· 2010-08-10 · Heights, Geelong West and Geelong North (See Figure 1.1). The catchment is...

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 O C E A N I C S A U S T R A L I A

Rippleside Catchment

Main Drain Augmentation

Final Report

Prepared For: City of Greater Geelong

Prepared By: WBM Oceanics Australia

Offices

Brisbane Denver

Karratha Melbourne

Morwell Newcastle

Sydney Vancouver

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 O C E A N I C S A U S T R A L I A

DOCUMENT CONTROL SHEET

Document: R.W00201.004.01.FinalReport.doc

Title: Rippleside Catchment

Main Drain Augmentation

Final Report

Project Manager: Allan Charteris

Author: Allan Charteris

Client: City of Greater Geelong

Client Contact: Richard Wojnarowski

Client Reference: Tender No. T00049

WBM Oceanics Australia

Melbourne Office: Level 5, 99 King Street MELBOURNE VIC 3000 Australia PO Box 604 Collins Street West VIC 8007 Telephone (03) 9614 6400 Facsimile (03) 9614 6966 www.wbmpl.com.au ACN 010 830 421

Synopsis: This report documents findings of flood investigations in the catchment of Rippleside, Geelong.

REVISION/CHECKING HISTORY

REVISION

NUMBER

DATE CHECKED BY ISSUED BY

1 28/02/2001 WJW ABC

DISTRIBUTION

DESTINATION REVISION

0 1 2 3 4 5 6 7 8 9 10

City of Greater Geelong

WBM File

WBM Library

2

1

1

2

1

1

CONTENTS I

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 IO C E A N I C S A U S T R A L I A

CONTENTS

Contents i

List of Appendices iii

List of Figures iii

List of Tables iv

1 INTRODUCTION 1-1

1.1 Background 1-1

1.2 Catchment Description 1-1

1.3 History of Flooding 1-2

1.3.1 Lantana Ave – Montgomery Ave 1-3

1.3.2 The Fairway and Geelong Golf Club 1-4

1.3.3 Calvert Ave and Lily Street 1-6

1.3.4 Other Areas 1-6

2 PROJECT METHODOLOGY 2-1

2.1 Preliminary Tasks 2-1

2.1.1 Project Initiation 2-1

2.1.2 Data Collation and Review 2-1

2.1.3 Barwon Water 2-2

2.2 Digital Elevation Model 2-2

2.3 Hydrological and Hydraulic Modelling, and Mapping of Existing Conditions 2-2

2.3.1 Hydrologic Analysis 2-2

2.3.1.1 Model Development 2-2

2.3.1.2 Design Event Modelling 2-3

2.3.2 Hydraulic Analysis 2-3

2.3.2.1 Model Selection and Development 2-3

2.3.2.2 Boundary Conditions 2-4

2.4 Mitigation Option Assessment and Mapping 2-4

2.4.1 Review of Existing Flooding Impacts 2-4

2.4.1.1 Impact Identification 2-4

2.4.1.2 Floor Level and Building Survey 2-5

2.4.1.3 Flood Damage 2-5

CONTENTS II

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 II O C E A N I C S A U S T R A L I A

2.4.2 Mitigation Option Assessment 2-5

3 DIGITAL ELEVATION MODEL 3-1

3.1 Catchment DEM 3-1

3.2 Study Area DEM 3-1

4 EXISTING CONDITIONS 4-1

4.1 Hydrology 4-1

4.1.1 Model Description 4-1

4.1.2 Global Parameters 4-1

4.1.2.1 Loss Parameters 4-1

4.1.2.2 Fraction Impervious 4-1

4.1.2.3 Reach Storage Relationships 4-2

4.1.3 Sub-Catchment Definition 4-2

4.1.4 Model Verification 4-3

4.1.4.1 Volume Checks 4-3

4.1.4.2 Rational Method Checks 4-3

4.2 Hydraulics 4-4

4.2.1 Model Selection 4-4

4.2.2 Model Development 4-5

4.2.2.1 Model Geometry 4-5

4.2.2.2 Model Resolution 4-5

4.2.3 Model Boundary Conditions 4-6

4.3 Flood Mapping 4-6

4.4 Building Inundation 4-7

4.5 Flood Hazard Mapping 4-7

4.6 Flooding Issues 4-8

5 MITIGATION ASSESSMENT 5-1

5.1 Mitigation Option Elements 5-1

5.2 Preferred Approach for Augmentation 5-4

5.3 Flood Hazard Mapping 5-5

5.4 Other Impacts 5-5

6 ECONOMIC ASSESSMENT 6-1

6.1 Flood Damages Assessment 6-1

6.1.1 Stage Damage Curves 6-1

LIST OF APPENDICES III

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 III O C E A N I C S A U S T R A L I A

6.1.2 Outside Buildings 6-1

6.1.3 Damages 6-2

6.2 Benefit Cost Ratio 6-3

6.2.1 Cost 6-3

6.2.2 Benefit 6-5

6.2.3 Benefit Cost 6-5

6.3 Intangible Damages/Benefits 6-5

6.4 Funding Mechanisms – Special Rates and Charges 6-6

6.5 Development Control in Flood Prone Areas 6-7

6.6 Discussion 6-8

7 STORMWATER MANAGEMENT PLAN 7-1

8 CONCLUSION 8-1

LIST OF APPENDICES

APPENDIX A: SURVEY REPORT A-1

APPENDIX B: MITIGATION OPTIONS – ELEMENT IMPACTS B-1

APPENDIX C: SPECIAL RATES AND CHARGES – LEGAL ADVICE C-1

APPENDIX D: DESIGN FLOW INFORMATION D-1

LIST OF FIGURES

Figure 1.1 Study Area 1-2

Figure 1.2 Flooding at Ballarat Road – December 1978 1-3

Figure 1.3 Flooding Cnr Marlo and Lantana – December 1978 1-3

Figure 1.4 Flooding at Montgomery Ave – December 1978 1-4

Figure 1.5 Flooding Downstream of Golf Club Car Park 1-4

Figure 1.6 Flooding Downstream of Golf Club Car Park 1-5

Figure 1.7 Flooding in The Fairway 1-5

Figure 1.8 Flooding in Baxter Road Retarding Basin – December 1992 1-6

Figure 2.1 Underground Drainage Network Error! Bookmark not defined.

Figure 3.1 5m DEM and Catchment Boundary 3-1

Figure 3.2 1m DEM of Flood Mapping Area 3-2

rw0724

Cross-Out

LIST OF TABLES IV

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 IV O C E A N I C S A U S T R A L I A

Figure 3.3 1m DEM of Flood Mapping Area - Perspective View 3-3

Figure 4.1 RORB (Hydrology) Model Layout Error! Bookmark not defined.

Figure 4.2 TUFLOW (Hydraulic) Model Layout Error! Bookmark not defined.

Figure 4.3 100y Design Event Flood Inundation Error! Bookmark not defined.

Figure 4.4 Inundation Above Floor Level Error! Bookmark not defined.

Figure 4.5 Hazard Mapping – Existing Case 100 Year Design EventError! Bookmark not defined.

Figure 4.6 Flooding Issues in the Rippleside Catchment 4-1

Figure 5.1 Weddell Road Retarding Basin Storage Characteristics 5-4

Figure 5.2 Mitigation Option Elements Error! Bookmark not defined.

Figure 5.3 Augmented System Elements Error! Bookmark not defined.

Figure 5.4 100y Design Event Flood Extent for Augmented SystemError! Bookmark not defined.

Figure 5.5 100y Above Floor Level Inundation – After AugmentationError! Bookmark not defined.

Figure 5.6 Hazard Mapping – Augmented Case 100 Year Design EventError! Bookmark not defined.

Figure 6.1 Rippleside Flood Damage Curves 6-2

Figure 6.2 Areas Suitable for Alternative Flood Relief Strategies Error! Bookmark not defined.

LIST OF TABLES

Table 4-1 Impervious Fraction for Planning Scheme Zone 4-2

Table 4-2 Hydrological Model Verification 4-4

Table 4-3 TUFLOW Manning’s n Coefficients 4-5

Table 4-4 Number of Properties Inundated Above Floor Level 4-7

Table 4-5 Hazard Categories 4-7

Table 5-1 Effect of Options on Existing Flooding 5-3

Table 6-1 Guideline Per metre Costs for Pipe Augmentation Works 6-3

Table 6-2 Estimated Cost of Augmentation Works 6-3

Table 6-3 Detailed Breakdown of Cost Estimate 6-4

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

rw0724

Cross-Out

INTRODUCTION 1-1

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 1-1 O C E A N I C S A U S T R A L I A

1 INTRODUCTION

1.1 Background

The City of Greater Geelong has embarked on a process to investigate existing drainage capacity and

to develop a plan for the upgrade of the system to mitigate existing flood problems. The Drainage

Augmentation Study for the Rippleside Catchment is specifically concerned with:

• defining (simulating) and mapping existing flooding characteristics and drainage system

deficiencies in the Catchment;

• assessing the nature and magnitude of impacts associated with existing flooding;

• identifying potential augmentation strategies to reduce damages associated with flooding

impacts; and,

• evaluating and identifying opportunities of funding capital and maintenance works associated

with the recommendations of the study.

