SEYMOUR FLOOD MITIGATION PROJECT PRELIMINARY DESIGN REPORT

Transcription

1 SEYMOUR FLOOD MITIGATION PROJECT PRELIMINARY DESIGN REPORT Report prepared for the SHIRE OF MITCHELL October

2 TABLE OF CONTENTS 1. Executive Summary 4 2. Background Previous Studies Modelled Flood Impacts Review of Structural Issues Bank Profile Levee Alignment Railway Line to High Street High Street to the Goulburn Valley Highway Goulburn Valley Highway Crossing (Wallis Street) Goulburn Valley Highway to Hanna Street Hanna Street Robert Street to Manners Street Manners and Tierney Streets 22 Goulburn Valley Highway Crossing (Tierney Street) 23 Goulburn Valley Highway to Railway Line Temporary Barriers Levee Use Internal/Cross Drainage Dwellings outside the Protected Area Services Planning & Legislative Issues Mitchell Planning Scheme Land Acquisition and Compensation Indigenous Cultural Heritage Non-indigenous & Cultural Heritage Native Vegetation Opportunities Created by the Levee Bank Climate Change Project Cost Review of Cost Cost/Benefit Maintenance Funding Federal & State Funding Local Funding Implementation References 56 2

3 Plan A Sheet 1 - Proposed Levee Alignment Sheet 2 Railway to High Street Sheet 3 High Street to Goulburn Valley Highway Sheet 4 Goulburn Valley Highway to Robert Street Sheet 5 Robert Street to Goulburn Valley Highway Sheet 6 Goulburn Valley Highway to Railway Line Plan B Drainage Catchments Plan C Land Acquisition Schedule 1 Alignment Photography Schedule 2 Dwellings Impacted by the Levee Bank Construction Schedule 3 Demountable Barriers Schedule 4 Project Cost Estimate Attachments; Seymour Levees, Preliminary Heritage Assessment, Executive Summary, Heritage Insight Pty Ltd. Heritage Advisor Report, Willys Keeble, Heritage Advisor, Shire of Mitchell. Geotechnical Report, Geotechnical Testing Services Pty Ltd. 3

4 1. Executive Summary This report provides a preliminary assessment of the design and construction options and cost to construct a levee bank to protect the section of Seymour township between the railway line, Whiteheads Creek and the Goulburn River. The report is based on the flood modelling data from the WBM Oceanics Australia (WBM) 2001 report, Seymour Floodplain Mapping Study. That report drew from the State Rivers and Water Supply Commission of Victoria (SR&WSC) study in 1981 and Flood Management Options Study of These initial Studies were done on behalf of the Eildon to Seymour Flood Warning Group. In 2002, WBM identified eight structural and non structural options to mitigate the impact of flooding on the section of the township. These options were put to the Seymour community through a survey. In conjunction with the Technical Steering Committee appointed to oversee the project, WBM recommended the construction of an earthen levee bank around the area to be protected as the preferred flood mitigation option. It is not the function of this report to determine if the levee bank should be constructed, but to provide the Shire of Mitchell with a more detailed assessment of the issues, cost and benefit of construction of a levee bank to protect the identified section of township from a flood of 1 in 100 year magnitude. It also outlines the process involved in constructing the levee bank, should Council determine to pursue the project through to construction. While this report has reviewed the proposal and carried out site investigations, further investigation during detailed design will be needed to confirm the various elements of the project. This report recommends that the levee alignment remain largely as proposed in the Seymour Flood Mitigation Communication Investigation, Final Consultants Report to Council, February 2006, with the only significant variations being shifting the highway crossings away from the Tierney Street and Wallis Street intersections and using private lands instead of constructed streets to avoid the need to reconstruct the streets along the top of the levee. Much of the recommended alignment is through privately owned property. Acquisition of land of suitable width will be required along the alignment to provide for the structure and enable access along it for management purposes. The bank will cause some dislocation of land use as it passes through private property. Hence land acquisition and compensation are significant aspects of the project costs. An estimate of the cost of acquisition of the land and compensation to the landowners is $1,700,000. The construction of a levee bank in the vicinity of the Goulburn River and Whiteheads Creek will constitute a high impact activity under the Aboriginal Heritage Act An initial cultural heritage assessment has been carried out along the proposed route of the levee. The assessment included a visual inspection of the ground surface and found that while there is no obvious evidence of cultural sites that 4

