THE South Coast NRM region includes 107 rivers or major tributaries, 33 estuaries and more than 300 conservation category wetlands. Groundwater resources are particularly significant as they perform essential ecological services and provide water for human consumption.
It is likely that additional assets have been included in the region through boundary changes and increased knowledge of water resources.
Water has a significant ecological, social and economic value for the South Coast community as the resources provide water supply and an avenue for recreational activities including boating, commercial fishing, tourism and amenities. Agriculture contributes significantly to the economic wellbeing of the region and its continuation, growth and diversification is dependent on water availability.
The region’s estuaries provide an important commercial place for fishing as well as opportunities for tourism and recreation. Other industries are dependent on water available from the coastal groundwater reserves and the expansion of industry is dependent on the future use of surface freshwater in the western part of the region.
The natural water systems of the region all have the same level of importance to Noongar spirituality, culture and identity. Many people appreciate water because of its necessity in consumption or production or because of where it sits in the natural landscape and is utilised and admired for its many social values.
A third of the 45 watercourses between the Deep River and Cheynes Bay streams were rated as having high social values when assessed as part of the Water Resource Assessment (Department of Water, 2010) with the Frankland, Denmark, Kalgan and Waychinicup rivers scoring highly across multiple categories.
Rivers with high social values tend to be significant, in close proximity to a settlement, are easily accessible and have historic significance and facilities for recreational use.
Our knowledge of the values of the region’s rivers, tributaries, estuaries and wetlands has significantly increased in the last five years, largely due to the identification of information gaps in the previous South Coast NRM strategy and the subsequent implementation of research, planning and application of projects.
Knowledge and baseline information has been established through surveys of:
Wetlands, rivers and estuaries to classify their environmental, cultural and social values.
Wetlands, rivers, estuaries and foreshores, generating information about environmental condition and values. Determination of river habitat values (with habitat mapping) has provided a greater understanding of ecological values.
Estuaries, including the evaluation and mapping of sea grass, fish habitat and other fauna communities.
New and on-going monitoring programs in estuaries, wetlands and rivers have provided information on species’ diversity and abundance, water chemistry, hydrology, nutrients and sedimentation.
Two broad aquatic bioregions have been identified for river systems in the South Coast region – the western South Coast, from Gardner River in the west to Bluff River and the Eastern South Coast, from the Pallinup River through to the Thomas River in the east. These are based on a hierarchical classification using a comparative assessment of the ecological values of selected rivers across the region.
Rivers belonging to the Eastern South Coast aquatic bioregion receive less rainfall, are significantly more saline, slightly more alkaline and have higher levels of total nitrogen than those belonging to the Western South Coast. Rivers of both aquatic bioregions have similar levels of turbidity, dissolved oxygen and total phosphorus levels.
Diverse river characteristics such as hydrology, geomorphology, catchment size and vegetation cover reflect the different management requirements.
Hydrological flow and ambient water quality monitoring is undertaken at 55 gauging stations on 40 river systems distributed across the region. Monitoring data is used for resource assessment and management, trend analysis, infrastructure design, floodplain mapping, model calibration, understanding catchment processes and detecting effects of changing climate.
Additional targeted resources and monitoring is required to calibrate and support catchment models to understand water quality characteristics of water systems into the future and to determine if the condition of these resources is improving or deteriorating.
Additional physio-chemical water quality monitoring has focused on water systems at Princess Royal and Oyster harbours, Wilson Inlet and Torbay Inlet catchments (for nutrient monitoring) and the Kent and Denmark river catchments (for salinity monitoring). Information gathered is used to gain knowledge of the nutrient and salinity status and to measure whether reduction targets are being met in accordance with the catchment management plans.
A number of macro-invertebrate species are considered to be characteristic of each of the two bioregions, with differences observed in the presence and abundance of particular species of amphipods, mayflies, stoneflies, caddis flies, dragonflies and damselflies.
The average total macro-invertebrate species’ richness is significantly higher in the western South Coast bioregion than the eastern, with the Frankland Gordon, Kent, Hay and Marbelup systems ‘hotspots’ in the western and the Bremer and Phillips West rivers ‘hotspots’ in the east. There are a number of taxa which can be used as ‘indicators’ for river health in western and eastern South Coast bioregions.
