The Dunsborough streams catchment includes (from north to south) Meelup, Dolugup, Dandatup and Dugulup brooks. All streams flow seasonally and discharge to Geographe Bay. Dolugup Brook occurs entirely within Meelup Regional Park (Class ‘A’ Reserve) and is one of the few waterways within the Geographe catchment that has a completely vegetated and relatively undisturbed catchment.
The Dunsborough waterways are of cultural significance to the Wardandi people and at least fifteen registered sites of significance occur within the catchment. The streams provide a diversity of habitat and food sources for native fauna and are known to support the Gilgie (Dandatup and Dugulup Brooks), Marron (Meelup Brook) and the Blue spot goby (Meelup Brook). A River Action Plan developed by the Cape to Cape Catchment Group in 2006 outlines the characteristics, values, condition and management issues of the Dunsborough streams.
Meelup Regional Park is located in the north-eastern part of the catchment. The park contains intact native vegetation with a few areas cleared for tourism purposes and fire control. Large urban lots with some areas of beef grazing occur in the western part of the catchment. In the south-western corner of the catchment is the town of Dunsborough, with surrounding land uses including urban residential areas, parks and golf courses, industrial and commercial businesses.
Image: Native vegetation and urban and rural living are the primary land-uses in the catchment.
The upper reaches of Dandatup and Dugulup streams flow through farmland and lifestyle properties before flowing through the Dunsborough townsite and discharging into Geographe Bay. The upper half of Meelup Brook flows through agricultural land and a vineyard before entering the Meelup Regional Park and discharging at Meelup Beach. Numerous on-stream dams are present on Dandatup and Meelup Brook. Dolugup Brook occurs entirely within Meelup Regional Park and discharges at Castle Bay. Since 2000, the mean annual flow for the Dunsborough streams catchment is 2.2GL/yr of a total of 203GL/yr for the waterways of the Geographe catchment.
All of the Dunsborough streams maintain very good water quality in terms of nitrogen and phosphorus. The Dunsborough streams catchment delivers comparatively low nutrient loads to Geographe Bay relative to other sub-catchments. The high phosphorus retention index (PRI) of soils in the catchment combined with good quality riparian vegetation and low stocking rates on agricultural land are likely reasons for the good water quality. Nutrients enter the waterways through diffuse urban and rural residential sources, fertiliser for beef pasture and septics. The highest proportion of total phosphorus is from septics.
The nutrient loads in the Dunsborough Streams are primarily sourced from urban and rural residential land-use, fertiliser for beef pasture and septics.
The Department of Water and Environmental Regulation has been monitoring the water quality of the Dunsborough streams fortnightly since 2006. Data from 2008-2017 is presented in the table below. The data shows total nitrogen and phosphorous concentrations to be consistently below water quality targets.
The Dunsborough streams catchment is categorised as a ‘protection’ catchment as waterways are currently meeting both the nitrogen and phosphorus targets.
Trends in nutrient concentrations
There is a significant decreasing trend in total nitrogen concentration in the Dunsborough Streams catchment from 2011 to 2017 and an increasing trend in total phosphorus for this period.
Since 2009 programs led by GeoCatch and partners have focussed on reducing nitrogen and phosphorus entering the Dunsborough waterways, and erosion control. Programs include working with farmers to reduce fertiliser use, working with businesses to reduce nutrients and pollutants leaving their site and completing revegetation and in-stream works in the riparian zone. These programs are likely to have contributed to continued low nutrient concentrations of these catchment waterways.
Key achievements by GeoCatch between 2009 and 2015 include:
Community volunteer groups such as Dunsborough Coast and Land Care and Meelup Regional Park Committee, in partnership with the City of Busselton, have been responsible for the co-ordination and implementation of a number of stream restoration programs. Key achievements between 2009 and 2015 include:
These actions have assisted with restoration of the riparian zone and increased sediment and nutrient attenuation by reducing flows.
Management programs will continue to focus on maintaining the good water quality of the waterways in the Dunsborough streams catchment under the Revitalising Geographe Waterways program.
Reducing nutrient input from urban sources, promoting best-practice agricultural fertiliser management in the catchment and raising community awareness to recognise the values of the Dunsborough streams are key goals for this ‘protection’ catchment.
Monitoring the water quality of the Dunsborough streams will continue in the Catchment Water Quality Monitoring Program and the Water Quality Improvement Plan will be reviewed and updated. GeoCatch will continue to work with community groups and partners to raise community awareness and promote best practice fertiliser management.
Image 1: Dandatup and Dugalup Brooks flow through the Dunsborough town-site, and have significant riparian restoration works on their lower reaches by local community groups (Photo courtesy Dunsborough Coast and Land Care).
Image 2: Actions to reduce nutrients entering the Dunsborough streams will continue as part of Revitalising Geographe Waterways program.