The Gynudup Brook catchment is located in the east Geographe catchment and consists of two major tributaries, Tren Creek and Gynudup Brook. With the exception of state forest in the upper catchment most of the catchment is cleared for agricultural use. A survey in 2009 by the Department of Water and Environmental Regulation found Freshwater shrimp, the Western minnow, Blue spot goby, Nightfish, Gilgie (a freshwater crayfish) and the Long neck turtle.
Gynudup Brook is of cultural heritage significance and three registered sites of significance are found in the catchment. The name Gynudup Brook means ‘good campground near water’, emphasising the importance of this waterway to Aboriginal people. A River Action Plan developed by GeoCatch in 2004 outlines the values, condition and management priorities of Gynudup Brook and Tren Creek.
Land-use in the catchment is primarily comprised of beef and dairy grazing. Six dairies occur in the catchment. The catchment also supports mineral sands mining, timber plantations, horticulture, viticulture and rural residential lots. Native vegetation is sparse with the exception of the upper catchment where the headwaters of Gynudup Brook occur in State Forest 27.
Image: Beef and dairy grazing are the primary land-uses in the catchment.
The Gynudup Brook catchment consists of two major tributaries, Tren Creek and Gynudup Brook. The headwaters of Gynudup Brook are in State Forest 27 then flow in a north-westerly direction across agricultural land before bending to the south-west to connect with the Capel River west of Bussell highway. The headwaters of Tren Creek are in low lying farmland and the creek flows in a north-westerly direction before connecting with the Gynudup Brook. Since 2000, the mean annual flow for Gynudup Brook is 14GLyr of a total of 203GL/yr for the waterways of the Geographe catchment.
The hydrology of the catchment has been extensively modified as a result of the long history of agriculture in the area. The catchment contains many artificial drains to alleviate water logging in winter months. The Elgin Main Drain, constructed in 1958, diverts all flow from Gynudup Brook upstream of Elgin road. The drain flows in a south-westerly direction and enters Tren Creek, which then connects to Gynudup Brook further downstream.
The majority of the nutrients delivered to Gynudup Brook are derived from agricultural land uses. Nutrient loads are primarily from fertiliser from beef and dairy grazing, with smaller contributions from dairy sheds.
Image: The majority of nutrients delivered to Gynudup Brook are derived from agricultural land uses
The Department of Water and Environmental Regulation has been monitoring the water quality of Gynudup Brook and Tren Creek fortnightly since 2006. Data from Gynudup Brook from 2008-2021 is presented in the table below. The data shows total nitrogen concentrations to be consistently above water quality targets. Overall phosphorus concentrations are exceeding water quality targets however concentrations have fluctuated above and below the water quality target of 0.1mg/L.
The combination of poor soils which do not retain nutrients, and a large proportion of agricultural land use is the likely cause for poor water quality in the catchment.
There is a significant decreasing trend in total nitrogen concentration in the Gynudup Brook catchment from 2011 to 2021.
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:
Twenty landholders completed soil testing and nutrient mapping to inform fertiliser decisions, assisting farmers to use only the phosphorous needed for the pasture growth required.
Two dairy effluent management plans were developed to support the re-use of dairy effluent, reducing nutrients entering the waterways.
Twenty-three landholders carried out 27km of riparian fencing and 8.45ha of revegetation with the aim to restore and protect native 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 Gynudup Brook catchment waterways under the Revitalising Geographe Waterways program. Implementation of best practice agricultural fertiliser management and dairy effluent management are key goals for this ‘recovery’ catchment.
Effluent upgrades are proposed with the aim to reduce the dairy industry nutrient footprint in the catchment. Upgrades at a dairy farm in Boyanup and one at Gynudup Brook are already being developed. Soil testing, whole farm nutrient mapping, agronomic advice and workshops will be carried out in the catchment by the implementation of best practise fertiliser management programs through the Fertiliser Management project.
A significant amount of riparian management has been completed in the catchment. This work will be continued with re-vegetation and fencing proposed for at least one property in the catchment with new approaches to riparian management being investigated.
Monitoring the water quality of Gynudup Brook and Tren Creek will continue in the Catchment Water Quality Monitoring Program and the Water Quality Improvement Plan will be reviewed and updated.
Image: Actions to reduce nutrients entering the Gynudup Brook and Tren Creek will continue as part of Revitalising Geographe Waterways program.