LARA WEST GROWTH AREA (LWGA)

Transcription

1 Neil M Craigie Pty Ltd ACN ABN Waterway Management Consultants LARA WEST GROWTH AREA (LWGA) SURFACE WATER MANAGEMENT STRATEGY For: SMEC Urban Pty Ltd 9 June 2012 Director Neil McKinnon Craigie BE(Civil), MEngSci, MIEAust, CPEng nmcraigie@bigpond.com 15 Mulawa Street Croydon, Vic. 3136, Australia Telephone & Fax: (03)

2 TABLE OF CONTENTS 1. INTRODUCTION 1 2. EXISTING CONDITIONS AND DRAINAGE CONTROLS Description Catchments to Windermere and Kees Roads Catchment to Patullos and O Hallorans Roads Catchments to Cameron Crescent Subdivision Flood Extents Peak Flows and Flood Levels Catchments to Windermere and Kees Roads Other Peak Flows Volumetric Runoff 9 3. FACTORS TO BE CONSIDERED FOR DEVELOPMENT Philosophical Approach Study Area Values, Constraints and Opportunities Strategy Objectives WSUD Options Application to Lara West Growth Area Catchments to Windermere and Kees Roads (the Northeast Sector) Catchment to Patullos Road Catchments to Cameron Crescent Subdivision THE NORTHEAST SECTOR WATERWAY CONCEPT Floodplain and Waterway Management Considerations Geology, Geomorphology and Groundwater Considerations Flora and Fauna Considerations Cultural Heritage Considerations Design Criteria for the Proposed Floodplain Wetland System The Concept Design Concept Layout Wetland/Retarding Basin Form Open Waterway Form Drainage Levels and Quantities Flood Modelling Results 35 Neil M Craigie Pty Ltd ii

3 5. THE BALANCE CATCHMENTS WATER QUALITY TREATMENT PERFORMANCE SUMMARY AND CONCLUSIONS ABBREVIATIONS AND DEFINITIONS REFERENCES 50 Figures 1-4 Photos 1-9 Neil M Craigie Pty Ltd iii

4 1. INTRODUCTION This report updates the 6 April 2010 first report and presents results of hydrologic, hydraulic and water quality modelling for proposed development of the area originally referred to as Area 4 in the Lara Structure Plan but now known as the Lara West Growth Area (LWGA). This update has been prepared to respond to the revised existing conditions twodimensional modelling of the area that has just been completed by BMT WBM at the request of City of Greater Geelong (CoGG). The Lara West Growth Area relates to the land encompassed by Bacchus Marsh Road in the west, Windermere Road in the north, O Hallorans Road in the east and Patullos Road in the south. The Manzeene Avenue LSP area abuts the LWGA on the east side of O Hallorans Road. Within the overall PSP there are some distinct property groupings which relate to existing subdivision and usage, as summarised in Table 1 and shown on Figure 1. TABLE 1 Property references in Lara West Growth Area (refer Figure 1) Land Reference Area (ha) Existing Use Parcel A 187 Cropping/Grazing Parcel B 76 ~2 ha low density residential and some intensive agriculture (West Gateway) Parcel C 48 Cropping/Grazing Parcel D 48 Cropping/Grazing Parcel E 29 ~2 ha low density residential (Patullos Road) Total LWGA area 388 Parcel F (Manzeene Ave) 59 ~2 ha low density residential The whole of the land is part of the Hovell Creek catchment and the primary proposed land use is conventional residential development averaging at least 15 lots/ha. The 6 April 2010 study utilised the flood mapping done by WBM Pty Ltd 1 to determine the extent and levels of flooding across Lara West Growth Area under present day conditions. However new hydrologic, hydraulic and water quality models better suited to requirements were derived for study design purposes. For this update report BMT WBM have revised all the existing conditions flood modelling using the latest LiDAR survey information. The revised hydraulic modelling outputs have been used to prepare this update report. 1 Lara Flood Study Stage 1, Revision 2, 8/1/02, WBM Oceanics Australia for CoGG. Neil M Craigie Pty Ltd 1

5 Section 2 describes existing drainage conditions. Section 3 sets out the philosophy underpinning the surface water management strategy and water sensitive urban design. Section 4 presents summary results for each flood modelling scenario for the main northeast sector catchments. Section 5 discusses requirements for the balance catchments. Section 6 discusses water quality treatment results. Section 7 presents summary and conclusions. Neil M Craigie Pty Ltd 2

6 Windermere Rd Parcel B (West Gateway) Hovell Creek Parcel C Parcel D Kees Rd Parcel A Parcel F (Manzeene Ave LSP) Bacchus Marsh Rd Patullos Rd Parcel E (Patullos Rd) Figure 1 Google Earth extract showing the Lara West Growth Area and property groupings Neil M Craigie Pty Ltd 3

7 2. EXISTING CONDITIONS AND DRAINAGE CONTROLS 2.1 Description Although the whole of the LWGA forms part of the Hovell Creek catchment, there are no direct outfalls to the creek within the LWGA boundaries. The component subcatchments, primary drainage paths and the area affected by inundation under existing conditions in the 100 year ARI flood event (as determined in the 2002 study) are shown on Figure 2.1. The latest flood modelling outputs generated by BMT WBM are shown on Figure 2.2. It is noted that the mapped flood extents are virtually identical to those shown on Figure 2.1, apart from the interaction with the tributary floodplain north of Windermere Road. The 2002 study by WBM did not include that tributary. Figure 2.3 shows the location and references used by BMT WBM to generate peak discharges from the 2D model across the LWGA Catchments to Windermere and Kees Roads The rural lands west of the LWGA boundaries are dominated by the steep escarpment which parallels Bacchus Marsh Road. Diffuse runoff from the flat headwater lands (generally above the 80 m contour), is concentrated into the steep gullies which are etched into the escarpment between contour levels of about 80 and 40 m. At the foot of the escarpment the gullies lose definition and the waters are mostly discharged as sheet flow towards Bacchus Marsh Road at about 2% slope. There are two primary drainage alignments; in the north near the West Gateway intersection, and in the south between Staceys Road and Patullos Road. Bacchus Marsh Road forms a barrier to the flows. In the south, a group of 3 sets of culverts discharges some of the water from the Staceys Road tributary and flanking smaller streams along a 300 m section of the road generally between Patullos Road and Staceys Road. However overtopping of the road extends at least 500 m in major floods. In the north another set of culverts discharges water under Bacchus Marsh Road just south of West Gateway. Again overtopping of the road occurs in major floods but to a lesser degree with extent of about 150 m. East of Bacchus Marsh Road the floodwaters are widely dispersed and shallow as shown by the mapped flood extents. This reflects the flat topography in the northsouth plane and good grade of 0.5-1% in the west-east direction. A smaller catchment area enters from south of Patullos Road. Drainage gradients on this tributary are very flat and both the 2002 and current hydraulic modelling extents shows surface flooding extending around both sides of a small rise within Lot A. A Neil M Craigie Pty Ltd 4

8 constructed open drain has been built from Patullos Road around the west side of the small rise, north to the West Gateway subdivision (picking up the western catchments), from where it turns east and northeast to Windermere Road. This drain serves as the main outfall (for low flows at least) for all catchments to the west, including the West Gateway subdivision. A set of culverts is constructed under Windermere Road but these appear to mainly drain table drain water from the road back into an existing dam on the south side of the road. Generally in the northeast sector of the Lara West Growth Area area, there are negligible defined drainage lines other than shallow table drains in road reserves and some minor drains in private lands. In times of flooding the waters extend more than 600 m wide and disperse as mostly shallow overland flow in two main directions which are dictated by natural surface levels: northeasterly across Windermere Road towards the Hovell Creek tributary at Duggans Lane, and easterly towards O Hallorans Road thence through to Kees Road and eventually out to Hovell Creek. Along O Hallorans Road the mapped flood extent is some 700 m wide, reducing to m at Kees Road, from which point it merges with the Hovell Creek floodplain. Topographic information indicates that the boundaries between land subject to or not subject to inundation are blurred and freeboard above flooding is minimal in the north-east sector of the LWGA. The most recent hydraulic modelling by BMT WBM shown on Figure 2.2 has confirmed interaction of flood flows between the LWGA depressions and the large tributary floodplain to the north of Windermere Road. As depicted by the flow locations on Figure 2.3, flows can cross Windermere Road from south to north at times towards O Hallorans Road (Locations Wind_1-3), but larger flows cross over the road from the north and enter the LWGA near Goulburn Park Drive (Wind_Rd) Catchment to Patullos and O Hallorans Roads This rural-residential subdivision falls southeasterly at grades of 0.5% to 1.5% to the intersection of Patullos and O Hallorans Roads. Drainage outfall is via the table drains in Patullos Road which have limited capacity at best. Flooding problems are significant downstream. Neil M Craigie Pty Ltd 5

9 The May 2012 mapping on Figure 2.2 shows areas of land being affected by flooding but these are just very shallow local catchment overland flows Catchments to Cameron Crescent Subdivision Two small catchments in this rural-residential subdivision in Manzeene Ave fall easterly to trapped lowpoints at the rear of existing residences in Cameron Crescent (south of Conole Court) and Denise Court. According to available information held by CoGG, small pipelines are provided to the rear of No s Cameron Crescent but not to the lowpoint near Denise Court. The May 2012 mapping on Figure 2.2 shows areas of land being affected by flooding extending from the very shallow local catchment overland flows within the LWGA across Manzeene Avenue and to the rear of the residential subdivisions and along the Patullos Road frontage. 2.2 Flood Extents The total area of land within the LWGA that is subject to inundation in the 100 year ARI event (as determined from the 2002 flood mapping by WBM Oceanics Australia) is just over 182 ha (about 47%) of the private lands, as set out in Table 2. TABLE 2 Property groupings and land subject to inundation in the 100 year ARI event in the LWGA (refer to Figure 2) Land Reference Area (ha) Area subject to inundation (ha) Area not subject to inundation (ha) Parcel A Parcel B (West Gateway) Parcel C Parcel D Parcel E (Patullos Road) Total Parcel F (Manzeene Ave) The 2012 mapping by BMT WBM shows larger areas are affected by shallow inundation. Water depths across the vast bulk of the area that is shown as subject to inundation on Figure 2.2 are very shallow (less than 100 mm). Subject to best practice outcomes being realised there are major opportunities to reduce flood extent and foster development of the LWGA lands, through strategic cut/fill earthworks. Neil M Craigie Pty Ltd 6

