local water management strategy rev b march 2016...a local water management strategy will detailed...
TRANSCRIPT
Cover Page
Local Water Management StrategyRev B March 2016
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ContentsBackground 4 Witchcliffe Village Strategy 5 Scheme Amendment 6 Proposed Development 8 Design Criteria 8 Framework 8 Water Conservation 9 Water Quantity Management 9 Water Quality Management 10 Predevelopment Environment 10 Landuse 10 Topography 10 Soil Geology 10 Environmental Conditions 13 Hydrology 13 Groundwater 13 Climate 16 Water sustainability initiatives 16 Water Supply 17 Water Consumption and Climate Change 19 Wastewater 20 Overview 20 Composting Toilets 21 Wastewater Collection and Primary Treatment 21 Secondary Treatment 22 Storage and Reuse 22 Scheme Ownership and Management 24 Contingency Planning 24 Stormwater Management Strategy 25 Overview 25 Table 4 Annual Stormwater Runoff Summary 27 Water Quality 28 Predevelopment and Post Development Runoff 29 Stormwater From Lots 29 Water Quality Monitoring 30 Detention of Peak Flows 31 Major Events 32 Streamline rehabilitation 33 Models and Assumptions 34 Construction Staging Issues 34 Further Investigations 35 Water Supply 35 Wastewater 35 Stormwater 35 Soils 35 Monitoring Program 35 Water Consumption 35 Wastewater 35 Stormwater 36 Appendix A - Stormwater Delivery Approach for WA, WA Stormwater Management Objectives 37 Appendix B - Local Water Management Strategy Plan 39
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Appendix C - Witchcliffe Ecovillage Urban Water Cycle 40 Appendix D - Water and Wastewater Calculations 41 Appendix E - Stormwater Cluster Summary 42 Appendix F - Witchcliffe Ecovillage Concept Plan 43 Appendix G - Typical Wastewater Catchment Concept Plan 44 Appendix H - Stormwater Catchment Diagram 45 Appendix I - Tank Sizing Chart 46
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Background The Witchcliffe Ecovillage is a 300 lot ecovillage planned for development in the town of Witchcliffe, 10kms south of Margaret River, in south-west Western Australia.
The Witchcliffe Ecovillage vision is to create a model of a highly sustainable, self reliant community in a regional village setting, with the best of 21st century technology that enables the community to produce as much energy as it consumes; be self-sufficient in water; care for the local environment; generate ongoing economic and social opportunities for the area, and be self-sufficient in fresh food produce. A place in which people live, work, socialise and provide for their material needs sustainably, where most of what they consume on a daily basis will be produced within the ecovillage, in harmony with the permaculture principles of “earth care, people care, and fair share.
The Witchcliffe Ecovillage is designed with an extensive range of onsite infrastructure and services to create an example of sustainable development that achieves:
• 100% net renewable power generation on site.
• 100% self -sufficiency in water through onsite rainwater harvesting (rooftops and dams).
• Self-sufficiency in seasonal fresh foods with surplus produce sold locally.
• A local micro energy grid that utilises smart grid technology.
• Class A recycled water.
• Highly efficient solar passive homes that all front public open space and/or community gardens.
• Employment and education opportunities on site and within the revitalised town centre.
• Revegetation and protection of remnant vegetation and creek lines to create wildlife corridors.
• Practical measures to encourage and prioritise alternative forms of transport—pedestrians, bikes, electric cars, car pooling and public transport.
The project has been recognised within the Shire of Augusta Margaret River’s Witchcliffe Village Strategy and Local Planning Strategy and amendments required to the Town Planning Scheme are currently progressing through the Local and State planning processes.
The urban/residential portion of the site is approximately 60 hectares of a total 120 hectares and includes 12 clusters of homes each surrounding a central community garden, a village centre cluster, a commercial cluster and larger lots as part of a buffer between urban areas and Bussell Highway. Homes in each cluster front landscaped open space that will include the communities’ vegetable and herb gardens, community shed, chook pen, wetland areas, etc.
Each cluster consists of affordable, cottage and standard lots to encourage a diversity of age and socio economic circumstances.
All Standard lots are on an east – west axis, and small lots are on a north - south axis with road access on the south side with building envelopes that guarantee maximum solar access to each home.
Roads are designed for vehicle access only, with pedestrian and cycle paths located within the community open space to encourage maximum pedestrian activity between clusters and into the town centre. The plan includes a centrally located full sized oval and education centre.
Adjacent to the existing town centre is a village square and community centre that will promote community interaction activities such as management meetings, social events, films, dance, music,
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performances, etc, as well as a mixed use building that is anticipated to include a small café and tourist accommodation. The mixed use lots adjacent to the town square will provide opportunities for small business and professional activities, artist studio’s, etc.
As part of structure planning documentation for the Witchcliffe EcoVillage at Lot 2807 and 2812 Bussell Highway Witchcliffe, Hulme Developments are completing a Local Water Management Strategy. This documentation addresses the requirement in Amendment 28 to Shire of Augusta Margaret River Local Planning Scheme 1. A copy of the Scheme amendment is attached at Appendix G.
The Shire of Augusta Margaret River has prepared the Witchcliffe Village Strategy which guides planning for urban developments within Witchcliffe including the Witchcliffe Ecovillage. The Witchcliffe Village Strategy provides guidance on water management and servicing requirements which are summarised below and addressed in the Local Water Management Strategy for the Witchcliffe Ecovillage. A copy of the Witchcliffe Village Strategy is attached at available on the Shire of Augusta Margaret River website at www.amrshire.wa.gov.au/council/publications/download/106/
Witchcliffe Village Strategy The following provisions of the strategy relate to water management and are addressed in this report.
Excerpt from “Witchcliffe Village Strategy” Shire of Augusta Margaret River, 2012.
The Witchcliffe Village Strategy has been based on a range of sustainability principles spanning environmental, social, locational, land use and servicing considerations. The Western Australian State Sustainability Strategy (September 2003) (WASSS) includes the following objectives of reducing water consumption; extending responsibility for water supply to the planning system (water sensitive design) and to local government (Regional Councils) for groundwater supplies; .and achieving significant greywater re-use; and Investigating long-term innovative water supply options that have broad sustainability outcomes.
The recommendation to investigate alternative servicing arrangements is consistent with the WASSS.
The suitability of the Strategy area for these proposals will require verification to the satisfaction of all the regulative agencies, including the Health Department of WA.
In line with the State Government’s objectives this Strategy proposes that investigation be undertaken into the:
suitability of alternatives to reticulated water and sewerage; and practicality of alternative on-site effluent disposal systems; suitability and practicality of provision of rainwater tanks, to provide a sole source of water, or to compliment a reticulated water supply; environmental assessment of the land and the impacts of these proposals; any potential public health impacts of the above.
The above investigations will be required to be undertaken prior to or during the detailed structure planning stage. Should it be determined that these options are inappropriate then provision for servicing by connection to reticulated water and sewerage services will be required to be extended from Brookfield at East Margaret River to Witchcliffe. Subdivision and development as provided for by this Strategy, will not be supported by the Shire, until such
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time as it can be appropriately serviced (either by alternative or conventional methods) with water and sewerage services to the satisfaction of the Shire, WAPC/DPI, Water Corporation, Health Department WA, Department of Water and Department of Environment and Conservation.
Scheme Amendment The Scheme amendment contains provisions regarding water including the strategic approach to provision of water and sewer services and commitment to preparation of a Local Water Management Strategy as part of the structure planning documentation.
Excerpt from Amendment 28 to Shire of Augusta-Margaret River Local Planning Scheme No1 Sussex Location 2807 & 2812 Bussell Hwy, Witchcliffe
9.1 Wastewater Processing Facility The proponents are fully committed to the AMRSC’s proposed Wastewater Treatment Plant (WWTP) for Witchcliffe, as outlined in the WVS. However, due to some reluctance from the AMRSC to commission, own and manage such a facility, they have recently appointed Marsden Jacob to undertake a review of the Shire’s WWTP policy in the WVS. The proponent views the WWTP as an important part of the overall sustainability of the project, through the objective of recycling all black and grey water to drinking water standard for re-use within the ecovillage. The objective is to provide treated wastewater back to homes for use in toilets, laundries and gardens, along with other agricultural uses within the ecovillage.
There are two current viable options for the future of a WWTP in Witchcliffe: (i) the AMRSC proceeds with constructing a WWTP on the Davis Rd refuse facility site as per the WVS; or
(ii) the proponents build a stand alone facility on adjoining lot 710 Mill Rd, which they own, to service the Witchcliffe Ecovillage only. The facility would be owned by the Strata and managed by a licensed WWTP provider. Such a facility will require AMRSC and Department of Health approval, but would not require ERA approval.
Subject to the proponent being able to enter into satisfactory arrangements with the Western Australian Economic Regulator Authority, AMRSC, Department of Health, and other major land developers in Witchcliffe, a third potential option would be for the proponent to construct and manage a WWTP onsite that would service the whole of Witchcliffe.
3.9.2 Water
The Witchcliffe Ecovillage is to achieve 100% water self-sufficiency by the following means:
• The existing 50ML dam and future 75ML dam will supply water for onsite horticulture and public open space.
• Each home will be required to install rainwater tanks on the basis that 800mm of rainfall allows harvesting of over 130,000 litres of water from a 162 sqm roof area. All homes will also be required to install water efficient plumbing and appliances.