This report documents the findings of WBM’s investigations of flooding in the Rippleside catchment

and presents mitigation options to minimise flooding impacts.

1.2 Catchment Description

The catchment of Rippleside is the largest urban catchment in Geelong (approximately 750 Ha) and

is located north of the city ranging over the suburbs of Hamlyn Heights, Herne Hill, Manifold

Heights, Geelong West and Geelong North (See Figure 1.1).

The catchment is characterised by significant and almost complete urbanisation with few “open

space” areas. These are limited to areas within the Geelong Golf Club, a dedicated drainage reserve

between Weddell and Baxter Roads, and a small portion of undeveloped area at the top of the

catchment.

The existing drainage infrastructure is typically very old, much of it in place and unchanged since

subdivision and development 30 to 60 years ago. Current drainage problems within the Rippleside

Catchment are similar to those experienced by many older urban catchments which contain

hydraulically constrained and aging stormwater systems. The characteristics of these catchments are

usually typified by high levels of development, extensive areas of imperviousness and limited

retention of dedicated drainage reserves or open channel systems. Additionally, the underground

drainage systems are typically under capacity and there is a lack of conveyance and/or storage

capacity above ground for major flows.

INTRODUCTION 1-2


Figure 1.1 Study Area

The topography of the catchment is somewhat different from the typical floodplain catchment. Where

one would usually find steeper upper catchment areas and a broad floodplain in lower areas,

Rippleside exhibits quite the opposite relief. The upper parts of the catchment (above Vines Road) are

very flat, almost as a plateau. The grade changes significantly below Vines Road and the lower parts

of the catchment are relatively steep. The drainage paths become well defined and somewhat incised,

particularly in the drain through the southern part of the Geelong Golf Club.

The outlet of the catchment is to Rippleside Beach via a culvert that runs from the retarding basin at

Baxter Road, below the Geelong-Melbourne Railway and under Rippleside Park. The railway

virtually forms a dam wall preventing overland flows from progressing further down the catchment.

1.3 History of Flooding

The flooding history in the catchment is varied with problems often attributed to limited underground

capacity resulting in overland flows for which there exists no defined floodway. In a number of cases,

dwellings have been built in the flowpath and occasionally as “slab on ground” (eg Lily and Graham

St).

INTRODUCTION 1-3


1.3.1 Lantana Ave – Montgomery Ave

Significant flooding was experienced in the Lantana Av – Montgomery Ave area due to a local storm

on 17 December 1978.

At Ballarat Road, the outbound road was cut and flood depths of approximately 0.5-1.0m were

observed due to ponding above the median strip (Figure 1.2). Ponding behind the railway lead to

flooding at the Lantana Ave Marlo St intersection (Figure 1.3), again with flood depths of

approximately 0.5-1.0 m observed. Significant overland flows were also observed in Montgomery

Ave (Figure 1.4).

Figure 1.2 Flooding at Ballarat Road – December 1978

Figure 1.3 Flooding Cnr Marlo and Lantana – December 1978

INTRODUCTION 1-4


Figure 1.4 Flooding at Montgomery Ave – December 1978

Flooding in this event was observed to be brief and property inundation above floor level was not

reported.

1.3.2 The Fairway and Geelong Golf Club

Numerous flooding incidents have been reported by the Golf Club with particular problems in the

carpark and practise fairway areas (See Figure 1.5 and Figure 1.6).

Figure 1.5 Flooding Downstream of Golf Club Car Park

INTRODUCTION 1-5


Figure 1.6 Flooding Downstream of Golf Club Car Park

Figure 1.7 Flooding in The Fairway

Figure 1.7 illustrates the effect of this type of flooding on The Fairway, the road directly downstream

from the effected Golf Club areas.

The Golf Club report that this type of flooding is relatively frequent, in 1994 suggesting that the type

of flooding presented in the above photos has occurred 2-3 times since 1989.

INTRODUCTION 1-6


1.3.3 Calvert Ave and Lily Street

Reports of flooding and inundation to almost floor level in these areas were recorded following flood

events in 1988. Several properties were inundated and evidence of flooding of garages and garden

sheds was observed.

Reports indicated that flooding in these areas was a relatively frequent occurrence. Photographic

documentation was not available.

1.3.4 Other Areas

Significant flooding has been observed on many occasions in the Baxter Rd retarding basin.

Figure 1.8 Flooding in Baxter Road Retarding Basin – December 1992

Minor flooding in December 1992 resulted in the inundation illustrated in Figure 1.8. On other

occasions, flood levels have been observed above the crest of Baxter Road (to the left of Figure 1.8).

While the purpose of the retarding basin is to provide flood storage and is fulfilling that role, there is

concern that peak flood levels in the area may impact upon adjacent housing during less frequent

events.

PROJECT METHODOLOGY 2-1


2 PROJECT METHODOLOGY

The methodology to undertake the Rippleside Drainage Augmentation Study was detailed in WBM’s

proposal and forms part of the contract documentation. This section provides a brief overview of the

methodology adopted during the project with particular reference to any alterations required to

overcome difficulties encountered during the course of the project.

The methodology was developed in accordance with the requirements of the study brief with a

particular emphasis on ensuring that recommended augmentation options are realistically

implemented within local hydraulic, economic and political constraints.

2.1 Preliminary Tasks

2.1.1 Project Initiation

Project initiation occurred in May 2000 with a meeting of the City of Greater Geelong’s Project

Officer (Mr Richard Wojnarowski) and WBM project staff (Allan Charteris, Wesley Walden, Lloyd

Heinrich). Following the meeting a ½ day site inspection was undertaken where Council’s Project

Officer identified key elements of the system and related flooding issues to WBM.

During the course of the project additional site inspections were undertaken by WBM staff to clarify

flood and drainage issues.

2.1.2 Data Collation and Review

Upon commissioning, all relevant data and information for the Catchment and its drainage systems

was obtained from Council and Barwon Water. Review of this information was undertaken to

identify any significant data gaps and to gain a complete understanding of issues in the Rippleside

catchment.

Council provided detailed information regarding systems that are currently under their responsibility

as well as some information suitable for providing infill to the data gaps identified in the City of

Greater Geelong data set.

Additional data was retrieved from Barwon Water, including cadastral information, ground level

contours over the entire catchment, and planning scheme information. The underground drainage

information has been comprehensively reviewed.

Figure 2.1 shows the major underground drainage network within the floodmapping area. The key

features of the drainage system, typically pipes with diameter greater than 600mm, are illustrated. In

some areas, limited or very old information has been provided for the drainage network. Additional

information regarding these areas was provided by the City of Greater Geelong and the data set was

deemed complete.



2.1.3 Barwon Water

Barwon Water have supplied the following data:

� Cadastre over the Rippleside catchment

� Planning Scheme Zones over the catchment

� 1m contours over the catchment

The initially supplied contour data set covered only part of the catchment of Rippleside. Additional

time was required to complete the data set by digitising the remainder of the catchment from the

Corio 2500 series maps.

2.2 Digital Elevation Model

Preparation of the Digital Elevation Models used in the study is discussed in Section 3. Briefly, the

process for the preparation of the DEMs is described below.

The DEM for the mapping area was developed using the points and break lines derived from

photogrammetry. Establishment of the DTM involved the development of Triangulated Irregular

Network (TIN) using these points and breaklines to establish a continuous triangular 3D shape of the

area. For mapping purposes the continuous TIN is sampled at the requisite model resolution to create

a grid of data points forming the DEM. Vertical Mapper, which operates within the MapInfo GIS

package, was used to create the DEM. Within the flood mapping area the sampling resolution for the

DEM is 1m. Based on our past experience, we have found that this level of detail is well suited to

simulating the topography of heavily urbanised environments.

The DEM was reviewed to identify any anomalies. Site inspections were undertaken to verify terrain

shape.

2.3 Hydrological and Hydraulic Modelling, and Mapping of Existing Conditions

This Section discusses our approach to developing hydrological and hydraulic models, simulating

existing flooding characteristics and developing flood maps for existing conditions.

2.3.1 Hydrologic Analysis

2.3.1.1 Model Development

A RORB (Version 4.2) hydrological model was developed for the entire catchment to simulate

rainfall runoff characteristics and generate inflows for the hydraulic model. The RORB hydrological

model simulates catchment storage and routing characteristics, including the incorporation of

retarding basins or areas that provide natural retardation of flows. The development of hydrological

model involves the following key steps:

• subcatchment definition was undertaken using available topographical information for the study

area. Existing information is considered sufficient in this regard. Subcatchment delineation took



into consideration compatibility with the required extent of hydraulic analysis as well as land use

characteristics.

