Australia and New Zealand are surrounded by the sea with coastal living, seaside views and access to water all playing a big part in our way of life. However, when the ocean or an open body of water intrudes too close to urban environments, seawalls are valuable assets for protecting low lying waterfront infrastructure, addressing safety hazards or overcoming access constraints.
While seawalls are often built in coastal or bayside areas, providing protection against large open waters, they can also be found along riverside or lakeside areas where erosion can have a negative impact on urban environments or restrict the enjoyment of recreational activities.
Typically made from steel, rock, or concrete, seawalls are constructed to suit the landscape and water conditions. Vertical seawalls, for example, are sturdy walls that block waves from ocean-facing coastlines while sloped seawalls, or revetments, are designed to dissipate the energy from smaller waves to lower the risk of erosion.
Left unprotected, natural foreshores can be at risk of flooding and weakened ground conditions, which can put waterfront structures in danger of collapse. This was the case at a Gold Coast waterfront property where canal water washed away fine sandy soil behind a revetment wall, causing the property’s footpath and retaining wall to subside and become unsafe.
The effect of deteriorating seawalls
While seawalls are engineered to withstand marine environments and extreme weather, old or poorly constructed seawalls can be hazardous to people, structures and the surrounding environment. A deteriorating seawall can cause waterfront infrastructure to subside, resulting in cracks that can lead to water ingress behind the seawall. This was seen in Sydney, where a historic sandstone seawall, protecting a waterfront apartment on Sydney Harbour, had started to deteriorate as a result of years of tidal currents and water movement. Without proper remediation, the wall would have continued to degrade until it could no longer support the apartment’s patio or the apartment block itself, which would be at risk of collapsing into the harbour.
Entire strips of tourist-attracting waterfront development may also be affected by old or deteriorating seawall infrastructure. Without suitable protection from waves and tides, or a long-term plan to mitigate the ongoing effects of water movement, structures may become unsafe, uninhabitable, and unviable for tourist operators and other businesses who rely on the location’s access and safety.
An example of this was the ongoing subsidence threatening the structural integrity of the stone walls protecting the banks of Lake Burley Griffin, a large artificial lake in the heart of Canberra that is a popular destination for locals and tourists. Mainmark was engaged by the National Capital Authority (NCA) to repair, strengthen and renew the stone wall and surrounding footpaths as part of a three-year lake wall renewal program. Mainmark’s Teretek resin injection was used to consolidate the soils, fill voids and re-stabilise the wall, as well as re-level the surrounding pathways and adjoining grasslands.
What is the solution?
A properly designed seawall is built to stand the test of time and when newly constructed, should last for many decades. However, due to constant contact with water that may be flowing or contain corrosives such as salt, seawalls should be regularly monitored and maintained for signs of deterioration. If sections of the wall are damaged, its footings have eroded, or the soil behind the wall is weakened, the wall may need to be reconstructed or reinforced.
Using tailored solutions that provide long-term stabilisation is key to revitalising ageing or deteriorating seawalls. This was a lesson that the City of Bunbury learnt when they discovered damage to the seawall protecting the Marlston waterfront entertainment precinct. Prolonged exposure to waves and tidal movements had allowed water to penetrate through the wall and under the foundations. A section of the wall had subsided and a large crack had formed in the face of the wall. There was real concern that the wall may collapse. The City of Bunbury carried out emergency grouting on the worst affected area, but it proved to be very expensive. Mainmark worked with the city’s engineers to develop an innovative and cost-effective solution for the entire wall repair. Mainmark’s Teretek engineered resin proved to be an ideal solution to strengthen the wall by densifying the soil and filling voids where sand had been washed out due to the tidal movement.
As urban development continues to increase, seawalls will remain crucial elements for protecting water frontages. When constructing seawalls, an asset remediation plan should be considered to help address issues that may arise over time, should sections of the wall start to deteriorate due to ground or water conditions.
Mainmark has extensive experience remediating seawalls, including revetments, using a range of proprietary cost-effective solutions that can protect the asset’s longevity and structural integrity without any detrimental effects on the environment.
While seawalls are engineered to withstand the forces of water, to function properly they must be well built and maintained. Using the right materials and reinforcement measures, a structurally sound seawall will allow communities to safely enjoy the waterfront lifestyle for which Australia and New Zealand are famous.
By Steve Piscetek
Steve Piscetek is Mainmark’s Divisional Manager, MCM (Mainmark Civil and Mining). Steve has extensive experience working in construction, road and water infrastructure, the mining and resources sector and offshore construction. At Mainmark, his technical acumen and pragmatic approach to safety and quality assurance has seen him successfully tackle many challenging and complex ground remediation projects.