• Each home and business connected to a wastewater treatment plant for treatment and recycling of all black and grey water.
• Recycled water to be treated to AA standard and returned for household use (toilets and laundry) and irrigation.
A Local Water Management Strategy will detailed in the final Structure Plan documentation.
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1256m²47
416
51
32
1017m²21
51
21
1017m²21
51
21
1017m²21
5121
1016m²21
51
21
1016m²21
51
21
1921m²30
64
3064
1586m²
15
26
34
35
50
1500m² 30
50
30
50
1501m²
50
30
50
30
1558m²
1342
32
50
21
1525m²
1746
30
53
14
1501m² 30
50
30
50
1527m² 30
50
18
13 49
1525m²
30
53
1515
50
1589m²
53
32
53
32
1504m² 30
50
30
50 1500m²
30
50
30
50
2027m² 41
41
51
1666m²56
3056
30
4338m²
50
85
50
87
1921m²30
64
30
64
1.48ha
1.01ha
1.31ha
8322m²
2954m²
6883m²
6812m²
1.28ha
7536m²
8000m² 7980m²
1680m²
1260m²
535m²
PERRON & HULME DEVELOPMENTS
land development & visuals
0 60 120 180 240 300m
SCALE - 1:5,000 @ A3 / 1:2,500@A1
Witchcliffe C
oncept 3d.d
gn I 2
9/7/2
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LOT 2807 & 2812 - DEVELOPMENT ANALYSIS
ECOVILLAGEWITCHCLIFFE
Highway, WitchcliffeLots 2807 & 2812 Bussell
community garden
legend
stage boundary (1 - 5)
CO
NC
EP
T V
9B
cottage lots (300m²-360m²)
family lots (735m²-1150m²)
lifestyle lots (1650m²-3340m²)
commercial lot (4338m²)
mixed use lots (1000m²-1250m²)
tourism lots (1650m²-1925m²)
community garden (10.27ha)
wvs urban cell (60.41ha)
affordable housing lots (1500m²-1900m²)
grouped housing lot (2027m²)
community facilities (2000m²-3000m²)
pos (9.74ha)
stream protection zone (6.25ha)
total land areas summary table
57.09ha
62.02ha
119.11ha
total site
2812
2807
combined
wvs cell
pos
community gardens
dams (within urban cell)
total pos
60.41ha
9.74ha
10.27ha
6.53ha
26.54ha
4.21ha
6.25ha
agricultural
remnant vegetation
stream protection zone
residential lot area
road reservepavementverge 7.41ha
47.02ha
23.93ha
3.75ha11.16ha
DRAFT
2808
2809
281041
42
43
44
45
46
1
1
2
UCL
49
2184
31
2812
2807
71
30
10
10
30
300m²
300m²
30
10
300m²
30
10
300m²
30
10
300m²
2796m² 30
90
34
72 8
2571m²
31
82
22
15
2336m²
31
74
30
2084m²
31
65
30
1818m²57
30
31
1736m²
31
58
32
2144m²
31
67
30
1771m²
29
59
28
1673m²
29
60
29
1694m²
29
61
29
1715m²
29
62
29
1839m²60
2240
3340m²
81
42
81
41
2847m²37
73
36
2
2216m²32
66
528
2054m²
29
32
63
3
2004m²32
63
32
2006m²32
63
32
2008m²32
63
32
2011m²32
63
32
2276m²
20
72
29
68
16
1827m²28
62
29
1810m²
10
30
60
20
1800m²30
60
30
1857m²26
61
35
10
32 12
30
360m²
10
30
300m²
11
30
331m²
12
30
360m²
10
30
300m²
360m²
30
12
30
300m²
10 10
30
300m²
30
12
360m²
10
30
300m²
10
30
300m²
10
30
300m²
12
360m²
30
10
30
300m²
320m²
3
4
5
300m²
30
10 300m²
30
10
300m²
30
10
1
2
Precinct
Education
360m²
30
1212
30
360m²
CourtsTennis
SquareCentre / Town Community
855m²45
19
45
19
855m²19
45 19
855m²19
45 19
855m²19
45 19
810m²18
40 19
2
945m²45
21
45
21
911m² 2045
20
911m² 2045
20
911m² 2045
20
889m²20
2045
1052m²45
23
23
855m² 1945
19
855m²
1919
45
855m²
1919
45
855m²45 1
919
966m²23
42
2342
899m²4325
18
948m²
204225
840m²42
20
20
924m²42
22
42
22
882m²21
42
21
851m²20
4 42 3
14
983m²42
2126
1103m²22
45
15
3
459
990m²45
22
22
1035m²45
23
23
885m²401
3
7
50
853m²
21
50
854m²
21
50
21
853m²50 1
20
21
738m²37
17
21
889m²30
3619
976m²46
21
22
836m²4619 19
836m²4619 19
948m²4515
27 946m²
21
45
21
946m²45
21
21
1115m²45
25
25 901m²
45
20
20
901m²45
20 20
901m²45
20 20
901m²45
20 20
906m²45
20 20 901m²
20
45
20
901m²45
20
20
901m²45
20
20
901m²45
20
20
924m² 21
21
45
855m²45
19 19
855m²
19
45
19
855m²
19
45
19
855m²45
19
19 860m²
45
19
19
860m² 17
2
45
19
855m²
1
194518
861m²
1445172 6
901m² 20
20
45
901m²45
20
20
901m²45
20
20
901m²45
20
20
991m²45
22
22
944m²45
11
14
24
37
900m²
204520
900m²452
0
20
922m²46
20 20
875m²46
1919
875m²46
1919
874m²46
1919
874m²46
1919
865m²11 45 6
138
1084m²46
27
21
842m²20
42
20
834m²20
41
20
935m²
810
15
41
13
895m²
1418
7 40
6
850m²
2023
40
800m²
20
20
40
800m²
20
20
40
840m²21
40
21
844m²43
1722
855m²
194519
855m²
194519
855m²
194519
855m²
194519
855m²
194519
855m²
194519
945m²
21
4521
990m²452
2
22
923m²21
45
21
923m²21
45
21
923m²21
45
21
1009m²
17
5 44
23
954m²
21 48
21
935m²11 45 3
1810
900m²45
20
20
900m²45
20
20
900m²45
20
20
896m²44
20
20
861m²10
10 45
11
8
864m²19
45
19
864m²19
45
19
864m²19
45
19
844m² 19
13
9 39
1050m²502
1
50
21
950m²50
1919
945m²21
45
21
945m² 2121
45
900m²
2020
45
990m²45
2222
1100m²50
22
50
22
1100m²22
50
22
1147m²
23
50
23
21
24
Bowls
DAVIS ROAD
SH
ER
VIN
GT
ON A
VE
BU
SS
ELL H
IGH
WA
Y
& BOAT PARKINGCARAVAN, TRAILER
SHEDMAINTENANCE
COMMUNITY
OLIV
ES
OLIVES
REDGATE ROAD
DAMAPPROVED
MILL ROAD
STAGE
COTTAGE LOTS
FAMILY LOTS
LIFETSTYLE LOTS
MIXED USE LOTS
TOURISM LOTS
COMMERCIAL LOTS
TOTAL LOTS
1
18
23
-
-
-
-
46
2
34
27
8
-
-
-
71
3
19
14
5
-
-
-
40
4
33
17
-
6
2
1
62
5
36
32
12
-
-
-
83
140
113
25
6
2
1
302
3 2 2 2 3 12
1 - - 1 - 2COMMUNITY LOTS
AFFORDABLE LOTS
1 1GROUPED LOT (R60)
Figure 1 Witchcliffe Ecovillage Development Plan
Proposed Development The proposed development is located on 2807 and 2812 Bussell Highway Witchcliffe. A concept plan for the development is included above in Figure 1.
The development includes 12 clusters of residential lots around community gardens, 2 clusters of larger ‘lifestyle’ lots along Bussell Highway but separated from the highway by a vegetated buffer strip, a village core and a commercial zone as an extension of the existing Witchcliffe village centre. Typical lot sizes range from 300m2 cottage lots, 900m2 family lots, 1500m2 affordable lots to 2000m2 lifestyle lots. Lots will be strata titled arranged into three strata lots; a northern, central and southern strata.
There is a total of 26.54Ha of open space including 10.27Ha of community gardens, a 2Ha oval and 6.5Ha of dam area within the residential development area. Community gardens around which the lots are clustered range in size from 0.7Ha to 1.5 Ha. Total lot area is 23.93 Ha, road reserve area is 11.16Ha and 4Ha of road pavement. The site also includes 47Ha of agricultural land, 4.2Ha of remnant vegetation and 6.2Ha of stream protection zone.
The site is located in the upper reaches of the Chapman catchment. Bussell Highway bounding the development site is typically the north west boundary of the catchment with surface water runoff generally flowing in an easterly direction.
The site has an existing centrally located 50ML dam, an approved 80ML dam on the south east side of the development and an existing small farm dam at the northern end of the property. The northern dam is proposed to be expanded to store additional stormwater runoff for reuse onsite as well as providing additional volume for detention of peak flows. Each dam provides the primary storage area to buffer stormwater peak flows, for storage of stormwater runoff and as a water supply for irrigation of community gardens and agricultural areas.