Our region’s waterways are home to a number of species endemic to southern WA, including rare types with narrow distribution ranges. Special macro-invertebrate fauna include amphipods, freshwater crayfish, mayflies, stoneflies, caddis flies, dragonflies and freshwater mussels and limpets.
Several new species have been identified, including four macro-invertebrates - an amphipod, an isopod, a caddisfly and a bivalve. The known ranges of a number of species, such as the western swamp emerald dragonfly and the koonac were extended.
Biological studies have been limited to snapshot surveys - there is no ongoing biological monitoring of rivers. Knowledge of aquatic flora is limited and additional macro invertebrate sampling is needed to clarify the delineation of the western and eastern bioregions between the Bluff and Pallinup rivers.
Key waterways including the Lort, Hamersley and King creeks, Angove and King rivers and several smaller systems remain unsampled. Ten species of native freshwater fish have been discovered, the rarest being western or spotted trout, minnows, salamander fish, Balston’s pygmy perch and a new undescribed species of pygmy perch from the Mitchell River near Denmark.
When the naturalness, diversity and rarity of a river were considered to obtain an overall assessment of ecological value, the top three in the western bioregion were the Shannon, Deep and Gardner rivers, while the top three in the eastern were the Bremer, Oldfield and Jerdacuttup.
A framework for prioritising waterways for management in WA is being developed to allow for a more detailed assessment of ecological values as undertaken in the study of South Coast river system. A matrix plotting these ecological value scores, against threatening processes for each river system is
Catchments and land use
There are 24 rivers with more than 89 per cent of their catchments still under native vegetation cover. The Forth, Saint Mary and Dempster rivers have been identified as priority one ‘Wild Rivers’, while the Doggerup and Blackwater creeks and Shannon, Deep and Inlet rivers have been assigned a priority two rating (Department of Water, 2009).
The upper catchments of the Oldfield, Young and Lort rivers remain substantially uncleared and have high environmental values. At the other end of the spectrum, 16 rivers have more than 80 per cent of their catchments cleared and as a consequence have substantially modified hydrology, often associated with increased sedimentation, erosion and increased turbidity and nutrient levels in their estuaries.
Catchment clearing and altered land use resulting in changed hydrology and increased salinity levels are major threats and can be associated with increased erosion, sediment transportation and altered turbidity and nutrient levels.
Other threats include loss of riparian vegetation (including through unmanaged livestock access), nutrient enrichment, unmanaged recreational use, pollution from rural and urban land uses, over-extraction of limited freshwater and physical alteration to river banks, channels and floodplains and inappropriate development in riverine and estuarine floodplain areas.
Diversity, species richness and rarity scores are considered better predictors of total ecological value compared to measures of naturalness, such as native remaining vegetation remaining.
The way land is managed affects the amount of water available and its quality. Hardwood plantations such as blue gums (Eucalyptus globulus) intercept precipitation, reduce soil moisture content and lower groundwater levels resulting in reduced stream flow and less recharge to groundwater systems compared to annual agricultural crops. Tree plantations also have beneficial effects on water levels especially in salt affected catchments.
Computer modelling has predicted streamflow and salt load reductions under various land use regimes (including plantations) in the Denmark catchment under several future climate scenarios, while monitoring data has confirmed the predicted salinity reductions (Department of Water, 2004). Farm dams and other infrastructure such as interception drains also reduce run-off and diminish streamflow.
Understanding the influence and relative impact of tree crops and infrastructure on hydrology will allow for more informed land management and water planning.
Estuaries and inlets
Of the region’s 33 estuaries and inlets, most are generally closed and only open to the Southern Ocean after heavy rainfall or high seasonal water levels. Manual bar openings occur in some locations.
Only four small estuaries and their catchments occur entirely within national parks and can be considered ‘pristine’, these are the Dempster and Saint Mary within the Fitzgerald River National Park and Jorndee and Poison creeks within the Cape Arid National Park.
