Healthy Land and Water’s Natural Asset Management and Protection (NAMP) team has been busy completing small and large earthworks projects as part of the Healthy Catchments Program, funded by the Department of Environment and Science (DES).
The aim of the program, which focuses on the engineered repair and vegetation of creek banks and gullies, is to reduce the volume of sediment entering the RAMSAR-listed Moreton Bay from the upper reaches of South East Queensland waterways.
Channel bank erosion is a major source of sediment and previous studies have identified the Upper Warrill, Upper Bremer, and Upper Laidley catchments as contributing high sediment export loads to Moreton Bay. Accordingly, the 2017-2020 program has focused on large in-stream bank stabilisation projects to reduce sediment and improve water quality in these priority areas.
During this time, the NAMP team has successfully stabilised 3.8km of creek and gully banks with earthworks, revegetation, and weed control. This included the repair of four gullies using engineered solutions, such as ‘drowned’ gully heads, controlling water flow through leaky weirs, and the creation of ‘refuge gullies’ with targeted vegetation to increase sediment deposition. Six large instream projects were also completed, including the installation of log jams, rock revetments, hybrid rock walls, and rock rip rap to support vertical banks and realign stream flows to protect vegetation efforts.
The images below were taken from a site located along a 10-meter area of the Bremer River, which over the past 11 years had eroded 4 meters deep. Approximately 14,000 cubic meters of sediment had eroded, leaving the bank with little vegetation and even more susceptible to erosion than before. Engineered log jams were utilised at this site to ensure long term bank stability and erosion control.
To build an engineered log jam, 10-metre logs were placed in a criss-cross stack with their roots facing upstream so the oncoming water cannot penetrate the structure. Piles were driven through gaps in the log stack, and gravel was pushed back over the structure. This structure deflects water, protecting the creek bank from further erosion.
Healthy Land and Water has become a leader in the design, implementation, and oversight of instream earthworks projects. Recent assessments have shown that between 10,000 and 12,000 tonnes of sediment have been prevented from polluting waterways each year as a direct result of the Healthy Catchments Program.
The sediment savings from the repair and stabilisation of actively eroding gullies and stream banks in the priority focal areas has been estimated at 9,072 tonnes annually – with a soil replacement value for this loss of approximately $272,160 (at $30/t).
Keeping this sediment in the landscape prevents it from being mobilised into waterways and endangering the ecosystems of Moreton Bay.
Healthy Land and Water will build on the work delivered in past projects after securing funding from DES for an additional three years of works. The new project will involve work to stop gullies forming or getting worse on steep hillslopes which will help prevent sediment from reaching main channels. The team will also be collaborating with graziers within the priority catchments to address erosion and improve grazing practices to prevent future gullies forming.