The Mary River discharges into the Great Sandy Strait and the southern area of the Great Barrier Reef (GBR) Lagoon near Fraser Island. The study area is a reach, near the township of Kenilworth.
This section has been identified as containing endangered Mary River turtle nesting habitat and habitat for the endangered Mary River Cod. In 2014 and 2015 Alluvium worked with a range of stakeholders to develop a restoration plan for the reach. We undertook a detailed multi-temporal spatial analysis to determine historic erosion rates, hydraulic modelling and assessments of riparian and geomorphic condition.
The study area has undergone significant land use pressures since European settlement. Riparian and floodplain vegetation has been predominately cleared and there has been extensive extraction of the alluvial sands and gravels from the channel. The changes have resulted in significant channel widening (approx. 40 -60 m) and channel straightening since the 1950s which has resulted in an estimated 1,900,000 m³ (9 m³ /m/year) of sediment export from this reach. The reach is considered one of the most actively eroding reaches in the GBR catchments.
Alluvium worked with a a range of stakeholders to develop the restoration plan. The plan made costed, prioritized recommendations for the management of riparian, instream and floodplain zones.
Since the development of the plan each of the key stakeholders have implemented significant works in the reach including:
- The implementation of a river bank stabilisation project (250 m total length) to protect Kenilworth town park and the town water supply offtake in 2015 -2019 (total budget $600,000)
- Revegetation and stock exclusion across 3.5 km of river frontage between 2015 -2019 (total budget $275,000)
- Three major river bank stabilisation projects (total length of 1 km) to reduce sediment loads to Great Sandy Strait and the GBR Lagoon completed in 2018 to 2019 (total budget $1,100,000)
- One major river bank stabilisation project (total length 500 m) currently being implemented (total budget $700,000)
- 20 hectares of weed control and dairy effluent management undertaken between 2017-2019
Due to these works there has been a significant improvement in riparian condition within the reach