Seasonally flowing streams are located on cleared farmland adjoining the site to the north and the south of the development area. There are no existing defined water courses within the residential development area (except the central dam) with drainage occurring via seasonally waterlogged shallow depressions and overland flow.
Stormwater from the northern part of the residential development area that outfalls to adjoining agricultural land which is part of the overall development site will be retained at the current locations and level. The existing central dam and approved southern dam have flow bypass structures to provide environmental water flows in line with Department of Water guidelines. Bypass structures will also be incorporated into the design for the expansion of the northern dam.
Design Criteria Framework An integrated water management system will be delivered in line with the objectives identified in the following documents:
State Planning Policy 2.9 Water Resources (2006)
Stormwater Management Manual for Western Australia (2004-2007); andShire of Augusta-Margaret River – PE53. Water Sensitive Urban Design Local Planning Policy
A district level water strategy has not been prepared for the Witchcliffe urban area however the Margaret River District Water Management Strategy was recently prepared as part of the Margaret River
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Supertowns Planning Process. Reference has been made to relevant aspects of the Margaret River District Water Management Strategy such as soil and groundwater conditions where similarities occur and with regard to stormwater quality objectives.
Water Conservation The Witchcliffe Ecovillage will deliver sustainable management of all aspects of the water cycle including:
- All houses self sufficient supplying their own potable water needs through rainwater collection and storage as per the current practice within Witchcliffe and rural and semi rural areas of the shire.
- Improving efficiency of potable water use. This will not only reduce the size of storage tanks, but will also reduce the costs of energy use for the future residents associated with water pumping and water heating.
- No imported water. Connection to the Margaret River Water Supply is not required and would conflict with sustainability objectives for the development and within the Witchcliffe Village Strategy for Witchcliffe.
- Water consumption target for potable water of 44kL/person/year (122L/p/d) which is consistent with the Western Australian State Water Plan (Government of Western Australia, 2007) target of 40 - 60kL/person/year of potable scheme water use.
- WA Health Department guidelines of 150L per person per day is used for planning for water collection and storage facilities. While the Witchcliffe Ecovillage aims to achieve water consumption targets less than the WA Health Department Guideline, the use of the higher figure for planning purposes will build additional resilience into the community in the case of lower than average annual rainfall.
- capture and use of treated stormwater runoff for use in irrigating community gardens and agricultural areas
- reuse of treated wastewater onsite for agricultural reuse on low risk crops and woodlots.
Within the Witchcliffe Ecovillage, water reuse is planned using principles of fit-for-purpose use of non-drinking water. Wastewater is treated and stored in maturation ponds for irrigation on low risk agriculture areas and stormwater is treated and stored in dams for use irrigating active POS, community gardens and agricultural production areas. This approach reduces the demand for potable water, maximises the use of energy efficient water treatment while maintaining appropriate water quality for each water use.
Water Quantity Management Post development stormwater flows will be maintained relative to pre-development conditions through application of the following design criteria:
Ecological protection - 1-year average recurrence interval (ARI) events are detained in rain water tanks, reconstructed stream stormwater conveyance system and stormwater treatment biofilter areas and wetlands and stored in storage dams with post-development discharge volume and peak flows maintained in line with pre-development conditions. The Witchcliffe Ecovillage will also ameliorate peak flows and increased stormwater volume from the existing Witchcliffe townsite which was constructed prior to introduction of water sensitive development principles.
Serviceability – 5-year ARI events are retained in dam storages, stormwater detention basin and treatment systems so that post-development flows do not exceed pre- development peak discharges and are conveyed within the proposed stormwater system.
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Flood management - Flow paths along roads, through community gardens and open space accommodate 100-year ARI events flowing overland, protecting property and infrastructure from peak flows. Dams incorporate spillways designed to safely accomodate flows in excess of the 100ARI event.
Water Quality Management Stormwater will be managed to maintain surface water quality exceeding pre-development levels and to improve the quality of water leaving the development area.
The following criteria will be applied:
- Runoff from the road reserves collected and treated in bioretention systems prior to discharge to downstream systems.
- Runoff from common garden areas, POS and private yards collected in bioretention and wetland treatment prior to discharge to receiving waters.
- Runoff from roofs collected in rainwater tanks for potable use. Overflow from tanks directed to rain gardens within lots.
- An area of 2% of the contributing catchment area is allowed for bioretention systems and an area of 10% of the contributing catchment area for wetland systems.
Predevelopment Environment Landuse The total land area of Lots 2807 and 2812 is currently 97% cleared and used for agriculture. The northern lot used for for grazing and the southern lot for grazing and viticulture. A
Topography The site is flat to gently undulating ranging from elevation between 73m and 86m AHD. The site generally falls from the Bussell Highway in the west toward agricultural land uses in the east.
Gradients within the residential part of the site range from:
1.2% east facing at the northern end of the site
0% (flat) at the northern end of the existing townsite
1.5% east facing typical over the southern portion of the site
6% maximum grade facing east in the south east corner of the site
Soil Geology The Karridale-Tooker sheet of the 1:50,000 scale Regolith-Landform Resources series map indicates that area is underlain by the following soil units:
- Residual soils described as ferruginous duricrust overlying mottled soil (weathered Leeuwin Complex),
including leached quartz sand. This is typically over the upper valley slopes;
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�11Figure 2 - Soil Classification Map
- Colluvial soils described as silty or gravelly sand over mottled sandy clay. Typically on the side slopes;
- Alluvial deposits described as silty clayey sand in the lower-lying drainage valleys.
Soils mapping provided for Lot L2807 indicates that the clayey and silty soils are relatively widespread across the site at a depth below about 0.5 m, with localised laterite outcrops.
The findings of a geotechnical site investigation by Galt Geotechnics indicate that the subsurface conditions on the site generally comprise silty and gravelly sands overlying either clayey sands or laterite. Subsurface conditions were relatively consistent across the majority of the site. The typical soil profile comprises:
- Silty SAND/SAND/Sandy GRAVEL (SM/SP/GP), fine to medium grained sand, fine to medium grained gravel, rounded to sub-angular, up to 30% non-plastic fines, pale brown to pale grey, locally very weakly cemented, trace roots and rootlets, generally medium dense to very dense, generally dry, present from the surface, extending to depths of between 0.3 m and 2.0 m; overlying
- Clayey SAND/Gravelly Clayey SAND/Clayey Sandy GRAVEL (SC/6C), 30% to 70% fine to medium grained sand, 20% to 40% low to medium plasticity clay fines, generally pale grey/orange brown/pale brown locally stained red-brown, variably iron cementedi, locally with up to 40% iron-cemented, fine to coarse grained gravel, localised COBBLE to BOULDER sized concretions, firm to hard, generally dry, locally moist to wet, extending to the maximum depth of investigation of 2.9 m.
The clayey material encountered across the site is variably iron cemented, ranging from very weakly cemented to well cemented laterite hardpan. Laterite hardpan was more frequently encountered towards the southern half of the site; however, was also locally present on the northern half of the site.
Acid Sulphate Soils
The acid sulphate soil risk map published by WAPC in 2005 identifies the majority of the site as no risk, with class 2 moderate to low soils along wetter soils associated with wet valley floors.
Class 2 categorises a moderate to low risk of acid sulphate soils occurring within 3m of the natural soil surface but high to moderate risk below 3m. It is unlikely that acid sulphate soils will occur on this location based on excavation of existing dams on the site in these areas and no history of acid sulphate soils being encountered on other sites in the Witchcliffe townsite area and acid sulphate soil testing carried out as part of the geotechnical investigation. (pH and oxidised pH tests)
Figure 3 - Acid Sulphate Soil Risk Map
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Environmental Conditions The site is located in the western most portion of the Chapman Brook catchment and is dominated by five ephemeral, waterways running approximately west to east across the property. Foreshore condition across these tributaries ranges from A3 in parts of the northern tributary through to D3 through parts of the central waterways . Three primary areas of remnant vegetation exist across the property including the Northern tributary, a 3 hectare patch of remnant vegetation near the middle of the eastern boundary of the block and degraded remnant vegetation along the downstream portion of the southern tributary. Vegetation condition across the site ranges from very good to completely degraded. The site contains some significant habitat values including habitat for or habitat immediately adjoining confirmed sightings of Western Ringtail Possum, Southern Brown Bandicoot, Brush tailed Phascogale and Baudin’s Black Cockatoo . The site also contains significant values for ecological connectivity including one of the South West Regional Ecological Linkages axis line.
Hydrology The site lies at the north western extreme of the Chapman Brook catchment with no surface water inflow onto the site. Drainage from the site moves in an easterly direction onto adjoining farmland. Runoff is also collected on the site in three water storage dams (two existing, one approved) and bypass structures provide streamflows downstream in line with Department of Water guidelines.
The properties support three main and one minor watercourse. The watersheds of each of the watercourses originate on site (with some minor offsite inflow to the northern most creek line) and flows into the Chapman Brook through properties to the east as shown in figure 4, Witchcliffe Ecovillage Site Features.
The middle creek line supports an existing 50ML dam. The northern creek line has been fenced and is in good overall condition. The northern minor creek is dominated by weed species and its natural stream form has been highly modified. The southern creek line contains a mix of vegetated and cleared areas that have undergone significant revegetation by the proponent.
