The 43-metre wall that holds back 18 billion litres of water dammed at Chichester - water that has services the Hunter for more than 100 years - is due for inspection.
Hunter Water conducts regular inspections on the dam wall's integrity every five years - a process which involves lowering the dam's water lever by 1.3 metres, or around 2000 megalitres, which is then transferred via Williams River at Seaham to Grahamstown Dam.
Teams of specialist staff begin assessing the wall's strength and viability for the next half-decade over the next few weeks. It's a process that involves examining 93 cable "tendons" that lash the enormous concrete wall to the bedrock.
The work is expected to be completed by September 18.
"Once the water level is correct, a safe working platform (trolley) is then placed on the spillway crest so maintenance crews can access and test the tension in the cables, or anchors, which run inside the dam wall," Glen Robinson, Hunter Water's acting executive manager for service delivery for customers, said.
"Chichester Dam's capacity has been lowered from 100% (and spilling) to 89%. Grahamstown Dam's capacity is increasing slightly during the period of recapturing the water but because of the different dam sizes the change in percentage storage at the two dams is not equal.
"As we have lowered Chichester Dam's level from 100% to 89% for this work, the Dam will be ready to capture runoff from rain that falls over its catchment."
The Bureau of Meteorology has recently forecast, in the long term climate outlook, weather patterns moving into the La Nina phase suggesting a wetter than average period in the months ahead.
The last inspection in 2015 coincided with the 100th anniversary of the wall's construction, which took around nine years to complete.
At that time, the Chichester pipeline that ferried water into the populated parts of the region was crafted from timber held together with metal bands and made watertight with tar.
Contructing the dam required an army of about 1000 people, who also added cinemas and dance halls to the area as they worked to create a dam that still serves the region's needs.
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