Tomago Sandbeds

Overview

The Tomago Sandbeds is an underground water source that provides about 20 per cent of the lower Hunter’s drinking water. The sandbeds are parallel to the coast between Newcastle and Port Stephens, starting at Tomago and extending north-east for 25 kilometres to Lemon Tree Passage.

An extensive system of underground bores and vacuum stations draws raw water from the sandbeds and pumps it to Grahamstown Water Treatment Plant. The maximum storage is about 100,000 megalitres of water above sea level, of which Hunter Water can access about 60,000 megalitres with existing infrastructure from a portion of Tomago Sandbeds covering about 100 square kilometres.

The sandbeds are a natural geological feature, consisting of a layer of highly permeable fine grained sands underlain by impervious clay and rock. The thickness of the sand layer reaches a maximum of 50 metres, but on average is 20 metres deep. The source of the water is the rainfall that lands directly on the sand surface. While a proportion of the rainfall is lost to plants and evaporation, sufficient water is stored in the sand to provide a viable and significant source of water for ongoing extraction.

The sandbeds are strategically important for both ongoing and backup water supply. Ongoing supply from the sandbeds reduces the load on surface water sources (Chichester Dam and Grahamstown Dam) and thereby allows greater overall yield from the total water supply system. This large storage volume can also be used as a reserve supply during drought, and is available as a backup supply in the event of water quality issues in the surface storages.

History

• 1916: Water Reserve declared over 25km² with Hunter Water assigned as trustee.
• 1939: Construct Vacuum Stations 1-2, spray basin, 500mm pipeline to Newcastle.
• 1940: Construct Tomago Vacuum Stations 3 and 4.
• 1941: Williamtown RAAF base established, Tomago Catchment Area gazetted 100km².
• 1942: Construct Vacuum Stations 5-15, second spray basin, 900mm pipeline.
• 1946: Start water treatment by lime/alum dosing into delivery pipelines with sedimentation into Waratah Reservoir and later North Lambton Reservoir.
• 1953: Construction of Tomago Bore Stations 16 to 20.
• 1957: Abandoned due to poor water quality.
• 1959: Tomago No. 1 Water Treatment Plant opened.
• 1965: Tomago No. 2 Water Treatment Plant opened.
• 1972: Heavy mineral sand mining commenced operations leading to the relocation and eventual abandonment of Station 6.
• 1973: Tomago No. 3 WTP opened (also known as Grahamstown WTP) to treat water from both Tomago Sandbeds and Grahamstown Reservoir.
• 1992: Construction of Bore Stations 21 to 23.
• 1999: Heavy mineral sand mining operations cease.
• 2000: Construction of Bore Stations 24 to 27.

Geological History

The Tomago Sandbeds were formed during the Pleistocene era with the original sand deposits occurring up to 250,000 years ago. Rising sea levels created a large bay extending from Newcastle to Port Stephens. The Hunter and Karuah Rivers both flowed into the bay and deposited large volumes of sand. A combination of wave and wind action spread the sand along the coastline and formed the series of shallow dunes that make up the Tomago Sandbeds.

The Tomago Sandbeds are no longer mobile and have evolved into a mature and well vegetated landform. Over time rainfall landing on the sandbeds has washed out any remnants of sea salt leaving the deep sand system full of fresh water.

The North Stockton Sandbeds, which form the current coastline between Newcastle and Port Stephens, were deposited much more recently than the Tomago Sands. They overlie the eastern extremity of the Tomago Sands and were deposited in the Holocene era (i.e. the last 10,000 years).