The property has Shire approval for a second dam approximately 80ML in size that is yet to be constructed. This dam has recently been endorsed by the Department of Water (DoW) after a request from Sustainable Developments P/L to undergo a full sustainability assessment by DoW. Dam bypasses will be incorporated to ensure that there are no associated negative downstream impacts from either of the dams on the property.
Stream gauging in the Forest Grove subcatchment of Chapman Brook indicates average annual runoff in the subcatchment is 2990kL/Ha (Surface Hydrology of the Cape to Cape Region, DoW 2007)
Groundwater Groundwater observed across the site is perched groundwater in the superficial aquifer. The superficial aquifer is present within the sandy upper surface layer which extends up to 2m deep overlying low permeability sandy clay. The depth to groundwater is affected by surface features and local variations in the aquifer profile. The depth to groundwater has been observed at greater than 1m in the northern part of the site and localised perched water observed in winter around the central western part of the site.
The Southern part of the site is well drained with sandy and gravelly soils, greater surface grades and depth to groundwater of 0.8m and greater.
Groundwater level monitoring has been carried out at 12 bores on the site with depths to maximum winter water levels ranging from 0m to 2.3m. Results from groundwater monitoring is shown in figure 6.
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Higher winter ground water levels were observed in close proximity to waterways at boreholes 4 and 7 (0.4m to 0m) and groundwater at depth of 0.2m below surface levels due to perched water was observed at boreholes 5, 9 and 11. Lots located in proximity to borehole 7 and the southern end of the oval will be filled to ensure adequate drainage in this area. Lots in areas with perched water tables, typically the flatter areas immediately east of Bussell Highway and the existing Witchcliffe Townsite will be provided with improved drainage via the proposed network of waterways extending through the community gardens.
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Figure 4 - Witchcliffe Ecovillage Site Features
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Figure 6 - Groundwater Monitoring Results
Dep
th, m
-3.00
-2.50
-2.00
-1.50
-1.00
-0.50
0.00
21/7/13 28/1/14 8/8/14 15/2/15 26/8/15
11 12 10 8 7 9 5 6 4 2 31
Figure 5 Groundwater Monitoring Bore Locations
Climate Witchcliffe has a mild mediterranean climate with cool wet winters and warm dry summers. Summer temperatures average between 14℃ minimum to 26℃ maximum and winter temperatures average from 8℃ minimum to 17℃ maximum. Average rainfall for Witchcliffe measured from the Bureau of Meteorology station located on the development site 100m south of the existing dam is 1007mm annually (Bureau of Meteorology 1999 to 2015 statistics) with the monthly distribution of rainfall shown in Figure 7.
Figure 7 - Witchcliffe Mean Monthly Rainfall
Water sustainability initiatives Water sustainability initiatives incorporated in the development include:
- all household water supplied by onsite collection and storage in rainwater tanks - potential reduction in household water demands and wastewater generation through encouraging use
of composting toilets with information about water and energy savings and reuse of nutrients by composting toilets provided to purchasers and construction of demonstration composting toilet technologies.
- reduction in irrigation water required for landscaping within private lots through landscape design and use of grey water for irrigation. Note that this criteria will be self regulating as lots will not be provided with an external scheme water supply.
- collection of surplus water (after meeting potable requirements) in rainwater tanks for garden irrigation on larger (lifestyle) lots.
- reduction in wastewater volumes for treatment through encouraging use of grey water irrigation within private lots.
- reduction in offsite agricultural water use through provision of onsite food production including edible fruit and nut tree and dedicated vegetable gardens. The average Australian family uses 100kL of water every ten days embodied in the food purchased from supermarkets.
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- reduction in offsite water use for coal fired power generation by onsite solar PV power generation. Approximately 3.7ML of water saved per year compared to conventional subdivision with average power consumption.
- establishing an information and education centre that demonstrates sustainable technologies within the Witchcliffe Ecovillage including composting toilets, rainwater management, grey water systems and sustainable gardening practices such as mulching and efficient irrigation techniques.
- Use of landscaping that requires minimum water use including mediterranean and native plants, e.g. olive production from landscape buffer strip.
- collection and storage of excess stormwater runoff in storage dams for use in onsite irrigation with each strata lot.
- onsite wastewater treatment and use of treated water for irrigation of low risk agriculture on farmland within each strata lot.
- use of low energy wastewater conveyance (gravity flow) where possible and low energy wastewater treatment technologies.
- establishing aquaculture and hydroponic (aquaponics) systems within each cluster as a low water use food production system.
Water Supply Water consumption for household use of 150L/person/day or 122L/person/day with the use of composting toilets has been adopted for the Witchcliffe Ecovillage based on Department of Health guidelines. The Department of Health guidelines are consistent with typical consumption for Perth households connected to scheme water.
Table 1 - Perth Household Water Consumption Studies
1981/82 Perth 98-2001
Perth 2008/09 Water Use using AAA water appliances
Showers and Bath 51 74 45 (5 min @ 9l/min) Note that 2008/9 study average was 6.7 min and Water Corporation target is to reduce average shower to 4 min.
Toilet 33 27 20 (4 flushes @5l/flush)
Washing Machine 42 115 40 (2.2kg @ 18l/kg for AAA front load washing machine) This equates to one 8.5kg load of washing per family of 4 per day or one 8.5kg load of washing per couple every second day
Tap 24 16 20
Evap Airconditioner 11
Dishwasher 2.7 5
Other 5
TOTAL 156 155 153 130
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All homes in the Witchcliffe Ecovillage will be supplied from rainwater tanks and will be required to use AAA rated appliances, thus the adopted consumption rate will be conservative.
Average consumption is likely to reduce to 130L/person/day and further reduction to 110L/person/day where composting toilets are used will be achieved. The following table shows a breakdown of standard water consumption based on average Perth household use and consumption goals by using water efficient appliances.
Existing water for household use in Witchcliffe is currently supplied by rain water tanks. There is some evidence that households occasionally run short of water and truck water in to refill tanks (Shire of Augusta Margaret River water services survey). To ensure that homes within the Witchcliffe Ecovillage are adequately supplied with water, design guidelines will be provided to ensure adequate roof area and tank volume is provided for rainfall collection for various household sizes. In addition design guidelines will specify use of water efficient appliances within households to minimise water consumption. A chart showing rainwater tank sizes modelled on rainfall data from the site since 1999 is included below in Figure 8 - Water Collection and Tank Sizing. The required water tank size is dependent on average consumption patterns, rainfall collection area (roof area) and the number of occupants in a dwelling. This digram shows the difference between tank sizing using the Department of Health standard requirement of 150 L/p/day and a reduced rate of 122L/p/day which excludes water for toilets flushing where a composting toilet is fitted.
Figure 8 - Water Collection and Tank Sizing
The Chart in figure 8 has been modelled based on historical daily rainfall records and average daily consumption and includes allowance for 10% losses from first flush devices and splashing and a further 10% reduction to allow for reduced rainfall years.
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Tank Sizing Chart, Witchcliffe Western Australia
Tank
Siz
e, L
0
15,000
30,000
45,000
60,000
75,000
90,000
105,000
120,000
135,000
150,000
Roof Area, m20 50 100 150 200 250 300 350 400 450 500
1 Occupant 122 L/day2 Occupants 122 L/day3 Occupants 122 L/day4 Occupants 122 L/day5 Occupants 122 L/day1 Occupant 150L/day2 Occupants 150 L/day3 Occupants 150 L/day4 Occupants 150 L/day5 Occupants 150 L/day
A summary of potable water requirements for the Witchcliffe Ecovillage by lot type and the expected total water use within the Witchcliffe Ecovillage is provided below in Table 2 - Potable Water Use Requirements
Water Consumption and Climate Change With climate change models predicting reduced rainfall in South Western Australia, it is important to ensure resiliency measures are incorporated within water supply measures for future residences. The following sources of resiliency within the water supply for Witchcliffe Ecovillage.- use of conservative figures for potable water requirements.- modelling rainwater tank sizes based on annual rainfall 10% lower than lowest recorded rainfall
year.- incorporating requirements for water efficient appliances in all households- promoting need for greater level of household water conservation during low rainfall periods
through community resources including community centre and village new letters- ability for residents to add additional rainwater tanks to provide additional water storage for
heavier users.
Table 2 - Potable Water Use Summary
TypeLot Numbers
Home Numbers
People/HH
Total People
Daily water use, L/p
Water use/HH
Occupancy Rate
Water Consumption kL/day
Cottage 140 140 1.5 210 150 225 0.90 28.4Family 113 113 3.0 339 150 450 0.95 48.3Family with Anncillary (assuming 100% takeup of lots over 900m2)
54 1.0 54 150 150 0.75 6.1
Lifestyle 25 25 4.0 100 150 600 0.90 13.5Lifestyle with Anncillary (assuming 100% takeup)
25 1.0 25 150 150 0.75 2.8
Affordable 12 60 1.3 75 122 153 0.90 8.2Grouped 1 3 10.0 30 150 1,500 0.90 4.1Mixed Use 6 6 3.0 18 180 540 1.00 3.2Tourist 2 2 25.0 50 130 3,250 0.90 5.9Commercial 1 1 5.0 5 80 400 1.00 0.4Community Lots 2 - 1.0
Total 302 429 906 121.8
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Wastewater Overview A distributed wastewater collection and treatment and onsite reuse model has been adopted in line with best practice for water sensitive cities. This approach has the lowest energy use for water transport and treatment, maximises beneficial reuse of water within the community from which it originates and provides ecological (wetlands habitat) benefits. The capture and reuse of biogas (methane) is also possible and could make the wastewater treatment process energy positive, however current advice indicates that the size of the community and scale of the treatment system is not sufficient to make biogas production feasible.
