Supervising Scientist Report 167
Supervising Scientist, 2001
ISBN 0 642 24373 5
- SSR167 - North-west rivers environmental review: A review of Tasmanian environmental quality data to 2001 (PDF - 800 KB)
About the report
This document provides an environmental review of the rivers, including estuaries, of north-west Tasmania. The document covers the natural environment, human uses and values, and pollution sources such as sewage treatment plants, mines, waste disposal sites, stormwater, industry, agriculture and forestry. An overview of current work and outstanding issues on a catchment by catchment basis is given.
The major river health issues in the region are acid mine drainage, dairy effluent, leachate from past waste disposal sites, and soil loss from agricultural land. Sewage and stormwater systems perform poorly at times with impacts primarily at the coast rather than in the rivers.
Acid mine drainage is a serious issue from old mine sites in the Waratah and Mt Bischoff region. Contaminated drainage has impacted tributaries of the Arthur River and created a ‘dead zone’ for approximately 20 km downstream in the Arthur. Acid mine drainage is a problem to a lesser extent in the Frankland River (tributary of the Arthur) from old mine workings at Balfour, and in the Forth River from old workings at Round Hill above Lake Cethana.
Agriculture is a major land use across north-west Tasmania. Notable impacts from dairying operations are evident in the far north-west at Edith Creek (tributary of the Duck River) and at Togari (Montagu River catchment). Due to the deep soils across much of the region and generally high rainfall, soil loss is a big issue that affects most rivers, particularly in areas of intensive cropping. The problem manifests in waterways as high turbidity, and high sediment bed load. Waterways that are particularly affected are those with small catchments in the central coast region such as Claytons Rivulet, Buttons Creek, Sulphur Creek and the Don River. These catchments tend to be intensively developed and the streams do not receive high volume flushing flows of clean water from forested or high altitude areas.
Closed waste disposal sites of particular concern in the region are: View Street waste depot in Burnie located in a gully with high water table; Port Sorell waste depot with pulp mill waste leachate to creek and groundwater; industrial waste landfill in Burnie that impacts upon tributaries of the Cam River upstream from a town water supply off-take; and an abattoir waste disposal site in Smithton that leaches to a tributary of the Duck River.
The biggest wastewater problem in the region is cross connections between the sewage and stormwater systems. Influxes of water to the sewer via stormwater connections create problems at sewage pump stations that can at times overflow to rivers. The Mersey estuary is particularly affected by this problem. Additionally stormwater infrastructure is absent in parts of Burnie and Devonport in which case stormwater is either connected to the sewer through lack of an option, or not connected at all.
The water quality of sewage effluent and stormwater is not perceived to be a major concern for river health on the north-west coast as most outfalls are to the ocean. Monthly monitoring data for sewage treatment plants on the north-west coast demonstrates that most plants perform close to or worse than current effluent quality guidelines. There have been no studies undertaken to characterise stormwater quality in the region.
There are many small towns in north-west Tasmania that are not serviced by reticulated sewerage systems and rely on septic tanks or similar systems. Cradle Valley is an area that has a number of individual sewerage systems at numerous locations that collectively may have some impact if not upgraded. Due to the high conservation status of the area and the increasing visitor usage there is an argument for upgrading and centralising the sewage collection and treatment facilities of the area.
Industrial wastewater is not a significant issue for the rivers of north-west Tasmania. Goliath Cement works in the Mersey catchment has a water management plan, and the old Tioxide site on the Blythe estuary has been rehabilitated to minimise off site impacts. The Leven estuary is sometimes affected by pump station overflows resulting from influx of vegetable processing factory effluent.
An assessment of estuaries using physico-chemical criteria, species diversity and level of human disturbance showed that estuaries of the north-west coast are generally degraded. Just the Black River estuary has high conservation significance. Several estuaries (the Welcome, Montagu, West Inlet, East Inlet and Detention) have moderate conservation significance.