addendum russell creek flood mitigation€¦ · table 2-6 design flows using ar&r 2016, il-23...

Addendum

Russell Creek Flood Mitigation

Russell Creek Flood Mitigation - As Constructed Flood Modelling

Warrnambool City Council

November 2017

Warrnambool City Council | November 2017 Russell Creek Flood Mitigation - As Constructed Flood Modelling

Document Status

Version Doc type Reviewed by Approved by Date issued

1 Draft Ben Hughes Ben Tate 17/03/2017

2 Draft Final Ben Tate Ben Tate 01/09/2017

3 Final Ben Tate Ben Tate 10/11/2017

Project Details

Project Name Russell Creek Flood Mitigation - As Constructed Flood Modelling

Client Warrnambool City Council

Client Project Manager Rohan McKinnon – Justin Hinch

Water Technology Project Manager Johanna Theilemann

Water Technology Project Director Ben Tate

Authors Johanna Theilemann

Document Number 2805_02R02

COPYRIGHT

Water Technology Pty Ltd has produced this document in accordance with instructions from Warrnambool City Council for

their use only. The concepts and information contained in this document are the copyright of Water Technology Pty Ltd.

Use or copying of this document in whole or in part without written permission of Water Technology Pty Ltd constitutes an

infringement of copyright.

Water Technology Pty Ltd does not warrant this document is definitive nor free from error and does not accept liability for

any loss caused, or arising from, reliance upon the information provided herein.

15 Business Park Drive

Notting Hill VIC 3168

Telephone (03) 8526 0800

Fax (03) 9558 9365

ACN 093 377 283

ABN 60 093 377 283


EXECUTIVE SUMMARY Water Technology was engaged by Warrnambool City Council to undertake “as constructed” flood modelling

of Russell Creek through North Warrnambool following the construction of structural flood mitigation works in

2016.

As part of this study the design hydrology for Russell Creek was also updated to conform with the new 2016

release of Australian Rainfall and Runoff: A guide to Flood Estimation (ARR2016). The new design peak flows

produced by this study utilise a combination of approaches suggested in ARR2016, including an ensemble

rainfall temporal pattern approach and a Monte Carlo approach to the RORB rainfall runoff modelling.

The design peak flows have reduced from previous assessments undertaken on Russell Creek. This change

can be attributed to several factors including the changed catchment delineation and routing, updated intensity

frequency duration (IFD) information from the Bureau of Meteorology, revised guidance on selection of

appropriate rainfall losses, and the newly available rainfall temporal patterns.

Location 1% AEP

Cardno Flows (2010)

(m3/s)

1% AEP

Water Technology Flows (2017)

(m3/s)

Aberline Rd 45.0 32.0

Wangoom Rd 18.6 17.3

Mortlake Rd 69.5 59.8

Merri River 76.9 64.9

Updated hydraulic modelling for a range of design events included the 4 constructed flood walls and two new

2.4 x 3.6 m box culverts under Mortlake Road. This modelling confirmed reductions in the extent, depth and

velocity of flooding during the range of design events. There were some notable instances of the flood extent

locally increasing due to the higher grid resolution of the hydraulic modelling using new topographic

information, compared to the previous modelling.

A detailed flood risk assessment of revised flood modelling was undertaken and revealed that the works have

reduced the estimated number of buildings likely to experience above floor flooding. Notably, the number of

properties likely to experience above floor flooding during the 1% AEP flood event has reduced from 146 to14

due to the construction of the flood mitigation works, as shown in the table below.

ARI (1 in X years) 1 in 200 yr 1 in 100 yr 1 in 50 yr 1 in 20 yr 1 in 10 yr 1 in 5 yr

AEP 0.5% 1% 2% 5% 10% 20%

Residential Buildings Flooded Above Floor

21 14 6 1 0 0

Commercial Buildings Flooded Above Floor

6 0 0 0 0 0

Properties Flooded Below Floor

369 205 99 69 57 36

Total Properties Flooded 396 219 105 70 57 36

The construction of the mitigation works sees a significant reduction in the population at risk from flooding

along Russell Creek under all flood events considered. Coupled with awareness programs and appropriate

land use planning this program of works will lead to a safer more resilient community.


CONTENTS

EXECUTIVE SUMMARY 3

1 INTRODUCTION 7

1.1 Overview 7

1.2 Study Area 7

1.3 Available Data 8

1.4 Previous investigations 8

1.4.1 North Warrnambool Flood Study for Merri River and Russell Creek (GHD, 2003) 9

1.4.2 Cardno (2007, 2010, 2012) 9

1.4.3 Design of North Warrnambool Flood Mitigation Works (Water Technology, 2015) 10

1.4.4 Discussion 10

2 HYDROLOGY 11

2.1 Overview 11

2.2 RORB Modelling 11

2.2.1 Model Setup 11

2.2.2 Adopted Design Flood Hydrographs 23

3 RACECOURSE CATCHMENT 25

4 HYDRAULIC MODEL 26

4.1 Overview 26

4.2 Hydraulic Model Schematisation 26

4.2.1 2D Grid Size and Topography 26

4.2.2 Roughness 29

4.2.3 Hydraulic Structures 30

4.2.4 Boundary Condition – Inlet Boundaries 31

4.2.5 Boundary Condition – Outlet Boundaries 31

4.2.6 Flood Walls and Culverts – As Constructed 32

4.2.7 Hydraulic Model Calibration 33

5 DESIGN HYDRAULIC MODELLING 34

6 FLOOD DAMAGES ASSESSMENT 38

6.1 Overview 38

6.2 Current Conditions AAD 38

6.2.1 Non-economic Flood Damages 38

6.2.2 Above Floor Flooding 39

7 SENSITIVITY TESTING 41

7.1 Overview 41

7.2 Climate change scenarios 41

7.2.1 Overview 41


7.3 No Flood Walls 43

7.4 No Mortlake Rd Culverts 43

7.5 Rain on Grid 48

8 CONCLUSION 51

8.1 Overview 51

8.2 Key Outcomes 51

8.3 Recommendations 51

APPENDICES Appendix A AR&R Data hub Output

Appendix B AR&R – Regional Flood Frequency Estimation tool

Appendix C Design Flood Mapping

Appendix D Russell creek structures

LIST OF FIGURES Figure 1-1 Study area 8

Figure 2-1 Russell Creek subareas and reaches 13

Figure 2-2 Russell Creek RORB Fraction impervious map 14

Figure 2-3 Arr 2016 – Recommended Median ILs(mm) (Bk5 Ch3 Fig 5.3.18) 18

Figure 2-4 ARR 2016 – Recommended median cl (mm/hr) 19

Figure 4-1 Creek Cross-section Comparrison 27

Figure 4-2 Model boundary 28

Figure 4-3 Model Topography 28

Figure 4-4 adopted mannings ‘n’ roughness values 29

Figure 4-5 Location of Hydraulic Structures 30

Figure 4-6 Model boundaries 31

Figure 4-7 Flood Wall Locations 32

Figure 4-8 Russell Creek Flood Levee Walls 32

Figure 4-9 Mortlake road flood mitigation culverts 33

Figure 5-1 1% AEP Flood Depth (New existing conditions) 35

Figure 5-2 1% AEP FlooD Depth (New Existing Conditions) 36

Figure 5-3 Comparison of Original and new 1% AEP Flood Depth 37

Figure 6-1 Above floor flooded properties (Red Dots) 39

Figure 7-1 Climate Change rainfall intensity Increase for 1% AEP Event 42

Figure 7-2 1% AEP Flood Depth – No Flood Walls 44

Figure 7-3 1% AEP,12 Hr - Difference Plot – No Walls minus existing 45

Figure 7-4 1% AEP Flood Depth – No Mortlake Road New Culverts 46

Figure 7-5 1% AEP, 12Hr - Difference Plot - No Culverts minus existing 47

Figure 7-6 Warrnambool Pit and Pipe network 48

Figure 7-7 1% AEP Rain of Grid 49


Figure 7-8 10% AEP Rain on Grid 50

Figure 8-1 Russell Creek - RFFE 60

LIST OF TABLES Table 1-1 Design Peak Flows - North Warrnambool Flood Study for Merri River and Russell CreeK 9

Table 1-2 Cardno RORB Continuing losses 9

Table 1-3 RORB Design Flows 10

Table 2-1 Design Rainfall Depth (mm) for storm Frequency and Duration 15

Table 2-2 Regional kc and Loss Parameters 16

Table 2-3 Calculated Kc parameters 16

Table 2-4 ARR 2016 – Range of Values Used in developing ILsPrediction Equations6 18

Table 2-5 ARR 2016 – Range of Values Used in developing CL Prediction Equations6 19

Table 2-6 Design Flows Using AR&R 2016, IL-23 mm, CL-4.6 mm/hr 20

Table 2-7 Design Flows using Original Losses, IL-20 mm, CL-4.6 mm/hr 20

Table 2-8 Comparison of rainfall depths at upstream and downstream ends of Russell Creek catchment 21

Table 2-9 1% AEP Regional Peak Flow Estimate Comparison 22

Table 2-10 1% AEP Peak Flow Comparison between studies 22

Table 2-11 RORB Monte Carlo peak flow output 23

Table 2-12 Final adopted design flow input and peak flow 24

Table 3-1 1% AEP Peak Flows and Critical Duration 25

Table 3-2 10% AEP Peak Flows and Critical Duration 25

Table 4-1 Mannings ‘n’ roughness values 29

Table 4-2 Hydrualic Structures 30

Table 5-1 1% AEP Flood Level Comparison 34

Table 6-1 Depth of above floor flooding 39

Table 6-2 Damages Assesment 40

Table 7-1 Climate change rainfall intensity increase – peak flows 41


1 INTRODUCTION

1.1 Overview

Water Technology was engaged by Warrnambool City Council to update and revise the existing Russell Creek

catchment design hydrology, following the construction of key flood mitigation infrastructure. The hydrology is

a key component to the updated flood modelling. The updated catchment hydrology was used to derive design

inflows for revised hydraulic modelling.

Russell Creek is part of the greater Merri River catchment. The Merri River is gauged at Woodford, while

Russell Creek is ungauged with limited available anecdotal flood height information. Due to the lack of

calibration information, this project developed a RORB model and verified the model results to a range of

regional peak flow estimates and estimates produced during previous investigations. A key objective of the

investigation was to update and revise the flood hydrology for the Russell Creek. This included:

Redefining the catchment characteristics based on existing catchment conditions, including the impact of

urban and industrial land use areas.

Determine appropriate catchment parameters including modelled losses.

