Lower Brown Hill Creek Channel Upgrade
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Lower Brown Hill Creek Channel Upgrade Stage 1 - Engineering Feasibility Report - Interim Report Brown Hill Keswick Creek Stormwater Project February 2014 Ref No. 2012.0679FR2D Document History and Status Rev Description Author Reviewed Approved Date A For Client Comment JO/CLB MDH 9 August 2013 B Draft for Client Comment CLB 21 August 2013 C Interim Report CLB MDH MDH October 2013 D Interim Report V2 MDH MDH MDH February 2014 © Tonkin Consulting 2012 This document is, and shall remain, the property of Tonkin Consulting. The document may only be used for the purposes for which it was commissioned and in accordance with the Terms of Engagement for the commission. Unauthorised use of this document in any form whatsoever is prohibited. Ref No. 2012.0679FR2D Lower Brown Hill Creek Channel Upgrade Stage 1 - Engineering Feasibility Report - Interim Report Contents Executive Summary i 1 Introduction 1 2 Lower Brown Hill Creek Description 2 2.1 Lower Brown Hill Creek 2 2.2 Current Planning Zoning 2 2.2.1 Residential Zone 2 2.2.2 Airfield Zone 2 2.3 Current Land Use 2 2.4 Current Ownership 4 2.5 Existing Form 5 2.5.1 Catchment 5 2.5.2 Channel Development 5 2.5.3 Creek Channel 5 2.5.4 Vegetation 11 2.5.5 Significant and Regulated Trees 11 2.5.6 Bridges 12 2.5.7 Services 12 2.6 Access and Circulation 12 2.6.1 Pedestrian 12 2.7 Amenity 15 2.7.1 Grassmere Reserve 16 2.7.2 Watson Avenue 16 2.7.3 Open Space 17 2.8 Biodiversity 17 2.8.1 Flora 17 2.8.2 Fauna 17 2.9 Geotechnical Assessment 19 2.10 Heritage 19 2.10.1 Local Heritage 19 2.10.2 Aboriginal Heritage 21 2.11 Environmental Assessment – Site History 21 3 Community Consultation – Key Issues 22 3.1 Context 22 3.2 Key Issues and Opportunities 23 3.3 Overall Most Desired Elements 24 4 Project Opportunities 25 4.1 Significant Trees 25 4.2 Biodiversity 25 Ref No. 2012.0679FR2D Lower Brown Hill Creek Channel Upgrade Stage 1 - Engineering Feasibility Report - Interim Report 4.3 Amenity 25 4.4 Recreation 26 4.5 Minimise Hard Infrastructure 26 4.6 Minimise Footprint 26 4.7 Improved Connectivity 26 4.8 Public Access 26 5 Channel Upgrade 27 5.1 Introduction 27 5.2 Design Criteria 27 5.2.1 Stormwater Management Plan 27 5.3 Cross Section options 27 5.3.1 Option 1 – Concrete Channel Vertical Sides 28 5.3.2 Option 2 – Box culvert with public access above 29 5.3.3 Option 3 – Gabion-lined open channel 30 5.3.4 Option 4 – Earth Channel 31 5.3.5 Option 5 – Low Flow Channel overtopping box culvert 32 5.3.6 Other Options 32 5.4 Hydraulic Modelling 33 6 Constructability and Opinion of Cost 36 6.1 Construction Cost 36 6.2 Constructability 37 6.3 Property Acquisition 37 6.4 Total Construction cost including Land Acquisition 38 7 Multi-Criteria Analysis 40 7.1 Total Score and Ranking Outcome from MCA Workshop 41 7.2 Discussion 42 8 Project Opportunities and Alternatives 43 8.1 Hydrology 43 8.2 Keswick Bypass Alignment (West Torrens) 43 8.3 Additional Geometry Option – Culvert underlaying an open space flood flowpath 44 9 Recommendations 45 10 References 47 Ref No. 2012.0679FR2D Lower Brown Hill Creek Channel Upgrade Stage 1 - Engineering Feasibility Report - Interim Report Tables Table 2.1 Significant tree locations within study area 11 Table 5.1 Channel upgrade options summary 35 Table 6.1 Linear metre construction pricing summary excluding land acquisition 36 Table 6.2 Property acquisition cost summary 38 Table 6.3 Total Cost Including Land Acquisition – 60 m3/s peak flow 39 Table 7.1 MCA Workshop Summary 41 Table 8.1 1:100 yr ARI flow (m3/s) in Brown Hill Creek immediately downstream of Anzac Highway - 43 Figures Figure 2.1 Locality Plan 3 Figure 2.2 Current Land Use 3 Figure 2.3 Current Ownership - East 4 Figure 2.4 Current Ownership - West 4 Figure 2.5 Existing creek - Anzac Highway to South Road 6 Figure 2.6 Existing Creek – South Road to Beauchamp St 7 Figure 2.7 Existing Creek - Downstream Beauchamp St. 8 Figure 2.8 Existing Creek – Grassmere Reserve 9 Figure 2.9 Existing Creek - Marion Rd. to Keswick Creek 10 Figure 2.10 Packard Street Pedestrian Bridge 13 Figure 2.11 Gray Street Pedestrian Bridge 13 Figure 2.12 Beauchamp Street Pedestrian Bridge 13 Figure 2.13 Cross Terrace Pedestrian Bridge 14 Figure 2.14 Location of Pedestrian Bridges 14 Figure 2.15 Bicycle lanes and designated pathways within study area (Source: City of West Torrens) 15 Figure 2.16 Grassmere Reserve 16 Figure 2.17 Watson Avenue Open Space 17 Figure 2.18 Local Heritage Items adjoining lower Brown Hill Creek (adapted from City of West Torrens Development Plan 2012) 20 Appendices Appendix A Planning Issues Report Appendix B HEC RAS Results Appendix C Constructability and Cost Estimate Report Appendix D MCA Analysis spreadsheet