2013 Wickliffe Flood Investigation

Wickliffe Flood Investigation

RM2365 v1.0 FINAL Prepared for Glenelg Hopkins CMA December 2012

Cardno Victoria Pty Ltd

ABN 47 106 610 913

150 Oxford Street Collingwood VIC 3066 Australia

Phone: 61 3 8415 7500 Fax: 61 3 8415 7788

www.cardno.com.au

In association with:

Michael Cawood & Associates Pty Ltd 8 Stanley Street Chirnside Park VIC 3116

Phone: 61 03 9727 2216

Document Control Version Status Date Author Reviewer 0.1 Draft Feb 2012 Heath Sommerville HCS Rob Swan RCS 0.2 Draft Apr 2012 Heath Sommerville HCS Rob Swan RCS 0.3 Draft May 2012 Heath Sommerville HCS Rob Swan RCS 0.4 Draft Aug 2012 Heath Sommerville HCS Rob Swan RCS 0.5 Draft Sep 2012 Heath Sommerville HCS Rob Swan RCS 0.6 Draft Nov 2012 Heath Sommerville HCS Rob Swan RCS 1.0 Final Dec 2012 Heath Sommerville HCS Rob Swan RCS

Cover image: January 2011 floods for Wickliffe Source: Glenelg Hopkins CMA

© 2012 Cardno Victoria Pty Ltd All Rights Reserved. Copyright in the whole and every part of this document belongs to Cardno Pty Ltd and may not be used, sold, transferred, copied or reproduced in whole or in part in any manner or form or in or on any media to any person without the prior written consent of Cardno Pty Ltd.

Cardno LJ5786 Cardno Pty Ltd Wickliffe Flood Investigation RM2365 v1.0 FINAL EXECUTIVE SUMMARY The Glenelg Hopkins Catchment Management Authority, in partnership with the Ararat Rural City Council received State and Australian Government funding to undertake the Wickliffe Flood Investigation. Funding for the Investigation has been made available through the Victorian Coalition Government’s Flood Warning Network – Repair and Improvement initiative and the Australian Government’s Natural Disaster Resilience Grants Scheme. Cardno have undertaken the Wickliffe Flood Investigation with the assistance of Michael Cawood and Associates. Michael completed the Flood Warning System review and recommendations and developed the VICSES Municipal Flood Emergency Plan (MFEP) Appendices for this investigation.

The Wickliffe Flood Investigation is primarily in response to significant flooding in January 2011. The primary aim of this work was to undertake definitive flood investigations for the Hopkins River floodplain at Wickliffe and to undertake a comprehensive analysis with all of the available data to determine appropriate flood warning and response arrangements for the township of Wickliffe, including the derivation of flood levels and extents for planning purposes.

Key Deliverables The Wickliffe Flood Investigation has examined the Wickliffe floodplain in detail and the findings of this investigation are summarised within this report. The key findings from the investigation include: x Developing background information for understanding the catchment upstream of Wickliffe. x Qualification of the January 2011 flood event. x Developing the design flood events for Wickliffe including the 20%, 10%, 5%, 2%, 1%, 0.5% and 0.2% AEP events and the PMF. x Developing the Victorian Flood Database (VFD) compliant maps. x Developing flood maps for Wickliffe including maps showing depth, water surface elevation, flood contours, velocity, hazard class and flood extents. x Developing possible planning maps for implementation by the Ararat Rural City Council including the Floodway Overlay (FO) and the Land Subject to Inundation (LSIO). These maps have been developed for the pre and post removal of the old Glenelg Highway Bridge decking by VicRoads (planned to be completed prior to July 2013). x Detailed review and recommendations of the Flood Warning System for Wickliffe. x Development of the Municipal Flood Emergency Plan (MFEP) Appendices for use in conjunction with the Victoria SES documentation. x The identification of the high risk areas within Wickliffe and properties that are at risk of overfloor flooding. x Assessment of possible mitigation options and a cost / benefit assessment of these options.

Background Information Wickliffe is located within the municipality of Ararat Rural City. The study area includes the majority of the residential and commercial areas of Wickliffe. The area has generally flat topography. The study area incorporates the reach of the Hopkins River between the Burdett Lane in the north to the intersection of Chatsworth-Wickliffe Road and Huckers Road in the south. Within this segment a number of smaller tributaries join the Hopkins River at or upstream of the Glenelg Highway. A flow gauge is situated at Wickliffe on the west side of the Hopkins River. There are currently no flood related controls in the Ararat Rural City Council planning scheme. The township has historically been subjected to flooding and has no flood warning system.

Cardno LJ5786 Page iii Cardno Wickliffe Flood Investigation RM2365 v1.0 FINAL flow to Wickliffe. Wickliffe lies on the Hopkins River and has a catchment area of approximately 1,347 km2. This upstream area includes the Grampians National Park and the western uplands areas around Ararat.

The elevation for the Wickliffe catchment and for the full Hopkins River is shown in Figure 1.2. The highest elevation within the catchment is Mt William which has a peak elevation of 1,167 mAHD. The township of Wickliffe is at approximately 200 mAHD. The average annual rainfall across the catchment is relatively uniform with rainfall varying from 550 to 600 mm from Wickliffe to the upper catchment.

Hydrology The catchment topography is varied with the upper reaches including parts of the Grampians National Park which are very steep. However, the majority of the catchment is flat with the Hopkins River meandering across a low grade floodplain. Antecedent conditions within the catchment play an important role in the losses within the catchment due to the flat nature and multiple storages along the tributaries of the Hopkins River. Table i shows a summary of the streamflow information used in the flood investigation. There are only two streamflow gauges on the Hopkins River upstream of Wickliffe.

Table i Streamflow data used in the Wickliffe Flood Study Gauge Gauge Name Source Flow type Start Date End Date Missing No. Periods ‘Red Book’ Monthly Inst. max Jul-1920 Dec-1981 1934 - 1942 236202 Hopkins River at Wickliffe Data Warehouse Daily Inst. max May-1964 Aug-2011 - 236219 Hopkins River at Ararat Data Warehouse Daily inst. Max Jun-1989 Nov-2011 -

Flood frequency assessment was undertaken on the Wickliffe streamflow gauge to determine the peak flow rates associated with the design Annual Exceedence Probability (AEP) events. The design events were simulated using the method specified in Australian Rainfall and runoff (AR&R, 1987) and using the rainfall runoff program RORB. The Probable Maximum Flood (PMF) was developed using the Generalised Southeast Australia Method (GSAM) in accordance with the Bureau of Meteorology (BoM, 2003). The peak design events are summarised in Table ii for the main Wickliffe gauge and for the tributary designated as the Floate Lane Tributary to the North West of Wickliffe.

Table ii Wickliffe RORB design results Floate Lane Wickliffe Tributary CL ARI (years) AEP IL (mm) Critical (mm/hr) Peak flow RORB Peak Peak Flow Rainfall target (m3/s) flow (m3/s) (m3/s) Duration 1 in 5y 20% 15 1.7 65 67.0 18h 3.6 1 in 10y 10% 19 1.8 85 85.3 24h 4.4 1 in 20y 5% 22 2.25 110 109.8 24h 5.6 1 in 50y 2% 25 2.7 152 152.1 18h 7.5 1 in 100y 1% 29 3 194 196.0 72h 9.1 1 in 200y 0.5% 33 3.2 246 249.1 72h 11.5 1 in 500y 0.2% 37 3.7 336 338.4 18h 15.0 PMF PMF 37 3.7 N/A 4,600 36h 30.0

Climate change was assessed with the maximum increase in rainfall intensity explored at 32%. The 10% AEP climate change peak flow is predicted to increase to 231 m3/s which is higher than the current 1% AEP peak flow rate. The 1% AEP climate change event has increased from approximately 200 m3/s up to 537 m3/s which is

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higher than the current 0.2% AEP flood event. Table iii shows the summary of the predicted climate change impacts.

Table iii Climate change scenarios run through the hydraulic model 32% increase rainfall intensity at Hopkins River at Hopkins River at Wickliffe Wickliffe AEP (%) Design Flow CC Design Flow Increase (% from Peak Duration Peak Duration Rate (m3/s) Rate (m3/s) current) 10% 85.3 24h 231.7 18h 272% 1% 196.0 72h 537.4 72h 274%

The 270% increases in peak flow rates are thought to be a result of the large catchment size and the sensitivity of the loss rates throughout the catchment. For the purpose of this investigation the increases in peak flow rates have been accepted as the applied method is the accepted approach to modelling climate change impacts. The resulting flood extents indicate that climate change has the potential to have a significant impact of the peak flow rates for the Hopkins River at Wickliffe.

Qualification of the January 2011 Event A specific focus of this investigation was to explore and define the recurrence interval for the January 2011 flood event at Wickliffe. The January 2011 flood event is the largest flood event recorded at the Wickliffe gauge since 1920 when gauged records began. The peak level reached at the Wickliffe gauge was 5.89 m recorded on the 15th January 2011. The January 2011 event occurred following unusual high intensity rainfall which led to large volumes of rainfall falling from the 10th to the 14th January 2011. Rainfalls were in the order of 112 to 172 mm over this period and were the highest in the north of the catchment. At this point in time the catchments were already reasonably saturated due to a wet summer across the region. There was approximately 24 hours delay between the peak at Ararat and the peak at Wickliffe.

During the investigation of the January 2011 event the peak flow rate was revised numerous times due to rating table changes and investigation by Cardno as part of this study. Initially the peak flow rate was set at 700 m3/s, preliminary examination of this peak flow rate using RORB and the hydraulic model showed that this peak flow rate was likely to be too high. At this point in the project Cardno undertook a detailed assessment of this peak flow rate using a variety of methods outlined in Appendix B. The result of this assessment was that the peak flow rate was revised to approximately 450 m3/s.

Following this revision Thiess advised that they had made provisions to undertake a reassessment of the gauge at Wickliffe to develop a revised rating table. Thiess are the primary authority in developing and maintain the rating tables for many of the streamflow gauges within Victoria. Their revision set the peak flow rate for the January 2011 event at 250 m3/s +/- 15%. Through the calibration of the hydraulic model the peak flow rate was determined to be 287 m3/s, which is the upper range of the Thiess estimate. As a result of the flood frequency assessment (FFA) the predicted recurrence interval for the January 2011 event was 0.33% AEP (~1 in 300 year ARI).

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Design Flood Details The design flood peak levels were simulated using hydrographs as derived in the hydrology using RORB which were based on the FFA results. The WL|Delft 1D2D modelling system, SOBEK, was used to compute the channel (1D) and overland flow (2D) components of the study. Details of the hydraulic model development are summarised in Section 5.1.

For the Wickliffe study area the main river channel and structures were respresented within the model as 1D elements embedded into the 2D topography. The topography was defined within a 4m x 4m grid with elevations taken from the 1m LiDAR data (levels were verified using survey).

Two major flood events have occurred in recent history at Wickliffe that had peak streamflow levels, peak flood levels and extents captured that can be used to calibrate the hydraulic model. The two events where levels have been captured included the September 2010 and January 2011 flood events. No other large events have occurred in recent history that have peak levels or photographs captured. The hydraulic model was calibrated to these events and a good calibration was achieved with the extents and depths matched closely. The January 2011 flood event was the primary calibration event as the September 2010 levels were not captured at the peak of the event. Head losses across structures were checked by developing a HEC-RAS model of the structure to verify the losses observed in the model. Details of the calibration results are discussed in detail in Section 5.3.

The design events were run though the hydraulic model and the results were processed and examined. The key findings from the design runs included: x The 20% AEP flood event is largely contained within the main floodplain, this event does not overtop any roads or impact and buildings. x The 10% AEP flood is largely within the main floodplain, however at the western side of Wickliffe the Glenelg Highway is overtopped for approximately 10m. x The 5% AEP flood increases the road area overtopped to the west of Wickliffe to approximately 200 m with a peak depth of 0.15 m. No other roads or buildings are impacted. x In the 2% AEP design event this breakout flow is very small at 0.6 m3/s and the breakout is only just beginning to form, at these flow rates there is expected to be minimal damage to the properties due to the breakout. In this event some floodwater is approaching buildings but no buildings are expected to have overfloor flooding. x The 1% AEP flood is the first event to cause overfloor flooding. This event is predicted flood 3 buildings to overfloor levels, 2 residential (max 5 cm) and the CFA shed (13 cm). The breakout into the township increases with a peak flow rate of 10 m3/s. x The 0.5% AEP design event results in 6 buildings flooded overfloor, 5 residential (max 20 cm) and the CFA shed (34 cm). The breakout entering the town increases to 34 m3/s. Most of the main highway is overtopped through the study area. x The 0.2% AEP design event results in 11 buildings flooded overfloor, 10 residential (max 38 cm) and the CFA shed (64 cm). The breakout flow into Wickliffe increases to 60 m3/s and this results in the large number of properties with damage. The majority or roads are overtopped within the study area.

The predicted Probable Maximum Flood (PMF) was modelled using a peak inflow of 4,600 m3/s for the Hopkins River at Wickliffe. The main purpose of this assessment is to demonstrate the likely maximum extent possible for the study area. All sixteen (16) properties within the township of Wickliffe would be inundated. The results show that the extent is confined to the floodplain by relatively steep slopes. The flood shape and depths show that the flood extent is unlikely to ever be outside this range as the floodplain is well defined by steep embankments. Depths are well over 5 m in the main floodplain and Wickliffe would be inundated by meters of water.

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Sensitivity was undertaken on the hydraulic model including: x The 10% and 1% AEP design events simulated with the 32% climate change. x The +/- 20% roughness case for the 1% AEP design event. x The +/- 20% peak flow case for the 1% AEP design event.

Increasing the roughness by 20% led to peak water surface elevations increasing by between 9 and 14 cm. Decreasing the roughness by 20% led to decreases in depths of between 10 and 15 cm throughout the main flood plain. Decreasing the peak flow rate by 20% led to peak water surface elevation changes of between 14 to 35 cm. Increasing the peak flow rate by 20% increased depths by between 13 and 24 cm.

Datasets and Mapping The calibrated SOBEK model for Wickliffe was used to analyse the extent, location and depths for the 20%, 10%, 5%, 2%, 1%, 0.5% AEP events and the Probable Maximum Flood. Key outputs from the project are developed as a result of the detailed hydraulic modelling. Key outputs include: x Peak flood depths for all flood events (Figure 5.9 to Figure 5.16) x Flood extents for all flood events x Flood planning controls (flood overlays) x 1% AEP event o Hazard class maps o Extent with water surface elevation contours (200mm contour intervals) o Velocity map x Properties impacted during each flood event will be shown on each flood map.

Planning The planning controls developed for this investigation included the Floodway Overlay (FO) and the Land Subject to Inundation (LSIO) overlay. The LSIO was defined as the 1% AEP flood extent. The FO was defined in three ways to ensure that it covered the appropriate areas, including: x Based on the 10% AEP flood extent x Based on the hazard class greater than 2 for the 1% AEP design event x Based on the depths greater than 0.5 m for the 1% AEP design event.

Upon review of the three FO layers the 10% AEP design event flood extent was recommended for this overlay. The preliminary overlays were based on the current conditions including the old bridge deck upstream of the Glenelg Highway Bridge. From discussions with the Ararat Rural City Council and VicRoads, the old bridge deck is to be removed by July 2013 and as such the Council requested flood overlays developed based on this bridge deck being removed. A second set of overlays was developed with this bridge deck removed for future implementation by the council. Cardno was advised during the project that the documentation for the flood overlay implementation would not be requires at the Council required time to review their options for planning scheme implementation.

Flood Warning Review A staged approach to the development of a flood warning system for Wickliffe is proposed. The stages have been ordered and the tasks within each stage grouped to facilitate growth of all elements of the TFWS in a balanced manner and with full regard for matters discussed in Section 8.1. While it may be tempting to immediately move to install additional rain and river gauges and to develop a forecast model, but there are other more fundamental matters that experience tells us need to be addressed first. Thus early attention is directed at ensuring roles and responsibilities are agreed, understood and accepted and that there is a firm foundation for the development of an effective flood warning system: one that does not fail when it is needed most. Attention is

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then directed to establishing a robust framework for communicating and disseminating flood related information so that immediate and maximum use can be made of available information as the ability to detect and predict flooding at Wickliffe improves. Next, attention is focussed on securing the funding needed to buy, install and operate field equipment as well as other services needed to build elements of the TFWS. The installation of data collection equipment follows, with a two tiered approach in the event that funding is not available or is delayed. Development of other technical elements and the build and delivery of on-going flood awareness activities can then occur in the knowledge that required data is / will be available and that robust and sustainable arrangements are in place that will enable maximum benefit to be derived from any information or programs delivered to the community.

Stage 1 1. Council, Glenelg Hopkins CMA, VICSES and other entities to determine the responsible entity in relation to “ownership” of each element of the total flood warning system for Wickliffe. Note that ownership is considered to denote overall responsibility for funding as well as the functioning of the system element and, in the event of failure, responsibility for either fault-fix or the organisation of appropriate fault-fix actions along with any associated payments. This includes resolving responsibility for funding the continued operation of equipment upgraded by the Glenelg Hopkins CMA at the Ararat and Wickliffe gauging stations. VFWCC (2001) provides guidance on data collection network aspects although recommendation 1 from the Comrie Review Report (Comrie, 2011) suggests that some clarifications may be required.

Stage 2 1. Council to champion and in conjunction with VICSES oversee the establishment of a flood action or flood warden group for Wickliffe. Clearly establish the role for this group along with its authority and structure with due regard for liability issues. Essentially the group would: x Collect and collate rain and water level / flow data and also monitor rain and river information via the Bureau’s website. x Make initial assessments of the likelihood and scale of flooding at Wickliffe based on available rainfall data, water levels and trends at Ararat and Wickliffe, and the indicative quick look ‘flood / no-flood’ tool developed for Wickliffe and included in the Ararat MFEP. x In the event of likely flooding, call VICSES to advise of likely flooding and, subject to discussion with the RDO or IC, call the Ararat Rural City MERO and initiate flood response actions within Wickliffe consistent with the MFEP. This may include door knocking and through the MFEP, identification of properties likely to be impacted and the coordination of removal of items susceptible to damage from floodwater from buildings likely to be flooded over-floor when conditions indicated it is warranted or necessary and thereafter work closely with VICSES, CFA and Council. x Maintain a watching brief on flood response arrangements within Wickliffe and provide feedback to Council on the adequacy and efficacy of arrangements in place at the time. 2. Council with the support of VICSES, Glenelg Hopkins CMA and the Wickliffe community to submit an application for funding under the Australian Government Natural Disaster Resilience Grants Scheme (or similar) for all outstanding elements of a TFWS for the Hopkins River to Wickliffe. 3. Council to share the MFEP with the Wickliffe community. 4. Council to establish arrangements for the timely supply of sandbags and sand within Wickliffe. 5. Council to load and maintain flood related material (including the MFEP) to its website. 6. Council and VICSES to encourage and assist residents and businesses to develop individual flood response plans.

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Stage 3 1. Install a set of staff gauges (up to 6 x gauge plates) immediately upstream of the Back Bolac Road on the Hopkins River and another set at Half Way Gully on Major Mitchell Road. Set to either AHD or local datum and survey to AHD. Establish on-going gauge reading and maintenance arrangements, the latter ideally through the Surface Water Monitoring Partnership. 2. Update the MFEP with staff gauge datums and other relevant details. 3. Council in conjunction with VICSES to establish and document in the MFEP arrangements for the timely: x Pick-up and removal of items susceptible to damage from floodwater from buildings likely to be flooded; x Supply of sandbags and sand within Wickliffe with sufficient lead time to enable buildings at risk of minimal over-floor flooding to be sandbagged / protected. 4. VICSES to initiate a community engagement program at Wickliffe in order to communicate how the flood warning system will work. This will need to be repeated as the system matures. 5. VICSES to develop and distribute a FloodSafe brochure for Wickliffe. 6. Council to oversee the development, printing and distribution of property-specific flood depth charts for properties within Wickliffe.

Stage 4A – to be actioned only if funding to undertake Stage 4B is either not available or is delayed 1. Either directly with the reader or possibly through Bureau of Meteorology, arrange for access to as-required rainfall data from the BoM daily-read rain gauges at Willaura and Wickliffe. Ideally this will involve the reader in providing data directly to the flood action or flood warden group at frequent intervals during heavy rain events. 2. If the outcome from 1 above is negative, determine the location of private rain gauges in close vicinity to Willaura and at Wickliffe and establish arrangements for the provision of rainfall data to the flood action or flood warden group at frequent intervals during heavy rain events. Alternatively, source two rain gauges and distribute to local residents willing to provide rainfall data at frequent intervals during heavy rain events in the general vicinity of: x Wickliffe (priority 1). x Willaura (priority 2).

Stage 4B 1. Using equipment similar to (or the same as) that already installed and operational at the Ararat gauging station: x Establish a telemetered rain and stream gauge at the Back Bolac Road site; x Add a rain gauge to the Wickliffe gauging station. 2. Establish on-going maintenance arrangements for all installed equipment, ideally through the Surface Water Monitoring Partnership. 3. Approach BoM to add all telemetered sites to appropriate rainfall and river level bulletins accessible via the BoM website. Requires telemetry systems used to be fully compatible with BoM systems. 4. Council to begin building a relationship between levels at the stream monitoring sites at Back Bolac Road, Half Way Gully on Major Mitchell Road and Wickliffe in order to assist flood assessment and response at Wickliffe and in order to inform the development and / or firming up of flood class levels at each site. 5. If appropriate and following achievement of full operational status of each telemetered site providing additional rain and river data, retire the manual readers in the general vicinity who have previously provided that data for the Wickliffe flood warning system.

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Stage 5 1. In conjunction with VICSES, Glenelg Hopkins CMA and the Wickliffe-based flood action or flood warden group, Council to determine appropriate rain and river trigger levels for the initiation of SMS alerts and / or email alerts from telemetry sites. 2. BoM to establish a rainfall-runoff based flood forecast model for the Hopkins River to Wickliffe.

Stage 6 1. Install flood depth indicator boards at key locations in and around Wickliffe (e.g. on both approaches to the Glenelg Highway Bridge at Wickliffe and at strategic locations on Walker Street as indicated by the flood inundation maps delivered by the Wickliffe Flood Investigation) and further afield.

Economic Damage Assessment A flood damage assessment was undertaken for the existing catchment and floodplain as part of the current study. The assessment is based on damage curves that relate to the depth of flooding on a property to the likely damage to a property. Details of the damage assessment are summarised in Section 7. The damage curve as developed as part of this investigation is shown in Figure i.

Figure i Flood damages used to estimate the Average Annual Damages

The Average Annual Damage (AAD) calculated for Wickliffe was determined to be $ 14,405 per annum. The AAD used the assumption that there was no damage for the 40% AEP event. The peak event used in the damage assessment was the 0.2% AEP design event.

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Mitigation Assessment The mitigation assessment looked at implementing four structural mitigation options and one option of clearing the vegetation from the main floodplain near the township. The assessment examined the 1% AEP design event and the impacts that the mitigation options had on the peak flood levels and flood behaviour. The January 2011 event was also simulated due to the historical context of this flood for Wickliffe. The five mitigation options are summarised in Table iv and are shown in Figure 9.2.

Table iv Nonclementure for the mitigation option assessment

Option Description Mitigation 1 Removing the old Glenelg Highway bridge deck Mitigation 2 Levee 1 (100m levee) Mitigation 3 Additional culverts (10 x 1,200 mm x 900 mm) (no. x width x height) Mitigation 4 Levee 2 (800m levee) Mitigation 5 Vegetation clearing (Area of 660 m2)

From the analysis it was found that removing the existing bridge deck from upstream of the current Glenelg Highway Bridge was the most effective mitigation option in reducing peak flood levels. This mitigation option was shows to have a payback period of approximately 17 years. Constructing a levee along McKenzie Road (Levee 1) was shown to be very effective in reducing the breakout flow that entered the town from the south east. The cost / benefit assessment showed that this mitigation option is not quite economically viable but is worth considering as a possible future mitigation option.

The remaining two structural mitigation options, the additional culverts and Levee 2, were both not viable options due to their prohibitive costs and impracticalities in construction. It is recommended that these mitigation options are not pursued as future options for the protection of Wickliffe.

Vegetation clearing on a large scale was shown to have some impact on reducing the peak flow rates during large flood events. An area of 660 m2 was considered as being cleared in the modelling for this mitigation option. Cardno would like to emphasise that the vegetation scenario modelled was as if the grass had just been cut at very low levels and that all bushes had been completely removed from the floodplain. Trees were modelled as remaining on the floodplain. It is unlikely the floodplain would be able to be maintained at these levels as this would require excessive maintenance but this simulation was to demonstrate the maximum possible impact that vegetation clearing could have on the system.

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Acknowledgements Cardno would like to acknowledge the contributions of the following organisations and individuals who provided invaluable assistance during the course of this investigation. x Michael Cawood and Associates who completed the Flood Warning System review and recommendations and developed the Municipal Flood Emergency Plan appendices. x Glenelg Hopkins CMA, in particular Jacinta Hermann who managed the project and provided assistance throughout the entire project. x Department of Sustainability and Environment, in particular Simone Wilkinson who provided great feedback and input at Steering Committee Meetings. x VicRoads, specifically David Hildebrand who provided feedback regarding mitigation options and provided costing for these options. x Bureau of Meteorology who attended meetings and provided feedback through the project. x Wickliffe Flood Action Group, in particular to Leesa Baker who attended all meetings and encouraged the Community to get involved with the project. x Ararat Rural City Council, in particular Alison Tonkin, Joel Hastings and Neil Manning. x VICSES, in particular Gavin Kelly. x Wickliffe CFA, in particular George Burdette who local knowledge and feedback was critical in understanding the January 2011 event and the Community requirements for flood warning. x Wickliffe Community, with thanks to George and Barbara Burdette, Mr and Mrs Ken Ford, David Hucker and Leesa baker for providing feedback via the detailed questionnaires for the Wickiffe flood Investigation.

Overall, this flood investigation was well supported by many organisations and especially by the Wickliffe Community. Cardno appreciates the involvement and contributions of the Community and hopes that they receive the benefits from the flood investigation in the future.

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Executive Summary ...... iii Glossary ...... iv Abbreviations ...... vii 1 Introduction and Study Objectives ...... 1 1.1 Study Area ...... 1 1.1.1 Catchment Characteristics...... 2 1.2 Study Objectives...... 5 2 Community Consultation ...... 6 3 Survey and Mapping ...... 7 3.1 Survey – Spot Heights, Cross Sections and Structures ...... 7 3.2 LIDAR Data ...... 8 3.2.1 LIDAR Data Validation ...... 9 3.3 Mapping ...... 12 4 Hydrology ...... 13 4.1 Background Information ...... 13 4.2 Available Data ...... 14 4.2.1 Rainfall data...... 14 4.2.2 Streamflow data ...... 15 4.3 Historic Event Discussion ...... 16 4.3.1 1909 Event ...... 16 4.3.2 1983 Event ...... 18 4.3.3 January 2011 Assessment ...... 19 4.4 Rainfall Assessment ...... 23 4.4.1 Rainfall Frequency Assessment (RFA)...... 23 4.4.2 Historic Rainfall Assessment ...... 24 4.4.3 Discussion ...... 26 4.5 Flood Frequency Analysis ...... 27 4.6 Review and Develop Hydrological Models ...... 29 4.6.1 Existing RORB Model...... 29 4.6.2 Developed RORB Model ...... 30 4.6.3 Alternative WBNM Model ...... 35 4.7 Design Events ...... 36 4.7.1 Tributary (North East of Wickliffe – Upstream Floate Lane) ...... 37 4.7.2 Verification of Design Flows ...... 37 4.8 Hydrologic Model Sensitivity...... 40 4.8.1 Sensitivity on the RORB kc parameter...... 40 4.8.2 Sensitivity on the RORB ‘m’ parameter ...... 41 4.8.3 Sensitivity on the RORB loss rate ...... 41 4.8.4 Discussion ...... 42 4.9 Climate Change Assessment ...... 43 4.10 Probable Maximum Flood ...... 45 4.11 Travel Time Assessment...... 46 4.11.1 Streamflow gauge assessment ...... 46 4.11.2 Calibrated RORB travel times ...... 48 4.11.3 Anecdotal travel time ...... 50 4.12 Summary and Recommendations...... 51 5 Hydraulic Modelling ...... 52 5.1 Hydraulic Model Establishment ...... 52 5.2 Hydraulic Model Development...... 52 5.2.1 Channel and Structure System (1D)...... 53 5.2.2 Topography (2D) ...... 53

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5.3 Hydraulic Model Calibration ...... 56 5.3.1 2010 Event ...... 56 5.3.2 2011 Event ...... 59 5.3.3 Calibration Summary ...... 64 5.4 Calibrated Model Parameters ...... 64 5.4.1 Hydraulic Roughness ...... 64 5.4.2 Boundary Conditions ...... 66 5.5 Design Event Results...... 67 5.5.1 20% AEP Event ...... 67 5.5.2 10% AEP Event ...... 67 5.5.3 5% AEP Event ...... 67 5.5.4 2% AEP Event ...... 68 5.5.5 1% AEP Event ...... 68 5.5.6 0.5% AEP Event ...... 69 5.5.7 0.2% AEP Event ...... 69 5.5.8 PMF Event ...... 69 5.6 Climate Change Results ...... 78 5.7 Hydraulic Model Sensitivity Assessment ...... 81 5.7.1 Roughness Assessment ...... 81 5.7.2 Low and High Flow Sensitivity ...... 84 6 Datasets and Mapping ...... 87 6.1 Design flood extents ...... 87 6.2 Flood Planning Controls ...... 126 6.3 Flood Related Planning Zones and Overlays ...... 127 6.3.1 Urban Floodway Zone (UFZ) ...... 127 6.3.2 Floodway Overlay (FO) ...... 128 6.3.3 Land Subject to Inundation Overlay (LSIO) ...... 134 6.3.4 Special Building Overlay (SBO) ...... 138 6.3.5 Recommended Planning Controls...... 138 6.4 Planning Amendment Documentation...... 138 7 Economic Damages ...... 139 7.1 Damage Analysis...... 140 7.1.1 Residential Damage Curves ...... 140 7.1.2 Commercial Damage Curves ...... 142 7.1.3 Industrial Damage Curves ...... 142 7.1.4 Road damages ...... 142 7.1.5 Property Damages ...... 143 7.2 Annual Average Damage ...... 144 7.3 Results ...... 144 7.4 Assumption and Qualifications ...... 146 8 Flood Response Plan Review ...... 147 8.1 Flood Warning Systems ...... 147 8.1.1 Overview ...... 147 8.1.2 Limitations of Flood Warning Systems ...... 147 8.1.3 The Total Flood Warning System Concept ...... 148 8.1.4 Total Flood Warning System Building Blocks ...... 149 8.2 Existing Flood Warning System – Hopkins River...... 150 8.3 The Task for Wickliffe ...... 150 8.3.1 Data collection and Collation ...... 152 8.3.2 Flood Detection and Prediction ...... 156 8.3.3 Interpretation...... 157 8.3.4 Message Construction and Dissemination...... 157 8.3.5 Response ...... 160

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8.3.6 Community Flood Awareness ...... 160 8.4 Suggested System for Wickliffe ...... 161 8.5 Estimated Costs for TFWS for Wickliffe ...... 166 8.6 Suggested Actions...... 170 9 Mitigation Assessment ...... 173 9.1 Identification of High Risk Flood Areas ...... 173 9.2 Identification of Possible Mitigation Options ...... 175 9.2.1 Mitigation 1 – Old Bridge Deck Removal ...... 176 9.2.2 Mitigation 2 – Levee 1 ...... 176 9.2.3 Mitigation 3 – Additional Culverts ...... 177 9.2.4 Mitigation 4 – Levee 2 ...... 177 9.2.5 Mitigation 5 – Vegetation Clearing ...... 177 9.3 Mitigation Results ...... 179 9.3.1 1% AEP Results...... 179 9.3.2 January 2011 Results...... 192 9.3.3 Selected Mitigation for Detailed Assessment ...... 198 9.4 Mitigation Costing ...... 198 9.5 Mitigation Cost / Benefit ...... 198 9.6 Recommendations...... 205 10 Conclusion ...... 206 11 References ...... 207

Cardno LJ5786 Page xv Cardno Wickliffe Flood Investigation RM2365 v1.0 FINAL List of Tables Table 3.1 Permanent survey marks ...... 7 Table 3.2 Assessed difference in LiDAR and Survey vertical data (m) ...... 10 Table 3.3 Assessed difference in adjusted LiDAR data and survey vertical data ...... 11 Table 4.1 Selected rainfall gauges in the Wickliffe catchment area...... 14 Table 4.2 Pluviograph data used in the Wickliffe Flood Study ...... 14 Table 4.3 Streamflow data used in the Wickliffe Flood Study ...... 15 Table 4.4 Rainfall depths leading to the August 1983 flood event ...... 18 Table 4.5 Rainfall depths leading to the January 2011 flood event (restricted) ...... 21 Table 4.6 Selected rainfall gauges in the Wickliffe catchment area...... 23 Table 4.7 Rainfall depths estimated for the 24, 48 and 72 hour duration events (non-restricted) ...... 24 Table 4.8 ARI assessment for each event assessed for the corresponding period ...... 25 Table 4.9 FFA results with the January 2011 event...... 27 Table 4.10 Wickliffe RORB Model Calibration Parameters ...... 31 Table 4.11 October 1975 calibration results ...... 32 Table 4.12 September 1983 calibration results ...... 32 Table 4.13 September 2010 calibration results ...... 33 Table 4.14 January 2011 calibration results ...... 34 Table 4.15 Design RORB parameters ...... 35 Table 4.16 Wickliffe Intensity Frequency Duration (IFD) parameters ...... 36 Table 4.17 Wickliffe RORB design results ...... 36 Table 4.18 Wickliffe tributary design flows ...... 37 Table 4.19 Estimated of regional 1% AEP ...... 38 Table 4.20 Sensitivity on the RORB kc parameter...... 40 Table 4.21 Sensitivity on the RORB ‘m’ parameter ...... 41 Table 4.22 Sensitivity on the RORB design loss rates ...... 41 Table 4.23 Results of the design loss rate sensitivity analysis ...... 42 Table 4.24 Wickliffe Intensity Frequency Duration (IFD) parameters for climate change ...... 43 Table 4.25 Climate change assessment for the Wickliffe hydrology...... 44 Table 4.26 Wickliffe PMP parameters for the GSAM ...... 45 Table 4.27 Estimated PMP rainfall depth...... 45 Table 4.28 Predicted Probable Maximum Flood at Wickliffe ...... 45 Table 4.29 Travel times for large events though the Wickliffe catchment ...... 46 Table 4.30 Travel time assessment results from RORB ...... 49 Table 4.31 Wickliffe design flow rates for the hydraulic model ...... 51 Table 4.32 Travel time assessment results from RORB ...... 51 Table 5.1 Topography grid size ...... 53 Table 5.2 Calibration results for the September 2010 flood event ...... 56 Table 5.3 Calibration results for the January 2011 flood event ...... 61 Table 5.4 Calibrated Roughness Parameters, Mannings ‘n’ ...... 64 Table 5.5 Climate change scenarios run through the hydraulic model ...... 78 Table 5.6 Sensitivity analysis on the roughness parameters ...... 81 Table 6.1 Melbourne Water Safety Risk Definition ...... 129 Table 7.1 Residential damage curve adjustment factor ...... 141 Table 7.2 Roads damage adjustment factor ...... 142 Table 7.3 Unit damages for roads and bridges (dollars per km inundated) ...... 143 Table 7.4 Assumed property damages (land use supplied from land.vic.gov.au)...... 143 Table 7.5 Summary of Economic Flood Damages ...... 145 Table 8.1 Flood Warning System Building Blocks and Possible Solution for Wickliffe with due regard for the EMMV, Commonwealth-State arrangements for flood warning service provision (BoM, 1987), VFWCC (2001) and EMA (2009)...... 162 Table 8.2 Estimated cost associated with the proposed Flood Warning System...... 166

