Profile of the Hunter Catchment
The Hunter River drains the largest coastal catchment in New South Wales, covering some 22,000 square kilometres. It supports a great diversity of land uses, industries and urban settlements, with agriculture, power generation and tourism some of the largest contributors to the regional, state and national economies.
Urban and industrial development in the Hunter Valley has impacted on the health of the Hunter catchment in various ways. Reduced water quality and water availability, declining native fish populations, reduced riparian vegetation cover, and stream bank erosion are some of the issues that are currently being managed (Department of Environment Water and Heritage).
From the alpine rainforests of the Barrington Tops in the north-east, to the dissected sandstone of the Great Dividing Range in the south-west, through undulating hills and rich flats of alluvial floodplains, to the coastal fringe the Hunter catchment is unique in its diversity. The health of the river system and catchment is dependent on carefully balanced management of the ecosystems within these landscapes (Hunter Catchment Management Trust, 2003).
When you think about any river catchment it is useful to think of the river as a conveyor belt that picks up sediment - rocks, pebbles, soil and sand - at the source of the river, and carries it along through the middle of the river, before depositing it at the end of its journey, at the mouth of the river.
The Hunter River begins its journey in the rugged Barrington Tops, which are the second highest point in NSW after the Snowy Mountains. The geology of this area is characterised by steep, faulted and folded rocks of the carboniferous period, some 286-360 million years old. Here you'll find mostly hard gravel or cobble stones in the streambeds, and because the landforms are so steep, the water flows very quickly through this area (CMA, 2006).
From the foothills of the Barringtons, the river flattens out as it passes through Moonan Flat and the undulating hills of Belltrees before it is stopped in its tracks at Glenbawn Dam. The dam, which was built in 1957 to mitigate flooding and secure water for agriculture, industry and the surrounding townships, actually traps all of the sediment that has travelled down the river from the upper reaches (Erskine, 1984 as in Spencer et al, 2004). Downstream of the dam the river is starved of sediment until the Rouchel Brook confluence. This tributary brings fine gravel into the Hunter River, which gets carried along the main stream down the catchment.
Downstream of the Rouchel Brook confluence, where the river heads inland towards Muswellbrook and Denman, the land begins to flatten out. The geology in this part of the catchment is characterised by softer rocks of conglomerate, shale, sandstone and coal from the Permian period (245-286 million years old). Soils in this area are softer, have a higher salt content and are highly erodible (CMA, 2006).
Just south of Denman is where the Goulburn River joins the Hunter, connecting it to the western part of the Hunter catchment. This area is characterised by hard thick layers of sandstone, dissected by valleys of sandy soils, which past events have shown, are very easily eroded. This is why, when the Goulburn River and the Wollombi Brook, which also joins the Hunter from the western part of the catchment, have flooded in the past, large deposits of sand have been found on the banks of the Hunter River at Singleton, Maitland and other areas south of the confluence. This is especially the case where there is less vegetation on the riverbanks to trap the sand and sediment.
As the river travels down to the lower Hunter Valley floodplains to Singleton and Maitland, the soils are finer-grained silts that have accumulated over millennia from sediment sources further up the valley, that have been trapped by vegetation along the floodplain.
At this point the catchment flattens out considerably and the river begins to widen as it reaches the tidal zone, where the freshwater that travels down from the upper reaches mixes with saltwater from the sea. The tidal limit of the Hunter River is at Oakhampton, 64 km upstream from the ocean.