10 2.3 Peak Flows and Flood Levels Catchments to Windermere and Kees Roads This SWMS study has included preparation of a new RORB hydrologic model of the primary catchment area to Hovell Creek for both existing conditions and future development conditions. This model utilised a much finer catchment subdivision setup than that for the original RORB model developed by WBM Pty Ltd in 2002 so as to be able to better simulate various drainage solutions in the majority of the LWGA. Figure 2.1 shows the subarea arrangement in the RORB model. The model parameter values used by WBM were initially adopted for this present investigation. To best suit urban design purposes the loss model was changed to the initial loss-runoff coefficient model. The loss model parameters were adjusted until peak flows reasonably replicated those obtained with the initial loss-continuing loss model. The adopted parameters are as follows: Kc=6.5, m=0.7, Initial Loss 20 mm, Pervious area runoff coefficient = 0.95 (>=5 year ARI), 0.85 (1 year ARI). The revised RORB model was then used by BMT WBM to assist in their new hydraulic modelling. The RORB model has in turn been updated again in this report to reflect the key outputs of the new existing conditions hydraulic modelling as well as adjustments to the proposed stormwater management system within the LWGA that have occurred through evolution of LSP planning. Hydrographs of inflow occurring at WG_Break and Wind_Rd generated from the 2D hydraulic model were input to the RORB model at those locations. Peak flow predictions for major flood discharges within and downstream of the LWGA to Hovell Creek match well with those from the BMT WBM study as shown by the comparison in Table 3.1. Critical duration for the 100 year ARI event was 9 hours in RORB as was also obtained by WBM (2002) and BMT WBM (2012). For 2 and 10 year ARI events the RORB model, at first glance, appears to overestimate flows compared with the 2D model. However the 2D hydraulic model results were only provided for 9 and 36 hour durations whereas the RORB results have considered all durations. As a check the RORB results for only the 9 and 36 hour durations are listed against the 2D model results for 2 year and 10 year ARI s in Tables 3.2 and 3.3. These tend to support the impression that RORB increasingly over-estimates peak discharge in the lower part of the catchment as ARI reduces. However the differences are not significant for events greater than 10 years ARI. Neil M Craigie Pty Ltd 7

11 To be conservative, the lower of the peak flow rates at O Hallorans Road as determined by RORB and BMT WBM will be used as the maximum permissible discharges for all future development scenarios in the LWGA. TABLE 3.1 Peak Discharges (m3/s) Location 2 year ARI 10 year ARI 100 year ARI (9 hr) RORB BMT WBM (2012) RORB BMT WBM (2012) RORB BMT WBM (2012) South trib y at Bacchus 3.4 (48) 3.0 (36) 7.1 (9) 6.5 (9) Marsh Road South trib y u/s confluence 4.3 (48) 8.0 (9) North trib y at Bacchus 2.4 (12) 2.0 (36) 5.2 (9) 5.0 (9) Marsh Road Goulburn Park Drive 7.1 (48) 13.3 (9) Power/Water Easement 7.1 (48) 6.7 (36) 13.3 (9) 14.0 (9) Windermere Road 7.2 (48) 5.3 (36) 13.7 (9) 12.9 (36) O Hallorans Rd * 8.1 (48) 5.7 (36) 15.5 (12) 13.9 (36) Kees Rd Outfall 8.5 (48) 5.7 (36) 15.5 (12) 14.0 (36) TABLE 3.2 Comparison of Peak Discharges (m3/s) for 2 yr ARI 9 and 36 hr duration Location RORB BMT WBM (2012) RORB BMT WBM (2012) South trib y at Bacchus Marsh Road South trib y u/s confluence North trib y at Bacchus Marsh Road Power/Water Easement Windermere Road O Hallorans Rd * Kees Rd Outfall TABLE 3.3 Comparison of Peak Discharges (m3/s) for 10 yr ARI 9 and 36 hr duration Location RORB BMT WBM (2012) RORB BMT WBM (2012) South trib y at Bacchus Marsh Road South trib y u/s confluence North trib y at Bacchus Marsh Road Power/Water Easement Windermere Road O Hallorans Rd * Kees Rd Outfall Peak flood levels were not listed in WBM (2002), however by cross reference against the 250 mm contour data reasonable estimates have been made and are summarised in Table 4, together with the output from the most recent modelling by BMT WBM. The two sets of estimates are very closely matched. Neil M Craigie Pty Ltd 8

12 The May 2012 levels determined by BMT WBM become the maximum permissible levels that can be created by any new drainage works within the LWGA. It would be expected that some reductions should be feasible via strategic earthworks design. TABLE 4 Estimated 100 year ARI flood levels (from WBM-2002 and 250 mm topographic data, and BMT WBM 2012) Location Estimated 100 year ARI flood level (m) WBM 2002 BMT WBM 2012 North trib y on west side of Bacchus Marsh Road North trib y on east side of Bacchus Marsh Road South trib y on west side of Bacchus Marsh Road South trib y on east side of Bacchus Marsh Road North side of Patullos Road Floodplain 300 m north of Patullos Road West side of Goulburn Park Drive South side of Windermere Rd (@ culverts) North side of Windermere Rd (@ culverts) West side of O Hallorans Rd * West side of Kees Rd Hovell Creek upstream of Windermere Road (east of Duggans Road) Hovell Creek at Kees Road outfall Other Peak Flows Peak flows in the small catchments in the southeast sector draining to Patullos Road and the existing subdivision in Cameron Circuit have been estimated using the Rational method and are summarised in Table 5. TABLE 5 Location Rational Method Peak Discharges (m3/s) Catchment 1 year 5 year 10 year 20 year 100 year (ha) ARI ARI ARI ARI ARI Patullos Road/O Hallorans Road intersection Rear Cameron Crescent Rear Denise Court Volumetric Runoff The MUSIC 2 model has been used in this study to assess volumetric runoff regimes, pollutant load regimes (for existing and developed conditions) and sizing and effectiveness of proposed water quality treatment facilities. The model was run with CoGG s standard 6 minute continuous dataset for Geelong North for the decade. The results are listed and discussed in Section 6. 2 MUSIC is the acronym used for the Model for Urban Stormwater Improvement Conceptualisation software developed by the Cooperative Research Centre for Catchment Hydrology to model urban stormwater quality management schemes. Neil M Craigie Pty Ltd 9

13 100 year ARI Flood Extents as mapped by WBM Oceanics Aust (2002). Areas within these extents are subject to inundation under existing conditions. Revised hydraulic mapping showing 200 mm flood surface contours is shown on Figure 2.2. N Denise Ct catchment Cameron Circuit catchment Patullos Rd/O Hallorans Rd catchment Figure 2.1 RORB subcatchemt plan for the primary drainage catchment and other minor catchments in the LWGA Neil M Craigie Pty Ltd 10

14 Figure 2.2 Revised flood extents and water surface contours incorporating the tributary floodplain north of Windermere Road (BMT WBM May 2012, Draft) Neil M Craigie Pty Ltd 11

15 Figure 2.3 Cross-sections for hydrographs extracted from the 2D hydraulic modelling (BMT WBM May 2012, Draft) Neil M Craigie Pty Ltd 12

16 3. FACTORS TO BE CONSIDERED FOR DEVELOPMENT 3.1 Philosophical Approach From a holistic viewpoint the surface water management strategy for any property development must address contemporary Best Management Practices, through application of the principles of Water Sensitive Urban Design (WSUD). As set out in Section 1.3 of Australian Runoff Quality A Guide to Water Sensitive Urban Design (Engineers Australia 2006), the guiding principles of WSUD are centred on achieving integrated water cycle management solutions linked to an ecologically sustainable development focus aimed at: 1. Treating urban stormwater to meet water quality objectives for reuse and/or discharge to surface waters; 2. Using stormwater in the urban landscape to maximise the visual and recreational amenity of developments; 3. Preserving the natural hydrological regime of catchments; 4. Reducing potable water demand through water efficient appliances, rainwater and greywater reuse; 5. Minimising wastewater generation and treatment of wastewater to a standard suitable for effluent reuse opportunities and/or release to receiving waters; In regard to stormwater (surface water) management, which is the subject of this report, ARQ 2006 lists best practice objectives as including: 1. providing flood protection and drainage; 2. protecting downstream aquatic ecosystems (including groundwater systems); 3. removing contaminants; 4. promoting stormwater elements as part of the urban form. Urban Stormwater-Best Practice Environmental Guidelines were developed by the Victorian Stormwater Committee in 1999 and have since been incorporated into the State Planning Policy Framework. These Guidelines define the best practice performance objectives for Total Suspended Solids (TSS), Total Phosphorus (TP), Total Nitrogen (TN) and Gross Pollutants (GP) to be 80%, 45%, 45% and 70% reduction of the typical urban annual loads respectively. Neil M Craigie Pty Ltd 13