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Table 9.1 Nonclementure for the mitigation option assessment ...... 175 Table 9.2 Nonclementure for the mitigation scenarios ...... 179 Table 9.3 Estimated installation costs for the selected mitigation options...... 198 Table 9.4 Unit damages for roads and bridges (dollars per km inundated) ...... 199 Table 9.5 Summary of Economic Flood Damages for Mitigation Scenario 1 (Mitigation 1)...... 200 Table 9.6 Summary of Economic Flood Damages for Scenario 2 (Mitigation 1 and 2) ...... 201 Table 9.7 Summary of Economic Flood Damages for Mitigation Scenario 3 (Mitigation 1 and 3) ...... 202 Table 9.8 Assumptions for the net present value calculations ...... 203

List of Figures Figure 1.1 Study area ...... 1 Figure 1.2 Elevation map for the Hopkins River catchment (DPI, 2011) ...... 2 Figure 1.3 Land use for the Hopkins River to Wickliffe (GHCMA, 2011) ...... 3 Figure 1.4 Geomorphological units for the Wickliffe catchment (DPI, 2008) ...... 4 Figure 3.1 Field survey information locations ...... 8 Figure 3.2 LiDAR data extent within the study area...... 9 Figure 3.3 Difference in LiDAR data and survey ...... 10 Figure 3.4 Adjusted LiDAR data set compared to field survey ...... 11 Figure 3.5 Topography for the study area ...... 12 Figure 4.1 Annual peak flow rates for the Hopkins River at Wickliffe ...... 13 Figure 4.2 Location of Pluviograph and Rainfall Gauges in the Wickliffe Catchment Area ...... 15 Figure 4.3 Images supplied from the Community for the flood occuring in 1909 ...... 17 Figure 4.4 Peak flows during the August 1983 flood event ...... 18 Figure 4.5 Revision to the rating table at Hopkins River at Wickliffe ...... 20 Figure 4.6 Rainfall depths for the January 2011 flood event ...... 21 Figure 4.7 Peak flows during the January 2011 flood event ...... 22 Figure 4.8 FFA results with the January 2011 event...... 28 Figure 4.9 Existing RORB model upstream of Hopkins River at Ararat gauge ...... 29 Figure 4.10 Wickliffe RORB model ...... 30 Figure 4.11 Peak flow travel times through the Wickliffe catchment during the January 2011 event ...... 47 Figure 4.12 Peak flow travel times through the Wickliffe catchment during the September 2010 event ...... 47 Figure 4.13 Locations assessed for the travel time within the RORB model ...... 49 Figure 5.1 Model boundary for the Wickliffe SOBEK Model ...... 53 Figure 5.2 Example cross section for the Hopkins River near Wickliffe ...... 54 Figure 5.3 Digital Terrain Models (DTM) for the Wickliffe Model ...... 55 Figure 5.4 Summary of the calibrated September 2010 flood event ...... 58 Figure 5.5 Rescue boat used during the Wickliffe floods ...... 60 Figure 5.6 Summary of the calibrated January 2011 flood event ...... 63 Figure 5.7 Calibrated roughness grid...... 65 Figure 5.8 Stage-Discharge relationship for the downstream boundary of the hydraulic model ...... 66 Figure 5.9 Maximum flood depths for the 20% AEP event ...... 70 Figure 5.10 Maximum flood depths for the 10% AEP event ...... 71 Figure 5.11 Maximum flood depths for the 5% AEP event ...... 72 Figure 5.12 Maximum flood depths for the 2% AEP event ...... 73 Figure 5.13 Maximum flood depths for the 1% AEP event ...... 74 Figure 5.14 Maximum flood depths for the 0.5% AEP event ...... 75 Figure 5.15 Maximum flood depths for the 0.2% AEP event ...... 76 Figure 5.16 Maximum flood depths for the Probable Maximum Flood (PMF) design event ...... 77 Figure 5.17 Climate change – 10% AEP with 32% increase in rainfall intensity ...... 79 Figure 5.18 Climate change – 1% AEP with 32% increase in rainfall intensity...... 80 Figure 5.19 Difference plot for the low roughness scenario (20% lower roughness) ...... 82

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Figure 5.20 Difference plot for the high roughness scenario (20% higher roughness) ...... 83 Figure 5.21 Flow sensitivity inflow hydrographs ...... 84 Figure 5.22 Flow sensitivity analysis – 1% AEP with 20% reduction in flows ...... 85 Figure 5.23 Flow sensitivity analysis – 1% AEP with 20% reduction in flows ...... 86 Figure 6.1 Flood extents for the 20%, 10%, 5%, 2%, 1%, 0.5% AEP and the PMF...... 125 Figure 6.2 Floodway overlay flood hazard criteria (NRE, 1998) ...... 129 Figure 6.3 FO using the 10% AEP flood extent and LSIO using the 1% AEP flood extent ...... 131 Figure 6.4 FO using the 1% AEP (Hazard Class > 2) flood extent and LSIO using the 1% AEP flood extent ...... 132 Figure 6.5 FO using the 1% AEP (Depth 50 cm) flood extent and LSIO using the 1% AEP flood extent ...... 133 Figure 6.6 Land Subject to Inundation Overlay using the 1% AEP flood extent ...... 136 Figure 6.7 LSIO using the 1% AEP flood extent with the old bridge deck removed (planned to be completed before July 2013 by VicRoads) ...... 137 Figure 7.1 Types of flood damage (Floodplain Development Manual (NSW Gov, 2005)) ...... 139 Figure 7.2 Damage curves applied to the Wickliffe flood investigation ...... 141 Figure 7.3 Flood damages used to estimate the Average Annual Damages...... 144 Figure 8.1 Hopkins River Catchment to Wickliffe ...... 151 Figure 9.1 Identification of high risk areas in Wickliffe (1% AEP design flood event)...... 174 Figure 9.2 Proposed mitigation options ...... 176 Figure 9.3 Mitigation 5 – Lowered roughness for vegetation clearing ...... 178 Figure 9.4 Capacity of the structures under the Glenelg Highway – pre and post mitigation ...... 180 Figure 9.5 Scenario 1 – 1% AEP change in peak depth due to the removal of the old bridge deck ...... 181 Figure 9.6 Scenario 2 – 1% AEP change in peak depth due to the removal of the old bridge deck and levee 1 ...... 183 Figure 9.7 Scenario 3 – 1% AEP change in peak depth due to the removal of the old bridge deck and additional culverts ...... 185 Figure 9.8 Scenario 4 – 1% AEP change in peak depth due to the removal of the old bridge deck, levee 1 and culverts ...... 187 Figure 9.9 Scenario 5 – 1% AEP change in peak depth due to the removal of the old bridge deck, levee 1 and 2 with additonal culverts ...... 189 Figure 9.10 Scenario 6 – 1% AEP change in peak depth due to the clearing of the vegetation ...... 191 Figure 9.11 Scenario 1 – Jan 2011 change in peak depth due to the removal of the old bridge deck ...... 193 Figure 9.12 Scenario 2 – Jan 2011 change in peak depth due to the removal of the old bridge deck and levee 1 ...... 194 Figure 9.13 Scenario 3 – Jan 2011 change in peak depth due to the removal of the old bridge deck with additonal culverts ...... 195 Figure 9.14 Scenario 4 – Jan 2011 change in peak depth due to the removal of the old bridge deck, levee 1 with additonal culverts ...... 196 Figure 9.15 Scenario 5 – 1% AEP change in peak depth due to the removal of the old bridge deck, levee 1 and 2 with additonal culverts ...... 197 Figure 9.16 Detailed design Scenario 1 net present value results...... 203 Figure 9.17 Detailed design Scenario 2 net present value results...... 204 Figure 9.18 Detailed design Scenario 3 net present value results...... 205

Appendices Appendix A Survey Information Appendix B January 2011 Assessment Appendix C Flood Frequency Assessment Appendix D RORB Vector, Storm Files and Calibration Plots Appendix E Flood Warning Services Provided by the Bureau of Meteorology Appendix F Mitigation Costing and Cost / Benefit Analysis

Cardno LJ5786 Page xviii Cardno Wickliffe Flood Investigation RM2365 v1.0 FINAL GLOSSARY 1D 1D – One Dimensional. In this report 1D refers to a hydraulic model where the flow direction of water is only calculated in one direction. A 1D model is often used to reduce model run times.

2D 2D – Two Dimensional. In this report 2D refer to a hydraulic model where the flow direction of water is calculated in two directions. Two dimensional models are used to model floodplains and overland flows.

Annual Exceedence Refers to the probability or risk of a flood of a given size occurring Probability (AEP) or being exceeded in any given year. A 90% AEP flood has a high probability of occurring or being exceeded; it would occur quite often and would be relatively small. A 1% AEP flood has a low probability of occurrence or being exceeded; it would be fairly rare but it would be relatively large.

Australian Height Datum (AHD) A common national surface level datum approximately corresponding to mean sea level.

Catchment The area draining to a site. It always relates to a particular location and may include the catchments of tributary streams as well as the main stream.

Design flood A design flood is a hypothetical flood that is used to plan for floods. Design floods are described in terms of how likely they are to occur (see definition for AEP).

Development The erection of a building or the carrying out of work; or the use of land or of a building or work; or the subdivision of land.

Digital Terrain Model (DTM) A Digital Terrain Model is a representation of the ground surface excluding objects such as buildings, trees, grass etc. In this report this DTM is in the form of a grid with each grid cell representing the surface elevation at that location.

Discharge The rate of flow of water measured in terms of volume over time. It is to be distinguished from the speed or velocity of flow, which is a measure of how fast the water is moving rather than how much is moving.

Flood Relatively high stream flow which overtops the natural or artificial banks in any part of a stream, river, estuary, lake or dam, and/or overland runoff before entering a watercourse.

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Flood Frequency Analysis The calculation of the statistical probability that a flood of a certain magnitude for a given river will occur in a certain period. This analysis is undertaken on recorded gauge data.

Floodplain A floodplain is the low-lying land bordering a river, stream, lake or coastal zone over which water will flow during a flood. Flooding is caused by runoff from heavy or prolonged rainfall exceeding the capacity of rivers and drainage systems.

Geographical information A system of software and procedures designed to support the systems (GIS) management, manipulation, analysis and display of spatially referenced data.

HECRAS Hydrologic Engineering Centres River Analysis System. HEC-RAS is a computer program that models the hydraulics of water flow through natural rivers and other channels.

Hydraulics The term given to the study of water flow in a river, channel or pipe, in particular, the evaluation of flow parameters such as stage and velocity.

Hydrograph A graph that shows how the discharge changes with time at any particular location.

Hydrology The term given to the study of the rainfall and runoff process as it relates to the derivation of hydrographs for given floods.

LiDAR Light Detection and Ranging (LiDAR) is a technology that uses laser pulses to generate large amounts of data about terrain and landscape features.

Losses For the hydrology, losses refer to the volumes of rainfall that are lost within a catchment prior to the runoff reaching the main flow paths through the catchment. This water is lost as evaporation, evapotranspiration, infiltration and surface storage.

Mathematical/computer The mathematical representation of the physical processes involved models in runoff and stream flow. These models are often run on computers due to the complexity of the mathematical relationships. In this report, the models referred to are mainly involved with rainfall, runoff, pipe and overland stream flow.

MSS Municipal Strategic statement. A concise statement of the key strategic planning, land use and development objectives for a municipality and includes strategies and actions for achieving those objectives.

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Planning Overlays Planning overlays are used to control development within areas at risk of flooding. Four planning overlays are used in Victoria: Urban Floodway Zone (UFZ), Floodway Overlay (FO), Land Subject to Inundation Overlay (LSIO) and Special Building Overlay (SBO).

Pluviograph A rainfall gauge that records rainfall depth at 6 minute intervals continuously.

Probability A statistical measure of the expected frequency or occurrence of flooding. For a fuller explanation see Annual Exceedence Probability.

Rainfall excess See definition of “Runoff”.

Risk The possibility of something happening that impacts your objectives. It is the chance to either make a gain or a loss. It is measured in terms of likelihood and consequence (AS/NZ 4360). For this report risk is used to describe both likelihood and consequence of flooding.

RORB RORB is a general runoff and streamflow routing program used to calculate flood hydrographs from rainfall and other channel inputs (Laurenson et al., 2005)

Roughness The resistance of the surface to the flow of water over it. For the hydraulic model the resistance is measured using Manning’s Roughness.

Runoff The amount of rainfall that actually ends up as stream or pipe flow, also known as rainfall excess. This is rainfall less losses equals rainfall excess.

Stage Discharge Relationship A relationship between a known water level at a location and the corresponding flow rate. This is used to translate recorded flood depth to flow rates.

Topography A surface which defines the ground level of a chosen area.

WBNM WBNM is a hydrologic catchment model that generates flood hydrographs from rainfall and catchment parameters.

Zoning Zoning is the process of planning for land use by a locality to allocate certain kinds of structures in certain areas. Zoning also includes restrictions in different zoning areas, such as height of buildings, use of green space, density (number of structures in a certain area), use of lots, and types of businesses.

Cardno LJ5786 Page vi Cardno Wickliffe Flood Investigation RM2365 v1.0 FINAL ABBREVIATIONS Abbreviation Full Description AAD Average Annual Damage AEP Annual Exceedence Probability AHD Australian Height Datum AMG Australian Map Grid ARCC or Council Ararat Rural City Council ARI Annual Recurrence Interval AR&R Australian Rainfall and Runoff AWS Automatic Weather Station BoM or ‘the Bureau’ Bureau of Meteorology CFA Country Fire Authority CMA Catchment Management Authority DPI Department of Primary Industry DSE Department of Sustainability and Environment DTM Digital Terrain Model ERTS Event-Reporting Radio Telemetry System FFA Flood Frequency Assessment FO Floodway Overlay GEV Generalised Extreme Value GenPareto Generalised Pareto distribution GIS Geographical Information System Glenelg Hopkins CMA Glenelg Hopkins Catchment Management Authority HECRAS Hydrologic Engineering Centres River Analysis System Hwy Highway IC Incident Control ISC Index of Stream Conditions LSIO Land Subject to Inundation Overlay LiDAR Light Detection and Ranging LPIII Log Pearson Type III Distribution MERO Municipal Emergency Resource Officer MFEP Municipal Flood Emergency Plan MGA Map Grid of Australia MSS Municipal Strategic Statement PMF Probable Maximum Flood PSM Permanent Survey Mark RDO Regional Duty Officer RFA Rainfall Frequency Assessment SBO Special Building Overlay SMS Short Message Service SOP Standard Operating Procedure SWMP Surface Water Monitoring Partnership TBRG Tipping Bucket Rain Gauge TFWS Total Flood Warning System UFZ Urban Flood Zone VFD Victorian Flood Database VICSES Victorian State Emergency Services

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1 INTRODUCTION AND STUDY OBJECTIVES The Glenelg Hopkins Catchment Management Authority, in partnership with the Ararat Rural City Council received State and Australian Government funding to undertake the Wickliffe Flood Investigation. Funding for the Investigation has been made available through the Victorian Coalition Government’s Flood Warning Network – Repair and Improvement initiative and the Australian Government’s Natural Disaster Resilience Grants Scheme.

The Wickliffe Flood Investigation is in response to significant flooding in January 2011. The primary aim of this work is to undertake definitive flood investigations for the Hopkins River floodplain at Wickliffe and to undertake a comprehensive analysis with all of the available data to determine appropriate flood warning and response arrangements for the township of Wickliffe, including the derivation of flood levels and extents for planning purposes.

1.1 Study Area

The Study Area is shown in Figure 1.1.

Figure 1.1 Study area

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Wickliffe is located within the municipality of Ararat Rural City. The study area includes the majority of the residential and commercial areas of Wickliffe. The area has generally flat topography. The study area incorporates the reach of the Hopkins River between the Burdett Lane in the north to the intersection of Chatsworth-Wickliffe Road and Huckers Road in the south. Within this segment a number of smaller tributaries join the Hopkins River at or upstream of the Glenelg Highway. A flow gauge is situated at Wickliffe on the west side of the Hopkins River. There are currently no flood related controls in the Ararat Rural City Council planning scheme. The township has historically been subjected to flooding and has no flood warning system.

1.1.1 Catchment Characteristics

The study area includes the plains immediately upstream and downstream of Wickliffe, however the hydrology and assessment of the catchment flood characteristics incorporates the full upstream catchment that provided flow to Wickliffe. Wickliffe lies on the Hopkins River and has a catchment area of approximately 1,347 km2. This upstream area includes the Grampians National Park and the western uplands areas around Ararat.

Figure 1.2 Elevation map for the Hopkins River catchment (DPI, 2011)

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The average annual rainfall across the catchment is relatively uniform with rainfall varying from 550 to 600 mm from Wickliffe to the upper catchment. The average annual rainfall for three gauges within the catchment is summarised (BoM, 2012) below. x Wickliffe (gauge 89033) annual average 550 mm x Willaura (gauge 89034) annual average 550 mm x Ararat (gauge 89085) annual average 594 mm.

Approximately 81% of the Glenelg-Hopkins Catchment Management Region has been developed for agricultural use. About 2% of the catchment area comprises pine forest, while 16% is native forest and less than 1% is used for urban and industrial development (Glenelg CaLPB, 1997). The main agricultural land uses are dominated by dryland pasture (over 2 million ha) and also include horticulture (GHCMA, 2011).

The Hopkins River Basin, which covers an area of roughly 968 000 ha in the eastern half of the Glenelg-Hopkins Catchment Management Region, is entirely cleared for pasture and other agriculture, except for a small area of forest in the north (GHCMA, 2011).

Figure 1.3 Land use for the Hopkins River to Wickliffe (GHCMA, 2011)

The geomorphological units present within the Wickliffe catchment includes primarily the western uplands comprising of ridges, hills, valleys and well defined floodplain. From upstream of Willaura the catchment transitions into western plains geomorphology with well defined drainage. The geomorphology is summarised in Figure 1.4.

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Figure 1.4 Geomorphological units for the Wickliffe catchment (DPI, 2008)

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1.2 Study Objectives

The flood investigation will: x Determine flood levels and extents for a range of flood modelling scenarios within the study area (see Figure 1.1 - Study Area); x Provide draft documentation for a planning scheme amendment to update the Ararat Planning Scheme to reflect the findings of the Investigation; x Consider and provide recommendations for provision of a flood warning system for the study area; x Draft documentation for inclusion in the Ararat Rural City Shire Municipality Flood Emergency plan; and x Consider and provide recommendations about achievable flood mitigation options.

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2 COMMUNITY CONSULTATION As the purpose of this flood investigation was aimed at developing flood information that was to provide protection to the community, the involvement and engagement of the community was extremely important throughout the consultation process.

To facilitate the engagement of the community Cardno and the Glenelg Hopkins Catchment Management Authority (Glenelg Hopkins CMA) presented a community consultation meeting at the inception of the project and also following the development of the key outcomes from the project.

The first meeting was held in December 2011 at the Wickliffe recreation reserve and 16 people from the community attended. The structure of the meeting was Cardno providing a short presentation outlining the scope and objectives of the project, following this presentation a question and answer session was held. This forum allowed the community to ask questions and provide suggestions regarding the investigation to be undertaken. At this meeting a community questionnaire was also released to the community to gather relevant information regarding the historical flooding of Wickliffe, in particular about the largest known event that occurred in January 2011.

The second community meeting was held in October 2012 and involved updating the community of the progress of the study and seeking feedback regarding the flood behaviour and mitigation options. This meeting was attended by the Glenelg Hopkins CMA, Ararat Rural City Council and approximately 10 members from the Wickliffe community.

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3 SURVEY AND MAPPING In order to develop the models to represent the area at Wickliffe detailed survey and mapping was required. This data was sourced from a number of agencies and was of varying degrees of accuracy. This section outlines the available data, the sources of this data and the validation of all data used in the study. The following sections outline the data and approach adopted: x Survey x LIDAR data sets x LIDAR data validation x Mapping

3.1 Survey – Spot Heights, Cross Sections and Structures

The ground survey was undertaken by Cardno’s in-house survey team of licenced surveyors. Peter Sullivan heads the survey team and is a licensed surveyor and Nick Lawson undertook the field survey. The work was reviewed by Peter Sullivan.

The field survey captured spot heights to validate the LiDAR data, cross sections for input into the hydraulic model and structure information. The location of these cross sections and structures are shown in Figure 3.1. The following information was captured during the field survey: x 13 cross sections x 1 Road Crossing (where the unnamed tributary crosses Floate Lane, labelled “Road Crossing” in Figure 3.1); x 1 Culvert (Glenelg Hwy, labelled “culvert” in Figure 3.1); x Information regarding the new and old Glenelg Highway Bridges over the Hopkins River.

The survey captured numerous spot heights using a mobile GPS device that was adjusted to Map Grid of Australia (MGA) Zone 54 using permanent markers located within the region. The field survey was set using three Permanent Survey Marks (PSMs) that were set in AMG Zone 54 reference system. These three PSMs were the only markers that were accessible and provided an accurate reference level. The other PSMs in Wickliffe were only accurate to +/- 100 mm which was not acceptable for the study. The PSMs used are summarised in Table 3.1.

Table 3.1 Permanent survey marks Height Name Easting Northing Comment (mAHD) Wickliffe SOUTH PM24 648890 5828254 230.094 MGA Zone 54 height adjustment marker Wickliffe SOUTH PM26 652100 5826297 209.767 AMG Zone 54 height adjustment marker Wickliffe SOUTH PM27 651091 5827576 209.141 AMG Zone 54 height adjustment marker

In addition to the field survey Cardno has received design plans for the new bridge along the Glenelg Highway over the Hopkins River from VicRoads. These plans are used in the development of the hydraulic model.

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Figure 3.1 Field survey information locations

3.2 LIDAR Data

Glenelg Hopkins CMA has provided Cardno with the 2009 LiDAR data of the study area. The LiDAR data was captured by Fugro Spatial Solutions as part of the ISC Rivers LiDAR Project in November/December 2009 and is supplied with a vertical accuracy of +/- 0.2 m for 69% of the data set.

Figure 3-1 shows the extent of the LiDAR compared to the model extent.

The LiDAR data was supplied in the form of 1m grid of points covering most of the model area. The provided dataset did not cover the entire model extent. The majority of the missing LiDAR area was not inundated during the January 2011 flood event which is the largest event on record (and larger than the 1% AEP flood event). The only area outside the supplied 1m LiDAR data coverage that may interact with peak flood levels has been highlighted in Figure 3-1. This area is unlikely to impact the floodplain storage as it is a very small part of the overall floodplain and this area is also a backwater to the Hopkins River and does not directly interact with the main flood waters. For this reason additional LiDAR was not obtained as the costs and time delays associated with capturing this data was not warranted due to the limited impacts that this area has on the model. The LiDAR information will be used to define the topographic grid for the hydraulic model.

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Figure 3.2 LiDAR data extent within the study area

3.2.1 LIDAR Data Validation In order to ensure that the LiDAR data information captured is accurate to the level of detail required for this flood study, the LiDAR data information has been assessed against field survey information. The field survey information was captured with a very high level of accuracy compared to the LiDAR data and as such can be used to verify and/or adjust the LiDAR data captured. This verification is important as the LiDAR data has been captured and adjusted by the supplier over a broad area and depending on the location of the verification points, may not have been cross checked or verified at this location.

LiDAR datasets were validated with point survey data collected during field survey undertaken by Cardno. The field survey was completed on the 10th February 2012. Field survey points were captured along key locations through the study area in order to provide a direct comparison to the LiDAR data. The ground survey has an improved accuracy compared with the LiDAR and if required will be used to apply a level shift to the LiDAR data. Details of the field survey are summarised in Section 3.1.

The differences between the field survey and the LiDAR data is shown in Figure 3.3.

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Figure 3.3 Difference in LiDAR data and survey

Assessment shows that there is a relatively constant difference between the two datasets. The field survey checks are 0.04 to 0.53 m lower than the LiDAR data. A summary of the points used in this assessment are shown in Table 3.2.

The average difference between the 106 field survey points and LiDAR data levels was found to be + 0.256 m. The standard deviation of the differences between the two data sets was found to be low. This supports a conclusion that a relatively constant shift can be applied to the data. Based on these findings, the LiDAR data set was adjusted uniformly down by 0.256 m.

Table 3.2 Assessed difference in LiDAR and Survey vertical data (m) Difference (m) Parameter [LiDAR less Survey] Count 106 Minimum (m) 0.042 Maximum (m) 0.526 Average (m) 0.256 St. Dev. (m) 0.078

The adjusted LiDAR data set differences with the field survey data is shown in Figure 3.4 and the adjusted LiDAR data comparison statistic are summarised in Table 3.3.

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Figure 3.4 Adjusted LiDAR data set compared to field survey

Table 3.3 Assessed difference in adjusted LiDAR data and survey vertical data Difference (m) Parameter [LiDAR less Survey] Count 106 Minimum (m) -0.214 Maximum (m) 0.270 Average (m) 0.000 Standard Deviation (m) 0.078

Analysis shows that the range of difference between the adjusted LiDAR data and the field survey locations was between -0.22 to 0.27 m. However, the average difference was reduced down to an exact match between the LiDAR and survey data. The resulting LiDAR data had 95% of data (2 standard deviations) within +/- 0.156 m of the surveyed levels which is an acceptable range of uncertainty for this flood study.

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The 1m LiDAR data was used create a 4m x 4m grid for mapping and modelling. The full DTM was modified to remove areas with high ground levels that would not be affected by flooding to reduce the grid size to improve model run times and limit the size of model results.

Figure 3.5 shows the amended topography which was used within the hydraulic model.

Figure 3.5 Topography for the study area

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4 HYDROLOGY

4.1 Background Information

Wickliffe is located on the Hopkins River with an approximate upstream catchment area of 1,347 km2 (Victorian Data Warehouse, 2012) to the gauge immediately upstream of the road bridge over the Glenelg Highway to the east of the township (Hopkins River at Wickliffe – 236202). Within the upstream catchment there are two streamflow gauges: x Hopkins River at Ararat (236219) x Hopkins River at Wickliffe (236202).

The catchment topography is varied with the upper reaches including parts of the Grampians National Park which are very steep. However, the majority of the catchment is flat with the Hopkins River meandering across a low grade floodplain. For details of the catchment characteristics, including land use, mean annual rainfall and geomorphology, see Section 1.1.1. Historically, Wickliffe has had not had significant flood events greater than 120 m3/s. However in January 2011 a significant flood event was experienced that placed much of Wickliffe under water. This event has been assessed within this chapter in great detail to ensure that adequate consideration is given to the magnitude and recurrence interval for this event.

A summary of the estimated peak flow rates are summarised in Figure 4.1.

Figure 4.1 Annual peak flow rates for the Hopkins River at Wickliffe

Figure 4.1 shows that historically Wickliffe has not experienced floods greater than 120 m3/s until January 2011. The highest peak flow following January 2011 was in 1983. Other years with significant floods include 1975, 1986 and 1988.

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Peak flow rates traditionally take approximately 24 hours to travel from the gauge at Ararat down to the gauge at Wickliffe. The timings of flood peaks throughout the catchment will be explored in more detail as part of this hydrology assessment and for the flood intelligence and warning related information.

The hydrological assessment will: x Define the available data for the study. x Undertake a detailed assessment of the historical peak flood events, particular focus will be on the January 2011 flood event as this is currently the most extreme event on recorded history for Wickliffe. x Undertake a rainfall assessment to explore the rainfall intensities and the associated ARIs of these events. This is assessed to gain an improved understanding of the catchment response behaviour for the hydrological model development. x Explore an individual flow gauge assessment including a flood frequency assessment (FFA) to explore the statistical return periods of the peak annual flow events. x Develop and review hydrological models for use in developing the hydrology. These models will be developed using RORB. x Complete a sensitivity assessment on the RORB model to determine the uncertainty associated with the predicted design flow rates. x Develop the Probable Maximum Flood (PMF) will be estimated to determine the likely maximum flood extent expected for the Wickliffe township.

4.2 Available Data

4.2.1 Rainfall data

The available rainfall data that was used as part of this study is summarised in Table 4.1, Table 4.2 and Figure 4.2. The data was used to assess the rainfall depths and to develop the inputs to the hydrological models. Table 4.1 Selected rainfall gauges in the Wickliffe catchment area Gauge No. Gauge Name Elevation Start Date End Date 079019 Great Western (Seppelt) 280 m 30/07/1891 Present 079034 Moyston 252 m 01/06/1886 31/21/2006 079050 Moyston (Barton Estate) 290 m 01/01/1906 Present 089033 Wickliffe 222 m 01/05/1879 Present 089034 Willaura (Main Street) 250 m 25/07/1902 Present 089037 Willaura (Yarram Park) 270 m 14/09/1890 31/10/2009 089075 Glenthompson (Post Office) 270 m 29/11/1965 Present 089080 Maroona (Hillenvale) 340 m 1/01/1968 Present 089085 Ararat Prison 295 m 29/04/1969 Present

Table 4.2 Pluviograph data used in the Wickliffe Flood Study Gauge No. Gauge Name Start Date End Date 089085 Ararat Prison 1/11/1981 Present 089019 Mirranatwa 9/05/1974 Present 089016 Lake Bolac 25/04/1968 Present 089082 Beaufort 10/05/1974 Present

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Figure 4.2 Location of Pluviograph and Rainfall Gauges in the Wickliffe Catchment Area

4.2.2 Streamflow data

Within the study area only two (2) streamflow gauging stations were available, one downstream of Ararat and one at Wickliffe. The available data is summarised in Table 4.3.

Table 4.3 Streamflow data used in the Wickliffe Flood Study Gauge Gauge Name Source Flow type Start Date End Date Missing No. Periods ‘Red Book’ Monthly Inst. max Jul-1920 Dec-1981 1934 - 1942 236202 Hopkins River at Wickliffe Data Warehouse Daily Inst. max May-1964 Aug-2011 - 236219 Hopkins River at Ararat Data Warehouse Daily inst. Max Jun-1989 Nov-2011 -

It should be noted that the Wickliffe gauge data prior to May 1964 was an incomplete dataset. The ‘Red Book’ dataset was only recorded when a large event occurred as this was a record of instantaneous maximum flows at the Wickliffe gauge. As this information was solely used for the FFA (which uses the maximum peak flow rate for each year) this was deemed of sufficient quality for the analysis. The information from the data warehouse was used in preference to ‘Red Book’ data where the two datasets overlapped as this is considered higher quality.

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Figure 4.1 shows the peak flood events for the gauged record at Wickliffe. Clearly the January 2011 flood event is the most extreme of these gauged events. The largest independent annual events include: 1. 2011 – 287 m3/s 2. 1909 - unknown m3/s 3. 1983 – 127.4 m3/s 4. 1986 – 102.7 m3/s 5. 1975 – 100.3 m3/s 6. 1960 – 93.2 m3/s

Another event of note in recent times is the September 2010 event which has a peak flow rate of 65.1 m3/s. In the period from 1992 – 2010 there are no large flood events as this was an extended period of drought for the Hopkins River catchment. This led to a general apathy and ignorance of the consequences of large floods on the Wickliffe community and as a result the residents were largely unprepared an event of the magnitude of the January 2010 flood event.

For the Hopkins River the 1909, 1983 and 2011 flood events have been discussed in the following sections to provide some information regarding the peak flood levels and flood behaviour of these events. The January 2011 flood event has been analysed in greater detail as this is a recent event, has the greatest amount of information available and is the largest flood event on record for Wickliffe.

4.3.1 1909 Event

In addition to the gauged peak floods there was a report of a major flood occurring in 1909 which led to the township of Wickliffe being inundated. The Argus newspaper reported: The Hopkins River is in flood at Wickliffe. The mail coach was unable to cross today, and the driver had to return to Bolac with the mail. This morning the flood at Wickliffe extended from Ford's store, on one side of the river, to the hill on the Chatsworth road on the opposite side. It will not be known until the flood waters subside whether the bridge has been washed away or not. Several families had to leave their homes. (The Argus, 21 August, 1909, page 18).

It should be noted that in 1909 that the old bridge was across the Hopkins River and this bridge is set at a lower level than the current Glenelg Highway Bridge. Similarly, the main road elevation is likely to be lower than the current road grade. There may have been significant land use changes in the catchment and in particular around the Wickliffe township that impacted the flood behaviour in 1909 that would be different today.

Figure 4.3 shows two photographs from the 1909 floods (supplied by members of the community). It is believed that the two images are taken of the 1909 flood but this is not 100% certain. The top image shows the flood extent reaching the Wickliffe Hotel (which is still in the town today). The second image shows the old bridge almost under water. It is not clear if these flood photographs capture the peak levels.

In the 2011 event the old bridge was completely inundated and the majority of the Glenelg Hwy was overtopped. This would imply that the 1909 flood event was a lower magnitude than the 2011 event. This cannot be stated for certain however as the construction of the new bridge and raising of the Glenelg Highway gradeline in 1993 altered the main floodplain considerably for Wickliffe. But anecdotally this event would be likely to rank second in the known flood events for Wickliffe.

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Figure 4.3 Images supplied from the Community for the flood occuring in 1909

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4.3.2 1983 Event

The 1983 flood event occurred in August following a relatively wet period for the Hopkins River catchment. This is reflected in the relatively low rainfall depths generating a large flood event. This catchment response occurs because the catchment is saturated and less water is lost in interception storages and to infiltration. The rainfall depths generating the events are summarised in Table 4.4.

Table 4.4 Rainfall depths leading to the August 1983 flood event Gauge 5/09/1983 6/09/1983 7/09/1983 8/09/1983 9/09/1983 TOTAL 79050 18.2 12.4 1.8 36.6 3.0 72.0 89033 20.0 4.0 3.4 13.2 8.6 49.2 89034 13.8 5.8 3.2 18.8 0.0 41.6 89045 3.2 5.4 2.6 26.6 4.0 41.8 89080 8.6 11.0 3.4 25.8 3.2 52.0 89085 5.8 10.4 2.0 35.8 4.6 58.6

The hydrograph for the event exhibits a fast rising limb and is punctuated by a long drawn out falling limb. This is typical of the Hopkins River catchment at Wickliffe and is partially due to the control of the Glenelg Hwy bridge. In 1983 the new Glenelg Hwy bridge was yet to be constructed and hence the flood conditions and behaviour may be different to the post 1993 flood events. The hydrograph is shown in Figure 4.4.

Figure 4.4 Peak flows during the August 1983 flood event

There are no known reports of significant damage occurring during the 1983 flood event. It is possible that the roads may have been closed due to inundation but there are no reports to confirm this.

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4.3.3 January 2011 Assessment

The January 2011 flood event has been the largest flood event recorded at the site since 1920 when gauged records began. This flood is important as the flood inundated the majority of the houses within the main street of Wickliffe and is the first major flood since the new Glenelg Hwy bridge was constructed adjacent to Wickliffe over the Hopkins River. This new bridge involved raising the Glenelg Hwy to the east of the township and would likely have changed the flood behaviour around the gauge and the township.