Redefine flows at 3 primary inflow locations including Wangoom Road, Aberline Road and the

Warrnambool Racecourse.

After completing the revision in hydrology, a new TUFLOW hydraulic model was created of the study area,

incorporating new Light Detection and Ranging (LiDAR) topography, and the “as constructed” flood mitigation

works.

1.2 Study Area

The study area covered the whole Russell Creek catchment as shown by the green outline in Figure 1-1. The

catchment of the Russell Creek covers an area of 37.5 km2. The area that was flood mapped covers the main

urban reaches of the Russell Creek as shown in red on Figure 1-1.


FIGURE 1-1 STUDY AREA

1.3 Available Data

The investigation utilised several existing datasets available from Warrnambool City Council including:

Topography – Light Detection and Ranging (LiDAR) data

VicMap Coastal DEM 1m resolution (2007) supplied by DELWP

Corrangamite DEM 5m resolution (2008) supplied by DELWP

Warrnambool City Council DEM 1m resolution (2017)

Digital Aerial Photography (2013) supplied by DELWP

Spatial Data – VicMap (2016) supplied by DEWLP

1.4 Previous investigations

Numerous flood investigations have been undertaken on this catchment, including:

North Warrnambool Flood Study for Merri River and Russell Creek (GHD, 2003)

Russell Creek Flood Modelling (Cardno Lawson Treloar, 2007)

Design of North Warrnambool Floodplain Management Plan (Cardno, 2010)

Design of North Warrnambool Floodplain Management Plan – Phase 2 (Cardno, 2012)

Design of North Warrnambool Flood Mitigation Works (Water Technology, 2015)

A summary of each of these investigations is included in the following sections outlining key findings.


1.4.1 North Warrnambool Flood Study for Merri River and Russell Creek (GHD, 2003)

GHD undertook a detailed assessment of the Merri River and Russell Creek utilising an Australian Water

Balance Model (AWBM). This investigation was the first formal analysis of flood flows in Russell Creek. At the

time, residential development was already encroaching on the Russell Creek catchment area. The study

derived peak flows for a range of design floods using AWBM, for input to HecRas and Delft FLS. GHD

calibrated the modelling to observed flood levels along Russell Creek and the Merri River. The estimated peak

flows along Russell Creek are shown in Table 1-1.

TABLE 1-1 DESIGN PEAK FLOWS - NORTH WARRNAMBOOL FLOOD STUDY FOR MERRI RIVER AND RUSSELL CREEK

Design Flood

AEP

Aberline Rd

(m3/s)

Mortlake Rd

(m3/s)

Queens Rd

(m3/s)

Merri River

(m3/s)

20% 6.94 15.05 16.20 17.36

10% 12.73 21.99 23.15 24.31

5% 15.05 25.46 27.78 27.78

2% 26.62 43.98 46.29 47.45

1% 34.72 59.03 62.5 62.5

1.4.2 Cardno (2007, 2010, 2012)

Cardno has undertaken numerous assessments of the Russell Creek floodplain, including the Russell Creek

Flood Modelling (2007), Design of North Warrnambool Floodplain Management Plan – Phase One (2010) and

Phase 2 (2012). During the 2007 study, a RORB model was developed for the Russell Creek catchment as

part of a broader Merri River catchment model, the model was validated at the Merri River at Woodford gauge

(236205) and other available historical flood data. The Russell Creek RORB model was developed based on

a catchment area of 32.7 km2. A total of 17 sub catchments were delineated in the RORB model, the modelled

fraction impervious values were as follows:

Rural land = 0.05

Existing residential areas = 0.52

Proposed residential areas and racecourse = 0.45

The study adopted a constant kc of 6.45, m of 0.8, Initial Losses (IL) of 20 mm, with Continuing Loss (CL)

varying with AEP. Table 1-2 shows the adopted CL values.

TABLE 1-2 CARDNO RORB CONTINUING LOSSES

Design AEP CL (mm/hr)

20% 1.35

10% 1.45

5% 1.79

2% 2.07

1% 2.13


The Cardno flood modelling determined higher peak flows in Warrnambool than the previous GHD

assessment. The determined peak flows across four locations are shown in Table 1-3. These flows were

modelled in the 1D/2D hydraulic modelling program SOBEK, subsequent concept flood mitigation designs

were based on this modelling. The hydrology developed as part of the Cardno investigations was rigorously

reviewed by Erwin Weinmann and Robert Keller through a peer review process at the time. The comments

made by the reviewers were actioned as part of the study delivery and have been considered as part of the

investigation.

TABLE 1-3 RORB DESIGN FLOWS

Design Flow

AEP

Flow at Aberline Rd

(m3/s)

Flow at Wangoom Road

(m3/s)

Flow at Mortlake Road

(m3/s)

Flow at Merri River Confluence

(m3/s)

20% 15.9 7.1 24.7 26.0

10% 20.4 8.9 32.6 34.5

5% 26.3 11.2 42.3 45.8

2% 36.5 15.1 56.3 61.8

1% 45.0 18.6 69.5 76.9

1.4.3 Design of North Warrnambool Flood Mitigation Works (Water Technology, 2015)

The previous Water Technology assessment assisted in the detailed design of flood mitigation structures. The

study utilised hydrology built into the existing SOBEK hydraulic model. These flow boundaries included in the

SOBEK model were based on extracted hydrographs from the Cardno Russell Creek RORB model as provided

by the Warrnambool City Council.

Water Technology did not alter the hydrographs produced by Cardno for use during the detailed design phase

of the mitigation projects, however it was noted that the hydrology was conservative and possibly

overestimated design flows. The SOBEK model only considered the two major inflows at north of Wangoom

Road and Aberline Road. The Racecourse catchment appears as a single sub-catchment draining directly to

Russell Creek and therefore was not included as an inflow boundary in the previous SOBEK modelling.

1.4.4 Discussion

Numerous assessments of Russell Creek have been undertaken in the past 15 years. These assessments all

build on our knowledge and understanding of this catchment. The previous assessments were all based on

best practice methodology at the time of their completion and in some cases, have been peer reviewed by

industry experts. These assessments are a source of comparison for the revised hydrology, which is based on

new techniques for undertaking design hydrology, emerging from the revised version of Australian Rainfall and

Runoff: A Guide to Flood Estimation (2016)1.

1 Ball J, Babister M, Nathan R, Weeks W, Weinmann E, Retallick M, Testoni I, (Editors), 2016, Australian Rainfall and Runoff: A Guide to Flood Estimation, Commonwealth of Australia.


2 HYDROLOGY

2.1 Overview

A hydrologic model of the Russell Creek catchment was developed to determine design flow hydrographs at

several locations within the Russell Creek catchment to be used as inflow boundary conditions in the hydraulic

model. The rainfall-runoff program, RORB, was utilised for this study.

RORB is a non-linear rainfall runoff and streamflow routing model for calculation of flow hydrographs in

drainage and stream networks. The model requires catchments to be divided into subareas, connected by a

series of conceptual reaches and storage areas. Observed or design storm rainfall is input to the centroid of

each subarea. Specific initial and continuing losses are then deducted, and the excess runoff is routed through

the reach network.

The adopted methodology described below is based on current guidelines described in ARR20161. A Monte

Carlo approach was adopted. Monte Carlo is a probabilistic approach whereby a large number of potential

parameter combinations are modelled and probability distributions considered to determine the design flow

AEPs. In this instance 10,000 model runs were simulated, with varying initial losses and temporal patterns, to

produce a probabilistic distribution of design flows. This allowed design peak flows for the range of design

events to be determined. A Monte Carlo approach results in less uncertainty than a traditional deterministic

approach. The final parameters adopted for each design event were based on selecting a combination of

parameters from the simulations which produced the peak flow along all reaches of Russell Creek within the

study area from the Monte Carlo analysis.

The Russell Creek catchment is ungauged, therefore the adopted design flows were validated against a range

of other flow estimate methods including past studies, regional peak flow estimation equations and an existing

RORB model developed as part of previous hydrological assessments.

2.2 RORB Modelling

2.2.1 Model Setup

2.2.1.1 Sub-area and Reach Delineation

Sub-area boundaries and reaches were delineated using ArcHydro and revised as necessary to allow flows to

be extracted at the points of interest. The RORB model was constructed using MiRORB (MapInfo RORB tools),

RORB GUI and RORBWIN V6.23.

Subareas and reaches were delineated based on the provided LiDAR data. Nodes were placed at areas of

interest (to extract flow hydrographs), the centroid of each sub-area and the junction of any two reaches. Nodes

were then connected by RORB reaches, each representing the length, slope and reach type. The RORB model

had 48 sub-areas ranging in area from 9 to 210 ha. The sub-catchment delineation and reach network is shown

in Figure 2-1.

The catchment area of the RORB model is 37.5 km2, this is slightly larger than the previous RORB model. The

new model includes an area of relatively flat rural land to the south east of the creek which had previously

been unaccounted for and a small catchment north of Wangoom Road which is along the crest of the Russell

Creek and Merri River catchments which drain to Russell Creek via an excavated channel. The catchment

area was validated against council own data and local knowledge.


Five different reach types are available in RORB. Reach types were selected based on aerial imagery and site

visits. The reach types were predominately “Natural” in the middle and upper catchment and “excavated and

unlined” or “lined channel or pipe” in the lower catchment.

2.2.1.2 Fraction Impervious

Fraction Impervious (FI) values were calculated using MiRORB. Default sub-area FI values were based on an

assessment of current Warrnambool City Council Planning Scheme Zones (current January 2017), and aerial

imagery. The spatial distribution of the fraction impervious data is shown in Figure 2-2. It can be seen there is

a considerable difference in fraction impervious between the lower urban areas of the catchment and the upper

agricultural areas.

The specified FI value for ‘rural areas’ was modelled at 0 (down from the 0.05 used in the previous modelling),

this is in line with industry best practice.


FIGURE 2-1 RUSSELL CREEK SUBAREAS AND REACHES


FIGURE 2-2 RUSSELL CREEK RORB FRACTION IMPERVIOUS MAP


2.2.1.3 IFD

Design rainfall depths were determined using the 2016 Bureau of Meteorology online IFD tool2. The rainfall

Intensity Frequency Duration (IFD) parameters were generated for a location in the approximate centre of the

Russell Creek catchment (38.375S, 142.5E) and are shown in Table 2-1 below. There are some variations

between the rainfall depths of the new 2016 and the older IFD values. This is further discussed in the previous

Water Technology Detailed Design report. In the frequent events, the IFD rainfall depths have reduced across

the range of storm durations. For the 1% AEP event the IFD rainfall depths have increased between 4-10%

across the range of storm durations.