17 Clause 56 of the Victorian Planning Provisions (Sustainable Neighbourhoods) was brought into effect in The Integrated Water Provisions of Clause 56 require all planning applications for subdivision lodged across Victoria to comply with the current Victorian best practice stormwater quality performance objectives through the use of WSUD and, unless approval is given to the contrary by the responsible authority and there are no detrimental impacts downstream, also ensure no increase in peak discharges of stormwater from the development. 3.2 Study Area Values, Constraints and Opportunities Selection of appropriate WSUD techniques must address the particular characteristics, constraints, opportunities and values to be protected in and around the study area. These are considered to be as follows: 1. There is no visible evidence of significant saline influences on the land but groundwater in this area is suspected to be at least brackish in quality. Regardless of any threat that may be posed by saline or brackish groundwater, lining of waterbodies is likely to be needed both to suppress the effects of soil dispersivity and to mitigate any seepage losses. Specific soil treatment measures will need to be determined by future geotechnical investigations. 2. Overland flooding problems are well known across the study area and along the Hovell Creek floodplain margins. Future development must not increase peak discharges in the existing outfalls, nor detrimentally impact on the passage or level of floodwaters. 3. Existing bed levels and low flow water levels along Hovell Creek cannot be lowered by any works associated with development in the LWGA. 4. No upgrading of culverts or changes to the pavement levels along Bacchus Marsh Road should be required to facilitate LWGA development. 5. No upgrading of culverts or changes to the pavement levels along Windermere Road (east of Kees Road) or Duggans Lane should be required to facilitate LWGA development. 6. No upgrade of existing table drains or culverts in Patullos Road should be required to facilitate LWGA development. 7. The transmission towers and the new recycle water main pass through the middle of the LWGA in the north-south direction with a gas main traversing east-west around 250 m north of Patullos Road. No other major services are known to traverse the study area. 8. The lands in the northeast sector are flat or gently sloping with inadequate outfall depths at present to service future development drainage systems. Upgrade and Neil M Craigie Pty Ltd 14

18 lowering of existing culverts under Windermere Road (west of Duggans Lane), O Hallorans Road and Kees Road are feasible options that must be considered. 9. The proposed development will generate increased stormwater runoff from roofs and other impervious areas which must be properly managed to avoid aggravating existing drainage quantity and quality problems. This additional runoff could offer reuse supply opportunities. It could also be used to support significant wetland development as part of the surface water management system. 10. Other than a few small patches of vegetation near Patullos Road in Parcel A, no significant remnant flora and fauna or archaeological heritage issues are known to affect the subject lands within the LWGA boundaries. 11. There are no significant remnant waterway, floodplain or wetland features remaining on the land in the LWGA. 12. The diversity of existing landownership and land use across the LWGA is likely to result in varying attitudes and opinions towards future development, waterway alignment and water management asset location and design. 3.3 Strategy Objectives In no order of priority, the specific surface water management strategy objectives for the study area are as follows: minimise offsite discharge of stormwater pollutants to Hovell Creek, Limeburners Bay and Port Phillip Bay, both during development and in the long term; ensure any offsite discharge of pollutants generated from the proposed urban development fully complies with best practice management objectives for environmental protection in Hovell Creek, Limeburners Bay and Port Phillip Bay; take up practical opportunities for reuse of site stormwater, to reduce mains water input to the property and discharge of stormwater and pollutants, and/or use the water to support wetland development within the site; maximise the economic, environmental, aesthetic and recreational benefits of surface water throughout the development, while ensuring that such use does not result in any loss of user safety or creation of nuisance; mitigate existing flood threats within and downstream of the study area by ensuring no increase in peak discharges from developments and by upgrading/deepening drainage outfalls where possible; protect all new development areas from flooding threats; Neil M Craigie Pty Ltd 15

19 design any future waterway and wetland system in sympathy with the natural topographic characteristics; layout and design all waterways and water management assets having regard to different landownership and use wherever practicable; subject to the above objectives being satisfactorily addressed, locate and design new surface water management assets to minimise capital investment and operation and maintenance costs in the long term. 3.4 WSUD Options Constructed wetlands are one WSUD approach, where management response is concentrated into one or more defined areas. Other techniques that are currently being actively promoted by bodies such as Melbourne Water Corporation (MWC), the Corangamite Catchment Management Authority (CCMA) and the Environment Protection Authority (EPA), focus on the site or precinct scale and are aimed at reducing runoff peaks, delaying runoff response and minimising transportation of sediments through the use of "natural" drainage line treatments, swale/trench infiltration systems, grass buffer strips and the like. WSUD techniques that can be applied at the site (individual lot) or precinct scale, offer potential for achieving required water quality treatment with reduced impact on developable land yield. More recently, additional emphasis has been placed on re-use potential of stormwater to reduce mains water usage and downstream impacts of increased stormwater runoff frequency and volumes. This has a significant public profile at present during the prolonged major drought we are experiencing and long term sustainability of potable water supplies are of considerable concern throughout the state. Better management and integration of the urban water cycle is seen by most as being imperative for maximising longer term environmental improvements in our receiving waterways, lakes and bays, as well as for lowering the need for further water harvesting. From the site values, constraints and opportunities, it is possible to short list and assess likely feasible WSUD options for water quality and quantity management on the subject site. Table 6 provides an overview of the general applicability of the range of WSUD techniques. Neil M Craigie Pty Ltd 16

20 TABLE 6 WSUD Technique Rain tanks - garden water supply only Rain tanks - toilet flushing and garden watering supply Rain tanks - toilet flushing, hot water supply, and garden watering Roof water conveyed directly to building landscaping. Roof water to constructed raingardens with underground drainage Greywater to gardens Greywater to toilet flushing Parking Lot Storage APPLICATION OF WSUD TECHNIQUES TO PROPOSED DEVELOPMENT IN THE LARA WEST GROWTH AREA STUDY AREA Applicability Discussion to study area (H - High, M - Medium, L - Low) M Reduces mains water use if used properly but is relatively costly. No practical value in mitigating runoff if not used properly by owner. Unless very large tanks are used does not reduce flood peaks in wet seasons in any case. H Reduces mains water use thoughout the year and is effective at reducing volume, frequency and peak rates of stormwater runoff, especially if large tanks are used (allowing some capacity to be reserved for flood event storage). If properly plumbed in to new housing during construction, operation is less dependent on owner acceptance and management as toilet flushing is constant through the year. Unless useable in industrial process systems, roofwater offers comparatively lesser value in industrial developments. H Further reduces mains water use throughout the year and is very effective at reducing volume, frequency and peak rates of stormwater runoff. However it is even more costly in capital and operating terms owing to treatment requirements and extra plumbing costs associated with use in hot water supply systems. May be some health concerns and resistance from agencies and the community with hot water use. Unless useable in industrial process systems, roofwater offers comparatively lesser value in industrial developments. L L-M L L-M L Low cost, reduces runoff from site, but is restricted to small areas. Needs soil with acceptable drainage characteristics so that waterlogging and growth of rank weeds does not occur. Needs additional works to prevent uncontrolled discharge from site through other properties (eg., overflow connections to property drains, grading of gardens to drainage point and/or sealed pavements graded out to street). May be difficult to manage in longer term with property turnover. Not suited to land with erosive/dispersive soils and/or very flat drainage gradients. Costly but reduces runoff from site. If combined with raintanks can reduce use of mains water but at further increased cost. Requires dedicated space and specialised vegetation and equipment and maintenance to function correctly. Best suited to higher density sites with body corporate management. Unless useable in industrial process systems, roofwater offers comparatively lesser value in industrial developments. Health and maintenance concerns. Special approvals and monitoring required. Not favoured under current regulatory environment in normal residential development. Does not in any way mitigate generation of stormwater from development. Storage difficulties and possible detrimental impacts on plants and soils. Possibility of off-site discharge over wet seasons. Does not in any way mitigate generation of stormwater from development. Uncertain public acceptance due to poorer quality visual and odour characteristics. Storage difficulties. No significant water quality benefits. Nuisance to owners at the lot scale. Not suited to steeply sloping land. Neil M Craigie Pty Ltd 17

21 TABLE 6 WSUD Technique Porous pavements Grass buffer strips Vegetated swales (supporting grass and or shrubs) Bioretention systems Gross Pollutant Traps Constructed wetlands Dry floor Retarding Basins APPLICATION OF WSUD TECHNIQUES TO PROPOSED DEVELOPMENT IN THE LARA WEST GROWTH AREA STUDY AREA Applicability Discussion to study area (H - High, M - Medium, L - Low) L High maintenance problems, noisy in residential environment. Porosity reduced by oil from vehicles. Little potential benefit in steeply sloping roads or lands where surface drainage is impeded. M Subject to traffic damage if not suitably protected. Problems with buildup of retained sediment along edge of pavement. Land slopes are suitable throughout the area. Erosion problems are unlikely unless flow is concentrated too much. Soil quality needs to be adequate to support grass cover in dry seasons and this may be a limiting factor in this situation. L-M Subject to traffic damage if not suitably protected. Can have problems with buildup of retained sediment but not to the extent of the grass buffer strips. Land slopes are suitable throughout the area. Not suited to small lot frontages - best used where roads front reserve areas and in median strips. L-M L H L Costly but reduces runoff peaks and improves water quality. Requires dedicated space, protection from significant sediment inputs, and specialised vegetation and maintenance to function correctly. Subject to traffic damage unless suitably protected. Subject to blockage by excess sediment load unless protected during estate and building construction phase. Not suited to small lot frontages - best used where roads front reserve areas and in median strips. Are most effective if placed on the outlets from ponds and wetlands. Land slopes are suitable through most of the area but outfall drainage depth is inadequate in the northeast sector. Elsewhere suspected soil dispersivity may require lining of the trenches to mitigate uptake of turbidity in drainage waters. Not considered necessary for normal or lower density development except in litter-generating areas such as fast food sites and commercial shopping centres or strips. Temporary Nettech bag-type fittings on pipe ends would suffice for construction period. Grated side-entry pits can also be used to exclude gross pollutants from drainage systems and should be considered throughout the study area. Wind blown litter needs to be controlled during building construction through appropriate site bins and cages. Water quality treatment performance is provided together with improved landscape and environmental values through good design. Airspace above the wetland systems can provide necessary flood storage capacity where maintenance of existing rural peak flows is a design requirement. Can also be used as a cut/fill technique to optimize developable land yield in areas where flooding threat is low. Likely to have great potential in the flat northeast sector. Peak flow mitigation is needed to maintain flows to capacity of existing drainage outfall, but dry floor retarding basins offer no ancillary advantages in this location and are wasteful of land. Neil M Craigie Pty Ltd 18