• landuse characteristics were identified from the current planning scheme zonings. This

information along with available aerial photography was used to derive proportions of

perviousness and imperviousness within each subcatchment.

• model loss parameters were applied in accordance with the catchment characteristics and based

on similar hydrological investigations in the region.

• channel routing methods within RORB was selected in consideration of reach type and

incorporating physical data relating to length and slope.

• storage and routing parameters (k and m) were determined from theoretical calculations for the

derivation of default values.

Historical stream flow information for hydrological model calibration does not exist in the study area.

Verification of peak flows generated by the RORB models was undertaken in consideration of values

derived using the Rational Method. As part of this process RORB model parameters were adjusted to

achieve consistency between both approaches.

2.3.1.2 Design Event Modelling

RORB was used to derive hydrographs as input to the hydrodynamic model of the drainage system.

Temporal patterns and design rainfall intensities were derived from Australian Rainfall and Runoff

IFD curves and maps. This process involved the derivation of design rainfall events covering a range

of return periods and durations for each drainage sub area. The 5, 10, 20, 50, and 100 year ARI events

were simulated.

2.3.2 Hydraulic Analysis

2.3.2.1 Model Selection and Development

Originally, the study was to be undertaken using MIKE11, a 1D hydraulic modelling package from

DHI. Initial testing of the model shows good correlation with anecdotal evidence of flooding within

the catchment, particularly in the lower portions. However, the complex distribution of flows in the

upper sections of the model has difficult to model with an appropriate degree of certainty. This is due

to a number of factors, including:

• The requirement in MIKE11 to predefine flow paths as model branches. These are typically

defined in consideration of relatively low flows. However the alignment of these paths can

change in higher flow situations, either by short circuiting, breakouts with looped anabranch

flows or transverse flow between parallel channels.

• The ability of MIKE11 to handle sheet flow situations through, for example, residential areas.

Predefinition of these types of flow paths as 1 dimension branches does not take into

consideration the effect of momentum in the 2D horizontal plane.



In consideration of these, and in consultation with the City of Greater Geelong, it was decided to

migrate the modelling to a 2D platform, TUFLOW, which has the capability to overcome the

problems above while providing the necessary level of detail.

Section 4.2 describes the selection and development of the 2D hydraulic model.

2.3.2.2 Boundary Conditions

The hydraulic model requires downstream boundary conditions and lateral inflow boundary

conditions representing the runoff from the catchment.

The downstream boundary condition has been specified as a constant tailwater level reflecting the

mean tidal level in Corio Bay.

Catchment runoff was modelled using the hydrological (RORB) model, as previously discussed, and

the output will subsequently provide inflows to the hydraulic model.

The hydrological model provides flow outputs at nodes at designated locations throughout the

catchment. The conventional approach is to then simulate these inflows in the hydraulic model as a

series of individual point discharges. This approach is suitable when simulating the discharge from a

single pipe outlet, however, in reality runoff will also enter the drainage system as dispersed inflows

(overland flows) along the length of the drainage system. Based on our previous experience with

modelling urban drainage systems similar to the Rippleside Catchment, we have found that the

performance of the hydraulic model in simulating discharges and water levels is sensitive to the

proposed method of simulating inflows.

In response to the above issue, WBM Oceanics Australia has developed in-house software that

interfaces hydrological model output and TUFLOW. This software provides the flexibility of

generating a number of smaller lateral inflow boundary conditions along flow paths in the model to

simulate dispersed overland flow more accurately.

2.4 Mitigation Option Assessment and Mapping

This section outlines our approach when assessing the flooding characteristics of the existing

drainage system and identifying possible mitigation options to alleviate flooding problems.

2.4.1 Review of Existing Flooding Impacts

2.4.1.1 Impact Identification

Results from the existing flood simulations would be reviewed to identify major constriction or

conveyance deficiencies that are contributing to flooding impacts. In this regard, the impact

identification involved:

• Design event simulation for a range a design flood events to consider the capacity of various

components of the existing system, and when and where flood problems are likely to occur;

• Identification and documentation of flood prone areas where properties and infrastructure are

subject to flooding under varying ranges of event frequency;



• Identification of under sized components of the system that may be causing flooding and

backwater effects;

• Assessment of the influence of hydrograph peak timings from various subcatchments within the

study area and the influence that this has on flooding impacts at particular locations; and

• GIS database analysis to provide a comprehensive list of all properties and infrastructure that is

affected by flooding in the catchment.

2.4.1.2 Floor Level and Building Survey

A detailed survey was conducted by City of Greater Geelong focussing on properties where model

results indicate a significant threat from flooding. Floor level, property size and condition and other

information was collected to be used in subsequent damages assessments.

2.4.1.3 Flood Damage

A damages assessment for properties and infrastructure was carried out based on the ANUFLOOD

method. The method contains appropriate relationships between depth of flooding and damages for a

range of building types (eg. low level house of low value, high set house of medium value, high value

commercial property) etc. These relationships account for such factors as the time of flood warning

and the relative degree of flood preparedness of the community.

Annual Average Damage predictions for urban areas are calculated from the damage curves and are

used as a starting point for establishing cost/benefit ratios of the augmentation options considered.

2.4.2 Mitigation Option Assessment

From the review of existing flooding a series of mitigation options were developed. Structural options

will be considered to alleviate drainage bottle necks and storage problem areas. Typical structural

measures considered included:

• Modification and resizing of major culverts and waterway openings which may be causing

flooding impacts;

• Development of structural measures such as levee banks to protect properties from flooding; and

• Construction of major flood retarding structures to protect downstream areas.

DIGITAL ELEVATION MODEL 3-1


3 DIGITAL ELEVATION MODEL

3.1 Catchment DEM

A broad scale Digital Elevation Model (DEM) was developed for the entire catchment for use in

hydrology components of the study. Barwon Water provided contours over the entire catchment at

approximately 1.5m intervals (data derived from 6’ contour information). These data were used to

create a DEM with a 5m horizontal resolution. Figure 3.1 shows the entire catchment DEM.

Figure 3.1 5m DEM and Catchment Boundary

3.2 Study Area DEM

The detailed Digital Elevation Model (DEM) of the study area was developed from a range of data

sources. It involved a combination of existing photogrammetry, new photogrammetry from existing

low level aerial photography and ground controlled terrestrial survey. Information collected as part of

the survey program was as follows:



• Existing Photogrammetry – existing photogrammetric data from within the study area gathered

as part of the 1992 survey.

• Low Level Aerial Photography (Barwon Water 1992) – low level aerial photography collected

by Barwon Water was obtained and reviewed for use in photogrammetric analysis. The

photography was used to prepare digital terrain information of the remainder of the study area.

• Aerial Survey Photo Control – photo control survey collected as part of the Barwon Water

survey in 1992 was used to validate photogrammetry.

Appendix A presents the survey report regarding the photogrammetry data extracted from the

existing photography. Vertical accuracy of the photogrammetry was 0.1m.

The DEM for the mapping area was developed using the points and break lines derived from

photogrammetry. Figure 3.2 and Figure 3.3 illustrate the detailed DEM of the study area.

Figure 3.2 1m DEM of Flood Mapping Area



Figure 3.3 1m DEM of Flood Mapping Area - Perspective View

The detailed 1m DEM was used as the basis for the preparation of the hydraulic model for the study

area. It also provides the foundation for the derivation of flood extent and presentation of other flood

mapping.

EXISTING CONDITIONS 4-1


4 EXISTING CONDITIONS

Assessment of the existing flood conditions throughout the catchment is presented in this section.

This information provides the base for the assessment of the effectiveness of mitigation measures

tested in Section 0.

4.1 Hydrology

4.1.1 Model Description

Hydrological modelling was performed in this study using the runoff and stream routing program

RORB (Laurenson and Mein, 1997). RORB simulates the hydrological behaviour of a catchment by

discretising the area into a series of sub-catchments joined by a series of reaches. Rainfall-runoff is

simulated for each catchment with the hydrographs routed through the stream network using a non-

linear storage routing procedure.

RORB is widely used in Victoria and is the package recommended by Melbourne Water for the

assessment of hydrological characteristics of ungauged catchment in metropolitan areas.

4.1.2 Global Parameters

4.1.2.1 Loss Parameters

RORB generates runoff by subtracting losses at each timestep from the rainfall occurring in that time

period, losses were assumed to comprise an initial loss followed by a continuing loss. An initial loss

of 12.5 mm was adopted, and continuing losses were considered as a constant proportion of the

rainfall in each timestep. Continuing loss in RORB for impervious areas is a predefined fraction of

the rainfall where 10% of the rainfall per timestep is lost. The following volumetric runoff

coefficients were adopted:

100y event 0.60

50y event 0.55

20y event 0.45

10y event 0.40

5y event 0.35

4.1.2.2 Fraction Impervious

The fraction of the catchment that is impervious is a key input to the hydrologic modelling.