5 would be disturbed, a number of locations along the route have the potential to contain items of cultural heritage significance. A Cultural Heritage Management Plan will need to be prepared should the project proceed at which time these locations of potential significance will be assessed in more detail. The attached report (appendix 2) provided by the Heritage Advisor to the Shire of Mitchell emphasised the heritage significance of the Emily Street environment. On the basis of the perceived disruption to the connectivity and visual amenity of the area from the historical sense, the report recommended that the construction of the permanent levee bank should not proceed through the Emily Street heritage overlay area. The principal concern of the heritage advisor is the proposed permanent earthen bank structure, given its scale would be approximately m high through the section of the township between Emily Street and the Goulburn River. Temporary barrier systems are available or could be designed that could be erected in time and provide protection to the height required. These systems would be approximately 5 times more costly to construct than the earthen bank of equivalent height. This is a cost that must be balanced up against the visual impact of the permanent wall and the need to provide flood protection to the town. There will be native vegetation clearance required as a result of any alignment adopted. The revised alignment is chosen to reduce the clearance required, particularly in the area of Tierney Street. The soil structure along the alignment is of a relatively uniform silt, clayey silt or silty clay. Each soil type is generally suitable as the base for a levee bank, hence there are no identified geotechnical reasons why the technical design of the levee bank would be complicated or that unexpected construction difficulties would be encountered. The levee will be a prominent physical structure on the generally flat landscape. The typical profile would be an earthen bank ranging between 2 and 3 metres high above ground level and 3 metres across the crest. With potentially a significant impact on the visual amenity of the township, some care will be required to either ensure that it does not create unwanted visual disconnection between the lands on either side or, where appropriate, is used as a feature. There is some opportunity to use the structure for additional purpose in some sections, such as relocating the walking track along the Goulburn River onto its crest. The estimate of cost provided in the WBM 2006 report was $3.91m. This cost was based largely on the direct construction costs and on making more use of road reserves for the bank route than is proposed in this report. A review of the project cost, taking into account estimated associated costs such as land acquisition and compensation, but without detailed technical design is $6.2million. The benefit/cost of the project based on the revised cost is While this is reduced from 1.54 in the initial report, it is still within the range of benefit adequate for Council to consider proceeding with the project. 5

6 It is assumed that if Council proceeds with the project, a funding application to the newly developed Natural Disaster Resilience Program will be made. It is intended that the federal government will provide up to 50% of the project funds, with the state government and local government providing the other 50% between them. The share between state and local government has not yet been advised. A range of local funding options have been discussed in this report. The method of providing the local contribution to the project cost is a matter for the Shire of Mitchell. Community support for the project will be an essential component of any funding application to be made. It is recommended that if Council does wish to further consider the project, a structured community consultation process be first undertaken, within the provisions of section 223 of the Local Government Act Section 223 of the Local Government Act 1989 provides the community with the ability to make formal submissions to Council on the project and requires Council to give consideration to each submission in determining whether to proceed further with the project. This provides a robustness in the consultation process that will enhance the funding application. The works to construct the levee bank are exempt from requiring planning permit within the urban floodway zone of the Mitchell Planning Scheme. A public acquisition overlay is required to provide for the future construction of the levee and the acquisition lf the portions required of private property along the route. A planning scheme amendment is required to implement the public acquisition overlay. The amendment process would provide the opportunity for consideration of other matters such as heritage and vegetation removal. The conditions or offset plans relating to these other matters should be considered at the amendment stage and provided for in the amendment. This will ensure that all planning and land use and development issues are identified and appropriate conditions can be put in place at an early stage to enable more efficient planning and design of the project and more accurate application for funding. Council should subsequently rezone the land identified in the public acquisition overlay along the proposed alignment to public use zone. Summary of recommendations It is recommended that Council: Accept this report for the purpose of going to community consultation regarding whether to proceed to a funding application for the detailed design and construction of the levee bank. Undertake a community consultation process inviting submissions under Section 223 of the Local Government Act 1989 regarding either aspects of the project or whether Council should proceed with the project Consider all submissions received. Determine whether to proceed with the construction of the levee bank as outlined in the report, or as later refined during detailed design. 6

7 It is recommended that the following form the preliminary design criteria for the levee bank: The levee alignment be adopted as shown on attached Plan A. The standard construction of the levee to be an earthen bank built to a height of 600mm above the modelled 1:100 flood level. The standard profile of the bank is a crest width of 3m and side slopes (batter) at a maximum of 1m vertical to 2m horizontal on the protected (town) side and 1m vertical to 2.5m horizontal on the flooded side. Where a road is to be located on top of the levee bank, to allow a safe shoulder width, the crest width be increased to 10 metres and either the batters flattened considerably or guardrails provided. The levee bank be discontinued at the two junctions with the Goulburn Valley Highway, with temporary barriers to be installed as required to close the levee opening across the highway. Should Council determine following public consultation to proceed with a funding application for the construction of the levee bank, it is recommended that Council: Commence an amendment process under Part 3 of the Planning and Environment Act The amendment to apply the Public Acquisition Overlay (PAO) to privately owned land on the alignment with the intention of purchasing the land at a later date at market value or acquiring an easement over the land. Make application to the Natural Disaster Resilience Program for the acquisition of the lands necessary, detailed design and construction of the levee bank and associated works. Subject to the funding application being successful, Council can then; Commence the acquisition of the portions of private titles along the alignment as recognised in the public acquisition overlay. Complete the detailed design of the levee construction and associated works. It is recommended that Council should give consideration to; Give consideration to the closure to traffic of the section of Tierney Street between Goulburn Street and the Goulburn Valley Highway. Review of the land south of Whiteheads Creek regarding its potential as a bulky goods retail precinct. 7

