Final Report Port Adelaide Seawater Stormwater Flooding Study

93 Pages·2005·6.82 MB·English

City of Port Adelaide Enfield
O C E A N I C S A U S T R A L I A
Volume 1 (cid:150) Final Report
Port Adelaide Seawater Stormwater Flooding Study
Principal Contacts
Drew Jacobi (Tonkin Consulting)
Bill Syme (WBM Oceanics Australia)
October 2005
Ref No 20020477RA3D
OCEANICS AUSTRALIA
Table of Contents
Table of Contents
City of Port Adelaide Enfield
Port Adelaide Seawater Stormwater Flooding Study
Final Report
VOLUME 1 (cid:150) FINAL REPORT
1. Introduction 1
2. Land Subsidence 2

2.1 Background 2

2.2 Causes of Land Subsidence 3

2.3 Measurement of Land Subsidence 4

2.3.1 E&WS Survey Mark Re-levelling 4

2.3.2 Deep Bench Mark Survey 6

2.4 Future Changes to Land Subsidence Rates 6

2.4.1 Changes in Groundwater Use 6

2.4.2 Land Reclamation 7

2.5 Recommendations 7

2.5.1 Adoption of Land Subsidence Rates for this Study 7

2.5.2 Further Work 8
3. Tide Analysis 9

3.1 Storm Tide Analysis Summary 9

3.1.1 Overview 9

3.1.2 Tide Datums 9

3.1.3 Storm Height and Duration Analysis 10

3.1.4 Storm Tide Hydrograph Synthesis 11

3.1.5 Summary of Highest 25 Events 12

3.1.6 Basic Equations 14

3.2 Relationship between storm surges and rainfall events 14
4. Seawater Inundation and Protection 17

4.1 Introduction 17

4.2 Seawater Hydraulic Modelling 18

4.2.1 Data Collation and Review 18

4.2.2 Digital Elevation Model (DEM) Development 18

4.2.3 Hydraulic Model 19

4.3 Seawater Model Calibration 20

4.3.1 Selection of Seawater Calibration Event 20

4.3.2 Calibration to 1999 Event 23

4.4 Preliminary Future Conditions Modelling 26

4.5 Damages Assessment 27

4.6 Structural Condition Assessment 31

4.7 Seawater Flood Protection 31

4.8 Concept Sea Defence Upgrade 31

4.8.1 Background 31

4.8.2 Design Requirements 32

4.8.3 Concept Design 32

4.8.4 Outer Harbour 34

4.8.5 Estimated Costs 34
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Table of Contents
5. Local Stormwater Inundation and Protection 36