22 TABLE 6 WSUD Technique Wetlands or sediment traps in retarding basins Irrigation/re-use pondages APPLICATION OF WSUD TECHNIQUES TO PROPOSED DEVELOPMENT IN THE LARA WEST GROWTH AREA STUDY AREA Applicability Discussion to study area (H - High, M - Medium, L - Low) H As set out in Section 7.9 of the Urban Stormwater Best Practice Environmental Management Guidelines, retarding basin sites can be easily adapted to incorporate water quality treatment facilities. For example, in the greater Melbourne area many of Melbourne Water s most prominent constructed wetland systems are located in flood retarding basins. Highly appropriate in this situation. L Part of a wetland area could be zoned out to provide some limited irrigation storage capacity. If pump distribution systems are provided this pond area could be pumped down for irrigation of reserve areas without endangering the wetland plantings. Reuse of the water is a valuable water quality treatment measure. Use is limited by landscape and recreation needs and by water level drawdown limitations. Unlikely to be viable in this situation. Water reuse via individual raintanks is the preferred approach. 3.5 Application to Lara West Growth Area Catchments to Windermere and Kees Roads (the Northeast Sector) Given the widespread, shallow, slow-moving, benign nature of flooding under existing conditions in the northeast sector, and subject to other constraints being satisfactorily addressed, major cut/fill works to vary the floodplain shape and create integrated wetland/retarding storage systems will likely be the optimal solution for servicing of future development in this part of the LWGA. Allied with such works will be the need for deeper low flow outfall facilities to Hovell Creek, either along existing open drain alignments or alternative routes within road reserves. It is usually the case that the wetland/flood storage facility size is governed by flood mitigation requirements and not by water quality treatment requirements so it makes sense to combine the two in one facility. The land area is then a function of wetland water surface area, flood storage depth, development offsets to waterlines, and safe access slopes, but with consideration also being given to landscape/recreation/environment values as well. This integrated design approach has proven to be the key to effectively servicing many major urban developments former flood-prone areas in and around greater Melbourne, including The Waterways at Braeside and Keysborough Waters at Keysborough. Most recently this approach won the 2009 UDIA Victorian Award for WSUD for Shearwater Estate at Cowes on Phillip Island. It is also the recommended strategy for the Armstrong Creek East precinct southeast of Geelong. Neil M Craigie Pty Ltd 19

23 In the airspace above the wetlands existing flood storage volumes can be maintained and additional flood storage added to offset the impacts of increased runoff from urbanization. Upstream of about the 15 m AHD contour there is ample grade available over most of the LWGA development area but currently minimal drainage capacity or definition. A linear waterway system will need to be created by excavation to: (a) provide outfall depth for future residential drainage systems, (b) confine the width of flooding, and (c) avoid significant land filling requirements and especially the need for levee banks. The waterway/s will need to be designed so as to: (a) maintain slow flow velocities for catchment runoff, (b) protect integrated water quality/quantity management systems for urban drainage. No untreated stormwater runoff should be allowed to directly enter the new open waterways. However pipe outfalls can occur where suitable sediment basin facilities can be integrated with the waterway design. Where waterways are replacing existing open drains which run along property titles the widened reserves can be centred on those title boundaries or the new waterway can be realigned to be fully in one title or the other. Actual alignments can be varied quite significantly without compromising design objectives and final alignment decisions should be the subject of future negotiation between affected parties. On the Bacchus Marsh Road frontage the design will need to be able to accommodate floodwater overflowing extensive lengths of the road pavement and ensure all such floodwaters are directed into the new constructed waterways without flooding new development or creating erosion or safety issues. On the Patullos Road tributary inflow drainage line a similar situation exists as in the flat northeast sector. Drainage grades fall to less than 0.1% over significant distances. The south tributary waterway design linking to Bacchus Marsh Road will need to be deep enough to provide effective outfall for drainage south to Patullos Road Catchment to Patullos Road Given there is no alternative outfall to the existing shallow table drains in Patullos Road the only feasible option is to provide water quality and retarding storage capacity in an integrated wetland/retarding basin at the lowpoint (~15.75 m) at the O Hallorans Road intersection. Bioretention systems are not a feasible alternative because of outfall depth limitation. Neil M Craigie Pty Ltd 20

24 3.5.3 Catchments to Cameron Crescent Subdivision Although not part of the LWGA, the Manzeene Avenue area drainage issues and requirements have been considered in this study. The lowpoint adjacent to Cameron Crescent has a surface level of about 12.5 m. To the north levels rise to a ridgeline at about 14.0 m at the rear of Tydman Court before falling out to Manzeene Ave/Kees Road at about m. To the south from the lowpoint at Cameron Crescent levels rise marginally to a local highpoint at about 12.7 m and then fall to the lowpoint of about 12.0 m adjacent to Denise Court. Further south the levels rise again to a ridgeline of about 13.0 m at the rear of Peck Court before falling again out to Patullos Road at level of about 12.5 m. Figure 2.2 also shows that these lowpoints are affected by the southeasterly spread of floodwaters from external catchments to the north as well. Filling of land can mitigate this threat and hence redevelopment of the Manzeene Avenue area does offer a means of mitigating external catchment flooding to the existing subdivisions in Cameron Crescent. Given the only existing constructed outfall is to the existing small pipes at Cameron Crescent and the lowpoint at Denise Court is below the table drain levels in Patullos Road and in Manzeene Avenue/Kees Road, there may be no alternative to providing retarding storage capacity to service development of the lands upstream in Manzeene Avenue. To integrate water quality treatment in the one asset the options are for a wetland/retarding basin or a bioretention/retarding basin. Due to the proximity of existing houses the wetland option will need to provide a comparatively greater setback from the existing rear fenceline. It may also prove to be feasible to fill the land sufficiently to allow all stormwater from the Manzeene Avenue development area to be directed north to the drainage system required across Kees Road. Detail design will require field survey to confirm existence, diameter and level of all available pipes in the existing developments as well as receiving table drains in Patullos Road. For now it would suffice to determine the effective landtake for the drainage worksrefer Section 5. Neil M Craigie Pty Ltd 21

25 4. THE NORTHEAST SECTOR WATERWAY CONCEPT 4.1 Floodplain and Waterway Management Considerations In assessing any development proposal which may affect a natural or modified floodplain, best practice management aims to ensure that no significant detrimental impacts result for other lands or public or private assets (whether upstream, adjacent or downstream), or for waterway or floodplain stability and environmental values including water quality. To realise these aims a best practice management (and true performance-based) approach would place requirements along the following lines for all events up to and including the 100 year ARI flood: No significant change to natural flood level or velocity regimes; No significant change to flood timing or peak flows; Retention and protection of active floodway alignments; Maintenance of flood storage; Protection of areas which are critical to waterway and floodplain stability in geomorphologic terms; Appropriate protection of areas of environmental, geomorphological and archaeological significance. 4.2 Geology, Geomorphology and Groundwater Considerations No geotechnical investigations have yet been completed in the LWGA. The Melbourne Groundwater Directory shows minimal shallow groundwater resources around Lara. If present, shallow groundwater is likely to be about 20 m below the surface with salinity ranging from 3,501-7,000 mg/l. Deep groundwater is available at about 100 m depth with salinity ranging from 1,001-3,500 mg/l. Yields in both cases are low. Although further work on soils and general subsurface conditions will be done as part of future detail design, the available information indicates that groundwater will pose no significant threat for any surface water assets to be excavated below natural surface. Liners are likely to be necessary to prevent leakage from the proposed wetlands to the deeper regional groundwater. However geotechnical investigations will be completed to confirm initial impressions and detail design requirements. Regardless of soil test results all subsurface areas of any wetland systems will be topsoiled to at least 100 mm depth. Neil M Craigie Pty Ltd 22

26 4.3 Flora and Fauna Considerations Other than a few small patches of vegetation near Patullos Road in Parcel A, no significant remnant flora and fauna or archaeological heritage issues are known to affect the subject lands within the LWGA boundaries. Future plantings should focus on indigenous species sourced from local provenance. Wetland and waterway designs should emphasise aquatic and terrestrial habitat values as well as water quality, flood conveyance and landscape values. 4.4 Cultural Heritage Considerations There are no known cultural or archaeological heritage issues associated with the LWGA. 4.5 Design Criteria for the Proposed Floodplain Wetland System The design proposal for the northeast sector has been determined to meet the following specific design criteria: Maintenance of or lowering of existing peak flow regimes across Windermere, O Hallorans and Kees Roads (as set out in Tables ); Maintenance of or lowering of 100 year ARI flood levels throughout the area (external to Hovells Creek floodplain) as set out in Table 4; Protection of transmission tower surrounds plus retention of access to same; Compliance with agreed horizontal and vertical alignment for the waterway crossing of the recycle water main; Wetland systems to be created by excavation below natural surface within the floodplain to balance flood storage needs, provide cut material for reclamation of developable land, provide water quality treatment capacity for development land, and to enhance environmental values and diversity within the area; Wetland systems to be sized so as to ensure best practice treatment objectives are achieved for all future urban stormwater flows; Wetlands to be designed as integrated components of the waterway system. In major flood they form part of the overall flood storage/conveyance system Neil M Craigie Pty Ltd 23

