the major valves.

Since 2017, WaterNSW has been working on a risk-mitigation project, aimed at protecting human life and property in the floodplain catchment area in case of major flooding, primarily by raising the dam wall by up to 17 metres (56 ft).[11] Infrastructure NSW's rationale is based on the fact that up to 134,000 people live and work on the floodplain, and urban growth could greatly increase this number in decades to come; giving the dam a greater capacity would enable holding back floodwaters before releasing it in a controlled fashion, reducing the need for urgent evacuations.[11]

However, there are concerns for the more than 50 recognised Aboriginal heritage sites in the 6,000 hectares (15,000 acres) of World Heritage Area that would be flooded, parts of which were badly burnt in the 2019–2020 bushfires in Australia. The box gum grassy woodlands are home to threatened species of birds, including up to 50% of the remaining population of the critically endangered regent honeyeater, as well as koalas and greater gliders.[12]

In September 2020, the New South Wales Government was ordered by the federal Department of Agriculture, Water and the Environment to re-do their Indigenous heritage work, concerned that NSW has not adequately addressed the concerns of Gundungurra and other traditional owners in their cultural heritage surveys.[13] The federal review also said that the environmental impact assessment lacked detail on how the project could affect species such as the platypus and echidna. Engineering experts have also questioned the modelling done by Infrastructure NSW.[14]

There have been times when drought has seriously depleted the dam. In March 1983, Lake Burragorang's level reached a low of 45.4% of capacity, only to reach maximum level in the mid 1990s; as a consequence the gates were opened (there was a significant spill in August 1998[14]). Between 1998 and 2007 the catchment area experienced extremely low rainfall (in December 2004, the dam dropped to 38.8% of capacity, the lowest on record to date[15]) and on 8 February 2007 it recorded an all-time low of 32.5% of capacity.[16]

The New South Wales State Government tried to reduce this risk by implementing water restrictions[17] and commissioned the construction of a desalination plant, at Kurnell. Heavy rains between June 2007 and February 2008 restored the dam level to around 67%. Despite this, Level 3 water restrictions remained in place until 21 June 2009.[18]

On 29 February 2012, it was reported that the dam was likely to overflow for the first time in fourteen years, due to continuing heavy rain in the region.[18] The dam began spilling at 18:53 (AEDT) on 2 March 2012 and again on 20 April 2012.[19][20][21][14]

It hit full capacity on 17 August 2020, compared with less than half full a year previously.[11]

• "Warragamba Dam". 2007.
• Attraction Homepage (2007). "Warragamba Dam".
• Johnson, Dianne (2009). 'The Katoomba Gully People's resistance to dispossession' in History Council of NSW Bulletin, Winter.
• Graham Brooks and Associates Pty Ltd (1996). Sydney Water Heritage Study.

This Wikipedia article was originally based on Warragamba Emergency Scheme, entry number 01376 in the New South Wales State Heritage Register published by the State of New South Wales and Office of Environment and Heritage 2018 under CC-BY 4.0 licence, accessed on 2 June 2018.