5.1 Introduction 36

5.2 Seawater (cid:150) Stormwater Interaction Methodology 36

5.3 TUFLOW Model 37

5.4 ILSAX Model 38

5.5 Design (cid:145)Average(cid:146) Tide Cycle 39

5.6 100 year ARI Tide Cycle 39

5.7 Stormwater Drainage Performance Measurement 40

5.8 Stormwater Drainage Performance Requirements 40

5.9 Possible Future Increases to Rainfall Intensities and Impacts 41

5.9.1 Literature Review 41

5.9.2 Rainfall Intensity Changes Adopted for this Study 42

5.10 Anthony Street Catchment 42

5.10.1 Existing System 42

5.10.2 Proposed Upgrade Works 43

5.11 Centre Street and Jetty Road Catchments 43

5.11.1 Existing System 43

5.11.2 Proposed Upgrade Works 44

5.12 Hamilton Avenue Catchment 44

5.12.1 Existing System 44

5.12.2 Proposed Upgrade Works 44

5.13 Osborne Catchment 45

5.13.1 Existing System 45

5.13.2 Proposed Upgrade Works 45

5.14 Port Adelaide Centre Catchment 46

5.14.1 Existing System 46

5.14.2 Proposed Upgrade Works 46

5.15 Semaphore Road Catchment 47

5.15.1 Existing System 47

5.15.2 Proposed Upgrade Works 48

5.16 Future Sea Level / Land Subsidence Scenarios 48

5.17 Upgrade Costs 48

5.18 Recommended Future Scenario 49

5.19 Further Work 50
6. Wetlands and Ponding Basins Inundation and Protection 51

6.1 Methodology and Procedure for Wetlands and Ponding Basins Modelling 51

6.1.1 Background 51

6.1.2 Hydraulic Model Development 51

6.1.3 Digital Elevation Model Development 52

6.1.4 Boundary Conditions 52

6.2 Wetlands and Ponding Basins Existing Drainage Systems / Existing Development 52

6.2.1 Barker Inlet Wetlands Management Plan 52

6.2.2 Sea Level Rise / Land Subsidence Combinations 53

6.2.3 Design Wetland Standing Water Level 53

6.2.4 Concept Seawall Alignment 54

6.2.5 Storm Duration 54

6.2.6 Flooding Scenarios (Sensitivity Tests) 56

6.3 Peak Flood Levels 57

6.4 Further Work 59
7. Summary 60
8. References 62

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Table of Contents
Tables

Table 2-1 Average Land Subsidence relative to Hope Valley Reservoir Bench Mark (Culver,

1970) 4

Table 2-2 Average Land Subsidence (1983-1994) relative to rock pin bench marks at the

Tollgate 6

Table 2-3 Discharge from Upper Tertiary Aquifer 6

Table 3-1 Tide Datums 9

Table 3-2 25 Highest Tidal Events 12

Table 3-3 Correlation Between Top 25 Storm Tide and Storm Surge Events 13

Table 3-4 Calculation Variables 14

Table 4-1 Dataset Acquisition and Sources 18

Table 4-2 Land Uses Types 19

Table 4-3 Meteorological Events with 25 Highest Peak Tide Heights 20

Table 4-4 Future Conditions Scenarios of Sea Level Rise and Land Subsidence 26

Table 4-5 Predicted Outer and Inner Harbour Levels 27

Table 4-6 RAM Damages for Large Non Residential Buildings 27

Table 4-7 Building Elevation Adjustments 28

Table 4-8 Building Size Classification 28

Table 4-9 100 year ARI Flood Damage Estimates 29

Table 4-10 Sea Defence System Required Threshold Levels 32

Table 4-11 Concept Sea Defence Upgrade Cost Estimates 34

Table 5-1 100 year ARI tide levels at Stormwater Outfalls 39

Table 5-2 Local Stormwater Drainage Upgrade Cost Estimates 49

Table 6-1 Design Standing Water Levels 53

Table 6-2 Wetland and Ponding Basins Peak Flood Levels 57

Table 6-3 100 Year Ponding Basin Peak Flood Levels Comparison 57

Table 6-4 Maximum Allowable Pond Flood Levels 58

Figures

Figure 2-1 Bench Mark Level Changes relative to Hope Valley (Culver, 1970) 5

Figure 3-1 Rainfall versus Tidal Anomaly (cid:150) Outer Harbour 16

Figure 3-2 Rainfall versus Tidal Anomaly (cid:150) Outer Harbour 16

Figure 4-1 June 1999 Seawater Calibration Event (Levels to mOHD) 22

Figure 4-2 Preliminary Model Calibration Results 24

Figure 4-3 Revised Model Calibration Results 25

Figure 4-4 Flood Damage Costs (Lower Case) 30

Figure 4-5 Flood Damage Costs (Upper Case) 30

Figure 4-6 Demountable Flood Defence System (Demflood System) 33

Figure 6-1 Magazine Creek Wetland Outlet 100 Year ARI Water Level Comparison 54

Figure 6-2 Range Wetland Outlet 100 Year ARI Water Level Comparison 55

Figure 6-3 Ponding Basin Outlet 100 Year ARI Water Level Comparison 55

Figure 6-4 Barker Inlet Wetland Outlet 100 Year ARI Water Level Comparison 56

Appendices

Appendix A Historical Upper Tertiary (T1) Aquifer Potentiometric Surface Levels (Gerges, 1996)