TABLE 2-1 DESIGN RAINFALL DEPTH (MM) FOR STORM FREQUENCY AND DURATION

EY Annual Exceedance Probability (AEP)

Duration 1EY 50% 20% 10% 5% 2% 1%

1 hour 11.6 13.5 19.8 24.4 29.3 36.1 41.6

2 hour 14.8 17.1 24.8 30.4 36.2 44.2 50.6

3 hour 17.1 19.7 28.5 34.8 41.2 50.2 57.5

6 hour 22 25.3 36.1 44 52 63.8 73.5

12 hour 28.1 32.2 45.7 55.7 66.2 82.1 95.7

24 hour 35.6 40.3 56.6 69.2 83 103.8 122

48 hour 44.3 49.3 67.7 82.8 99.9 124.1 145.2

72 hour 49.9 55.1 74.2 90.1 108.4 133 154.1

96 hour 54.4 59.7 79.2 95.2 113.5 137.6 158

120 hour 58.4 63.8 83.6 99.4 117.1 140.5 160.1

144 hour 62 67.8 87.8 103.2 119.8 142.5 161.6

168 hour 65.6 71.7 92 106.8 122.1 144.4 163

2.2.1.4 Areal Reduction Factors

Areal reduction factors were used to convert point rainfall to areal estimates and are used to account for the

variation of rainfall intensities over a large catchment. AR&R (2016) areal reduction factors were applied to the

catchment area and extracted from the AR&R data hub3. The catchment lies within the Southern Temperate

Zone of aerial reduction factors and these were applied for all design modelling.

2.2.1.5 Regional kc

kc is the primary routing parameter in RORB. As Russell Creek is an ungagged catchment with no streamflow

record, it is not possible to calibrate the RORB model against known catchment flows and rainfall records. As

such, a comparison between regional equation estimates was made against values determined by other

studies in the south-west coastal region. kc values from four nearby calibrated RORB models were compared

2 Bureau of Meterology Web Tool, http://www.bom.gov.au/water/designRainfalls/revised-ifd/?year=2016 3 AR&R 2016 Data Hub, http://data.arr-software.org/


along with the available previous Russell Creek RORB models. Models with similar catchment characteristics

were used with floodplains on or near the southern Victoria coast.

kc has been shown to be related to the average stream length from subarea centroid to catchment outlet. In

order to compare kc values adopted across catchments a ratio of average stream length and kc can be made,

as outlined in Equation 1.

𝑘𝑐 𝑅𝑢𝑠𝑠𝑒𝑙𝑙 𝐶𝑟𝑒𝑒𝑘 = 𝑘𝑐 𝐶𝑎𝑡𝑐ℎ𝑚𝑒𝑛𝑡

𝐷𝑎𝑣 𝐶𝑎𝑡𝑐ℎ𝑚𝑒𝑛𝑡

× 𝐷𝑎𝑣 𝑅𝑢𝑠𝑠𝑒𝑙𝑙 𝐶𝑟𝑒𝑒𝑘

Equation 1 kc comparison scaling

Where:

kc Russell Creek kc parameter for Russell Creek catchment

kc Catchment kc parameter for regional catchment

Dav Russell Creek Average distance from centroid of subarea to model outlet (Russell Creek)

Dav Catchment Average distance from centroid of subarea to model outlet (regional catchment)

Table 2-2 shows the adjusted kc values as well as the adopted loss values. It should be noted that the Surry River catchment results were not considered due to unique catchment characteristics as noted by the relatively high kc to Dav ratio and low losses. The new Russell Creek RORB model has a Dav of 9.29.

TABLE 2-2 REGIONAL KC AND LOSS PARAMETERS

Location kc m Dav IL CL Russell Creek

Adjusted kc

Merri River 58 0.8 64.24 20.0 2.13 8.38

Moyne River 46 0.8 31.06 15.0 1.3 13.75

Surry River 75 0.8 20.42 4 1.3 34.12*

Wattle Hill Creek 12.5 0.8 12.27 15 2 9.46

Fitzroy River/Darlot Creek 55 0.8 54.76 20 2 9.33

* To be ignored due to the skewed results from unique catchment characteristics

The adjusted kc parameters range between 8.38 to 13.75 (discounting the Surry River model as mentioned

above). The original GHD (2003) model used a kc value of 4.5. The model was revised and updated by Cardno

(2010), and used regional equations based on the calibrated Merri River model, and determined a kc of 6.45.

Several kc estimation equations are available within the RORB software, the range of equations and their

respective determined kc values are shown in Table 2-3.

TABLE 2-3 CALCULATED KC PARAMETERS

kc Equations kc

Default RORB Eqn. 13.48

Victoria data (Pearse et al, 2002) 11.62

Aust Wide Dyer (1994) (Pearce et al) 10.60

Victoria Mean Annual Rainfall > 800mm 13.14

Victoria – Mean Annual Rainfall < 800mm 5.17


A number of sensitivity tests were undertaken varying the modelled kc value within the 8.38 to 13.75 range,

and a kc of 8.38 was adopted. This is due to the close relationship between the Merri River and the Russell

Creek. Furthermore raising kc towards the higher end of the estimates resulted in dramatically lower peak

flows than all of the previous validated hydrologic assessments. Adopting a kc of 8.38 was justified given the

kc fell within the range of the various regional approximations and donor catchments, and it provided flows that

were relatively consistent with past studies. The kc value adopted for the Russell Creek model was based on

previously modelled values and scaling using the Kc:Dav ratio of the calibrated Merri River model. This Kc is

entirely reasonable, sits well within the range of acceptable Kc values, and is comparable to the previous

modelling by Cardno. This will be further validated in later sections of this report when comparing adopted and

previous design flows.

2.2.1.6 Routing Parameter - m

The RORB m value is typically set at 0.8. This value remains unchanged and is an acceptable value for the

degree of non-linearity of catchment response (Australian Rainfall and Runoff, 1987). It is rare to vary the m

value and there were no reasons to do so in this study, particularly given the lack of calibration data.

2.2.1.7 Temporal Patterns

Temporal patterns from AR&R (2016) were utilised in the analysis and extracted from the AR&R data hubError!

Bookmark not defined.. As previously described a Monte Carlo approach was adopted in RORB and the full ensemble

of temporal patterns were included within the Monte Carlo simulation. The range of temporal patterns are

included in Appendix A, with relevant ID numbers assigned as referred to in the RORB model output. The

Southern Slopes (Vic/NSW) Zone of temporal patterns was utilised.

The AR&R (2016) approach using Monte Carlo analysis with various temporal patterns allows for exhibited

variability in rainfall events of similar magnitude. The new temporal patterns are based on historical storms

using the extensive network of pluviograph data collected by the Bureau of Meteorology (BoM).

The AR&R (2016) design temporal patterns are broken into a number of AEP groupings and the subsequent

suitable AEP range for application, these include:

Very Rare – Rarest 10 within region

Rare – Suitable AEP range 3.2% AEP and rarer

Intermediate – Suitable for AEP range 3.2% - 14.4%

Frequent – Suitable for AEP range more frequent than 14.4%

Previous assessments using the earlier ARR (1987) used a single temporal pattern across all design events. The ARR (2016) approach recommends that at least 10 temporal patterns be used for each event. These 10 temporal patterns change depending on the duration and the event considered.

2.2.1.8 Design Losses

Design losses were estimated by using several methods including use of the new AR&R datahub tool3, the

guidance provided in Book 5 Chapter 3 of ARR (2016), the design loss prediction equations developed by Hill

et al (1998)4 and Hill et al (2014)5, and previous investigations. The estimated losses produced by the

recommended methods in AR&R (1987) are lower for both IL and CL, which would produce higher peak flow

4 Hill, P., Mein, R. and Siriwardena, L. (1998) How much rainfall becomes runoff? Loss modelling for flood estimation. Cooperative Research Centre for Catchment Hydrology 5 Hill, P. I., Graszkiewicz, Z., Taylor, M. and Nathan, R. J. (2014) Loss models for catchment simulation. State 4 Analysis of rural catchments. May 2014. ARR Revision project


estimates than when using losses following ARR (2016) guidance. Book 5, Chapter 3 of the new Australian

Rainfall and Runoff provides guidance on the application of losses at a regional level. Figure 2-3 shows the

mapped recommended median storm ILs in mm. The ILs map indicates that 30 mm is a recommended median

ILs in the study area. The Region 3 prediction equations shown in Table 2-4 indicate the median initial loss at

27.5 mm.

FIGURE 2-3 ARR 2016 – RECOMMENDED MEDIAN ILS(MM)6 (BK5 CH3 FIG 5.3.18)

TABLE 2-4 ARR 2016 – RANGE OF VALUES USED IN DEVELOPING ILSPREDICTION EQUATIONS6

Region N Equation Parameter Min Max Median

Region 3 11 5.5.10

SOLPAWHC 0.9 15.9 3.0

DES_RAIN_24HR 106.1 238.9 137.7

ILs 17.0 47.0 27.5

For application in the design rainfall runoff modelling the storm ILs was adjusted to be consistent with the

application of burst rainfall as no preburst rainfall was added to the IFD design rainfall depths. The ARR (2016)

6 AR&R (2016), Ball J, Babister M, Nathan R, Weeks W, Weinmann E, Retallick M, Testoni I, (Editors) Australian

Rainfall and Runoff: A Guide to Flood Estimation, © Commonwealth of Australia (Geoscience Australia), 2016.


data hub provides information relating to pre-burst rainfall depths for the range of design storms. At this location

pre-burst depth ranges from between 1 to 3.8 mm for the 6 hour storm to between 0.8 and 5.4 mm for the 12

hour storm. Given that an ILs of 27.5 to 30 mm is reasonably high a preburst depth of 5 mm was subtracted

from the storm ILs giving the final burst ILb of between 22.5 to 25 mm. Sensitivity testing was performed with

an IL of 20 and 25 mm/hr. Given that the design flows were lower than those estimated from previous studies

it was felt that a degree of conservatism was required and an IL of 20 mm/hr was adopted.

The continuing loss in Figure 2-4 from Book 5 Chapter 3 of ARR (2016) provides a recommended median CL

of 6 mm/hr. The median continuing loss devised from the prediction equation for Region 3 in Table 2-5 shown

below is 3.1 mm/hr.