27 provided that non-scouring velocities are maintained in all wetland areas in the 100 year ARI event; All wetlands to incorporate sufficient active flood storage in the airspace overhead to comply with peak flow objectives at Windermere, O Hallorans and Kees Roads (as set out in Tables ); Provision of culverts sized to ensure existing flood protection standards are maintained or improved for Windermere, O Hallorans and Kees Roads; Locating and sizing of wetland/retarding basins to best suit the identified land parcels so that development may proceed for each parcel with water management assets as self-contained as practicable; Provision of suitable pipes, pits and valves to allow the main treatment wetland systems to be drained down for maintenance purposes. 4.6 The Concept Design Concept Layout Figure 3.1 illustrates the recommended concept arrangement for the main northeast sector catchments. The layout and components of the concept are designed to maintain all existing flood overflow pathways and are summarised as follows: A 30 m wide reserve along Bacchus Marsh Road (55 m at West Gateway end) to provide for cut/fill works to intercept waters overflowing the road and redirect them north and south to the new waterways; Linear open waterways east of Bacchus Marsh Road in reserves of 35 and 45 m width for the north and south tributaries respectively, 55 m downstream of the confluence at Goulburn Park Drive to Windermere Road, and 55 m wide thereafter to Hovell Creek (see Figures 3.2 and 3.3 for typical cross-sections); A total of 6 wetland/retarding basins (WLRB s), strategically located to service urban drainage subcatchments within the various land parcels (including one hypothetical asset in the Manzeene Avenue area); 1 year (nominal) and 5 year ARI capacity pipelines as standard across the development areas, connecting to the WLRB s, and thence to the new waterways, including the southern connection to Patullos Road; Diversion of all piped and overland flows from the LWGA north and south along O Hallorans Road so as to maximise protection afforded to existing allotments in Manzeene Avenue and in the existing Cameron Crescent subdivision. Neil M Craigie Pty Ltd 24

28 A 1200 mm diameter pipeline draining low flows from WLRB4 on Windermere Road, along Windermere Road to O Hallorans Road; A 1200 mm diameter pipeline draining low flows from WLRB5 on O Hallorans Road, along the latter to Windermere Road; A combined 1500 mm diameter pipe outfall east of O Hallorans Road to Hovell Creek; Waterway alignments are negotiable between the affected parties, to best suit development layout needs. However the crossing of the power/water easement is fixed. The critical link between WLRB4 and WLRB5 must be maintained so as keep floodplain continuity with the tributary system north of Windermere Road and Hovells Creek via Kees Road but may be realigned to best suit development layouts. The pipeline alignments serving WLRB4 and WLRB5 have been located along and within existing Windermere and O Hallorans Road reservations. Again actual alignments could be varied and Council may require pipes to be placed within the development areas. All other pipe alignments indicated on Figure 3.1 are indicative only and entirely dependant on subdivision layout and servicing needs. Development of all land west of O Hallorans Road can proceed without any other downstream works being required. The WLRB s and the 1200/1500 mm pipelines in O Hallorans and Windermere Roads provide a complete service for these areas. Manzeene Avenue Although not part of the LWGA, the Manzeene Ave subdivision works have been considered as well to ensure system compatibility in the long term. The works derived in this study are scaled to service development of that area in isolation, with the 55 m reserve extended to Kees Road and being excavated to confine floodwaters, incorporate the necessary flood storage, and deepen the drainage system to receive urban inflows from piped drainage systems. To service new development in the Manzeene Avenue area that deeper drainage invert must continue east of Kees Road out to Hovell Creek. This may be achieved through piping of flows to say 5 year ARI capacity with the balance continuing as shallow widespread overland flow. Actual works design east of O Hallorans Road will be the subject of a separate investigation by others acting for the Manzeene Avenue landowner group. Neil M Craigie Pty Ltd 25

29 4.6.2 Wetland/Retarding Basin Form Integrated wetlands within flood retarding basins are common drainage management assets. Many of the original retarding basins constructed in greater Melbourne in the 1970 s and 1980 s have since been retrofitted with wetland systems. Photos 1 and 2 provide examples of similar WLRB s elsewhere in the greater Melbourne region whilst photo 3 is a google view of an existing facility soon after construction Open Waterway Form The concept layout provides for a fully excavated channel profile with varying batter slopes, incorporating a small rocky vegetated low flow channel meandering across a wide gently graded and densely vegetated ephemeral base area. In general there are to be no pipe outlets from any developed land direct to the new waterways. All drainage outlets are to the integrated sedimentation basins and wetlands. However it is recognised that in some instances cost implications may require some minor pipe outfalls to be made. Small sacrificial sediment ponds would be inserted at intervals to act as construction-era sediment traps where such small pipeline connections occur. It is also feasible to incorporate small online pools in the waterway to enhance habitat and aesthetic values. All reserves are wide enough to incorporate trails doubling as maintenance access on both sides. The primary aim is for flood flow velocities and depths to be kept below the limits specified in current floodway safety standards so as to maximise public safety, water quality performance and protection of habitat, whilst slowing down and attenuating peak flow rates downstream. The key features of the waterway design are as follows: a small low-capacity meandering rocky low flow channel is provided in the base of the floodway to localise wetter zones and inhibit spread of weed species; whenever significant storm flows occur the capacity of the low flow course is quickly exceeded, flow spreads over the wide floodway base and water borne pollutants, particularly organic materials and silts, are filtered and removed; indigenous vegetation species are selected for ability to resist the impacts of flowing water, to maintain filter performance during flow events, to cope with highly variable water supply including drought, and to enhance landscape appeal and habitat diversity; the waterway cross-section does not require mowing or irrigation; Neil M Craigie Pty Ltd 26

30 with low velocities and gentle cross-section slopes, significant opportunity is retained for trail provision (including boardwalk crossings) and for landscape design to enhance aesthetic and recreational values. Photos 4-8 illustrate the design intent for the main waterways. Photo 9 shows an example of an alternative form for a drier vegetated floodway that could be appropriate for the segments immediately downstream of Bacchus Marsh Road which carry only rural catchment flows. Figures 3.2 and 3.3 illustrate the typical crosssections for the main waterways. Photos 1 and 2 show examples of existing constructed wetland/retarding basins in urban settings Neil M Craigie Pty Ltd 27

31 Photo 3 shows a google aerial view of the wetland/retarding basin at Tenterfield Estate in Taylors Hill not long after plantings were complete. Neil M Craigie Pty Ltd 28

32 Photos 4 (upper) and 5 (lower). Aerial views of densely vegetated constructed waterways terminating at waterfall-inlet sedimentation pondages in Watervale and Tenterfield Estates as at February The Watervale channel has had 3 years additional establishment time as reflected in the denser shrub coverage. The following photos are ground-level shots of these waterways. Neil M Craigie Pty Ltd 29

33 Examples of meandering low flow course and dense vegetation plantings in associated floodways (Tenterfield Estate at Taylors Hill). Photo 6 above is soon after initial plantings. Photo 7 below is about 2 years later and matches the aerial view on Photo 2. Neil M Craigie Pty Ltd 30

34 Photo 8 above is the similar but more established system in Watervale Estate at Taylors Hill (see aerial view on Photo 1). Major floods have passed through this waterway on several occasions without damage. A similar stream form but with locally indigenous vegetation species is proposed for the basal areas of the waterways in the LWGA in Lara. Velocities of flow are slow. Photo 9 Alternative form for a drier vegetated floodway that could be appropriate for the segments immediately downstream of Bacchus Marsh Road which carry only rural catchment flows Neil M Craigie Pty Ltd 31

35 4.6.4 Drainage Levels and Quantities It is intended that the new drainage system will be excavated to levels sufficient to facilitate urban development outside the waterway and WLRB reserves, without importation of fill. Cut volumes generated within the area are to be used to locally raise flat areas to provide minimum freeboard to flood levels. Normal Top Water Levels (NTWL s) for all wetlands are set so as to provide free drainage outfall for subdivisional piped drainage systems (2-2.5 m below natural surface). Each WLRB is sized to include a sedimentation/wetland area sufficient to achieve best practice stormwater management outcomes as determined using MUSIC, with total site area allowing for safe batter slopes and recreational and maintenance access. Extended detention depth for water quality treatment is set at 0.5 m with 72 hour detention time. Table 7 summarises preliminary design quantities for each WLRB shown on Figure 3.1. Location, levels and shapes are able to be manipulated to best suit subdivisional layout and earthworks quantities, during future design. Table 8 summarises preliminary design information along the main waterway and pipeline network. Table 9 summarises the stage-storage-discharge relations for each WLRB based on preliminary design. TABLE 7 WLRB Quantities for North East Sector drainage system (preliminary and subject to detail design variation) Asset Urban Catchment Wetland Comments Area (ha) Description WLRB1 68 Part Parcel A plus two western titles in Parcel E (Patullos Road) WLRB2 66 Part Parcel B (West Gateway) and part Parcel A WLRB3 77 Balance Parcel B (West Gateway) WLRB4 30 Part Parcel A, part Parcel C and part Parcel D WLRB5 131 Balance Parcels A, C and D Water Surface Area (ha) NTWL (m) Online wetland system Online sedimentation pondage Online wetland system Online wetland system that accepts major flood inflows from the north across Windermere Road. 1200/1500 mm pipe discharge along Windermere Rd to Hovells Ck 2.30 >=11.5 Online wetland system with 1200 mm pipe outlet to Windermere Road outfall and surface overflow across O Hallorans Road when levels exceed m (natural surface) Totals for LWGA WLRB6 32 Manzeene Ave 0.56 ~11.5 Hypothetical asset Neil M Craigie Pty Ltd 32

