Stanage Bay Boat Ramp - Department of Transport and Main …Breakwater Design Report...

Stanage Bay Boat Ramp

Breakwater Design Report

Projex Partners

July 2017

Projex Partners | July 2017 Breakwater Design Report

4987

-01_

R01

v01

.doc

x

Document Status

Version Doc type Reviewed by Approved by Date issued

01 Draft Final CLA POB 25/07/2017

Project Details

Project Name Breakwater Design Report

Client Projex Partners

Client Project Manager Mitchell Turner

Water Technology Project Manager Paul O’Brien

Water Technology Project Director Christine Lauchlan Arrowsmith

Authors Joanna Garcia-Webb / Ryan Dermek / Paul O’Brien

Document Number 4987-01_R01v01.docx

COPYRIGHT

Water Technology Pty Ltd has produced this document in accordance with instructions from Projex Partners for their use only. The concepts and information contained in this document are the copyright of Water Technology Pty Ltd. Use or copying of this document in whole or in part without written permission of Water Technology Pty Ltd constitutes an infringement of copyright.

Water Technology Pty Ltd does not warrant this document is definitive nor free from error and does not accept liability for any loss caused, or arising from, reliance upon the information provided herein.

Level 3, 43 Peel Street

South Brisbane QLD 4101

Telephone (07) 3105 1460

Fax (07) 3846 5144

ACN 093 377 283

ABN 60 093 377 283


4987

-01_

R01

v01

.doc

x

25 July 2017

Mitchell Turner Engineer Projex Partners PO Box 219 MAROOCHYDORE QLD 4558 Dear Mitch,

Stanage Bay Boat Ramp - Breakwater Design

Please find enclosed the report summarising our methodology and design outcomes for the above project. Should you have any questions please do not hesitate to get in touch.

Yours sincerely

Paul O’Brien Senior Principal Coastal Engineer

[email protected]

WATER TECHNOLOGY PTY LTD


4987

-01_

R01

v01

.doc

x

CONTENTS 1 INTRODUCTION 6

1.1 Background 6

1.2 Scope of Work 7

1.3 Survey and Concept Design Information 7

2 DESIGN CRITERIA 9

2.1 Selection of the Design Event 9

2.2 Characteristics of the Design Event 10

2.3 Operational Performance 10

3 OCEANOGRAPHIC CONDITIONS 11

3.1 Ocean Water Levels 11

3.1.1 Astronomical Tidal Levels 11 3.1.2 Storm Tide 12 3.1.3 Water Levels for Assessment of Operational Performance 13 3.2 Wind Climate 14

3.2.1 Design Wind Speeds 15 3.3 Wave Climate 16

3.3.1 Offshore Wave Climate 16 3.3.2 Nearshore Wind Waves 19 3.4 Wave Modelling 21

3.4.1 Bathymetry 21 3.4.2 Model Input 22 3.4.3 Wave Model Scenarios 22 3.4.4 Model Results 23

4 BREAKWATER DESIGN 26

4.1 Design Methodology 26

4.2 Required Armour Characteristics 26

4.3 Potential Impacts on Adjacent Foreshores 27

5 REFERENCES 30

APPENDICES Appendix A TMR’s Concept 3 Breakwater Arrangement

Appendix B Typical Cross-Section of Breakwater

Appendix C Technical Specification for Breakwater Works


4987

-01_

R01

v01

.doc

x

LIST OF FIGURES Figure 1-1 Site Location 6 Figure 1-2 Survey of Foreshore and Concept Design 8 Figure 3-1 Components of a Storm Tide Event 12 Figure 3-2 Middle Percy Island (2004 – 2017) Wind Rose 15 Figure 3-3 ARI of Offshore Wave Heights 17 Figure 3-4 Wave Angle (Upper) and Period (Lower) for Large (>2.0m Hs) Waves at Emu Park

Waverider Buoy 17 Figure 3-5 Offshore wave fetches affecting the site 18 Figure 3-6 Local Wind Wave Fetch to Site 20 Figure 3-7 DEM for wave modelling 21 Figure 3-8 Mesh Resolution at the Breakwater 22 Figure 3-9 Model Extraction Locations 24 Figure 3-10 Model results – wave heights along pontoon for 1-year ARI 24 Figure 3-11 Wave Shadow from Breakwater 25 Figure 4-1 Longshore transport assessment points 28