Ref No. 2012.0679FR2D Lower Brown Hill Creek Channel Upgrade Stage 1 - Engineering Feasibility Report - Interim Report Executive Summary The Stormwater Management Plan (SMP) for the catchments of Brown Hill and Keswick Creeks released in 2012 nominated a number of infrastructure upgrades required to mitigate a 1:100 year Annual Recurrence Interval (ARI) storm event (Worley Parsons 2012). The upgrade addressed in this feasibility study is the lower Brown Hill Creek channel, the boundaries of which are Anzac Highway upstream and the confluence with Keswick Creek downstream. The SMP nominated a design capacity for this section of channel of 60m3/s, whereas the current capacity is nominally 25m3/s. This report concerns the findings of the feasibility study stage of the design. The purpose of this study is to investigate the technical feasibility of the upgrade as well as the environmental and social impacts. The existing lower Brown Hill Creek channel is a combination of a natural earth and concrete trapezoidal cross sections with box culverts or bridges at road crossings. The community consultation process has identified a preference for a creek upgrade to incorporate some community benefit such as amenity upgrades, safety improvements and pedestrian and cyclist access. This study investigated a number of cross section geometry options to accommodate the 60m3/s design flow in terms of hydraulics, cost, environmental impact and social impact. These options included: Concrete channel with vertical sides Box culvert with public access or low-flow channel above Gabion-lined, stepped open channel Earth-lined trapezoidal channel (Natural channel) A single culvert underlying on open space floodway. Leed Engineering and Construction Pty Ltd completed a construction cost estimate of above cross section options, with the lowest cost being the vertical sided open concrete channel which was determined to be $59.8 million including contingencies. In addition to this, the cost of the property acquisition was estimated by Maloney Field Services and estimated conservatively to be between $7.4 million and $60.8 million depending on the cross section option required. However a “best case” scenario cost assuming the majority of the creek upgrade is within the existing creek corridor, favourable location of existing property boundaries and resale of surplus acquired land was estimated to be $2.6 million. A total construction cost including land acquisitions is in the order of $67.2M for the vertical sided channel. The above options were evaluated using a multi-criteria analysis (MCA) which considered social, environmental and financial factors. The highest ranked option was the earth-lined trapezoidal channel, but all scores were comparable. During the course of this study, the original hydrology and therefore peak design flow has been reviewed by DPTI as a result of recent changes to Intensity Frequency Duration (IFD) data as part of the 2013 revision of Australian Rainfall and Runoff and revised assumptions in the hydrologic modelling. In addition, the option of a bypass culvert running in the road network to reduce the scope of the main channel upgrade was investigated. The key outcomes of the study are as follows: For a design capacity of 60 m3/s, the vertical sided open concrete lined channel for the full length of the creek is the most cost-effective option at an estimated cost of $67.2 million (or $62.4 million with enhanced/rationalised land acquisition) Other options would also satisfy the design flow capacity, and provide social, environmental and amenity enhancements, but at significantly increased cost ranging from $89 million to $110 million. Alternatively, enhanced options could be constructed over limited sections of the creek, subject to project cost limitations. Ref No. 2012.0679FR2D Lower Brown Hill Creek Channel Upgrade Stage 1 - Engineering Feasibility Report - Interim Report i Based on revised hydrologic criteria the following options merit detailed investigation of two or more types of channel upgrade design: Vertical sided open concrete channel (with width for pathway alongside) Stepped gabion channel Twin-culvert underlying open space linear path Single culvert underlying an open space floodway Based on revised hydrologic criteria the option of a bypass culvert in the road network together with minor upgrades to Lower Brown Hill Creek meant further investigations. Ref No. 2012.0679FR2D Lower Brown Hill Creek Channel Upgrade Stage 1 - Engineering Feasibility Report - Interim Report ii 1 Introduction Tonkin Consulting has been engaged by the City of Unley, acting as the contracting party for the Brown Hill Keswick Creeks Stormwater Project (BHKCSP) to undertake the lower Brown Hill Creek Upgrade Study.