Appendix B Storm Tide Analysis Additional Information

Appendix C Historical Storm Tide Meteorological Profiles

VOLUME 2 (cid:150) DRAWINGS

City of Port Adelaide Enfield
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Document History and Status
Document History and Status
Rev Description Author Rev(cid:146)d App(cid:146)d Date

A Issued for review DJ/WJS KSS DJ 29/04/05
B Sec 3.2, 4.5 added DJ/WJS KSS DJ 18/05/05
C Final DJ/WJS KSS DJ 29/07/05
D Revised Ponding Basin Levels DJ/WJS KSS DJ 10/10/05

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Introduction
1. Introduction

The City of Port Adelaide Enfield together with project partners including the Coast
Protection Board, Flinders Ports, Torrens Catchment Water Management Board,
Land Management Corporation and Transport SA have commissioned this Study to
evaluate seawater and stormwater flood risks in Port Adelaide. Funding for the
Study has also been obtained from the Commonwealth Government under the
Natural Disasters Risk Management Studies Program.

The aim of the Flood Risk Management Study is to identify the risks and develop and
implement a strategy to protect the vulnerable areas of the City from the risk of
seawater and stormwater flooding taking into account the possible sea level rise and
land subsidence over the next hundred years. This Study is intended to be
conducted in three phases as follows:

 Phase 1: Risk Assessment/Preliminary Treatment (cid:150) Analyse and evaluate
risk of seawater and stormwater flooding and identify concept strategies.
 Phase 2: Risk Treatment Study (cid:150) Develop detailed strategies, including
design and development of management measures and development
controls.
 Phase 3: Treatment Implementation (cid:150) Implementation of control measures.

This report examines Phase 1 of the Flood Risk Management Study.

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Land Subsidence
2. Land Subsidence

2.1 Background
Historically land subsidence has been identified as a factor to be taken into account
in the analysis of tidal records. It is of particular importance in the estimation of rates
of sea level rise, and some studies have been undertaken to quantify land
subsidence along the Adelaide coastline in order to allow proper interpretation of tidal
records.

Land subsidence was first identified as potentially occurring in Port Adelaide and the
surrounding coastal regions as part of a Beach Erosion Assessment Study (Culver,
1970). This Study identified a trend in the change of Engineering and Water Supply
Department bench mark levels across metropolitan Adelaide during the period of
1872 to 1969, relative to a reference bench mark associated with the Hope Valley
reservoir that was assumed to be (cid:145)stable(cid:146). A spatial variation across the 42 bench
marks was observed, with calculated land subsidence rates increasing from nil in the
CBD to 0.6 ft/century (1.8 mm/yr) in the Port Adelaide (cid:150) Semaphore area.

In order to provide greater certainty to the suggested land subsidence rates
described above, particularly with respect to the stability of the reference bench
mark, the then South Australian Coastal Management Branch performed a precise
levelling survey. A network of deep benchmarks isolated from movement of the
surface sediments were linked to (cid:145)stable(cid:146) rock pin benchmarks in the foothills by
levelling to a high precision standard. Since the benchmarks were established in
1982, precise levelling surveys have been repeated in 1985, 1987 and 1994. The
results from the relatively short time period over which measurements have been
taken are in general agreement with the findings of the earlier Culver Study.

Some additional levelling surveys have been undertaken using GPS however the
vertical accuracy of this method is not considered to be adequate for this type of
analysis, particularly over a short period of observation.

More recently, land subsidence rate estimates were made from geological evidence
including radiocarbon dated palaeosea level indicators (Belperio, 1993). Land
subsidence rates ranging from 1.8 (cid:150) 10 mm/yr were calculated for a number of areas
in the region, with the major causes of the subsidence concluded to be surficial
compaction associated with wetland reclamation and groundwater withdrawal from
the upper Tertiary aquifer. Significantly, this work provides the only documented land
subsidence rates for Gillman.

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Land Subsidence
The discussion in this Section reviews the information provided by these
investigations.

2.2 Causes of Land Subsidence
Land subsidence factors that have been identified as being relevant to the Port
Adelaide region are discussed below.