Impervious fractions for various planning scheme codes were identified based on previous experience

in similar studies within metropolitan Melbourne (undertaken on behalf of Melbourne Water) and

adopted in consultation with City of Greater Geelong. Key impervious fractions are presented in

Table 4-1 below:



Table 4-1 Impervious Fraction for Planning Scheme Zone

Zone Impervious Fraction

General Residential 0.4

General Commercial 0.8

General Industrial 0.8

Public Open Space 0.1

Roads 0.9

General Farming 0.1

Special Public Purpose (e.g. school) 0.6

The planning scheme data were used to establish a spatially weighted average of the impervious

fractions for each hydrologic modelling sub-area.

4.1.2.3 Reach Storage Relationships

RORB simulates the linkages between sub-catchments as reach storages with the storage discharge

relationship defined by the following equation;

S = 3600kQm

Where S represents the storage (m3), Q is the discharge (m3/s), m is a dimensionless exponent and k is

non-dimensional empirical coefficient. k is defined by the product of the catchment value kc and the

individual reach ki. Both m and kc are defined as calibration parameters. These were defined based

on previous experience in RORB modelling in metropolitan Melbourne.

For all catchments m was assumed to be equivalent to 0.8 and kc was calculated using the following

equation;

kc = 1.53A0.53

where A is equivalent to the catchment area. This equation was sourced from Melbourne Water and is

recommended by Melbourne Water for use in urban catchments throughout metropolitan Melbourne.

Melbourne Water has undertaken considerable research to establish this relationship and is

considered the most appropriate for use in metropolitan Melbourne.

4.1.3 Sub-Catchment Definition

Sub-catchments used in the hydrologic modelling process were defined using a combination of City

of Greater Geelong drainage scheme plans and topographic data. Where drainage scheme data was

not available sub-catchments were defined using topographic data.

Assessment of the hydrological characteristics of the catchment was undertaken using RORB.

Sub-catchment breakdown is presented in Figure 4.1, also showing the location (in red) of

checkpoints for hydrological model verification (Section 4.1.4).



4.1.4 Model Verification

No data were available for model calibration. To determine the overall validity of the hydrologic

modelling, checks of peak flow against recognised calculation methods were undertaken and are

presented below.

4.1.4.1 Volume Checks

As a preliminary check to ensure the RORB model was correctly configured, the runoff volume

generated by the numeric model was compared against the volume derived by distributing the rainfall

depth over the catchment area. The primary purpose of this check is to ensure there were no model

leaks or short circuits.

The runoff volume for each catchment was estimated by distributing a 2 hour 100yr ARI rainfall

event over the catchment and recording the volume of runoff generated at the outlet of the catchment.

To ensure no loss of rainfall occurred the catchment parameters were set as follows, initial loss = 0

mm and runoff coefficient = 1. The volume of runoff generated by the model was compared to the

volume calculated by multiplying the catchment area by the rainfall depth.

In all cases, the difference in runoff volume estimated by both methods was less than 1% of the total

runoff volume and thus the volume checks were satisfied.

4.1.4.2 Rational Method Checks

In addition to the volume checks a further check of each RORB model was performed to verify the

peak flows generated. The RORB model was configured and run assuming that the catchment

contained no storages, these results were compared to the peak flow estimated using the Rational

Method, defined by the following equation;

Q C I Atc100 100 1000 278= . . ,

Where Q100 Peak discharge

C100 Runoff coefficient for a 1% probability event

Itc,100 100 year ARI rainfall intensity for a storm of duration tc

tc Time of concentration of the catchment

A Catchment Area

A runoff coefficient of 0.6 was adopted in line with the hydrologic modelling assumptions. The

rainfall intensity was estimated using the Algebraic Method outlined in Book 2 of Australian Rainfall

and Runoff (Institution of Engineers, 1998). The critical storm duration was checked by comparing

the duration of the critical storm from the RORB results with the time of concentration estimated

using the Bransbury Williams method.

Bransbury Williams

The Bransbury Williams formula is recommended as a reasonable approach to estimate the time of

concentration of a catchment as it includes provision to allow for slope of the catchment when

calculating response times;



tL

A Sc

e

=

58

0 1

0 2

.

.

Where tc time of concentration

L mainstream length measured from catchment divide

A catchment area

Se equal area slope of the main stream projected to the catchment divide

The Bransbury Williams method is used principally for the estimation of flows in ungauged rural

catchments. Limitations in the use of this method in urban areas chiefly relate to the lumping of

parameters at a single point in the catchment such that there is no distribution of catchment

characteristics. Nevertheless, past experience has shown these methods to be very useful in providing

first pass estimates of time of concentration and peak flow.

Table 4-2 below presents the results of the model verification.

Table 4-2 Hydrological Model Verification

Location Rational Method Flow

(m3/s)

RORB Peak Flow

(m3/s)

Node 13 19.3 17.0

Node 35 21.0 21.3

Node 52 North 12.4 12.1

Node 52 South 21.6 21.8

Node 52 Total 41.8 43.1

The estimates of flow obtained from the Bransbury Williams method agree with the values obtained

from RORB. This comparison yields a high degree of confidence in the performance of the RORB

model and is considered suitable for use in the preparation of design event hydrology information for

subsequent hydraulic modelling.

4.2 Hydraulics

4.2.1 Model Selection

Hydraulic assessment of the flooding characteristics within the Rippleside catchment was undertaken

using a fully 2D modelling approach that included the provision of key elements of the underground

drainage system. The model provided full dynamic interaction of the overland and underground

systems. WBM’s modelling system TUFLOW was favoured over other similar systems (eg. Mike21)

for the following reasons:

• Fully geo-referenced flood modelling capability allowing direct integration of the DEM

information within the model.



• Dynamic simulation of 1D elements means that culverts, bridges, weirs and other 1 dimensional

elements are modelled at the same time as the overland system and allow direct interaction

between the two conveyance mechanisms.

• Fully integrated with GIS for floodmapping of the resulting flood extent and inundation depths

allowing easy interrogation of flood information against other GIS related data (eg. floor levels,

property boundaries).

• Suitability for time varying simulations with robust wetting and drying algorithms promoting

model stability and accurate representation of floodplain hydraulics.

4.2.2 Model Development

Drainage design information was used to provide detailed information in the development of the

TUFLOW hydraulic model. Overland flood flow paths were established from on-site inspections and

review of the detailed Digital Elevation Model.

4.2.2.1 Model Geometry

The geometry of the 2D model was established by constructing a uniform grid of rectangular cells

using the following information:

• The detailed Digital Elevation Model developed from photogrammetry of the study area;

• Major waterway openings associated with road crossings (eg. Weddell Rd); and

• Key control points based on specific ground survey.

• As discussed previously, 1D components of the model included key elements of the underground

drainage system, hydraulic structures and extensions upstream and downstream of the 2D

modelling domain. These components of the model were established using the detailed drainage

information provided by City of Greater Geelong.

The model was developed using typical roughness parameters for the urban areas. Table 4-3 below

presents the key Manning’s n coefficients used in the model.

Table 4-3 TUFLOW Manning’s n Coefficients

Commercial/Industrial 0.280

Residential 0.280

Roads 0.022

Grassed Floodways 0.033

Railway 0.080

4.2.2.2 Model Resolution

One of the key considerations in establishing a 2D hydraulic model relates to the selection of an

appropriate grid size. Grid size or model resolution must be balanced in consideration of the goals of



the study and computation efficiency. Accordingly, the grid resolution must be selected to provide a

suitable compromise of the following:

• The grid resolution must be fine enough to provide sufficient representation of the modelling

domain to accurately simulate the physical characteristics the study area; and

• The grid resolution must result in a model with number of elements that will not result in

unrealistically long run times. Model run times of greater than 10 hours are generally not

considered to be practical.

The computation cell size for the TUFLOW model was set at 5m. In adopting the grid size for the

Rippleside 2D model the above mentioned issues were considered in accordance with the final

objectives of the study and production of detailed flood maps. A 5m grid size over the study area

provides a good definition of land shape, key controls and waterways.

In TUFLOW, the computation nodes are located at cell centres, midsides and corners, such that the

spatial resolution of the underlying terrain is twice that of the model (ie. 2.5m). Water levels are

calculated at cell corners and velocities at cell midsides.

The model domain and underground network are shown in Figure 4.2. All hydraulic parameters

describing the underground pipe network were provided in the City of Greater Geelong data set. It

has been assumed that there is no restriction to the entry of stormwaters into the underground system

and that the pipes are free from debris, etc such that they flow at design capacity.

4.2.3 Model Boundary Conditions

Boundary conditions for flood water inflows are provided by the hydrologic (RORB) modelling.

Point inflows, from an adjoining sub-catchment, are input at the edge of the model. Local inflows,

derived from a catchment within the 2D model domain, are distributed as inflows at a number of

locations along the reach, depending on the length of reach and size of catchment.