4.3.3.1 Revision of the peak flow rate During the course of this project the peak flow rate for the January 2011 flood event has been the subject of some discussion and has been revised three times. Cardno have included a discussion of the assessment of this event during the project and final outcome of the discussions. This has been included to demonstrate that the robustness of the final January 2011 event is acceptable for this flood investigation.

At the inception of this project the January 2011 event was estimated at being a 700 m3/s peak flow event based on a rating table that was developed back in the 1980’s for the Wickliffe gauge. During the preliminary assessment of the hydrology using this peak flow rate Cardno identified that this estimate for the flow rate was likely to be too high given the recorded flood heights during and after this event captured by the Glenelg Hopkins CMA. At this point in the project Cardno undertook a detailed assessment of this peak flow rate using a variety of methods including: x Running the peak flow rate through the hydraulic model x Assess the gauge location using Manning’s calculations and the known peak gauge level x Undertake hydrologic analysis using the standard Flood Frequency Assessment (FFA) methods as defined in Australian Rainfall and Runoff. x Examine the floodplain in the area adjacent to the flow gauge to determine if there could be any backwater effects that could adversely impact the recorded gauge levels and slow the flow rate. x Using the RORB model and WBNM models to calibrate the pluviograph and rainfall information to the recorded streamflow information. x Undertake analysis of upstream and downstream flow gauges to check consistency of the peak flood estimate during this flood event.

The details of this assessment have been included in Appendix B as a reference. Ultimately Cardno recommended that the peak flow rate of 700 m3/s was too high and recommended a reduction of the peak flow rate. Given that little additional information was known Cardno adopted a substantial reduction in the peak flow rate to 450 m3/s.

At this point in the project Thiess advised that they had made provisions to undertake a reassessment of the gauge at Wickliffe to develop a revised rating table. Thiess are the primary authority in developing and maintain the rating tables for many of the streamflow gauges within Victoria. The Manager of Hydrology provided the advice that Thiess were going to perform detailed survey of the Wickliffe gauge and revise the rating table. The revised rating table is summarised in Figure 4.5.

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Figure 4.5 Revision to the rating table at Hopkins River at Wickliffe

From discussions with Thiess the revisions have been based on a rigorous analysis utilising the additional cross section survey, rainfall analysis and runoff rates from the upstream and nearby catchments and a detailed assessment of the complicated structure downstream of the streamflow gauge. Information from the January 2011 event was used from the community and from the Glenelg Hopkins CMA during Thiess’ assessment of the rating table. It is important to note that this rating table must be applied retrospectively to when the new bridge over the Hopkins River along the Glenelg Hwy was constructed. Cardno have plans that date back to April 1993 and believe the new bridge was constructed in 1993/94.

The only retrospective adjustments that have been made are to the January 2011 and August 2010 flood events. The remaining years had no significant flood events that required the use of the upper portion of the rating table. It is important to note that Thiess stated that the old bridge, new bridge and fish ladder impacted the flow rates at the Hopkins River at Wickliffe gauge. The fish ladder was installed prior to 2007 and had only a small impact on the rating table. If in the future the old bridge is removed then the rating table will require further revision to account for this.

The revised estimate of the January 2011 flood event was set at 250.7 m3/s by Thiess. The largest event aside from the January 2011 flood event was the 1983 flood event which was 4.54 m against the gauge. This means that the rating table above 4.54 m on the gauge is an extrapolation which increased the uncertainty around the conversion from depth at the gauge to flow rates. The January 2011 flood event was 5.89 m against the gauge which is well within the extrapolated section of the rating table and Thiess Services have stated that they estimate a +/- 15% uncertainty around the estimated peak flow rate of 250.7 m3/s. The hydraulic modelling during the course of the project (Section 5) identified that the peak flow estimate of 250.7 m3/s was not sufficient to replicate the January 2011 flood event within the hydraulic model. As a result the peak flow rate was set at the upper 15% limit of the Thiess rating curve at 287 m3/s for this project.

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4.3.3.2 Event description The January 2011 event occurred following unusual high intensity rainfall which led to large volumes of rainfall falling from the 10th to the 14th January 2011. At this point in time the catchments were already reasonably saturated due to a wet summer across the region. In the preceding 19 days to the event there had been no rainfall over the Wickliffe catchment.

The rainfall depths recorded across the catchment from the 10th to the 14th January 2011 are summarised in Table 4.5 and the location of these gauges are shown in Figure 4.6.

Table 4.5 Rainfall depths leading to the January 2011 flood event (restricted) Gauge 10/01/2011 11/01/2011 12/01/2011 13/01/2011 14/01/2011 TOTAL 79050 11.6 2.0 73.6 0.0 84.8 172.0 89033 5.0 3.6 50.0 N/A1 53.4 112.0 89034 5.4 4.8 57.6 0.0 50.4 118.2 89045 3.0 36.5 58.0 N/A1 74.0 171.5 89075 N/A1 7.0 51.0 0.0 68.0 126.0 89085 5.5 22.6 62.3 0.2 78.6 169.2 1 N/A – not recorded and accumulated into the following days reading.

Figure 4.6 Rainfall depths for the January 2011 flood event

The rainfall depths we much higher to the north of the catchment with the gauges all recording approximately 170 mm for the period leading up to the flood event. Rainfall depths at Wickliffe were much lower at 112 mm. This indicates that the majority of the floodwaters were supplied from the upper reaches of the catchment with

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some flows contributed from the lower lying areas within the catchment. The rainfall for this event is assessed in detail in Section 4.4.2.

The peak flow rate of 287 m3/s occurred at approximately 10:30 am on the morning of the 15th January 2011. The peak flow rates and flood hydrographs for this event are shown in Figure 4.7. There was 24 hours between the peak at Ararat and at Wickliffe. The peak was maintained at Wickliffe for a number of hours.

Figure 4.7 Peak flows during the January 2011 flood event

Approximately 80% of the dwellings and businesses within the town were flooded above floor level. The Glenelg Hwy was impassable to traffic from approximately 6:00 am on the 15th January to Monday 17th January (Hucker (resident), 2012) (time of opening unknown). A primary concern to come out of the event was the distinct lack of warning time and coherent response to the event. It is reported than the members of Wickliffe were alerted informally on Friday (14th January) evening by the Police, however, as there is no flood warning gauges upstream of Wickliffe, no official warning was ever released.

Finding an approach to manage the lack of flood warning at Wickliffe was one of the objectives for this flood investigation. As suggested by the community in Wickliffe there should be adequate warning for future events to ensure that the community can prepare and respond appropriately during large flood events.

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The rainfall data that has been used as part of this study is presented in Section 4.2. The rainfall data was required for a number of purposes including: x Rainfall depths were required for calibrating the RORB model. x Pluviograph information was required for providing a distribution for the rainfall depth for calibrating RORB. x Background assessment of rainfall historically over the Wickliffe catchment and for the historical event analysis (see Section 4.3).

In order to provide some background information for the Hopkins River at Wickliffe catchment some preliminary assessment of the rainfall pattern, depths and historic recurrence intervals was undertaken. This section includes a rainfall frequency assessment (RFA) which examines the recurrence intervals of rainfall depths that have fallen over the Hopkins River catchment to Wickliffe. The purpose of this assessment is to examine the distribution of rainfall across the catchment via assessments of various gauges, as well as to establish the historical intensities of known peak flood events.

This assessment has been used to provide some discussion on the importance and relevance of antecedence conditions within this study.

4.4.1 Rainfall Frequency Assessment (RFA)

A RFA was undertaken on four rainfall gauges within the Hopkins River catchment. Gauges were selected that were distributed across the Wickliffe catchment, as well as having the longest continuous record for assessment. The gauges used are outlined in Table 4.6 and shown graphically in Figure 4.2.

Table 4.6 Selected rainfall gauges in the Wickliffe catchment area Gauge No. Gauge Name Start Date End Date 079034 Moyston 01/06/1886 31/21/2006 089033 Wickliffe 01/05/1879 Present 089034 Willaura (Main Street) 25/07/1902 Present 089037 Willaura (Yarram Park) 14/09/1890 31/10/2009 089085 Ararat Prison 22/05/1969 Present

The primary aim of this rainfall analysis was to determine the rainfall depths for a range of recurrence intervals including 20%, 10%, 5%, 2%, 1% and 0.5% AEP events. These AEPs can then be used to determine the recurrence interval for historic rainfall events leading up to the 1975, 1983, 1986, 2010 and 2011 flood events and to provide a discussion on the results. These are the largest events recorded at Wickliffe that have recorded data captured. The following section outlines the derivation of the AEPs at the selected stations and the process for the determining the recurrence intervals for key historic floods. This assessment considered if the events were classified as 24, 48 or 72 hour rainfall events.

The rainfalls at each gauge are recorded as 9am to 9am rainfall totals and as such are restricted totals. A suitable adjustment factor has been developed for restricted rainfall periods and the factor applied was 1.15, 1.11 and 1.05 for the 24, 48 and 72 hour rainfall totals respectively (Boughton et al. 2008). These factors account for the temporal restrictions that are present in the recorded rainfall totals. Table 4.7 shows the 24, 48 and 72 hour rainfall totals for each ARI at each of the selected gauges. The Rainfall analysis was undertaken by fitting a Log

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Pearson Type III distribution to the annual maximum rainfall depths recorded at each gauge. The approach follows the methods specified in AR&R (1987).

Table 4.7 Rainfall depths estimated for the 24, 48 and 72 hour duration events (non-restricted) AEP 79034 - Moyston 89033 - Wickliffe (%) 24h 48h 72h 24h 48h 72h 20 % 79.0 76.3 78.7 61.2 72.9 74.4 10 % 95.0 91.7 94.3 74.4 86.9 87.5 5 % 110.8 106.9 109.3 87.9 100.3 99.8 2 % 131.8 127.2 129.0 106.5 117.9 115.5 1 % 148.2 143.0 144.0 121.4 131.3 127.1 0.5 % 165.0 159.2 159.2 137.2 144.8 138.6 0.2 % 188.0 181.5 179.6 159.5 162.9 153.6

89034 - Willaura (Main 89037 - Willaura (Yarram 89085 – Ararat Prison AEP Street) Park) (%) 24h 48h 24h 48h 72h 24h 48h 72h 20 % 62.8 72.8 75.1 56.9 70.6 73.6 59.8 74.5 77.8 10 % 74.7 86.6 88.8 68.9 84.3 86.9 72.9 91.7 95.7 5 % 85.9 99.7 101.6 81.2 98.0 99.8 86.2 109.9 114.8 2 % 100.4 116.7 117.8 98.5 116.5 116.8 104.8 136.4 142.2 1 % 111.2 129.4 129.6 112.5 131.0 129.8 119.8 158.6 165.1 0.5 % 122.0 142.2 141.3 127.5 146.1 143.1 135.8 182.9 190.0 0.2 % 136.3 159.2 156.6 148.9 167.1 161.1 158.5 218.8 226.7

This assessment provides a guide to the likely depths of rainfall that would be expected during the more frequent events 20% AEP up to the rarer large events 0.2% AEP. The more frequent events within the catchment are generally caused by rainfall totals of 60 to 80 mm. The large rare events are expected to have rainfall depths ranging from 110 mm up to 230 mm.

4.4.2 Historic Rainfall Assessment

The rainfall depths for each recurrence interval (Table 4.7) give an indication as to the magnitude of rainfall events that can occur across the Hopkins River catchment upstream of Wickliffe. The rainfall depths recorded are reasonably uniform across the catchment with increased rainfall falling in the north of the catchment. This is assumed to occur due to the influence of the Grampians National Park and higher elevations which are likely to generate a large amount of orographic rainfall. The difference in rainfall for the 1% AEP between Ararat (89085) and Wickliffe (89033) for the 72 hour rainfall depths was 73 mm.

From the rainfall assessment it is evident that the larger rainfall depths fall on the upper reaches of the Wickliffe catchment with the plains getting less rainfall on average. An assessment of the rainfall that generated the peak flow events in 1975, 1983, 1986, 2010 and 2011 was undertaken for the 24, 48 and 72 hour periods. This assessment was undertaken to gain an understanding of the likely calibration events for the hydrology. The recorded peak rainfall depths for each event have been summated and assessed the FFA rainfall depths for each AEP. Table 4.8 shows the results of the event assessment.

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Table 4.8 ARI assessment for each event assessed for the corresponding period Event 79034 - Moyston 89033 - Wickliffe 89034 - Willaura (Main 89037 - Willaura (Yarram 89085 – Ararat Prison Street) Park)

24h 48h 72h 24h 24h 48h 72h 48h 72h 24h 48h 72h 24h 48h 72h Rainfall (mm) 45.3 69.0 65.3 21.9 30.0 28.4 21.6 32.9 31.1 22.5 30.1 28.5 44.9 70.8 68.5 Oct - 75 ARI (years) 1 4 3 1 1 1 1 1 1 1 1 1 2 9 8 Rainfall (mm) 55.2 56.8 67.6 15.2 24.2 26.5 21.6 24.4 29.2 15.2 20.2 28.6 41.2 44.8 44.5 Sep - 83 ARI (years) 2 2 3 1 1 1 1 1 1 1 1 1 2 2 2 Rainfall (mm) 28.8 42.2 40.1 29.9 28.9 38.2 28.1 39.3 37.8 43.7 61.1 63.0 22.8 39.1 39.9 Oct - 86 ARI (years) 1 1 1 1 1 1 1 1 1 2 3 3 1 2 2 Rainfall (mm) 10.4 17.1 16.6 10.4 10.0 15.1 33.4 44.8 44.3 Sep - 10 ARI (years) < 1 1 1 1 < 1 1 1 2 2 Rainfall (mm) 61.4 59.3 108.6 66.2 69.3 113.4 90.4 87.5 148.2 Jan - 11 ARI (years) 5 3 34 6 4 39 25 21 363

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For the five selected events assessed, four of them occurred during the wetter winter periods and as such would be likely to have experienced reduced initial losses due to the wet antecedent catchment conditions. This is evident with the relatively low recurrence intervals for the rainfall events with all ARIs for the 1975, 1983, 1986 and 2010 events, with all being below a 33% AEP (1 in 3 year ARI).

For the January 2011 flood event the rainfall depths were much higher with the 72 hour rainfall depth having approximately a 2.5% AEP (1 in 40 year ARI) for the Willaura and Wickliffe gauges. For the upper reaches the Ararat gauge indicated that the 72 hour 2011 event was a 0.3% AEP (1 in 360 year ARI). The higher recurrence intervals are expected as the January 2011 flood event was an extreme event and the additional rainfall depth is required to overcome the dryer antecedent conditions experienced during the summer months. However, the losses may not have been as significant as previous summer periods as the summer of 2010-11 was reasonably wet with large floods occurring during September and December 2010. These floods would have recharged the groundwater system and the soil column resulting in some reduction in losses during the January 2011 event.

The combination of the extreme rainfall event on the upper catchment (0.3% AEP) and the moderate rainfall event across the plains of the Wickliffe catchment (2.5% AEP) combined to give the generated flood peak at Wickliffe of 287 m3/s. The predicted recurrence interval of this flood event is discussed in detail in Section 4.5.

4.4.3 Discussion

The rainfall assessment has focused on demonstrating the importance of the catchment antecedence conditions and to provide an understanding of the rainfall patterns across the Wickliffe catchment. On average the catchment receives more intense rainfall over the upper reaches of the catchment to the north and reduced rainfall depths over the southern part of the catchment upstream of Wickliffe. The timing of these rainfall events is also very important with antecedent conditions determining the loss rates and rates of runoff from the catchment. The antecedent conditions give an indication to the expected loss rates that may be required within the hydrological models for calibration to known events. For the drier months larger losses will be required to represent the losses to the catchment, whereas during the wetter periods much lower losses would be expected.

Many of the large flood events that have occurred at Wickliffe have been generated by relatively frequent rainfall depths occurring during the wetter months of the year. An exception to this was the January 2011 flood event which occurred following a very high three days of rainfall.

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4.5 Flood Frequency Analysis

Cardno have undertaken the FFA using the full dataset available from the “Red Book” and from the gauged record at the Hopkins River at Wickliffe. This provided an annual maximum time series from 1920 to 2011. There was 10 years of missing data from 1934 to 1943. The remaining dataset for the FFA was 82 years in length.

The FFAs have been completed using the Gumbel, Log Pearson Type III (LPIII), Generalised Extreme Value (GEV) and Generalised Pareto (GenPareto) distributions within the program FLIKE which was developed as part of Australian Rainfall and Runoff (AR&R). The distributions were fitted to the annual maximum peak flow rates. The distributions were fit to the data using a Bayesian approach.

Peak flow rates below 54 m3/s were censored from the fitted distribution to allow the events of interest (< 20% AEP) to be fitted with more certainty. Censored data implies that the data is still utilised in the recurrence interval estimation but it is not used in fitting the distribution. This implies that the fitted distributions should not be used to estimate peak flow rates below the 20% AEP (1 in 5 year ARI) events as the distribution may not be accurate for low flow events. This approach was adopted in line with the recommendations within AR&R for improving the fit to the more extreme events to provide a more certain estimate of the expected flood frequency within a catchment.

The results of the FFA are presented in Table 4.9 and in Figure 4.8.

Table 4.9 FFA results with the January 2011 event Average Recurrence Interval (years) Distributions 5 10 20 50 100 200 500 Log Pearson Type 3 65 85 110 152 194 246 336 Lower 90% Conf. 58 73 88 111 130 150 179 Upper 90% Conf. 75 102 142 228 331 486 817 Gen. Extreme Value 65 84 109 152 196 253 355 Lower 90% Conf. 59 73 89 114 133 154 183 Upper 90% Conf. 76 105 151 271 452 780 1641 Generalized Pareto 69 92 119 162 203 252 332 Lower 90% Conf. 60 75 92 116 135 155 181 Upper 90% Conf. 78 107 149 243 361 549 968

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Figure 4.8 FFA results with the January 2011 event

The 1% AEP flood event has been estimated at between 194 to 203 m3/s with 90% confidence intervals of between 130 and 442 m3/s. The uncertainty in the estimation of the 1% AEP flood event is increased due to the January 2011 flood event being an extreme flood event. The record was not long enough to provide certainty to the exact recurrence interval of the January 2011 event but the fitted FFA distributions suggest it was approximately a 0.33% AEP (1 in 300 year ARI). All three distributions provide similar peak flow rate estimations of the 20%, 10%, 5%, 2%, 1% and 0.5% AEP events.

A key observation from the historical record for Wickliffe is that there was a significant flow event in 1909. From records this event seems to be smaller than the January 2011 flood event. This would imply that the 2011 flood event is the largest flood event at Wickliffe over a period of 102 years and would increase the ARI estimate to 0.58% AEP (1 in 172 year ARI). This would shift the recurrence interval for the January 2011 event to the right in Figure 4.8 which would match the fitted curve more closely. This approach has not been adopted due to the uncertainties in the data set around the 1933-1942 period of missing data and because the record does not extend back to 1909 to determine if 1909 was larger or smaller than the 2011 flood event. That being said the fact that 2011 seems to be larger than 1909 and there are no known larger floods occurring at Wickliffe before this date supports the prediction that the 2011 flood event was approximately a 0.33% AEP flood event.

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4.6 Review and Develop Hydrological Models

The hydrology for the Wickliffe Flood Investigation is dependent on the hydrological model to develop the design flow hydrographs. This section will outline the models that are available for this study as well as the models that have been created to meet the objectives of the flood investigation.

4.6.1 Existing RORB Model

For the study area a RORB model exists for the area upstream of the Hopkins River at Ararat gauge. This model was created by the Glenelg Hopkins CMA and is shown in Figure 4.9.

Figure 4.9 Existing RORB model upstream of Hopkins River at Ararat gauge

This model covers the upper reaches of the catchment upstream of the Ararat streamflow gauge over an area of 258 km2. This model is only a small portion of the full catchment upstream of Wickliffe which has an area of 1,419 km2. The RORB sub-catchments of the Ararat model were used as a guide for the development of the Wickliffe RORB model.

The Ararat RORB model was not suitable for the current study as the sub-catchment size was inconsistent with the sub-catchments generated for the remaining Wickliffe upstream catchment. The sub-catchments within the Ararat RORB model were used as a guide to the development of the Wickliffe RORB model sub-catchments.

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4.6.2 Developed RORB Model

The Wickliffe RORB model was required to cover the full area upstream of 1,347 km2 which extends from upstream of Ararat down to Wickliffe. The RORB model was developed with 40 sub-catchments with the catchments being relatively uniformly sized with the sub-catchments having an area of approximately 35 km2. MiRORB was used to develop the model and the model was developed as a *.catg file. The topographic data used to delineate the catchments was the NASA USGS/SRTM (Jarvis et al., 2006) elevation dataset.

The RORB model is shown in Figure 4.10 and the Wickliffe RORB model vector is summarised in Appendix D.

Figure 4.10 Wickliffe RORB model

Following the development of the RORB model the catchment area was found to be 1,419 km2 which is higher than the reported Victorian Data Warehouse value. The catchment areas supplied on the Victorian Data Warehouse have an unknown origin and the disclaimer on the website states “The content of this Victorian Government website is provided for information purposes only. No claim is made as to the accuracy or authenticity of the content of the website”. Based on this statement the larger area as defined by the topography for the RORB model is deemed to be more accurate.

The average distance from the centroid of each sub-catchment to the outlet (Dav) from RORB was 44.63 km.

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4.6.2.1 Calibration The Wickliffe RORB model was calibrated to four (4) separate storms. This included the 1975, 1983, 2010 and 2011 events. The largest of these events was the January 2011 flood. The primary aim of the hydrologic model calibration was to determine the two key parameters within the RORB model that represent the catchment response to rainfall events, kc and ‘m’. kc is an empirical coefficient being the primary parameter controlling the lag of the runoff through the model. The ‘m’ parameter represents the catchment nonlinearity (i.e. the relationship of the catchment response to rainfall magnitude). The initial and continuing losses used in the calibration are of less importance as they relate specifically to the flood being calibrated. However, these loss rates can give some understanding of the depths of rainfall being lost within the catchments during various times of the year.

The four calibration storms were selected as they are the largest floods within the record which have concurrent streamflow, rainfall depth and pluviograph information available. The 1986 event was also considered for calibration, however there was insufficient information available to include this storm in the calibration process. For the four storms calibrated the January 2011 event was the largest and had the most recorded information. The 1975 and 1983 flood events were the next largest floods however the pluviograph information was limited. Although the 2010 flood was relatively small compared with the other calibration events it had a comprehensive set of data and was included. The final calibrated parameters to these events are summarised in Table 4.10.

The RORB vectors, storm files and calibration plots are shown in Appendix D.

Table 4.10 Wickliffe RORB Model Calibration Parameters IL CL Event k m Comments c (mm) (mm) Pluviographs: 089016, 089019, 089025 Rainfall approach: Distance Weighting to catchment centroid Oct. 1975 120 0.7 31.5 0.4 Rainfall gauges: 079050, 089033, 089034, 089037, 089045, 089080, 089085 Note: None Pluviographs: 089016, 089019, 089082 Rainfall approach: Distance Weighting to catchment centroid Sept. 1983 120 0.72 17.0 1.25 Rainfall gauges: 079050, 089033, 089034, 089037, 089045, 089080, 089085 Note: Baseflow removed from Wickliffe hydrograph. Pluviographs: 089016, 089019, 089082 25.0 1.80 Rainfall approach: Distance Weighting to catchment centroid Sept. 2010 120 0.73 Rainfall gauges: 079050, 089033, 089034, 089037, 089045, 089080, 089085 42.0 0.40 Note: None 55.0 3.35 Pluviographs: 089016, 089019, 089025, 089082 Rainfall approach: Distance Weighting to catchment centroid Jan. 2011 150 0.74 Rainfall gauges: 079050, 089019, 089033, 089034, 089037, 089045, 089080, 089085 108 0.40 Note: None

Following the final calibrated parameters are statistics of the fit obtained within RORB for each event. These statistics highlight three (3) key calibration objectives: x Peak discharge (m3/s) – shows the calibration match to the peak flows. x The time to the peak – shows the calibration to the routing of the rainfall through the catchment. x Volume (m3) – shows the match to the overall volume of runoff for the calibration event.

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1975 Calibration The first event to be calibrated was the October 1975, with a recorded peak of 100.3 m3/s. The event occurred during the winter months and as such had reasonably low initial and continuing loss rates as the catchment was already reasonably saturated. The calibration achieved a good match to the peak flow and was within 1% of the peak. Similarly, the time to the peak from the model was well matched with the modelled peak arriving only 1.5 hours after the recorded peak. Given the distances between rainfall gauges and pluviograph stations this is an accurate estimate for the timing.

The volume for this event was under predicted by 8%. This is influenced by baseflow not being removed from the model but also the fact that the catchment is very large (> 1,400 km2) and the runoff across the catchment varies from the steep upper reaches to the flat plains. A volume calibration of +/- 10% is deemed reasonable for a catchment of this size. The statistics for the 1975 event are summarised in Table 4.11.

Table 4.11 October 1975 calibration results Hydrograph Error Wickliffe Modelled Value Recorded Absolute Percentage (m3/s) Value (m3/s) Difference Difference (%) Peak discharge,m³/s 99.6 100.3 -0.7 -0.7 Time to peak, h 75 73.5 1.5 2 Volume,m³ 1.28E+07 1.39E+07 -1.14E+06 -8.2

1983 Calibration The September 1983 event had a peak discharge of 115.3 m3/s. The RORB model matched this peak very accurately to 0.1%. The timing to the peak was also very close with a difference of 3 hours. In this instance the volume of the modelled event was 20% larger than the recorded event. The main problem with this calibration was insufficient pluviograph data and rainfall depths and this introduced uncertainty around these parameters. This led to the flood hydrograph shape not matching the recorded data over the full length of the event. Ultimately the hydrograph rising and falling limbs were accurately represented by the model but the volume estimated was too large. This was the poorest calibration out of the four calibrated events. The statistics are summarised in Table 4.12.

Table 4.12 September 1983 calibration results Hydrograph Error Wickliffe Modelled Value Recorded Absolute Percentage (m3/s) Value (m3/s) Difference Difference (%) Peak discharge,m³/s 115.4 115.3 0.1 0.1 Time to peak, h 105 108 -3 -2.8 Volume,m³ 2.21E+07 1.81E+07 3.92E+06 21.6

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2010 Calibration The September 2010 event was calibrated at two locations, the Ararat streamflow gauge and the Wickliffe streamflow gauge. This allowed the calibration to establish if the RORB model was representing the area upstream of Ararat accurately. Overall this calibration was very good with peaks at Ararat and Wickliffe being matched within +/- 1%. Similarly the peak flow timing was accurately modelled. Both calibrated hydrographs show a 10% lower volume from the model as compared to the gauged hydrographs. This was expected as the baseflow components of the model had not been removed and only the rainfall information that drives the peak has been included as the peak flow response is the ultimate aim of the calibration process. The statistics for this calibration are summarised in Table 4.13.

Table 4.13 September 2010 calibration results Hydrograph Error Ararat Modelled Value Recorded Absolute Percentage (m3/s) Value (m3/s) Difference Difference (%) Peak discharge,m³/s 37.0 36.9 0.1 0.5 Time to peak, h 89.0 93.0 -4.0 -4.3 Volume,m³ 103 114 -11 -9.7 Hydrograph Error Wickliffe Modelled Value Recorded Absolute Percentage (m3/s) Value (m3/s) Difference Difference (%) Peak discharge,m³/s 64.5 65.1 -0.61 -0.9 Time to peak, h 134 133 0 0.4 Volume,m³ 1.13E+07 1.24E+07 -1.12E+06 -9

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2011 Calibration The largest calibration event included was the January 2011 flood event. From the analysis this event is very extreme for the Hopkins River and was estimated as an approximate 0.33% AEP event at Wickliffe. The calibration to this event was at the Ararat and Wickliffe gauge locations. The overall calibration to this event was very good with the peaks being matched closely. Similarly, the timing of these events was also matched very well. The volumes were also matched within +/- 10% which is reasonable as this is a large catchment and only the rainfall in the direct lead up to this event has been included. The statistics for this calibration are summarised in Table 4.14.

It is important to note that for the January 2011 flood event the kc parameter was much higher than for the other three calibration events. It is likely that the catchment response during the January 2011 event differed from the smaller events due to the magnitude of the rainfall depths recorded. It should also be noted that the loss rates for this calibration are very high, again as a result of the extreme nature of this event and that this event occurred in the middle of Summer.

Table 4.14 January 2011 calibration results Hydrograph Error Ararat Modelled Value Recorded Absolute Percentage (m3/s) Value (m3/s) Difference Difference (%) Peak discharge,m³/s 94.55 94.82 -0.27 -0.3 Time to peak, h 104 106 -3 -2.8 Volume,m³ 1.11E+07 1.17E+07 -0.55E+06 -4.7 Hydrograph Error Wickliffe Modelled Value Recorded Absolute Percentage (m3/s) Value (m3/s) Difference Difference (%) Peak discharge,m³/s 287.6 287.8 -0.3 -0.1 Time to peak, h 128 130 -2 -1.5 Volume,m³ 4.88E+07 4.55E+07 3.34E+06 7.4

Discussion

Overall, the events calibrated within RORB were well matched. The kc parameter varied between 120 for the 1975, 1983 and 2010 events up to 150 for the 2011 event. The primary reason for the 2011 event requiring a

higher kc parameter was due to the generated hydrograph shape not being adequately matched with a lower kc. This was thought to be because of the magnitude of the 2011 event which resulted in the flood peak passing through the catchment at a faster rate than for the 1975, 1983 and 2010 flood events.

This is explored in more detail in Section 4.11.1 where the travel time of the peak from Ararat to Wickliffe have been assessed for historic flood events. Of note is the fact that the travel time during the 2011 flood event from Ararat to Wickliffe was approximately 24 hours, whereas is the more frequent events the travel time ranges from 36 to 68 hours. This implies the catchment response changes between the extreme event in 2011 and the remaining calibration events.

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4.6.2.2 Design Parameters

The calibration parameters (see Table 4.10) indicate that there was a relatively uniform estimate for the kc parameter for the three smaller calibration events with the kc parameter being 120. For the larger January 2011 the kc parameter was 150 but this may reflect the fact that this was a very large and extreme event and the catchment response varied accordingly. Due to the majority of the events being calibrated using a kc of 120 this was used for the design events.

The ‘m’ parameter varied between 0.7 and 0.74, the majority of the events were calibrated using a ‘m’ parameter of 0.72 and 0.73. The design runs will use an ‘m’ value of 0.73.

The initial and continuing losses were set based on matching the peak flows with the FFA peak flow rates for each recurrence interval. These peak flow rates and design RORB parameters are summarised in Table 4.15. The peak flow rates are taken as the peak flow estimated from the Log Pearson Type 3 for each recurrence interval as this had the lowest uncertainty and is the primary distribution recommended in AR&R.

Table 4.15 Design RORB parameters

kc 120 ‘m’ 0.73 Average Recurrence Interval (years) Distributions 5 10 20 50 100 200 500 Design Peaks (m3/s) 65 85 110 152 194 249 336

4.6.3 Alternative WBNM Model

An alternative approach was explored during the project using WBNM to develop a similar model to the RORB model. This approach was adopted when there was uncertainty around the magnitude of the peak flow for January 2011. Cardno explored an alternative rainfall and runoff model to determine if the routing methods may improve the calibration to the 700 m3/s peak flow rate originally predicted to for January 2011 flood event.

The WBNM model produced similar calibrations to the RORB model and subsequent revisions to this event by Thiess which reduced the peak to 287 m3/s made this model redundant. It has been noted here that this model verifies the RORB model calibrations.

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4.7 Design Events

The design events have been derived using RORB with the target peak durations as summarised in Section 4.6.2.2 - Table 4.15. The design storm events have been derived using the AR&R design generated storms as based on the Bureau of Meteorology (BoM) Intensity Frequency Duration (IFD) parameters. The parameters were taken from the approximate centroid of the Wickliffe catchment and the parameters and location are summarised in Table 4.16.

Table 4.16 Wickliffe Intensity Frequency Duration (IFD) parameters IFD Coefficient Value

2I1 19.5

2I12 3.48

2I72 0.89

50I1 40.24

50I12 6.86

50I72 1.73 G (skew) 0.4 F2 4.35 F50 14.79 Zone 6 Location Latitude 37.450 S Longitude 142.450 E

In order to match the peak design flow for each recurrence interval the initial losses and continuing losses were varied by recurrence interval. The design events were run within RORB using the following: x Uniformly distributed rainfall distributions x Areal reduction factors based on Siriwardena and Weinmann estimates x Temporal pattern was based on AR&R87, Volume 2, Zone 6, filtered patterns

x kc was set to 120 x ‘m’ was set at 0.73.

The resulting matched peak design events have been summarised in Table 4.17. The peak design event durations varied from the 18 hour event up to the 72 hour event. All design peaks were matched to within +/- 3%.

Table 4.17 Wickliffe RORB design results Critical ARI IL CL Peak flow RORB Peak AEP Rainfall (years) (mm) (mm/hr) target (m3/s) flow (m3/s) Duration 1 in 5y 20% 15 1.7 65 67.0 18h 1 in 10y 10% 19 1.8 85 85.3 24h 1 in 20y 5% 22 2.25 110 109.8 24h 1 in 50y 2% 25 2.7 152 152.1 18h 1 in 100y 1% 29 3 194 196.0 72h 1 in 200y 0.5% 33 3.2 246 249.1 72h 1 in 500y 0.2% 37 3.7 336 338.4 18h

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4.7.1 Tributary (North East of Wickliffe – Upstream Floate Lane)

In order to determine the design inflows for the tributary to the north east of Wickliffe, upstream of Floate Lane, the Rational Method was used. This catchment has an approximate area of 3.0 km2 upstream of the hydraulic model area. The Rational Method was applied using the design IFD parameters (see Table 4.16). The fraction impervious was set at 0.05 which is appropriate for rural areas. The design peak flow rates are summarised in Table 4.18.

Table 4.18 Wickliffe tributary design flows Peak Flow ARI (years) AEP (m3/s) 1 in 5y 20% 3.6 1 in 10y 10% 4.4 1 in 20y 5% 5.6 1 in 50y 2% 7.5 1 in 100y 1% 9.1 1 in 200y 0.5% 11.5 1 in 500y 0.2% 15.0

4.7.2 Verification of Design Flows

In order to verify the design flow estimates for Wickliffe some additional methods have been assessed that provide support to the selected design flow rates. In particular support to the estimate that the January 2011 flood event was approximately a 0.5% AEP event. The three methods assessed included: x Rainfall frequency assessment x Approximate methods x Regional flow comparisons.

4.7.2.1 Rainfall frequency assessment validation The rainfall frequency assessment suggested that the rainfall that fell during the January 2011 flood event at Willaura and Wickliffe was around a 2.5% AEP flood event and approximately 0.3% AEP at Ararat. The combination of the extreme rainfall event at Ararat and the relatively moderate rainfalls across the plains of the catchment upstream of Wickliffe are likely to have combined to generate flood event that is somewhere between a 2.5% and 0.3% AEP event. The rainfall recurrence intervals across the Wickliffe catchment support the estimate of the January 2011 flood event as a 0.33% AEP flood event.

4.7.2.2 Regional Approximate Method Validation An additional method for reviewing the design flow estimates was suggested by the technical review group for this study. This method uses the regional estimation equation from Grayson et al (1996) for the estimation of 1% AEP floods for rural catchments near the Great Dividing Range in Victoria. This estimation technique gave a 1% AEP estimate of 1140 m3/s which is significantly higher than the design 1% AEP peak flow rate. However, this equation is based on a large number of design flood estimates for Victorian catchments but is associated with very wide confidence limits as it only considers catchment area as an explanatory variable. It is also known that it tends to significantly overestimate design floods for larger catchments such as the catchment to Wickliffe.

