Beach renourishment update December 10, 2020...

Work being done to relocate sand from the south of Mount Martha Beach has been stopped as of Thursday 3 December due to public safety concerns.

Public safety is our highest priority and, while there were plans in place to ensure this, the dynamic nature of moving large vehicles along a popular beach requires constant monitoring and assessment.

WorkSafe Victoria’s recommendation was that for operations to safely continue the whole beach was required to be closed. DELWP does not intend to fully close Mount Martha Beach to complete works during summer nor at any other time of year.

Unfortunately plans to make use of the 2,000-3,000m3 sand that had been stockpiled at Balcombe Creek to widen the beach by up to 5 metres (without requiring beach closure) has been washed away following the weekend storm with flood flows from Balcombe Creek, high sea levels and large waves.

In addition to WorkSafe Victoria’s assessment, recent storm damage coupled with adverse weather forecast to continue for most of this week (7 to 11 December), and contractor commitments in the following weeks, has meant that all renourishment works have ceased and will not be able to restart this summer.

What's next...

Water Technology has been engaged to advise further on delivery of future beach renourishment works. The recommendations will focus on offshore dredging and placement on MMNB, to be delivered in 2021.

We will continue to keep the community updated on progress.

Overview

Over the past ten years, Mount Martha North beach has experienced severe coastal erosion. The Department of Environment, Land, Water and Planning (DELWP) has taken a number of short-term actions to limit the impacts of erosion, including beach renourishment and construction of revetments.

Sand loss at Mount Martha North beach is part of ongoing natural processes. Winter weather conditions generally move sand offshore and to the south, and summer weather moves some sand back along the beach to the north. Overall, there is a net loss of sand from Mount Martha North beach towards the Mount Martha South beach.

DELWP’s objectives for managing the beach are to ensure public safety and to protect natural and public assets.

To help determine the best possible engineering solutions to stabilise sand loss from the beach area, a technical study was commissioned in 2018. To ensure that community values regarding Mount Martha North beach are considered in the study, beach users were invited to complete a brief survey in early 2019. The survey results were used to influence criteria weightings in the technical study.

The study has now been completed and the report is available for download on this webpage, with the key findings summarised below.

Finding solutions and taking next steps

In 2018 DELWP commissioned a technical study of beach erosion and cliff stability issues at Mount Martha North Beach (MMNB). The study was carried out by water, coastal and environmental engineering consultants Water Technology, and looked at a range of engineering options to best manage the issues. The study also incorporated the findings of a survey that was carried out in late 2018–early 2019, which captured community values of the area.

This process highlighted that some community members believe that construction of hard structures, particularly groynes, is the right solution for MMNB.However, the Water Technology investigation found that such engineering solutions are not suitable to MMNB because they would adversely impact other sites along the adjacent coast, and would not be effective in keeping sand on the beach in the long-term.

The Water Technology study, released in July 2019, recommended that the best way to control cliff erosion would be to formalise the temporary emergency rock revetment behind the bathing boxes at MMNB. It also indicated that beach renourishment is the most technically and cost-effective way to provide an accessible beach through winter when the beach usually narrows.

Based on the evidence that no engineering treatment would return sand long-term to Mount Martha North Beach without adverse impacts, DELWP decided not to pursue hard structure options such as seawalls and groynes for the beach.

Please refer to the timeline and document library on this page for further details.

In August 2019, DELWP held a forum to provide this information to the community and answer questions on the modelling and analysis. The forum was attended by over 180 people, many with a strong interest in preservation of MMNB.

Funding secured and works begin

In February 2020, the Victorian Government signed a funding agreement with the Commonwealth Government for a commitment of $1.5 million for MMNB. This agreement will support beach renourishment to protect the adjacent shoreline and associated vegetation by increasing the beach width.

Water Technology has been engaged to provide advice on future beach renourishment works, focusing on two methods:

  • Sand relocation, trucking sand from Mount Martha South Beach to Mount Martha North Beach,
  • Offshore dredging and placement on Mount Martha North Beach.

In May 2020, a stakeholder group was established, and an inaugural meeting was held in early June.

In the meeting, it was agreed DELWP would resume regular stakeholder updates and finalise the Terms of Reference for the group.

The first beach renourishment under the Commonwealth Government agreement was started in November 2020.This sand relocation may last up to 5 years, after which either dredging or sand relocation will occur to replenish the beach.

Monitoring cliff instability

A land slip on the cliff behind the bathing boxes, reduced beach width, and damage to bathing boxes have led to public safety risks and reduced beach amenity at MMNB. Several short-term actions have been carried out in the past to limit the impacts of erosion, including beach renourishment and construction of a temporary rock revetment behind the bathing boxes.

Since the early 2000s a range of geotechnical investigations have been carried out to assess the instability of the cliffs behind the bathing boxes along MMNB.

In March 2019, three ground movement monitoring bore holes were installed in the cliff behind the bathing boxes.This survey indicated that, while ground movement continues, the rate of movement has not increased. Monitoring is now carried out every six months.

However, due to the nature of our coastline, unpredictable and unforecastable natural hazards, such as landslides and rock falls, may occur along this foreshore. So beach and bathing box users should always remain vigilant.

Additional geotechnical assessments and a risk assessment are currently being carried out, with the report expected before Christmas 2020.

Project context

Moutn Martha North beach looking south on a calm day. Includes view of beachboxes backing onto cliffs, with water at base. Some sand reamins on the beach.

Mount Martha North beach

Mount Martha North beach is located on the eastern side of Port Phillip Bay and runs approximately 600 metres from the mouth of Balcombe Creek at the southern end, to a headland separating it from Hawker Beach, to the north.

Please refer to the map in the Document Library section on the right hand side of the screen for more details.

Recognising that the coastal process of sand movement will always occur, the primary objectives for DELWP are to maintain public safety for the Mount Martha North beach and protect public infrastructure and natural assets.

Multi-criteria analysis

As touched on above, DELWP engaged Water Technology, a specialist water, coastal and environmental consultancy, to carry out a multi-criteria analysis of four engineering options that were recommended in a 2017 coastal processes study, aimed at slowing sand loss from the beach.

The full coastal processes study may be viewed in the Document Library section on the right hand side of the screen.

The following criteria were applied in assessing each engineering option:

  • environmental (impacts and benefits)
  • financial (life-cycle cost)
  • social
  • technical
  • upfront (construction) cost.

The multi-criteria analysis scored and ranked each option and selected two of the highest ranked options to model in detail. The modelling developed and tested options to determine what scale, design and positioning would be required for preferred engineering works to stabilise Mount Martha North beach.