Stabilisation works protect Swan RiverThe City of Belmont in Western Australia is employing unique stabilisation methods while undertaking erosion protection works along the Swan River foreshore.
The four-month project, which began in January 2013, is being carried out along 124 metres of the Swan River foreshore adjacent to the Ascot Racecourse. The Swan River Trust identified the area as ‘Priority 1’ for riverbank and shoreline works in the
‘Swan and Canning Rivers Foreshore Assessment and Management Strategy’.
The works are being implemented with the assistance of funding through the Swan River Trust’s Riverbank Program and a Department of Environment and Conservation Environmental Community Grant.
The project required a unique approach, given the proximity of the racecourse, the narrow width of the reserve (3.5 metres in some areas) and access limitations, as well as the issue of timing in relation to optimal tides and the racing season.
The works involved:
- excavation and removal of previous fill material, failed vegetated geogrid and shotcrete
- installation of a rock revetment approximately four metres wide, underlain by geotextile and geogrid;
- installation of a rock scour toe extending to toe stones, located approximately eight metres from the path edge, with variation at the drainage outlets
- extension of three existing drainage outlet pipes from the Matheson Road stormwater catchment and installation of tidal flaps
- additional protection at drainage outlet locations and
- replacement of the footpath guardrail.
Additional works will also be undertaken at Gould Reserve, including the installation of natural logs and planting of native sedges. Wherever possible, locally sourced materials have been used in the construction of the revetment.
The proposed stabilisation methods were developed by coastal engineers in consultation with the City of Belmont and and the Swan River Trust and were selected following a geomorphic assessment that determined the causes of the erosion and the best solution for its mitigation.
Past dredging of the river contributed to the erosion, increasing the pressure on the banks and modifying the river processes, such as the accumulation of sediment at the Bayswater Main Drain delta, which is located on the opposite side of the river. The site is also subject to overbank runoff from the path, drift from the racecourse irrigation and suspected groundwater flow from the racecourse lakes.
Prior to works commencing, consultation was undertaken with Aboriginal groups due to the proximity of the site to the Swan River — a registered Aboriginal Heritage Site. Consultation was also undertaken with other stakeholders, including the WA Horse Trainers Association, Perth Racing and Belmont Bicycle Users Group.
The project represents a successful partnership between the City of Belmont and the Swan River Trust and is one of several foreshore stabilisation projects currently under development within the Rivervale and Ascot areas.