The fact that this estimate is much greater than the design 1% AEP estimate gives some validation to the design flow estimate as this method is expected to over predict the 1% AEP peak flow rate for larger catchments.

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4.7.2.3 Region Flow Comparison Validation The Glenelg-Hopkins CMA has undertaken a number of flood studies and frequency analyses for catchments within its area of responsibility. Results provided by GHCMA (pers. com. GHCMA, 2010) have been used to compile the data shown in Table 4.19. The last column shows the individual estimates scaled to a catchment area of 1,419 km2 using the ratio of catchment areas to the power of 0.7. Some observations that come from this assessment include: x The 1% AEP flood estimate for Wickliffe is of similar order of magnitude but lower than the scaled estimates for the neighbouring catchments of Fiery Creek at Streatham and Mt Emu Creek at Skipton. x The catchments of similar size but closer to the coast (Merri River, Moyne River and Crawford River) produce larger design floods, presumably due to heavier rainfalls. x The magnitude of the 1% AEP design flood does not necessarily increase with the size of the catchment, as indicated by the estimates for the lower parts of the Hopkins River catchment and the Glenelg River catchment. x The predicted 1% AEP peak flow rate of 196 m3/s is higher than the scaled estimated for the downstream Hopkins River gauges. This is in line with expectations as the catchment upstream of Wickliffe contains the steeper upper reaches of the Hopkins River catchment. Downstream of Wickliffe the catchment is mainly plains and has a very low slope. This is expected to cause the peak flows to gradually reduce as the flood water spread across the floodplain. x Neighbouring catchments experience higher scaled peak flow rates than the Hopkins River. This is due to the catchment characteristics of the Hopkins River. The Hopkins River catchment upstream of Wickliffe has steep upper catchments which feed into low sloping plains. These plains are likely to be a source for significant interception storage which results in lower overall runoff rates. An example of this interception storage can be seen in the Cockajemmy Lakes near Willaura and the area around Lake Muirhead. These lakes would intercept large volumes of water which reduce the peak flows generated from the catchment relative to the neighbouring catchments.

Table 4.19 Estimated of regional 1% AEP 1% AEP Scaled to Stream Location Area (km2) Peak Flow at 1,419 km2 ^ site Hopkins River Framlingham 5157 381.6 154.6 Hopkins River Hopkins Falls 8355 623.9 180.4 Fiery Creek Streatham 956 208.9 275.4 Mt Emu Creek Skipton 1251 321.5 351.1 Merri River Woodford 899 405.0 557.5 Moyne River Toolong 570 229.7 434.9 Crawford River Lower Crawford 606 249.0 451.7 Glenelg River Fulham 2010 208.7 163.6 Glenelg River Dartmoor 11914 913.0 205.9 ^ The catchment area has been based on the RORB model area which is larger than the Victorian Data Warehouse estimate.

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4.7.2.4 Discussion Overall the methods assessed support the Design Event flow estimates for Wickliffe. The rainfall assessment for the January 2011 flood event indicated that the event was likely to be generated primarily within the upper reaches of the catchment and overall that the Wickliffe catchment would experience a flood event between a 2.5% and 0.3% AEP flood event. This is in-line with the prediction that the January 2011 event was approximately a 0.33% AEP flood event.

The regional prediction method provided some validation in the fact that this method predicted a 1% AEP peak flow rate much higher than the 1% AEP design event. This again is in-line with findings for large catchments using this method.

Finally, the regional assessment demonstrates that the design peak flow rates for Wickliffe on the Hopkins River are: x Consistent with the scaled downstream gauges on the Hopkins River. x Consistent with neighbouring catchments when catchment characteristics are taken into account.

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4.8 Hydrologic Model Sensitivity

In order to assess the sensitivity of the RORB model to the selected parameters for the design events the kc, ‘m’ and loss rate will be examined to determine the impact these have on the design peak flow rate. The sensitivity assessment aims to determine the uncertainty of the hydrology with regard to the hydrologic model peak flow estimates.

4.8.1 Sensitivity on the RORB kc parameter

The primary calibration parameter is the empirical coefficient kc which represents the lag of the response of the catchment to rainfall events. The sensitivity assessment here has considered a range of kc values around the calibrated value selected at 120.

The recommended kc values as suggested by Equation 2.5 from the RORB manual and these estimated values are dependent on the ‘m’ and peak flow rate. For the design event the recommended kc was: 3 x For the smallest event in 2010, the peak flow rate was 65 m /s, m was 0.73 and the suggested kc was 105. 3 x For the largest event in 2011, the peak flow was 287 m /s, m was 0.74 and the suggested kc was 122. 3 x For the 1983 event, the peak flow was 115 m /s, m was 0.72 and the suggested kc was 114. 3 x For the 1975 event, the peak flow was 100 m /s, m was 0.7 and the suggested kc was 122.

The suggested range of kc parameters was from 105 to 122 based on the default equation with RORB, however this is only a generalised estimate of the kc that may be expected. In order to test the model a lower estimate of the kc of 100 was selected as this was just below the lower estimate and an upper estimate of 150 was selected as this was the calibrated kc value for the January 2011 flood event.

The results of the assessment are summarised in Table 4.20. The range of kc from 100 to 150 generated a difference in peak flow rate of between +/- 30%. For the large flow events (i.e. > 1 in 50 year ARI) the sensitivity using the kc of 100 and 150 generated peak flow rates that were within the 90% confidence intervals of the fitted

Log Pearson Type 3 distribution. This shows that using a wide range of kc values generates peak flow rates that lie within the uncertainty of the FFA fitted distribution and that the model is not overly sensitive to the selected value of kc for the model relative to the uncertainty within the FFA.

Table 4.20 Sensitivity on the RORB kc parameter 90% confidence limits kc = 120 kc = 100 kc = 150 for the design FFA ARI (years) AEP Lower Upper RORB Peak RORB Peak Diff. RORB Peak Diff. 90% 90% flow (m3/s) flow (m3/s) (%) flow (m3/s) (%) (m3/s) (m3/s) 1 in 5y 20% 67.0 58 75 85.9 28% 49.5 -26% 1 in 10y 10% 85.3 73 102 108.7 27% 63.1 -26% 1 in 20y 5% 109.8 88 142 134.3 22% 84.0 -23% 1 in 50y 2% 152.1 111 228 194.0 28% 112.6 -26% 1 in 100y 1% 196.0 130 331 249.7 27% 145.1 -26% 1 in 200y 0.5% 249.1 150 486 320.2 29% 184.3 -26% 1 in 500y 0.2% 338.4 179 817 429.7 27% 251.1 -26%

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4.8.2 Sensitivity on the RORB ‘m’ parameter

During the calibration process the ‘m’ parameter was set within the range of 0.7 to 0.73 for the calibrated events. To assess the impact that this parameter would be likely to have on peak flow rates a range around the calibrated ‘m’ value of 0.73 was selected. The values of 0.7 and 0.76 were considered to determine if this parameter was likely to have a significant impact on the peak flow rate estimation.

Overall the change in ‘m’ from 0.7 to 0.76 generated peak flow rates that were within +/- 20% of the calibrated peak flows. As with the kc sensitivity the sensitivity assessment using the ‘m’ values of 0.7 and 0.76 generated peak flows which were within the 90% confidence limits of the fitted distribution for the FFA generation of the design flows. This shows that using a wide range of ‘m’ values generates peak flow rates that lie within the uncertainty of the FFA fitted distribution and that the model is not overly sensitive to the selected value of ‘m’ for the model relative to the uncertainty within the FFA.

The results of this sensitivity assessment are summarised in Table 4.21.

Table 4.21 Sensitivity on the RORB ‘m’ parameter 90% confidence limits m = 0.73 m = 0.7 m = 0.76 for the design FFA ARI (years) AEP Lower Upper RORB Peak RORB Peak Diff. RORB Peak Diff. 90% 90% flow (m3/s) flow (m3/s) (%) flow (m3/s) (%) (m3/s) (m3/s) 1 in 5y 20% 67.0 58 75 75.7 13% 59.9 -11% 1 in 10y 10% 85.3 73 102 96.6 13% 75.7 -11% 1 in 20y 5% 109.8 88 142 122.8 12% 98.1 -11% 1 in 50y 2% 152.1 111 228 176.7 16% 132.0 -13% 1 in 100y 1% 196.0 130 331 229.7 17% 168.4 -14% 1 in 200y 0.5% 249.1 150 486 296.8 19% 211.4 -15% 1 in 500y 0.2% 338.4 179 817 405.0 20% 285.1 -16%

4.8.3 Sensitivity on the RORB loss rate

In order to test the sensitivity of the RORB model to the loss rates four scenarios were tested with the losses being at +/- 10% and at +/- 20%. The revised loss rates are summarised in Table 4.22.

Table 4.22 Sensitivity on the RORB design loss rates DESIGN Loss -20% Loss -10% Loss +10% Loss +20% ARI AEP IL CL CL CL CL CL (years) IL (mm) IL (mm) IL (mm) IL (mm) (mm) (mm) (mm) (mm) (mm) (mm) 1 in 5y 20% 15.0 1.70 12.0 1.36 13.5 1.53 16.5 1.87 18.0 2.04 1 in 10y 10% 19.0 1.80 15.2 1.44 17.1 1.62 20.9 1.98 22.8 2.16 1 in 20y 5% 22.0 2.25 17.6 1.80 19.8 2.03 24.2 2.48 26.4 2.70 1 in 50y 2% 25.0 2.70 20.0 2.16 22.5 2.43 27.5 2.97 30.0 3.24 1 in 100y 1% 29.0 3.00 23.2 2.40 26.1 2.70 31.9 3.30 34.8 3.60 1 in 200y 0.5% 33.0 3.20 26.4 2.56 29.7 2.88 36.3 3.52 39.6 3.84 1 in 500y 0.2% 37.0 3.70 29.6 2.96 33.3 3.33 40.7 4.07 44.4 4.44

The results indicated that with a loss rate +/- 10% that the peak flow would vary between approximately +/- 30%. The loss rates of +/- 10% generally produced peak flow rates that were within the 90% confidence intervals of the

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fitted distribution for the FFA. There was more observed variation in the flood response with the more frequent events with a change in the loss rate relative to the more extreme flood events.

For the scenario with the losses set at +/- 20% the resulting flow variability was increased. The peak flow rates in this scenario varied from approximately 50-70%. This shows clearly that the model is very sensitive to a large change in the loss rate. For most events a +/- 20% change in loss rates generated peak flows which were well outside the 90% confidence intervals generated by the FFA. The resulting difference in peak flow rates are summarised in Table 4.23.

Table 4.23 Results of the design loss rate sensitivity analysis 90% confidence DESIGN limits for the Loss -20% Loss -10% Loss +10% Loss +20% ARI design FFA AEP (years) RORB Lower Upper Peak Peak Peak Peak Diff. Diff. Diff. Diff. Peak flow 90% 90% flow flow flow flow (%) (%) (%) (%) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) 1 in 5y 20% 67.0 58 75 118 76% 93 38% 51 -24% 42 -38% 1 in 10y 10% 85.3 73 102 151 77% 113 33% 68 -20% 44 -48% 1 in 20y 5% 109.8 88 142 180 64% 150 36% 87 -21% 60 -45% 1 in 50y 2% 152.1 111 228 251 65% 196 29% 109 -28% 90 -41% 1 in 100y 1% 196.0 130 331 336 71% 259 32% 139 -29% 113 -42% 1 in 200y 0.5% 249.1 150 486 418 68% 327 31% 182 -27% 148 -41% 1 in 500y 0.2% 338.4 179 817 534 58% 422 25% 259 -23% 189 -44%

4.8.4 Discussion

The sensitivity analysis explored the implications for the design peak flow rates for variations in the key model parameters of kc, ‘m’ and the catchment losses. The primary outcomes from this analysis include:

x Variation in the kc from 100 to 150 generated a difference in peak flow rate of between +/- 30%. x The change in ‘m’ from 0.7 to 0.76 generated peak flow rates that were within +/- 20% of the calibrated peak flows. x The results indicated that with a loss rate +/- 10% that the peak flow would vary between approximately +/- 30%. x For the scenario with the losses set at +/- 20% the resulting flow variability was increased. The peak flow rates in this scenario varied from approximately 50 - 70%.

The sensitivity analysis demonstrates the expected variability in the peak design flow based on the full realistic range of each model parameter. The sensitivity showed that the design flows could be expected to vary by as much as +/- 30% due to the assumptions regarding each parameter. This indicates that if a different set of parameters were selected based on the calibration this would produce peak flow rates within +/- 30% of the current design peaks and this gives an upper limit to the uncertainty associated with the peak flow rates set for the design events.

The results of the sensitivity analysis confirm that there is a considerable margin of uncertainty in the estimated design flood hydrographs. The magnitude of this uncertainty is broadly consistent with the band of uncertainty indicated by the 90% confidence limits around the flood frequency estimates shown in Table 4.9 and Figure 4.8. It will be important to assess how this uncertainty in design peak flows translates into uncertainty in flood levels, and to take this uncertainty into account in any flood management decisions.

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In order to assess the possible future impact of climate change an analysis of the impacts of increased rainfall intensity of 32% was explored. This section outlines the derivation and summary of the IFD parameters applied and the associated flow rates predicted from RORB.

The selected percentage increases in rainfall intensity are in line with the Melbourne Water (MW) Technical Specifications for Climate Change within Victoria. The basis for the rainfall intensity increases is the IPCC Fourth Assessment Report. This report assumes a 5% increase in rainfall intensity for every 1 ÛC rise in average temperature. The report has an upper limit of the expected temperature rise of 6.4 ÛC which gives the upper limit to the increase in rainfall intensity of 32%.

The increased rainfall intensity of 32% correspond to increases in average temperature of 6.4 ÛC and has been examined to show the expected upper limit of increased rainfall intensity on the catchment runoff rates and peak flows for the Wickliffe area. The increase in temperature has been applied to correspond with the recommendations within the MW Technical Specifications. The 32% increase in rainfall intensity has been related to approximate climate change time period of 2110.

It should be noted that this climate change assessment only focusses on the change in rainfall intensity and does not explicitly assess any changes in catchment antecedent conditions and predicted loss rates. Losses may change in line with the expectation that the catchment may be drier for longer between more frequent intense rainfall events.

The increased IFD parameters are summarised in Table 4.24.

Table 4.24 Wickliffe Intensity Frequency Duration (IFD) parameters for climate change IFD Coefficient Current Conditions 32% Climate Change

2I1 19.5 25.7

2I12 3.48 4.59

2I72 0.89 1.17

50I1 40.24 53.12

50I12 6.86 9.06

50I72 1.73 2.28 G (skew) 0.4 0.4 F2 4.35 4.35 F50 14.79 14.79 Zone 6 6 Location Latitude 37.450 S Longitude 142.450 E

The RORB model presented in Section 4.6.2 was used in conjunction with the revised IFD parameters to determine the revised climate change peak flows at Wickliffe. The results are presented in Table 4.25.

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Table 4.25 Climate change assessment for the Wickliffe hydrology 32% increase rainfall intensity at Hopkins River at Hopkins River at Wickliffe Wickliffe AEP (%) Design Flow CC Design Flow Increase (% from Peak Duration Peak Duration Rate (m3/s) Rate (m3/s) current) 20% 67.0 18h 187.0 12h 279% 10% 85.3 24h 231.7 18h 272% 5% 109.8 24h 288.4 24h 263% 2% 152.1 18h 408.4 30h 268% 1% 196.0 72h 537.4 72h 274% 0.5% 249.1 72h 672.3 72h 270% 0.2% 338.4 18h 841.5 72h 249%

The results indicate that a 32% increase in rainfall intensity is likely to have a number of influences over the catchment response during flood events. Some key observations can be made from the results presented, including: x For the more frequent events the peak duration as a result of climate change has changed from longer duration events for the current design events to shorter duration events. For the rarer, large events there was largely no change in duration. x That the flood peaks are expected to increase significantly as a result of a 32% increase in rainfall intensity, by as much as 279% in the shorter duration events. x The percentage increase in peak flow rate for the more common events are expected in increase more than the larger, rarer events.

For this assessment only the 10%, 1% and 0.2% climate change scenarios are to be modelled through the hydraulic model.

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The probable maximum flood (PMF) has been derived using the Generalised South Eastern Australian Method (GSAM). This allows for the estimation of the PMF for durations of 24 hours to 96 hours. In this instance the Generalised Short Duration Method (GSDM) cannot be used as this process has a maximum catchment area of 1000 km2. As the GSDM cannot be used the PMF will be derived solely as a 24 to 96 hour duration event.

The GSAM is an approach that estimates the Probable Maximum Precipitation (PMP). The information required to derive the PMP is summarised in Table 4.26. The resulting PMP depths are summarised in Table 4.27 for the 24 to 96 hour rainfall durations.

Table 4.26 Wickliffe PMP parameters for the GSAM Parameter Value Catchment Area 1,419 GSAM Zone Coastal Topographic adjustment factor (TAF) 1.2

EPWSummer 57.8

MAFSummer 0.72

EPWAutumn 47.2

MAFAutumn 0.66

Table 4.27 Estimated PMP rainfall depth Duration (hours) PMP depth (mm) 24 450 36 510 48 540 72 590 96 630

The GSAM method provides temporal distributions for the rainfall to be distributed over for the various durations. These temporal distributions were used to create storm files and the PMP events were run through RORB to determine the Probable Maximum Flood (PMF). The peak flow rate was generated by the 36 hour duration storm event and this had a predicted peak of 4,600 m3/s. The peak flow rates are summarised in Table 4.28.

Table 4.28 Predicted Probable Maximum Flood at Wickliffe Duration (hours) PMF (m3/s) 24 3,450 36 4,600 48 4,150 72 4,100 96 2,800

As the 36 hour duration event was the largest event from the analysis it is unlikely that there are shorter duration events that would produce a larger PMF. However, in order to determine if any shorter duration events were expected to cause larger peak flow rates at Wickliffe, other methods (such as Hydrological Recipes (Grayson et al., 1996) and the GSDM) were explored. Ultimately it was found that these methods could not be applied as the catchment area threshold for these methods is a catchment area of 1,000 km2.

The PMF is primarily used to define the maximum extent that would ever be expected on the Hopkins River at Wickliffe.

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An important part of this hydrological assessment is the analysis of the travel times through the Wickliffe catchment. Information on travel times for flood peaks is important for the purposes of flood warning and preparedness. This travel time assessment will examine x The two (2) streamflow gauges, at Ararat and Wickliffe, to determine the known travel time between the peaks at these two locations across their concurrent records. x Calibrated event timings within RORB for the four (4) calibrated events, 1975, 1983, 2010 and 2011. The 2010 and 2011 events have been calibrated at both Wickliffe and Ararat. x Anecdotal evidence from the community consultation and from discussions with relevant agencies.

Overall the aim is to develop an understanding of the average travel times for peak flows through the catchment. Each flood event is different and travels times will vary but an understanding of historic travel times is important for flood preparedness, planning and response.

4.11.1 Streamflow gauge assessment

The two streamflow gauges that are located upstream of Wickliffe are: x Hopkins River at Ararat (236219) x Hopkins River at Wickliffe (236202).

The concurrent streamflow data for the Ararat and Wickliffe gauges runs from June 1989 to February 2012. Within this concurrent period there are very few large flood events which occurred at Ararat and at Wickliffe due to the extended drought conditions through the majority of this record. From this period five flood events occurred on a catchment wide scale that had peaks in Ararat and Wickliffe. These events are summarised in Table 4.29.

Table 4.29 Travel times for large events though the Wickliffe catchment Hopkins River at Ararat Hopkins River at Ararat Travel RORB Event Peak Peak time travel time Date and time Date and time (m3/s) (m3/s) (hours) (hours) Jun/Jul 1989 50.2 31/07/1989 12:30 pm 51.1 2/08/1989 14:36 pm 38 h N/A Aug 1992 43.4 30/08/1992 2:33 am 65.1 31/08/1992 14:50 pm 36 h N/A Sep 2010 36.9 4/09/2010 21:09 pm 65.1 6/09/2010 12:45 pm 40 h 44.5 h Dec 2010 30.4 8/12/2010 9:00 am 56.7 11/12/2010 5:00 am 68 h N/A Jan 2011 95.9 14/01/2011 10:43 am 287 15/01/2011 11:15 am 24 h 26 h

For these events the largest event with the most consistent rainfall timing and depth across the catchment was the January 2011 flood event. This event has a 24 hour lag time from Ararat to Wickliffe for the peak flows that were recorded (see Figure 4.11). The remaining four flood events have a lag in the peak from Ararat to Wickliffe of between 36 and 40 hours. The September 2010 event hydrographs are shown in Figure 4.12. The smallest event at Ararat in December 2010 has a lag of 68 hours to Wickliffe but it is unclear as to whether the peak at Ararat was the direct cause of the peak at Wickliffe or whether it was other tributaries downstream of Ararat contributing additional flows.

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Figure 4.11 Peak flow travel times through the Wickliffe catchment during the January 2011 event

Figure 4.12 Peak flow travel times through the Wickliffe catchment during the September 2010 event

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The main problem with this approach to examining the timing of flows is that upstream of the Ararat gauge the catchment area is only 258 km2 (from Victorian Data Warehouse), whereas the full area contributing to the Wickliffe gauge was 1,419 km2 (from the RORB model). Only 18% of the Wickliffe catchment is upstream of the Ararat gauge and that leaves a lot of ungauged area where the runoff behaviour is not recorded which can influence the peak flow rate at Wickliffe.

Overall, the largest event in January 2011 had a travel time between the gauges of 24 hours and this is likely to be close to the minimum travel time between the gauges, the smaller events indicate that during more widespread and lower magnitude events the peak flows travel at a reduced rate through the system and accordingly the travel times between the peak at Ararat and at Wickliffe increase to 36 - 40 hours or more.

The fact that the Ararat gauged area is only 18% of the catchment upstream of Wickliffe and that the travel times can vary from this gauge to Wickliffe from 24 to 40 hours suggest that additional information is required for future flood warning. A gauge located closer to Wickliffe could give a more reliable warning and additional information regarding peak flow travel times through the catchment for future plod planning. The gauge location(s) will be discussed later in this report.

4.11.2 Calibrated RORB travel times

In order to get a more complete picture of the travel times through the catchment the hydrological model RORB has been assessed for the calibrated events during 1975, 1983, 2010 and 2011. Both the September 2010 and January 2011 event had a calibration location at Ararat and Wickliffe, whereas the 1975 and 1983 events were only calibrated at Wickliffe. The RORB model allows for the routed flows to be extracted at key locations throughout the catchment to provide some guidance as to the travel times between locations. Some key assumptions about the RORB model should be noted including:

x The rainfall depths are applied using known pluviographs for each event. Many of these pluviographs are located a substantial distance from the catchment and this may cause some impact on the timing of flows. x Rainfall depths are determined from gauges throughout the catchment and as such the spatial distribution of rainfall may have varied for the calibrated events. x The calibrated model statistics and parameters for each event can be found in Section 4.6.2.1 and the calibrated hydrograph plots in Appendix D.

For the travel assessment of the flood peaks during these events, information has been extracted at 9 locations (including the Ararat and Wickliffe gauges). The locations to be extracted are summarised in Figure 4.13.

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Figure 4.13 Locations assessed for the travel time within the RORB model

The results of the travel time assessment from RORB are summarised in Table 4.30. The results are presented with all location peaks being set using the time of the Wickliffe peak as a reference (i.e. for the 1975 event the peak arrived at Major-Mitchell Road 5.5 hours before it arrived at Wickliffe). Presenting the table in this format shows the travel time relative to the peak at Wickliffe and shows you response time available once the peak is observed at the upstream locations before it is expected to reach Wickliffe.

Table 4.30 Travel time assessment results from RORB Location 1975 1983 2010 2011 1% AEP Design Peaks Peaks Peaks Peaks Average Event (72 hr) HOPKINS RIVER (hours) (hours) (hours) (hours) Peaks (hours) Upstream of Western Hwy (Ararat) 33.0 28.0 53.5 28.5 35.8 24.0 Ararat Gauge 30.0 25.0 44.5 26.0 31.4 20.0 Maroona 20.0 17.5 33.0 19.5 22.5 8.0 Ross Bridge (Mortlake-Ararat Road) 16.0 17.5 23.5 15.5 18.1 8.0 Delacombe Way 11.0 11.0 14.5 12.0 12.1 8.0 Major-Mitchell Drive 5.5 5.0 7.0 6.0 5.9 4.0 Wickliffe Gauge 0 0 0 0 0 0 TRIBUTARY Upstream of Lake Buninjon (Good 21.5 17.5 24.0 27.5 22.6 12.0 Morning Bill Ck, Nekeeya Ck, Mason Ck) Upstream of Cockajemmy Lakes N/A1 17.5 17.5 16.0 17.0 16.0 (Willaura-Wickliffe Road) 1 No flows supplied from this area due to losses applied

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The results show that the location at Major-Mitchell Drive, the average travel time to Wickliffe is between 5 to 6 hours. Moving upstream to Delacombe Way the average travel time is 12 hours, to Ross Bridge is 18 hours, to Maroona is approximately 22 hours and the peak arrives at the Ararat gauge on average 31 hours before Wickliffe. This average is based on the four calibrated events and from Table 4.30 it is evident that the September 2010 event propagated through the Wickliffe catchment relatively slowly when compared to the other three events calibrated.

The two tributary systems to the Hopkins River have travel times to Wickliffe that reflect their size and location of their confluence with the Hopkins River. The tributaries have been reported as a separate section as they do no lie on the main Hopkins River which is of primary interest.

The design event travel times has been included to examine of the design event is capturing the travel time appropriately. The travel times are slightly less than the calibrated events at most locations but are only about 4 hours faster than the January 2011 event. This increased flow rate is primarily due to the fact that AR&R can only provide storm duration up to the 72 hour duration. The peak 1% AEP (1 in 100 year ARI) design flow was obtained from the 72 hour duration event this may cause the catchment to respond a little faster under the design event as compared to the calibrated events. AR&R does not have provisions for extended duration events past the 72 hour event. The design event also assumes that flows occur over the entire catchment simultaneously and this will impact the timing as real storm events tend to move through the catchment over a period of days or hours.

4.11.3 Anecdotal travel time

From discussions with the Community, Council and the Glenelg Hopkins CMA Cardno has gathered information regarding the travel times during recent events and historic observations. The Community was engage in December 2011 via a Community consultation session in Wickliffe and again in April 2012 via a Steering Group Meeting. As a result of these discussions the primary observations that have been supplied were:

x During the January 2011 flood event the peak flow was estimated to have a travel time of 6 hours from when it was observed at Major-Mitchell Drive to the time it reached Wickliffe. This information was supplied by Leesa Baker of the Wickliffe Flood Action Group. x Travel times have been expressed by the Community as being approximately 1 day from Ararat to Wickliffe.

Both of these observations tie in well with the data received and the analysis of the travel times. These travel times supplied from the Community help to validate the models and assessment.

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4.12 Summary and Recommendations

The aim of this hydrological assessment was primarily to determine the design inflows for the Wickliffe hydraulic model. The design flows were based on a calibrated RORB rainfall-runoff model and AR&R design generated rainfall events. The RORB parameters for kc and ‘m’ were 120 and 0.73 respectively. The initial and continuing losses varied over the range of recurrence intervals so that the design peaks could match the FFA predicted peak flow rates for each recurrence interval. The design flows for the tributary upstream of Floate Lane were derived using the Rational Method.

The design flows that were derived for the Hopkins River at Wickliffe and for the tributary upstream of Floate Lane are summarised in Table 4.31.

Table 4.31 Wickliffe design flow rates for the hydraulic model Hopkins River at Floate Lane Peak ARI (years) AEP Wickliffe Design Tributary Design Duration flow (m3/s) Flow (m3/s) 1 in 5y 20% 67.0 18h 3.6 1 in 10y 10% 85.3 24h 4.4 1 in 20y 5% 109.8 24h 5.6 1 in 50y 2% 152.1 18h 7.5 1 in 100y 1% 196.0 72h 9.1 1 in 200y 0.5% 249.1 72h 11.5 1 in 500y 0.2% 338.4 18h 15.0

Additional analysis was undertaken regarding the travel times throughout the Wickliffe catchment based on the RORB calibrated events and known gauged data. The average travel times from the four calibrated events (1975, 1983, 2010 and 2011) have been summarised in Table 4.32. Recommendations on gauge locations to allow for appropriate flood warning for Wickliffe in the future will be discussed in the risk assessment and flood warning sections to follow the hydraulic model section.

Table 4.32 Travel time assessment results from RORB Location Average Travel HOPKINS RIVER Times (hours) Upstream of Western Hwy (Ararat) 35.8 Ararat Gauge 31.4 Maroona 22.5 Ross Bridge (Mortlake-Ararat Road) 18.1 Delacombe Way 12.1 Major-Mitchell Drive 5.9 Wickliffe Gauge 0 TRIBUTARIES Upstream of Lake Buninjon (Good 22.6 Morning Bill Ck, Nekeeya Ck, Mason Ck) Upstream of Cockajemmy Lakes 17.0 (Willaura-Wickliffe Road) 1 No flows supplied from this area due to losses applied

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5 HYDRAULIC MODELLING

5.1 Hydraulic Model Establishment

The WL|Delft 1D2D modelling system, SOBEK, was used to compute the channel (1D) and overland flow (2D) components of the study. SOBEK is a professional software package developed by WL|Delft Hydraulics Laboratory, which is one of the largest independent hydraulic institutes in Europe (situated in The Netherlands) and is world-renowned in the fields of hydraulic research and consulting (WL|Delft, 2005).

This combined package allows for the computation of channel and pipe flow (including structures such as culverts, weirs, gates and pumps, and pipe details such as inverts, obverts, pipe sizes and pipe material) by the 1D module, which is then dynamically linked to the 2D overland flow module. The 1D and 2D domains are automatically coupled at 1D-calculation points (such as manholes) whenever they overlap each other. The model commences with the 1D component operating as the inflow increases until such time as the pipe or channel is full and overflows, with the flow then moving to the 2D domain. The 1D network and the 2D grid hydrodynamics are solved simultaneously using the robust Delft scheme that handles steep fronts, wetting and drying processes and subcritical and supercritical flows (Stelling et al., 1999).

The advantages of this system are that the channel/pipe system is explicitly modelled as a sub-system within the two-dimensional overland flow computation. This means that generalised assumptions regarding the capacity of the channel/pipe system are not required. This system employs a unique implicit coupling between the one and two-dimensional hydraulic components that provides high accuracy and stability within the computation.

5.2 Hydraulic Model Development

The hydraulic models consist of two main hydraulic components: x The channel network for structures (1D); and x 2D grid of the surface topography. The establishment of these two components of the model is described in the following sections.

For the Wickliffe Flood Investigation the Hopkins River was the primary river flowing through the study area. To the north-east of the Wickliffe township an unnamed tributary flows to the Hopkins River. The model area is shown in Figure 5.1.

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Figure 5.1 Model boundary for the Wickliffe SOBEK Model

5.2.1 Channel and Structure System (1D)

Survey was captured for the study area and this information has been presented in Section 3.1. The locations of the cross sections and structures captured are summarised in Figure 3.1. Overall there were 13 cross sections and 4 structures surveyed. All channels and structures were represented within the 1D domain of the hydraulic model.

5.2.2 Topography (2D)

The topography was defined using a Digital Terrain Model (DTM) of the region. The DTM was derived from the 2009 LiDAR data within the software package 12D. The dimensions of the grids are summarised in Table 5.1.

Table 5.1 Topography grid size Parameter Grid

Cell size 4m x 4m Grid Cells (x direction) 1088 Grid Cells (y direction) 850

The topography layer was set using the grid cell size of 4m x 4m as this provided enough detail to capture the surface elevation details without causing computation run times and size of results to be excessive. The DTM is shown in Figure 5.3. The grid cell size selected was the finest detail possible without causing runtimes of multiple days while also replicating the known surface appropriately. The major bridge opening within the study area was

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approximately 35 m wide which corresponds to 8 or 9 grid cells within the model. This is an adequate number of grid cells for the interaction at the critical infrastructure in the model.

An example cross section is shown in Figure 5.2. The major flood plain at this location was approximately 300 m in width which corresponds to 75 grid cells. This indicates that the hydraulic model has sufficient grid cells to convey the peak flows through the main flood plain without causing instabilities within the hydraulic model.

Figure 5.2 Example cross section for the Hopkins River near Wickliffe

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Modifications to the topography along the river in the 2D grid were undertaken because the main river channel was represented using 1D elements within the model. Figure 5.2 shows that the main channel is approximately 40 m in width which corresponds to 10 grid cells. Within the 2D model the 10 grid cells corresponding to the 1D channel were infilled to ensure that there was no double counting of floodplain storage within the hydraulic model.

Figure 5.3 Digital Terrain Models (DTM) for the Wickliffe Model

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5.3 Hydraulic Model Calibration

Two major flood events have occurred in recent history at Wickliffe that had peak streamflow levels, peak flood levels and extents captured that can be used to calibrate the hydraulic model. The two events where levels have been captured included the September 2010 and January 2011 flood events. Of these events the January 2011 flood event had a significantly larger set of recorded flood heights that captured the peak flows at Wickliffe. Each of these calibration events have been used in order to calibrate the hydraulic model. The main calibration variables within the hydraulic model include the roughness parameters and the losses across the structures.

5.3.1 2010 Event

The September 2010 flood event had 8 recorded flood depths recorded during the event. From discussions with the Glenelg Hopkins CMA it was established that these flood depths were not captured at the peak of the event. The CMA stated that the levels were captured during the event and the levels recorded were not the peak flood heights. As such, it is likely that these recorded flood heights are lower than the ultimate flood peak reached during this event.

An additional peak flood level has been estimated at the gauge using the gauge zero level of 197.62 mAHD and the peak depth recorded at the gauge of 4.13 m. The peak flood depth was estimated at 201.75 mAHD. The gauged peak depth was the only level that could reliably be stated as the peak level for the September 2010 flood event. The flood hydrograph was applied to the model at the upstream boundary using a flood hydrograph of the gauged flow rates. The downstream boundary was set using the existing cross section and using the Manning’s Equation to determine a stage-discharge relationship. This boundary information has been summarised in Section 5.4.2.

The calibrated model results are summarised in Table 5.2. The difference between the recorded peak flood heights and the modelled flood depths have been calculated even though the recorded information did not capture the peak flows to demonstrate that the model is reaching levels higher than the recorded data. This is as expected as the flood data captured was below the peak of the flood event.

The streamflow gauge was the only point to capture the peak of the event and the model reproduced a peak for this event 0.07 m higher than the recorded peak gauge height. This was considered an acceptable calibration to this event at the gauge.

Table 5.2 Calibration results for the September 2010 flood event Name Description Peak Recorded? Flood Height Model Height Difference (Model (mAHD) (mAHD) less Observed) (m) WICK01 Peg mark N 200.66 200.90 0.24 WICK02 Peg mark N 200.70 200.93 0.23 WICK03 Peg mark N 200.84 201.03 0.18 WICK04 Peg mark N 200.79 201.35 0.55 WICK05 Peg mark N 201.27 201.57 0.30 WICK06 Peg mark N 200.86 201.49 0.63 WICK07 Peg mark N 201.27 201.66 0.39 WICK08 Chisel mark N 201.29 201.73 0.43 GAUGE Gauge Y 201.75 201.82 0.07 Average Difference: + 0.34

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The location of each of the calibration points and the difference between the model and recorded flood heights are shown in Figure 5.4.