The downstream boundary condition for the mapping area is a constant tail water level set at mean

sea level in Corio Bay. Sensitivity testing indicated that setting this level at high or low water did not

influence flooding in the study area of the Rippleside catchment.

4.3 Flood Mapping

For each event, simulations of the range of selected durations were undertaken. The maxima of these

simulations provides the flood level envelope. Flood extents are derived from comparison of these

data with the DEM and are shown in Figure 4.3.

Figure 4.3 displays the inundation extent for the design 100y event. Complete mapping for the

existing conditions for the 5y, 10y, 20y, 50y and 100y design flood events is provided on separate

plans. The number of properties inundated above floor level is shown in Table 4-4.



Table 4-4 Number of Properties Inundated Above Floor Level

Design Event 5y 10y 20y 50y 100y

Number of Properties

Inundated above Floor Level

5 5 6 13 21

4.4 Building Inundation

The modelling indicates flood inundation to a number of residential and commercial properties in the

drainage system. Floor level survey was gathered by City of Greater Geelong and compared with the

inundation depths generated by the model. In total, approximately 130 floor levels were gathered and

of these it was found that 21 properties were inundated above floor level.

Figure 4.4 below shows the 100y design flood extent and surveyed property locations. Properties

shown in red indicated a flood level above the floor level at that location, while points in green

indicate a floor level above 100y design flood level.

The floor level survey revealed many properties with floor levels near the 100y design flood level. Of

the 130 properties surveyed, 56 were within 25mm of the 100y design flood level at that location.

Due to sub-scale features (ie topographic features on a less than 5m scale) flooding of individual

properties may or may not occur.

4.5 Flood Hazard Mapping

Public Safety is a significant issue for Council. In terms of flooding and drainage, public safety

relates to direct risks from flooding (eg. injury or death resulting from drowning) and indirect (eg.

injury from car accidents resulting from poorly drained roadways).

A measure of Public Safety or Risk is often defined relating to flood depth and/or flood velocity. In

this investigation, safety criteria have been adopted using velocity and depth criteria as defined by

Melbourne Water (as instructed by Council). The criteria are defined in Table 4-5 below. The

quantity RISK is defined as:

RISK = maximum ( Velocity x Depth , Depth )

Table 4-5 Hazard Categories

Risk Category Criteria

Low RISK ≤ 0.4

Moderate 0.4 < RISK ≤ 0.8

High RISK > 0.8



Within the catchment of Rippleside RISK is presented for the existing case (related to the 100 year

design event) in Figure 4.5. The figure indicates that areas of high and unacceptable RISK are

limited to flooded areas of significant depth inundation. Areas of particular concern are:

• Lantana Ave

• Grace McKellar

• Golf Course areas

• Lily Street

• Retarding basins upstream of Weddell Road

• Baxter Road Retarding Basin

4.6 Flooding Issues

The design flood modelling has illustrated a number of flood related issues for investigation.

Residents within the area have previously identified many of these issues. Figure 4.6 below identifies

the key flooding issues for which subsequent mitigation options will seek to minimise.

1 Flooding in Colville Ct

2 Overland flow through Bayview Parade properties

3 Overland flow through Lily St properties

4 Flooding Behind Railway in Lantana Ave and Marlo St

5 Flooding through Montgomery Street properties

6 Flooding along Hepner Place

7 Overland flow along The Fairway

8 No increase in Flooding at Baxter Road

The identification of these issues leads to the preparation of mitigation options. These are presented in

the next section.

It should be noted that:

• Floods greater than the one percent flood can occur. During such floods an area greater than that

shown would be inundated. Conversely properties within the area shown can be affected by

floods of lesser magnitude.

• Local flooding of other areas, or in excess of levels shown, may occur. The extent of flooding

shown relates to flooding from mapped reaches of Council's drainage systems only, and does not

adjacent catchments or private drainage systems.

• Local increases in flood levels, depths and/or velocities shown may result from local factors such

as drain blockages, and local obstructions to overland flows such as fences, buildings and cars.



rw0724

Typewriter

4

MITIGATION ASSESSMENT 5-1


5 MITIGATION ASSESSMENT

Review of the existing flood situation in Rippleside has identified a number of significant flooding

issues. In this section drainage augmentation options to address these issues are evaluated.

5.1 Mitigation Option Elements

Figure 5.2 below presents the various mitigation option elements tested at Rippleside. Following

consultation with the City of Greater Geelong a range of option elements were developed. The

following describes 12 of the elements tested (selected as practical options for addressing individual

flooding issues). A brief rationale behind their development is included.

0 Do Nothing

The “Do Nothing” or maintain the status quo option needs to be considered as a base from

which comparisons can be made.

1 Lily Street – Augment pipe system along the length of Lily Street

This option is aimed at addressing flooding issues in Lily Street and potentially in the

Bayview Parade area. Pipes located under Lily St as locating the pipes under the drainage line

would require placement through properties with residences (some as slab on ground)

1a Lily Street – Augment pipe system in lower Lily Street only

The most sever flooding in Lily Street is at the lower end. This option to address the most

severe flooding directly with possible follow on improvements in the upper system

2 Retarding Basin upstream of Lantana Ave

This option is designed to reduce/control the volume of floodwater entering the Lantana Ave

area from the upper catchment. Some redirection of upper cathcment flows in included to

minimise the depth of flooding in Lanatana Ave with possible follow on effects downstream

in Montgomery Ave and Ballarat Rd

3 Upgrade pipe capacity under Ballarat Rd

This option is to directly address the lack of capacity under Ballarat Rd with follow on effects

at Montgomery Ave

4 Upgrade pipe capacity under Hepner Pl

This option is to address flooding in Hepner Place due to exceeded pipe capacity.

4a Upgrade pipe capacity under Hepner Pl and add Retarding Basin below Hepner Pl

Increasing flow conveyance in Hepner Pl may increase flooding in downstream areas. This

option is aimed at reducing any such adverse impacts

5 Retarding Basin upstream of Hepner Place

An alternative to Option 4/4a. Construction of a retarding basin upstream of Hepner Place in

the Golf Course to reduce/control flood flows along Hepner Place

6 Pipe upgrade through Grace McKellar

An attempt to reduce flooding in the Grace McKellar property by increasing the capacity of

the underground system. Includes pipe upgrades under Ballarat Rd.

7 Retarding Basin in Hurst Reserve

This option designed to reduce/control overland flood flows through the Bayview Parade

area. Some excavation of the park is included to maximise storage

8 Pipe upgrade along The Fairway

Flood flows along The Fairway restrict access to and from properties in the street and pose a



public safety risk. This option is designed to minimise that risk by providing additional

underground capacity.

9 Upgrade pipe capacity from Lantana Ave through to Ballarat Rd

This option designed to address flooding issues in the Lantana Ave/Montgomery Ave area

and at Ballarat Rd.

Each of these elements has various impacts on the existing flood characteristics of Rippleside.

Appendix B illustrates the flooding impact graphically as an increase or decrease in flood level

resulting from the hydraulic influence of each element.

The floor level survey data has been integrated with the option assessment. Of the 130 properties that

were surveyed, comparisons of flood and floor levels indicate that 21 buildings are inundated above

floor level in the 100y design event. Only 9 floors are inundated by greater than 0.1m. Table 5-1

below indicates the relief provided to relevant flooded floors by each of the elements tested. In the

table, Floors Affected means the number of floors flooded in the existing case for which the element

is attempting to provide relief. Floors Relieved is the number of those floors for which relief is

provided. Elsewhere indicates secondary flood effects (positive or negative) of the option.

Within the catchment there are two areas where flooding is of particular concern due to the frequency

of flooding (from resident complaints) and the severity of the depth of flooding leading t a significant

public safety risk. These areas are:

• Drainage line parallel to Lily Street

• Lantana Ave through to Ballarat Rd

In both cases only a limited number of properties are inundated above floor level for the 100y design

event.

Lily Street

Although only 2 floors are inundated in the 100y event, 27 properties in this area are affected by

flooding. Pipe upgrades in Lily Street (Option 1 and 1a) appear to adequately address the flooding of

floors at units at the corner of Lily and Graham Streets and reduce flood levels in the area. However,

the gully line runs through many properties and complete flood relief through the provision of 100y

capacity drainage is unlikely to be practical.

Lantana Ave to Ballarat Rd

Flooding in this area is due primarily to the ponding of flood waters behind barriers. In Lantana Ave

the Railway line constrains flood conveyance while on Ballarat Rd, the road and the median strip

prevent adequate flood conveyance. In total, some 30 properties are affected with 5 properties

inundated above floor level.

Options 2, 3, 6 and 9 all provide differing mechanism for flood relief. However, in each case, flood

levels reduce below floor level for only 2 of the properties flood affected above floor level.



