Sydney’s Lane Cove Valley is projected to be impacted by sea level rise later this century. The risk to vegetation communities and key infrastructure is significant, particularly for mangrove and saltmarsh ecosystems along with riverside infrastructure. This report looks at opportunities for sea level rise mitigation and adaptation in the Lane Cove area.
Due to climate change, high tide sea levels are predicted to rise between 44 and 74 centimetres by the year 2100 affecting many regions in the world including the Lane Cove Valley in Sydney, Australia (Coastal Risk Australia, 2020). The Lane Cove Valley is an area with unique vegetation communities and important infrastructure which will be impacted by this sea level rise. To avoid stranded assets and the loss of vegetation communities, it is necessary to implement strategies to mitigate these impacts.
Estuarine and coastal flats communities are the most at risk vegetation communities in the Lane Cove Valley and are likely to be severely impacted by rises in sea level. Estuarine Swamp Oak Forest and Estuarine Reedland are currently at risk due to non-climate related factors such as stormwater pollution and are listed as endangered communities by the Threatened Species Conservation Act 1995 (OEH, 2016). These communities, along with Estuarine Mangrove Forest and Coastal Flats Tall Moist Forest, are particularly vulnerable to sea level rise as they are typically found in low-lying swamps, mudflats and coastal flats (OEH, 2016).
Also of concern is increasing levels of salinity which can alter the composition of existing ecosystems (Oppenheimer et al., 2019). As common reeds in Estuarine Reedland are a vigorous species, they may be able to adapt to sea level rise by migrating into adjacent forest and this can be encouraged by planting into this area (OEH, 2016). In the case of Estuarine Swamp Oak Forest, it may be difficult for the community to migrate. The narrow community located at Little Blue Gum Creek may be lost due to steep terrain and urban development with similar issues along Blue Gum Creek and Mowbray Park while competition with the more prevalent Estuarine Mangrove Forest is a further pressure. One strategy is to reduce weeds along Wirong Flat and expand the Estuarine Swamp Oak Forest into this area by planting natives in place of exotics.
Although the Estuarine Mangrove Forest is common in some parts of the Lane Cove River, this community is predicted to be inundated by 2100. Mangrove forests have previously adapted to disturbances by establishing in new locations and this could occur along the Lane Cover River, however, they may not adapt fast enough for the community to completely re-establish (DECCW, 2010).
Two possible locations where Estuarine Mangrove Forest could re-establish include in place of the parking and picnic area adjacent to the Rotary Athletics Field or along the strip of riverside land north of Swaines Creek. Coastal Flats Tall Moist Forest is the other vegetation community at risk, as this low-lying community does not have sufficient space to move from its current location around Schwartz Point or near the Lane Cove Boatshed. This community will diminish in size although it could expand into the area towards the weir, at the expense of the picnic area and playground. Replacing exotic shrubs, grasses and herbs with natives would improve what remains of this vegetation community, however, as a community dominated by tall trees, it would take time for trees to re-establish (OEH, 2016).
Strategies to mitigate against the impact of sea level rise on infrastructure involve reinforcing structures, building barriers or seawalls, floating infrastructure, raising or relocating critical infrastructure or simply abandoning assets (Tam, 2009). In the Lane Cove Valley, infrastructure including bridges, roads, trails, boardwalks, picnic spots and historic sites are of most concern.
To guard against sea level rise, walking trails and bicycle paths that line the riverbank can be replaced by elevated boardwalks while existing boardwalks can be raised. Smaller bridges like those crossing Little Blue Gum Creek will be inundated and require raising to maintain access to Max Allen Road and Naamaroo Drive. These two roads along with Fullers Park Road and River Avenue would need to be protected by using barriers such as bulkheads.
While the Lane Cove Weir is currently used as a crossing point over the river, a new footbridge could be built and the weir left abandoned. Sewer pipes located at Chatswood Golf Course and Blue Gum Creek would need to be elevated or relocated to mitigate the risk of untreated sewerage entering the Lane Cove River while increased salinity will corrode pipe infrastructure (Wright, 2013). With vegetation communities along the Lane Cover River at risk, riverside picnic spots could be set aside to allow native vegetation to migrate and re-establish in these locations while new picnic spots could be built at higher elevations or existing facilities expanded.
While implementing strategies to relocate or protect infrastructure from sea level rise will be costly, the impact on estuarine vegetation communities will also be significant. If these communities can’t rapidly adapt to the effects of climate change, there is a risk the most vulnerable communities will be lost from the Lane Cove Valley.