The wastewater system comprises:
1. Composting toilets required for affordable dwellings to enable reduced roof areas. Composting toilets encouraged for all other dwellings.
2. Collection of wastewater from lots by gravity sewers to an anaerobic digester such as a baffled tank reactor or imhoff tank digester in each cluster. Primary treatment includes settlement of solids, nutrient reduction and pathogen removal in the anaerobic digester. There is also potential to recover energy and reduce greenhouse gas emissions from the primary treatment system by collection of methane gas and use for energy generation within the village.
3. Secondary treatment of wastewater in subsurface flow treatment wetlands with 7 treatment wetlands located within each strata lot within the agricultural zone. Treatment wetlands are situated to maximise gravity flow of primary treated effluent from the anaerobic digesters.
4. Storage and polishing of treated water in storage dams sized for winter storage of treated water
5. Irrigation of treated water from storage dams for agricultural use on low risk crops including vineyard for wine production, tree fruit and tree nut crops and woodlots.
The wastewater treatment system follow BORDA guidelines for DEWATS (Decentralised Wastewater Treatment Systems DEWATS and Sanitation in Developing Countries). These guidelines are based on robust treatment technologies that can be reliably operated and maintained without specialised knowledge and equipment. These same principles will ensure the wastewater management system at Witchcliffe Ecovillage is a robust system that can be maintained and operated by local contractors under the management of the Village corporate body.
A schematic wastewater layout of a typical wastewater catchment is shown in the diagram below. An overall plan of the wastewater layout for the Witchcliffe Ecovillage is included in the Local Water Management Strategy Plan at Appendix B and and a plan showing one of the wastewater catchments in greater detail is attached at Appendix G - Typical Wastewater Catchment Concept Plan.
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Anaerobic Digestor
Subsurface Treatment Wetland
Maturation Pond
Solar Irrigation Pump
Drip Irrigation to Woodlot or Tree Crop
Witchcliffe Ecovillage Wastewater Treatment Schematic
Composting Toilets Composting toilets face significant user perception challenges however they present the most sustainable solution for collection and disposal of human waste, requiring very minimal energy (ventilation fan <10 watts), require no water and enable nutrients in human waste to be recycled. By reducing potable water requirements for households, composting toilets will provide a direct financial saving to residents through reduced rainwater tank size and indirectly through reduced infrastructure costs for wastewater conveyance, treatment and disposal.
The Witchcliffe Ecovillage project will promote use of composting toilets for all lot types and will require the use of composting toilets in affordable dwellings. Composting toilets will be required in affordable dwellings to enable the smaller size of such dwellings to remain self sufficient in water supply.
Planning for wastewater management is however being carried out on the basis lots being serviced for 100% flushing toilet use as it is not possible to determine composting toilet use. Planning may be reviewed as the project progresses if there is a significant take up of composting toilets. If there is a much higher proportion of composting toilets installed than anticipated, this will result in less nutrients and water entering the wastewater system which will not adversely affect the proposed wastewater treatment system.
Lots under 1000m² with composting toilets are considered too small for reuse of stabilised compost onsite and a maintenance contract and formal agreement will be established for all lots with composting toilets to service toilets including collection, composting and application of compost to agricultural land. Agreements will be similar to those for ATU service contracts under current Department of Health guidelines.
Composting toilets will be promoted through information about their sustainability benefits, provision of quality composting toilet facilities in community areas such as a community centre, information and sales site and in display houses containing composting toilets.
A case study of a demonstration project utilising composting toilets in a high density apartments development in Melbourne by GHD for Benson Property Group can be found at http://www.ghd.com/PDF/ToiletFeasibilityVolume1_Report.pdf
A number of composting toilet suppliers have been approved for installation in Western Australia by the Health Department of Western Australia and composting toilets for installation at the Witchcliffe Ecovillage will be selected from approved models.
Wastewater Collection and Primary Treatment Seven wastewater collection catchments have been identified based on the topography of the site to maximise use of gravity sewers draining to below ground collection points within the agricultural area. Wastewater collection catchments are shown on the Local Water Management Strategy Plan in Appendix B. Primary treatment will occur within a below ground anaerobic reactor; a baffled tank reactor or imhoff tank digester located at the collection point at the lowest point of each subcatchment. Detailed design of anaerobic digesters will be completed at a later stage, however indicative sizing for a baffled tank anaerobic digester suitable for treating an average catchment flow of 17.5kL per day based on a hydraulic retention time of 12 hours is 9kL. The anaerobic digester will settle out grit and heavier
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Figure 9 - Baffled Tank Reactor Layout
suspended solids and facilitates bacterial digestion of organic load. It is capable of reducing BOD by 60% however it provides minimal reduction in nutrients. It enhances the performance and longevity of downstream process such as treatment wetlands.
Secondary Treatment Primary treated effluent will undergo additional treatment in a subsurface flow wetland to reduce nutrients to secondary treated sewerage standards and to provide further reduction in pathogens. In addition further reductions in BOD can be achieved and the filtration action of subsurface flow wetlands is highly effective if removing suspended solids. Indicative sizing for a subsurface flow wetland suitable for treating domestic wastewater (grey and black water) in the Witchcliffe climate is 4m² per person and would be split into an initial vertical flow stage followed by a horizontal flow stage. Nutrient removal is achieved in the wetland primarily for nitrogen by aerobic biological activity on a large surface area of media and plant roots and for phosphorus by adsorption within filter material with some additional nutrient uptake by plants. A plan showing locations for treatment wetlands positioned to maximise gravity flows is included in the Local Water Management Strategy Plan in Appendix B
A subsurface flow wetland uses a similar approach to stormwater biofilters that are now commonly used in Australia to improve urban stormwater quality and while there are limited examples of subsurface flow treatment wetlands for treatment of domestic wastewater in Western Australia there are municipal treatment plants treating sewerage with subsurface flow wetlands in UK, Scandinavia, Germany and USA and over 2000 municipal wastewater treatment plants in France. There is comprehensive literature covering the design, operation and performance of subsurface flow wetlands backed by extensive research, testing and monitoring demonstrating that this is a mature and proven treatment method.
Within a pacific context Lismore Shire and Australia and National Institute of Water and Atmospheric Research in New Zealand have developed guidelines for domestic subsurface flow wastewater treatment systems with many smaller examples being constructed and community scale systems constructed on pacific islands including Cook Island.
Storage and Reuse Treated water will be stored in maturation ponds for up to 4 months prior to irrigation on agricultural crops on adjoining farmland on the site. A total storage volume of 16.6ML in seven excavated ponds (one per wastewater catchment) has been calculated based on the monthly water balance and includes allowance for treated water inflows, collection of rain in treatment wetlands and dams and evaporation from dam storages. A table showing the monthly water balance and annual totals is included below.
Irrigation of treated water on agricultural crops will be carried out on agricultural land on site, that is within the respective strata lot. Irrigation of treated water within the lot has been incorporated to meet the requirements of the WA Health Act and Country Sewerage policy for onsite wastewater treatment and disposal.
Tree and vine crops will be established for treated water irrigation to meet requirements of low risk treated water reuse under National Water Recycling Guidelines. Examples include vines for wine production (existing), woodlots for timber and wood chips and tree fruit and tree nut crops such as olives, macadamias, pecans, almonds and walnuts with above ground drip irrigation and withholding periods between irrigation application and fruit picking. Irrigation areas have been provided based on maximising the efficient reuse of water for productive agriculture at 5000kL per Ha per year which is equivalent to applying 1/2 of the average winter rainfall volume on the irrigation area during the summer period. CSIRO Guidelines for Effluent Irrigated Plantations (Myers et al, 1995) indicate that irrigation volumes of 10,000kL per Ha per year could be sustainably applied to the site.
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The selection of crops for use with treated water irrigation will be determined as part of the the approval process for the recycled water system and will be required to be detailed in a Recycled Water Quality Management Plan to be submitted to the Department of Health as part of the subdivision design stage. Crops such as root crops or with above ground fruit close to the soil requiring continuous irrigation (eg tomatoes) are high risk crops and would not be permitted. Crops such as nut and orchard trees with appropriate management arrangements in place such as irrigation withholding periods prior to harvesting, trickle irrigation, post processing of fruit such as shelling or cooking and harvesting only from trees not from the ground may be low risk and can be suitable for irrigation with treated water. The management arrangements that are required to be put in place for irrigation of treated water including the specific management requirements for any food crops will be required to be specified in the Recycled Water Quality Management Plan.
Table 3 Annual Treated Water Balance
The treated water storage has been incorporated so that treated water is only irrigated crops in line with crop demands to increase the productive use of the treated water rather than just maximising treated water disposal. The water storages are sized so that no irrigation is scheduled during winter months when there are increased groundwater levels or after heavy rainfall when soils may be saturated. As such the areas for treated water for irrigation are not restricted by winter groundwater levels as they would for conventional leach drain disposal or ATU irrigation areas which require year round dispersal. Details of the proposed irrigation volumes on a month by month basis are included in the water balance table above. Even though irrigation will only occur when there is adequate demand from vegetation to use water that is applied, irrigation areas have still been selected based on providing well drained soils.