5.3.1.1 Structure head loss As there are no peak flood observations immediately upstream and downstream of the new and old Glenelg Highway bridges and the structure is quite complicated with the old bridge being just upstream of the new bridge, a HECRAS model has been developed to provide verification of the head loss across the structure during the calibration flood events. The HECRAS model was developed using cross sections from the LiDAR data and from the structure design drawings from VicRoads. The roughness parameters were set to match the 2D hydraulic model. The HECRAS version used in this assessment was version 4.1.0.

The HECRAS model was run as a steady state model with the flow rate set at the September 2010 peak flow. The head loss across the structure from upstream of the old bridge to downstream of the new Glenelg Highway bridge was 0.26 m. For the SOBEK model the upstream level was 201.86 mAHD and the downstream level was 201.64 mAHD, a difference of 0.22 m. The head loss across the structure in the SOBEK model matches the HECRAS head loss well and this verifies the losses set for the structures.

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Figure 5.4 Summary of the calibrated September 2010 flood event

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5.3.2 2011 Event

The January 2011 flood event had the most data recorded during the event and hence is the primary calibration event for the hydraulic model. There were 23 recorded data points captured within the hydraulic model extent however each of these points had a varying degree of accuracy. In addition to these recorded data points the peak flood height at the Hopkins River at Wickliffe gauge has been estimated using the gauge zero elevation and the peak recorded flood depth.

The peak flow for the event was estimated by Thiess Services to be 250 m3/s. Preliminary modelling using this peak flow rate indicated that the hydraulic model was predicting lower flood peaks than observed at both the gauge as well as all observed flood peak locations. Based on this preliminary analysis and discussion with the Glenelg Hopkins CMA the calibration explored the upper limit set by Thiess on the uncertainty of the peak flow of +/- 15%. The peak flow was increased by 15% to 287 m3/s and this peak flow rate was ultimately used in the model calibration. The rationale for adopting this higher peak flow rate is based on the discussion in Section 4.3.3 around the uncertainty of the predicted January 2011 peak flow rate.

From discussions with the Glenelg Hopkins CMA it was evident that the recorded flood information had a varying degree of accuracy in the capture of the peak flood height. The captured data has been categorised into the following quality sets: x High – data captured is likely to accurately have captured the peak flood level and the mark is free from influence by vehicles and rescue equipment. x Medium – some variability in the level may be experienced and there may be some influence by vehicles and rescue equipment. x Low – there is some uncertainty that the peak level has been captured in this case, the level recorded was not clear and there is some uncertainty as to the level recorded. x Extent Only – these levels were pegged at the approximate flood extent of the event. They are not appropriate for calibration of flood height as the vertical accuracy of the recorded information is highly uncertain. They are to be used as a guide of flood extent only. x Gauge – this is the estimated peak flow at the streamflow gauge based on a gauge zero level and the peak flood height recorded at the gauge.

The peak flood observations were captured post event, predominantly from flood marks and debris lines. This can introduce some uncertainty into the observation dataset, particularly where the debris line is not very clear. For some of the observations photographs were taken of the flood mark surveyed which allowed for additional assessment of the quality of the recorded flood height.

During the event and in the post event clean up an SES rescue boat was used throughout the township while floodwaters were still high. The rescue boat at Wickliffe is shown in Figure 5.5. The wake of the boat may influence some of the debris lines in and around the town. It was thought that this would not be a major influence but as it may impact debris lines it has been presented here. In a similar way, any vehicles that may have driven through the town during the period of inundation may cause waves to propagate through the township which may impact on the recorded levels.

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Figure 5.5 Rescue boat used during the Wickliffe floods

A summary of the observed peak flow locations and the model results are shown in Table 5.3 and in Figure 5.6.

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Table 5.3 Calibration results for the January 2011 flood event Description Peak Quality1 Flood Height Model Height Difference (Model Recorded? (mAHD) (mAHD) less Observed (m) WICK04 Y High 203.25 203.33 0.08 WICK07 Y High 202.47 202.53 0.06 WICK15 Y High 202.51 202.53 0.01 WICK02 Y Medium 203.37 203.22 -0.15 WICK05 Y Medium 203.37 203.26 -0.11 WICK08 Y Medium 202.57 202.43 -0.14 WICK10 Y Medium 202.28 202.12 -0.16 WICK12 Y Medium 202.33 202.13 -0.20 WICK13 Y Medium 202.61 202.44 -0.18 WICK03 Y Low 203.48 203.38 -0.11 WICK06 Y Low 202.89 202.69 -0.20 WICK09 Y Low 202.59 202.28 -0.30 WICK14 Y Low 202.57 202.42 -0.15 WICK16 Y Low 202.22 202.28 0.05 WICK01 Y Extent Only2 203.92 203.62 -0.30 WICK17 Y Extent Only2 203.37 203.58 0.21 WICK18 N Extent Only2 201.94 201.84 -0.10 WICK19 N Extent Only2 202.04 201.91 -0.14 WICK20 N Extent Only2 202.13 201.98 -0.15 WICK21 N Extent Only2 202.13 201.99 -0.14 WICK22 N Extent Only2 202.12 201.99 -0.13 WICK23 N Extent Only2 202.12 201.99 -0.13 WICK24 N Extent Only2 202.16 202.01 -0.15 GAUGE Y Gauge 203.51 203.55 0.04

Average Difference (High Quality & Gauge only): + 0.05 Average Difference (High, Gauge & Medium Quality): - 0.07 Average Difference (High, Medium, Gauge and Low Quality): - 0.10 Average Difference (All): - 0.10

1 Quality information was specified by the GHCMA following a review of the peak flood information 2 Extent only recorded flood peaks are estimates which captured the extent of the flood but have poor vertical accuracy. These recorded flood peaks have been assessed but Cardno have been advised to use the recorded peak flood depths with caution.

The hydraulic model produced a peak flood height at the gauge of 203.55 mAHD which was 0.044 m higher than the recorded flood peak. This was considered an acceptable calibration at the gauge.

From the observed data points there were three high quality observations. The average difference between the hydraulic model results and the observed peak levels was + 0.048 m. The model produced three high quality observations were slightly above the observed peak flood levels. All three levels were within 0.077 m of the observed levels which is a good calibration.

The medium and low quality observed data points varied between + 0.053 m and -0.303 m. The majority of the observer flood peaks were below the hydraulic model levels. The average of the differences between all of the observed and modelled data was - 0.096 m. The average was lowered due to the low and medium quality observations.

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The extent only observations had the differences recorded in Table 5.3, however these should be viewed with caution as most of these were not captured at the peak of the event and there was a high degree of uncertainty in the vertical accuracy of the levels. This is demonstrated by the modelled levels for WICK01 being 0.30 m lower than the observed levels and the modelled levels for WICK17 being 0.21 m higher than the observed levels even though the peak flood height observations are in similar locations on the floodplain. For the extent only observations the model matches the extent very well, which gives confidence that the model is reproducing the historic events accurately.

5.3.2.1 Structure Head Loss For the January 2011 event the HECRAS model was used to validate the head loss across the structure. The HECRAS model was developed as the structure (consisting of the old and new Glenelg Highway Bridges) was very complex and the head losses were unknown. During the January 2011 flood event the Glenelg Highway was overtopped and the old and new Glenelg Highway bridges were inundated and interacting with the flood waters. This increased the head loss across the structure at this location and HECRAS was used to validate the head loss observed from the SOBEK hydraulic model results.

The predicted head loss across the structure in HECRAS was 0.76 m between the gauge upstream and immediately downstream of the new Glenelg Highway Bridge. Within the SOBEK hydraulic model the upstream peak water level was 203.56 mAHD and downstream peak level was 202.79 mAHD. This is a head loss of 0.77 m. This matches the predicted head loss from HECRAS and validates the losses applied across the structures in this area.

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Figure 5.6 Summary of the calibrated January 2011 flood event

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5.3.3 Calibration Summary

The primary calibration event was the January 2011 flood event, with the September 2010 flood event providing some verification that the hydraulic model can replicate the observed flood levels.

The calibration of the January 2011 flood event was within appropriate levels with the peak at the Hopkins River at Wickliffe gauge being within 0.04 m of the recorded flood peak. High quality observed data matched the modelled peak flood levels well throughout the floodplain. The flood extent for this event was very well matched with all flood extent observations matched closely. The head loss across the main structure within the model was validated through a comparison of a HECRAS model of this structure which provides confidence in the losses used across the structure.

The September 2010 event was well matched at the gauge with modelled flood levels being 0.07 m higher than the recorded peak flood depth. The observed flood levels were not recorded at the peak of the event so a detailed calibration was not possible, however the flood extent produced by the model matches the observed flood locations well and the model produces flood depths that are all higher than the observed level (this is to be expected as the levels captured were below the peak of the event). The head loss across the structure was validated against the HECRAS model and the head loss predicted by both models matched well.

To put the hydraulic calibration in context, the differences between the LiDAR data and the field survey locations was between -0.22 to 0.27 m. The resulting LiDAR data had 95% of data (2 standard dev.) within +/- 0.16 m of the surveyed levels which is an acceptable range of uncertainty for this flood study. The hydraulic model was calibrated to an average difference of 0.04 m of the recorded flood peaks (Jan 2011) which is a good calibration, especially considering that the ground surface has been captured to levels of between +/- 0.16 m when compared to the field survey results.

Overall, the hydraulic model reproduced the two calibration events well and the SOBEK model is fit for use for the assessment of the design flood events.

5.4 Calibrated Model Parameters

5.4.1 Hydraulic Roughness

The roughness was the primary calibration method for the hydraulic model calibration. The roughness parameters are within the recommended ranges as specified in Open Channel Hydraulics (Chow, 1973). The calibrated roughness parameters are summarised in Table 5.4 and in Figure 5.7.

Table 5.4 Calibrated Roughness Parameters, Mannings ‘n’ Parameter Roughness Description Range Manning’s ‘n’ Sealed Roads 0.018 Asphalt or rough concrete 0.014 – 0.020 Dirt Roads 0.022 Earth – clean, after weathering 0.018 – 0.025 Main river channel 0.035 Natural stream on plain with stones and weeds 0.030 – 0.040 Cleared Farmland 0.045 Cultivated areas 0.030 – 0.050 Low Grassland and Trees 0.050 Light brush and trees 0.035 – 0.060 Dense Grassland and Trees 0.060 Medium to dense brush 0.045 – 0.110 Buildings and Infrastructure 0.500 High blockage rate for buildings -

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Figure 5.7 Calibrated roughness grid

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5.4.2 Boundary Conditions

The boundary conditions for the calibrated model include inflow hydrographs at the upstream boundary of the model on the Hopkins River and a steady state inflow boundary for the unnamed tributary to the north-west of the township. No other inflows were used in the hydraulic model.

The downstream boundary was controlled using a stage-discharge boundary. The stage discharge relationship was developed using a cross section at the downstream end of the hydraulic model and the Manning’s Equation in order to generate flow rates at the full range of depths at the boundary. The stage-discharge relationship is shown in Figure 5.8.

500

450

400

350

300 /s) 3 250

200 Flow Rate (m Rate Flow

150

100

0 195.5 196 196.5 197 197.5 198 198.5 199 199.5 200 Water level (mAHD)

Figure 5.8 Stage-Discharge relationship for the downstream boundary of the hydraulic model

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5.5 Design Event Results

Each of the design events have been assessed and presented in the following sections. The discussion is based on the associated peak depth plot presented for each scenario. Each peak depth plot has the peak water surface elevations shown in point form in the Australian Height Datum (AHD). Key events, such as roads overtopping and breakouts occurring, have been discussed for each event.

5.5.1 20% AEP Event

The 20% AEP design flood event had a peak design flow rate of 67 m3/s down the Hopkins River which was derived from an 18 hour duration flood event. The 20% AEP design flood results are shown in Figure 5.9.

From the depth map the flood peak is contained in the immediate floodplain, however there are some overbank flows. No roads are overtopped in the study area. Through the main bridge under the Glenelg Highway the peak flow rate was 45.3 m3/s with a peak velocity of 1.6 m/s.

5.5.2 10% AEP Event

The 10% AEP flood event had a design peak of 85 m3/s down the Hopkins River which was based on a 24 hour duration flood event. The 10% AEP design flood results are summarised in Figure 5.10.

The flood extent for the 10% AEP was largely unchanged from the 20% AEP scenario. This was primarily due to the well defined nature of the Hopkins River floodplain. The depths within the floodplain increased on average by 0.2 m over the 20% AEP event.

The peak flow through the Glenelg Highway Bridge was 54.6 m3/s with a peak velocity of 1.7 m/s through the structure. Water begins to encroach on the Glenelg Highway on the north west side of Wickliffe and overtops the road over a 10 m length but at very shallow depths of less than 0.05 m.

5.5.3 5% AEP Event

The 5% AEP design flood had a peak flow rate of 110 m3/s for the Hopkins River. The peak flood depths are shown in Figure 5.11.

As for the more frequent events the flood extent has not changed significantly for the 5% AEP flood event, however the flood depths increase by approximately 0.2 m across the floodplain. The peak flow rate through the Glenelg Highway Bridge increased to 68.4 m3/s with peak velocities approaching 2 m/s through the structure.

In this scenario the Glenelg Highway is overtopped to the north east of Wickliffe for a length of 200 m. The maximum depth over the road is 0.15 m. This is the only road in the study area that is overtopped during this event.

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5.5.4 2% AEP Event

The peak flow rate for the 2% AEP flood event was 152 m3/s for the Hopkins River. The peak depths are summarised in Figure 5.12.

The flood extent for the 2% AEP scenario shows a number of breakouts from the main floodplain. Notably the flood extent has increased upstream of the Glenelg Highway Bridge. The Glenelg Highway Bridge had a peak flow rate of 93.7 m3/s and the levels at the structure have begun to interact with the old bridge. This has led to flood depths upstream of this structure increasing by 0.5 m relative to the 5% AEP event and the flood extent increasing in this area.

A breakout begins to form on the eastern side of the Glenelg Highway upstream of the Glenelg Highway Bridge which leads to water pooling along the Glenelg Highway (Main Street of Wickliffe), Water is over the road through the township, however this is at very minor levels (< 0.05 m) and is over approximately 20 m of length. Floodwaters are interacting with properties through the township, however, no buildings are at threat of overfloor flooding during this scenario.

Downstream of the Glenelg Highway Bridge the peak flood levels increased by approximately 0.2 m over the 5% AEP flood event. This increase is lower than upstream of the stricture due to the restriction of the floodwaters by the Glenelg Highway Bridge and culverts (to the south of the Glenelg Highway Bridge).

The Glenelg Highway to the north east of Wickliffe is overtopped for approximately 300 m with a maximum depth of 0.3 m.

5.5.5 1% AEP Event

The peak flow rate for the 1% AEP flood event was set at 196 m3/s. The peak depths are summarised in Figure 5.13. For this event both the 72 hour duration and 18 hour duration events were modelled to determine if the shorter duration (which had a lower peak flow) caused additional flooding within the Wickliffe catchment. The model results indicated that the 72 hour flood event produced the greatest depths throughout the floodplain.

The peak flood extent has increased relative to the 2% AEP event and the depths throughout the flood plain have increased by approximately 0.3 m. The breakout through the south eastern end of Wickliffe has substantially increased and floodwaters are now impacting numerous properties in this area. The majority of the Glenelg Highway (Main Street) has flood water along the road and over the road. The peak depths over the road through the township are < 0.15 m so the road may still be trafficable in this area. The peak flow rate through the Glenelg Highway Bridge was 115 m3/s, with a peak velocity of 3 m/s.

The Glenelg Highway to the north west of the township is overtopped for over 300 m to a maximum depth of approximately 0.5 m. The road would require closure as this depth is not trafficable.

Properties through Wickliffe are impacted during this flood event. Three (3) buildings are expected to experience overfloor flooding.

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5.5.6 0.5% AEP Event

The 0.5% AEP flood event is a similar design event to the January 2011 flood event. The peak design flow rate was 249 m3/s and was based on a 72 hour duration event. The peak flow estimated for the January 2011 event was 250 m3/s, however during the calibration of this event the peak estimate was increased to 287 m3/s (the upper limit of the peak flow estimate by Thiess). This event is the closest design run to the event experienced in January 2011.

The peak flood extent has increased compared with the 1% AEP flood event. The peak depths are summarised in Figure 5.14. The depths throughout the floodplain have increased by approximately 0.3 m as compared to the 1% AEP event.

The township of Wickliffe is severely impacted during this event. The Glenelg Highway is overtopped for approximately 1.3 km. It is overtopped from south of the Glenelg Highway Bridge to north of the township. The road is not trafficable. The new Glenelg Highway Bridge is almost overtopped but should still be above the floodwaters. The main street of Wickliffe is overtopped to a depth of approximately 0.3 – 0.4 m.

All properties along the main road would be impacted during this event. Six (6) buildings are expected to have overfloor flooding and three (3) additional buildings are within centimetres of experiencing overfloor flooding. Properties in the area of the breakout (south east of Wickliffe) are expected to have substantial overfloor flooding.

5.5.7 0.2% AEP Event

The 0.2% AEP flood event had a peak flow rate of 338 m3/s. The peak flood depths are shown in Figure 5.15.

The flood extent has increased throughout the model area. The depths through the model increased by 0.2- 0.3 m as compared to the 0.5% AEP flood event. The Glenelg Highway is overtopped for over 1.3 km and has depths over the road of over a metre in some locations. The Glenelg Highway Bridge is now overtopped to depths of < 0.1 m.

Eleven (11) buildings within Wickliffe would have overfloor flooding during an event of this magnitude. Most properties would have substantial overfloor flooding.

5.5.8 PMF Event

The predicted Probable Maximum Flood (PMF) was modelled using a peak inflow of 4,600 m3/s for the Hopkins River at Wickliffe. The resulting peak flood depths are summarised in Figure 5.16. The main purpose of this assessment is to demonstrate the likely maximum extent possible for the study area. All sixteen (16) properties within the township of Wickliffe would be inundated.

The results show that the extent is confined to the floodplain by relatively steep slopes. The flood shape and depths show that the flood extent is unlikely to ever be outside this range as the floodplain is well defined by steep embankments. Depths are well over 5 m in the main floodplain and Wickliffe would be inundated by meters of water.

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Figure 5.9 Maximum flood depths for the 20% AEP event

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Figure 5.10 Maximum flood depths for the 10% AEP event

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Figure 5.11 Maximum flood depths for the 5% AEP event

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Figure 5.12 Maximum flood depths for the 2% AEP event

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Figure 5.13 Maximum flood depths for the 1% AEP event

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Figure 5.14 Maximum flood depths for the 0.5% AEP event

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Figure 5.15 Maximum flood depths for the 0.2% AEP event

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Figure 5.16 Maximum flood depths for the Probable Maximum Flood (PMF) design event

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5.6 Climate Change Results

The climate change was assessed within the hydraulic model for the 10% and 1% AEP flood events. The climate change scenarios were assessed for the 32% increase in rainfall intensity. The details regarding the hydrology of the climate change are summarised in Section 4.9. The two scenarios modelled as part of the climate change sensitivity are summarised in Table 5.5.

Table 5.5 Climate change scenarios run through the hydraulic model 32% increase rainfall intensity at Hopkins River at Hopkins River at Wickliffe Wickliffe AEP (%) Design Flow CC Design Flow Increase (% from Peak Duration Peak Duration Rate (m3/s) Rate (m3/s) current) 10% 85.3 24h 231.7 18h 272% 1% 196.0 72h 537.4 72h 274%

The 10% AEP climate change peak flow is predicted to increase to 231 m3/s which is higher than the current 1% AEP peak flow rate. The 1% AEP climate change event has increased from approximately 200 m3/s up to 537 m3/s which is higher than the current 0.2% AEP flood event.

The 10% AEP and 1% AEP climate change flood depths are summarised in Figure 5.17 and Figure 5.18 respectively.

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Figure 5.17 Climate change – 10% AEP with 32% increase in rainfall intensity

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Figure 5.18 Climate change – 1% AEP with 32% increase in rainfall intensity

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5.7 Hydraulic Model Sensitivity Assessment

5.7.1 Roughness Assessment

The roughness parameters used in the hydraulic model were calibrated against the known flood events. The details of the roughness layer is summarised in Section 5.4.1. In order to test the model sensitivity to the calibrated roughness, the roughness factors were modified by +/- 20%. The Manning’s ‘n’ parameters used for the sensitivity are summarised in Table 5.6.

Table 5.6 Sensitivity analysis on the roughness parameters Parameter Roughness Manning’s ‘n’ Calibrated - 20% + 20% Sealed Roads 0.018 0.014 0.022 Dirt Roads 0.022 0.018 0.026 Main river channel 0.035 0.028 0.042 Cleared Farmland 0.045 0.036 0.054 Low Grassland and Trees 0.050 0.040 0.060 Dense Grassland and Trees 0.060 0.048 0.072 Buildings and Infrastructure 0.500 0.400 0.600

The primary aim of the sensitivity assessment was to determine the sensitivity of the peak depths to the roughness within the hydraulic model. The 1% AEP design event was used to test the sensitivity of the peak flood depths to a +/- 20% change in model roughness. The results of the assessment are shown in the form of difference plots for the peak depths recorded. The difference plots show the change in the peak flood height for each of the sensitivity model runs.

Figure 5.19 and Figure 5.20 show the -20% and +20% roughness difference plots respectively. Each plot shows the differences between the sensitivity run and the existing 1% AEP flood depths. Spot differences are also shown at point locations in the figures. The differences shown are the sensitivity model result less the existing flood depth (i.e. if this is negative then the sensitivity flood depth was lower than the existing flood depth).

Decreasing the roughness by 20% reduced the depths on the floodplain by between 0.1 and 0.15 m. The changes in flood depth were constant across the entire floodplain. Increasing the roughness by 20% increased the depths on the floodplain to between 0.09 and 0.14 m. Again the changes in flood depth were relatively uniform across the entire catchment.

It is evident from the sensitivity analysis that the model is not significantly sensitive to the roughness parameters with a +/- 20% change in roughness resulting in a +/- 0.15 m change in peak flood depths.

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Figure 5.19 Difference plot for the low roughness scenario (20% lower roughness)

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Figure 5.20 Difference plot for the high roughness scenario (20% higher roughness)

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5.7.2 Low and High Flow Sensitivity

The final sensitivity assessment was to examine the hydraulic model’s sensitivity to the model inflows. In order to examine the relationship between the inflows and the resulting flood depths, the 1% AEP design event was used and the inflows were modified by +/- 20% to examine the resulting change in peak flood heights.

The existing peak flow rate for the 1% AEP flood event was set at 196 m3/s. For the sensitivity assessment the inflow hydrograph was factored by +/- 20% which resulted in peak inflows of 157 and 235 m3/s. The inflow hydrographs are summarised in Figure 5.21.

250 1% AEP - 72 hour duration Design flow -20% Design Flow +20% 200

150 /s) 3

100 Flowrate (m

0 0 20 40 60 80 100 120 140 Time (hours)

Figure 5.21 Flow sensitivity inflow hydrographs

Figure 5.22 and Figure 5.23 show the -20% and +20% inflow difference plots respectively. Spot differences are shown at point locations in the figures. The differences shown are the sensitivity model result less the existing flood depth (i.e. if this is negative then the sensitivity flood depth was lower than the existing flood depth).

Reducing the 1% AEP design peak flow rate by 20% results in a decrease in the peak flood depths of between 0.14 and 0.35 m. The main reduction in flood depths occurs upstream of the Glenelg Highway Bridge where the peak flood level reduction was 0.35 m. The reason for the larger decrease in flood depths upstream of the structure is that during the 1% AEP flood event the structure is flowing at capacity and flood waters are backing up from the structure, by reducing the inflows by 20% there is less backing up of the flows from this structure. The majority of the floodplain has reduction in peak depth of between 0.14 and 0.22 m. Increasing the inflows by 20% resulted in increases in flood depths of 0.13 to 0.24 m across the floodplain. Again, the changes in flood depth were higher upstream of the Glenelg Highway Bridge as this is a restriction within the floodplain.

Overall changing the inflows by +/- 20% produced a change in flood depths between -0.35 m to +0.24 m. This indicates that the model is more sensitive to the inflow rates than to the roughness parameters.

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Figure 5.22 Flow sensitivity analysis – 1% AEP with 20% reduction in flows

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Figure 5.23 Flow sensitivity analysis – 1% AEP with 20% reduction in flows

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6 DATASETS AND MAPPING The calibrated SOBEK model for Wickliffe was used to analyse the extent, location and depths for the 20%, 10%, 5%, 2%, 1%, 0.5% AEP events and the Probable Maximum Flood. Key outputs from the project are developed as a result of the detailed hydraulic modelling. This section outlines the datasets and mapping that are to be supplied as part of this process. Key outputs include: x Peak flood depths for all flood events (Figure 5.9 to Figure 5.16) x Flood extents for all flood events x Flood planning controls (flood overlays) x 1% AEP event o Hazard class maps o Extent with water surface elevation contours (200mm contour intervals) o Velocity map x Properties impacted during each flood event will be shown on each flood map.

All datasets and mapping have been supplied along with the final report as the final deliverables to the project.

6.1 Design flood extents

The final flood extents for the design flood events for Wickliffe have been derived from the hydraulic model with some adjustments applied. The adjustments to the final model grid results included: x A filter was applied to the final flood depth for each recurrence interval and depths less than 2 cm were removed. Floodwaters below this depth are nuisance waters and are not expected to cause any damage within the floodplain. x Wet and dry islands were removed where they were less than 6 gridcells (96 m2). This ensures consistency and continuity in the mapped flood extent for planning purposed. x The gridded model output was combined and smoothed using AutoCAD to generate a more realistic flood shape for final viewing. This process removes the square edges of the grid cells from the proposed flood extent.

The modifications to the flood extent are designed to produce a clear consistent flood shape for each of the flood events. The final flood extents are shown in Figure 6.1.

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Figure 6.1 Flood extents for the 20%, 10%, 5%, 2%, 1%, 0.5% AEP and the PMF

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6.2 Flood Planning Controls

The current planning framework for the floodplain is encapsulated in the Ararat Planning Scheme. The Planning Scheme, prepared in accordance with Victorian State Planning Policy Framework (VPP), documents all planning controls in the study area. The scheme consists of a written document as well as maps, plans and related documents. It contains (as outlined in the accompanying User Guide): x The objectives of planning in Victoria. x Purposes of the planning scheme. x A User Guide. x The State Planning Policy Framework. x The Local Planning Policy Framework. x Zone and overlay requirements. x Particular provisions. x General provisions. x Definitions. x Incorporated documents.

The State Planning Policy Framework (SPPF) covers strategic issues of State importance. It lists policies under six headings: settlement, environment, housing, economic development, infrastructure, and particular uses and development. Every planning scheme in Victoria contains this policy framework, which is identical in all schemes.

The Local Planning Policy Framework (LPPF) contains a municipal strategic statement and local planning policies. The framework identifies long term directions for land use and development in the Wickliffe region; presents a vision for its community and other stakeholders; and provides the rationale for the zone and overlay requirements and particular provisions in the scheme.

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6.3 Flood Related Planning Zones and Overlays

The planning scheme allows for a number of flood related overlays to identify land liable to flooding and flood characteristics. In general, the nature of the flood risk and available flood information will determine to what extent the provisions are applied in the planning scheme. The flood zone and overlay provisions allow for control of the land use and development through the use of a planning process to ensure that development is in-line with the level of flood risk.

There are four flood zones and overlays available for use: x Urban Floodway Zone (UFZ) x Floodway Overlay (FO) x Land Subject to Inundation Overlay (LSIO) x Special Building Overlay (SBO).

Each of these zones and overlays are defined more clearly in the following sections. Currently within the Ararat Planning Scheme there are no defined flood overlays. Cardno has been advised by the Ararat Rural Council that they wish to explore the development of possible overlays for Wickliffe as part of this Flood Investigation.

6.3.1 Urban Floodway Zone (UFZ)

The Urban Floodway land use zoning is intended to protect land in urban areas that has a primary function of floodwater conveyance. It applies to urban areas where the potential flood risk is high due to the presence of existing development or to pressures from new or more intensive development. The UFZ restricts, to a very limited number, the use of land to those that are consistent with the primary function of flood conveyance.

In Urban Floodway Zone areas, the following uses are allowed without a permit: x Apiculture - Must meet the requirements of the Apiary Code of Practice, May 1997. x Extensive animal husbandry x Informal outdoor recreation x Mineral exploration x Mining x Natural systems x Search for stone - Must not be costeaning or bulk sampling. x Telecommunications facility.

The following uses are allowed with a planning permit: x Agriculture (other than Apiculture and Extensive animal husbandry) x Leisure and recreation (other than Informal outdoor recreation, Indoor recreation facility, and Motor racing track) x Mineral, stone or soil extraction (other than Mineral exploration, Mining, and Search for stone) x Road x Utility installation (other than Telecommunications facility).

The following land uses are prohibited in an Urban Floodway Zone: x Indoor recreation facility x Motor racing track x Any other use not listed above.

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All planning permits and subdivisional applications are also subject to the same controls as required for an application on land covered by the Floodway Overlay described below.

6.3.2 Floodway Overlay (FO)

The purpose of the Floodway Overlay, as described in the planning scheme, is as follows: x To implement the State Planning Policy Framework and the Local Planning Policy Framework, including the Municipal Strategic Statement and local planning policies. x To identify waterways, major floodpaths, drainage depressions and high hazard areas, which have the greatest risk and frequency of being affected by flooding. x To ensure that any development maintains the free passage and temporary storage of floodwater, minimises flood damage and is compatible with flood hazard, local drainage conditions and the minimisation of soil erosion, sedimentation and silting. x To reflect any declarations under Division 4 of Part 10 of the Water Act, 1989 if a declaration has been made. x To protect water quality and waterways as natural resources in accordance with the provisions of relevant State Environment Protection Policies, and particularly in accordance with Clauses 33 and 35 of the State Environment Protection Policy (Waters of Victoria).

A planning permit is required to construct a building or to construct or carry out works, including fences and roadworks on land covered by the floodway overlay, with some limited exemptions for public infrastructure works.

Subdivision of land covered by a FO/RFO can only be accomplished with a planning permit and under the following conditions: x The subdivision does not create any new lots, which are entirely within this overlay. This does not apply if the subdivision creates a lot, which by agreement between the owner and the relevant floodplain management authority, is to be transferred to an authority for a public purpose. x The subdivision is the re-subdivision of existing lots and the number of lots is not increased, unless a local floodplain development plan incorporated into this scheme specifically provides otherwise.

All planning applications where a local floodplain development plan has not been incorporated into the scheme require a flood risk study to be undertaken with regard to the following points: x The State Planning Policy Framework and the Local Planning Policy Framework. x The existing use and development of the land. x Whether the proposed use or development could be located on flood-free land or land with a lesser flood hazard outside this overlay. x The susceptibility of the development to flooding and flood damage. x The potential flood risk to life, health and safety associated with the development. x Flood risk factors to consider include: The frequency, duration, extent, depth and velocity of flooding of the site and accessway The flood warning time available The danger to the occupants of the development, other floodplain residents and emergency personnel if the site or accessway is flooded. The effect of the development on redirecting or obstructing floodwater, stormwater or drainage water and the effect of the development on reducing flood storage and increasing flood levels and flow velocities. The effects of the development on environmental values such as natural habitat, stream stability, erosion, water quality and sites of scientific significance.

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Possible methods for development of the FO are outlined in the “Advisory Notes for Delineating Floodways” (NRE, 1998). These methods include: x Flood frequency x Flood hazard x Flood depth

For the flood frequency the advisory notes (Appendix A1) suggest that areas which have a high consequence of flooding, has flood depths that are moderate or high and flood frequently should generally be regarded as floodway. For the Wickliffe Flood Investigation the frequency method used the 10% AEP flood extent. This is shown in Figure 6.3.

The flood hazard is defined by combining the flood depth and flow speed to form a hazard category for a given design event. The advisory notes suggest using Figure 6.2 for delineating the floodway based on flood hazard.

Figure 6.2 Floodway overlay flood hazard criteria (NRE, 1998)

An alternate definition of flood hazard (or safety risk) is provided by Melbourne Water based on both the velocity- depth product and the total flood depth. Melbourne Water defines 5 classes of safety risk as shown in Table 6.1. The Melbourne Water hazard approach was considered for this investigation. The flood overlay selection criteria was based on a hazard greater than 2. The Flood Overlay is shown in Figure 6.4.

Table 6.1 Melbourne Water Safety Risk Definition Safety Risk Category Definition V*D or Depth High 5 > 0.84 m2/s > 0.84 m Moderate to High 4 0.6 - 0.84 m2/s 0.6 - 0.84 m Moderate 3 0.4 - 0.6 m2/s 0.4 - 0.6 m Low to Moderate 2 0.2 - 0.4 m2/s 0.2 - 0.4 m Low 1 < 0.2 m2/s < 0.2 m

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The final method for defining the flood overlay was the flood depth method. The flood overlay was set using this method where the flood depths were greater than 0.5 m within the 1% AEP flood event. The Flood Overlay is shown in Figure 6.5

For this investigation all three methods were developed and assessed in order to generate the appropriate Flood Overlay. From the assessment the flood frequency method was determined to be the most appropriate as the flood hazard and depth methods generated inconsistent and incomplete Flood Overlays. The 10% AEP provided a consistent flood shape that was well defined within the main floodway. No existing properties were located within the proposed Flood Overlay. The developed flood overlay is shown in Figure 6.3.

During the course of the study it was identified that the existing old bridge decking (located immediately upstream of the current Highway Bridge) was to be removed by VicRoads. As a result the FO and LSIO will be required to be updated to the 10% and 1% AEP flood extents respectively with the original bridge decking removed. At the time of the study this work was being planned, and hence this does not constitute part of the current recommended LSIO and FO.

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Figure 6.3 FO using the 10% AEP flood extent and LSIO using the 1% AEP flood extent

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Figure 6.4 FO using the 1% AEP (Hazard Class > 2) flood extent and LSIO using the 1% AEP flood extent

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Figure 6.5 FO using the 1% AEP (Depth 50 cm) flood extent and LSIO using the 1% AEP flood extent

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6.3.3 Land Subject to Inundation Overlay (LSIO)

The LSIO aims to include land which is likely to be inundated by overland flow during the 1% AEP flood. The LSIO is covered under Clause 44 of the VPPF for Wickliffe. Currently there are no flood overlays within the Ararat Planning Scheme.

The purpose of the Land Subject to Inundation Overlay as described in the planning scheme is as follows: x To implement the State Planning Policy Framework and the Local Planning Policy Framework, including the Municipal Strategic Statement and local planning policies. x To identify land in a flood storage or flood fringe area affected by the 1% AEP flood or any other area determined by the floodplain management authority. x To ensure that development maintains the free passage and temporary storage of floodwaters, minimises flood damage, is compatible with the flood hazard and local drainage conditions and will not cause any significant rise in flood level or flow velocity. x To reflect any declaration under Division 4 of Part 10 of the Water Act, 1989 where a declaration has been made. x To protect water quality in accordance with the provisions of relevant State Environment Protection Policies, particularly in accordance with Clauses 33 and 35 of the State Environment Protection Policy (Waters of Victoria). x To ensure that development maintains or improves river and wetland health, waterway protection and flood plain health.

A planning permit is required to construct a building or to construct or carry out works, including fences and roadworks on land covered by the LSIO, with some exemptions for public infrastructure works. Any subdivision of land requires a planning permit and the number of lots can be increased.