8 Acknowledgements This report is based on the flood modelling and technical information contained in the WBM Oceanics Australia 2001 report, Seymour Floodplain Mapping Study. The proposed flood mitigation works are drawn from Seymour Flood Mitigation Communication Investigation, Final Consultants Report to Council, February 2006, The author of this report would like to acknowledge the assistance of the following persons in the preparation of this Report: Climate Change research was carried out by Michael Reynolds. Planning advice was provided by David Merrett, Director, ISIS Planning. Review of the technical content of the report was provided by John McCartney, Director, MC Solutions. Survey information and advice was provided by Duncan Salter, Eric Salter Pty Ltd 8

9 2. Background; 2.1 Previous Studies This report relies on the previous flood modelling and protection options assessment done by WBM Oceanics Australia (WBM). WBM carried out extensive flood modelling of the Goulburn River and other waterways, provided in the 2001 Report, Seymour Floodplain Mapping Study. That report drew from the State Rivers and Water Supply Commission of Victoria (SR&WSC) study in 1981 and Flood Management Options Study of These two initial studies were done on behalf of the Eildon to Seymour Flood Warning Group. WBM and the project Technical Steering Committee identified eight structural and non structural options to mitigate the impact of flooding on the section of Seymour generally between the Goulburn River, Whiteheads Creek and the railway line. WBM carried out a survey of residents in Seymour in 2002 to determine whether the residents would prefer either structural or non structural solutions to combat the possibility of flooding of the township in the future. Most residents identified mainly non-structural options which include community education and awareness programs closely followed by land acquisition and land use planning as the preferred options. Highly ranked though was flood proofing or raising of individual buildings. The residents saw this approach as adequate to provide protection from flooding and perceived it to be better than other structural approaches such as construction of levee banks and enlargement of existing waterways. The survey did not appear to indicate to the respondents the cost of the options nor the effectiveness of each in actually preventing the township from flooding. In conjunction with the Technical Steering Committee, WBM subsequently concluded that although the construction of a levee bank was one of the less preferred options by the community, protection of the township from flood inundation could only be feasibly provided by a physical flood barrier. The broad outline of the preferred option was presented to Council in the Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council, February It recommended construction of a levee bank and individual structural protection for isolated dwellings outside of the protected area. It also recommended the inclusion within the protected area of the urban area between the hospital and Catholic school by constructing the levee along Whiteheads Creek. The recommended solution is construction of a levee bank to protect the identified section of the Seymour township to the west of the railway line from the modelled 1 in 100 year flood. An alignment, which is almost entirely through properties or along road reserves within the Urban Floodway Zone, was suggested. However the report acknowledged this proposed alignment included no detailed design or technical analysis of issues and would be reviewed at the detailed design stage. That report provided a levee bank design profile but recommended further detailed technical investigation and community consultation to identify any issues impacting on the cost and ultimately the feasibility of the recommended option. 9

10 The option proposed was presented to an open community meeting. There was also ongoing communication with a community based focus group which provided some additional feedback to the community about the preferred option. Council subsequently gained additional funding Natural Disaster Mitigation Program to undertake an additional step in the usual funding phases for a flood mitigation project. It is this report that provides a more detailed assessment of the issues and cost of the preferred option. The assessment is provided to assist the Council to decide whether to undertake further community consultation on the project and to determine if there is sufficient community support to proceed with a funding application to the federal and state government for the detailed design and construction of the levee bank. The Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council, February 2006 needs also to be presented to the community as an adjunct to this report, as it contains information and conclusions that this report relies upon. This report does not review the recommendation of the WBM in a levee bank being the preferred flood mitigation option, but seeks to provide additional information to assist Council and the community to determine whether to proceed on that recommended basis. 2.2 Modelled Flood Impacts Flood modelling has been done by WBM over the Goulburn River, Whiteheads Creek and Sunday Creek catchments in determining the design flood levels and duration affecting the western area of the township. The 1 in 100 year flood level was determined as varying from 139.4m Australian Height Datum (AHD) at the upstream section of the levee to 137.0m AHD in the area of the junction of the Goulburn River and Whiteheads Creek. This is influenced by flood flows in both the Goulburn River and Whiteheads Creek. The flood level profile is provided in figure Year ARI (annual recurrence interval) Levee Long-Section within the 2006 WBM report. The profile indicates a level of inundation by a 1:100 year flood of generally between 1.5m and 2.5m depth of water along the levee alignment. Flooding of Seymour is often influenced by combined high flows in the Goulburn River and Sunday Creek. The report used 100 year ARI flows in both catchments at the same time (section 5.5.4) to calculate peak flood height. This is a conservative approach, but it has been estimated that the water level through the town under this scenario would be increased by only 50mm compared to a 1:100 year flood in the Goulburn River coinciding with a 1:20 year flow in Sunday Creek. Hence the more conservative approach has been used to determine the modelled 1:100year flood levels in the township. Although the impact of Whiteheads Creek has been taken into account in the hydraulic modelling, it is not included in calculation of the flood peak or mapping as 10