The proposed location of treated water storage and maturation ponds and irrigation areas is shown on the Local Water Management Strategy Plan in Appendix B.
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Month Treated water produced, kL
Monthly rainfall input kL
Evap, kL Net treated water, kL
Irrigation %
Irrigation Volume
Daily Irrigation, L/m²
Storage kL
j 3588 110 1049 2649 15 6966 27 8448f 3588 90 907 2770 15 6966 27 4253m 3588 249 765 3071 15 6966 27 358a 3588 722 471 3839 9 4179 16 18
m 3588 1464 312 4740 7 3251 12 1507j 3588 1825 272 5141 5 2322 9 4326j 3588 2016 266 5337 0 0 0 9663
a 3588 1576 323 4841 0 0 0 14504s 3588 1238 397 4428 5 2322 9 16610o 3588 646 567 3666 8 3715 14 16562n 3588 404 868 3125 9 4179 16 15507d 3588 150 907 2831 12 5573 21 12765
TOT 43052 10491 7105 46438 100 46438 16610
Annual Wastewater, kL
43052
Treatment Area, m²
4917
Storage Area, m² 5670 (avg 3m deep)
Irrigation Area, Ha
8.62
As part of the detailed design and subdivision process, the developer will prepare nutrient irrigation management plans in line with Department of Water Guidelines for treated water irrigation to ensure long term sustainability of the nutrient and soil health. Information from the Margaret River Water Recycling Nutrient Irrigation Management Plan has been used to provide guidance in the planning process.
Scheme Ownership and Management The wastewater conveyance and treatment infrastructure will be located on common property owned jointly by landowners of each strata lot. Treated water storage and maturation ponds and irrigation areas will also be located on common land within each strata lot in the agricultural area.
After establishment of the infrastructure by the developer, collection and treatment infrastructure as part of the wastewater management system will be owned, operated and managed by the landowners through the strata body corporate. The body corporate will employ qualified persons or contract a business with qualified personnel to operate and fulfil reporting requirements for the scheme.
Arrangements for the operation of the scheme will be made initially by the developer and the strata body may continue with these arrangements or they may employ their own staff and contractors to operate and manage the wastewater scheme. Details of management arrangements will be provided at a later stage. This will typically include:
- local licensed plumber for maintenance of all gravity sewer pipes, pumps and irrigation mainlines
- staff or contract gardener for maintenance of the wetland plantings, woodlots and agricultural crops and to monitor irrigation programs and carry out regular inspections and maintenance of the drip irrigation system.
- local controlled waste contractor to carry out sediment removal from the digester - contractor or catchment group staff to undertake water quality monitoring - Strata administrator / office manager to maintain scheme records and submit reports
Contingency Planning The wastewater treatment strategy is based on robust, low maintenance systems that have been well proven in international applications however with limited local experience of these systems additional system redundancy will be provided. Redundancy available in the proposed system includes:
- provision of a treated water storage pond at each treatment wetland. While this is provided primarily for managing treated water irrigation, the storage pond could be utilised to store untreated water as an emergency measure.
- double the land area required for treated water irrigation is provided within each strata lot. This enables half of the irrigation system to be shut down for maintenance of the irrigation system of to undertake management operations for the irrigated crop / woodlot area.
- An establishment period will occur where the number of occupants connected to the system will be less than the capacity of the system, thus the system will gradually ramp up to its operating capacity and will be monitored during this phase. This will occur due to progressive sales and construction of houses that occurs within a new land development. The developer will be responsible for operation and management of the system during the establishment phase and the system will be monitored to confirm that it is performing in line with design parameters, environmental and health standards prior to transferring management to the strata bodies.
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Stormwater Management Strategy Overview Water collected from stormwater runoff in the Witchcliffe Ecovillage will be collected, treated, detained and conveyed in vegetated surface features comprising reconstructed natural streams and bioretention swales and basins. The use of pits and pipes will be minimised, being required primarily for road and path crossings.
Three water storages within the development area capture the majority of the development’s catchment area ensuring peak flows exceeding the recommended 5 year ARI event are maintained in line with pre development flows. The capture and storage of treated stormwater also allows the additional stormwater generated from the development area to be used for irrigation on landscaping, active active recreation and food production areas within the development. These storages will have bypass systems and assist in maintaining the seasonal streamflow patterns downstream from the development.
The use of rehabilitated surface water features to collect and convey stormwater has the following outcomes:
• minimises use of concrete pipes and pits,
• reduce water velocities within the system,
• increases water storage in the conveyance and treatment system,
• contributes to the landscape amenity of the community,
• promotes re-establishment of populations of native wetland dependent wildlife and
• increase soil water recharge promoting healthy plant growth.
The approach is consistent with WA Stormwater Management Objectives and the “Stormwater Delivery Approach for Western Australia” and an analysis of the Witchcliffe stormwater management system against these principles is contained in Appendix A - Stormwater Delivery Approach for Western Australia.
There are three major catchments within the development area which are shown in Figure 10 Witchcliffe Ecovillage Catchment Diagram. The northern catchment is 39.6Ha with an increased average annual runoff as result of urban development of 57ML p.a. and a proposed 60ML storage dam. The central catchment is 30.4 Ha and includes the existing Witchcliffe townsite. The catchment will be highly urbanised post development and increased average annual runoff from the catchment post development is estimated to be 52ML p.a. compared to predevelopment flows (including the existing townsite). This catchment includes an existing 50ML dam. The southern catchment is 43.7Ha and will be approximately 1/3 urban and 2/3 agricultural and includes an approved 80ML dam. An additional 24ML p.a. of average annual stormwater runoff is generated from the urban area post development, not including increased runoff from cleared agricultural land.
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Figure 10 Witchcliffe Ecovillage Stormwater Catchments
The total increase in average annual runoff from urban development within the Witchcliffe Ecovillage including runoff from existing townsite areas within the catchment is 114ML. The total increase in average annual runoff from redeveloped flows from the total Ecovillage site is 165ML and a breakdown showing estimated runoff coefficients, areas and flows from different land uses within the Witchcliffe Ecovillage is included below in Table 3 Stormwater Runoff Summary.
A diagram showing the Witchcliffe Eco Village Water Cycle including typical annual water volumes is shown in Figure 11 Witchcliffe Ecovillage Water Cycle and a larger copy in Appendix C.
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Figure 11 - Witchcliffe Ecovillage Water Cycle
31 ML irrigated annually (3ML increase from rainfall
and evaporation)
Agricultural Use 74 ML p.a.
Environmental Flow approx. 87ML p.a.
Witchcliffe Ecovillage Water Cycle
!!!
Dam 2 (proposed)80ML
43.7 Ha catchment
Dam 150ML
30.4 Ha catchment
Treated Water
17ML Storage
175ML runoff from catchment
193ML runoff from
catchment
10ML p.a. Fire Safety 6Ml p.a. village
irrigation6ML p.a. POS irrigation
7ML p.a. Village irrigation for community gardens
Environmental Flow approx. 82 ML p.a.
45ML p.a. rainfall captured on roofs
28ML p.a. wastewater treated
15ML of grey water reused on larger
lots, Spring to Autumn
184 ML p.a. Stormwater runoff predevelopment,
472 ML p.a. post development
Dam 360ML
39.6 Ha catchment
134ML runoff from
catchment
Environmental Flow approx. 92ML p.a.
10ML p.a. for village irrigation
50ML p.a. to agriculture
23 ML Evaporation
25 ML Evaporation
30 ML Evaporation
Table 4 Annual Stormwater Runoff Summary
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Area, Ha pre development runoff coefficient
predevelopment runoff, kL
post development runoff coefficient
post development runoff, kL
difference, kL
Total Site 119.11 0.296 356,091
WVS Cell 60.41 0.296 180,602
Development Area
Community Open Space 30.42 0.296 90,944 0.35 107,535 16,591
Community Garden 11.88 0.296 35,516 0.4 47,995 12,479
Dams 8.9 0.296 26,607 1 89,890 63,283
POS 1.82 0.296 5,441 0.4 7,353 1,912
Conservation 8.84 0.296 26,428 0.296 26,428 0
Residential Lots 24.85 0.296 74,292 0.5 125,493 51,201
Light Industry 1 0.296 2,990 0.7 7,070 4,080
Road verges 4.09 0.296 12,227 0.5 20,655 8,427
road pavement 3.9 0.296 11,659 1 39,390 27,731
agriculture 23.41 0.296 69,987 0.40 94,576 24,590
SUBTOTAL Development Site
119.1 356,091 0.471 566,384 210,293
Potable Water collected from roofs
45,000
NET runoff from development site
0.438 521,384 165,293
Runoff from existing townsite onto development site
26.0 0 77,730 0.471 123,634 45,904
Water Quality Water runoff from roads will be collected at source in verge vegetated swales and flows up to the 1 year ARI event will be treated through bioretention systems with an area min 2% of the paved road and driveway area. Flows in excess of the 1 year ARI event will be conveyed by vegetated swales into reconstructed streamlines flowing through the community garden areas where further detention and treatment is provided before flowing into the storage dams and natural water courses.
Water runoff from lots together with water from community gardens and POS areas will be collected in swales and directed both into small offline wetland features for treatment and reconstructed wetlands along rehabilitated streamlines. The wetland water features and reconstructed wetlands will be sized to provide 10% of the contributing catchment area and will provide both attenuation of peak flows as well as stormwater quality outcomes. A stormwater management concept plan is included as part of the LWMS plan in Appendix B and shows flow patterns and the general location and layout of road drainage, bioretention treatment areas, swales, wetland treatment and reconstructed streamlines.