Table 5-1 Effect of Options on Existing Flooding

Case Floors Affected Floors Relieved Elsewhere

1. Lily St Pipe Upgrade 2 2 Increase in flood

levels in Baxter

Rd RB

1a. Lower Lily St Pipe Upgrade 2 2 Increase in flood

levels in Baxter

Rd RB

2. Lantana Ave Retarding Basin 5 2 1 additional floor

relieved

3. Ballarat Rd Pipe Upgrade 5 2

4. Hepner Pl Pipe Upgrade 2 2 Increase in flood

levels in Baxter

Rd RB

4a. Hepner Pl Pipe Upgrade and

Weddell Road RB

2 2

5. Hepner Pl Retarding Basin 2 2

6. Grace McKellar Pipe Upgrade 6 2 1 additional floor

relieved

7. Hurst Reserve Retarding Basin 5 1 4 additional floors

flooded

8. The Fairway Pipe Upgrade 0 0

9. Lantana Ave – Ballarat Rd Pipe

Upgrade

5 3



5.2 Preferred Approach for Augmentation

From review of the affect of each of the flood options a combination of elements was identified that

best addresses flooding issues in the Rippleside catchment. Figure 5.3 below illustrates the combined

elements, as listed below:

1a Lily Street – Augment pipe system in lower Lily Street (2 x 1350 RCP x 150m)

4a Upgrade pipe capacity under Hepner Place (1 x 1500 RCP x 25m, 2 x 1200 RCP x 235m,

2 x 1350 RCP x 35m) and add Retarding Basin below Hepner Place

6 Pipe upgrade through Grace McKellar (1 x 1050 RCP x 70m, 1 x 1200 RCP x 70m,

2 x 1050 RCP x 130) and under Ballarat Rd (4 x 1050 RCP x 20m, 4 x 1200 RCP x 20m)

8 Pipe upgrade along The Fairway (2 x 900 RCP x 380m)

The retarding basin proposed below Hepner place is designed with a bund wall set to a level of

14.5m AHD. The design capacity at full level is 15,850m3. The storage curve for the retarding basin

is shown in Figure 5.1 below

12

12.5

13

13.5

14

14.5

15

0 5000 10000 15000 20000

Storage (m3)

Wa

ter

Le

ve

l (m

AH

D)

Figure 5.1 Weddell Road Retarding Basin Storage Characteristics

Existing Case design flow information is provided in Appendix D.

Figure 5.4 displays the inundation extent for the design 100y event for the preferred combination of

options. Complete mapping for the preferred case for the 5y, 10y, 20y, 50y and 100y design flood

events is provided on separate plans.

Of the 21 properties that experience flooding above floor level in the 100y design event the

augmentation relieves the threat to only 7. Properties that remain likely to be inundated in the 100y

design event are shown in Figure 5.5.



For the properties in the Grace McKellar and Montgomery Ave areas it is likely that sub-scale

features will dominate local flooding behaviour and that above floor level inundation will not occur in

the existing or preferred cases. This is also likely to be true also for the property in Calvert St.

None of the mitigation options assessed adequately deals with flooding in the Colville Ct area.

Mitigation options further upstream (outside the study area) may need to be employed to reduce the

threat of flooding in these areas.

5.3 Flood Hazard Mapping

Figure 5.6 illustrates flood hazard following the introduction of the augmentation scheme. As with

the existing case, areas of high and unacceptable risk are limited to those areas of significant flood

inundation depth. Areas that remain categorised as high risk are:

• Lantana Ave

• Golf Course areas

• Retarding basins upstream of Weddell Road

• Baxter Road Retarding Basin

Significantly, high risk areas in Lily Street and through Grace McKellar have been reduced as a result

of the augmentation works.

5.4 Other Impacts

Any drainage augmentation scheme will have other impacts beyond those directly associated with

flooding. Most apparent are those impacts that effect the community and environment during

construction works.

Social impacts during construction can include disruption to traffic flows and significant

inconvenience for residents in those areas that are nearest to the proposed works. Where works are

proposed in industrial or commercial areas, there may be impacts to trade or manufacture for the

companies in the area as a result of restricted access for larger vehicles due to, for example, road

closures.

For this augmentation scheme, such social impacts to residential areas would be limited to those

works associated with the Lily Street upgrade. The commercial areas in Hepner Place could also be

impacted during construction works. Careful management of the construction activities along with

planning of the timing of such works to coincide with lower traffic volumes will assist in minimising

disruptions. Residents would also need to be informed of the impending likely disruptions to allow

for time for the resident to implement any compensatory action (eg commercial business stocking

up).

Works to increase the drainage capacity under Ballarat Rd could have a major impact on the

community through disruption to traffic flows. As Ballarat Rd is the responsibility of VicRoads,

management and construction of the augmentation works in this area may also be the responsibility of

VicRoads.



The environmental impacts associated with construction site activities are well documented and relate

primarily to impacts associated with uncontrolled export of sediment from the construction site, either

as dust or in stormwater runoff. Sediment control and construction site environmental management

are now recognised elements of the management of any construction site. A range of management

strategies are available for the identification of environmental threats and values associated with the

construction site activities as well as methods to minimise any such impacts (eg silt screens and

siltation basins).

Minor earthworks would be required in areas where augmentation of the underground pipe system is

required. More significant earthworks would be required for the construction of the retarding basin

below Hepner Place. In all cases, recognised environmental management and sediment control

techniques would need to be employed throughout the construction phase.

The social and environmental impacts of drainage augmentation construction activities are generally

well known and predictable. Through adequate management their impact is generally low.

ECONOMIC ASSESSMENT 6-1


6 ECONOMIC ASSESSMENT

An economic evaluation of the proposed augmentation has been undertaken to consider the

benefit/cost of the proposed works and to assess possible funding mechanism available to the City of

Greater Geelong.

6.1 Flood Damages Assessment

Flood damage assessment is an important component of any flood plain management framework.

This type of analysis enables the flood plain manager to gain an understanding of the magnitude of

assets under threat each year by flooding.

6.1.1 Stage Damage Curves

ANUFLOOD residential stage damage curves were used for this flood damage assessment. These

curves were sourced from the RAM (Rapid Appraisal Method) report (NRE, 2000). The non-

residential stage-damage curves, also ANUFLOOD curves, were sourced from a journal paper by

Smith (1994) “Flood Damage Estimation – A review of urban stage-damage curves and loss

functions”. The curves used are in 1993-dollar terms and have been indexed to 2000 units using a

CPI factor of 1.14.

ANUFLOOD has 15 non-residential stage damage curves. For each building size (small, medium

and large), there are 5 curves representing 5 value classes. As the Rippleside Study considered only 3

value classes (poor, average and good) the ANUFLOOD curves were reduced to 3 value classes per

building size by averaging the 2 lowest and the 2 highest curves. This reduces the number of curves

used for the non-residential damage assessment from 15 to 9.

For the Large non-residential curves, a building size in m2 is required as the damage values are given

in $/m2. As this data was not collected in the Rippleside survey, it was assumed that the average large

non-residential building size was 1000m2. This assumption is consistent with the RAM classification

of buildings as large if the area exceeds 1000m2.

It is widely recognised and documented in the RAM report (NRE, 2000) that the ANUFLOOD

curves underpredict flood damages. Increases of 60% have been applied to both the residential and

non-residential curves as recommended in RAM.

Ratios to convert Potential damages to Actual damages are used as per the recommendations from the

RAM report. That is, for a relatively unprepared community with less than 12 hours warning time a

factor (ratio) of 0.7 is used to reduce the potential damages to actual damages. Flood damages were

calculated from water surface profiles generated for the 5, 10, 20, 50 and 100 year design events.

6.1.2 Outside Buildings

Damages to equipment outside of the building are not included in the stage damage curves used.

Such damages may include damage to fences, driveways, lower level laundries, outdoor equipment

etc. The loss of plants, lawn, landscaping is difficult to quantify and is not included in this but rather

should be included in the intangibles. Thus, an estimate of “ground equipment damages” has been



made as a function of ground level inundation. That is, assume a sliding scale from $0 to $1000 with

$1000 being the maximum. The full $1000 damage is experienced once the flood level has reached

the floor level of the building. The sliding scale works on the difference between the ground level

and the floor level (eg a ground level of 1m, floor level of 2m, flood level of 1.5m receives ground

equipment damages of $500).

Ground damages for properties where floodwaters enter the property for which there is no

information on floor level (as it has been assumed not to overtop floorlevel) has been arbitrarily set at

the average ground damages cost for properties where floor level surveys have occurred.

6.1.3 Damages

Using the ANUFLOOD curves for the catchment of Rippleside the AAD (Average Annual Damage)

has been calculated to be $63,000 for the existing situation.

This Damages Assessment has been integrated with a “board brush” mitigation option assessment. In

this manner the cost benefit of measures likely to reduce the impact of flooding on the community

within Rippleside can be assessed. For the preferred approach the AAD has been calculated as

$59,000.

Figure 6.1 illustrates the event based flood damage curves.