FIGURE 2-4 ARR 2016 – RECOMMENDED MEDIAN CL (MM/HR)

TABLE 2-5 ARR 2016 – RANGE OF VALUES USED IN DEVELOPING CL PREDICTION EQUATIONS6

Region N Equation Parameter Min Max Median

Region 3 11 5.5.11

DES_RAIN_24HR 1.6.1 128.9 137.7

S0max 17.5 62.8 42.6

CL 0.5 6 3.1

The continuing loss needs to be adjusted according to the RORB model timestep, as per the Figure 5.3.29

from Book 5 Chapter 3 of ARR (2016). A factor of 1.5 is recommended for RORB models with a 5 min timestep.

This resulted in a CL of 4.6 mm/hr to be adopted for RORB design modelling.


The above losses were applied within the RORB Monte Carlo simulation. The CL was set at 4.6 mm/hr for all

scenarios, with the IL sampled using the median IL of 20 mm and the statistical distribution provided within

ARR (2016) and the RORB manual. Extensive sensitivity testing was performed, comparing flows to previous

estimates, see the following section. On balance, the above adopted loss values were felt to provide

reasonable design flow estimates.

2.2.1.9 RORB Model Losses Sensitivity Test

Table 2-6 shows design peak flows and event critical durations using a Monte Carlo simulation, for a median

IL slightly higher than the final adopted median IL shown in Table 2-7. As shown, the change in median IL

does alter the design peak flows, but they are not overly sensitive. Given that the catchment is ungauged,

either of the median IL values could be adopted, as they are both reasonable, but given that the design flows

are lower than that adopted previously, it was decided that the lower median IL value of 20 mm would be

adopted.

TABLE 2-6 DESIGN FLOWS USING AR&R 2016, IL-23 MM, CL-4.6 MM/HR

Location AR&R 2016 – VIC Losses - kc 8.38, IL 23 mm (median), CL4.6 mm/hr

20% AEP 10%AEP 5% AEP 2% AEP 1% AEP

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Aberline Rd 3.37 6hr 7.50 6hr 13.01 3hr 21.60 6hr 30.29 6hr

Wangoom Rd 1.87 6hr 4.28 6hr 7.44 3hr 12.35 3hr 16.73 3hr

Racecourse 6.70 1hr 9.31 1hr 12.85 1hr 17.79 2hr 21.67 1hr

Mortlake Rd 10.60 2hr 17.92 3hr 28.14 3hr 43.79 3hr 57.55 3hr

Merri River 12.72 2hr 20.97 3hr 31.38 3hr 47.78 3hr 62.88 12hr

TABLE 2-7 DESIGN FLOWS USING ORIGINAL LOSSES, IL-20 MM, CL-4.6 MM/HR

Location AR&R 2016 – VIC Losses - kc 8.38, IL 20 mm (median), CL4.6 mm/hr

20% AEP 10%AEP 5% AEP 2% AEP 1% AEP

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Aberline Rd 4.18 3hr 8.79 6hr 14.18 6hr 22.98 6hr 32.01 6hr

Wangoom Rd 2.27 3hr 5.02 6hr 8.31 2hr 13.22 2hr 17.34 3hr

Racecourse 6.91 1hr 10.09 1hr 13.51 1hr 18.72 2hr 22.73 2hr

Mortlake Rd 11.95 2hr 20.47 2hr 31.24 2hr 47.63 2hr 59.83 6hr

Merri River 14.19 3hr 23.03 2hr 34.35 2hr 50.94 2hr 64.94 6h

A comparison of the Cardno adopted 2.5 mm/hr continuing loss and the adopted 4.6 mm/hr was also

undertaken. The results of the assessment show an increase in peak flows across the various inflow locations

for the lower continuing loss. For the 1% AEP flood event peak flows at the Aberline Road and Wangoom

Road inflow locations reduce 15-20% with the adoption of the higher continuing loss value.


2.2.1.10 Spatial Patterns

An analysis of design rainfall was made across the Russell Creek catchment to determine if a non-uniform

spatial pattern should be utilised. The AR&R (2016)6 guidelines recommend that for catchment areas of more

than 20 km2 non-uniform spatial patterns should be considered. Gridded rainfall data is not yet available on

the BoM IFD website7 however a comparison was undertaken of the variation in rainfall depths between two

points at the upper and lower ends of the catchment.

TABLE 2-8 below shows a comparison of design rainfall between the upper and lower ends of the Russell

Creek catchment for the critical duration events. The difference in rainfall is minor at generally less than 1% in

the 1 hour and less than 2.5% in the 6 and 12 hour duration events. Based on this analysis it was deemed

appropriate to adopt a uniform rainfall pattern for the design modelling.

TABLE 2-8 COMPARISON OF RAINFALL DEPTHS AT UPSTREAM AND DOWNSTREAM ENDS OF RUSSELL CREEK CATCHMENT

Duration 10% AEP event 1% AEP event

Downstream (mm)

Upstream (mm)

Difference (mm)

Downstream (mm)

Upstream (mm)

Difference (mm)

1hr 24.5 24.7 0.2 42.0 42.2 0.2

6hr 43.3 44.3 1.0 72.7 73.9 1.2

12hr 54.6 55.9 1.3 94.2 95.7 1.5

2.2.1.11 Flow Verification

A number of area based regional peak flow estimation equations were used to calculate the Russell Creek

peak flow for comparison with the new RORB outputs, as shown in Table 2-9.

These estimation methods were applied for the whole of catchment and the primary inflow locations for the

hydraulic modelling, these include Mortlake Road, Aberline Road and the Racecourse. Whilst the result below

show both RORB outputs to have higher design flows than a number of the estimation methods, it is important

to note that the confidence limits associated with these methods are general +/-30 to 50%.

The Vic Roads Rational Method does produce similar results to the new adopted flows using the AR&R (2016)

RORB approach at the Aberline and Wangoom Road inflow locations. Based on the similarity of the output

results from both RORB models and in line with current best practice recommendations to use the information

available in the AR&R data hub, the RORB model design flow produced using the AR&R (2016) losses and

data hub outputs will be adopted.

7 Bureau of Meterology (2017), www.bom.gov.au

http://www.bom.gov.au/


TABLE 2-9 1% AEP REGIONAL PEAK FLOW ESTIMATE COMPARISON

Location

Catchment Area

Rational Method

(m3/s)

Vic Roads Method

(m3/s)

Hydrologic Recipes –

Rural Estimate

(m3/s)

AR&R

RFFE Tool

(m3/s)

Cardno

(2010) Output

(m3/s)

New RORB

Original Losses

(Cardno)

(m3/s)

New RORB AR&R 2016

Adopted Flow

(m3/s)

Merri River Confluence

37.5 km2 33.1 39.3 74.2 17.5 76.9 78.8 64.9

Wangoom Road

7.7 km2 11.5 19.7 22.2 NA 18.6 20.5 17.3

Aberline Road

21.5 km2 22.9 32.6 48.5 NA 45 40.4 32.0

Racecourse

2.7 km2 5.7 11.3 22.2 * NA NA 25.34 22.7

• The urban racecourse catchment used the Urban Estimate equation from the Hydrologic Recipes: Estimation Techniques in

Australian Hydrology (Grayson, 1996)

2.2.1.12 Comparison to Previous Estimates

Comparison of peak flow estimates between this study and those produced during the previous study by

Cardno (2010) are shown in Table 2-10. The variation in flows ranges between 7 - 29% in comparison to the

previous results.

There are several factors which have contributed to the variation between the old and new RORB peak flow

results. These include a change in method in accordance with AR&R (2016); specifically, a change in IFD

rainfall depths and design losses, rainfall temporal patterns, and changes in the catchment area and subarea

delineation (particularly in the Racecourse catchment). Further to this, the RORB parameter kc used in the

models is also different.

TABLE 2-10 1% AEP PEAK FLOW COMPARISON BETWEEN STUDIES

Cardno Flows (2010)

(m3/s)

Water Technology Flows (2017)

(m3/s)

Difference

Aberline Rd 45.0 32.0 - 29%

Wangoom Rd 18.6 17.3 - 7%

Mortlake Rd 69.5 59.8 - 14%

Merri River 76.9 64.9 - 15%

Water Technology acknowledge that the flows produced at Aberline road particularly, show a significant

variation to those from the previous RORB modelling. This has resulted due to that significant changes in the

model set up and how flows have been routed through the new model. The number of reaches and sub-

catchments has been increased from the previous modelling. Furthermore use of the new ARR temporal

patterns and loss parameters has also contributed to this.


2.2.2 Adopted Design Flood Hydrographs

Flows on the Russell Creek were extracted from the simulated Monte Carlo analysis using the new ARR (2016)

approach described earlier. Flows were extracted at Aberline Road, Wangoom Road, Racecourse Outlet,

Mortlake Road and the confluence with the Merri River.

The flows shown in Table 2-11 were adopted for this project, with the full hydrographs extracted and modelled

in the new TUFLOW model. The Monte-Carlo assessment produces an array of results varying the temporal

pattern and loss values to produce a probabilistic distribution of design flows. Which then enables peak flows

for a range of design events to be determined using a flood frequency analysis on the simulated results. The

final adopted design peak flows for the critical storm durations are provided in Table 2-11.

The storm durations of 1, 3, 6, 12 and 24 hours were selected for modelling in the TUFLOW model. The longer

duration events were included because of the numerous structures which cross Russell Creek attenuating

volume making these events important to consider. In this case, sometimes the peak flood level is driven by

longer duration storm events, and these should be considered in the hydraulic modelling as well as the shorter

duration peak flow events. For each AEP and duration a scenario from the Monte Carlo analysis was selected

that produced peak flows as close as possible to the Monte Carlo analysis design peak flow. This scenario

was then run in the hydraulic model. Each scenario has a slightly different combination of temporal pattern,

and initial loss. The scenarios selected for each design flood AEP and duration event combination are

summarised in Table 2-12.

Whilst the 2 hour event is shown to be critical in some locations within the RORB modelling it is important to

note that the peak flows of either the 1 hour or 3 hour were within 0.5 m3/s and therefore it was decided that

in order to provide a good spread of durations whilst keeping the number of model runs to a manageable

number, it was appropriate to adopt the 1, 3, 6, 12 and 24 hour storm durations.

It is important to note that the Russell Creek model is considered uncalibrated due to the ungauged nature of

the catchment and a level of uncertainty is inherent in the catchment modelling for ungauged catchments.