A summary of impervious areas and treatment areas by cluster is provided in Table 4 - Stormwater Treatment Areas.
The treatment of stormwater from the development area to a high standard is necessary not only to achieve stormwater management goals of Better Urban Water Management, but also to maintain water quality and prevent sedimentation of the two water storage dams.
Examples of bioretention treatment systems in narrow road verges to collect and treat road drainage is shown above in Figure 12. Examples of treatment wetlands within an urban environment are shown in Figure 13.
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Figure 12 Narrow Roadside Bioretention Swale
Figure 13a - Stormwater wetland treatment system, Margaret River
Figure 13b - Stormwater Wetland shortly after establishment
Predevelopment and Post Development Runoff The predevelopment conditions are estimated based on average values for the Chapman brook subcatchment at Forest Grove which is the nearest stream gauging station. Approximately 30% of the annual rainfall over the subcatchment is recorded as streamflow.
The change of lands to urban development will result in increased hard surfaces and drainage infrastructure resulting in increased runoff volumes from roads, driveways, paths, paving however runoff from roofs will be captured in rainwater tanks and used as potable water significantly reducing stormwater runoff from roof areas in the development.
Estimated changes to runoff volumes are summarised in Table 4 Stormwater Runoff Summary with major sources of increased runoff is residential lots with increases in paved areas, POS with improved drainage measures and roads due to paving of roads, parking and driveways.
With a relatively large roof area required for collection of rainwater for potable use, the majority of runoff from roofs will be required to be captured and stored for use. In order to meet the potable water use requirements of 150L/person/day, an average roof area of 184m² per lot is required to capture a total potable water volume within the Witchcliffe Ecovillage of 45ML for residential use.
Stormwater From Lots Stormwater from lots will be minimised due to collection of roof runoff in rainwater tanks for potable use, thus stormwater runoff from lots will be restricted to tank overflows, runoff from impervious areas such as paving and driveways, runoff from ancillary structures that are not connected to tanks (although most
Table 4 - Stormwater Treatment Areas
Cluster 1
Cluster 2
Cluster 3
Cluster 4
Cluster 5
Cluster 6
Cluster 7
Cluster 8
Cluster 9
Cluster 10
Cluster 11
Cluster 12
Cluster 13
Cluster 14
Cluster 15
Total
AREAS CONNECTED TO BIORETENTION TREATMENT SYSTEMSRoad Length m 795 170 355 545 540 285 - 430 145 560 95 825 390 305 400 5,840 Pavement Area m² 3,975 850 1,775 2,725 2,700 1,425 - 2,150 725 2,800 475 4,125 1,950 1,525 2,000 29,200 Diveways m² 360 420 450 450 720 840 360 570 660 900 390 1,080 810 570 480 9,060Portion of lots paved, not connected to water tank
10% 3,063 2,412 2,806
Bioretention Area 2% of contributing area
m² 148 25 45 64 68 45 55 54 28 74 73 104 55 42 50 931
AREAS CONNECTED TO WETLAND TREATMENT SYSTEMSCommunity Garden Area m² - 4,214 6,812 6,883 8,322 13,100 - 14,800 10,100 8,000 - 12,800 9,216 8,000 7,980 110,227Portion of lots paved, not connected to water tank
10% - 1,563 2,374 2,133 2,650 3,589 - 3,498 3,577 3,049 - 4,873 3,120 2,409 2,555 35,389
Wetland Treatment Area m² - 578 919 902 1,097 1,669 - 1,830 1,368 1,105 - 1,767 1,234 1,041 1,053 14,562
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ancillary structures will be connected to assist with water collection) and any overland flow from landscaped areas. Runoff from driveways will flow overland into road systems while remainder of stormwater from lots will flow overland into community garden areas which will be graded toward treatment areas and drainage lines within the community gardens. There will be no requirement for stormwater management devices within lots for any structures connected to rainwater tanks. Any roofs that are not connected to rainwater tanks must have a small rain gardens provided within the lots to avoid any discharge onto neighbouring property or to prevent concentrated runoff into community garden areas.
Water Quality Monitoring Water quality has been carried out for existing streams and dams as shown in the locations shown in Figure 14 and described in Table 5. Monitoring is to be carried out in winter (July / August) by the developer for 12 months post completion.
Table 5 - Water Quality Monitoring Locations Description
Monitoring Location Description
North 1 Northern stream at site boundary
Central 1 Central stream at entry to dam
Central 2 Central Dam
South 1 Southern stream from development at entry to dam
South 2 Southern stream from agricultural area at entry to Dam
South 3 Southern dam (to be constructed)
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Table 6 - Detention Volumes in Stormwater Treatment Areas
Detention Volume @ 100mm in wetland areas
Detention Volume @ 300mm in bioretention areas
Total Volume in Treatment areas
Detention Volume in Dams @ ∆h=50mm
kL kL kL kLCluster 1 - 44 44Cluster 2 58 8 65Cluster 3 92 13 105Cluster 4 90 19 109Cluster 5 110 21 130Cluster 6 167 14 180Cluster 7 - 17 17Cluster 8 183 16 199Cluster 9 137 8 145Cluster 10 110 22 133Cluster 11 - 22 22Cluster 12 177 31 208Cluster 13 123 17 140Cluster 14 104 13 117Cluster 15 105 15 120Total 1,456 279 1,735 3,265
Detention of Peak Flows Peak flows from storm events are attenuated by considerable storage volumes within the development area including on lot rainwater collection tanks, stormwater treatment systems (bioretention and wetland treatment areas), streamlines and water storage dams. Detailed modelling has not been prepared at this stage as the provision of dam storages within the development area provide detention volumes considerably in excess of that required for managing peak flows and calculation of storage within the conveyance system requires more detailed earthworks and landscape design.
To provide an indication of the capacity of the water storages within the development to attenuate peak flows the following example is provided. A 5 year ARI event in the central dam catchment with a time of concentration of 15min has a rainfall intensity of 58mm/h and a total runoff volume of approximately 1,200m³ from the development area and an increase in peak flows post development (prior to detention) of approximately 500m³ . The surface area of the dam is approximately 2 Ha, thus the increase in flow for the event represents 1% of the dam capacity and is retained in the dam with an increase in water level of 25mm excluding dam outflows i.e. this increase in level of the dam will only occur if the dam
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Figure 14 - Surface Water Monitoring Locations
does not overtop the spillway. The dam outflows (both bypass flows and spillway flows) provide flow patterns more consistent with the predevelopment natural environment.
In addition to dam and detention basin storage volumes, approximately 1,700m³ is provided in stormwater treatment areas and approximately 30,000m³ of rainwater tank storage capturing 44,500m³ of roof runoff will be provided within the development. A breakdown of stormwater storages in bioretention and wetland treatment systems is summarised in Table 6 - Stormwater Detention Volumes in Treatment Areas.
Major Events All roads and lots are graded to stream corridors or community gardens. A overland flow path from each community garden to stream corridors is provided. All major events including the 100 year ARI event flow overland through community gardens into stream corridors. All lots are to be finished at least 300mm above adjoining 100 year ARI water levels in community gardens or stream corridors.
The existing dam has a constructed spillway designed to protect the structural integrity of the dam in major events and while there is expected to be a small increase in peak flows for the 100 year ARI event into the dam post development, the large surface area of the dams (6.5Ha) will mitigate peak flows out of the dam, no significant increase in peak flows is likely and no down stream safety risks have been identified. Notwithstanding a review of the spillway capacity will be carried out and guidelines prepared for future management of the spillways to ensure long term safe operation and management of the dams. The proposed dam will have a spillway capacity constructed to cater for greater than 100 year ARI flows from the dam. The minimum event for which the spillway capacity will be designed will be determined as part of the spillway review and dam design and is likely to allow for 1:1000 year event based on best practices for small dams.
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Streamline rehabilitation Existing streamlines within the urban areas are currently cleared and grazed and are heavily degraded. A photograph showing their existing condition is shown in figure 15. An example of a streamline where the developer has commenced rehabilitation of a degraded streamline on the site on agricultural land to the south of the urban area is shown in Figure 16 (after fencing) and Figure 17 showing recent progress of plantings.
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Figure 15 - Existing degraded streamline, Northern Catchment
Figure 17 - Southern streamline rehabilitation progress
Figure 16 - Southern streamline, after fencing prior to revegetation
Models and Assumptions Annual flows are based on average catchment areas and runoff rates with predevelopment runoff coefficients are determined based on average values for the Chapman Brook catchment at Forest Grove, average 30% runoff.
Detailed stormwater calculations have not been carried out at this stage and will be competed as part of the Urban Water Management Plan and detailed design prior to subdivision. Rational method and regional flood frequency factors for South West Western Australia will be used to model peak flows for the stormwater conveyance system. Rainfall data for flood estimation will be based on intensity, Frequency and Duration data for Margaret River. Design of stormwater systems as per Australian Rainfall and Runoff Volume 1 Chapter 14 is based on water being collected and transferred by an underground pit and pipe system with an overland flow path for major event. The Witchcliffe Ecovillage stormwater management concept has water transfer predominantly by surface drainage features, thus design of the system will include calculation of the capacity of surface water feature section by section using manning formula, however the same principals and use of rational method for peak flow estimation will be used. It is likely that this approach will overestimate peak flows in the system as it will not make allowance for the storage volume within the conveyance network however given that the catchments are small, well defined and have gentle grades it is considered unnecessary to use runoff routing methods which are more complex and lack calibration data for catchments in this area.