11 it has a very short time of concentration and generally peaks well before the main flows in the Goulburn River and Sunday Creek. It is assumed there is little chance of the two flood peaks coinciding. There is a view locally that it is Whiteheads Creek which causes the nuisance floods, which is possibly so, but the report found that the main impact through flood level and duration comes from convergence of the other two streams, and mainly from the Goulburn River. While the flood modelling indicates that not all of the section of township within the proposed protected area will be inundated during a 100 year flood, Figure 6.2 in the 2006 WBM Report indicates only the north-east section between the hospital, railway line and a line 100m east of Wallis Street will remain above water. Four hundred buildings within the section of township to the west of the railway line were identified as impacted by flooding at 1:100 year ARI. The 1974 flood inundated 200 buildings and is now regarded as a 1:30 year event. Only localised flooding occurred in WBM calculated the existing Average Annual Damage (AAD) to the township due to flooding at $715,000. It was assumed that the residents of Seymour are sufficiently experienced with floods that they are regarded as prepared residents and are subsequently able to carry out some flood minimisation works to reduce the impact. The existing AAD was therefore reduced to $490,000. The 2006 report assessed the capital cost of the levee bank and associated works at $3.91M with a construction life of 30 years before substantial rebuilding would be required of the bank. In the event of the levee being built as recommended in that report, the protection afforded to the township by the levee would reduce the AAD to an estimated $20,000. At that reduced AAD the benefit cost ratio (BCR) of constructing the levee was calculated as

12 3. Review of Structural Issues The 2006 WBM report acknowledged the need for review of the construction cost and a closer examination of the issues which were not considered in the assessment. To identify the issues and to review the assumptions regarding the alignment and profile of the levee structure in the previous reports, a series of further investigations were done. These included a land level survey, a preliminary archaeological assessment, and a geotechnical investigation of the existing soil structure along the route and local earthfill sources. 3.1 Bank Profile The recommended levee structure is a compacted earthen bank. The general standard profile of a flood protection bank is a crest width of 3m and side slopes (batter) at a maximum of 1m vertical to 2m horizontal on the protected (town) side and 1m vertical to 2.5m horizontal on the flooded side. The side batter on the flood side is flatter to reduce the erosive impact of the flood waters. The bank profile proposed in the 2006 WBM report was flatter side slopes of 1vertical to 3 horizontal on both sides. While this would provide additional structural strength to the bank, its wider base by on average 3m would also infringe more on the properties through which it passed, and the earthworks cost of the bank construction would be approximately 15-20% more than the standard proposed in this report. For these reasons this report has adopted for discussion and costing the side batters of the levee bank of 1:2 on the protected side and 1:2.5 on the flooded side be adopted. The height of bank (freeboard) above the modelled 100 year flood level is 600mm as proposed in the 2006 WBM report. Freeboard provides a margin of safety in the modelled flood levels and minimises the risk of erosion by wave action and failure of the top of the bank. Portion of the levee alignment was proposed to run along road reserves to minimise the impact on the private lands. The road reserves are either 20 or 30 12

13 metres in width and some contain constructed and sealed streets with kerb and channel. The footprint width of the standard (non trafficked) bank profile at 2m height is 13m across. This makes it generally not possible to locate a separate levee bank and constructed road within the 20m road reserve, particularly where there is the need to provide vehicle access to properties on both sides of the bank. Where it is proposed that the levee bank be constructed along a road reserve, to allow for reconstruction of the roadway along the top of the levee, then a widened bank profile is proposed. The bank crest would be sealed to prevent excessive wear of the surface level and protect the freeboard height required above flood level. To provide an adequate and safe road shoulder the crest width is increased to 10 metres and either the batters flattened considerably or guardrails are required. The bank base width then increases to 19m at a bank height of 2m above the existing road surface. Access for vehicles from the road on top of the levee to adjoining properties can be provided by a ramp down into the property. Generally this is only an option within rural areas as a ramp would become a significant imposition on a residential property so that levee bank construction along the road reserve within the residential areas is generally not appropriate. Generally, the bank profile and location will be determined by the environment and land use along its length. Much of the length is through paddocks, which have the potential to contain stock. It is proposed the bank that be fenced out of the paddock to confine the points where stock and vehicles can cross to protect the bank from excessive wear. Where stock and vehicle crossing is provided, the crest and sides of the bank will be gravel paved, and sealed if necessary. 3.2 Levee alignment The alignment proposed in the 2006 WBM report generally skirts the developed area of the section of town to be protected. However the report acknowledged a more detailed ground truthing of the proposed alignment and cost of construction of a bank was required. This review of the route issues was done with the aim of not constricting the extent of the floodplain significantly beyond that proposed by the WBM report and without 13