Groundwater withdrawal
Intensive groundwater pumping has occurred within the Port Adelaide region which
has resulted in a significant modification to the potentiometric surface of the upper
Tertiary (T1) aquifer. A major cone of depression has developed (refer Appendix A),
attributable to the pumping regime at Penrice ICI and until recently, SAMCOR. This
extraction began in 1957.

The reduced water pressure within the aquifer allows for the slow drainage of clay
and silt layers within or adjacent to the sand and gravel layers. Due to the
compressibility of the clay and silt material compaction occurs which results in a
lowering of the land surface.

Land reclamation by draining of wetlands
The Gillman region has been subject to the artificial lowering (draining) of tidal
wetland areas through the construction of levee banks and low-tide discharge sluice
gates. This work commenced in 1894 and continued in stages to 1974. Levees and
pond construction works drained the Gillman area in 1935.

Lowering of the water table has caused consolidation, compaction and densification
of exposed, previously saturated sediments, leading to land subsidence.

In addition, portions of land reclaimed by the activities described above are underlain
by Coastal Acid Sulphate Soils (CASS). The extent of soils with acid sulphate
potential throughout South Australia was recently mapped (PIRSA, 2001). CASS
occur in both the sulfide rich potential state and the oxidised activated actual state.

Draining activities have resulted in the aeration of sulfide rich soils, allowing:

 the previously saturated soil to dry out, consolidate and compact;
 microbial oxidation of organic matter resulting in mass loss (Stephens et al,
1984)
 oxidation of iron sulfide material to occur resulting in the production of
sulphuric acid. The acid has generated highly acid groundwaters in the
Gillman area (pH 3.5-5.0) promoting extensive decalcification of sediments
to depths greater than 2m within and beneath the mangrove peat layer
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Land Subsidence
resulting in mass loss (Belperio, 1985; Belperio & Rice, 1989; Postma,
1983);
 flushing of carbonate dissolution products as a result of the use of the
reclaimed land as stormwater ponding basins (Belperio, 1993).

The land subsidence effects are most pronounced in areas where mangrove
woodland has been cleared and the sediment subjected to the processes described
above (Belperio, 1993).

Land reclamation by filling
Extensive areas throughout the Study Area have been subjected to the placement of
fill to achieve the current surface level. The weight of this overburden compresses
underlying low density layers, in particular, the Holocene substrate which results in a
lowering of the land surface.

Current knowledge of the depth and extent of historical filling activities across the
Study Area is fragmented and largely incomplete.

Long term subsidence of St Vincent Basin
The Study Area is located within the St Vincent Basin. Long term subsidence rates
within the basin are insignificant relative to the other factors described above.

2.3 Measurement of Land Subsidence
2.3.1 E&WS Survey Mark Re-levelling
The E&WS bench mark re-levelling data collected as part of a Beach Erosion
Assessment Study in 1970, provides land subsidence statistics as summarised in
Table 2-1 and shown spatially in Figure 2-1 below.

Table 2-1 Average Land Subsidence relative to Hope Valley Reservoir Bench
Mark (Culver, 1970)
Location Average Subsidence (mm/yr) Period
Port Adelaide -1.55 1872 - 1969
Largs Bay -1.65 1890 - 1969
Largs Bay -1.83 1899 - 1969
Largs Bay -1.13 1899 - 1969
LeFevre Peninsula -5.67 1899 - 1969
Largs Bay -1.83 1899 - 1969
Largs Bay -1.71 1899 - 1969
Semaphore Park +0.21 1901 - 1969
Semaphore Park -2.19 1901 - 1969
Semaphore Park -0.18 1901 - 1969
Semaphore Park -1.80 1901 - 1969

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Land Subsidence

Figure 2-1 Bench Mark Level Changes relative to Hope Valley (Culver, 1970)

The following comments are made in relation to the land subsidence rates indicated
by this Study:

 The higher rates of land subsidence were found in the Port Adelaide /
Semaphore region.
 No land subsidence rates were estimated within the Gillman / Dry Creek
region affected by the Port Adelaide wetland draining activities (completed
in 1935).
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