What is the expert report? What does it say?
The Danish Hydraulics Institute (DHI) has completed a report on West Beach coastal processes modelling: assessment of coastal management options. The report was commissioned by the Department for Environment and Water, the Coast Protection Board, the City of Charles Sturt and West Beach Parks.
At West Beach (the section of coastline running north from the West Beach boat harbor at West Beach Parks to the Torrens Outlet), the loss of sand each year is significant, and the new research undertaken by DHI has shown that it is greater than previously estimated.
The report makes it clear that even if current management activities are maintained, dune erosion will continue around West Beach and Henley Beach South, and progressively move north.
The report sets out three alternative options for managing the beach and dune erosion at West Beach, with their results modelled. All three options involve beach replenishment, and vary by bringing in differing amounts of sand in differing timescales. One of these options also includes extending the West Beach seawall. The summary paper explains the options and their likely results.
A fourth option – do nothing – was considered, but does not help the situation.
The state government is now determining an approach for West Beach that will best meet the community’s needs when environmental, recreational, practical and financial considerations are taken into account.
Who commissioned the report and why?
In 2017, the Department of Environment, Water and Natural Resources (now Department for Environment and Water) commissioned a coastal processes modelling study in order to better understand the coastal processes at West Beach and to examine alternative management options. This was needed because of the ongoing loss of sand each year at West Beach, which is causing significant dune erosion and loss of beaches compared to other metropolitan beaches. The scope also included an assessment of the West Beach boat harbor and modelling options to reduce the wave penetration into the harbor (which damage the pontoons) and also limit the entry of seagrass.
During the course of the study, the scope was amended to expand the analysis of beach profiles along the entire system from Kingston Park to Largs Bay, to enable a better understanding of the influence of management of adjacent beaches on West Beach and vice versa. This expanded analysis also provides insight into the management of the entire Adelaide beach system.
The study was jointly funded by the Department for Environment and Water, the Coast Protection Board, the City of Charles Sturt and West Beach Parks. Following a competitive tender process, DHI was commissioned to undertake the study.
What is causing the problems at West Beach?
Along Adelaide’s metropolitan beaches, sand naturally moves from south to north, with very little sand coming into the beach system from south of Kingston Park. This, combined with human disturbances and development on the coastline means that sand is continuing to be lost from our beaches, particularly from the southern end of the beach system.
The West Beach area has been eroding since the 1960s, and has received many hundreds of thousands of cubic metres of sand to manage the area over the years. When the Adelaide’s Living Beaches strategy was developed in 2005, it was estimated that sand loss from the West Beach area was about 50,000 cubic metres (m3)/year. Most of this is through northward movement, with very little lost offshore.
The new research undertaken by DHI estimates that annual losses are actually two to three times that rate, meaning that even when current replenishment activities are taken into account there is a net annual loss of approximately 60,000 m3.
Why is the estimated sand movement from the new investigation so different from the old studies?
The technology used to model coastal processes is continually improving, and the technology available in the earlier modelling was less sophisticated than the models used in the latest study by DHI.
Are the previous modelling results accurate for other parts of the beach system?
Over the years, surveys undertaken by the state government show that the beach replenishment program has stabilised the southern beaches and increased the size of sand dunes at Seacliff. This is a good indication that the modelling undertaken previously provided good estimates of sand movement along this part of the coast. The build-up of sand north of Henley Beach indicates that the earlier modelling results are at the lower end of the range of results from the current study.
Why hasn't West Beach erosion been fixed already?
Successive governments have been working with local councils since 1973 to actively manage Adelaide’s metropolitan beach system – which runs 28 kilometres from Kingston Park to Outer Harbor.
The West Beach area has been eroding since the 1960s, and has received many hundreds of thousands of cubic metres of sand to manage the area over the years.
A significant variation to managing beaches was introduced in 2005 with the adoption of the Adelaide’s Living Beaches strategy.
The 2005 strategy determined that while we essentially have one long beach with several built structures that interrupt natural sand movement, it could be more effectively managed in discrete sections or 'cells'. These cells were necessary because of the impact the built structures were having on sand movement. Decisions, including sand movement, are made in relation to individual cells, while still providing for the movement of sand between cells as required.
The original proposal in the 2005 strategy was to provide sand pumping infrastructure along the entire metropolitan coast, but this proved to be cost prohibitive at the time. Pumps were installed to allow sand movement within some cells, with trucks used to cart sand elsewhere.
Three things have become apparent since the 2005 strategy was adopted:
The northward movement of sand along the middle part of our coast at West Beach is greater than previously estimated.
There has been a net decline in the volume of sand along the total metropolitan beach system since 2011.
Some cells are affected more than others.
Why are there no management options that include sand retaining structures modelled in the report?
The expert report does not model any management options that use structures to retain sand on the beaches. Options involving the construction of hard engineering structures to re-orientate the West Beach shoreline were considered by DHI and included offshore breakwaters and headland control structures. A range of risks and disadvantages were identified with these options and are discussed on page 22 of the report. The Coast Protection Board, when reviewing the report, requested that a scenario combining sand retention structure(s) and any necessary beach replenishment be modelled. DHI will undertake this task, and a sand retaining structure scenario will be selected for modelling shortly.
Can't we just get more sand?
There is a limited amount of sand in Adelaide’s beach system. Beach management strategies focus on using sand from areas of build-up to replenish eroding beaches. In addition, rising sea levels have an erosive effect on the beach and extra sand should be added to the beaches to offset this effect and maintain beaches and dunes. Sand can be brought in from external sources for beach replenishment – however there are challenges to this. Suitable sand sources need to be identified, and the economic, social and environmental costs associated with trucking, or dredging, the sand need to be considered.
The state government is investigating new sources of sand for beach replenishment as part of the $5.2 million New Life for our Coastal Environment commitment.
What is the government going to do next?
As an immediate measure, the state government is investing $1 million over the next two years, in addition to the existing sand management budget, to replenish the West Beach Parks dunes with sand from the Semaphore South breakwater. This will be done as part of the annual beach replenishment program, starting in mid-October 2018 and is being delivered through the state government’s $5.2 million New Life for our Coastal Environment program.
For the long term, the state government will be looking at the best way to get sand to West Beach from areas where sand is accumulating and also from external sources.
The state government has also allocated $1 million into research and development to find the best ways to manage beach replenishment into the future. This will include investigating new sand sources.
The state government is committed to a long term management approach for West Beach that will best meet the community’s needs when environmental, recreational, practical and financial considerations are taken into account.
Feedback from local government, industry and community stakeholders, together with the best available research will be taken into consideration in making the final decision about the long term management options for West Beach.
Can I read the report?
Yes. View the technical report.
View a summary paper.
Where can I get more information?
More information is available on this website, or you can contact the Coastal Management Branch, Department for Environment and Water via email at DEWCoasts@sa.gov.au.