TABLE 2-11 RORB MONTE CARLO PEAK FLOW OUTPUT

Location AR&R 2016 – VIC Losses - kc 8.38, IL 20mm (mean), CL24.6mm/hr

20% AEP 10%AEP 5% AEP 2% AEP 1% AEP 0.5%

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow

m3/s

Critical

Duration

Flow m3/s

Critical Duration

Aberline Rd

4.18 3hr 8.79 6hr 14.18 6hr 22.98 6hr 32.01 6hr 41.43 12hr

Wangoom Rd

2.27 3hr 5.02 6hr 8.31 2hr 13.22 2hr 17.34 3hr 21.82 3hr

Racecourse 6.91 1hr 10.09 1hr 13.51 1hr 18.72 2hr 22.73 2hr 27.46 1hr

Mortlake Rd

11.95 2hr 20.47 2hr 31.24 2hr 47.63 2hr 59.83 6hr 77.56 12hr

Merri River 14.19 3hr 23.03 2hr 34.35 2hr 50.94 2hr 64.94 6h 84.73 12 hr


TABLE 2-12 FINAL ADOPTED DESIGN FLOW INPUT AND PEAK FLOW

Design Event AEP

Duration Rainfall Depth (mm)

TPat IL Aberline Inflow (m3/s)

Wangoom Inflow (m3/s)

RC Inflow (m3/s)

20%

1 12.3 10 9.4 2.42 1.32 6.79

3 19.5 9 10.6 4.29 2.28 4.98

6 25.4 9 15.4 3.70 2.17 4.04

12 39.6 8 25.4 2.95 1.56 2.96

24 44.5 7 28.4 0.97 0.46 1.38

10%

1 25.7 12 17.8 6.3 3.77 10.03

3 31.7 12 12.8 8.67 4.84 7.66

6 53.4 17 32 8.86 5.09 6.36

12 61.4 20 44.2 6.31 3.44 4.5

24 71.4 19 4.2 2.77 1.44 2.09

5%

1 22.7 13 9.4 11.04 6.18 13.48

3 30.6 12 5.2 13.98 8.45 10.67

6 48 11 15.8 13.96 7.55 8.90

12 60 19 26.8 11.33 6.19 5.72

24 84.8 12 14.4 4.88 2.64 2.92

2%

1 40.9 22 23 18.43 10.33 18.72

3 45.8 22 12.6 22.03 12.59 13.21

6 78.7 24 38.2 22.8 12.87 10.92

12 77.4 22 17.2 20.78 11.61 8.95

24 91.1 25 27.8 12.73 6.52 5.12

1%

1 34.3 26 10.8 24.71 14.92 22.12

3 52.1 29 17.8 29.17 17.24 15.95

6 65.8 23 17.4 31.54 16.83 16.12

12 92.8 22 16 31.22 16.10 11.03

24 119.7 26 22.6 18.79 9.57 6.13

0.5%

1 48.5 24 23.2 30.04 17.22 27.52

3 74.9 28 39.4 37.47 21.42 20.72

6 75.4 23 18.6 41.27 21.15 19.04

12 117.8 22 32 41.04 22.69 14.72

24 130.7 30 6.8 27.22 13.37 9.33

• Rainfall depths shown correspond to the storm AEP which produced the peak flow at the respective inflow

location. This may not directly correspond with the streamflow AEP, as in many cases 1% storms do not result

in 1% floods.


3 RACECOURSE CATCHMENT The racecourse catchment, south of Russell Creek has been the source of a number of drainage issues in the

past with frequent nuisance inundation over Moore Street following heavy rainfall events. Following the

expansion of the Warrnambool urban and industrial development areas to the east, additional drainage

pressure has been placed on this and neighbouring catchment areas. In addition to the existing pressure on

drainage infrastructure in this location are the issues around the functionality and capacity of the Simpson

Street drain which discharges overland flows east of the racecourse to the Hopkins River. In consideration of

future changes to natural drainage patterns in this area, assessment of retardation requirements from this

catchment are required to ensure that flooding on Russell Creek is not adversely impacted.

Based on the adopted design flows from the existing conditions of the Racecourse catchment, maximum peak

flow outputs can be set to ensure future diversion of drainage, and treatments and retardation of existing

stormwater is appropriately managed. In determining peak flow values at this location consideration must be

given to the critical duration of the peak flows in both the Racecourse catchment and the main Russell Creek

reaches downstream of the point of discharge. The Racecourse catchment is shown to have a critical duration

of 1 hour under all events, with the Mortlake Road location, immediately downstream of the point where the

Racecourse catchment discharges into the Russell Creek, having a critical duration of 6 hours during the 1%

AEP event and 2 hours in the 10% AEP event. The Mortlake Road peak flow does not change significantly

across the 2 to 6 hour duration events.

TABLE 3-1 1% AEP PEAK FLOWS AND CRITICAL DURATION

Duration 1Hr 2Hr 3Hr 6Hr 12Hr 24Hr

Racecourse 22.56 22.73 16.83 15.61 11.71 6.7

Mortlake Road 53.3 59.38 59.49 59.83 58.11 35.44

TABLE 3-2 10% AEP PEAK FLOWS AND CRITICAL DURATION

Duration 1Hr 2Hr 3Hr 6Hr 12Hr 24Hr

Racecourse 10.09 9.07 7.61 6.18 4.32 2.12

Mortlake Road 18.08 20.47 19.9 19.3 13.69 6.81

The flows generated at the Racecourse as part of the new hydrology assessment, as shown above, have been included in the revised flood mapping.


4 HYDRAULIC MODEL

4.1 Overview

A new hydraulic model was constructed of Russell Creek through North Warrnambool using TUFLOW. This

allows the model to be used for a variety of purposes by a wider number of organisations. The old hydraulic

model was developed in Sobek, which is used by only a small number of consultants.

A detailed combined 1D2D hydraulic modelling approach was adopted for this study. The hydraulic modelling

approach consisted of the following components:

One dimensional (1D) hydraulic model of key waterways cross-sections, key drainage and hydraulic

structures;

Two dimensional (2D) hydraulic model of the broader floodplain; and

Linked one and two dimensional hydraulic model to accurately model the interaction between in bank

flows (1D) and overland floodplain flows (2D).

The hydraulic modelling suite, TUFLOW, was used in this study. TUFLOW is a widely used hydraulic model

that is suitable for the analysis of riverine floodplains and overland flows in urban areas. TUFLOW has four

main inputs:

Topography and drainage infrastructure data;

Inflow data (based on catchment hydrology);

Roughness; and,

Boundary conditions.

This section defines the scope of the hydraulic analysis, details the hydraulic model construction, and

discusses the hydraulic model calibration.

4.2 Hydraulic Model Schematisation

The TUFLOW model was constructed using MapInfo V11.0 and text editing software. This section details key

elements and parameters of the TUFLOW model which utilises best practice as described in AR&R (2016)

Book 6, the Melbourne Water 2D Modelling Guidelines, and elements of the TUFLOW User Manual.

The double precision version of the latest TUFLOW release was used for all simulations (TUFLOW Version:

2016-03-AD). Hydraulic model timesteps of 1s and 0.5s respectively were adopted for the 2D and 1D elements.

4.2.1 2D Grid Size and Topography

A single-domain approach was utilised to ensure the small areas of interest were modelled at an appropriate

scale, while achieving practical model run-times. A relatively fine grid size of 3 m was selected for the

Warrnambool Russell Creek area to ensure the urban area and narrow creek corridor could be accurately

represented and mapped. The 2D model extents are shown below in Figure 4-2.

The model topography adopted was based on the new Warrnambool Lidar. This data was collected on the 27th

of February 2017. The DEM grid resolution is 1m with a horizontal accuracy of 0.15 m and a vertical accuracy

of 0.1 m. The new topography was compared to existing available lidar and cross-sectional data and the main

channel of the Russell Creek immediately downstream of Wares Road to Daltons Road was checked and the

creek centreline added to ensure the lowest points in the lidar (representing the channel) was picked up in the


model. This ensured that the low flow channel of Russell Creek, where the channel is only 1-2 grid cells wide

was accurately represented.

An assessment of the topography around and within the creek was undertake as part of the model

development. Whilst we appreciate that the creek is relatively narrow in some areas 1-2 grid cells wide the use

of new accurate lidar and zlines has ensured that the creek is well represented. The lidar and the 2d model

check z file was compared at numerous locations within the model in order to ensure that the creek was well

represented. It is important to note that the capacity of the creek is exceeded early in the significant flood

events. The following cross-sections show a comparison of the 2d check z file and the Warrnambool lidar set

at three locations along the creek

FIGURE 4-1 CREEK CROSS-SECTION COMPARRISON

The adopted model topography is shown in Figure 4-3.


FIGURE 4-2 MODEL BOUNDARY

FIGURE 4-3 MODEL TOPOGRAPHY


4.2.2 Roughness

The 2D model roughness values were produced based on Land Use Zones, with further refinement using

aerial photographs and site visits. The final adopted Manning’s ‘n’ roughness values are listed in Table 4-1

and shown graphically in Figure 4-4.

TABLE 4-1 MANNINGS ‘N’ ROUGHNESS VALUES

Land Use Manning’s n Roughness Coefficient

Residential zones 0.30

Agricultural / Rural / Pasture 0.04

Low Density Residential 0.15

Paved Roads 0.02

Medium Density Vegetation 0.04

Vegetated Riparian Area 0.05

Vegetated Waterway Channel 0.1

FIGURE 4-4 ADOPTED MANNINGS ‘N’ ROUGHNESS VALUES


4.2.3 Hydraulic Structures

Twenty waterway structures were included in the hydraulic model. These consisted of a range of bridges and

culvert crossings. Information relating to the size and inverts of the respective structures was obtained from

detailed plans and survey undertaken up Warrnambool City Council. A list of the locations of the included

structures is shown in Table 4-2 and the locations of these structures is shown in Figure 4-5. Information

including the type and size of these structures is included in Appendix D.

TABLE 4-2 HYDRUALIC STRUCTURES

Location

Ians Road Moonah Drive Pedestrian Crossing

Wagoom Road Oak Court Pedestrian Crossing

Aberline Road Upstream Mortlake Road Pedestrian Crossing

Whites Road (West Crossing) Mortlake Road Culverts (Original)

Whites Road (East Crossing) Mortlake Road Culverts (New)

Whites Road Pedestrian Crossing Downstream Mortlake Road Pedestrian Crossing

Wares Road Queens Street

Renior Pedestrian Crossing St Joseph’s Primary Pedestrian Crossing

Upstream Garden Street Footbridge Bromfield Street

Garden Street Daltons Road

FIGURE 4-5 LOCATION OF HYDRAULIC STRUCTURES


4.2.4 Boundary Condition – Inlet Boundaries

One of the principal considerations in constructing the model was the location of inflow boundaries to ensure

all runoff from the catchment was being adequately represented in the modelling. The model boundaries for

the Russell Creek model included the Northern and Eastern Arms of the Creek along with an inflow location

from the Warrnambool Racecourse catchment. The inflows from the northern and eastern arms of Russell

Creek are the main contributors to peak flows within the study area and were determined by the RORB model.