Rippleside Flood Damages

Existing and Augmented Condition

$-

$100

$200

$300

$400

$500

$600

$700

$800

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50%

AEP (%)

Da

ma

ge

s (

$1

00

0)

Existing

Augmented

Limit of Flood Data. Curves formed by

extrapolation beyond this line

Figure 6.1 Rippleside Flood Damage Curves



6.2 Benefit Cost Ratio

Benefit Cost Ratio (BCR) is a measure of the benefit of implementing a project, in consideration of

the direct and tangible costs. A BCR greater than 1 indicates that the total benefit received over the

lifetime of the project exceeds the cost of undertaking the works. A BCR less than 1 indicates that the

costs exceed the benefits over the lifetime of the project.

6.2.1 Cost

To calculate BCR an estimate of undertaking the construction works for the augmentation is required.

The City of Greater Geelong has provided indicative costs for pipe augmentation works as presented

in Table 6-1 below.

Table 6-1 Guideline Per metre Costs for Pipe Augmentation Works

Pipe Size Works Under

Unpaved Areas Works Under Roads Areas

(mm) ($ / linear m) ($ / linear m)

900 $350 $650

1050 $450 $800

1200 $500 $900

1350 $700 $1,150

1500 $850 $1,350

1650 $1,050 $1,600

Where pipe augmentation works include the provision of parallel pipes, rather than adopting a cost of

twice the linear cost, a saving of 20% per m is applied as an estimate to account for construction

savings.

Additionally the cost of works to create a Retarding Basin (option 4a) below Hepner Place are

estimated based on the length of the bund wall required, in this case approx 150m. An estimated cost

of $250 per linear metre of bund wall has been adopted. Maintenance costs for the basin have not

been included in the calculations.

The estimated cost of works for the augmentation is shown in Table 6-2 below with a detailed

breakdown of Costs in Table 6-3. Note that a contingency amount, typically 10-20% of the total

project cost, has not been included in the cost estimate.

Table 6-2 Estimated Cost of Augmentation Works

Option Element Cost ($)

Option 1a $ 350,000.00

Option 4a $ 636,250.00

Option 6 $ 329,500.00

Option 8 $ 504,000.00

Total $ 1,819,750.00



Table 6-3 Detailed Breakdown of Cost Estimate

Option Item No Length/Area Unit Rate Amount Sum

Option 1a $ 350,000.00

Supply, trench, bed, lay, joint, backfill, compact and reinstate surface for 2x1350 RCP 2 150 m 1150 345000

Pits at 100m intervals 2 ea 2500 5000

Acquire reserve / easement Ha 150000

Option 4a $ 636,250.00





Acquire reserve / easement at end of Hepner Place 0.02 Ha 150000 3000

Retarding Basin Construction Costs 1 8000 m3 15 120000

Option 6 $ 329,500.00








Option 8 $ 504,000.00




Project $1,819,750.00



6.2.2 Benefit

The benefit of the augmentation works is the difference between the average annual damages before

and after the augmentation represented as a Present Value over the design lifetime of the project. The

Present Value (PV) of the benefit was calculated using a discount rate of 6% and a project life of 30

years, as suggested by RAM, using the following formula.

t

t

ii

iaPV

)1(

1)1(

+

−+=

Where a is the AAD benefit, i is the discount rate and t is the term.

The AAD benefit is $4,000 ($63,000 - $59,000). The Present Value of this benefit over a 30 year

lifetime is $55,000. RAM suggests that a planning and discount horizon of 30 years be adopted for

assessment of economic benefits, even though there may be longer term benefits. It should be noted

that due to the asymptotic nature of the calculation of Present Value, use of a longer term does not

provide significant enhancement to the calculation of benefit (eg. PV for $4000 over a 50 year term at

6% discount rate is $63,000)

6.2.3 Benefit Cost

The Benefit Cost Ratio for the augmentation works is $55,000 / $1.74M = 0.03. This is an extremely

low BCR.

The BCR is low because the AAD benefit is low ($4,000). The benefits gained by the augmentation

works are only recognised over a few properties and provide benefit only in the less frequent events

(>20y return period).

6.3 Intangible Damages/Benefits

Floods impose intangible damages on the community. These include the emotional, mental and

physical ill health of the victims of the flood. It is always difficult to assess these damages in terms of

financial loss or cost but is clear that reduction in frequency or severity of flooding will have

considerable benefit to the well being of the community. This could in turn result in follow-on effects

relating to greater community support and acceptance strategies for flood mitigation proposed by

Council.

The emotional costs of flooding can persist for many years. A survey of flood victims undertaken 15

months following the 1974 floods of the Brisbane River found that approximately ¼ of victims had

not recovered from the emotional trauma of the flooding (Chamberlain, et al 1981). Hardest hit were

elderly members of the community and others of lower socio-economic status.

Communities that are prepared and aware of the risks of flooding tend to suffer less financial and

emotional hardship than those that are poorly prepared. The calculation of financial loss specifically

takes into consideration community preparedness in estimating damages. Damages in an unprepared

community can be as much as twice that of a prepared community. It is reasonable to assume that

intangible damages will react in a similar fashion with respect to community preparedness.



Loss of life in floods is remarkably low in Australia. For example, in the 1974 Brisbane floods 30,000

homes were inundated with the loss of only 12 lives. Typically loss of life in floods is due to

accidents such as road accidents or electrocution rather than people being swept away.

Floods can result in significant emotion stress within the community. Education and awareness, along

with suitable flood relief, provide an effective mechanism for the reduction in such intangible

damages.

6.4 Funding Mechanisms – Special Rates and Charges

Funding mechanisms available to Council for the upgrade of drainage infrastructure typically fall into

one of two categories:

• Private Benefit for which a user-charge typically applies associated with a direct link between

the infrastructure provided and the benefit received

• Public Benefit is related to infrastructure that provides a benefit to the wider community

throughout the municipality

Clearly, augmentation works undertaken within the catchment of Rippleside are for the direct benefit

of those residents with an existing flooding problem or threat. There exists an indirect benefit to those

residents within the catchment associated with increased trafficability of roads subject to flooding as

well as public health and safety issues and other intangible benefits.

Special Rates and Charges are the typical mechanism for funding of drainage works. Section 163 of

the Local Government Act 1989 sets out the provisions for the issue of a special rate, charge or

combination of these. The purpose of the rate or charge is to recoup costs associated with the

provision of infrastructure. The charge is typically a one-off payment while a rate is an incremental

payment made over a number of years.

Recent decisions handed down at the Administrative Appeals Tribunal suggests a more confined

application of special rates and charges particularly in relation to drainage augmentation schemes. In

essence the Ball decision (Appeal No 1993/37685) concluded:

• A special rate or charge can only be levied where a special benefit is received

• The special benefit must be received by the land owners (rather than the property)

• In this context, a special benefit was recognised by the Tribunal as an increase in property

values.

That is, while every property in the catchment receives, to a greater or lesser degree, a benefit from

the drainage augmentation works, that benefit does not translate into an increase in property values

and therefore not a special benefit. Thus, funding via special rates and charges is not applicable.

Furthermore, the Tribunal ruled that where:

… properties are already drained to lawful points of discharge and the provision of

additional capacity in the main drainage system, although obviously required to drain

the entire catchment, will not provide a special benefit to them as owners of their land.

Appeal No 1993/37685 pg 7



This would indicate that drainage augmentation works for any undersized drainage system does not

provide a special benefit to property owners in the catchment and therefore the ruling would imply

that in the case of the Rippleside Main Drain Augmentation funding cannot be sourced via special

rates and charges.

However, several other related rulings have occurred since the 1993 AAT decision regarding Ocean

Grove. Some of the decisions take an alternative interpretation of the application of Special Rates and

Charges to drainage infrastructure projects.

Additional legal advice in this regard has been sought (See Appendix C).

6.5 Development Control in Flood Prone Areas

The Victorian Planning Provision and the City of Greater Geelong Planning Scheme provide a

number of mechanisms, via zones and overlays, for the control of development in flood prone areas.

The zones and overlays that relate to flooding include:

• Urban Floodway Zone (UFZ)

• Floodway Overlay (FO)

• Rural Floodway Overlay (RFO)

• Land Subject to Inundation Overlay (LSIO)

• Special Building Overlay (SBO)

Overlays are shown on the planning scheme in addition to zonings and apply in addition to the

provisions of the zone. The application of the appropriate overlay is set out in the Geelong Planning

Scheme documentation as follows:

Applying Zones and Overlays

• Applying the Urban Floodway Zone to locations in the urban areas that are high

hazard and active floodways and where strict control over land use is required.

• Applying the Floodway Overlay to locations in the urban areas that are high

hazard and active floodways.

• Applying the Rural Floodway Overlay to locations in the rural areas that are

high hazard and active floodways.

• Applying the Land Subject to Inundation Overlay to locations in both the

urban and rural areas that are subject to periodic inundation but which are not

high hazard nor active floodplains.