36 TABLE 8 Asset Segment Reserve width (m) Bacchus Marsh Road frontage Patullos Road to West Gateway 30 south of North tributary Preliminary Main Drainage Design Data Pipe Upstream Downstream Diameter invert (m) invert (m) (mm) Average grade (%) Comments May be formed as cut/fill depression and/or including service road or carpark (subject to floodway safety guidelines) 55 in northern title Effectively shaped as an extension of the downstream waterway Linear waterway (south tributary) Bacchus Marsh Road to First road crossing ~0.9 Type cross-section shown on Figure 3.2. No pipe drain connections. First road crossing to WLRB ~0.9 Type cross-section shown on Figure 3.2. One pipe drain connection. WLRB1-WLRB ~0.9 Type cross-section shown on Figure 3.2. No pipe drain connections. Linear waterway (north tributary) Bacchus Marsh Road to WLRB ~0.9 Type cross-section shown on Figure 3.3. No pipe drain connections. Main waterway WLRB3 (SPAusnet easement) to WLRB ~0.33 Type cross-section shown on Figure 3.2. No pipe drain connections. Link Floodway WLRB4-WLRB ~0.33 Dry waterway. Type cross-section shown on Figure 3.3. No pipe drain connections. WLRB4 Outlet pipe WLRB4-O Hallorans Rd WLRB5 Outlet pipe WLRB5 to Windermere Rd Windermere Rd outfall pipe O Hallorans Rd to Hovell Creek Outfalls on downstream (south) side of Windermere Road. Manzeene Ave waterway Kees Road outfall O Hallorans Road to Kees Road Kees Road to Hovell Creek 55 nominal 55 nominal External to LWGA boundaries and subject to negotiation in regard to waterway design and alignment and reserve width Neil M Craigie Pty Ltd 33

37 TABLE 9 Stage-area-storage-discharge characteristics for key retarding storages Storage NTWL (m) Stage (m) Area (m2) Storage (m3) Outlet Controls Discharge (m3/s) WLRB , weir ,500 9, m weir ,000 12, ,500 19, ,050 32, m weir ,150 63, WLRB , m weir ,200 5, m weir ,000 7, ,000 11, m weir ,425 20, ,275 41, WLRB ,300 0 Naturalised waterway ,500 5,070 downstream ,600 13, ,600 21, ,825 28, ,050 36, ,500 51, WLRB , mm pipe ,200 4, , ,700 11, ,200 17, ,500 Overflow waterway , , ,200 42, , ,600 56, WLRB , mm pipe ,000 11, ,500 17, ,000 45, ,250 65, m spillway 2.09 (O Hallorans Road) ,500 85, ,000 94, WLRB , m weir ,000 11, m weir ,500 17, m weir ,000 45, ,250 65, ,500 85, Note: Detail design of each asset may result in adjustments to the NTWL s and stage-storage-discharge relations. Neil M Craigie Pty Ltd 34

38 4.6.5 Flood Modelling Results The RORB hydrologic model setup shown on Figure 2 was adjusted to include development areas at average 60% impervious with piped drainage systems to each WLRB. The proposed new waterway reaches within the urban area were set using reach code 2 with slopes matching natural surface or adopted new grades between NTWL s in relevant WLRB s. The model was run in trial and error mode to confirm all WLRB and pipeline sizings and key flood levels in WLRB s and peak flows at O Hallorans Road. Table 10 summarises the results for 1, 2, 5, 10, 20 and 100 year ARI events. Peak flow results for 2, 10 and 100 year ARI events are also compared with those for existing conditions in Table 11. The modelling shows that: existing flow regimes are maintained or reduced at all critical points throughout the area for all ARI s up to and including the 100 year event; the Manzeene Ave area east of O Hallorans Road is fully protected from external inflows for almost the 2 year ARI event. Peak flows for all events are significantly reduced compared with existing conditions; floodplain continuity is effectively maintained between Windermere Road, O Hallorans Road and Kees Road for the 100 year ARI event; development of lands west of O Hallorans Road can proceed independently of the Manzeene Ave area, subject to the outfall pipeline system being constructed to Hovells Creek via Windermere and O Hallorans Roads; no works other than the pipeline outfall are required to service full development of the LWGA. Neil M Craigie Pty Ltd 35

39 TABLE 10 RORB Model Results for fully developed conditions ARI (years) Location Peak Outflow (m3/s) Critical duration (hrs) Water Level (m) Storage (m3) 1 South tributary at BM Rd WLRB ,500 North tributary at BM Rd WLRB ,000 WLRB ,700 WLRB ,300 Overflow to WLRB WLRB ,100 Overflow across O Hallorans Rd 0 WLRB , mm outfall South tributary at BM Rd WLRB ,800 North tributary at BM Rd WLRB ,300 WLRB ,000 WLRB ,400 Overflow to WLRB WLRB ,800 Overflow across O Hallorans Rd WLRB , mm outfall South tributary at BM Rd WLRB ,300 North tributary at BM Rd WLRB ,500 WLRB ,000 WLRB ,000 Overflow to WLRB WLRB ,000 Overflow across O Hallorans Rd WLRB , mm outfall South tributary at BM Rd WLRB ,100 North tributary at BM Rd WLRB ,800 WLRB ,400 WLRB ,300 Overflow to WLRB WLRB ,700 Overflow across O Hallorans Rd WLRB , mm outfall South tributary at BM Rd WLRB ,500 North tributary at BM Rd WLRB ,500 WLRB ,700 Neil M Craigie Pty Ltd 36

40 TABLE 10 RORB Model Results for fully developed conditions ARI (years) Location Peak Outflow (m3/s) Critical duration (hrs) Water Level (m) Storage (m3) WLRB ,900 Overflow to WLRB WLRB ,600 Overflow across O Hallorans Rd WLRB , mm outfall South tributary at BM Rd WLRB ,900 North tributary at BM Rd WLRB ,500 WLRB ,300 WLRB ,700 Overflow to WLRB WLRB ,100 Overflow across O Hallorans Rd WLRB , mm outfall TABLE 11 Comparison of Peak Discharges (m3/s) and flood levels for Existing (EX) Conditions and Fully Developed (FD) Conditions (Note: the lowest peak flows listed in Table 3.1 are used for EX conditions) Location 2 year ARI 10 year ARI 100 year ARI EX FD EX FD EX FD South trib y at Bacchus Marsh Road North trib y at Bacchus Marsh Road Power/Water Easement Windermere Rd mm pipe in Windermere Rd to O Hallorans Rd 1200 mm pipe in O Hallorans Rd Crossing O Hallorans Rd mm Windermere Rd outfall Kees Rd Outfall Neil M Craigie Pty Ltd 37

41 5. THE BALANCE CATCHMENTS Sizing of wetland/retarding basins to service the balance catchments in Parcels E and F is based on the rates generated from modelling in the northeast sector catchments; that is, wetland water surface area is 1.75% of urban catchment and contained within site areas of 2*wetland water surface area. Table 12 and Figure 4 summarise the preliminary design recommendations. All inlet drainage to the WLRB s will be 5 year ARI (minimum) capacity pipelines. Overland flows will be conveyed in roads. The final location, levelling, sizing and design form of these assets will be dependant on detail field survey to confirm available pipe and table drain outfall levels and capacities. Works within parcel F are provided for guidance only. Final strategy development and design are the responsibility of others working for the Manzeene Avenue landowners group. TABLE 10 WLRB Quantities for balance catchments in Parcels E and F (preliminary and subject to detail design variation) Asset Urban Catchment Wetland Site Comments Area (ha) Description Water Surface NTWL (m) Area (ha) WLRB Part Parcel E (Patullos Road) Area (ha) 0.46 ~ Located at intersection of O Hallorans Road and Patullos Road 0.28 ~ Located at rear WLRB Part Parcel F (Manzeene Ave) Cameron Crescent WLRB Part Parcel F 0.23 ~ Located at rear Denise (Manzeene Ave) Court Totals % of urban development catchment Neil M Craigie Pty Ltd 38

42 6. WATER QUALITY TREATMENT PERFORMANCE The MUSIC (V3) model was assembled using the Geelong North minute rainfall data sequence. Table 13 summarises the consolidated results for the LWGA assets. These results plus assessment of the diversion capacity of the 1200 mm pipes out of WLRB4 and WLRB5 show that: The proposed WLRB s in the LWGA are sufficient to exceed minimum requirements for compliance with best practice stormwater pollutant removal targets; 87% of the mean annual volumetric discharge from the total LWGA catchment to WLRB4 will be conveyed to Hovells Creek via the 1200/1500 mm diameter pipe outfall; The mean annual volumetric discharge across O Hallorans Road into the Manzeene Ave land is reduced to close to zero compared to existing conditions, even after full development of the LWGA catchments; Taken together the pipelines out of WLRB4 and WLRB5 reduce mean annual volumetric discharge to Manzeene Avenue by just under 90%. The balance catchments to the existing residential development east of Manzeene Ave were also modelled. All external runoff input from the LWGA is diverted north to WLRB5 and south to WLRB7. Table 14 summarises the results which show that the proposed WLRB s are sufficient to exceed minimum requirements for compliance with best practice stormwater pollutant removal targets. TABLE 13 MUSIC Model Results-Lara West Growth Area Assets (Geelong North minute data sequence) Asset/Parameter Input Loads Residual % load removal Loads WLRB1 Flow (ML/yr) Suspended Solids (Kg/yr) 109,000 45, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) 1,930 1, Gross Pollutants (kg/yr) 10, WLRB2 Flow (ML/yr) Suspended Solids (Kg/yr) 125,000 58, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) 2,670 2, Gross Pollutants (kg/yr) 8, Neil M Craigie Pty Ltd 39