Additional flows from the RORB model from the local urban catchment downstream of the hydraulic model

boundaries were also included as SA boundaries within the creek.

4.2.5 Boundary Condition – Outlet Boundaries

A 2D height flowrate (HQ) boundary was used at the downstream model boundary to convey Russell Creek

flows from the model. HQ boundaries are a commonly used boundary type in TUFLOW which compute a water

level based on the flow and topography slope at the boundary.

The hydraulic model boundaries are shown in Figure 4-6.

An additional outlet boundary was included to the north-west of Wangoom Road where during initial test runs

it was established that in extreme flow events the water banking up behind Wangoom Road and spilling to the

Merri River via a low point in the topography south of Conheadys Road.

FIGURE 4-6 MODEL BOUNDARIES


4.2.6 Flood Walls and Culverts – As Constructed

The flood walls were represented in the model as z lines which used the as constructed height of the walls to

represent the structures. The walls were represented as closed structures, assuming the drop boards were in

place at the locations of the various openings within the levee. The locations of the various flood walls are

shown in Figure 4-7 below and photographs of 2 sections of the walls shown in Figure 4-8.

FIGURE 4-7 FLOOD WALL LOCATIONS

FIGURE 4-8 RUSSELL CREEK FLOOD LEVEE WALLS


FIGURE 4-9 MORTLAKE ROAD FLOOD MITIGATION CULVERTS

The mitigation works also included the construction of two 2.4 x 3.6 m box culverts at Mortlake Road, pictured

above. The previous culvert under Mortlake Road has also been upgraded, with the walkway cut out to

maximise the capacity. These new structures were included in the model as 1D structures.

4.2.7 Hydraulic Model Calibration

It is important to note that given the ungauged nature of this catchment and the scope of works for this

modelling, calibration of Russell Creek was not possible. Whilst little information is available regarding the flow

and flood extent of historical and recent flooding events it is hoped that as part of proposed future works,

additional information relating to the creek flows, height and extent coupled with accurate rainfall data will

enable accurate calibration of the developed model.

The model was run with the previous hydrology and the model was validated to the previous model results,

with particular attention paid to the headloss across the major road crossings. The head loss parameters were

chosen to produce very similar head loss across Garden Street and Mortlake Road as compared to the

previous Sobek model.


5 DESIGN HYDRAULIC MODELLING Design hydraulic modelling was completed adopting the hydraulic model roughness values, hydraulic

structures and boundary conditions shown in the previous section. Modelling was completed for the full suite

of design events including the 20%, 10%, 5%, 2%, 1% and 0.5% AEP events. Storm durations including the

1, 3, 6, 12 and 24 hour were modelled for each design event. The results of the 5 duration events were

combined for each AEP design event to provide a maximum water surface elevation, depth, velocity and

hazard output.

Figure 5-1 and Figure 5-2 show the new flood depth and extents for the 1% AEP flood event. Flood depth

mapping for the range of design events are presented in Appendix C. A comparison of the original and new

flood mapping shows reductions in flood depth and extent within the Russell Creek corridor as shown in

Figure 5-3. A comparison of the modelled 1% AEP flood levels at locations along the creek corridor are shown

in Table 5-1

TABLE 5-1 1% AEP FLOOD LEVEL COMPARISON

Wangoom Rd

Aberline Rd

Whites Rd

Garden St

La Bella Crt

US Mortlake Rd

DS Mortlake Rd

Queens Road

Pre Construction – Existing Conditions – WSE (mAHD) (SOBEK)

34.34 22.27 19.14 12.7 9.9 9.469 7.91 5.37

New Existing Condition –

WSE (mAHD) (TUFLOW)

34.43 22.37 19.15 12.48 9.54 8.74 7.54 4.97


FIGURE 5-1 1% AEP FLOOD DEPTH (NEW EXISTING CONDITIONS)


FIGURE 5-2 1% AEP FLOOD DEPTH (NEW EXISTING CONDITIONS)


FIGURE 5-3 COMPARISON OF ORIGINAL AND NEW 1% AEP FLOOD DEPTH


6 FLOOD DAMAGES ASSESSMENT

6.1 Overview

A flood damage assessment for the study area was undertaken using the range of design events modelled

(20%, 10%, 5%, 2%, 1%, 0.5%, 0.2% AEP design events) for existing conditions. Existing conditions includes

the as constructed flood mitigation works. The damage assessment was used to determine the monetary flood

damage for the design floods in the North Warrnambool study area.

Water Technology has developed an industry best practice flood damage assessment methodology that has

been utilised for many studies in Victoria, The NSW Office of Environment and Heritage stage damage curves

are utilised, which represent far superior damage estimates at low depths above floor and below floor than

earlier stage damage curves used in Victoria. Recent advice from the insurance industry is that these damage

curves may still underestimate the damage, so it is likely that these damage estimates are a lower bound of

that which would be incurred during a real flood, but it is the best damage data available at present. Water

Technology utilises WaterRide to undertake the property inspections and apply the appropriate stage damage

curves.

The model results for all mapped flood events were processed to calculate the numbers and locations of

properties affected. This included properties with buildings inundated above floor, properties with buildings

inundated below floor and properties where the building was not impacted but the grounds of the property

were. In addition to the flood affected properties, lengths and damages of flood affected roads for each event

were also calculated.

The Average Annual Damage (AAD) was determined as part of the flood damage assessment. The AAD is a

measure of the flood damage per year averaged over an extended period. This is effectively a measure of the

amount of money that must be put aside each year in readiness for when a flood may happen in the future.

6.2 Current Conditions AAD

The flood damage assessment for existing conditions, with as constructed flood mitigation works, is shown

below in Table 6-2. The Average Annual Damages (AAD) for existing conditions is estimated at approximately

$69,571. The AAD determined as part of this assessment is showing results which are significantly lower than

previous assessments for the mitigation works. The previous existing conditions modelling determine a AAD

of $491,783, demonstrating a reduction in the AAD of $422,212. This significant reduction is also reflected in

the number of above floor flooded properties During the 1% AEP flood event the number of properties expected

to be flooded above floor has reduced from 146 to 14.

6.2.1 Non-economic Flood Damages

The previous discussion relating to flood damages has concentrated on monetary damages, i.e. damages that

are easily quantified. In addition to those damages, it is widely recognised that individuals and communities

also suffer significant non-monetary damage, i.e. emotional distress, health issues, etc.

The intangible non-monetary flood related damage is also likely to be high, further contributing to the flood

damages. The benefit-cost analysis presented in this report has not considered this cost. Any decisions made

that are based on the benefit cost ratios need to understand that the true cost of floods in and along the Russell

Creek is far higher than the economic damages alone. These intangible costs have the effect of increasing the

benefit-cost ratio, improving the argument for completing further flood mitigation and flood warning.


6.2.2 Above Floor Flooding

The number of above floor flooded properties has significant reduced as a result of the constructed mitigation

works. Whilst 14 properties are still shown to be flooded above floor, a number of these properties are shown

to be flooded by relatively shallow depths. A breakdown of the depth of above flood flooding during the 1%

AEP flood event is shown in the table below.

TABLE 6-1 DEPTH OF ABOVE FLOOR FLOODING

Depth of Above Floor Flooding Number of Properties Impacted

< 0.1 metres 5

0.1 To 0.2 meters 5

0.2 to 0.3 meters 2

Above 0.3 meters 2

All of the properties shown to be flooded above floor following the mitigation works had previously been

identified at being at risk from above floor flooding during the 1% AEP flood events. The depth of above floor

flooding has reduced for all but 1 of the 14 properties. The average depth of above floor flooding has reduced

by 100mm. The locations of the above floor flooded properties are focused on three areas Wangoom Road,

Whites Road and within the breakout area around Moonah Drive.

FIGURE 6-1 ABOVE FLOOR FLOODED PROPERTIES (RED DOTS)


TABLE 6-2 DAMAGES ASSESMENT

ARI (1in Y years) 1 in 200 yr 1 in 100 yr 1 in 50 yr 1 in 20 yr 1 in 10 yr 1 in 5 yr

AEP 0.5% 1% 2% 5% 10% 20%

Residential Buildings Flooded Above Floor

21 14 6 1 0 0

Commercial Buildings Flooded Above Floor

6 0 0 0 0 0

Properties Flooded Below Floor

369 205 99 69 57 36

Total Properties Flooded

396 219 105 70 57 36

Direct Potential External Damage Cost

$1,070,242 $490,987 $331,469 $250,022 $168,447 $64,008

Direct Potential Residential Damage Cost

$1,263,246 $809,937 $327,627 $61,861 $0 $0

Direct Potential Commercial Damage Cost

$33,766 $0 $0 $0 $0 $0

Total Direct Potential Damage Cost

$2,367,254 $1,300,924 $659,096 $311,883 $168,447 $64,008

Total Actual Damage Cost (0.8*Potential)

$1,893,803 $1,040,739 $527,277 $249,506 $134,758 $51,206

Infrastructure Damage Cost

$326,489 $243,184 $196,212 $135,350 $113,458 $66,009

Total Cost $2,220,292 $1,283,923 $723,489 $384,856 $248,216 $117,215

Average Annual Damage (AAD)

$69,521


7 SENSITIVITY TESTING

7.1 Overview

The project brief required a number of sensitivity tests to be completed, these included:

Climate Change

Complete Blockage of new - Mortlake Road Culverts

Removal of Flood Walls

Rainfall on grid modelling to represent local stormwater drainage behind the levee

These tests were completed using both RORB and hydraulic modelling techniques.

7.2 Climate change scenarios

7.2.1 Overview

The assessment of climate change was modelled in RORB for rainfall intensity increases of 10%, 20% and

30% to provide a range of potential flows that may occur along Russell Creek due to climate change.

The latest guidance in AR&R (2016) predicts a 5% rainfall intensity increase per degree of warming. A scenario

of 2°C of warming is consistent with ‘Climate Change in Australia Projections’8 report which suggests for an

intermediate climate scenario, a temperature increase of between 1.1°C to 2.0°C is likely for the Southern

Slopes of Australia. This climate change scenario would result in a 10% increase in rainfall intensity. The

impact of climate change on flows was determined for the catchment using the existing RORB model and then

modelled in the hydraulic model. The increase in peak flow for the 1% AEP event in each climate change

sensitivity scenario is shown in Table 7-1.