• Applying the Special Building Overlay to land in urban areas that are subject to

inundation by surcharge flows from urban drainage systems, such as Barwon

Heads and Corio.

In the catchment of Rippleside, the Special Building Overlay can be used by Council as a method to

control development in flood prone areas, particularly where the flooding is as a result of surcharged

underground drainage (as is the case here).



6.6 Discussion

AAD is calculated from an integral of the Damage Curves (Figure 6.1). Although considerable

benefit from less frequent (and more severe) floods has been achieved, there is no discernible change

in the damage curves for events more frequent than 20 years. Properties in the flow path as “slab on

ground” do not receive any benefit from the augmentation works. Benefits to these properties would

significantly improve the Benefit Cost Ratio.

Benefits to these properties would be via mechanism other than drainage augmentation works. The

most appropriate mechanisms would appear to be:

• Individual flood protection (levees etc)

• Buy back of the property (with a view to creation of flood conveyance)

The suitability of each mechanism would need to be investigated on a case by case basis, which is

beyond the scope the current investigation. Nevertheless, a cursory review of the available survey

information and site inspection have been undertaken to provide some guidance in this regard. With

reference to Figure 6.2, it is considered that

• units at 257 Church Street would benefit from individual flood protection

• flood prone properties in the Montgomery Ave area could fall under a buyback scheme to create

a flood conveyance and/or storage in this critical area within the catchment

STORMWATER MANAGEMENT PLAN 7-1


7 STORMWATER MANAGEMENT PLAN

There have long been public health issues relating to the discharge of stormwater from the catchment

to the waters of Corio Bay at Rippleside Beach. Chiefly, these relate to high E. coli counts at the

beach leading to frequent beach closures. In addition, issues relating to the control of catchment

runoff containing a high nutrient load are also of concern.

Stormwater management and the preparation of a Stormwater Management Plan were originally

within the scope of this Drainage Augmentation Project. However, In recognition of the importance

of these issues, Council expanded the scope of the Stormwater Management component of the study

and released this as a separate brief.

WBM have undertaken preparation of a stormwater management plan as a separate project for

Council. However, in recognition of the linkages between stormwater management and flooding

cross-over between the two projects has occurred to ensure consistency between the two projects, as

follows:

• Stormwater modelling assessments for the design of wetlands and other stormwater control

features utilise equivalent hydrological and hydraulic modelling components. Hydraulic model

outputs are used to provide hydraulic boundary conditions for the stormwater management

modelling procedures.

• Stormwater control features in the main flood flow path are included in the hydraulic

assessments to ensure the features do not exacerbate existing flooding problems in the

catchment.

These feedback loops provide the flooding and stormwater assessments with a fully integrated

assessment of the impacts of proposed works in the catchment.

CONCLUSION 8-1


8 CONCLUSION

The Rippleside Drainage Augmentation study provides a comprehensive evaluation of flooding threat

within the catchment. Key findings of the study are as follows:

• Areas in the catchment are prone to frequent flooding due to the typically undersized

underground drainage capacity and/or little or no overland flood flow conveyance capacity

• The 100y design flood event inundates 727 properties in the flood mapping area. Of these,

modelling indicates a total of 21 are inundated above flood level (9 with above floor level

inundation of greater than 0.1m).

• Within the flood mapping area, model results indicate inundation above floor level for 6

properties during the 20y design flood.

• Few options for significant reductions in flood levels at properties inundated above floor level

exist due to the age of the system and limited opportunity to provide additional overland

conveyance and storage capacity.

• The Average Annual Damage due to flooding in the Rippleside catchment has been calculated as

$63,000 for the existing case and $59,000 for the augmentation option with an Average Annual

Benefit of $4,000.

Note that the findings of this study and the conclusions above relate to flood modelling results within

the designated study area (See Figure 1.1). Flooding in other areas of the catchment may occur and as

such may influence that assessment of flood risk in the catchment as well as the assessment of

Average Annual Damages and Benefit.

SURVEY REPORT A-1

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 A-1O C E A N I C S A U S T R A L I A

APPENDIX A: SURVEY REPORT

MITIGATION OPTIONS – ELEMENT IMPACTS B-1

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 B-1O C E A N I C S A U S T R A L I A

APPENDIX B: MITIGATION OPTIONS – ELEMENT IMPACTS

The following figures provide an illustrative presentation of the impact of each flood mitigation option element

tested with respect to the 100y design flood event. Increases and decreases in peak flood level are presented.

Mitigation Option ImpactsElement 1 - Lily Street Pipe Upgrade

Figure B-1

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 1a - Lower Lily Street Pipe Upgrade

Figure B-1a

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 2 - Vines Road Retarding Basin

Figure B-2

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 3 - Pipe Upgrade Under Ballarat Rd

Figure B-3

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 4 - Pipe Upgrade Along Hepner Place

Figure B-4

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 4a - Pipe Upgrade Hepner Pl & Retarding Basin

Figure B-4a

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 5 - Retarding Basin Upstream of Hepner Pl

Figure B-5

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 6 - Pipe Upgrade Ballarat Rd and Grace McKellar

Figure B-6

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 7 - Retarding Basin Hurst Reserve

Figure B-7

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 8 - Pipe Upgrade The Fairway

Figure B-8

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

Mitigation Option ImpactsElement 9 - Pipe Upgrade Lantana Ave to Ballarat Rd

Figure B-9

OCEANICS AUSTRALIA

Lege

nd

0.5

- 0.

7 D

ecre

ase

0.3

- 0.

5 D

ecre

ase

0.1

- 0.

3 D

ecre

ase

No

Impa

ct

0.1

- 0.

3 In

crea

se

0.3

- 0.

5 In

crea

se

0.5

- 0.

7 In

crea

se

0.7

- 0.

9 In

crea

se

>0.9

Incr

ease

SPECIAL RATES AND CHARGES – LEGAL ADVICE C-1

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 C-1O C E A N I C S A U S T R A L I A

APPENDIX C: SPECIAL RATES AND CHARGES – LEGAL ADVICE

DESIGN FLOW INFORMATION D-1

K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 D-1O C E A N I C S A U S T R A L I A

APPENDIX D: DESIGN FLOW INFORMATION


K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 D-2O C E A N I C S A U S T R A L I A

Design Flows

Design flows for the 100, 50 and 20 year design events have been extracted from the model at each of

the augmentation option elements to provide information for future detailed design considerations.

Figure D1 shows the location of the extracted information. Table D-1 below summarises the design

event results and Figures D2-D5 present flow hydrographs for each event at each location.

Table D-1 Design Flow Summary

100y Design Flows

Lily Street Hepner Pl The Fairway Grace McKellar

Peak Time 1:15:00 1:35:00 0:55:00 1:30:00

Peak Flow 14.2 13.0 9.2 14.3

Overland 8.0 8.4 6.6 10.7

Underground 6.2 4.6 2.6 3.6

50y Design Flows


Peak Time 1:10:00 1:25:00 1:00:00 1:20:00

Peak Flow 12.3 11.2 7.4 12.0

Overland 5.8 6.6 4.8 8.4


20y Design Flows


Peak Time 0:50:00 1:35:00 1:00:00 1:20:00

Peak Flow 8.5 8.6 5.2 8.7

Overland 1.9 3.8 2.7 5.2



K:\INFRA_MGMT\RW\FLOOD STUDIES\RIPPLESIDE CAT FS\8. FINAL DOCS - MAPS\R.W00201.004.01.FINALREPORT.DOC 6/8/10 13:08 D-3 O C E A N I C S A U S T R A L I A



Figure D-2 100 Year Design Flow Hydrographs

Lily Street

-1

0

1

2

3

4

5

6

7

8

9

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

Hepner Place

-1

0

1

2

3

4

5

6

7

8

9

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

The Fairway

-1

0

1

2

3

4

5

6

7

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

Grace McKellar

-2

0

2

4

6

8

10

12

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground




Lily Street

-1

0

1

2

3

4

5

6

7

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

Hepner Place

-1

0

1

2

3

4

5

6

7

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

The Fairway

-1

0

1

2

3

4

5

6

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

Grace McKellar

-1

0

1

2

3

4

5

6

7

8

9

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground




Lily Street

-1

0

1

2

3

4

5

6

7

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

Hepner Place

-1

0

1

2

3

4

5

6

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

The Fairway

-0.5

0

0.5

1

1.5

2

2.5

3

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

Grace McKellar

-1

0

1

2

3

4

5

6

0:00:00 1:12:00 2:24:00 3:36:00 4:48:00

Time (Hours)

Flo

w (

cu

me

cs

)

Overland

Underground

· 2010-08-10 · Heights, Geelong West and Geelong North (See Figure 1.1). The catchment is...

Documents

Transcript of · 2010-08-10 · Heights, Geelong West and Geelong North (See Figure 1.1). The catchment is...