43 TABLE 13 MUSIC Model Results-Lara West Growth Area Assets (Geelong North minute data sequence) Asset/Parameter Input Loads Residual % load removal Loads WLRB3 Flow (ML/yr) 1,180 1,160 2 Suspended Solids (Kg/yr) 103,000 58, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) 3,000 2, Gross Pollutants (kg/yr) 9, WLRB4 Flow (ML/yr) 1,240 1,230 1 Suspended Solids (Kg/yr) 76,100 52, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) 2,790 2,540 9 Gross Pollutants (kg/yr) 3, WLRB5 Flow (ML/yr) Suspended Solids (Kg/yr) 74,700 11, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) 1, Gross Pollutants (kg/yr) 16, WLRB7 Flow (ML/yr) Suspended Solids (Kg/yr) 12,900 2, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) Gross Pollutants (kg/yr) 2, Total LWGA Assets Source Load Loads Total Catchment LWGA only removed in LWGA Assets % removal of source loads Total Catchment LWGA only Flow (ML/yr) 1,750 1, Suspended Solids (Kg/yr) 336, , , Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) 5,470 3,303 2, Gross Pollutants (kg/yr) 51,700 48,620 51, TABLE 14 MUSIC Model Results-Manzeene Avenue Assets (Geelong North minute data sequence) Asset/Parameter Input Loads Residual % load removal Loads WLRB6 Flow (ML/yr) Suspended Solids (Kg/yr) 18,100 3, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) Gross Pollutants (kg/yr) 3, Neil M Craigie Pty Ltd 40

44 TABLE 14 MUSIC Model Results-Manzeene Avenue Assets (Geelong North minute data sequence) Asset/Parameter Input Loads Residual % load removal Loads WLRB8 Flow (ML/yr) Suspended Solids (Kg/yr) 9,010 1, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) , Gross Pollutants (kg/yr) WLRB9 Flow (ML/yr) Suspended Solids (Kg/yr) 7,400 1, Total Phosphorus (Kg/yr) Total Nitrogen (Kg/yr) Gross Pollutants (kg/yr) 1, Neil M Craigie Pty Ltd 41

45 7. SUMMARY AND CONCLUSIONS This report updates the 6 April 2010 first report and presents results of hydrologic, hydraulic and water quality modelling for proposed development of the area originally referred to as Area 4 in the Lara Structure Plan but now known as the Lara West Growth Area (LWGA). This update has been prepared to respond to the revised existing conditions twodimensional modelling of the area that has just been completed by BMT WBM at the request of City of Greater Geelong (CoGG). The LWGA relates to the land encompassed by Bacchus Marsh Road in the west, Windermere Road in the north, O Hallorans Road in the east and Patullos Road in the south. The Manzeene Avenue LSP area abuts the LWGA on the east side of O Hallorans Road. The whole of the land is part of the Hovell Creek catchment and the primary proposed land use is conventional residential development averaging at least 15 lots/ha. The 6 April 2010 study utilised the flood mapping done by WBM Pty Ltd 3 to determine the extent and levels of flooding across the LWGA under present day conditions. However new hydrologic, hydraulic and water quality models better suited to requirements were derived for study design purposes. For this update report BMT WBM have revised all the existing conditions flood modelling using the latest LiDAR survey information. The revised hydraulic modelling outputs have been used to prepare this update report. Existing Flooding and Drainage Conditions The component subcatchments, primary drainage paths and the area affected by inundation under existing conditions in the 100 year ARI flood event (as determined in the 2002 study) are shown on Figure 2.1. The latest flood modelling outputs generated by BMT WBM are shown on Figure 2.2. It is noted that the mapped flood extents are virtually identical to those shown on Figure 2.1, apart from the interaction with the tributary floodplain north of Windermere Road. The 2002 study by WBM did not include that tributary. Water depths across the vast bulk of the area that is shown as subject to inundation are very shallow (less than 100 mm). Subject to best practice outcomes being realised 3 Lara Flood Study Stage 1, Revision 2, 8/1/02, WBM Oceanics Australia for CoGG. Neil M Craigie Pty Ltd 42

46 there are major opportunities to reduce flood extent and foster development of the LWGA lands, through strategic cut/fill earthworks. Topographic information indicates that the boundaries between land subject to or not subject to inundation are blurred and freeboard above flooding is minimal in the north-east sector of the LWGA. The most recent hydraulic modelling by BMT WBM shown on Figure 2.2 has confirmed interaction of flood flows between the LWGA depressions and the large tributary floodplain to the north of Windermere Road. As depicted by the flow locations on Figure 2.3, flows can cross Windermere Road from south to north at times towards O Hallorans Road (Locations Wind_1-3), but larger flows cross over the road from the north and enter the LWGA near Goulburn Park Drive (Wind_Rd). To the south and east of the LWGA Figure 2.2 shows areas of land being affected by flooding extending from the very shallow local catchment overland flows within the LWGA across Manzeene Avenue and to the rear of the existing residential subdivisions in Camerons Crescent and along the Patullos Road frontage. This SWMS study has included preparation of a new RORB hydrologic model of the primary catchment area to Hovell Creek for both existing conditions and future development conditions. The RORB model has been updated in this report to reflect the key outputs of the new existing conditions hydraulic modelling as well as adjustments to the proposed stormwater management system within the LWGA that have occurred through evolution of LSP planning. Hydrographs of inflow occurring at WG_Break and Wind_Rd generated from the 2D hydraulic model were input to the RORB model at those locations. Peak flow predictions for major flood discharges within and downstream of the LWGA to Hovell Creek match well with those from the BMT WBM study as shown by the comparison in Table 3.1. Critical duration for the 100 year ARI event was 9 hours in RORB as was also obtained by WBM (2002) and BMT WBM (2012). Objectives In no order of priority, the specific surface water management strategy objectives for the study area are as follows: minimise offsite discharge of stormwater pollutants to Hovell Creek, Limeburners Bay and Port Phillip Bay, both during development and in the long term; ensure any offsite discharge of pollutants generated from the proposed urban development fully complies with best practice management objectives for environmental protection in Hovell Creek, Limeburners Bay and Port Phillip Bay; take up practical opportunities for reuse of site stormwater, to reduce mains water input to the property and discharge of stormwater and pollutants, and/or use the Neil M Craigie Pty Ltd 43

47 water to support wetland development within the site; maximise the economic, environmental, aesthetic and recreational benefits of surface water throughout the development, while ensuring that such use does not result in any loss of user safety or creation of nuisance; mitigate existing flood threats within and downstream of the study area by ensuring no increase in peak discharges from developments and by upgrading/deepening drainage outfalls where possible; protect all new development areas from flooding threats; design any future waterway and wetland system in sympathy with the natural topographic characteristics; layout and design all waterways and water management assets having regard to different landownership and use wherever practicable; subject to the above objectives being satisfactorily addressed, locate and design new surface water management assets to minimise capital investment and operation and maintenance costs in the long term. Catchments to Windermere and O Hallorans/Kees Roads (the Northeast Sector) Given the widespread, shallow, slow-moving, benign nature of flooding under existing conditions in the northeast sector, and subject to other constraints being satisfactorily addressed, major cut/fill works to vary the floodplain shape and create integrated wetland/retarding storage systems will likely be the optimal solution for servicing of future development in this part of the LWGA. Allied with such works will be the need for deeper low flow outfall facilities to Hovell Creek, either along existing open drain alignments or alternative routes within road reserves. Upstream of about the 15 m AHD contour there is ample grade available over most of the LWGA development area but currently minimal drainage capacity or definition. A linear waterway system will need to be created by excavation to: (d) provide outfall depth for future residential drainage systems, (e) confine the width of flooding, and (f) avoid significant land filling requirements and especially the need for levee banks. The waterway/s will need to be designed so as to: (c) maintain slow flow velocities for catchment runoff, (d) protect integrated water quality/quantity management systems for urban drainage. Neil M Craigie Pty Ltd 44

48 The design proposal for the northeast sector has been determined to meet the following specific design criteria: Maintenance of or lowering of existing peak flow regimes across Windermere, O Hallorans and Kees Roads (as set out in Tables ); Maintenance of or lowering of 100 year ARI flood levels throughout the area (external to Hovells Creek floodplain) as set out in Table 4; Protection of transmission tower surrounds plus retention of access to same; Compliance with agreed horizontal and vertical alignment for the waterway crossing of the recycle water main; Wetland systems to be created by excavation below natural surface within the floodplain to balance flood storage needs, provide cut material for reclamation of developable land, provide water quality treatment capacity for development land, and to enhance environmental values and diversity within the area; Wetland systems to be sized so as to ensure best practice treatment objectives are achieved for all future urban stormwater flows; Wetlands to be designed as integrated components of the waterway system. In major flood they form part of the overall flood storage/conveyance system provided that non-scouring velocities are maintained in all wetland areas in the 100 year ARI event; All wetlands to incorporate sufficient active flood storage in the airspace overhead to comply with peak flow objectives at Windermere, O Hallorans and Kees Roads (as set out in Tables ); Provision of culverts sized to ensure existing flood protection standards are maintained or improved for Windermere, O Hallorans and Kees Roads; Locating and sizing of wetland/retarding basins to best suit the identified land parcels so that development may proceed for each parcel with water management assets as self-contained as practicable; Provision of suitable pipes, pits and valves to allow the main treatment wetland systems to be drained down for maintenance purposes. Figure 3.1 illustrates the recommended concept arrangement for the main northeast sector catchments. The layout and components of the concept are designed to maintain all existing flood overflow pathways and are summarised as follows: Neil M Craigie Pty Ltd 45