LIST OF TABLES Table 2-1 Probability of occurrence of various Average Recurrence Interval events 9 Table 3-1 Tidal Planes at Thirsty Sound 12 Table 3-2 Tide levels used for assessment of operational performance (existing conditions) 14 Table 3-3 Summary of Available Wind Data 14 Table 3-4 Design Wind Speeds, Existing conditions 15 Table 3-5 Model Scenarios 23 Table 3-6 Design Conditions 25 Table 4-1 Indicative longshore sediment transport 29


4987

-01_

R01

v01

.doc

x

1 INTRODUCTION

1.1 Background Stanage Bay is located on the Queensland Coast approximately 150km north of Rockhampton. Development consists of a small settlement with residences to the east and west of Stanage Point. Boating and fishing are popular activities in the area, and this is primarily facilitated by the dual-lane concrete Stanage Bay Boat Ramp, located adjacent to the western part of the township and fronting onto Thirsty Sound (refer Figure 1-1).

The boat ramp is naturally protected from incoming wave energy by Stanage Point to the east and northeast; and by Quail Island to the north and west. Whilst this protection typically allows for boat-launching conditions at the boat ramp, during strong winds and stormy conditions, adverse wave conditions can be experienced on the boat ramp. As well as detracting from the purpose of the ramp, it also impedes access to shore by visiting yacht owners seeking to provision at Stanage township.

This study establishes existing conditions at the site to allow for assessment of the feasibility of a floating pontoon to assist access to shore-based facilities and better facilitate boat launching / retrieval. It also presents the engineering design outcomes for a breakwater structure adjacent to the boat ramp to reduce waves during adverse weather conditions.

Figure 1-1 Site Location

Boat Ramp


4987

-01_

R01

v01

.doc

x

1.2 Scope of Work Water Technology was commissioned by Project Partners to undertake the nominated scope of works. Initially, technical assistance for the concept design and certification of the proposed rock breakwater adjacent to the Stanage Bay Boat Ramp was to be provided, including the following:

Collection of the relevant data for the design (i.e. winds, waves, tides and storm surge).

Development of a general arrangement of the rock breakwater (i.e. foundation and toe details, face slope, crest level and filter zones if required), based on a concept layout developed by Queensland’s Department of Transport & Maim Roads (TMR).

Specification of proposed armour rock and any other material (including sizing) required for the structure.

Provision of sketches of the breakwater design, for subsequent documentation into other aspects of ramp upgrading works being prepared by Project Partners.

Provision of RPEQ certification of the design.

After preliminary design of the breakwater, the scope of works was expanded to include additional information regarding the benefits of providing a breakwater at the site. This additional scope of works included:

Calculating the 1-year Annual Recurrence Interval (ARI) wave event at the boat ramp site.

Calculating the breakwater crest level to avoid overtopping during the 1-year ARI event.

Defining the maximum length of breakwater possible to keep the intrusion of the structure beyond the Mean Low Water (MLW) boundary of the Great Barrier Reef Marine Park to less than 1,000m2.

Estimating the sheltering benefit of two breakwater options to the floating pontoon for the 1-year ARI event.

Estimating sediment transport trends at the site.

This report discusses the outcomes of the above studies.

1.3 Survey and Concept Design Information Project Partners provided a feature and level survey, along with a concept design for the breakwater, (documented as “Concept 3”). The survey covers the existing boat ramp and surrounding bathymetry to approximately 40m offshore. The concept breakwater design nominated a crest level of +5.0m AHD, with a 4m wide crest battered down to existing surface levels with side slopes of 1 vertical to 1.5 horizontal (i.e. 1:1.5). The concept breakwater design also had an area of approximately 338m2 beyond MLW (i.e. the Great Barrier Reef Marine Park boundary) at -2.01m AHD.

Figure 1-2 presents the survey information provided by Project Partners in CAD format, and the concept design provided in PDF format.


4987

-01_

R01

v01

.doc

x

Figure 1-2 Survey of Foreshore and Concept Design

The following features are evident from an enlargement of this image:

The footprint of the conceptual breakwater structure starts where the topography is approximately 3.6m AHD, and extends seaward to depths of approximately -2.4m AHD.