Quarterly monitoring of physio-chemical status has been undertaken by the Department of Water at the Oldfield, Wellstead, Beaufort estuaries and the Hamersley, Gordon, Wilson, Parry and Walpole/Nornalup inlets since 1998.
The suite of monitored estuaries was extended in 2006 to include the Stokes and Culham inlets and Princess Royal, Oyster and Bandy Creek harbours. Water quality monitoring enables the condition of the estuaries to be tracked.
A matrix based on five water quality indicators; chlorophyll-a, dissolved oxygen, algae bloom events, fish kill events and catchment inputs of dissolved inorganic nitrogen is used to describe and compare waterway condition.
Seagrass decline, algal growth and nutrient sources have been extensively studied for the Albany harbours, especially from 1988 to 1990. Seagrass mapping has been conducted in the harbours approximately every four years between 1962 and 2006 and percentage cover of grass species has been compared. This was the first system in Australia to document increases in seagrass coverage.
Environmental Water Requirement studies have been undertaken for the Wilson and Torbay inlets, Lake Powell and Manurup Lagoon. These studies have attempted to quantify the amount of water that could be harvested from these systems without unacceptable impacts on the environmental, social and economic values. Inclusion of estuaries in the EWR process is also an Australian first.
Climate change scenarios predict a rise in height of wave-dominated estuary bars, less frequent openings and shallower estuaries with greater sediment movement. Less river and possibly more erratic delivery of flow, stronger salt wedge further upstream, increased low oxygen events, productivity and algae bloom and fish kill events are all strong possibilities.
Possible impacts of climate change need to be investigated as there are gaps in our understanding of implications of habitat modification and the likely impacts on diversity and fisheries.
Baseline and spatial information increased across for wetlands across the region, including:
Greater accuracy for location and boundaries of significant sites
Information about 15 previously unidentified sites
Development and implementation of management plans for eight regionally significant suites
Flora and fauna lists
Development of indicator species for determining health
Improved understanding of ecological functioning
Datasets of ecology and condition
Classification based on improved assessment methodology of wetland values
Identification of the cultural significance for Aboriginal people
Increased community awareness of wetlands and susceptibility to environmental change
Increased protection of through impact assessment and management planning
Assessment of the conservation status of water assets, such as those poorly represented in the conservation reserve system.
Wetlands of International Significance (under the Ramsar Convention) include lakes Gore and Warden and part of the Lake Muir system. Lake Warden is a Biodiversity Recovery Catchment and revegetation, monitoring and hydrology studies have been undertaken.
An additional 11 systems are listed in the Directory of Important Wetlands in Australia (Environment Australia, 2001) and 15 are on the Register of the National Estate. About 300 wetland systems have been identified as being in the conservation category as defined by the Environmental Protection, South Coast Agricultural Zone, Policy 1997 but only broad scale surveys and classifications have been undertaken.
The South Coast Wetland Monitoring Program has produced snapshot reports describing individual wetlands, their salinity, nutrient and macro-invertebrate characteristics.
There is a good level of understanding about the condition of wetlands across the region and threatening processes including secondary salinisation, increased run-off, hydrological changes and acidification, have been clearly identified. Monitoring is essential for wetland and water resource planning to protect and conserve these assets.
Mapping, classification and the evaluation of wetland condition close to urban areas where development pressure and groundwater resources exist, has been undertaken in priority areas of Albany, Hopetoun and Esperance.
The definition of precise wetland boundaries as well as social and economic values has been used in guiding management and future land use development planning. Bremer Bay is a growing community with potential future demands for water resources and development and will be the next priority for wetland mapping and classification.
Aquatic invertebrates are increasingly being recognised as critical indicators of wetland health due to their importance to processes such as sediment biogeochemistry, nutrient and carbon cycling and controlling phytoplankton.
They also constitute the primary food resource for most of the migratory waterbirds which give wetlands international significance. Aquatic invertebrate communities are being monitored in the Ramsar wetlands of Lake Warden and Gore system to guide responses to present and future management actions.