14 excessively increasing the length of the bank. Any significant additional restriction of the floodplain could have an upstream impact of raised flood levels. The focus of the project is to protect the urban or potential urban areas, with protection of rural lands to occur generally as a consequential benefit from adopting the most efficient and logical route and connection between sections of the bank. There are a number of unused road reserves around the perimeter of the township. To minimise the impact on private properties it is preferred where possible to run the bank along unused road reserves where available, or sections of private land which is either not intensively developed or is not likely to be developed. Constructing the bank along constructed roads or streets is possible and is considered along some sections. This however is generally not appropriate, particularly in a developed urban setting, due to the increased width required of the bank making it difficult to provide access to the adjoining residential properties and the high cost to reconstruct streets including the kerb and channel and drainage infrastructure into the bank. Hence the levee would of necessity pass through a number of private titles along the route. The impact on the private lands varies depending on their use or level of development. The Goulburn Valley Highway passes through the area to be flood protected. The levee alignment was proposed to cross the highway at the Wallis Street and Tierney Street intersections. Wallis Street is a major link from the highway to the town centre and is fully constructed with kerb and channel. Tierney Street is constructed and sealed to a rural standard on the south side of the highway, but is a formed earthen track on the north side. The location of the highway crossings is discussed in some detail in this report. Some variation is proposed to the levee alignment so that the crossing points are not at the road intersections. There is generally a discernable broader secondary stream channel outside of the main stream channel of the Goulburn River and Whiteheads Creek. This would largely contain the higher stream flows that spill out of the main channel, at a level prior to the water breaking out overland. There is no building development within this secondary channel. It is wholly contained within the Urban Floodway Zone, so no development is allowed that would restrict any flood flow. There is then a plateau above this which is the more general natural ground surface level on either side of the streams. This is the point at which the water would break out overland. To reduce the bank height and cost and to not reduce the floodway of the two streams too significantly it is proposed that the alignment of the bank is generally on the higher land just outside the secondary channel. On review of the levee alignment, variation is proposed to any significant extent only over two sections. For the purpose of describing the proposed alignment and 14

15 the issues the overall levee length has been broken down into six segments as below, and as outlined in Plan A: Levee Alignment. Schedule 1, Alignment Photography, provides a photographic representation of the existing conditions along the proposed levee alignment Railway line to High Street, through the catholic school grounds; This segment of approximately 280m length links the raised railway embankment and High Street through the catholic school grounds. The design bank height is generally between 2.0m above the ground level at the railway embankment, diminishing to 1.8m toward High Street. The land rises rapidly up to the High Street road formation so that the bank diminishes to virtually nothing at the road shoulder. The connection to the High Street road formation is approximately 20m from the bridge abutment. At this point the centreline of the sealed road surface is only 0.1m below the design height of the levee. The road formation will need to be lifted by 0.2m so the whole of the road and shoulders is at or above the levee bank height. The road shoulders should also be sealed to reduce the traffic wear on the road structure. The alignment passes through a number of undeveloped titles, all in the ownership of the school. There are though no major physical impediments to the construction of the levee bank. The bank would generally skirt the school buildings and carpark areas and the playing oval. The land on the creek side of the route is open grassland and treed. The alignment is proposed to provide a reasonable floodway width for the creek, but to protect the physical assets on the site High Street to the Goulburn Valley Highway; The initial route through this segment proposed following Callen, Gloster and Wallis Streets from the hospital to the highway crossing at Wallis Street. The sections of Callen Street and Wallis Street proposed to be used are both sealed with kerb and channel. Gloster Street is unconstructed but provides access to one residential property. Callen Street provides access to two residences and to the hospital and ambulance base. The levee bank height that would be required in the areas of Callen and Gloster Streets is approximately 1.2m above ground. If the levee ran along the road reserves and the streets were reconstructed along the top of the bank, it would be at least 15m wide at the base, effectively the width of the Callen and Gloster Street reserves. Wallis Street is a major link road from the highway into the township centre. It is a wider sealed road with kerb and channel both sides. It is suggested that to build the sealed and kerbed Callen St and Wallis St road structures up to the top of bank height would cause a considerable additional cost. Access to the residential properties fronting Callen and Gloster Streets would be very difficult, with a ramp required to intrude some distance into the properties. 15

