The existing town of Gracetown is built on 27ha of steeply
sloping ground rising from the south-eastern shore of the
north-facing Cowaramup Bay in Western Australia. The lowest part of
the town is set back from the beach approximately 100m from the
shoreline and is approximately 10m above sea level.
The existing town extends approximately 0.5 km up the slope to
an elevation of approximately 90m Australian Height Datum. The
underlying geology is characterised by shallow weathered
limestone-based sands and limestone overlying a granite bedrock (at
depths of approximately 20-30m below ground level).
Extensive areas of high integrity coastal heath vegetation,
mostly in national park or unallocated crown land, surround
Gracetown. There is a known spring/soak north of the town
discharging to a small stream that flows into Cowaramup Bay.
Gracetown currently consists of around 150 houses of which about
one third are home to permanent residents and the remainder mainly
used as holiday accommodation.
There is currently no sewerage system or reticulated town water
supply in Gracetown. Individual houses rely on roof runoff
collected in rainwater tanks for all their water needs. There is a
town bore for fire fighting and a small number of domestic bores in
the lowest part of the town, although the groundwater is of limited
availability and variable quality. Wastewater is treated by
septic tanks at each house. Recent investigations suggest that
septic tank effluent has contaminated the shallow groundwater, with
elevated nitrogen concentrations posing a potential environmental
threat to the near shore coastal environment.
The proposed development will consist of approximately 140
residential lots on the slope above and to the south of the
existing town with small short-stay development consisting of
approximately 50 units, possibly in the area to the west of the
existing town.
A key aim for this project is to develop Gracetown as a
demonstration of sustainable settlement that can be used for other
land development projects in regional Western Australia.
GHD was engaged to develop water and energy concepts for the
proposed new development at Gracetown, with consideration for
supplying services to the existing town of 152 residences and small
commercial area. The proposed concept design was required to
consider the area’s environmental significance, spatial constraints
and water resource limitations, and to address the following
water-related sustainability objectives:
- Provide a self-sufficient water supply
- Improve water use efficiency
- Decrease nutrient discharge to the environment
- To meet the project objectives the following tasks were
undertaken:
Identification and assessment of the potential alternative water
resources
- Conceptual development and evaluation of options for an
integrated water supply system taking into consideration
opportunities for water saving, recycling and other
non-conventional sources
- Examination of institutional and governance issues that might
affect the implementation of integrated water management in
Gracetown
- Identification of potential service providers with the capacity
to effectively manage water and wastewater services in
Gracetown
- Assessment of the implications of the solution in terms of
capital and operational costs, health and environmental management,
maintenance requirements and funding
The options for both drinking and non-drinking water supply were
assessed with respect to local water balances, environmental
impacts, public health risk, level of assessment/approvals required
and likelihood of public support. The following options for water
supply were investigated:
- Reticulated water
- Roof run-off for drinking and non-drinking uses
- Desalinated seawater (from wind/wave powered)
- Treated wastewater (centralised treatment)
- Treated wastewater (on-site treatment)
- Domestic greywater recycling for reuse
- Stormwater (from urban run-off)
- Shallow groundwater (from bores)
Many or these options were ruled out during the concept
development as they did not meet the sustainable outcomes required
for the project or became cost prohibitive or due to specific
technical limitations.
- The final concept which gained community,
agency and client support was to supply drinking water for each
home from lot scale tanks which would harvest roof runoff from
individual properties. This runoff would then be directed into a
large storage, modelled to be no less then 45,000 litres when
connected to a 230sq m roof area. It is expected, given typical
occupancy, that this would provide 99 percent reliability of use
proposed.
The non-drinking water supply and recycled water treatment plant
(RWTP), recycles all wastewater from the existing and future
residences and treats it using the latest technology. Domestic
wastewater will be recycled for domestic reuse in toilets, cold
water inlet in washing machines and irrigation along with
subsurface irrigation of public open spaces. The distribution
network also enables a reticulated fire-fighting supply to be
available to the entire town. The supply is intended to be
backed up from groundwater which would be recharged though the use
of water sensitive urban design and excess recycled water.
This project demonstrated:
- The application of integrated water management at a development
scale
- The ability to integrate residential scale water savings
measures with community scale water savings measures
- The opportunity available to harness renewable energy for
coastal developments
- Through participative community involvement pioneer projects
can move forward in environmentally sensitive areas
GHD continues to be involved with this project as it moves
through the preliminary design phase.
