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Best Practice Guideline 3 - Seawalls
Introduction
“Seawalls are commonly used as foreshore protection structures in estuaries, with objectives such as armoring the shore against erosion and preventing inundation of low lying areas. In the past, little consideration was given to the intertidal habitats that were destroyed or fragmented through the creation of seawalls, nor to how seawalls could be designed to more closely mimic natural shores. As a result, large sections of natural shorelines have been replaced with seawall-lined shorelines with a number of negative consequences.” DECCW
The aim of this guideline is to avoid the construction of vertical seawalls that have little to no habitat value, and to encourage the modification of existing vertical seawalls which improve the habitat value for foreshore vegetation and fauna.
What you need to consider
- First assess if a seawall is actually the best solution for an eroding bank. Instead, start by investigation ‘soft’ stabilization solutions such as replanting native estuarine vegetation (e.g. mangroves, saltmarsh) and using temporary structures where necessary to allow the vegetation to properly establish
- A combination of site suitable approaches will likely be required for the design of environmentally friendly seawalls. Seek professional advice from governmental agencies (such as HNCMA and DECC) to devise suitable options including options that don’t involve seawall construction. Refer to the detailed guidelines listed in the further information section below “How to make your seawall more environmentally friendly”
- Approval from Pittwater Council and government agencies will be required to build or upgrade a seawall. Consult Pittwater council first.
- Follow the following principles when designing an upgrade or new seawall:
* Maximise the use of native foreshore vegetation including:
- Saltmarshes within benches in the seawall
- Planting native vegetation behind the seawall and in gaps between the rocks
- Establishing mangroves in front of the seawall to reduce erosion
* Maximise the diversity and complexity of the seawall structure
- Create the walls of weathered boulders of varying shapes and sizes
- Include pools and crevice areas to retain water at low tide
- Include blocks that protrude outwards to mimic natural rock pools
* Create low-sloping seawalls or include change in slope to provide for different habitats to colonise the different regions along the slope as in nature. Ways to do this include:
- Building bolder seawalls with a gentle slope
- Using benches or steps to break up and vary the slope
- Never build vertical seawalls
To access the full details of the Best Practice Guidelines click here
Further Information
- How to make your Seawall more environmentally friendly - Sydney CMA
- Environmentally Friendly Seawalls – A guide to improving the environmental value of seawalls and seawall-lined foreshores in estuaries - Sydney CMA
- Building Seawalls to sustain intertidal biodiversity in altered urbanized estuaries – University of Sydney
- Native plant species list and vegetation map