Applications for planning permits in areas covered by the LSIO have the following decision guidelines with respect to flooding: x The State Planning Policy Framework and the Local Planning Policy Framework. x Any local floodplain development plan. x Any comments from the relevant floodplain management authority x The existing use and development of the land. x Whether the proposed use or development could be located on flood-free land or land with a lesser flood hazard outside this overlay. x The susceptibility of the development to flooding and flood damage. x The potential flood risk to life, health and safety associated with the development. x Flood risk factors to consider include: The frequency, duration, extent, depth and velocity of flooding of the site and accessway The flood warning time available The danger to the occupants of the development, other floodplain residents and emergency personnel if the site or accessway is flooded. The effect of the development on redirecting or obstructing floodwater, stormwater or drainage water and the effect of the development on reducing flood storage and increasing flood levels and flow velocities. The effects of the development on environmental values such as natural habitat, stream stability, erosion, water quality and sites of scientific significance.

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As the LSIO defines flood areas which carry lower risk due to the frequency of inundation and impacts of flooding it is typically defined as the extent of less significant events. The LSIO covers areas that are not included within the FO or UFZ but are still exposed to flood risk. For the Wickliffe region it was considered appropriate to use the 1% AEP event as the extent for the LSIO. This extent is shown in Figure 6.6.

During the course of the investigation it was noted that VicRoads were planning to undertake works to remove the old bridge decking upstream of the current Glenelg Highway Bridge. The old bridge decking impedes the flows through the current structure and impacts the flood levels reached in the 1% AEP design event. This is directly linked to the definition of the LSIO. Once VicRoads have removed the old bridge deck the revised LSIO (which has been modelled as a mitigation option in this investigation) should be implemented in the place of the current layer shown in Figure 6.6. The revised LSIO is shown in Figure 6.7. This revised LSIO should only be used after the works have been carried out by VicRoads. Advice to Cardno (in October 2012) was that this old bridge deck was to be removed before July 2013. Further investigation of the impact of removing the old bridge deck is explored in Section 7 (Mitigation).

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Figure 6.6 Land Subject to Inundation Overlay using the 1% AEP flood extent

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Figure 6.7 LSIO using the 1% AEP flood extent with the old bridge deck removed (planned to be completed before July 2013 by VicRoads)

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6.3.4 Special Building Overlay (SBO)

The SBO applies to areas that are subject to stormwater flooding in urban areas. That is to say areas which are inundated due to the inability of the stormwater infrastructure to convey the flood flows. This overlay is considered as many stormwater systems were implemented prior to current design standards and there has been substantial development since the infrastructure was completed.

Stormwater systems and modelling was not included in this project and as such Cardno does not recommend any areas to be covered under a Special Building Overlay.

6.3.5 Recommended Planning Controls As the Wickliffe study area is already well established, Cardno do not believe that there is a need to implement an Urban Floodway Zone in the catchment. Similarly, a SBO is unlikely to be required as the predominant flooding is from main channel flows rather than from stormwater flooding. Stormwater flooding was not specifically assessed as part of this project.

The recommended flood controls to be put in place are a FO and LSIO. The method of deriving the FO included using the 10% AEP extent, the hazard class exceeding 2 for the 1% AEP event and where the depths were greater than 0.5 m during the 1% AEP event. The three possible extents for the FO varied with each method protecting different areas. The main difference was that the FO included parts of the Wickliffe township using the hazard class and depth based methods. This is not desirable as the FO is a strict overlay that tends to prohibit development. Cardno recommend the implementation of the 10% AEP extent as the FO as this includes the high risk areas and is limited to the main floodplain.

The results of the three methodologies were provided to the Glenelg Hopkins CMA and Council to determine a final Floodway Overlay shape. The LSIO would include all areas inside the 1% AEP flood extent that are not covered by the final FO shape. It is reiterated here that the proposed removal of the deck of the structure upstream of the Glenelg Highway Bridge can be taken into account once this work has been carried out.

6.4 Planning Amendment Documentation

As part of this flood investigation Cardno have not developed the planning amendment documentation at the request of the Glenelg Hopkins CMA and the Ararat Rural City Council. The planning documentation is likely to be developed by the Ararat Rural City Council following a detailed assessment of the methods of implementing planning controls.

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7 ECONOMIC DAMAGES The economic impact of flooding can be defined by what is commonly referred to as ‘flood damages’. These flood damages can be defined as being direct, indirect or intangible as defined in Figure 7.1.

Figure 7.1 Types of flood damage (Floodplain Development Manual (NSW Gov, 2005))

The direct damage costs are just one part of the flood damage overall cost. The flood damages are broken down into two distinct groups, tangible and intangible damages. The damage assessment in this report is restricted to the tangible damages and makes no estimate of the costs associated with the ‘intangible’ costs, such as social distress and loss of memorabilia.

The ‘tangible’ damages are further divided into direct and indirect damages. The indirect damages are damages caused by the disruptions of the flooding (such as clean up costs and accommodation costs), whereas the direct damages are caused by contact with the flood waters directly (such as damage to carpets and household contents).

For Wickliffe it has been assumed that the residents will have little to no warning time and hence no allowance has been made for the residents protecting or removing their valuables. This assumption has been made as it gives a more conservative estimate of flood damages as the maximum ‘potential’ damage is assessed. At present there is no working warning system for the residents of Wickliffe and limited warning time has been a problem in past events.

Flood damages can be assessed by a number of methods including the use of computer programs such as FLDAMAGE, ANUFLOOD or via more generic methods such using spreadsheets. For the purposes of this project, generic spreadsheets have been used based on experience by Cardno in this area. The use of both the Floodplain Management Manual (NSW Gov, 2005) and The Rapid Appraisal Method for Floodplain Management (NRE, 2000) were utilised in this flood damage assessment.

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7.1 Damage Analysis

A flood damage assessment has been undertaken for the existing catchment and floodplain as part of the current study. The assessment is based on damage curves that relate to the depth of flooding on a property to the likely damage to a property.

Ideally, the damage curves would be calibrated to the specific catchment for which the study was undertaken, however, damage data in most catchments is not available and as a result damage curves from other catchments are utilised. The Department of Environment, Climate Change and Water NSW (DECCW) has carried out research and prepared a methodology to develop damage curves based on state-wide historical data. This methodology is only for residential properties and does not cover industrial or commercial properties.

The DECCW methodology is only a recommendation and there are currently no strict guidelines regarding the use of damage curves in Victoria. The Rapid Appraisal Method (RAM) suggests specific damage values for residential, commercial and industrial buildings, however, these values are not specific to Victoria and the flood damage curves developed by DECCW are based on a more robust methodology.

The following sections provide an overview of the methodology applied for the determination of damages within the floodplain at Wickliffe.

7.1.1 Residential Damage Curves

The Floodplain Management Guideline No. 4 Residential Flood Damage Calculation prepared by DIPNR (now DECCW) (DIPNR, 2004) has been used in this residential damage assessment. These guidelines include a template spreadsheet program that determines damage curves for three types of residential buildings;

x Single storey, slab on ground, x Two storey, slab on ground, and x Single storey, high-set.

The floor level survey data collected by Cardno during this study did not specify the residential property construction, however from site visits and street view (Google) it has been identified that all residential properties in Wickliffe are slab on ground. This is the most conservative estimate of damages for the residential properties.

Damages are generally incurred on a property prior to any over floor flooding. There are two possibilities:

x The flooding overtops the representative ground level but does not necessarily reach the base of the house. When this representative ground level is exceeded by a depth of 10 cm (see Table 7.4). x The flooding overtops the garden and also reaches the base of the house. The DECCW curves allow for a damage of $10,090 (May 2012 dollars) to be incurred when the water level reaches the base of the house (the base of the house is determined by the floor level less 0.3 m for slab on ground houses). This accounts for the garden damage as specified in the point above, but also includes some damage to cars and structures.

Residential damages associated with the building was only applied when the flooding reached 0.3 m below the floor level of the house using the DECCW damage curves (adjusted to current dollar values). This equates to $10,090 (May 2012 dollars) for flooding depths between 0.3 m below the floor height, when the flood water overtop the floor level the DECCW damage curves are used to determine the economic damage.

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The residential damage curve is shown in Figure 7.2.

Figure 7.2 Damage curves applied to the Wickliffe flood investigation

7.1.1.1 Average Weekly Earnings

The DECCW curves are derived for late 2001 and have been adjusted to represent May 2012 dollars. General recommendations by DECCW are to adjust values in residential damage curves by the increase in Average Weekly Earnings (AWE), rather than by the inflation rate as measured by the Consumer Price Index (CPI). DECCW proposes that AWE is a better representation of societal wealth, and hence an indirect measure of the building and contents value of the home. The most recent data for AWE from the Australian Bureau of Statistics (ABS) was in May 2012. Therefore all ordinates in the residential flood damage curves were updated to the May 2012 dollars. In additional, all damage curves include GST as per the DECCW recommendations.

While not specified, it was assumed that these curves were derived in November 2001, which therefore assumes the use of the November 2001 AWE (issued quarterly) would be appropriate. November 2001 and May 2012 AWE statistics were obtained from the ABS website (www.abs.gov.au). The AWE figures and percentage adjustment factor is summarised in Table 7.1.

Table 7.1 Residential damage curve adjustment factor Month Year AWE November 2001 $ 898.50 May 2012 $ 1,352.7 Change 50.6 %

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Consequently, all ordinates on the damage curves were increased by 50.6 %. It has been assumed that May 2012 values are representative of current dollars.

7.1.1.2 Other Parameters There are a number of input parameters required for the DECCW curves, such as the area of the floor of houses in the floodplain and level of flood awareness. The damage assessment adopted values within the recommended range specified by the DECCW guidelines. The average house size for Wickliffe was estimated based on the delineated buildings within the 0.2% AEP flood extent. The average was approximately 200 m2. This area reflects the ground floor only.

Conservatively, the Effective Warning Time has been assumed to be zero as Wickliffe has no currently working flow gauge. A long Effective Warning Time allows residents to prepare for flooding by moving valuable household contents (e.g. the placement of valuables on top of tables and benches).

The Wickliffe catchment, while rural, has access to Hamilton, Ararat, Ballarat and Melbourne via multiple access routes and as a result it is assumed that there are no post-flood inflation costs. These inflation costs are generally experienced in regional areas where re-construction resources are limited and large floods can cause a strain on these resources.

7.1.2 Commercial Damage Curves

Within the township of Wickliffe there are no commercial properties and hence no damage curve was required. There is a local pub but this is infrequently opened and as such has been treated using the residential damage curve as the business is not run on a commercial scale.

7.1.3 Industrial Damage Curves

Within the township of Wickliffe there are no industrial properties and hence no damage curve was required. There is a CFA shed within the township, the damages to this structure have been estimated based on the residential curves and adjusted manually.

7.1.4 Road damages

Road damage was assessed based on the Rapid Appraisal Method (RAM) which assigns a damage value for major roads, minor roads and unsealed roads. The RAM was developed in May 2000 and the damages are quoted in May 2000 dollars. To convert these to June 2012 dollars, the CPI was used to adjust for inflation. The adjustment factor is shown in Table 7.2.

Table 7.2 Roads damage adjustment factor Month Year CPI May 2000 126.2 June 2012 177.7 Change 40.8 %

The RAM uses a single estimate cost per km for roads which are inundated and includes:

x Initial repairs to roads x Subsequent additional maintenance to roads

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x Initial repairs to bridges (based on 1/3 of road damages) x Subsequent additional maintenance to bridges.

The RAM estimates of the costs per km of inundated road are shown in Table 7.3. These unit damages were adjusted using the CPI adjustment factor. The RAM also states that the damages to roads and bridges generally outweighs the costs associated with other infrastructure such as water, electricity, gas and sewerage services and is a good approximation for the overall damage to the regional infrastructure.

Table 7.3 Unit damages for roads and bridges (dollars per km inundated) Subsequent Total cost applied Total cost applied Initial bridge repair Initial road accelerated per km to per km to and increased repair deterioration of inundated roads inundated roads maintenance roads (May 2000 $) (Mar 2012 $) Major sealed $ 32,000 $ 16,000 $ 11,000 $ 59,000 $83,072 roads Minor sealed $ 10,000 $ 5,000 $ 3,500 $ 18,500 $26,048 roads Unsealed roads $ 4,500 $ 2,250 $ 1,600 $ 8,350 $11,757

7.1.5 Property Damages Property damage has been applied to account for damage that is expected to occur to a property due to flood waters impacting the site, during the event and post-event. This damage includes damages such as garden damage, fence damage, damage due to extended inundation etc. This damage is only applied to properties if the building on that property is not impacted. This is because this damage is included in the derived damage curves and when the damage curves are activated the property damage is included in the building damage.

Property damage was applied to any delineated property that experienced flooding to a depth greater than 10 cm deep and covering over 1% of the property area but did not have a building that was impacted. These factors have been applied as flood depths less than 10 cm and for an area of less than 1% will not generally cause significant damage to a property.

In order to provide a more robust assessment of the likely property damage the land use types were used to determine the property zone for the impacted properties. This information was obtained from the Department of Sustainability and Environment (DSE) land use section of land.vic.gov.au.

The assigned economic damages are summarised in Table 7.4 for each of the land use types.

Table 7.4 Assumed property damages (land use supplied from land.vic.gov.au) Assumed Damage (if property has inundation >1% of area and Land Use Zone Description at least 10cm of depth) FZ Farming $500 TZ Township Zone $800 PPRZ Public park and Recreation $500

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7.2 Annual Average Damage

Annual Average Damage (AAD) is calculated on a probability approach, using the flood damages calculated for each design event. Flood damages (for a design event) are calculated using the ‘damage curves’ described in the sections above. These damage curves approximate the damage occurring on a property for varying depths of flooding. The total damages in the summation of the damage to all houses and properties within the flood extent for that design event.

The AAD attempts to quantify flood damage that a floodplain would receive on average during a single year. It does this by using a probability approach. A probability curve is drawn, based on the flood damages calculated for each design event. This is shown in Figure 7.2. The 1% AEP design event has a 1% chance of occurring in any given year, and as such the 1% AEP damage is plotted at this point on the AAD curve. AAD is then calculated by determining the area under the curve.

Figure 7.3 Flood damages used to estimate the Average Annual Damages

Further information on the calculation of the AAD can be found in the Floodplain Development Manual (NSW Government, 2005).

7.3 Results

The results of the flood damage assessment are shown in Table 7.5. Based on the analysis as described in the above section the annual average damages (AAD) for the floodplain under existing conditions is approximately $ 14,405 per annum.

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Table 7.5 Summary of Economic Flood Damages Recurrence Interval 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP 0.5% AEP 0.2% AEP Property Damage Total property damages $ 21,900 $ 23,400 $ 24,200 $ 51,280 $ 87,351 $ 118,922 $ 83,261 Inundated properties (> 10cm depth, > 1% area) 42 45 46 57 71 79 87

Building Damage Residential 0 0 0 0 2 5 10 CFA Shed 0 0 0 0 1 1 1 Total buildings with overfloor flooding 0 0 0 0 3 6 11

Residential $ - $ - $ - $ - $ 60,496 $ 202,074 $ 471,003 CFA Shed $ - $ - $ - $ - $ 1,000 $ 2,000 $ 3,000 Total overfloor damages $ - $ - $ - $ - $ 61,496 $ 204,074 $ 474,003

Road Damage Major $ - $ 415 $ 17,661 $ 36,726 $ 84,733 $ 107,254 $ 121,534 Minor $ - $ - $ - $ 450 $ 1,243 $ 2,703 $ 6,277 Total road damages $ - $ 415 $ 17,661 $ 37,176 $ 85,976 $ 109,957 $ 127,811

Total $ 21,900 $ 23,815 $ 41,861 $ 88,457 $ 234,824 $ 432,952 $ 685,075

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7.4 Assumption and Qualifications

A significant assumption in the calculation of the AAD was the assumption that the damages below the 20% AEP were extrapolated with the assumption that there are no damages at the 40% AEP event. Assuming a different slope for this line or a different AEP for zero damages will result in a change in the AAD calculated value. A paper was presented at the 2006 Floodplain Management Conference (Thomson et al, 2006) highlighting the issues associated with this assumption.

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8 FLOOD RESPONSE PLAN REVIEW

8.1 Flood Warning Systems

8.1.1 Overview

Put simply, flood warning systems provide a means of gathering information about impending floods, communicating that information to those who need it (those at risk) and facilitating an effective and timely response. Thus flood warning systems aim to enable and persuade people and organisations to take action to increase personal safety and reduce the damage caused by flooding. Effective flood warning systems maximise the opportunity for the implementation of public and private response strategies aimed at enhancing the safety of life and property and reducing avoidable flood damage.

It is essential that flood warning systems consider not only the production of accurate and timely forecasts / alerts but also the efficient dissemination of those forecasts / alerts to response agencies and threatened communities in a manner and in words that elicit appropriate responses based on well-developed mechanisms that maintain flood awareness. Thus, equally important to the development of flood warning mechanisms is the need for quality, robust flood awareness (education) programs to ensure communities are capable of response.

8.1.2 Limitations of Flood Warning Systems

No single floodplain management measure is guaranteed to give complete protection against flooding. For example, levees can be overtopped (when a flood exceeds design height, as happened at Nyngan in 1990) or fail (when construction standards are poor or maintenance is inadequate). Likewise, flood response plans can be poorly formulated or applied ineffectually.

Flood warning systems are, by their very nature, complex. They are a combination of technical, organisational and social arrangements. To function effectively they must be able to forecast coming floods and their severity (using data inputs that may include rainfall and upstream river heights and / or flows along with modelling techniques) and the forecast must be transmitted to those who will be affected (the at-risk communities) in ways that they understand and which result in appropriate behaviours on their part (for example, to protect assets or to evacuate out of the path of the floodwaters).

It is therefore not surprising, that flood warning systems often work imperfectly and have, on occasions, failed. Indeed, as Handmer (2000) points out, “flood warnings often don’t work well and too frequently fail completely ņ and this despite great effort by the responsible authorities.” While in some cases the problem is the result of a physical mechanical or technical failure (for example of gauges or telemetry or of communications equipment during a flood event) or perhaps in defining what constitutes success (or failure), the more common reason is that the systems have not been properly conceptualised at the design stage and in terms of their operation, despite the considerable and conscientious efforts of those involved. All too often, too little attention has been paid to issues of risk communication. In particular: x To building a local awareness of flood risk along with knowledge of what can be done to minimise that risk; x Determining what information is required by the at-risk community and with what lead times; x How warnings and required information will be distributed to and within the target communities;

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x Ensuring that recipients of warning messages understand what the message is telling them and what it means for their property and individual circumstances in terms of the damage reducing actions they need to take. The outcome of the above is that many flood warning systems have an inbuilt likelihood of failing.

In numerous cases where flood warning systems have been developed, the bulk of the effort has been devoted to creating and strengthening data collection networks, devising and upgrading forecasting tools and facilities and utilising new dissemination technologies to distribute the forecast to at-risk communities. While all these things are important, they are never sufficient by themselves to ensure that flood warnings are heeded by those who receive them. Other equally vital elements of the system such as risk communication and the comprehension that people have of the flood problems they may face (and the value that warnings can offer) need at least as much attention at the design stage and in system operation. The lesson from many studies of flood warning systems (e.g. Smith and Handmer, 1986; Phillips, 1998; Handmer, 1997; 2000; 2001; 2002, Comrie, 2011) is that the status of all elements of the system must be given appropriate resourcing if the system is to be made capable of functioning effectively.

Studies of flood warning system failures (e.g. Brisbane in 1974, Charleville and Nyngan in 1990, Benalla in 1993, Canada in 1997, England in 1998, Kempsey and Grafton in 2001, New Zealand in 2005) suggest that the most common reasons for poor system performance are that those in the path of floods, whether emergency responders, householders, the owners of businesses or the operators of infrastructural assets, have either not understood the significance of the warnings they have received or have not known that there were things (or the most appropriate things) they could do to mitigate the effects of flooding. The result has all too often been unnecessary loss of private belongings and commercial and industrial plant, stock and records (for example, through late or non-existent responses) and / or unnecessary risk to life (for example, due to evacuation after it became dangerous rather than when it was relatively safe). Most studies report that warnings were of an adequate technical standard (that is, they were accurate and delivered with good lead times), but the information was poorly communicated and not understood by the target communities. As reported by Anderson-Berry (2002) and Soste & Glass (1996), there is often insufficient attention to ensuring that people in flood liable areas understand the flood gauge or forecast heights which are incorporated in warning messages. The result is that those who have been warned fail to appreciate that the information contained in the message has meaning for their own circumstances. Consequently, they fail to take appropriate or adequate protective measures. Such people often claim afterwards that they received no flood warnings. In many cases warnings were issued but the gap between the information provided and what was understood by those at risk was too large. The problem is one of poor communication.

It is clear that a major problem with many flood warning systems is one of inadequate conceptualisation. Flood warning systems (and investments in their implementation) that over-emphasise the collection of input data and / or the production of flood forecasts relative to the attention given to other elements (such as message construction, the information provided in the messages and the education of flood prone communities about floods and flood warnings) will fail to fully meet the needs of the at-risk communities they have been set up to serve.

8.1.3 The Total Flood Warning System Concept

In 1995 the Australian Emergency Management Institute, following a national review of flood warning practices after disastrous flooding in the eastern states in 1990, published a best-practice manual entitled ‘Flood Warning: an Australian Guide’ (AEMI, 1995). In describing practices for the design, implementation and operation of flood warning systems in Australia, the manual introduced the concept of the ‘total flood warning system’ (TFWS). It

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also re-focused attention on flood warning as an effective and credible flood mitigation measure but made it clear that successful system implementation required the development of some elements that hitherto had been given little attention as well as the striking of an appropriate balance between each of the elements. In particular, it was noted that more attention needed to be given to risk communication and the education of communities about the flood risk, the measures that people could take to alleviate the problems that flooding causes and the place of warnings in triggering appropriate actions and behaviours. It also clearly enunciated the need for several agencies to play a part, with clearly-defined roles and with the various elements carefully integrated, and for the members of flood liable communities to be involved. Put another way, “effective warning systems rely on the close cooperation and coordination of a range of agencies, organisations and the community” (DoTARS, 2002).

The philosophy that underlies the TFWS concept coupled with the need for a coherent set of linked operational responsibilities and overlapping functions are documented and discussed in the context of guiding principles for effective early warning in UN (1997). While the original manual has been updated and republished as Manual 21 of the Australian Emergency Manuals Series (EMA, 2009), the concepts, practices and key messages from the original manual endure.

8.1.4 Total Flood Warning System Building Blocks

An effective flood warning system is made up of several building blocks. It comprises much more than a data collection network, forecasting model and flood level (or flow) prediction. Each building block represents an element of the Total Flood Warning System. The blocks (derived from EMA, 2009) along with the basic tools to facilitate delivery against each of the TFWS elements are presented in Table 8.1.

Experience shows that flood warning systems that are not designed in an integrated manner and that over- emphasise flood detection (say) at the expense of attention to the dissemination of warnings, local interpretation and community response inevitably fail to elicit appropriate responses within the at-risk community. It is essential that the basic tools against each of the building blocks are appropriately developed and integrated. Such a system considers not only the production of a timely alert to a potential flood but also the efficient dissemination of that alert to those, particularly the threatened community, who need to respond in an appropriate manner. A community that is informed and flood aware is more likely to receive the full benefits of a warning system.

Therefore, it follows that action to improve flood response and community flood awareness using technically sound data (such as produced by the Wickliffe Flood Investigation) will by themselves result in some reduction in flood losses.

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A formal flood forecasting and warning system does not exist for communities within the Hopkins River catchment. The 2010-11 flood events highlighted this as a critical deficiency in existing arrangements and demonstrated that the arrangements failed to meet community and emergency agency expectations regarding the provision of accurate and timely flood information aimed at facilitating appropriate response actions. These issues were discussed in the Glenelg Hopkins CMA submission (Water Technology, 2011) to the Comrie Review (Comrie, 2011). While a range of matters were covered in that submission, it was noted in particular that: x The rain and river level data collection network is sparse and is inadequate for the need: it is not sufficiently dense or accessible; x There is a clear need for a more dense network of rain and stream gauges. x Rain and stream gauges need to be automated and to report in real-time. x Resulting data needs to be uploaded to the Bureau of Meteorology website so that it is accessible to communities and response and related agencies and available to assist their maintenance of an up-to- date appreciation of event development. x At-risk communities within the Hopkins River catchment are not provided with any guidance on likely future flood conditions (i.e. a flood forecast or other information about the time to rise above predetermined critical levels, time to peak, likely peak level, etc) with the result that appropriate damage reducing actions are not implemented with sufficient lead time. x There is need for an improved flood forecast capacity based on robust hydrologic (i.e. rainfall-runoff) models that use rainfall data to predict stream flows and levels at key locations. x Flood class levels need to be established for all at-risk / forecast locations. x Other elements of the total flood warning system need to be fully established and / or strengthened.

8.3 The Task for Wickliffe

The Hopkins River catchment area upstream of Wickliffe is approximately 1,419 km2 and includes the Grampians National Park as well as the western uplands areas around Ararat. The river rises to the north east of Ararat and includes a number of smaller tributaries as well as storage areas such as Lake Muirhead, Mount William swamp, Lake Buninjon and the Cockajemmy Lakes.

The Bureau of Meteorology obtains daily-read rainfall data from a number of sites within or close to this part of the Hopkins River catchment: at Ararat, Willaura and Wickliffe within the catchment and to the east at Beaufort within the relatively close-by Mt Emu Creek catchment. The Bureau also operates a number of AWS’ in the general vicinity: at Westmere to the east of Wickliffe in the adjacent Fiery Creek catchment, at Ben Nevis near the top end of the Wimmera catchment near Mt Cole and at Mt William also in the Wimmera catchment but near Halls Gap in the Grampians. The location of these gauges is shown in Figure 8.1.

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Figure 8.1 Hopkins River Catchment to Wickliffe

Stream gauges currently exist on the Hopkins River in the upper parts of the catchment at Ararat (236219) and Wickliffe (236202).

Since the January 2011 flood event, the Glenelg Hopkins CMA has funded the installation of telephone based telemetry (i.e. Campbell logger which provides current data via SMS when interrogated by telephone and directly when interrogated remotely by computer) at the Ararat and Wickliffe gauges. The CMA also funded the installation of a rain gauge at the Ararat site. Data from both sites is now available from the Bureau of Meteorology website. As at November 2012, the CMA is continuing to pay all maintenance costs for both sites as responsibility for the long-term funding of on-going maintenance activities remains unresolved.

In order to establish an effective flood warning system for Wickliffe, attention will need to be given to each of the TFWS building blocks. Developing or augmenting the existing data collection network will not be sufficient.

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8.3.1 Data collection and Collation

8.3.1.1 Introduction There is a large amount of equipment available that will ‘collect’ rain and river level data and make it available to a single entity or to a group of entities, either from the site, through a post box or delivered to a predetermined address. There are a number, but fewer, systems that collect the data, make it available in the desired format at the desired location(s), provide an alert of likely flooding (i.e. detect or predict the likelihood of flooding) after checking the data against pre-determined criteria and that also quality check and collate the data so that it is ready for use. Some of these systems are “turn-key” while others are user built. All are modular in that fault-fix maintenance is generally via component plug-out / plug-in and expansion is easy to achieve.

8.3.1.2 Possible Additional Data Collection Sites There is one rain gauge, possibly three if the AWS’ at Ben Nevis and Mt William are used, covering the upper reaches of the Hopkins River catchment and providing data at a time scale suitable for flood warning purposes. This solitary rain gauge is located at the Hopkins River at Ararat stream gauge site. Taken together, these four gauges provide reasonable spatial and temporal coverage of rainfall at what is probably an acceptable density given the topography and likely flood producing weather mechanisms and conditions. There is, however an argument for improved coverage in the middle and lower parts of the catchment to Wickliffe based on consideration of prevailing rain producing weather conditions. While there are daily-read rain gauges at Willaura and at Wickliffe and an AWS at Westmere to the east of Wickliffe, more accessible data would assist the timely determination of likely flooding at Wickliffe.

The two stream gauges already in place within the Hopkins River catchment (at Ararat and at Wickliffe) provide some indication of flows likely to be observed at Wickliffe. However, while the Ararat gauge picks up flows from the upper parts of the catchment, contributions from the middle and lower reaches are not captured other than in a qualitative manner as a result of local observations until they get close to Wickliffe. It is therefore suggested that a new stream gauge on the Hopkins River either at Back Bolac Road (just downstream from the Cockajemmy Lakes) or at Delacombe Way (around mid-way between Lake Buninjon and the Cockajemmy Lakes) would be beneficial. Travel time from Delacombe Way to Wickliffe is of order 11 to 12 hours and from Back Bolac Road is of order 7 or 8 hours. Both sites feature a wide flat floodplain and a road to act as a flow control. The Back Bolac Road site is favoured as tributary inflows between the site and Wickliffe are minimal.

The cost of adding a rain gauge to a stream gauging site is not prohibitive. It is therefore suggested that while exposure may not be ideal, both the Back Bolac Road installation and the existing Wickliffe stream gauge site should include a rain gauge.

If all the installations identified above were completed, there would be a minimum of six (6) rain gauges and three (3) stream gauges available to inform flood forecasting and warning activities at Wickliffe.

Note that it is suggested that the existing rain gauges together with the proposed additional rain gauges will provide a sufficient indication of rainfall across the catchment to enable the indicative quick look ‘flood / no-flood’ tool developed for Wickliffe and included as an Appendix in the Ararat Municipal Flood Emergency Plan to be used with good lead time to provide an initial heads-up of the likelihood and scale of possible flooding. Flow conditions at the Ararat site but more particularly at the Back Bolac Road site would provide confirmation of the likely scale and timing of flooding.

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8.3.1.3 Turn-Key Data Collection & Alerting Systems Turn-key systems are ‘complete’ or integrated systems. The vendor provides all equipment including the base station software and then installs and configures all components. Maintenance is usually undertaken under contract to the vendor. Systems are generally scalable.

Greenspan Greenspan (part of TYCO Integrated Systems) is a local supplier of turnkey flood warning systems with operational systems in Australia, Asia and the Philippines. Standard or customised solutions are offered that include site investigation, system design services, installation, testing, commissioning, operation and maintenance. Solutions are tailored to the location and include integrated hydrologic and hydraulic modelling that trigger alerts of likely flooding. Processing is generally done off-site in Greenspan’s office and authorised users log-in to obtain data and forecasts. Alarms set within the system enable SMS and email messages to be sent to nominated persons. Systems can also be configured to initiate remotely controlled (radio linked) warning signs and other alerting equipment.

A number of Greenspan flood warning focussed systems are in operation and include: x Sipan Sihaporas Hydro Electric Power Scheme in Indonesia; x San Roque Dam and Hydro Power Scheme in the Philippines; x SMART (Stormwater Management and Road Tunnel) in Kuala Lumpur in Malaysia; x Public protection system for the Bruce Highway at Proserpine for Queensland Main Roads; x Flash flood warning system for Warringah Mall in Brookevale in NSW.

Capital and operating costs are not available “off-the-shelf” but are generally more expensive than the loggers already installed in the Hopkins River catchment. The technology used however offers significantly more functionality.

8.3.1.4 Other Automated Data Collection and Alerting Systems Other automated systems in the context of this report are those that are built up by the system owner using readily available hardware that is compatible with existing hardware and that can easily operate with existing data interrogation and storage software.

Campbell Data Logger Campbell data loggers provide a level of functionality and reliability that has seen them installed at many water resources sites across Victoria over the past 10 years or so. They generally collect data at a combination of predetermined frequencies and exceedance criteria. When paired with a modem, they can be interrogated by computer via the telephone system (fixed and mobile) and can also be set to send an SMS to one or more predetermined telephone numbers or to email to one or more addresses when alarm criteria (either single or multi- parameter with simple or conditional rules) are exceeded. The alarm rules are user-specified and can be used (say) to alert to the likelihood of flooding and the detection of flooding. One of these loggers is installed at each of the stream gauging sites at Ararat and Wickliffe. Quality control of data accessed direct from site is an end-user responsibility. Any data loaded to the State Data Warehouse for long-term archive is subject to rigorous quality control and correction.

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Other Data Loggers A variety of other data loggers with similar functionality and pricing are readily available within Australia, mostly off-the-shelf. However, they are not as widely used as the Campbell logger within Victoria. It is suggested that while there are no functional reasons for not considering these alternatives for the Hopkins River catchment, there are likely to be additional costs associated with their use. These are likely to include, for example, additional capital cost as at least one logger is likely to be required for the equipment maintenance pool, additional installation costs due to need to gain familiarity with logger setup, and additional on-going operating and maintenance costs due to the need to establish new procedures for data retrieval and on-site activity.

Event-Reporting Radio Telemetry System. Event-Reporting Radio Telemetry System (ERTS) equipment has been installed at a number of sites across Victoria including in the Wimmera catchment. Base stations are operational at agreed local offices (e.g. the Wimmera CMA’s office in Horsham) and at the Bureau of Meteorology’s office in Melbourne. All base stations host Bureau of Meteorology supplied and maintained by Enviromon software. This software manages all the data checking, collation and alerting functions.

Each ERTS flood monitoring system installation sends a signal by radio to one or more base stations every time there is a change in state of the parameter being measured – each increment of rainfall (can be 0.2mm, 0.5mm or 1mm) and a predetermined rise in stream level (usually every 10mm).

Quality and other checks are performed automatically against pre-determined parameters (threshold checking and alerting) on the data as it is received in real-time at each base station. These checks include a comparison of rainfall and river level data received from each of the stations against a pre-set rainfall amount in a specified time period and / or against a pre-set river level threshold. The values selected reflect typical catchment response times as well as catchment and stream characteristics. For Wickliffe, a useful rainfall trigger may be the rainfall intensity over the time of concentration for the catchment or the critical duration that produces the first overbank flows in the vicinity of the town. Any river height thresholds would be set based on consideration of a range of factors particular to each gauge location. Trigger values can be adjusted based on experience so that alarms do not trigger unnecessarily or too often but do provide sufficient lead time on a potential flood event. The local base station can be programmed to initiate an SMS message to the mobile phone (or pager) of key personnel as soon as the trigger rate is exceeded.

The SMS alert provides a ‘heads up’ to a possible flood event. It is aimed at flagging the need for people to more closely monitor rainfall and other flood indicators (e.g. continuing heavy rain and other local indicators of a developing flood, radar imagery and rainfall data available from the Bureau’s website, etc), and at enabling early activation of flood response and related plans in order to minimise the risk to life and property. For Wickliffe, the ‘heads up’ would also provide the trigger to use an indicative quick look ‘flood / no-flood’ tool developed for the town and included as an Appendix in the Ararat Municipal Flood Emergency Plan.

A more detailed explanation of ERTS systems and their benefits is provided in Wright (1994).

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8.3.1.5 Manual Data Collection and Alerting Recognising that funding may not be available (either now or into the future) to purchase, install and maintain an automated data collection, collation and flood detection system, a simple and cheap alternative is outlined herein.

The simplest data collection network would comprise the existing telemetered data sites (i.e. the AWS’ at Ben Nevis, Mt William and Westmere, the telemetered rain gauge at Ararat and the telemetered water level sites at Ararat and Wickliffe) plus additional manually read rain gauges and staff gauges. Data from all existing telemetered sites are available in near real-time from the Bureau’s website.

The Bureau maintains manually read rain gauges at Wickliffe, Willaura and Ararat Prison. Either the Bureau’s rain gauge readers at Wickliffe and Willaura could be approached to read the gauge at short time intervals during heavy rain events and provide each reading to a nominated person or an alternative local person could be supplied with a rain gauge and recruited to provide readings on an as-required basis. Note that the owners of existing private rain gauges within these general areas may be willing to take on this task.