The boat ramp slopes at approximately 1 (vertical) in 8 (horizontal) offshore. The adjacent beach slopes at approximately 1 in 3 from a height of 2.0m AHD to -1.0m AHD, before flattening to 1 in 30, and a flatter slope further offshore.


4987

-01_

R01

v01

.doc

x

2 DESIGN CRITERIA

2.1 Selection of the Design Event When considering the design of the proposed breakwater, it is necessary to select a particular storm “event” which the structure must accommodate.

This selection is typically based on an acceptable probability of that event occurring within the length of time that the structure is intended to serve its given purpose (this is termed the design life of the structure). The selection of an appropriate design event therefore becomes a decision that acknowledges and accepts a particular level of risk that this event (i.e. the particular combination of wave conditions and ocean level that the revetment structure is required to accommodate) might be equalled or exceeded within the design life of the structure.

Australian Standard AS4997-2005 “Guidelines for the design of maritime structures” nominates appropriate design criteria for a range of marine structures. AS4997-2005 dominates a 25-year design life1 for a “small facility” such as the Stanage Bay boat ramp. This means that the proposed breakwater is to be designed for climate conditions (including sea level rise) expected in the year 20142.

The severity of a design event is quantified by assigning it an Average Exceedance Probability (ie. AEP, which can also be referred to as Average Recurrence Interval or return period). AS4997-2005 nominates an Annual Exceedance Probability2 of 1/50 for small craft facilities where potential breakwater damage/failure represents a low degree of hazard to life or property. This corresponds to 50-year Average Recurrence Interval (ARI) event. A 50-year ARI event is one which is expected to be equalled or exceeded on average once every 50 years. However, since such events occur randomly in any particular timeframe under consideration (rather than at precise regular or cyclical intervals), they have a probability of occurrence within that time.

Table 2-1 presents a summary of the percentage probability that various ARI events are likely to be equalled or exceeded within particular timeframes. For example, the 50-year ARI design event adopted for the proposed breakwater has a 39.3% probability of being equalled or exceeded in a structure’s 25 year design life. It also has a 2% chance of occurring or being exceeded in any particular year.

Table 2-1 Probability of occurrence of various Average Recurrence Interval events

Number of years

within the period

Average Recurrence Interval (years)

5 10 25 50 100 200 500

1 18.1% 9.5% 3.9% 2.0% 1.0% 0.5% 0.2%

2 33.0% 18.1% 7.7% 3.9% 2.0% 1.0% 0.4%

5 63.2% 39.3% 18.1% 9.5% 4.9% 2.5% 1.0%

10 86.5% 63.2% 33.0% 18.1% 9.5% 4.9% 2.0%

25 99.3% 91.8% 63.2% 39.3% 22.1% 11.7% 4.9%

50 100.0% 99.3% 86.5% 63.2% 39.3% 22.1% 9.5%

100 100.0% 100.0% 98.2% 86.5% 63.2% 39.3% 18.1%

200 100.0% 100.0% 100.0% 98.2% 86.5% 63.2% 33.0%

1 AS4997 – 2005 Guidelines for the Design of Maritime Structures. Table 6.1, p.30. 2 AS4997 – 2005 Guidelines for the Design of Maritime Structures. Table 5.4, p.25.


4987

-01_

R01

v01

.doc

x

The engineering design of the proposed revetment has adopted the following design criteria:

Design for 50-year ARI event.

The design methodology uses the characteristics of the 50-year ARI event to size the armour arrangements, and to determine the cross-sectional form of the breakwater. The following Section 3 of this report offers discussion on the particular wave and ocean water levels that constitute the design event for the proposed breakwater alongside the Stanage Bay boat ramp.

2.2 Characteristics of the Design Event The primary components of the storm that constitutes the 50-year ARI design event for the revetment are the wave conditions and the ocean water level.