16 The bank would also provide a considerable visual impact on the residences, which would generally be no more than 10metres from the toe of the structure. Two dwellings on the north side of Gloster Street route would be left outside the protected area if the route followed Callen and Gloster Streets. It is not apparent these dwellings have been accounted for in the WMB 2006 report regarding impact on dwellings due to the increased height of floodwater outside the levee bank. Consequently it is not regarded as appropriate that the route follow developed residential streets and an alternative route through this part of the township is proposed. The levee crossing of the highway is proposed to be between the Wallis Street intersection and Whiteheads Creek. The preferred location of the highway crossing is reviewed in section There is an unused road reserve (Federation Street) running across the open paddock area between the hospital and the (former Wallis Street) road reserve where the large open drain is located. The paddock area was initially proposed to be outside the levee bank; excluded from flood protection. The paddocks on either side of this unused road reserve are subdivided into a number of undeveloped residential size lots. All of the lots are in the same ownership, except for one owned by the Shire of Mitchell. The modelled flood level through this section reduces rapidly from the High Street bridge to about the helipad, from where the flood plain opens out more considerably. The levee bank height need only be about 1.1m as it passes around the hospital and raised helipad area. It increases to 2.0m across the paddock area and along the open drain. The bank height increases to approximately 2.7m inside the property at the High Street end. Constructing the levee bank along the road reserve between the paddocks will cause a dislocation to existing use of the property (although it is in a number of titles) but it will include the southern portion of the paddock inside the levee. This alignment will include an additional (potential) seventeen residential lots within the protected area. It will also include the two residences fronting onto Callen Street. The unused Federation Street reserve intersects the unused Wallis Street reserve at about 90m from Whiteheads Creek. The overall length of the open drain is approximately 220m from the pump station to Whiteheads Creek. It discharges into Whiteheads Creek immediately upstream of the highway bridge. The open drain is up to 10metres across and 2m deep, occupying about half of the road reserve area. It is therefore not possible to build the levee bank within the reserve without relocating or piping the open drain. If the levee bank is built, the drain from the pump will need to be piped to the outside of the levee bank to enable the pump station to discharge stormwater from inside the protected area during periods of flooding and to prevent entry of floodwater back up the drain. Piping the drain would enable the levee to be constructed along the reserve to the highway. 16

17 Whiteheads Creek passes within 20m of the property between the highway and unused road reserves. There is insufficient room to construct the levee bank entirely on the or the drain reserves while maintaining an adequate distance from the creek to avoid either intruding on the flow of water approaching the highway bridge crossing or to enable the bank to be constructed without collapsing the creek bank. The levee bank is proposed to cross the northern portion of the private property to the highway reserve to ensure an adequate setback from the creek. It is proposed that the northern most 20m of the lot, approximately 200m2, would be acquired for the bank. The trade off for the lot is that the balance would be flood protected whereas it was initially proposed to be on the flood side of the bank and therefore excluded from protection. The unused road reserve contains a number of trees and shrubs. The majority are red gum trees ranging in height from saplings to 15m. It is mainly the saplings growing within the open drain. The largest of the trees are along each side of the reserve. To minimise the number of mature trees affected, it is proposed that the levee bank be located generally centrally within the reserve. On review it is proposed that the levee run as proposed from High Street to the hospital, where it skirts the helipad to ensure it is flood protected. From this point the levee is proposed to run westward within the unused road reserve to meet the former Wallis Street reserve and open drain. It will then follow this reserve to the highway. While additional land will be included by this route, it is not considered that the loss of flood storage outside the levee bank will have an adverse impact on the flood levels in the immediate area. The proposed length of the levee bank is reduced by approximately 170m and the need to raise both Wallis and Callen Streets and the highway is removed. Two additional dwellings would be included within the protected area. Piping the open drain is an additional cost to the project to the initial proposed route Highway Crossing (Wallis Street) The modelled flood level at the eastern highway crossing, in the area of Wallis Street and Whiteheads Creek is 137.1metres Australian height datum (AHD). The Whiteheads Creek bridge deck height is approximately 137.1m AHD; about the modelled flood level for the location. The highway level falls by about 0.6m from the bridge to the Wallis St intersection. The design height of the levee bank above the highway is 0.6m at the bridge and 1.2m at Wallis Street. So a location toward Wallis Street is to be chosen. It is preferred to maintain a reasonable width of waterway for Whiteheads Creek, particularly at the bridge approach, to reduce the backing up of water levels caused by the highway and bridge flow constriction. VicRoads officers raised concerns regarding the raising of the highway affecting sight distance for vehicles at the Whiteheads Bridge and the need to also lift and reconstruct Wallis Street to grade back from the intersection with the highway. 17

