Coastal Sand Dune Degradation and Rehabilitation

James Ruediger

Coastal Sand Dunes, Little Dip National Park, South Australia

Why are Coastal Dunes so important?

• Dunes are critical to the health of a beach system.

• Storage of sand to replace beach sand lost during storm events

• Essential havens for wildlife and plant species.

Healthy dune vegetation, South Port beach.

Case Study: Adelaide’s beach and dune system.

• Every coastal system is different.

• Adelaide has a rather unique system with strong coastal currents and very limited input of material.

• Large levels of development on coast has affected dune systems significantly

Courtesy of SA Dept. of Planning

Case Study Site: South Port Beach• One of the best

examples of a healthy beach system in Adelaide.

• Mouth of Onkaparinga River

• Extensive upkeep by volunteers and environment groups

• Restricted from development to preserve environment. South Port beach showing dunes and river

Case Study Site: Hallett Cove• Unusual beach system, all

material for small dune system is from erosion of cliffs above.

• Beach system heavily influenced by development, first shacks, then housing, then Conservation park reserve.

• Site of recent rehabilitation work by National Parks and community groups Hallett Cove Beach

Case Study Site: Glenelg North Beach

• One of the most developed beach areas on the Adelaide coastline.

• Dunes levelled and sealed with housing and roads

• Main river, The Patawalonga, heavily flow controlled.

• Beach non existent at high tide, and storms often wash onto roadways.

• Riprap walls installed to protect housing cause even greater scouring of beaches by waves.

Aerial view of Glenelg North beach, courtesy City of Holdfast Bay.

So what's so special about Adelaide's Dune system?

• Adelaide, being built on a gulf, experiences strong South-North coastal currents

• Very limited material input into system, Three main rivers, Onkaparinga, Sturt/Patawalonga, Torrens, All dammed.

• Sand migration in current scours southern beaches and deposits on northern beaches

• High level of urban development onto dune fields and beach fronts.

And the result of this?• Most of Adelaide's beaches

are severely degraded.• Many beaches vanish

completely at high tide.• Loss of breeding sites for

fauna and important flora.• Storm events can cause

waves to overtop coastal embankments and damage houses and roads.

• Costs to society- Sand cartage, Dredging, replenishment, Aesthetics, Infrastructure repairs.

Henley Beach, 1953 showing storm damage. Courtesy of DENR

Rehabilitation?

• Whilst it is impossible to easily restore a lot of Adelaide's dune systems, short of demolishing very expensive houses, it is possible to restore and maintain those areas that remain.

• Several key areas, as part of the parks and reserves system, such as Aldinga Beach, South Port, Hallett Cove and Tennyson are being managed and rehabilitated.

Where to start?• DENR recently undertook

works at Hallett cove to protect the remnant dune system.

• Boardwalks to limit erosion.• Fencing to exclude people

from sensitive areas• Revegetation• Sand matting to limit

erosion.• Community Education• Weed species removal• Only the beginning- much

more work still needed.

Fencing, Reveg area and boardwalks at Hallett Cove

Hallett Cove- Lots to be done…

New vegetation growing through sand matting Sand grass slowly rehabilitating dune/beach interface

Getting There….• South Port beach is an

example of a much better maintained ecosystem.

• Strong vegetation communities

• Active community groups and council support for the area.

• Sustainable balance of conservation and public utilisation.

Healthy dune-beach interface, South Port Beach

Dunes. Using them the RIGHT way.

Boardwalks keep foot traffic off dunes, limiting erosion and vegetation destruction

Area of erosion controlled with fencing and replanting

Storm damage repaired with compostable seagrass sand bags

Conclusions

• No “quick fix” - much of the damage has already been done and is essentially irreversible

• Critical to maintain and rehabilitate the areas we have left.

• No “One solution fits all” - coasts in Adelaide differ to coasts in other capital cities and require different management methods.

References

• Department of Environment and Natural resources: Coastal Management Branch

• Coast care SA• City of Holdfast Bay• Adelaide and Mount Lofty Natural Resource

Management Board.• All photographs by author unless otherwise

noted.