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Catchment

A catchment is an area of land that collects water which has drained to the lowest point in that area. This could be a lake, a dam, or underground reservoir. Rain that falls on land will make its way to this lowest point, through creeks, rivers, stormwater systems, groundwater, wastewater and water-related infrastructure. As water cycles through a catchment, its condition is affected by the:

  • surfaces with which it comes into contact 
  • degree to which the area has been changed by human activity such as land clearing, farming, urban development, etc.

Keeping catchments clean is an essential first step in maintaining water quality. As we all live in a catchment, this is an area where we can all co-operate to protect water quality.

We have three main catchments in the Hunter Water system:

  • Grahamstown Dam Catchment
  • Chichester Catchment
  • Tomago and Anna Bay Sandbeds Catchment

 

Grahamstown Dam Catchment

Grahamstown Dam is the lower Hunter region’s major urban water supply dam – supplying 30-45% of our water. The catchment is nearly 100 square kilometres and is located in the Williams River area between Seaham and Raymond Terrace. Grahamstown Dam itself is located relatively close to the river at Raymond Terrace.

There are many different activities and land uses in the Grahamstown Dam catchment – including agriculture, residential and urban developments, tourism and recreation.

Hunter Water routinely monitors water quality in the lower Williams River for nutrients and pathogen quality before any transfer to Grahamstown Dam. Like most Australian rivers, the Williams is highly influenced by climatic conditions and is consequently highly variable in its amount of daily river flow.

 

Chichester Catchment

The Chichester catchment is around 197 square kilometres and supplies about 40% of the lower Hunter’s drinking water. It is bound on the north and east by the Great Dividing Range, which separates it from the Gloucester, Barrington and Manning Rivers.

The catchment for Chichester Dam is largely incorporated into the Barrington Tops National Park and is a declared wilderness area. As a result, it is one of the most pristine catchments in Australia with large areas unaffected by human activity. The extensive virgin forests and the high ranges at the head of the rivers ensure a large rainfall and minimum evaporation, resulting in a high runoff with good water quality. The catchment receives water from the Chichester and Wangat Rivers.

Because Hunter Water extracts water under the Water Act of 1912 we must meet strict conditions outlined in the Water Management Licence, which came into effect in 1998. Therefore, we have increased environmental flow releases from Chichester Dam into the Williams River to manage and minimise environmental impacts. These flows help sustain natural ecosystems along the Chichester River.

 

Tomago Sandbeds Catchment

Groundwater reserves also form an integral part of Hunter Water’s bulk water supply, augmenting surface sources as required and providing critical backup during periods of drought. The Tomago Sandbeds are a major source and the sole supply to Tilligerry Peninsula.

The Anna Bay Sandbeds supply the Tomaree Peninsula, which is also augmented from Grahamstown Dam, while the North Stockton Sandbeds act as a potential drought reserve.

The Tomago-Tomaree-Stockton aquifers cover an area of 275 square kilometres, along a coastal strip some 10 to 15 kilometres wide, extending from the Hunter estuary (in the south) to Port Stephens (in the north) and Raymond Terrace (in the west). Most of the aquifer area has porous sandy soils lying over porous sand. This allows rain to percolate down to the aquifer quickly and hence, there is very little surface run-off and little defined drainage pattern, except in areas of bedrock.

Tilligerry Creek is the most prominent surface drainage feature. Fields of complex dunes contribute to the characteristic hilly dune terrain. The porosity of the sand allows for considerable groundwater storage and direct rainfall is the major method of recharge, or filling, of the groundwater reserves. The groundwater is then either used by vegetation, is extracted for human use or drains to low lying parts of the land surface (such as wetlands) or to the ocean and local estuaries.

 

Catchment management


The land in the groundwater catchments is used for a wide variety of purposes, including:

  • Residential
  • Industry
  • Manufacturing
  • Construction
  • Transport (road and air)
  • Agriculture (dairying, animal grazing, poultry, vegetable growing)
  • Mining
  • Utilities
  • National park and nature reserves
  • Defence force activities
  • Recreational sites
  • Viticulture.

There are two important issues that can potentially affect groundwater quality within the aquifer system:

  • The presence of many domestic septic tanks scattered across the area
  • The past history of sand mining in the catchment.

Therefore, careful management of the catchment area is needed to protect the water supply system in conjunction with the other land use functions as well as protect the interests of adjoining land holders. For example, the impact of heavy mineral sandmining on sections of the sandbeds between 1972 and 1999 led Hunter Water to cease water extraction from these zones.

Catchment management practices at Tomago include monitoring water levels using an extensive network of water level monitoring piezometers to ensure that water is extracted on a sustainable basis. Special attention is given to ensuring that water levels remain high enough at all times to prevent the drawing in of salt water from the periphery of the system. Other catchment management practices at Tomago include feral animal and weed control and bushfire management.

The Department of Water and Energy (DWE) regulates water extraction from Tomago by way of a Water Management Licence with Hunter Water Corporation. Port Stephens Council, in conjunction with Hunter Water and DWE, regulates development in the area, and there are special development controls in place within the Tomago catchment area.

Some parts of the groundwater catchments are declared Water Reserves under the Crown Lands Act, 1989 and Hunter Water is the nominated Trustee of these reserves.
A National Park was gazetted over the Anna Bay Sandbeds in 1996, further protecting water quality of the area. A Water Sharing Plan developed for the Tomago/Tomaree/Stockton Ground Water Sources was implemented on 1 July 2004.