Jingarmup Brook is the westernmost waterway in the Geographe catchment, located close to Cape Naturaliste. It flows seasonally, and its catchment lays entirely on the Leeuwin-Naturaliste Ridge. A large area of the upper catchment lies within the Leeuwin Naturaliste National Park. The brook provides habitat for the Gilgie, a native freshwater crayfish, the Blue spot goby and Sea mullet. A River Action Plan developed by the Cape to Cape Catchments Group in 2006 outlines the characteristics, values, condition and management issues of Jingarmup Brook.
Native vegetation dominates the western half of the Jingarmup Brook catchment. The eastern half of the catchment is primarily beef grazing with pockets of native vegetation. The northern area of the catchment is predominately urban residential use at Eagle Bay.
Image: Beef grazing and native vegetation are the primary land-uses in the catchment.
Jingarmup Brook is approximately 17.3km long with headwaters on the eastern slopes of the Leeuwin Naturaliste Ridge, discharging into Geographe Bay at Eagle Bay. Since 2000, the mean annual flow for Jingarmup Brook is 2.3GL/yr of a total of 203 GL/yr for the waterways of the Geographe catchment.
The Jingarmup catchment delivers comparatively low nutrient loads to Geographe Bay relative to other sub-catchments.
Phosphorus and nitrogen loads in the Jingarmup Brook are primarily from fertiliser from cattle grazing. A significant proportion of the total phosphorus load is from septics, with smaller contributions from rural lifestyle properties and urban residential areas. Septics, urban residential and rural lifestyle properties (together) contribute approximately a third of the total nitrogen load to Jingarmup Brook.
Nutrient loads in the Jingarmup Brook are primarily sourced from fertiliser from cattle grazing.
The Department of Water and Environmental Regulation has been monitoring the water quality of Jingarmup Brook fortnightly since 2006. Data from 2009-2021 is presented in the table below. The data shows total phosphorus concentrations to be fairly stable at around 0.02mg/L, well below the water quality target of 0.1mg/L. Total nitrogen concentrations are also meeting the water quality target of 1.0mg/L since 2019.
The Jingarmup Brook catchment is categorised as an ‘intervention’ catchment as this waterway is currently meeting the phosphorus target but not the nitrogen target.
Image: Trends in nutrient concentration of Jingarmup Brook
There is a significant decreasing trend in total nitrogen concentration in the Jingarmup Brook catchment from 2011 to 2021.
The Jingarmup catchment delivers comparatively low nutrient loads (both nitrogen and phosphorus) to Geographe Bay and has not been a priority for nutrient reduction actions.
The Meelup Regional Park Management Commiteee have made significant efforts to restore the riparian zone and were responsible for co-ordinating half a hectare of riparian revegetation, rock armouring, fencing and mulching was conducted on lower section of the brook between 2009 and 2013.
Management programs will continue to focus on preventing phosphorus loads rising and reducing nitrogen loads entering the Jingarmup Brook under the Revitalising Geographe Waterways program. Implementation of best practice agricultural fertiliser management, riparian management and reducing nutrient loads from urban sources are key goals for this ‘intervention’ catchment.
Monitoring the water quality of the Jingarmup Brook will continue in the Catchment Water Quality Monitoring Program and the Water Quality Improvement Plan will be reviewed and updated. GeoCatch will work with the community to support sustainable behaviours in urban areas and best management practices in fertiliser management.