18 The estimate to construct the highway over the levee bank and raising Wallis Street to match is $400,000. To provide a reasonable sight distance from Wallis Street and to provide adequate waterway for the creek, a crossing point at approximately 50m from the bridge is proposed. The level of the centre of the highway carriageway at this location is 136.8m AHD. The design bank height on either side of the highway is 0.9m above the carriageway. The level of the highway is generally lower than Whiteheads Creek bridge for approximately 1km to the east. In this section there are two significant dips in the highway, at 0.8m and 1.0m below the level of the bridge deck and the design flood level. Each dip is approximately 200m in length. This means the highway outside the protected area will be under up to 1m of water before the Whiteheads Bridge deck is inundated. Hence there is no purpose in building up the highway over the levee as the highway outside the levee will not be trafficable in any case during a 1:100 flood event. The preferred option is to leave the existing highway at its existing level, and to leave a gap in the levee across the road width. The gap is to be closed with a temporary barrier as required. The temporary barrier will not need to be installed until the water outside the protected area makes the highway non trafficable in any case Goulburn Valley Highway to Hanna Street The proposed alignment through this section is generally in accord with that in the WBM 2006 report. The height of the bank (including 0.6m freeboard above flood level) would range from 1.5m in the private property at the highway to 2.5m at Hanna Street. The height of the bank at the Hanna Street section is largely a result of the steep flood level gradient along the Goulburn River, which would be exaggerated due to the floodplain confinement caused by the levee bank. The alignment would skirt the sewerage pump station to include it within the protected area. From that point it crosses the paddock behind to link to Hanna Street. The Hanna Street reserve extends past Bolton Street, with another unused road reserve linking back down toward the highway. These would provide options for the levee alignment, but the bank would then intrude further into the flood plain and would include additional rural land within the protected area. Neither is the intention of this investigation, so it is proposed that the levee alignment follow and skirt the developed sections of the properties along Bolton Street to Hanna Street. At the bank height approaching 2.5m toward Hanna Street, it is not considered appropriate to locate the bank immediately adjacent to the dwellings. It is proposed that the bank be located 40m from the dwellings Hanna Street Hanna Street runs parallel with the Goulburn River. There are three properties between the street and the river. The most northern property at the Bolton Street intersection contains a dwelling; the middle contains a shed and the third (closest to Robert Street) contains some fruit trees, but no buildings. 18

19 The northern property is of significance as it is the site of the original brewery recognised in the Mitchell Planning Scheme. The dwelling is not the original brewery building. The three lots between the river and Hanna Street are within the Urban Floodway Zone, within which they will remain unless they receive flood protection. Within the Urban Floodway Zone there can be no further buildings constructed which would retard flood flow. Consequently a dwelling cannot be constructed on the central or southern lots. The height of the bank along the Hanna Street section would need to be approximately 2.3m to 2.5metres (including freeboard) above the existing road surface. The three properties will be inundated by up to 1.9m of water during a 1:100 flood. The dwelling is already on raised stumps, but to get the floor level to 300mm above the flood level it will need to be lifted a further 1.6m. The alignment initially proposed was along the road reserve, with the road to be located on top of the levee bank. The Hanna Street reserve width is 20metres. To include the road structure the width of the bank crest would need to be 10metres. Without the road structure, the crest width can be reduced to 3metres. At the batter gradients proposed of 1:2 on the protected side and 1:2.5 on the flood side, the width of the base of the bank would be; 20.8m to include the road structure along the crest, or 13.8m without the road structure on the crest. Hanna Street provides rear access to the majority of the properties on the protected side, most of which front onto Emily Street. There are two properties on the Emily Street side with either legal or developed frontage to Hanna Street. The main function of Hanna Street appears to be to provide access to the lots fronting onto it. The options considered included reducing Hanna Street to an access road providing access only to the abutting lots. The Bolton Street reserve continues past Hanna Street toward the river, to an informal rest area. There is a property to the east of Bolton Street which relies on this extension of the road reserve for access. Hence access over the levee at Bolton Street is required to be maintained in any case. The depth of the properties is only up to 50m, reducing to 35m at the Robert Street end. So there is little area between the buildings or the road and the river bank. The river bank is only approximately 30m from the sheds associated with the residence. An option considered is to construct the bank between the properties and the river. However the river has eroded the bank adjacent to the properties to the extent that the waterway is now partially outside the river reserve and has consumed about 50% of the vacant southern lot and intrudes into the middle lot containing the shed. 19

20 Due to the heavy vibration required to achieve the soil compaction requirements for the levee bank, it is not appropriate to construct the levee bank within 10m of the river bank. The footprint of the levee at 2.5m height would be about 14m width. Due to the proximity of the buildings there is insufficient room to construct the levee along the river side of the properties due to the intrusion of the river channel toward and into the properties. At the Robert Street end the river has eroded into the Hanna Street reserve by approximately half of its width. To retain a sufficient distance between the bank and the river bank, the levee bank route will need to pass through the tennis court section at the rear of the rear of the hotel property. Acquisition will be required from the rear of the hotel site to provide for the bank construction. The width of the land acquisition will depend on whether it is determined to maintain access to Hanna St from Robert St. The options considered and their issues and impacts is summarised below. Option 1. Construct the bank within the road reserve, with the road constructed along the crest. the minimum base footprint is approximately 21m width. The road reserve is 20m wide. A low retaining wall structure can be used to confine the bank to the road reserve. the toe of the bank would still be within 10metres of the dwelling on the northern lot. a ramp is required from the top of the bank if it is needed to maintain access into the property. Council s design standard is a maximum gradient of 10% so the ramp would extend 20metres into the properties. access to the dwelling property could be altered to the Bolton St frontage. the southern and central properties on the river side of the street rely entirely on Hanna St for access. it is not considered feasible to provide a ramp for vehicle access into the properties. most of the properties on the protected side have main access from Emily Street, using Hanna Street as a secondary access. Option 2. Construct the bank along the road reserve, but with the minimum 3m crest width. requires a bank footprint of 14m width. vehicle access along the toe of the bank is required to maintain access to the lots on either side. width of at least 3.6metres is required on either side, sufficient to provide laneway access. Hanna Street could cease to be a public road, providing access only to the adjacent properties. Option 3. Construct the bank through the properties to the river side of the road. 20