A marginally more developed data collection network would include additional water level sites. The initial priority would be to install a set of staff gauges on the Hopkins River at the Back Bolac Road. The gauges would need to be either set to AHD (refer to discussion on page 56 of the Comrie Review Report, Comrie 2011) or to a local datum with the correction to AHD determined as part of installation. They would also need to be spread out so that they could be read when the road was flooded. A local resident would need to be instructed on how to read the gauge during high flow events and recruited to provide each reading to a nominated person. In addition, a theoretical rating would need to be developed for the site so that levels could be loosely tied back to the flood extent and depth maps delivered by the Wickliffe Flood Investigation. This would enable the Back Bolac Road levels to inform future flood response activities at Wickliffe with some lead time.

A second priority would be to install a set of staff gauges at “Half Way Gully” on Major Mitchell Road. As for Back Bolac Road, the gauges would need to be either set to AHD (refer to discussion on page 56 of the Comrie Review Report, Comrie 2011) or to a local datum with the correction to AHD determined as part of installation. A local resident would also need to be instructed on how to read the gauge during high flow events and recruited to provide each reading to a nominated person. While a theoretical rating for the site would be “nice to have” it is suggested that a peak level relationship between this site and Wickliffe (with due regard for levels at Back Bolac Road) could be established over time in order to assist in the firming up flood severity at Wickliffe.

In addition to the above, a person (or group – see Sections 8.3.4.4 and 0 regarding the establishment of a community flood action group or similar and their role) would need to be nominated to receive rain and river level readings and to initiate local actions in the event of trigger levels being exceeded. These trigger levels should be set by the Wickliffe community. It is suggested that a level 80 mm or so below the 10% AEP (1 in 10 year ARI) flood level (i.e. 4.40 m on the Wickliffe gauge which is situated on the right hand bank of the Hopkins River immediately upstream of the Glenelg Highway Bridge) might be a useful initial alerting level but that the indicative quick look ‘flood / no-flood’ tool located in an Appendix of the MFEP would provide initial guidance and additional lead time on the need to initiate a local response.

It should be noted that even if an automated data collection system is installed, staff gauges will need to be installed at the Back Bolac Road stream level monitoring site.

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8.3.2 Flood Detection and Prediction

An overview of flood warming services provided within Victoria by the Bureau of Meteorology is available at Appendix E.

It is necessary to know the levels at which floods begin to impact on the community in order to establish an effective flood warning system. In effect, to ensure that flood warnings are only provided when the consequences of flooding within an at-risk community are sufficient to warrant a warning and the coordinated mobilisation of resources to affect an appropriate response. Flood class levels, determined against standard definitions are used to establish a degree of consistency in the categorisation of floods. Using the flood intelligence and inundation maps generated by the Wickliffe Flood Investigation, preliminary flood class levels are proposed for the Hopkins River at Wickliffe as follows: x Minor flood level 4.40m (202.02 mAHD) x Moderate flood level 5.00m (202.62 mAHD) x Major flood level 5.30m (202.92 mAHD)

There are currently no specific flood warning systems or arrangements in place for the Hopkins River catchment or for Wickliffe township. The tool provided in an Appendix to the Ararat MFEP does however provide some guidance on the likelihood and severity of flooding at Wickliffe. Rainfall in the upper and middle parts of the catchment is used to indicate the likelihood and severity of flooding from the Hopkins River at Wickliffe.

The approach adopted by the Glenelg Hopkins CMA during the floods from August 2010 to January 2011 involved plotting the flood peak travel time from the most upstream gauge against river distance travelled from that gauge. Historical gauge records were plotted and curves fitted to the data for each flood event. During the 2010-11 flood events, real-time data was sourced from telemetered gauges or on-ground observers and plotted on the graph. Once three observed levels were plotted, a curve was fitted and predictions made for the time of peak at downstream locations. The curve was updated and predictions re-forecast as further observations were made during the downstream progress of the flood peak. While this approach makes good use of available intelligence and data, predictions can change significantly as more data becomes available. Further, it does not work well for locations in close proximity to the most upstream gauge and where there are substantial tributary inflows and / or opportunities for significant floodplain storage between the upstream gauge and the forecast location, as can occur for the Hopkins River between Ararat and Wickliffe.

It is suggested that a rainfall – runoff model that makes use of data telemetered from each of the proposed data collection sites would provide a timely and best available flood prediction for Wickliffe. The Bureau of Meteorology are best positioned, as the agency responsible for the monitoring of situations likely to lead to flooding and for the prediction of floods throughout rural Victoria (VFWCC, 2001) to develop the model and to run it in the lead up to and during flood events. The RORB model developed as part of the Wickliffe Flood Investigation may provide a good starting point for the development and refinement of such a forecasting model.

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8.3.3 Interpretation

The flood inundation maps and Ararat MFEP Appendices developed as part of the Wickliffe Flood Investigation provide the base information to enable the community and stakeholder agencies to determine the likely effects of a potential flood. This means however that the flood inundation maps and the relevant Appendices of the MFEP will need to be readily available to the Wickliffe community.

8.3.4 Message Construction and Dissemination

8.3.4.1 Available Alerting and Notification Tools and Technologies According to Rogers and Sorensen (1988), warning people of impending danger encompasses two conceptually distinct aspects—alerting and notification. Alerting deals with the ability of emergency officials to make people aware of an imminent hazard. Alerting frequently involves the technical ability to break routine acoustic environments to cue people to seek additional information. In contrast, notification focuses on how people interpret the warning message. It is the process by which people are provided with a warning message and information.

There are a number of alerting and notification tools and technologies available, some of which both alert and notify. Molino et al (2002) provide a summary worth considering in the context of Wickliffe. Only those that have the potential to quickly provide property owners and occupiers with an alert or notification have been considered herein.

A summary of available tools / technologies and their applicability to the Wickliffe area is provided below. x Those that alert only: o Sirens / alarms – do not alert those who live outside the immediate area. o Aircraft – impractical due to time, weather and noise limitations. o Modulating electrical supply voltage – frequent false alarms. o Modulating electrical supply frequency (e.g. NZ MeerKat system) – unlikely to be cost effective. o Coded visual signals (cf. fire danger signs) – not practical due to access issues and timing of flooding. o Laser lights – health risks and high potential for theft of equipment. x Those that alert and notify: o Personal notification – may be impractical due to access issues and resourcing but worth considering. o Fixed and mobile public address systems – only serves immediate area. o Tone alert radios – not cost effective for a small area. o Dial-out systems and related technologies – worth considering. o Enhanced dial-out system – similar to above but more expensive and reliant on local power supply. o Paging and mobile phones – potential if local community is flood aware. x Those that provide notification only: o Mass media (radio, television) - already used, for example ABC radio (1026AM and 774AM). o Internet – Bureau website displays warnings and data from local rain and river sites. o FM-88 with community awareness program – per capita cost would be high for Wickliffe.

From the above it can be seen that while some information about flooding is available to the community through the internet there is need to, as a minimum, alert the Wickliffe community in a timely manner to the likely on-set of flooding and to then back this up with information about likely consequences.

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The need to alert the community to flooding is not restricted to Wickliffe. Where time permits, the community alerting task is often achieved via local radio announcements. Active alerting is usually only undertaken occasionally and generally involves door knocking although in NSW the SES has employed loud-hailers to make street announcements. In rapidly responding areas (i.e. areas subject to flash flooding) in South Australia and Queensland, the Bureau of Meteorology alerts and notifies selected stakeholder agency staff using an SMS message system provided by StreetData. Within Victoria, many of the Councils involved in flood warning system upgrades in recent years and that utilise ERTS equipment have implemented Premier Global Services’ Xpedite VoiceREACH system to alert and notify residents and property owners in flood-prone urban areas. Melbourne Water are piloting an in-house developed SMS alerting system for residents in an area subject to flash flooding alongside Brushy Creek in the City of Maroondah which is triggered by the exceedance of rain or water level alarm criteria.

Both Xpedite (http://www.pgi.com/au/en/company/press-room/press-releases.php/(folder)/2003-06/(release)/release_2003-06-04.php) and StreetData (www.streetdata.com.au) are available and operational within Victoria. Both use existing technology, are quick and effective, are relatively cheap to implement and maintain, but require good quality broadband internet access from the host computer. For either to be truly effective, the at-risk or target community needs to be flood aware.

The national Emergency Alert (EA) system provides VICSES with a means of providing short messages to selected areas. While the EA has application for all emergency situations, it is unlikely for a number of reasons to be used during smaller flood events.

8.3.4.2 VoiceReach A number of Councils within Victoria have had to address the issue of how best to alert their flood–prone urban communities to the on-set of flooding. In all cases (City of Greater Shepparton for Shepparton and Mooroopna, Latrobe City for Traralgon, Strathbogie Shire for Euroa, Moira Shire for Nathalia, City of Benalla for Benalla, City of Geelong for selected areas within the Municipality and City of Maribyrnong for Maribyrnong Township) Premier Global Services’ Expedite VoiceREACH system was selected to perform the alert and notify task. A number of the Municipality also secured an FM-88 licence and associated equipment in order to provide a means of distributing flood and other emergency messages more widely including to visitors, road users, etc.

VoiceREACH is simple to set up, implement, use and maintain. When flooding is likely, a message is scripted by Council staff and, following log-in (from any computer with broadband internet access) to the VoiceREACH website, is read into a file by the user. The message is confirmed via playback and either edited or accepted for transmission. On acceptance for transmission, VoiceREACH delivers the voice message almost simultaneously to all telephone numbers in the user-managed telephone number file located on the VoiceREACH website.

VoiceREACH provides a message despatch report and delivers (by email to the user) a delivery success or failure report for each number in the telephone number file. This provides a template for follow-up door knocking or other personal approaches, if and as appropriate.

While not confirmed, it is understood that VoiceREACH message delivery may be able to be initiated by Enviromon through delivery of a pre-formatted voice file on triggering of a field station sensor alarm level. Enviromon has the capability. The issue is whether VoiceREACH requires real-time interaction with the user or whether it can be automated. If it can, automatic activation driven by river and rainfall alarms should be possible.

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This would, however, require additional configuration of the existing Enviromon software and the establishment of a base station somewhere within the Rural City of Ararat. At this stage, it is not clear how soon or to what extent the Bureau would be able to undertake the re-programming work required.

8.3.4.3 StreetData StreetData offers an SMS delivery service. The disadvantage of StreetData is that it can only deliver an SMS message. This means that unless a telephone handset recognises SMS protocols, only mobile phone owners can receive the message. Further, there is no guarantee of delivery, delivery is not necessarily immediate and there is no confirmation that the message has been received: it is essentially a “fire and forget” system.

When coupled with Enviromon, StreetData can deliver a pre-scripted SMS message to a local user-maintained list of telephone numbers on the exceedance of alarm criteria on each sensor reporting into or interrogated by the base station. The alarm system operates on filtered rather than raw data which reduces but does not eliminate the opportunity for errors.

To set up the system, alarm criteria are set for each sensor, message scripts are develop and loaded to Enviromon and a StreetData account is opened. The Bureau has established a streamlined procedure with StreetData that makes this last step very easy. Essentially, all that is required is a credit card with which to purchase initial credits.

Enviromon can be set up to send the message to StreetData with a single, block of or all listed telephone numbers. The Bureau of Meteorology recommends however that the message is sent to StreetData for each telephone number. This reduces the risk of message loss as, if there is a failure, only single, rather than many recipients fail to receive the message.

Enviromon can be configured to automatically drive the alerting process. It will monitor data from each sensor at each site and can drop real time data into the pre-scripted messages.

StreetData credits expire at the end of each 12-month period unless further credits are purchased in which case they roll-over for a further 12-months. StreetData send a reminder email when credits are about to expire. Costs per call reduce with the number of credits purchased.

The BoM is in the process of finalising documentation for the use of StreetData with Enviromon.

8.3.4.4 Community Involvement It is generally recognised that a critical issue in developing and maintaining a flood warning system is the active and continued involvement of the flood-liable community in the design and development of the total system so that their warning needs are satisfied. It is therefore suggested that the Rural City of Ararat give strong consideration to championing the formation of a community flood action group (or similar) and / or the establishment of volunteer community based flood wardens.

Members of this group (the wardens) could play a key role in local flood warning operations.

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8.3.4.5 A Solution for Wickliffe As it is not currently clear whether the Bureau of Meteorology is (or will be) in a position to provide flood forecasting services for Wickliffe in the near future, it is suggested that an automated message dissemination system such as Xpedite or StreetData should not be implemented in the short term. This is because the data collection network equipment upstream of Wickliffe is based around loggers (rather than ERTS) and while Enviromon is able to interrogate loggers, site partners have in the past been reluctant for a third party to take on this task, particularly as the data is available from the Bureau’s website. Further, AWS rainfall data is only available from the Bureau’s website.

In order to make maximum use of currently available rain and river data, other data if and as it becomes available and the indicative quick look ‘flood / no-flood’ tool for Wickliffe included in the Ararat Municipal Flood Emergency Plan, it is suggested that a local flood warden system is established at Wickliffe. The primary role of the flood wardens would be to monitor rain and river information via the Bureau’s website, assess the likelihood of flooding using the quick look ‘flood / no-flood’ tool and in the event of likely flooding, call VICSES to advise of likely flooding and, subject to discussion with the Regional Duty Officer or Incident Controller, call the Ararat Rural City MERO and initiate flood response actions within Wickliffe consistent with the MFEP. The wardens must however recognise that VICSES is the Control Agency for flood and must follow directions or instructions issued by the Incident Controller.

8.3.5 Response

The Ararat Municipal Flood Emergency Plan (MFEP) Appendices have been populated for Wickliffe as part of the Wickliffe Flood Investigation. Information in the MFEP includes all available intelligence relating to flooding in Wickliffe from the Hopkins River along with an indicative quick look ‘flood / no-flood’ tool based on rainfall depths across the upper and middle catchment. Flood inundation extent and depth maps are included together with a list of properties likely to be flooded and the expected depth of that flooding at each property. A flood intelligence card has also been prepared.

A critical issue for flood response at Wickliffe is the determination of whether buildings should be sandbagged / protected or emptied of items susceptible to damage from floodwater and evacuated. Arrangements established in conjunction with Council and VICSES should be detailed in the MFEP.

8.3.6 Community Flood Awareness

Following is a list (not exhaustive) of some of the more common misconceptions held by people who live in flood- prone areas. These misconceptions often act as a major barrier to improving flood preparedness and awareness within the community and thus hinder efforts to minimise flood damages and the potential for loss of life. x The largest flood seen by the community / individual is often confused with the maximum possible flood (i.e. the next flood couldn’t be bigger). This idea becomes more entrenched the bigger the flood witnessed previously. x Areas that haven’t flooded before will not flood in the future. This is an extension of the first bullet point. x The stream cannot be seen from the house so the house couldn’t possibly be at risk. x A levee designed to hold the 1% Annual Exceedence Probability (AEP) flood will protect the community from all floods and therefore a flood warning system is not required. x The 1% AEP flood (often referred to as the 1 in 100 year ARI flood), once experienced, will not occur for another 100 years. x The statistics and estimates that underpin hydrology are exact.

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Studies repeatedly show that communities that are not aware of flood hazard are less capable of responding appropriately to flood warnings or alerts and experience a more difficult recovery than a flood-aware community. Plain language flood awareness campaigns should aim to erase these misconceptions.

There are a number of activities that could be initiated to maintain and renew flood awareness at Wickliffe. The emphasis should be on an awareness of public safety issues (including the flood monitoring system) and on demonstrating what people can do to stay safe and protect their property from flooding. Typical initiatives include: x Making the MFEP publicly available (Council Offices, library, website) with a summary provided in Council welcome packages for new residents and business owners and with annual rate notices; x Championing a community flood action group and the establishment of volunteer community based flood wardens (or similar); x Periodically providing feature articles to local media on previous flood events and their effects on the community; x Installing flood markers indicating the heights of previous floodwaters (e.g. on power poles, street signs, public buildings, sides of bridges, etc); x Preparing and distributing property specific flood depth charts for all properties likely to be affected by flooding within Wickliffe (the data to inform the charts can be extracted from the hydraulic model developed for the Wickliffe Flood Investigation); x Photo displays of past flood events in local venues (these could be permanent); and x Preparing and distributing (as an on-going program) a flood action guide or brochure (e.g. FloodSafe brochure and as described by Crapper et al, 2005 in relation to Shepparton and Mooroopna) aimed specifically at encouraging local residents and businesses to take a pro-active role in preparing their property and themselves for a flood as well as describing what people need to do in a flood event. These could be given out at local events and with council rate notices and / or other council communications. A further initiative could involve the installation of flood depth indicators where there is appreciable danger to human life due to flood depth and / or velocity. However, the flood hazard maps delivered by the Wickliffe Flood Investigation indicate that other than in the main stream channel, flood hazard is generally low in the vicinity of Wickliffe.

8.4 Suggested System for Wickliffe

Table 8.1 provides a brief description of the basic tools needed to deliver against each TFWS building block together with an outline of possible solutions that would be applicable to Wickliffe.

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Table 8.1 Flood Warning System Building Blocks and Possible Solution for Wickliffe with due regard for the EMMV, Commonwealth-State arrangements for flood warning service provision (BoM, 1987), VFWCC (2001) and EMA (2009) Flood Warning System Basic Tools Possible Solution for Wickliffe Building Blocks INITIALLY: Install a set of staff gauges at Back Bolac Road (and possibly also at Half Way Gully on Major Mitchell Road) and nominate a person or group to collect and collate Data collection network (e.g. rain and stream gauges) data, and make initial assessments of the likelihood of flooding. NEXT if funding not available: Recruit manual rainfall readers at Wickliffe and Willaura. LATER: Using equipment similar to (or the same as) that already installed and System to convey data from field to central location and operational at Ararat, establish a telemetered rain and stream gauge at the Back Bolac DATA COLLECTION & / or forecast centre (e.g. radio or phone telemetry). Road site and add a rain gauge to the Wickliffe gauging station. COLLATION Will require Bureau of Meteorology to add sites to data tables accessible via the BoM Data management system to check, store, display data. website. Arrangements and facilities for system / equipment Require commercial arrangement with a service provider for maintenance. Ideally this maintenance and calibration. For example, the would be through the Surface Water Monitoring Partnership. Include all capitalised Regional Surface Water Monitoring Partnership, data system components on asset management register. warehousing, etc. Rainfall rates and depths likely to cause flooding INITIALLY: Using data from the existing rainfall network together with water levels and together with information on critical levels / effects at trends at Ararat and Wickliffe, determine the likelihood and scale of possible flooding key and other locations. using the tool described below. LATER: In order to initiate local alerting of potential flooding, use rainfall rates and depths Appropriately representative flood class levels at key from the MFEP tool to set rainfall gauge alarm criteria and use river levels from the flood locations plus information on critical levels / effects. inundation maps to set river level alarm criteria. This may lead to the refinement of flood DETECTION & PREDICTION class levels at Wickliffe. (i.e. Forecasting) INITIALLY: The indicative quick look ‘flood / no-flood’ tool developed for Wickliffe and included in the MFEP provides guidance on the likelihood and scale of possible flooding. Flood forecast techniques (e.g. hydrologic rainfall - Council responsible for maintaining the tool. runoff model, stream flow and / or height correlations, Decide how this tool is to be used and who by – Council, VICSES, GHCMA, community? simple nomograms based on rainfall). LATER: Rainfall-runoff forecasting model developed and used by Bureau of Meteorology to provide quantitative flood forecasts for the Hopkins River at Wickliffe.

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Flood Warning System Basic Tools Possible Solution for Wickliffe Building Blocks

INTERPRETATION (i.e. an Interpretative tools (i.e. flood inundation maps, flood Deliverables and intelligence arising from the Wickliffe Flood Investigation have been ability to answer the question information cards, flood histories, local knowledge, captured to the MFEP. The quick look tool described above together with the MFEP “what does this mean for me - flood response plans that have tapped community enable those at risk to determine whether they are likely to be flooded with some lead will I be flooded and to what knowledge and experience, flood related studies and time. depth”. other sources, etc). INITIALY: Implement local arrangements.

Warning messages / products and message LATER: Implement formal warning system triggered by Bureau of Meteorology flood MESSAGE CONSTRUCTION dissemination system. forecasts for the Hopkins River.

Role for the Emergency Alert during a severe flood event. Formal media channels1 – TV, radio and print. Fax / faxstream, phone / pager (e.g. SMS, voice), voice messaging systems (e.g. Xpedite), tape message In the lead up to system implementation, establish a Council championed community services, community radio, internet (e.g. BoM & flood action group. VICSES websites, email, social media), national MESSAGE DISSEMINATION Emergency Alert system. On exceedance of alarm criteria, site loggers could be programmed to send an SMS (i.e. Communication and Flood wardens message and / or email to key Municipal and / or VICSES personnel as well as perhaps Alerting) to key community members who could then initiate a local phone-based information Door knocking dissemination tree. Informal local message / information dissemination systems or ‘trees’. Alternative alerting mechanisms could include use of a siren or similar. Opportunity for at-risk communities to confirm warning details.

1 ABC Radio has entered into a formal agreement with the Victorian Government and the Bureau of Meteorology to broadcast, in full, weather related warnings including those for flood. The agreement provides for the interruption of normal programming at any time to allow the broadcast of warning messages. This agreement will ensure that flood (and other) warnings issued by the Bureau are broadcast in their entirety and as soon as possible after they are received in the ABC’s studio.

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Flood Warning System Basic Tools Possible Solution for Wickliffe Building Blocks Flood management tools (e.g. Municipal Flood Establish arrangements for the timely pick-up and removal of items susceptible to Emergency Plan complete with inundation maps and damage from floodwater from buildings likely to be flooded. Arrangements established in ‘intelligence’, effective public dissemination of flood conjunction with Council and VICSES should be detailed in the MFEP. information, local flood awareness, individual and business flood action plans, etc). Establish arrangements for the supply of sandbags and sand within Wickliffe with Flood response guidelines and related information (e.g. sufficient lead time to enable buildings at risk of minimal over-floor flooding (see list in Standing Operating Procedures). MFEP) to be sandbagged / protected. Arrangements established in conjunction with RESPONSE Council should be detailed in the MFEP.

Initiate a community engagement program to communicate how the FWS will work. Comprehensive use of available experience, knowledge Following (or perhaps in concert with) acceptance of the MFEP, encourage and assist and information. residents and businesses to develop individual flood response plans. A package that assists businesses and individuals is available from VICSES and provides an excellent model for community use.

Post-event debriefs (agency, community), etc. Review and update of alarm criteria, local flood intelligence (i.e. flood characteristics, Data from Rapid Impact Assessments. impacts, etc), local alerting arrangements, response plans, local flood awareness material, etc (initially) after every flood that triggers an alarm. Best done by Council with Flood ‘intelligence’ and flood damage data from the input from VICSES, GHCMA and the Council championed community flood action group. REVIEW event collected by residents, Council, GHCMA, etc. Council to develop review and update protocols => who does what when and process to Review and update of personal, business and other be followed to update material consistently across all parts of the flood warning and flood action plans. response system, including the MFEP.

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Flood Warning System Basic Tools Possible Solution for Wickliffe Building Blocks Identification of vulnerable communities and properties Develop, print and distribute flood awareness material (FloodSafe brochures, property (i.e. flood inundation maps, information on flood levels / specific flood depth charts, etc), including information on how the flood warning system depths and extents, etc). operates using information collated for the MFEP and available within the Wickliffe Flood Activities and tools (e.g. participative community flood Investigation report and from the web. education, flood awareness raising, flood risk communication) that aim to build flood resilient Load and maintain material (including the MFEP) on Council’s website with appropriate communities (i.e. communities that can anticipate, prepare for, respond to and recover quickly from floods links to relevant useful sites (e.g. the Flood Victoria website while also learning from and improving after flood http://www.floodvictoria.vic.gov.au/centric/home.jsp). events). AWARENESS Community education and flood awareness raising Routinely revisit and update awareness material to accommodate lessons learnt, including VICSES FloodSafe and StormSafe programs. additional or improved material and to reflect advances in good practice. Local flood education plans – developed, implemented and evaluated locally (e.g. Cities of Maroondah, Routinely repeat distribution of awareness material and consider other measures. Whitehorse, Wodonga, Benalla and Greater Geelong). Flood response guidelines, residents’ kits, flood Decide whether to alert residents and visitors to the risk of flooding in more direct ways. markers, flood depth indicators, flood inundation maps This could include the installation of flood depth indicator boards at key locations within and property listings, property specific flood depth Wickliffe (e.g. on both approaches to the Glenelg Highway Bridge at Wickliffe and at charts, flood levels in meter boxes and on rate notices, strategic locations on Walker Street as indicated by the flood inundation maps delivered etc for properties identified as being subject to flooding by the Wickliffe Flood Investigation) and further afield. through the Wickliffe Flood Investigation (see MFEP).

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8.5 Estimated Costs for TFWS for Wickliffe

Table 8.2 provides indicative costs associated with the implementation and on-going operation of each of the TFWS elements proposed for Wickliffe as discussed above.

Table 8.2 Estimated cost associated with the proposed Flood Warning System Estimated cost Item as at 2012 Comments (excl GST)

In-kind estimates developed using at-cost (not commercial) rates for time, consumables, etc

1. Data Collection and Collation 2 x set of 6 x staff gauge plates at Back Bolac Road and at Half Way Gully on Major Mitchell $3,800 per site Road. Set to AHD or local datum. Includes $7,600 total Cost covers supply, installation and survey to AHD. commissioning of equipment. It also New gauging station at Back Bolac Road (as includes estimated allowances for above). Includes concrete instrument housing on cultural heritage assessment and concrete pad, HS dry bubbler and pressure $25,000 service checks and marking at site. transducer, Campbell logger, modem, solar panel, Cost could be reduced by ~$2,000 antenna, cabling. per site by the installation of less Add rain gauge to Wickliffe gauging station. robust instrument housing. Includes BoM spec TBRG, bird guard, enclosure, $6,000 lightning protection, cabling.

Manually read rain gauges (if BoM readers unable to provide readings as required): ~$150 per site

¾ In close vicinity to Willaura. ~$300 total

¾ At Wickliffe.

Recurrent costs: Indicative costs only and dependent

¾ Staff gauge site. $1,000/year/site on the work scope and whether the

¾ Manual rain gauge site (if established). nil sites are brought into the Surface Water Monitoring Partnership. ¾ Rain - river site (no gauging). $4,500/year/site

Council to champion and oversee the Will need to clearly establish the role for this group along with its authority establishment of a flood action or flood warden In-kind estimated at group for Wickliffe. This group would collect and and structure. VICSES should be ~$5,000 to set up collate rain and river data and undertake the initial invited to be involved in setting up the assessment of the likelihood and scale of flooding ~$500/yr ongoing group / wardens. at Wickliffe. Liability issues need to be resolved.

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Estimated cost Item as at 2012 Comments (excl GST)

In-kind estimates developed using at-cost (not commercial) rates for time, consumables, etc

2. Flood Detection and Prediction The indicative quick look ‘flood / no-flood’ tool MFEP intelligence will need to be together with the MFEP enable those at risk to In-kind estimated at updated by Council, VICSES and determine whether they are likely to be flooded ~$3000/flood event GHCMA following flooding at with some lead time. Wickliffe. Council to maintain tool. Could include plotting flood producing rainfall events and resulting flooding Use the indicative quick look ‘flood / no-flood’ tool In-kind estimated at on the chart along with the event developed for Wickliffe to determine the likelihood ~$500/flood event date. May achieve refinement of tool and scale of possible flooding. over time. Calibration events from Wickliffe Flood Investigation could be utilised. Establishment: In-kind estimated at Establish and set rain and river level triggers at ~$500 total each telemetered site. Setup at site: ~$500/site

In-kind estimated at Council to establish and maintain. Build relationship between river levels at Back ~$2,000 to setup Will take some time to establish due Bolac Road, Half Way Gully and Wickliffe. ~$500/flood event to need to collect data. In-kind by BoM Currently no indication of likely estimated at timetable for this. Establish rainfall – runoff model for the Hopkins ~$7,000 to setup. The RORB rainfall-runoff model River to Wickliffe. Operational and developed for the Wickliffe Flood ongoing costs not Investigation would be suitable for included. this.

3. Interpretation Make relevant parts of the MFEP and flood In-kind estimated at Council to work with community on inundation and related mapping available to the ~$1000 how best to achieve access. Wickliffe community. The indicative quick look ‘flood / no-flood’ tool As costed above, MFEP intelligence will need to be together with the MFEP enable those at risk to in-kind estimated at updated following flooding at determine whether they are likely to be flooded ~$500/flood event Wickliffe. with some lead time.

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Estimated cost Item as at 2012 Comments (excl GST)

In-kind estimates developed using at-cost (not commercial) rates for time, consumables, etc

4. Message Construction and Dissemination Council to champion and oversee the establishment of a flood action or flood warden group for Wickliffe. The primary role of the group / Will need to clearly establish the role wardens would be to: for this group along with its authority and structure. VICSES should be ¾ Collect and collate rain and water level / flow data and also monitor rain and river As costed above, invited to be involved in setting up the information via the Bureau’s website in-kind estimated at group / wardens.

¾ Assess the likelihood of flooding using the ~$5,000 to set up Liability issues need to be resolved. quick look ‘flood / no-flood’ tool ~$500/yr ongoing Establish SOPs acceptable to all ¾ In the event of likely flooding, call VICSES to TFWS stakeholders. advise of likely flooding and, subject to discussion with the RDO or IC, call the Ararat Establish a local telephone-based Rural City MERO and initiate flood response information dissemination tree. actions within Wickliffe consistent with the MFEP. Program site loggers to send an SMS message Establishment: Is an extension of action identified and / or email to key Municipal and / or VICSES In-kind estimated at under ‘flood detection and prediction’. personnel as well as perhaps to key community ~$500 total members who could then initiate a local phone- Setup at site: based information dissemination tree. ~$500/site In-kind as part of Will depend on BoM workloads and established other matters outside Council and Implement formal warning system triggered by incident VICSES control. BoM flood forecasts for the Hopkins River. management arrangements

5. Response Will assist the implementation of an Council to share relevant parts of the MFEP with In-kind estimated at informed local response when it next the Wickliffe community. ~$500 to set up floods. Establish arrangements for the timely pick-up and Arrangements established in In-kind estimated at removal of items susceptible to damage from conjunction with Council and VICSES ~$1000 to set up floodwater from buildings likely to be flooded. should be detailed in the MFEP. Establish arrangements for the timely supply of Arrangements established in sandbags and sand within Wickliffe with sufficient In-kind estimated at conjunction with Council and VICSES lead time to enable buildings at risk of minimal ~$1000 to set up should be detailed in the MFEP. over-floor flooding to be sandbagged / protected.

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Estimated cost Item as at 2012 Comments (excl GST)

In-kind estimates developed using at-cost (not commercial) rates for time, consumables, etc Encourage and assist residents and businesses to In-kind estimated at Council and VICSES. develop individual flood response plans. $500 to promote In-kind estimated at VICSES with assistance from Initiate a community engagement program to ~$3000 to initiate Council. Will need to be repeated as communicate how the FWS will work. ~$1000 to repeat the system matures.

6. Review and Keeping the System Alive Post-event review and on-going maintenance of In-kind estimated at the system in order to keep it alive within the ~$2000/year for community (e.g. exercises to test procedures, activities while asset replacement, operational costs, involvement Costs will vary year to year and will operational costs with a community flood action group and so on). depend on rainfall and seasonal are absorbed into Assuming that replacement spares were conditions. incident purchased as part of the initial capital investment, management asset replacement expenses are considered to be activities. included in site recurrent costs.

7. Community Flood Awareness Up to $12,000 but Cost will depend on how much of the expected to be Develop and distribute a FloodSafe brochure for work is out-sourced and how much is covered by other Wickliffe. done by VICSES as an in-kind funding through contribution. VICSES Cost will depend on how much of Develop, print and distribute property-specific $3,000 chart build and distribution is out- flood depth charts for properties within Wickliffe. sourced.

Load and maintain flood related material In-kind estimated at In-kind estimated at (including the MFEP and inundation maps) to ~$1000 initial load ~$500 to set up Council’s website. ~$500 ongoing Install flood depth indicator boards at key ~$500/board locations in and around Wickliffe.

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A staged approach to the development of a flood warning system for Wickliffe is proposed. The stages have been ordered and the tasks within each stage grouped to facilitate growth of all elements of the TFWS in a balanced manner and with full regard for matters discussed in Section 8.1. While it may be tempting to immediately move to install additional rain and river gauges and to develop a forecast model, but there are other more fundamental matters that experience tells us need to be addressed first. Thus early attention is directed at ensuring roles and responsibilities are agreed, understood and accepted and that there is a firm foundation for the development of an effective flood warning system: one that does not fail when it is needed most. Attention is then directed to establishing a robust framework for communicating and disseminating flood related information so that immediate and maximum use can be made of available information as the ability to detect and predict flooding at Wickliffe improves. Next, attention is focussed on securing the funding needed to buy, install and operate field equipment as well as other services needed to build elements of the TFWS. The installation of data collection equipment follows, with a two tiered approach in the event that funding is not available or is delayed. Development of other technical elements and the build and delivery of on-going flood awareness activities can then occur in the knowledge that required data is / will be available and that robust and sustainable arrangements are in place that will enable maximum benefit to be derived from any information or programs delivered to the community.

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2. Council with the support of VICSES, Glenelg Hopkins CMA and the Wickliffe community to submit an application for funding under the Australian Government Natural Disaster Resilience Grants Scheme (or similar) for all outstanding elements of a TFWS for the Hopkins River to Wickliffe.

3. Council to share the MFEP with the Wickliffe community.

4. Council to establish arrangements for the timely supply of sandbags and sand within Wickliffe.

5. Council to load and maintain flood related material (including the MFEP) to its website.

6. Council and VICSES to encourage and assist residents and businesses to develop individual flood response plans.

2. Update the MFEP with staff gauge datums and other relevant details.

3. Council in conjunction with VICSES to establish and document in the MFEP arrangements for the timely: x Pick-up and removal of items susceptible to damage from floodwater from buildings likely to be flooded; x Supply of sandbags and sand within Wickliffe with sufficient lead time to enable buildings at risk of minimal over-floor flooding to be sandbagged / protected.

4. VICSES to initiate a community engagement program at Wickliffe in order to communicate how the flood warning system will work. This will need to be repeated as the system matures.

5. VICSES to develop and distribute a FloodSafe brochure for Wickliffe.

6. Council to oversee the development, printing and distribution of property-specific flood depth charts for properties within Wickliffe.

2. If the outcome from 1 above is negative, determine the location of private rain gauges in close vicinity to Willaura and at Wickliffe and establish arrangements for the provision of rainfall data to the flood action or flood warden group at frequent intervals during heavy rain events. Alternatively, source two rain gauges and distribute to local residents willing to provide rainfall data at frequent intervals during heavy rain events in the general vicinity of: x Wickliffe (priority 1). x Willaura (priority 2).

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2. Establish on-going maintenance arrangements for all installed equipment, ideally through the Surface Water Monitoring Partnership.

3. Approach BoM to add all telemetered sites to appropriate rainfall and river level bulletins accessible via the BoM website. Requires telemetry systems used to be fully compatible with BoM systems.

4. Council to begin building a relationship between levels at the stream monitoring sites at Back Bolac Road, Half Way Gully on Major Mitchell Road and Wickliffe in order to assist flood assessment and response at Wickliffe and in order to inform the development and / or firming up of flood class levels at each site.