The selection of the 50-year ARI event to be used in the assessment of the revetment is not a straight forward or simple process, as it consists of a combination of severe waves and extreme ocean water levels. When considering the adequacy of coastal defences, it is necessary to consider the likelihood of both conditions occurring simultaneously. The assumption of complete dependence between waves and ocean levels in an analysis of joint occurrence would lead to a conservative assessment - since the 50-year ARI design event would have to comprise a 50-year ARI storm tide level occurring at the very same time as the 50-year ARI wave conditions.

Conversely the assumption of complete independence between waves and water levels could lead to under-assessment of structural performance, since any increase in the probability of large waves occurring during storm tide events would have been ignored - clearly an understatement of likely waves. The actual correlation between waves and storm tide levels during a severe storm event will lie between these two extremes of complete dependence and complete independence. Quite comprehensive and specialised studies are typically required to establish this joint probability, however these are beyond the scope of the design activities for the proposed breakwater.

The approach adopted when developing structural designs for the breakwater has been to instead consider the following conservative scenario as constituting the 50-year ARI event:

50-year ARI Design Event = the 50-year ARI storm tide level occurring simultaneously with the 50-year ARI wave characteristics.

2.3 Operational Performance Subsequent to the commission to undertake the structural design of the breakwater, TMR requested an investigation of the benefits of the breakwater to the wave climate along the length of a proposed floating pontoon to be provided in the lee of the structure. This investigation of operational performance was undertaken using local sea conditions indicative of a 1-year ARI event.

The following scenarios have been considered as potentially constituting the 1-year ARI event, and to then adopt the one having the most adverse effect on the performance of the breakwater:

Scenario 1: 1-year ARI tide level occurring simultaneously with wave characteristics that could be expected on average 3 to 4 times in any year; or

Scenario 2: 1-year ARI wave condition occurring simultaneously with a high ocean water level that could be expected to occur at Stanage Bay on average 3 to 4 times in any year.


4987

-01_

R01

v01

.doc

x

3 OCEANOGRAPHIC CONDITIONS

3.1 Ocean Water Levels When determining the forces that affect foreshore structures it is necessary to consider the ocean water levels that prevail from time to time. This appreciation not only relates to the day-to-day tidal influences, but also to the storm surges which occur as a result of extreme weather conditions.

Due to complex local bathymetry and the surrounding oceanographic features at the Stanage Bay site, ocean water levels will have a considerable influence on the wave energy that propagates into and through Thirsty Sound to the breakwater location. As ocean waves propagate shoreward into shallower water, they begin to “feel” the seabed. The decreasing depths cause the waves to change direction so as to become aligned to the seabed contours and to also shoal up in height until such time as they may break - dissipating their energy as they do so.

Just how much wave energy reaches a foreshore is therefore determined largely by the depth of water over the seabed approaches. Ocean water levels and the seabed bathymetry are important aspects in this process of wave energy transmission.

Consequently, it is necessary to consider the following ocean levels in the vicinity of the Stanage Bay boat ramp:

Astronomical Tide - this is the “normal” rising and falling of the oceans in response to the gravitational influences of the moon, sun and other astronomical bodies. These effects are predictable and consequently the astronomical tide levels can be forecast with confidence.

Storm Tide - this is the combined action of the astronomical tide and any storm surge that also happens to be prevailing at the time. Surge is the rise above normal water level as a consequence of surface wind stress and atmospheric pressure fluctuations induced by synoptic events.

3.1.1 Astronomical Tidal Levels

The tidal rising and falling of the oceans is in response to the gravitational influences of the moon, sun and other astronomical bodies. Whilst being complex, these effects are nevertheless predictable, and consequently past and future astronomical tide levels can be forecast with confidence at many coastal locations.

Tidal plane information (Department of Transport and Main Roads, 2016) is available at the Secondary Port of Thirsty Sound, located offshore of the Stanage Bay Boat Ramp site. As can be seen in Table 3-1, the maximum possible astronomical tidal range at Stanage Bay is 7.57 metres, with an average range during spring tides of 5.23 metres and 2.43 metres during neap tides.


