The Annie Brook catchment is located in the west of the Geographe catchment and contains three streams: Station Gully, Annie Brook and Mary Brook. The three streams converge and discharge directly into Geographe Bay via Station Gully Drain.
The catchment supports a diversity of vegetation (including poorly represented vegetation complexes) primarily located in the Yelverton National Park and nature reserves. The endangered Dunsborough burrowing crayfish is known to occur in the waterways of the catchment. Recent surveys in October 2017 by the Department of Water and Environmental Regulation found a variety of invertebrates and fish including the Gilgie, Marron, Nightfish, Western minnow the Western pygmy perch.
The upper catchment has a diversity of land-uses including beef grazing, one dairy, viticulture, horses and the Yelverton National Park and State Forest (native vegetation). The land use in the mid to lower catchment is dominated by beef grazing with pockets of horticulture, viticulture, rural residential and timber plantations. There is a strip of urban residential land-use where the streams meet Geographe Bay.
Image: Beef grazing is the primary land-use in the catchment.
The tributaries of Station Gully, Annie Brook and Mary Brook have their headwaters in the Whicher scarp and the Leeuwin-Naturaliste Ridge, and are artificially straightened on the Swan Coastal Plain where they converge into Station Gully drain that discharges to Geographe Bay. Since 2000, the mean annual flow for the waterways of the Annie Brook catchment is 20GL/yr of a total of 203GL/yr for the waterways of the Geographe catchment.
Image: Three tributaries converging to a single drain (Station Gully Drain)
The majority of nutrients delivered to Annie Brook and its tributaries are derived from agricultural land uses.
Fertiliser from beef grazing contributes to the vast majority of the overall nutrient load. Other key sources
include the Waste Water Treatment Plant, rural living, dairy grazing and horticulture.
Nutrients delivered to Annie Brook and its tributaries are mostly derived from beef grazing
The Department of Water and Environmental Regulation has been monitoring the water quality of the Annie Brook catchment fortnightly since 2006. The sampling location is just north of where the tributaries of Station Gully, Annie Brook and Mary Brook meet. Data from 2008-2021 is presented in the table below. The data shows total nitrogen concentrations to be consistently above water quality targets. Total phosphorus concentrations have remained below the water quality target of 0.1mg/L.
The Annie Brook catchment is categorised as an ‘intervention’ catchment as waterways meet the phosphorus target but not the nitrogen target established in the Water Quality Improvement Plan.
Image: Trends in nutrient concentrations of the Annie Brook catchment
There is a significant decreasing trend in total nitrogen concentration in the Annie Brook catchment from 2011 to 2021.
Since 2009 programs led by GeoCatch and partners have focussed on reducing nitrogen and phosphorus entering the waterways. These programs included working with farmers to reduce fertiliser use, managing dairy effluent and completing fencing and re-vegetation in the riparian zone. Key achievements between 2009 and 2015 include:
Ten landholders carried out soil testing and nutrient mapping to inform fertiliser decisions, assisting farmers to use only the phosphorus needed for the pasture growth required.
One dairy effluent management plan was developed to support the re-use of dairy effluent, reducing nutrients entering the catchment waterways.
Two landholders completed 5.7 km of riparian fencing and 1.5 ha of riparian re-vegetation with the aim to restore and protect riparian vegetation, prevent stock access, increase the absorption of nutrients and to reduce sedimentation and pollution.
Management programs will continue to focus on reducing nutrients entering the Annie Brook catchment waterways under the Revitalising Geographe Waterways program. Implementation of best practice agricultural fertiliser management and dairy effluent management and targeted riparian management are key goals for this ‘intervention’ catchment.
A river health assessment is being conducted to measure and report on the ecological health of Annie Brook , Station Gully and Mary Brook.
GeoCatch will work with at least four landholders to undertake fencing and re-vegetation in the riparian zone. Monitoring the water quality of the Annie Brook catchment waterways 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 the community to support sustainable behaviours and best management practices in fertiliser and effluent management.
Image: Actions to reduce nutrients entering the Annie Brook catchment will continue as part of Revitalising Geographe Waterways program.