5. If appropriate and following achievement of full operational status of each telemetered site providing additional rain and river data, retire the manual readers in the general vicinity who have previously provided that data for the Wickliffe flood warning system.

2. BoM to establish a rainfall-runoff based flood forecast model for the Hopkins River to Wickliffe.

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9 MITIGATION ASSESSMENT The Wickliffe Flood Investigation has examined the flooding that can occur within the township of Wickliffe. A key aspect of this assessment is the identification and methods for dealing with the risks associated with flooding to the community. Generally the mitigation can be split into structural and non-structural mitigation. The non- structural approaches are presented in Section 8 and includes aspects such as improved flood warning and developing an increased understanding of flood behaviour to assist in flood response and preparedness.

Mitigation options are presented within this section of the report and target utilising structures and/or modifications to the floodplain to reduce the impact of flooding on the Wickliffe community. This section will firstly examine the critical areas within study area that require protection and subsequently present the proposed mitigation options, their costs and their likely benefits in economic terms.

9.1 Identification of High Risk Flood Areas

To identify the high risk areas within Wickliffe, the design model runs were examined in detail using the full model simulations. This allows for the identification of the key flow paths of the flood waters that lead to property and building damages during large floods. It was identified from this assessment that the township of Wickliffe is not expected to experience flood waters within the township for the 5% AEP flood (1 in 20 year ARI) and for the more frequent events. These events are contained within the floodplain. The 5% AEP flood event is shown in Figure 5.11.

Within Wickliffe there are 16 buildings identified for this assessment. Of the 16 building identified 14 were residential, 1 was the local pub and 1 was the CFA shed. The identified buildings were restricted to buildings used as primary residence or serving a use to the Community. Sheds and out buildings were not included in this assessment. The locations of the identified buildings are shown in Figure 9.1. The CFA shed and local Pub are marked, the remaining buildings are residential. Figure 9.1 shows the 1% AEP deign flood event at the peak levels.

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Figure 9.1 Identification of high risk areas in Wickliffe (1% AEP design flood event)

For the larger flood events it was evident from the hydraulic modelling and from anecdotal sources that the flood waters are constricted by the Glenelg Highway embankment (Location A on Figure 9.1) and the capacity of the existing bridge structure (new Glenelg Highway Bridge with the old Highway Bridge upstream) and the culverts (to the south east of the township) are not sufficient to convey the large flows experienced in the 2% AEP (1 in 50 year ARI) and for all rarer events.

Once the flood waters begin to be restricted by the culvert and bridge capacity they begin to rise on the upstream side of the Glenelg Highway (Location A). This leads to a breakout flow entering the town via Location B which causes significant flooding to a number of properties for large flood events including in January 2011.

In the 2% AEP design event this breakout flow is very small at 0.6 m3/s and the breakout is only just beginning to form, at these flow rates there is expected to be minimal damage to the properties due to the breakout. In this event some floodwater is approaching buildings but no buildings are expected to have overfloor flooding.

The breakout peak flow rates increase to 10 m3/s, 34 m3/s and 60 m3/s for the 1%, 0.5% and 0.2% AEP flood events respectively. The January 2011 flood event is expected to be between the 0.5% and 0.2% AEP design flood events. The primary reason for the increase in the peak flow rate of the breakout is that the breakout is driven by the limited peak flows that can be transferred through the existing bridge (with old bridge upstream) and through the culverts.

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The number of buildings with overfloor flooding includes: x 1% AEP event – 3 buildings flooded overfloor, 2 residential (max 5 cm) and the CFA shed (13 cm). x 0.5% AEP event – 6 buildings flooded overfloor, 5 residential (max 20 cm) and the CFA shed (34 cm). x 0.2% AEP event – 11 buildings flooded overfloor, 10 residential (max 38 cm) and the CFA shed (64 cm).

The assessment identified that the key areas to focus the mitigation options are around providing a barrier to the breakout that enters the township from the south-west and to provide additional capacity for flood waters to flow under the existing Glenelg Highway. The mitigation options discussed and presented focus on these targets. The use of levees, additional culverts and removal of flow obstructions are all included in the mitigation option assessment.

9.2 Identification of Possible Mitigation Options

A set of mitigations options has been developed via consultation between Cardno, Glenelg Hopkins CMA, Ararat Rural City Council, VicRoads and the Wickliffe Community. This set of mitigation options includes all suggested mitigation options. Preliminary assessment will be carried out on all options using the 1% AEP design flood event and detailed assessment will be carried out on selected options.

For the Wickliffe investigation five (5) mitigation options have been developed. These mitigation options are shown in Figure 9.2. The options include; x Removing the old bridge deck upstream of the current Glenelg Highway Bridge x Developing Levee 1 (~120m in length) x Adding a set of culverts under the Glenelg Highway x Developing Levee 2 (~800m in length) x Clearing vegetation from the main floodplain in and around the township.

For this assessment the mitigation option nonclementure will be as per Table 9.1.

Table 9.1 Nonclementure for the mitigation option assessment

Option Description Mitigation 1 Removing the old Glenelg Highway bridge deck Mitigation 2 Levee 1 Mitigation 3 Additional culverts Mitigation 4 Levee 2 Mitigation 5 Vegetation clearing

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MODEL OUTPUT

Figure 9.2 Proposed mitigation options

9.2.1 Mitigation 1 – Old Bridge Deck Removal

The removal of the old bridge deck is to be carried out by VicRoads and has been included as they have stated that they are planning to remove the bridge deck by July 2013. The removal of this structure would allow additional flows to pass under the existing bridge and this is expected to reduce levels upstream of the Glenelg Highway. This in turn aims to reduce the flow rates breaking out into Wickliffe that were identified in Section 9.1. As this mitigation option is to be carried out it has been included in the examination of all mitigation options.

9.2.2 Mitigation 2 – Levee 1

Levee 1 is proposed to run on the south eastern side of McKenzie Road joining the high point of the hill with the Glenelg Highway embankment. This levee is proposed to be set at the 1% AEP flood height plus 300 mm freeboard. The current 1% AEP flood level is 203.2 mAHD and hence the levee would be set at 203.5 mAHD. The levee aims to provide a barrier to the breakout identified in Section 9.1.

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9.2.3 Mitigation 3 – Additional Culverts

The additional culverts have been included between the current Glenelg Highway Bridge and McKenzie Road. These culverts have been recommended by VicRoads to be 10 x 1,200 mm x 900 mm (number x width x height). The size of these culverts is limited by the available space between the township and the existing structure. The culverts have been set with an upstream invert level of 201.4 mAHD and downstream invert of 201.3 mAHD. This requires some reshaping of the existing embankments along the Glenelg Highway. It is assumed the existing 450 mm pipe at this location would be removed as part of the installation of the new culvert set.

9.2.4 Mitigation 4 – Levee 2

Levee 2 is proposed to run along the southern edge of Wickliffe at the 1% AEP peak depth plus 300 mm freeboard. This levee is designed to stop water encroaching on the township from the southern side of the Glenelg Highway. It is expected that some peak flood waters may come around the western end of the culvert, however it is not possible to prevent this without increasing the height of the Glenelg Highway which is not practical or feasible in this scenario.

The levee would have an elevation of 202.7 mAHD where it meets the Glenelg Highway on the eastern side of the town, graded to a level of 202.0 mAHD at the western side of Wickliffe adjacent to the Pub.

9.2.5 Mitigation 5 – Vegetation Clearing

The final mitigation option considered was based on improving the hydraulic capacity of the flood plain adjacent to the township of Wickliffe by clearing the low vegetation of the area referred to as the “Commons”. The vegetation clearing focuses on removing the low lying grasses and shrubs from the floodplain to reduce the hydraulic roughness. No trees were planned to be removed as part of this mitigation option. The revised roughness grid after the vegetation clearing was applied is shown in Table 9.1.

It should be noted that the vegetated area that was cleared within the model covered 660 m2 and this would require significant maintenance. The cleared vegetation area includes some private land area that may be used for cropping. The purpose of including a larger area was to determine the maximum possible benefit that could be achieved using clearing techniques.

The reduction in roughness within the 660 m2 area is such that the grass would be required to be cut to a very low level to achieve the lowered roughness of Mannings ‘n’ of 0.036. This level of roughness is at a similar level as the main channel of the Hopkins River. No trees would be required to be removed but any shrubs or low lying bushed would need to be completely cleared. It should be noted that the benefits shown in the results of the vegetation clearing mitigation option are the best result that would be possible and that as the grasses and shrubs regrow the reductions in peak flood height would return to the current existing levels.

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Figure 9.3 Mitigation 5 – Lowered roughness for vegetation clearing

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9.3 Mitigation Results

The mitigation options assessment was initially undertaken using the 1% AEP flood event in isolation to determine the appropriate mitigation options and scenarios that would be investigated in additional detail. The preliminary assessment is discussed in Section 9.3.1. The mitigation runs were also simulated using the calibrated January 2011 flood event and the results are discussed in Section 9.3.2.

Following the assessment using the 1% AEP and January 2011 flood events, three mitigation options were examined in additional detail using the 20%, 10%, 5%, 2%, 1%, 0.5% and 0.2% AEP flood events. The development costs for these options were estimated and a cost benefit assessment was undertaken. The results of this assessment are included in Section 9.4.

9.3.1 1% AEP Results

Five scenarios were assessed using the 1% AEP flood event. This process was undertaken to undertake preliminary analysis on the mitigation options and to remove options which are unlikely to be developed for Wickliffe. This primary aim is to reduce the number of mitigation option to be included in the detailed assessment.

Five scenarios (combinations of mitigation options) were considered, these are summarised in Table 9.2. The bridge deck removal has been included in each scenario as this mitigation option was planned to be carried out by VicRoads prior to July 2013.

Table 9.2 Nonclementure for the mitigation scenarios

Options Mitigation included Description Scenario 1 Mitigation 1 Deck removal only Scenario 2 Mitigation 1 & 2 Deck removal and levee 1 Scenario 3 Mitigation 1 & 3 Deck removal and additional culverts Scenario 4 Mitigation 1, 2, 3 and 4 Deck removal, levee 1, levee 2 and additional culverts Scenario 5 Mitigation 5 Mitigation 5

9.3.1.1 Scenario 1 – Bridge Deck Removal Scenario 1 included the removal of the old bridge deck upstream of the current Glenelg Highway Bridge. This structure poses a significant blockage to peak flood flows, especially in flood events at the 2% AEP and greater level. From discussions with VicRoads this bridge deck is expected to be removed before July 2013. Due to cultural and heritage reasons the piers and abutments are unlikely to be removed. This has been accounted for within the model with the abutments and piers retained within the topography.

The results for the 1% AEP difference plot are shown in Figure 9.5 in the form of a difference plot comparing the mitigated peak flood depths directly with the existing peak flood depths. The removal of the bridge deck reduces the losses and constriction through the structure which allows additional flows through. Figure 9.4 shows the flow rates under the Glenelg Highway for the duration of the 1% AEP event for the Glenelg Highway Bridge in isolation and the Glenelg Highway Bridge in combination with the set of culverts to the south east. The breakout flow into Wickliffe was not included.

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Figure 9.4 Capacity of the structures under the Glenelg Highway – pre and post mitigation

The bridge prior to the deck of the old structure being removed had a peak discharge rate of 115 m3/s in the 1% AEP. This discharge rate increased to 142 m3/s once the old bridge deck was removed. The increased capacity of the structure leads to large decreases of up to - 0.33 m of the peak flood depths upstream of the Glenelg Highway. It should be noted that when the peak discharge rates from the combined bridge and culverts are examined the peak discharges go from 184 m3/s up to 194 m3/s. The smaller increase here is due to the fact that the peak flood levels are reduced and hence the culverts are required to transfer less of the floodwaters.

The decreases in the peak flood depths are extend upstream from the Glenelg Highway with the reduction in peak depths reducing as we progress further upstream. The peak reduction in flood depths was observed immediately upstream of the Glenelg Highway Bridge and was 33 cm. This reduction led to the breakout into Wickliffe reducing. The reduction in flood extent is shown in Figure 9.5 as magenta. In this scenario the only building to have overfloor flooding is the CFA shed.

A small area downstream of the Glenelg Highway Bridge shows increased flood depths, however this is limited to the immediate vicinity of the bridge. The majority of the peak flood depths downstream of the Glenelg Highway remained unchanged.

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Figure 9.5 Scenario 1 – 1% AEP change in peak depth due to the removal of the old bridge deck

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9.3.1.2 Scenario 2 – Bridge Deck Removal and Levee 1 Scenario 2 examined including a levee that would target the breakout flows that enter Wickliffe during large flood events. This levee is approximately 100 m long and would be sized to be at the current 1% AEP level plus 300 mm freeboard. The current 1% AEP peak water surface elevation at this location is 203.2 mAHD and as such the levee is recommended to be set at 203.5 mAHD. This levee would extend from the Glenelg Highway along McKenzie Road and tie in with the existing gradient of the hillside.

The results of Scenario 2 are shown in Figure 9.6. The levee can be seen to block the breakout flows that are entering the township completely, and accordingly reduce the flood extent by the area shown. The peak flood depths are reduced by similar levels as compared to Scenario 1. In the 1% AEP flood event the breakout flow if very small so there is no noticeable increase in flood depths once the levee is included. It would be expected that for larger events where the levee block larger volumes of flow that this would increase the depths upstream of the Glenelg Highway.

Overall the levee is effective in stopping the breakout flows from entering Wickliffe. This would result in less floodwater impacting properties. As for Scenario 1 only the CFA shed has overfloor flooding.

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Figure 9.6 Scenario 2 – 1% AEP change in peak depth due to the removal of the old bridge deck and levee 1

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9.3.1.3 Scenario 3 – Bridge Deck Removal and Additional Culverts Scenario 3 examined including additional culverts between the township of Wickliffe and the existing Glenelg Highway Bridge. The culverts included were 10 x 1,200 mm x 900 mm (number x width x height). The culverts were located specifically between Wickliffe and the current bridge structure with the aim of increase the discharge under the Glenelg Highway to stop the breakout flows entering Wickliffe during large events.

The difference plot is shown in Figure 9.7. The figure shows that the depths upstream of the Glenelg Highway have been further reduced with the reduction in peak flood depths increasing to 0.44 m. The additional culverts carry an additional 24.5 m3/s peak discharge. It is important to note that although the peak flood depths reducing relative to Scenario 1, the breakout flow into Wickliffe was not removed. This indicates that the levee may be a more reliable method for managing the breakout flow through the township. As for Scenario 1 only the CFA shed has overfloor flooding.

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Figure 9.7 Scenario 3 – 1% AEP change in peak depth due to the removal of the old bridge deck and additional culverts

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9.3.1.4 Scenario 4 – Bridge Deck Removal, Levee 1 and Additional Culverts Scenario 4 examined including additional culverts between the township of Wickliffe and the existing Glenelg Highway Bridge in combination with a levee to block the breakout through Wickliffe. The culverts included were 10 x 1,200 mm x 900 mm (number x width x height).

The difference plot is shown in Figure 9.8. The figure shows that the depths upstream of the Glenelg Highway have been maintained at the peak reduction of 0.44 m and the breakout flow has been blocked by Levee 1. As for Scenario 1 only the CFA shed has overfloor flooding.

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Figure 9.8 Scenario 4 – 1% AEP change in peak depth due to the removal of the old bridge deck, levee 1 and culverts

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9.3.1.5 Scenario 5 – Bridge Deck Removal, Levee 1, Levee 2 and Additional Culverts Scenario 5 couples all of the proposed structural mitigation options together; x Levee 1 to stop the breakout flows entering Wickliffe x Additional Culverts (10 x 1,200 mm x 900 mm (number x width x height)) x Levee 2 to stop flows entering the Wickliffe township from the south.

Levee 2 is a substantial levee that would be approximately 800 m long and this would be built as near a practical to the properties on the southern side of the township of Wickliffe. The levee would have an elevation of 202.7 mAHD where it meets the Glenelg Highway on the eastern side of the town, graded to a level of 202.0 mAHD at the western side of Wickliffe adjacent to the Pub. This level is set at the current 1% AEP flood level plus 300 mm freeboard.

Levee 2 can be seen to be an effective method of removing the floodwaters from the township of Wickliffe. The magenta areas cover most of Wickliffe indicating flood free zones. At the western end of the levee system some water can be seen to bypass the levee and start to flow back towards the township. In larger events this effect would be magnified and a system would be required to have active pumps to remove this water from behind the levee. In this scenario no buildings have overfloor flooding.

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Figure 9.9 Scenario 5 – 1% AEP change in peak depth due to the removal of the old bridge deck, levee 1 and 2 with additonal culverts

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9.3.1.6 Scenario 6 – Vegetation clearing Scenario 6 examines the impact on the 1% AEP peak flood depths when the floodplain is cleared of obstructions. The results of this scenario are shown in Figure 9.10. For this scenario the old bridge deck has been retained so that the impacts of clearing the vegetation can be seen in isolation.

For the vegetation clearing scenario a large area was specified as being cleared (~660 m2). A large area was selected to determine the largest possible benefit from using this method. Within the hydraulic model the roughness within the area shown in Figure 9.10 has been substantially reduced. The level this has been set is effectively as if all of the shrubs, bushes and grasses have either been removed or cut to very low levels. The trees have been left within the floodplain. It should be noted that the results shown are as if this area has just been cut and as the grasses and bushed regrow the benefits of clearing the vegetation will reduce until levels return to normal levels. To obtain the full benefit of the vegetation clearing mitigation option regular maintenance would be required on this area to ensure the grasses were maintained at very low levels.

The reductions in the peak flood levels are observed across the entire floodplain as a result of the vegetation clearing. The maximum reductions were observed at the southern edge of Wickliffe at approximately 0.14 m. The peak depths throughout the breakout through Wickliffe were reduced by approximately 0.06 m. The breakout flood extent was maintained even after the vegetation was cleared.

Clearing the vegetation has a noticeable impact and it is recommended that some reduction in the obstructions within the main floodplain be undertaken in the future. Removal of shrubs, bushed and cutting of the long grass can be seen to provide some benefit to increasing the discharge rates through the main floodplain. It is unlikely that the full reduction in peak flood levels shown within the model can be achieved as this would require almost constant maintenance and some of the land adjacent to the river is private land. However, it has been demonstrated that reducing the obstructions within the floodplain in the area shown in Figure 9.10 can reduce peak flood depths in large events.

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Figure 9.10 Scenario 6 – 1% AEP change in peak depth due to the clearing of the vegetation

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9.3.2 January 2011 Results

Due to the magnitude of the January 2011 flood event (a predicted peak of 287 m3/s and a 0.33% AEP) and because the hydrograph for the event was known, each of the mitigation scenarios was run to see what impact they would have had during this event. It should be noted that the levees in this scenario have been set at sufficient height that they will not fail during this event. In reality the levees may have been overtopped depending on the constructed levels and whether sandbagging occurred on the levees to increase their effective height.

Each of the difference plots for each of the scenarios are shown in Figure 9.11 to Figure 9.15.

Scenario 1 shows that opening the existing bridge structure through the removal of the old bridge deck leads to a decrease in the January 2011 peak depth by approximately 0.2 m upstream of the Glenelg Highway. This reduction is not as large as for the 1% AEP scenario as a large proportion of the peak flows are being blocked by the Glenelg Highway road embankment. The benefit of removing the old bridge decking in the January 2011 event is evident throughout the township but is limited to upstream of the Glenelg Highway. Downstream of the Highway the peak flood levels remain largely unchanged.

Scenario 2 includes levee 1 and from Figure 9.12 it is evident that the levee is capable of stopping the bulk of the breakout flows that passes through the township. It should be noted that the peak level reached against the levee location was 203.45 mAHD which is below the proposed current levee constructed height. Levee 1 is shown to protect a number of houses from overfloor flooding even in an extreme event such as January 2011.

Scenario 3 was less effective during the January 2011 event due to the large size of the breakout. The additional culverts managed to reduce the peak depths upstream of the Highway by a further 0.1 m over Scenario 1 but this was not sufficient to stop the breakout throughout the township occurring.

Scenario 4 shows the results of including additional culverts and levee 1. The additional culverts reduce the peak levels reached against levee 1 to 203.33 mAHD which is below the proposed levee 1 construction height. The inclusion of the additional culverts with levee 1 reduces the levels against the levee by approximately 0.13 m.

Scenario 5 does not work effectively in the January 2011 flood event as floodwaters bypass the levee to the west of the town. Water is likely to pool behind the levee in this scenario and cause ongoing problems within the town.

Overall for the January 2011 flood event the removal of the old bridge deck, the inclusion of levee 1 and the additional culverts all provided some benefit to the town. None of the mitigation scenarios managed to protect the entire township during the January 2011 event.

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Figure 9.11 Scenario 1 – Jan 2011 change in peak depth due to the removal of the old bridge deck

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Figure 9.12 Scenario 2 – Jan 2011 change in peak depth due to the removal of the old bridge deck and levee 1

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Figure 9.13 Scenario 3 – Jan 2011 change in peak depth due to the removal of the old bridge deck with additonal culverts

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Figure 9.14 Scenario 4 – Jan 2011 change in peak depth due to the removal of the old bridge deck, levee 1 with additonal culverts

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Figure 9.15 Scenario 5 – 1% AEP change in peak depth due to the removal of the old bridge deck, levee 1 and 2 with additonal culverts

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9.3.3 Selected Mitigation for Detailed Assessment

From the preliminary assessment Mitigation Options 1, 2 and 3 were selected for detailed assessment. The mitigation options were run with the following scenarios: x Design Scenario 1 – Bridge deck removed (mitigation 1) x Design Scenario 2 – Bridge deck removed (mitigation 1) and levee 1 (mitigation 2) x Design Scenario 3 – Bridge deck removed (mitigation 1) and additional culverts (mitigation 3)

The inclusion of levee 2 was not seen to be practical. The levee is likely to be very expensive and would be prone to being bypassed during large events. During the Community meeting concerns were raised that the levee would involve too many properties for construction and require too much ongoing maintenance. It is for these reasons that levee 2 was not progressed to the detailed assessment.

The vegetation clearing was not included within the detailed assessment as this was not a structural mitigation option. This option could be partially or fully implemented for some benefit to the flood depths within the floodplain but as discussed the benefit of clearing the grass and shrubs is only temporary as soon as they are cut they begin to regrow. This option has maintenance costs involved but this assessment is targeting permanent structural mitigation options only.

9.4 Mitigation Costing

The three selected options for the detailed assessment have been costed in order to undertake a cost / benefit assessment of their feasibility for implementation. A summary of the costs for each option is summarised in Table 9.3. Details of the costing for Mitigation 2 is summarised in Appendix E.

Table 9.3 Estimated installation costs for the selected mitigation options Estimated costs AEP Description ($2012) Mitigation 1 Old bridge deck removal $ 20,0001 Mitigation 2 Construction of Levee 1 $ 20,800 Mitigation 3 Installation of additional culverts $ 205,0002 1 estimate only, this is being implemented and has not been costed in detail 2 estimate provided by VicRoads

9.5 Mitigation Cost / Benefit

The mitigation scenario cost benefit assessment has been undertaken using the costing summarised in Section 9.3.3 and the Annual Average Damage (AAD). The three scenarios were selected to be assessed in detail were run through the hydraulic model for the 20%, 10%, 5%, 2%, 1%, 0.5% and 0.2% AEP events. As for the existing conditions the Annual Average Damage (AAD) was calculated on a probability approach, using the flood damages calculated for each design event.

A summary of the damages for each run are shown in Table 9.4 for the detailed mitigation scenarios.

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Table 9.4 Unit damages for roads and bridges (dollars per km inundated) Damages ($ 2012) Scenario 2 Scenario 3 AEP Scenario 1 Existing (bdg deck removed, (bdg deck removed, (bdg deck removed) levee 1) additional culverts) 20% $ 21,900 $ 22,900 $ 21,900 $ 22,900 10% $ 23,815 $ 23,815 $ 23,815 $ 23,815 5% $ 41,861 $ 41,061 $ 41,861 $ 42,661 2% $ 88,457 $ 69,474 $ 76,674 $ 70,274 1% $ 234,824 $ 124,926 $ 121,746 $ 123,336 0.5% $ 432,952 $ 297,895 $ 231,486 $ 238,894 0.2% $ 685,075 $ 614,442 $ 500,909 $ 573,895

AAD $ 14,405 $ 12,532 $ 11,871 $ 12,222 Reduction in AAD ($) $ 1,873 $ 2,534 $ 2,183 Reduction in AAD (%) 13.0 % 17.6 % 15.2 %

By developing Mitigation 1 (removing the bridge deck) the AAD is shown to reduce by $1,873. This translates to an average annual reduction in damages that is 13% lower than the current situation. The removal of the old bridge deck has the largest impact on the damages of all of the mitigation options. The detailed summary of the results for this scenario is summarised in Table 9.5. For the 1% AEP event 2 residential buildings are no longer flooded to an overfloor depth.

The inclusion of levee 1 reduces the damages further with the AADs reducing to $ 11,871, however, only 4.6% of the reduction can be attributed to the levee with the bridge deck removal accounting for 13% of the reduction. The main reason for the reduction in damages in this scenario was that the breakout flow entering the township was blocked completely. The detailed summary of the results for this scenario is summarised in Table 9.6. For the 1% AEP event 2 residential buildings are no longer flooded to an overfloor level. The number of buildings with overfloor flooding decreases for the larger events as a result of the levee as well.

The inclusion of the additional culverts has the least impact on the AAD for the three options considered. The reduction attributed to the additional culverts was only 2.2% once the impact of the bridge deck removal was accounted for. The smaller reduction in damages was a result of the breakout flow still being allowed to enter the township for the 1% AEP and larger events. The additional culverts do lower the peak water depths upstream of the Glenelg Highway but their capacity is not sufficient to stop the breakout for the larger events. The detailed summary of the results for this scenario is summarised in Table 9.7. The inclusion of the additional culverts protects one additional building from overfloor flooding compared to Scenario 1.

Overall, removing the old bridge deck has the greatest reduction in damages for the model at 13%, this is followed by the inclusion of levee 1 with 4.6% and lastly by the additional culverts which reduced the AAD by approximately 2.2%.

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Table 9.5 Summary of Economic Flood Damages for Mitigation Scenario 1 (Mitigation 1) Recurrence Interval 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP 0.5% AEP 0.2% AEP Property Damage Total property damages $ 22,900 $ 23,400 $ 23,400 $ 34,790 $ 54,971 $ 85,241 $ 74,351 Inundated properties (> 10cm depth, > 1% area) 44 45 45 48 50 53 51

Building Damage Residential 0 0 0 0 0 3 9 CFA Shed 0 0 0 0 1 1 1 Total buildings with overfloor flooding 0 0 0 0 1 4 10

Residential $ - $ - $ - $ - $ - $ 125,270 $ 415,261 CFA Shed $ - $ - $ - $ - $ 1,000 $ 2,000 $ 3,000 Total overfloor damages $ - $ - $ - $ - $ 1,000 $ 127,270 $ 418,261

Road Damage Major $ - $ 415 $ 17,661 $ 34,234 $ 68,285 $ 83,163 $ 115,553 Minor $ - $ - $ - $ 450 $ 670 $ 2,221 $ 6,277 Total road damages $ - $ 415 $ 17,661 $ 34,684 $ 68,955 $ 85,384 $ 121,830

Total $ 22,900 $ 23,815 $ 41,061 $ 69,474 $ 124,926 $ 297,895 $ 614,442

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Table 9.6 Summary of Economic Flood Damages for Scenario 2 (Mitigation 1 and 2) Recurrence Interval 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP 0.5% AEP 0.2% AEP Property Damage Total property damages $ 21,900 $ 23,400 $ 24,200 $ 41,990 $ 51,790 $ 84,161 $ 105,041 Inundated properties (> 10cm depth, > 1% area) 42 45 46 57 70 76 80

Building Damage Residential 0 0 0 0 0 2 6 CFA Shed 0 0 0 0 1 1 1 Total buildings with overfloor flooding 0 0 0 0 1 3 7

Residential $ - $ - $ - $ - $ - $ 59,941 $ 271,037 CFA Shed $ - $ - $ - $ - $ 1,000 $ 2,000 $ 3,000 Total overfloor damages $ - $ - $ - $ - $ 1,000 $ 61,941 $ 274,037

Road Damage Major $ - $ 415 $ 17,661 $ 34,234 $ 68,285 $ 83,163 $ 115,553 Minor $ - $ - $ - $ 450 $ 670 $ 2,221 $ 6,277 Total road damages $ - $ 415 $ 17,661 $ 34,684 $ 68,955 $ 85,384 $ 121,830

Total $ 21,900 $ 23,815 $ 41,861 $ 76,674 $ 121,746 $ 231,486 $ 500,909

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Table 9.7 Summary of Economic Flood Damages for Mitigation Scenario 3 (Mitigation 1 and 3) Recurrence Interval 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP 0.5% AEP 0.2% AEP Property Damage Total property damages $ 22,900 $ 23,400 $ 25,000 $ 35,590 $ 53,380 $ 90,551 $ 102,941 Inundated properties (> 10cm depth, > 1% area) 44 45 47 49 60 72 77

Building Damage Residential 0 0 0 0 0 2 8 CFA Shed 0 0 0 0 1 1 1 Total buildings with overfloor flooding 0 0 0 0 1 3 9

Residential $ - $ - $ - $ - $ - $ 60,959 $ 346,124 CFA Shed $ - $ - $ - $ - $ 1,000 $ 2,000 $ 3,000 Total overfloor damages $ - $ - $ - $ - $ 1,000 $ 62,959 $ 349,124

Road Damage Major $ - $ 415 $ 17,661 $ 34,234 $ 68,285 $ 83,163 $ 115,553 Minor $ - $ - $ - $ 450 $ 670 $ 2,221 $ 6,277 Total road damages $ - $ 415 $ 17,661 $ 34,684 $ 68,955 $ 85,384 $ 121,830

Total $ 22,900 $ 23,815 $ 42,661 $ 70,274 $ 123,336 $ 238,894 $ 573,895

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In order to determine if the implementation of any of the options is feasible, a net present value (NPV) assessment was undertaken examining the reduction in AAD against the cost to develop the mitigation option and ongoing maintenance costs. It should be noted that for this assessment a discount rate of 7% has been applied. The assumptions for the assessment are shown in Table 9.8.

Table 9.8 Assumptions for the net present value calculations Estimated Estimated Reduction in Design Life Scenario Description capital costs Maintenance AAD ($2012) (years) ($2012) Costs ($2012) Mitigation 1 Old bridge deck removal $ 20,000 $ 0 $ 1,873 - Mitigation 1 & 2 Construction of Levee 1 $ 40,800 $ 500 p.a. $ 2,534 50 Mitigation 1 & 3 Installation of additional culverts $ 225,000 $ 0 $ 2,183 50

The NPV assessment was applied for each of the detailed design runs in turn for the full design life of the asset. For the bridge deck removal no design life was required as no assets were constructed. The NPV assessment has discounted all cash flow back to 2012 dollars. The capital cost is applied in year 0. A cumulative cost / benefit has been determined from the cash flows to determine when, and if, the mitigation options become economically viable. The results are discussed in this section and the detailed calculations are summarised in Appendix E. It should be noted that positive values indicate a cost and negative value indicate a benefit in this assessment.

The results for the detailed design scenario 1 (Mitigation 1 – bridge deck removal) is shown in Figure 9.16. The figure shows that with a discount rate of 7% the payback period for this option is approximately 17 years. After this point the benefits of the removal of the bridge structure outweigh the costs. Based upon this assessment it is recommended that the removal of the bridge deck be undertaken.

Figure 9.16 Detailed design Scenario 1 net present value results

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The results for the detailed design Scenario 2 (Mitigation 1 and 2 – bridge deck removal and levee 1) is shown in Figure 9.17. The graph shows the cumulated cash flows that have been discounted to 2012 dollars over the 50 year design life of the levee. A maintenance cost of $500 per annum has been included to account for the cost of cutting the grass on the levee and undertaking any repair works as necessary. Figure 9.17 indicates that the inclusion of levee 1 is never cash flow positive over the design life of the project. Over the design life of the asset the total cost for Scenario 2 was $ 10,700 (2012 dollars). Although this scenario is not cash flow positive it is a relatively low cost option that could be considered for development for Wickliffe.

Figure 9.17 Detailed design Scenario 2 net present value results

The results for the detailed design Scenario 3 (Mitigation 1 and 3 – bridge deck removal and additional culverts) are shown in Figure 9.18. No maintenance costs have been assumed for the culverts over their design life of 50 years. The capital costs for installing the culverts are very high and this is reflected in the overall costs for the mitigation scenario being at a net cost of $192,700 (2012 dollars) over the design life of the culverts. This mitigation option is very expensive relative to the more effective options of Mitigation 1 and 2. This mitigation scenario is not recommended for development as it is not economically viable.

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Figure 9.18 Detailed design Scenario 3 net present value results

9.6 Recommendations

The mitigation assessment looked at implementing four structural mitigation options and one option of clearing the vegetation from the main floodplain near the township. The assessment examined the 1% AEP design event and the impacts that the mitigation options had on the peak flood levels and flood behaviour. The January 2011 event was also simulated due to the historical context of this flood for Wickliffe.

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10 CONCLUSION The Wickliffe Flood Investigation has examined the Wickliffe floodplain in detail and the findings of this investigation are summarised within this report. The key findings from the investigation include: x Developing background information for understanding the catchment upstream of Wickliffe. x Qualification of the January 2011 flood event. x Developing the design flood events for Wickliffe including the 20%, 10%, 5%, 2%, 1%, 0.5% and 0.2% AEP events and the PMF. x Developing the Victorian Flood Database (VFD) compliant maps. x Developing flood maps for Wickliffe including maps showing depth, water surface elevation, flood contours, velocity, hazard class and flood extents. x Developing possible planning maps for implementation by the Ararat Rural City Council including the Floodway Overlay (FO) and the Land Subject to Inundation (LSIO). These maps have been developed for the pre and post removal of the old Glenelg Highway Bridge decking by VicRoads (planned to be completed prior to July 2013). x Detailed review and recommendations of the Flood Warning System for Wickliffe. x Development of the Municipal Flood Emergency Plan (MFEP) Appendices for use in conjunction with the Victoria SES documentation. x The identification of the high risk areas within Wickliffe and properties that are at risk of overfloor flooding. x Assessment of possible mitigation options and a cost / benefit assessment of these options.

The Wickliffe Flood Investigation had two main objectives, one to provide a detailed set of information for use in the flood planning and preparedness for the Wickliffe community and the second to provide advice on the potential for a future flood warning system for Wickliffe. This report and the development of the MFEP Appendices constitute the primary outputs for the first objective of this study. The recommendations made in Section 8 aim to meet the second objective.

The important thing to note about the flood warning system development for Wickliffe is that the implementation of the recommended system will take a lot of work and cannot be achieved without the drive and collaboration from all of the stakeholders involved. The main stakeholders (the Community, BoM, Glenelg Hopkins CMA, Ararat Rural City Council and VICSES) must work together to implement the recommendations and to improve the flood warning for Wickliffe. It is important that the Community engages with this process and is involved through the development process because, as stated in Section 8 the most common failure of warning systems is the engagement and communication with the Community.

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11 REFERENCES Anderson-Berry, L. (2002): Flood Loss and the Community. In: Smith, D.I & Handmer, J. (Eds), Residential Flood Insurance. The Implications for Floodplain Management Policy. Water Research Foundation of Australia, Canberra.

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