TABLE 7-1 CLIMATE CHANGE RAINFALL INTENSITY INCREASE – PEAK FLOWS

% increase in rainfall intensity

Aberline Road 1% AEP peak flow (m3/s)

(critical duration)

Wangoom Road 1% AEP peak flow (m3/s) (critical duration)

Racecourse 1% AEP peak flow (m3/s)

(critical duration)

Critical Duration 6 hr 3 hr 1 hr

Existing Conditions 31.77 17.35 22.2

10 % 39.14 (23% increase) 20.69 (19% increase) 25.09 (13% increase)



The hydraulic model was run for all of the five storm durations (24hr,12hr, 6hr, 3hr and 1hr) for the 1% AEP

flood event with the various climate related rainfall intensity increases. The maximum envelope of the resulting

flood depths was derived and a comparison of the various flood extents is shown below.

8 CSIRO. (2005). Climate Change in Eastern Victoria - Stage 1 Report: The effect of climate change on coastal wind and weather patterns. CSIRO.


FIGURE 7-1 CLIMATE CHANGE RAINFALL INTENSITY INCREASE FOR 1% AEP EVENT


7.3 No Flood Walls

An assessment of the effect of the removal or failure of the flood walls was undertaken for the 1% AEP flood

event. The flood walls were completely removed from the hydraulic model. Changes to land topography around

the walls was also smoothed.

All durations of the 1% AEP flood event were modelled and the maximum envelope of the combined extent

mapped and displayed in Figure 7-2. A comparison of the modelled extent with the current 1% AEP flood

extent and depths results indicates that’s maximum water surface elevations between Garden Street and

Mortlake Road are approximately 2-5 cm lower than the existing conditions (Figure 7-3). However, the 1%

AEP flood extent without the flood walls is greater, most notably to the south of the creek around the Garden

Street area. This can be attributed to the change in the nature of the flow through the areas which are confined

by the flood walls. In the absence of the flood walls the floodplain is broader and flood levels lower.

7.4 No Mortlake Rd Culverts

It is important to note the significant number of waterway structures along Russell Creek. These structures

effect the conveyance and storage of flows within the waterway during significant flood events. Of these

structures the Mortlake Road culverts and road embankment is the largest and most significant hydraulic

control within the Russell Creek floodplain.

An assessment of the effect of the new culverts being completely blocked/removed was undertaken to

demonstrate the efficacy of the new culverts and the sensitivity of the flood levels locally to this structure. The

scenario included the as constructed flood walls but not the 2 new box culverts. All durations of the 1% AEP

flood events were modelled and the maximum envelope of the combined extent mapped and displayed in

Figure 7-4. A comparison of the modelled (no culvert) event to the existing conditions assessment indicates

that in the absence of the culverts at Mortlake Road water levels on the upstream side of Mortlake Road are

increased in excess of 50 cm (Figure 7-5). This increase results in increased water levels up stream of the

culverts and outflanking of the levees immediately upstream and around Garden Street.


FIGURE 7-2 1% AEP FLOOD DEPTH – NO FLOOD WALLS


FIGURE 7-3 1% AEP,12 HR - DIFFERENCE PLOT – NO WALLS MINUS EXISTING


FIGURE 7-4 1% AEP FLOOD DEPTH – NO MORTLAKE ROAD NEW CULVERTS


FIGURE 7-5 1% AEP, 12HR - DIFFERENCE PLOT - NO CULVERTS MINUS EXISTING


7.5 Rain on Grid

As part of the sensitivity testing some limited rain on grid modelling was completed to test the existing

stormwater network behind the flood walls. The pit and pipe information used in this assessment was supplied

by Engeny (Figure 7-6) and was not validate with any on ground checks or surveys. The 1% AEP (Figure 7-7)

and 10% AEP (Figure 7-8) flood events were run for the 30 minutes and 2 hour storm durations. This scenario

adopted zero loss and is likely to have over-estimated the volume of runoff within the urban area. The results

provide an indication of potential problem areas including low lying land north of Russell Creek where drainage

infrastructure may be undersized. Water Technology recommends that further investigation of this be

undertaken. The flood depth results shown below have been filtered to remove maximum flood depths of less

than 0.05 metres and puddles of less than 100m2.

It is important to consider that the primary driver of the rain on grid assessment was to confirm if areas behind

the flood walls could drain effectively and if additional hazard was being created by the flood walls. Having

regard to this it is noted that the land behind the Moore Street levee is low and given the orientation of local

drainage around the racecourse it is possible that water may pool behind the levee at this location. This is also

reflected at la Bella Court where water is shown to pool within the court bowl. It is important to note that the

local drainage network is not designed to cope with 1% AEP flows and that it is likely that increased water

depths would be experienced within the road network and low-lying land.

Whilst the primary focus of this report is to asses and present revised flood mapping following the construction of mitigation works on Russell Creek. The assessment focuses on riverine flooding and does not consider inundation resulting from stormwater flooding. It is possible that in some instances properties will be subject to flooding from both stormwater and riverine flooding. The risk of stormwater flooding in Warrnambool is greatest when the capacity of the stormwater drainage network is exceeded and the excess accumulates in the road networks which often then drain to low lying land, as is observed in the rain on grid stormwater mapping shown in Figure 7-8. Where our urban areas have experienced rapid growth, as has been observed in Warrnambool, these issues can be compounded due to the increased runoff from hard surfaces along with ageing and often undersized infrastructure. For these reasons it is important to have a clear understanding of the areas within the drainage network which may be undersized and at greatest risk from stormwater flooding.

FIGURE 7-6 WARRNAMBOOL PIT AND PIPE NETWORK


FIGURE 7-7 1% AEP RAIN OF GRID


FIGURE 7-8 10% AEP RAIN ON GRID


8 CONCLUSION

8.1 Overview

The North Warrnambool Flood Mitigation Study provides a comprehensive analysis and review of current flood risk in the North Warrnambool Russell Creek area following the construction of extensive flood mitigation work. This analysis has been completed based on current floodplain conditions and includes the 4 new flood levees and two new culverts at Mortlake Road. This document provides detailed mapping of the existing flood risk under a range of flood magnitudes. The study involved:

Development of detailed best practice flood hydrology in accordance with Australian Rainfall and Runoff

(2016) guidelines.

Development of a detailed hydraulic model, validated to previous modelling and used to simulate a range

of design flood events with the as constructed flood mitigation works representing the current conditions

of the Russell Creek floodplain.

Quantification of flood risk in terms of properties impacted and likely future flood damages.

Sensitivity testing for a range of various model parameters.

8.2 Key Outcomes

The project has developed revised hydrology and hydraulic models using todays best practice ARR (2016)

guidelines. The hydrology and hydraulic models can be used for future floodplain assessments of Russell

Creek.

The flood mapping has confirmed that the flood mitigation works constructed recently along Russell Creek has

greatly reduced the flood risk for the residents of North Warrnambool. The modelling has highlighted the

sensitivity of flood levels around the Garden Street area, with breakouts onto the floodplain occurring at that

location. The higher resolution modelling has shown that flood waters may outflank the levee flood wall to the

south, this was not previously shown in the coarser flood modelling.

8.3 Recommendations

Following this investigation, it is recommended that:

The revised 1% AEP flood mapping be adopted for the purposes of future planning scheme overlays and

strategic planning investigations. Furthermore, designation of the declared flood prone land in accordance

with Building Regulation 802 should also be considered.

Further investigation be undertaken into minor engineering works around the Garden Street area where

the modelling shows minor outflanking of the levee. Minor raising of the surface level will improve the

performance of the southern levee which will be outflanked in large flow events.

Undertake a more comprehensive assessment of the local drainage network capacity and function to

ensure problem drainage areas within the overland flow paths are appropriately managed. This

assessment should also include a condition assessment and comprehensive culvert blockage

assessment.

Further investigate the local impact of predicted climate variability on stormwater and catchment flooding

and where necessary investigate measures to manage the associated risks.


Consider as part of long term floodplain management future upgrade works on the Garden Street

waterway crossing with the aim of improving conveyance and reducing flooding within the breakout area

north of Russell Creek.

Furthermore, given the completed modelling will superseded current best available flood mapping the

following recommendation should also be considered:

In conjunction with VICSES, the Warrnambool City Council and GHCMA should continue to

engage the community in the treatment of flood risks through regular flood awareness programs

such as the VICSES FloodSafe program. Whilst local flood guides have already been produced

for this area a revised guide would be necessary following the completion of the proposed works.

In consultation with VICSES, the Warrnambool City Council and GHCMA the Municipal Flood

Emergency plan (MFEP) should be updated to reflect the as constructed flood mitigation works

and revised flood mapping.

Warrnambool City Council and GHCMA to consider recommendations from the recent flood

warning investigation for Russell Creek along with the revised flood impacts from this

investigation, to inform further improvements to the Total Flood Warning System for Russell

Creek. This should include the installation of a gauge within Russell Creek to ensure accurate

rainfall and stream flow data can be recorded for future use and on which to base early flood

warning.


APPENDIX A AR&R DATA HUB OUTPUT


Results - ARR Data Hub

[STARTTXT]

Input Data Information

[INPUTDATA]

Latitude,-38.34035228

Longitude,142.533923

[END_INPUTDATA]

River Region

[RIVREG]

Division,South East Coast (Victoria)

RivRegNum,11.0

River Region,Hopkins River

[RIVREG_META]

Time Accessed,06 March 2017 11:37AM

Version,2016_v1

[END_RIVREG]

ARF Parameters

[LONGARF]

Zone,Southern Temperate

a,1.58E-01

b,2.76E-01

c,3.72E-01

d,3.15E-01

e,1.41E-04

f,4.10E-01

g,1.50E-01

h,1.00E-02

i,-2.70E-03

[LONGARF_META]


Version,2016_v1

[END_LONGARF]

Storm Losses

[LOSSES]


[LOSSES_META]


Version,2016_v1

[END_LOSSES]

Temporal Patterns

[TP]

CODE,SSmainland

LABEL,Southern Slopes (Vic/NSW)

[TP_META]


Version,2016_v1

[END_TP]

Areal Temporal Patterns

[ATP]

CODE,SSmainland

LABEL,Southern Slopes (Vic/NSW)

[ATP_META]


Version,2016_v1

[END_ATP]

BOM IFD Depths

[BOMIFD]

[BOMIFD_META]

[END_BOMIFD]

Median Preburst Depths and Ratios

[PREBURST]

min (h)\AEP(%),50,20,10,5,2,1,

60 (1.0),1.8 (0.135),2.7 (0.135),3.3 (0.133),3.8 (0.129),2.2 (0.061),1.0 (0.024),