21 requires acquisition of the lots and removal of the dwelling. enables a bank of 3m crest width to be built. Provides sufficient land width to locate bank so as to avoid removal of mature red gum trees. Option 4. Construct the bank through the properties on the protected side of the road. requires acquisition of 20m width from the frontage of all lots. requires acquisition of one entire lot. There are large red gum trees along the road/property boundary. Option 5. Construct the bank within the properties between the dwelling and shed and the river. Requires a minimum of 10m setback from river bank, to prevent adverse impact from compaction of bank. Need to acquire a minimum of 16m from the rear of the properties. There is insufficient space between the dwelling and river for the levee bank, with the toe adjacent to the dwelling Requires removal of all sheds from the properties. Conclusion The lots to the river side of Hanna Street cannot be further developed unless they are flood protected. Effectively though they cannot be protected to enable their development. There is not sufficient room between the dwelling and river to construct the bank without acquiring at least 26m from the rear of the properties and having a significant impact on the dwelling. The dwelling is set back approximately 10metres from the road title boundary. The proposed levee structure would have a significant impact on the lands adjacent to Hanna Street and particularly those between the proposed structure and the river, from the aspect of vehicular access and from the visual and amenity disruption of an earthen bank of 2.5m high within 10m of the dwelling. Access to the dwelling outside the levee could be gained via the Bolton Street reserve at the side of the property. However access could not be physically provided to the other two lots due to the presence of the levee bank. On balance it is concluded that the levee bank would have such a significant access and amenity impact on the three lots along the river side of the road that Council should consider acquiring them to enable the levee bank to be constructed through these properties Robert Street to Manners Street There is a row of mature Monterey Cypress trees along the south side of Robert Street. There are two very large red gum trees at approximately 18m apart at the trunk and located at about either side of the preferred alignment. Between the red 21

22 gum trees are three of the pines which will require to be removed for the levee bank construction. There are four properties throughout this segment, each of which front onto Emily Street and run through to the river reserve. Any buildings on the lots are located toward the Emily Street frontage. The rear portion of each is not developed and is within the Urban Floodway Zone. As such they are currently not able to be developed in any way that causes an impediment to flood flows. The natural surface at the Emily Street frontage is approximately 136.7m AHD. The surface level falls to approximately 136.2m at about 10-20m inside the rear boundary of the lots. The rear portions of the four properties then fall relatively steeply away toward the river. As recommended by the WBM 2006 report, to reduce the height of the bank it is proposed to locate the bank within the rear portion of these properties, on approximately the line where they start to drop awat toward the river. The bank height would be approximately 2.2m to 2.3m through this section. A 20m width strip of the rear of each of the properties is proposed to be acquired for the levee construction Manners and Tierney Street Manners Street is a sealed roadway providing access from the highway to the New Crossing Place Lions Park boat ramp and picnic area at the Goulburn River. Tierney Street is a formed earthen road providing an alternative connection from Manners Street back to the highway. The section of Manners Street along the levee route is crown reserve (river frontage). The sealed road is located in a cleared section along the edge of the reserve of about 22m width adjacent to the private title. The private land is higher than the road area by up to 0.8m. The road structure, including gravel shoulders, is approximately 15m from the private property boundary. So adequate space is available to locate the levee bank between the road and private property. The height of the levee bank at the point where it would intersect Manners Street is about 1.7m to 1.8m. The road level falls by approximately 1.6m toward the intersection with Tierney Street. The design bank height would increase to 3.1m at the river end if it were combined with the roadway. The bank height at the fenceline would need to be less at 2.7m. Manners Street does not provide direct access to any private property over this section. Given that the boat ramp and picnic area on the river bank are not accessible during floods there is no incentive to ensure the roadway remains open to traffic during such times. If the road and the bank were separate structures the bank base width would be 10.2m at the highway end, increasing to approximately 17m at Tierney Street. It is proposed that the levee bank be built immediately adjacent to the private title boundary to reduce the height of the bank required and to retain the road between the bank and the tree area. 22