49 A 30 m wide reserve along Bacchus Marsh Road (55 m at West Gateway end) to provide for cut/fill works to intercept waters overflowing the road and redirect them north and south to the new waterways; Linear open waterways east of Bacchus Marsh Road in reserves of 35 and 45 m width for the north and south tributaries respectively, 55 m downstream of the confluence at Goulburn Park Drive to Windermere Road, and 55 m wide thereafter to Hovell Creek (see Figures 3.2 and 3.3 for typical cross-sections); A total of 6 wetland/retarding basins (WLRB s), strategically located to service urban drainage subcatchments within the various land parcels (including one hypothetical asset in the Manzeene Avenue area); 1 year (nominal) and 5 year ARI capacity pipelines as standard across the development areas, connecting to the WLRB s, and thence to the new waterways, including the southern connection to Patullos Road; Diversion of all piped and overland flows from the LWGA north and south along O Hallorans Road so as to maximise protection afforded to existing allotments in Manzeene Avenue and in the existing Cameron Crescent subdivision. A 1200 mm diameter pipeline draining low flows from WLRB4 on Windermere Road, along Windermere Road to O Hallorans Road; A 1200 mm diameter pipeline draining low flows from WLRB5 on O Hallorans Road, along the latter to Windermere Road; A combined 1500 mm diameter pipe outfall east of O Hallorans Road to Hovell Creek; Waterway alignments are negotiable between the affected parties, to best suit development layout needs. However the crossing of the power/water easement is fixed. The critical link between WLRB4 and WLRB5 must be maintained so as keep floodplain continuity with the tributary system north of Windermere Road and Hovells Creek via Kees Road but may be realigned to best suit development layouts. The pipeline alignments serving WLRB4 and WLRB5 have been located along and within existing Windermere and O Hallorans Road reservations. Again actual alignments could be varied and Council may require pipes to be placed within the development areas. All other pipe alignments indicated on Figure 3.1 are indicative only and entirely dependent on subdivision layout and servicing needs. Neil M Craigie Pty Ltd 46

50 Development of all land west of O Hallorans Road can proceed without any other downstream works being required. The WLRB s and the 1200/1500 mm pipelines in O Hallorans and Windermere Roads provide a complete service for these areas. Manzeene Avenue Although not part of the LWGA, the Manzeene Ave subdivision works have been considered as well to ensure system compatibility in the long term. The works derived in this study are scaled to service development of that area in isolation, with the 55 m reserve extended to Kees Road and being excavated to confine floodwaters, incorporate the necessary flood storage, and deepen the drainage system to receive urban inflows from piped drainage systems. To service new development in the Manzeene Avenue area that deeper drainage invert must continue east of Kees Road out to Hovell Creek. This may be achieved through piping of flows to say 5 year ARI capacity with the balance continuing as shallow widespread overland flow. Actual works design east of O Hallorans Road will be the subject of a separate investigation by others acting for the Manzeene Avenue landowner group. It is intended that the new drainage system will be excavated to levels sufficient to facilitate urban development outside the waterway and WLRB reserves, without importation of fill. Cut volumes generated within the area are to be used to locally raise flat areas to provide minimum freeboard to flood levels. Table 7 summarises preliminary design quantities for each WLRB shown on Figure 3.1. Location, levels and shapes are able to be manipulated to best suit subdivisional layout and earthworks quantities, during future design. Table 8 summarises preliminary design information along the main waterway and pipeline network. Table 9 summarises the stage-storage-discharge relations for each WLRB based on preliminary design. Table 10 summarises the peak flow results for 1, 2, 5, 10, 20 and 100 year ARI events, obtained using the RORB model. Peak flow results for 2, 10 and 100 year ARI events are also compared with those for existing conditions in Table 11. The modelling shows that: existing flow regimes are maintained or reduced at all critical points throughout the area for all ARI s up to and including the 100 year event; the Manzeene Ave area east of O Hallorans Road is fully protected from external inflows for almost the 2 year ARI event. Peak flows for all events are significantly reduced compared with existing conditions; Neil M Craigie Pty Ltd 47

51 floodplain continuity is effectively maintained between Windermere Road, O Hallorans Road and Kees Road for the 100 year ARI event; development of lands west of O Hallorans Road can proceed independently of the Manzeene Ave area, subject to the outfall pipeline system being constructed to Hovells Creek via Windermere and O Hallorans Roads; no works other than the pipeline outfall are required to service full development of the LWGA. The Balance Catchments Sizing of wetland/retarding basins to service the balance catchments in Parcels E and F is based on the rates generated from modelling in the northeast sector catchments; that is, wetland water surface area is 1.75% of urban catchment and contained within site areas of 2*wetland water surface area. Table 12 and Figure 4 summarise the preliminary design recommendations. All inlet drainage to the WLRB s will be 5 year ARI (minimum) capacity pipelines. Overland flows will be conveyed in roads. The final location, levelling, sizing and design form of these assets will be dependent on detail field survey to confirm available pipe and table drain outfall levels and capacities. Works within parcel F are provided for guidance only. Final strategy development and design are the responsibility of others working for the Manzeene Avenue landowners group. Water Quality Treatment Performance The MUSIC (V3) model was assembled using the Geelong North minute rainfall data sequence. Table 13 summarises the consolidated results for the LWGA assets. These results plus assessment of the diversion capacity of the 1200 mm pipes out of WLRB4 and WLRB5 show that: The proposed WLRB s in the LWGA are sufficient to exceed minimum requirements for compliance with best practice stormwater pollutant removal targets; 87% of the mean annual volumetric discharge from the total LWGA catchment to WLRB4 will be conveyed to Hovells Creek via the 1200/1500 mm diameter pipe outfall; Neil M Craigie Pty Ltd 48

52 The mean annual volumetric discharge across O Hallorans Road into the Manzeene Ave land is reduced to close to zero compared to existing conditions, even after full development of the LWGA catchments; Taken together the pipelines out of WLRB4 and WLRB5 reduce mean annual volumetric discharge to Manzeene Avenue by just under 90%. The balance catchments to the existing residential development east of Manzeene Ave were also modelled. All external runoff input from the LWGA is diverted north to WLRB5 and south to WLRB7. Table 14 summarises the results which show that the proposed WLRB s are sufficient to exceed minimum requirements for compliance with best practice stormwater pollutant removal targets. Neil M Craigie BECivil, MEngSci, MIEAust, CPEng Neil M Craigie Pty Ltd 49

53 8. ABBREVIATIONS AND DEFINITIONS AHD Australian Height Datum. Common base for all survey levels in Australia. Refers to height in metres above mean sea level. ARI Average Recurrence Interval. The average length of time in years between two floods of a given size or larger Ephemeral Waterways which flow for only short periods of time after significant rainfall events. Also refers to wetlands which are either rarely inundated or only inundated for a very short period of time. Evapotranspiration The loss of water to the atmosphere by means of evaporation from free water surfaces (eg. dams or lakes or wetlands) or by transpiration by plants Groundwater All water stored or flowing below the ground surface level Ha Hectare (10,000 square metres) Km Kilometre (1000 metres) m 3 /s Unit of discharge = cubic metre/second ML Megalitre (1000 cubic metres) NTWL The Normal Top Water Level (m AHD) or water surface level of a waterbody when just full to low flow overflow level. Pond A small artificial body of open water (eg. dam or small lake) Retarding basin A flood storage dam which is normally empty. May contain a lake or wetland in its base Sedimentation A pond that is used to remove sediments from inflowing water mainly by basin (sediment settlement processes. Edge zones may have similar appearance to wetland margins. pond) Surface water Swale Waterlogging Wetland All water stored or flowing above the ground surface level A drainage line with essentially trapezoidal cross-sectional form. Can have rocky or soil bed form, be fully vegetated with indigenous species, or grassed. The base can be fitted with a filter zone to further assist in pollutant removal (termed a bioretention swale). Foundations can be ripped to encourage seepage losses in suitable soils. Term used to describe saturated surface soil conditions where some free surface water may also be present A transitional area between land and water systems which is either permanently or periodically inundated with shallow water and either permanently or periodically supports the growth of aquatic macrophytes (eg. swamp, marsh, fen, bog) 9. REFERENCES Institution of Engineers, Australia (1987), Australian Rainfall and Runoff, A Guide to Flood Estimation Stormwater Committee, Victoria (1999), Urban Stormwater Best Practice Environmental Management Guidelines. Pub. CSIRO Engineers Australia, (2006), Australian Runoff Quality. A Guide to Water Sensitive Urban Design Melbourne Water (2005), WSUD Engineering Procedures, Stormwater. Pub. CSIRO Neil M Craigie Pty Ltd 50

54 WLRB4 (Windermere) 1200 mm pipe 1500 mm pipe to Hovell Ckdownstream side of Windermere Rd WLRB3 WLRB mm pipe WLRB6 (Manzeene) WLRB5 (O Hallorans) WLRB1 100 yr ARI flows diverted to WLRB5 (5 year ARI pipes and overland flows) Figure 3.1 LWGA Catchments WLRB7 (Patullos) 100 year ARI flood pondage extents confined to proposed drainage reserves and WLRB s for fully developed conditions Signifies 5 year ARI pipelines-indicative alignments only Neil M Craigie Pty Ltd 51

55 Dense flexible shrub plantings with sedge understorey-no trees on flat benches. Trees restricted to bank zones. 45 m reserve Stepped rock and planted edges to 1.0 m above waterway invert on average Rocky low flow course meanders back and forth across flat benches 55 m reserve Figure 3.2 LWGA Catchments Typical waterway cross-sections Neil M Craigie Pty Ltd 52

56 55 m reserve 35 m reserve Figure 3.3 LWGA Catchments Typical waterway cross-sections Neil M Craigie Pty Ltd 53

57 WLRB8 (31-37 Cameron Crescent Catchment) Pipeline extension may be required WLRB9 (Denise Court catchment) WLRB7 (O Hallorans Rd/Patullos Rd Catchment) 100 yr ARI flows diverted to WLRB5 (5 year ARI pipes and overland flows) N Q5 pipe=5 year ARI capacity pipeline Figure 4 Balance Catchments Concept layout for WLRB s for fully developed conditions (indicative only for Manzeene Avenue) Neil M Craigie Pty Ltd 54