Changes to hydrology as a result of clearing and/or climate change are considered to be the most significant threats and are compounded by increased salinity levels, clearing through grazing, inappropriate drainage, nutrient enrichment, invasion by weeds and over-extraction of water for supply purposes.
In terms of water supply, the most significant resource issue is identifying and securing future public water sources for drinking water supplies and industry and agriculture without detrimental impact on the environment. Demand for water is growing beyond the capacity of current resources, especially in light of declining rainfall in the western part of the region.
To make decisions about future supplies, we must have in-depth understanding of resources such as groundwater, social values, ability sustained usage, the extent of ecosystems dependent on the resource and volumes of water likely to be required.
This knowledge, with community consultation, will provide a sound basis for public water planning for the short, medium and long-term.
The Western South Coast Water Resources Assessment collated information on likely water sources in the region, assessed their social, cultural and environmental values and considered demand and impacts of climate change and land use.
The region contains limited fresh groundwater, with the exception of coastal quaternary aquifers (sand dune aquifers), which provide critical supplies for Albany, Bremer Bay, Hopetoun and Esperance.
In other areas, knowledge of groundwater is vague or the resource is of limited extent and quality. Planning and management must have a strong focus on wastewater discharge, water use and conservation (residential, agricultural and industrial) and management of increase in demand, especially for industrial uses.
Planning activities for sustainable water supply in the Lower Great Southern (Walpole, Denmark, Albany and Mt Barker) have included the publication of Water Forever: Lower Great Southern (Water Corporation, 2010) which seeks community and industry input about securing water services in the future.
The challenge facing the region is to provide water for people and environment in an even drier climate, with twice the population and less environmental impact. To meet these challenges, government agencies need to work with the community to reduce usage, increase water recycling and develop new sources.
The Lower Great Southern: Water Resource Development Strategy explains the planning process and principles on how new water source proposals will be assessed. The objectives for water source planning are to assist responsible development, improve supply security and provide guidance for developing sources. To complement this strategy, a Great Southern Water Plan is currently being developed.
Drinking water source protection plans have been prepared for most drinking water sources in the South Coast NRM region with additional plans being produced annually.
The Kent and Denmark rivers were designated Public Water Supply Recovery Catchments under the WA Salinity Action Plan. Revegetation and high water use farming systems were implemented in these catchments with the aim of reducing river salinity levels. Results indicate it is unlikely water quality will be improved in the Kent River in the medium term. However, salinity in the Denmark River was classified fresh in 2012.
Environmental Water Requirement studies have been undertaken in the Angove River, Wilson and Torbay inlets, wetlands within the Torbay catchment, Marbelup Brook and Denmark River.
These studies have attempted to quantify the amount of water required to prevent unacceptable impacts on the environmental, social and economic values of these systems.
Urban stormwater management initiatives have been developed to provide guidance on improved design and management, including capturing stormwater for reuse, preparing and implementing management plans and engaging stakeholders and community for optimal outcomes.
Climate change will alter the dynamics of surface and groundwater as well as plant and animal water needs. These changes will affect aquatic species and many others dependent on rivers, wetlands, floodplains and groundwater for food, water or habitat. Reduced rainfall in south west Australia will result in reduced inflows into water storages, reduced stream flows in major catchments and reduced recharge of groundwater.
The associated indirect impacts of increased temperature and reduced rainfall include higher risks of algal blooms, changes in the salt loads of streams and possible changes in ecological water requirements. There is already a great deal of variability in seasonal rainfall which has led to inconsistent drying and wetting of resources such as wetlands.
The relationship between rainfall and streamflow is non-linear. The 10 to 20 per cent decline in rainfall in the south west of WA since the 1970s is associated with a 40-50 per cent reduction in streamflow into Perth reservoirs, which has significantly impacted on surface and groundwater resources.
This reduced streamflow has led to the increased utilisation of groundwater, which has the potential to increase pressure to groundwater dependent parts of the South Coast.
It has been predicted that within 100 years, around one third of aquatic freshwater invertebrates and a similar proportion of halophytic invertebrates will disappear from wetlands in WA’s Wheatbelt. Catastrophic losses of aquatic plants and waterbirds are also predicted.