The Abba River is located in the central Geographe catchment. The river discharges into the Vasse-Wonnerup Wetland system, a significant habitat for waterbirds. The name ‘Abba River’ was first recorded by Fredrick Ludlow in 1834 and is of Aboriginal origin.
Surveys of the Abba River by Wetland Research Management in 2006 found a diversity of native fish including the Western Minnow, Nightfish and Western Pygmy Perch. The long-necked turtle is known to occur in the Vasse-Wonnerup Wetlands system and may occur in the lower reaches of the Abba River. A River Action Plan developed by GeoCatch in 2002 outlines the characteristics, values, condition and management issues of the Abba River System.
The upper catchment (headwaters of the Abba River) occur within the Millbrook State Forest. Land-use is predominately beef and dairy grazing with scattered vineyards and horticulture farms in the central catchment where the river flows across the Swan Coastal Plain. The lower reaches of the river flow through the Ludlow Tuart Forest before entering the Vasse-Wonnerup Wetland System.
Image: Beef and dairy grazing are the primary land-uses in the central catchment.
The headwaters of the Abba River are in the Millbrook State Forest on the Whicher Range. As the River leaves the state forest it flows in a north-westerly direction across the Swan Coastal Plain eventually discharging at the Vasse Estuary next to Malbup Creek. The River is approximately 24km long and flows seasonally. Since 2000, the mean annual flow for the Abba River is 14GL/yr of a total of 203GL/yr for the waterways of the Geographe catchment.
The Abba River has better water quality than the neighbouring Ludlow and Sabina rivers. This is likely due to fewer dairies and heavier soils that are found throughout the catchment (with a higher phosphorus retention index) combined with a larger flow.
The nutrient loads in the Abba River are driven by intensive land-uses, with a high proportion agricultural grazing in the catchment. The largest contributors to nutrient loads are beef and dairy grazing (fertiliser). Point sources (from dairy shed effluent) are is also a major contributor.
Image: Point-source dairy effluent and fertiliser used for dairy and beef grazing delivers a large nutrient load to waterways in the Abba catchment.
The Department of Water and Environmental Regulation has been monitoring the water quality of the Abba River fortnightly since 2006. Data from 2008-2016 is presented in the table below (as data from 2008 represents data from 2006-2008). 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 Abba River catchment is categorised as a ‘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 Abba River
No statistically significant trend in nutrient concentration was observed in the data.
Since 2009 programs led by GeoCatch and partners have focussed on reducing nitrogen and phosphorus entering the waterway. These programs included working with farmers to reduce fertiliser use, managing dairy effluent and undertaking fencing and re-vegetation in the riparian zone. Key achievements between 2009 and 2015 include:
For the next three years management programs will continue to focus on reducing nutrients entering the Abba River under the Revitalising Geographe Waterways program. Implementation of best practice agricultural fertiliser management and dairy e effluent management and targeted riparian management are key goals for this ‘interven on’ catchment.
GeoCatch will work with at least two landholders to undertake fencing and re–vegetation on in the riparian zone. Monitoring the water quality of the Abba River 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 e ffluent management.
Image: Actions to reduce nutrients entering the Abba River will continue as part of Revitalising Geographe Waterways program.