Calculation of storage volumes in bioretention areas is based on water depth of 300mm and storage volumes in wetland treatment areas are based on increase in water depth of 100mm. Calculation of water storage volumes in dams is based on increase in water depth in dams of 50mm. This will be achieved through flow depth of 50mm over the dam spillway. A review of the capacity of the dam spillway will also be carried out by the developer.
Potable water consumption is calculated based on Health Department guidelines of 150L/person/day which is consistent with average water use excluding outdoor (garden water use) in Perth water consumption studies. This figure is likely to be conservatively high for Witchcliffe Ecovillage as design guidelines will require AAA rated water use appliances and responsibility of homeowners for managing their own tank water supply will drive greater water efficiencies.
Rainwater tank volume requirements are based on potable water use of 150L/person/day or a reduced consumption of 122L/person/day where dwellings are required to have composting toilets (affordable housing). Affordable housing lots will be required to have composting toilets as the smaller roof areas of affordable dwellings will not be adequate for rainwater collection if flushing toilets are used. Rainwater tank volumes have been based on Bureau of Meteorology rainfall records for Witchcliffe which have been collected on the property since 1996. Model includes a 10% reduction to allow for drier years than recorded during this period and a further 10% reduction to allow for losses including splashing and first flush diversion.
Construction Staging Issues The development will be constructed in three stages in line with strata lot boundaries with the number and timeframe for stages dependent on uptake of lots by the market. The lots are arranged in clusters around community gardens and the minimum size stage will be at the cluster level. In addition to housing clusters there is a village core with community facilities and commercial lots and a strip of larger lots (Lifestyle Lots) along Bussell Highway providing a buffer between the highway and more intensive land uses. The cluster numbering is shown on the Water Management Strategy Plan attached at Appendix X. Cluster numbers are also given to village core and a lifestyle lots.
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Further Investigations Water Supply Water supply requirements for the residential components of the development are well defined and based on established demand figures in other areas of Western Australia however it is expected that the Witchcliffe Ecovillage will achieve lower water consumption. Investigation of actual water consumption achieved is proposed and use of this data to refine water storage models is proposed.
Further investigation of water requirements thus roof collection area and tank storage for community and commercial areas is required. There is considerable scope for flexibility in water supply requirements to these areas as more detailed development proposals emerge due to availability of non potable dam water, not withstanding the potable water requirements for community purposes will need to be supplied by onsite collection and storage.
Wastewater The treatment and onsite reuse of wastewater for agricultural purposes will require further investigations and studies including a Nutrient Irrigation and Management Plan and Recycled Water Quality Management Plan.
Composting toilets present the best sustainability outcome in terms of reduced water and energy use and nutrient capture and reuse but suffer from poor user perceptions. It is proposed to carry out further research into user attitudes of potential future residents and carry out a program to promote the benefits and construct examples of composting toilets to improve familiarity with domestic composting toilet systems.
Stormwater Stormwater quality monitoring to determine baseline information for surface water quality is in progress and will be ongoing as the project is developed.
A dam spillway capacity review will be carried out to ensure risk management is in line with best practice guidelines.
Soils As part of geotechnical investigations for the development soil testing will establish nutrient retention capacity of soils in irrigation areas (part of nutrient irrigation management plan).
Field monitoring of soils in lower valley areas identified as moderate to low risk of acid sulphate soils will be carried out to confirm assumptions and past experience that acid sulphate soils are not present on site.
Monitoring Program Water Consumption Potable water consumption is closely linked to wastewater generation and will be derived from recording wastewater flow volumes
Irrigation water use will be monitored including both energy consumption of irrigation pumps and flow meters at irrigation water sources.
Wastewater Wastewater quality will be monitored and reported as per licensing requirements for wastewater treatment systems.
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Wastewater flows will be monitored to determine the volume of water treated which is required for managing treated water storage and reuse. It will also be used to derive potable water consumption within the village. Note that both inflow and outflow volumes will need to be monitored where the system is subject to rainfall, evaporation and transpiration effects.
Stormwater The developer is committed to monitoring stormwater quality at surface water quality monitoring locations as identified in Figure 14. Further monitoring of water quality by residents will also be encouraged at a cluster level to assist residents to have a greater understanding of their place in the catchment and their role in managing stormwater treatment bioretention systems on their verges and stormwater treatment wetlands within their community garden. While the details of such a program will need to be developed in conjunction with representatives from the community, it is envisaged that this will include educational component, collaboration with the local catchment group and would include sampling and testing of water quality and sharing the information at a village level through a community newsletter.
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Appendix A - Stormwater Delivery Approach for WA, WA Stormwater Management ObjectivesObjectives Witchcliffe Ecovillage Approach
Protect water quality Stormwater remains clean and retains its high value Implement best management practice on-site.Implement non-structural controls, including education and awareness programs. Install structural controls at source or near source.Use in-system management measures.Undertake regular and timely maintenance of infrastructure and streetscapes.
Water collected from roofs for potable use Road runoff treated at source (roadside bioretention) Treated stormwater collected and stored for reuse in development. Community involvement in stormwater management, particularly in stormwater management systems within community gardens.
Protect infrastructure from flooding and inundation Stormwater runoff from infrequent high intensity rainfall events is safely stored and conveyed Safe passage of excess runoff from large rainfall events towards watercourses and wetlands. Store and detain excess runoff from large rainfall events in parks and multiple use corridors. Safely convey excessive groundwater to the nearest watercourse.
Lot layout designed around surface water flow patterns with direct overland flow path from every lot to community garden. Overland flow paths from community gardens linked to multiple use corridors.
Minimise runoff Slow the migration of rainwater from the catchment and reduce peak flows Retain and infiltrate rainfall within property boundaries.Use rainfall on-site or as high in the catchment as possible.Maximise the amount of permeable surfaces in the catchment.Use non-kerbed roads and carparks.Plant trees with large canopies over sealed surfaces such as roads and carparks.
Stormwater collected in rainwater tank storage on lots. Collection of stormwater in vegetated swales (bioretention systems) alongside roads. Re-creation of natural pools to slow water runoff within community gardens. Infiltration of excess runoff from lots in private raingardens and frog ponds and infiltration in impermeable areas within community gardens.
Maximise local infiltration Fewer water quality and flooding problems Minimise impervious areas.Use vegetated swales.Use soakwells and minimise use of piped drainage systems. Create vegetated buffer and filter strips.Recharge the groundwater table for local bore water use.
Stormwater collected and conveyed above ground in surface features including streamlines, bioretention swales and ephemeral wetland systems. Minimal piped systems only to provide for road and path crossings. Revegetated streamlines Site soils generally not suited to use of soak wells, however onsite retention in rainwater tanks and surface water features is provided.
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Make the most of nature’s drainage Cost effective, safe and attractive alternatives to pipes and drains Retain natural channels and incorporate into public open space.Retain and restore riparian vegetation to improve water quality through bio-filtration.Create riffles and pools to improve water quality and provide refuge for local flora and fauna. Protect valuable natural ecosystems.Minimise the use of artificial drainage systems.
✔ Minimal piped drainage - only as required for road and path crossings. Riparian vegetation established in degraded waterways.
Minimise changes to the natural water balance Avoid summer algal blooms and midge problems and protect our groundwater resources Retain seasonal wetlands and vegetation.Maintain the natural water balance of wetlands.No direct drainage to Conservation Category Wetlands or their buffers, or to other conservation value wetlands or their buffers, where appropriate.Recharge groundwater by stormwater infiltration.
Season wetlands and vegetated streamlines recreated.
Integrate stormwater treatment into the landscape Add value while minimising development costs Public open space systems incorporating natural drainage systems.Water sensitive urban design approach to road layout, lot layout and streetscape. Maximise environmental, cultural and recreational opportunities.
A recreated natural stormwater management system comprising wetlands and streamlines is a prominent feature in every community garden with lots developed around the community garden and these natural water features. The stormwater management system will be at the core of the community’s environment, cultural and recreational areas.
Convert drains into natural streams Lower flow velocities, benefit from natural flood water storage and improve waterway ecology Create stable streams, with a channel size suitable for 1 in 1 year ARI rainfall events, equivalent to a bankfull flow. Accommodate large and infrequent storm events within the floodplain.Create habitat diversity to support a healthy, ecologically functioning waterway.
✔ iAll stormwater is collected in and flows through re-created natural streams and wetland treatment systems. Revegetation of streams and variety of wetland areas will create a diverse range of aquatic and riparian habitats.
Objectives Witchcliffe Ecovillage Approach
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Appendix B - Local Water Management Strategy Plan
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Appendix C - Witchcliffe Ecovillage Urban Water Cycle
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Appendix D - Water and Wastewater Calculations
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Appendix E - Stormwater Cluster Summary
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Appendix F - Witchcliffe Ecovillage Concept Plan
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Appendix G - Typical Wastewater Catchment Concept Plan
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Appendix H - Stormwater Catchment Diagram
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Appendix I - Tank Sizing Chart
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