90 (1.5),1.1 (0.069),1.7 (0.074),2.1 (0.075),2.5 (0.074),2.0 (0.048),1.6 (0.034),

120 (2.0),1.9 (0.11),2.0 (0.081),2.1 (0.068),2.2 (0.06),2.1 (0.047),2.1 (0.04),

180 (3.0),2.4 (0.121),2.3 (0.079),2.2 (0.062),2.1 (0.05),2.5 (0.049),2.8 (0.048),

360 (6.0),0.7 (0.028),1.0 (0.028),1.2 (0.027),1.4 (0.026),2.6 (0.041),3.6 (0.048),

720 (12.0),0.0 (0.0),0.5 (0.012),0.9 (0.016),1.3 (0.019),3.4 (0.041),5.0 (0.052),

1080 (18.0),0.0 (0.0),0.0 (0.001),0.1 (0.001),0.1 (0.001),0.7 (0.007),1.1 (0.01),


1440 (24.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

2160 (36.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

2880 (48.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

4320 (72.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

[PREBURST_META]


[END_PREBURST]

10% Preburst Depths

[PREBURST10]

min (h)\AEP(%),50,20,10,5,2,1,

60 (1.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

90 (1.5),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

120 (2.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

180 (3.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

360 (6.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

720 (12.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

1080 (18.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

1440 (24.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

2160 (36.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

2880 (48.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

4320 (72.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

[PREBURST10_META]


Version,2016_v1

[END_PREBURST10]

25% Preburst Depths

[PREBURST25]

min (h)\AEP(%),50,20,10,5,2,1,

60 (1.0),0.1 (0.005),0.0 (0.002),0.0 (0.001),0.0 (0.0),0.0 (0.001),0.0 (0.001),

90 (1.5),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

120 (2.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

180 (3.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

360 (6.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

720 (12.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

1080 (18.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

1440 (24.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),


2160 (36.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

2880 (48.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

4320 (72.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

[PREBURST25_META]


Version,2016_v1

[END_PREBURST25]

75% Preburst Depths

[PREBURST75]

min (h)\AEP(%),50,20,10,5,2,1,

60 (1.0),7.3 (0.543),10.7 (0.536),12.9 (0.523),15.0 (0.507),13.6 (0.373),12.6 (0.299),

90 (1.5),9.8 (0.633),10.6 (0.468),11.2 (0.399),11.7 (0.349),12.7 (0.311),13.5 (0.288),

120 (2.0),9.8 (0.57),10.1 (0.406),10.4 (0.338),10.6 (0.29),13.7 (0.308),16.1 (0.315),

180 (3.0),8.4 (0.427),9.8 (0.342),10.7 (0.305),11.5 (0.277),13.4 (0.265),14.8 (0.256),

360 (6.0),4.9 (0.193),10.7 (0.295),14.5 (0.329),18.2 (0.348),20.9 (0.326),22.9 (0.31),

720 (12.0),1.5 (0.046),6.0 (0.13),8.9 (0.159),11.7 (0.177),15.8 (0.192),18.9 (0.196),

1080 (18.0),0.4 (0.011),2.9 (0.055),4.5 (0.07),6.0 (0.079),9.0 (0.095),11.3 (0.101),

1440 (24.0),0.1 (0.002),3.1 (0.054),5.0 (0.072),6.9 (0.083),8.2 (0.079),9.2 (0.075),

2160 (36.0),0.0 (0.0),0.5 (0.008),0.8 (0.011),1.2 (0.012),3.1 (0.027),4.6 (0.034),

2880 (48.0),0.0 (0.0),0.1 (0.001),0.1 (0.002),0.2 (0.002),0.9 (0.007),1.4 (0.009),

4320 (72.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),0.0 (0.0),

[PREBURST75_META]


Version,2016_v1

[END_PREBURST75]

90% Preburst Depths

[PREBURST90]

min (h)\AEP(%),50,20,10,5,2,1,

60 (1.0),15.9 (1.175),24.6 (1.236),30.4 (1.233),35.9 (1.214),29.6 (0.812),24.9 (0.591),

90 (1.5),16.0 (1.031),22.4 (0.987),26.6 (0.952),30.7 (0.918),32.8 (0.801),34.4 (0.731),

120 (2.0),21.5 (1.254),20.2 (0.809),19.3 (0.631),18.5 (0.506),32.8 (0.736),43.5 (0.853),

180 (3.0),18.4 (0.927),21.8 (0.764),24.1 (0.69),26.3 (0.635),31.9 (0.631),36.1 (0.624),

360 (6.0),16.8 (0.664),23.1 (0.637),27.2 (0.617),31.2 (0.597),34.8 (0.543),37.5 (0.508),

720 (12.0),6.4 (0.197),13.9 (0.304),18.9 (0.339),23.7 (0.357),30.8 (0.374),36.2 (0.376),

1080 (18.0),5.9 (0.16),11.5 (0.22),15.2 (0.238),18.7 (0.246),25.1 (0.265),29.9 (0.269),

1440 (24.0),7.8 (0.192),12.4 (0.218),15.4 (0.222),18.3 (0.22),20.9 (0.201),22.9 (0.187),


2160 (36.0),1.4 (0.032),5.7 (0.089),8.5 (0.109),11.2 (0.119),22.3 (0.191),30.6 (0.223),

2880 (48.0),0.9 (0.018),3.7 (0.054),5.6 (0.067),7.3 (0.073),8.8 (0.07),9.8 (0.067),

4320 (72.0),0.4 (0.007),6.4 (0.086),10.4 (0.114),14.2 (0.13),20.3 (0.151),24.8 (0.16),

[PREBURST90_META]


Version,2016_v1

[END_PREBURST90]

Interim Climate Change Factors

[CCF]

2030,0.719 (3.6%),0.739 (3.7%),0.822 (4.1%),

2040,0.925 (4.6%),0.915 (4.6%),1.119 (5.6%),

2050,1.123 (5.6%),1.085 (5.4%),1.449 (7.2%),

2060,1.271 (6.4%),1.294 (6.5%),1.865 (9.3%),

2070,1.394 (7.0%),1.526 (7.6%),2.333 (11.7%),

2080,1.477 (7.4%),1.778 (8.9%),2.776 (13.9%),

2090,1.527 (7.6%),2.009 (10.0%),3.21 (16.1%),

[CCF_META]


Version,2016_v1

Note,ARR recommends the use of RCP4.5 and RCP 8.5 values

[END_CCF]

Baseflow Factors

[BASEFLOW]

DOWNSTREAM,0.0

AREA_SQKM,1018.877

CATCH_NO,11213.0

R3RUNOFF,0.129

R1RUNOFF,0.047

[BASEFLOW_META]


Version,2016_v1

[END_BASEFLOW]

[ENDTXT]


APPENDIX B AR&R – REGIONAL FLOOD FREQUENCY ESTIMATION TOOL


AR&R (2016) has developed a new Regional Flood Frequency Estimate (RFFE) (Rahman, et al, 20159). This

method was used to compare Russell Creek flows to other regional methods. The online tool uses the

catchment centroid, catchment outlet and size to estimate peak flow outputs for a range of flood magnitudes.

The tool was developed utilising data based on gauged catchments to form region based flood relationships.

The RFFE tool has several limitations to its application and should be avoided where:

The catchment includes greater than 10% urban,

Catchment storage significantly altered the natural rainfall runoff behaviour,

Catchment where large scale clearing has taken place,

Catchments which are greatly affected by irrigation activity and or drainage.

The reliability of the tool is also considered less accurate for catchment less than 0.5 km2 and or greater than

1,000 km2 or where a catchment exhibit atypical characteristics.

Whilst several of the Russell Creek catchment characteristics suggest that the method is not suitable as a

means as providing a comparison to the RORB model, the results of the tool output are provided below in

Figure 8-1. The results yielded from this assessment show estimated peak flows significantly lower than those

produced by the RORB modelling.

FIGURE 8-1 RUSSELL CREEK - RFFE

9 AR&R (2016) - http://data.arr-software.org

http://data.arr-software.org/


APPENDIX C DESIGN FLOOD MAPPING


APPENDIX D RUSSELL CREEK STRUCTURES


Structure Name TUFLOW

Structure Type Size

Horne Road 1d_nwke 4 (3m x 1.5m)

Ians Road 1d_nwke 1 (0.6m)

Ians Road 1d_nwke 2 (0.6m)

Wangoom Road 1d_nwke 2 (0.9m x 0.9m)

Aberline Road 1d_nwke 5 (1.5m x 1.5m)

Whites Road (West Crossing) 1d_nwke 2 (1.5m)

Whites Road (East Crossing) 1d_nwke 1 (1.35m)

Whites Road Pedestrian Crossing 2d_lfcsh -

Wares Road 2d_lfcsh -

Renior Pedestrian Crossing 1d_nwke 1 (0.45m)

Upstream Garden Street Footbridge 1d_nwke 4 (0.9m)

Garden Street 1d_nwke 4 (0.9m)

Moonah Drive Pedestrian Crossing 2d_lfcsh -

Oak Court Pedestrian Crossing 2d_lfcsh -

Upstream Mortlake Road Pedestrian Crossing 2d_lfcsh -

Mortlake Road Culverts (Original) 1d_nwke

Irregular (height/flow)

Mortlake Road Culverts (New) 1d_nwke 2 (3.6m x 2.4m)

Downstream Mortlake Road Pedestrian Crossing 2d_lfcsh -

Queens Street 1d_nwke 2 (1.2m)

St Joseph’s Primary Pedestrian Crossing 2d_lfcsh -

Bromfield Street 1d_nwke 6 (0.6m)

Daltons Road 1d_nwke 1 (5.7m x 1.95m)


Melbourne 15 Business Park Drive Notting Hill VIC 3168 Telephone (03) 8526 0800 Fax (03) 9558 9365

Brisbane Level 3, 43 Peel Street South Brisbane QLD 4101 Telephone (07) 3105 1460 Fax (07) 3846 5144

Wangaratta First Floor, 40 Rowan Street Wangaratta VIC 3677 Telephone (03) 5721 2650

Perth PO Box 362 Subiaco WA 6904 Telephone 0407 946 051

Geelong PO Box 436 Geelong VIC 3220 Telephone 0458 015 664

Gippsland 154 Macleod Street Bairnsdale VIC 3875 Telephone (03) 5152 5833

Wimmera PO Box 584 Stawell VIC 3380 Telephone 0438 510 240

www.watertech.com.au

[email protected]

http://www.watertech.com.au/

mailto:[email protected]

addendum russell creek flood mitigation€¦ · table 2-6 design flows using ar&r 2016, il-23...

Documents