4987

-01_

R01

v01

.doc

x

Table 3-1 Tidal Planes at Thirsty Sound

Tidal Plane Level (m LAT) Level (m AHD) 3

Highest Astronomical Tide (HAT) 7.57 4.01

Mean High Water Springs (MHWS)

6.08 2.52

Mean Low Water Springs (MHWN)

4.68 1.12

Australian Height Datum (AHD) 3.56 0.00

Mean Sea Level (MSL) 3.45 -0.11

Mean Low Water Neaps (MLWN) 2.25 -1.31

Mean Low Water Springs (MLWS)

0.85 -2.71

Lowest Astronomical Tide (LAT) 0.00 -3.56

3.1.2 Storm Tide

The level to which ocean water can rise on a foreshore during the passage of an extreme storm event is typically a result of a number of different effects. The combination of these various effects is known as storm tide. Figure 3-1 illustrates the primary water level components of a storm tide event. A brief discussion of each of these various components is offered below.

Figure 3-1 Components of a Storm Tide Event

Astronomical Tide: The astronomical tide is the normal day-to-day rising and falling of ocean waters in response to the gravitational influences of the sun and the moon. Astronomical tide is an important component of the overall storm tide because if the peak of a severe storm were to coincide with a high spring tide for instance, severe flooding of low lying coastal areas can occur and the upper sections of coastal structures can be subjected to severe wave action.

3 Australian Height Datum (AHD) was derived by the Queensland Government’s Hydrographic Services and is reported on Plan No. G100-005, dated 21st January 2016, titled “Stanage Point – Stanage Bay Banksia Road Boat Ramp – Hydrographic and Land Detail Survey”. Plot File G100005.pdf.

ASTRONOMICAL TIDE

SURGE

WAVE SETUP

WAVE RUNUP

STORM TIDE

INCOMING WAVES BROKEN WAVES WAVES ARE BREAKING

LOW WATER DATUM

COASTLINE

Storm Tide = Astronomical Tide + Storm Surge + Breaking Wave Setup


4987

-01_

R01

v01

.doc

x

Storm Surge : This increase in ocean water levels is caused by meteorological effects during severe storms. Strong winds blowing over the surface of the ocean forces water against the coast at a greater rate that it can flow back to sea. Furthermore, sea levels can rise locally when a low pressure system occurs over the sea - resulting in what is termed an “inverted barometer” effect.

A 10mb drop in atmospheric pressure results in an approximate 10 cm rise in sea level. In order to predict the height of storm surges, these various influences and their complex interaction are typically replicated by numerical modelling techniques using computers.

Breaking Wave Setup: As storm waves propagate into shallower coastal waters, they begin to shoal and will break as they encounter the nearshore region. The dissipation of wave energy during the wave breaking process induces a localised increase in the ocean water level shoreward of the breaking point which is called breaking wave setup. Through the continued action of many breaking waves, the setup experienced on a foreshore during a severe wave event can be sustained for a significant timeframe and needs to be considered as an important component of the overall storm tide on a foreshore.

Wave Runup: Wave runup is the vertical height above the local water level up to which incoming waves will rush when they encounter the land/sea interface. The level to which waves will run up a structure or natural foreshore depends significantly on the nature, slope and extent of the land boundary, as well as the characteristics of the incident waves. Consequently, because this component is very dependent upon the local foreshore type, it is not normally incorporated into the determination of the storm tide height. Nevertheless, it needs to be considered separately during the assessment of the storm tide vulnerability of the proposed revetment.

The most recently published results of storm tide investigations in the region are included in a study of climate change and community vulnerability to tropical cyclones (James Cook University, 2004). That study also addresses the effect of future climate change on sea level rise and tropical cyclone intensity and occurrences.

It is pertinent to note that the 2004 study only considered tropical cyclone induced influences on storm tides. The study notes that:

“For return periods below about 100 years, non-cyclonic events will be increasingly important; therefore, the combined curve of tropical and extra-tropical storm tides will be higher than the cyclone-induced storm surge plus tide curves shown in this report. the increase due to non-cyclonic events is expected to be about 0.2m at 10 years reducing to 0.0m at about the 200 year return period.”

To account for this effect on lower ARI events, when designing the proposed breakwater, the more onerous 100-year ARI storm tide level is adopted instead of the 50-year ARI level.

The 100-year ARI storm tide level reported by the 2004 study for Clairview (approximately 55kms to the west-north-west of Stanage Bay) is RL+5.12m AHD. This includes an allowance of 0.3 metres for future sea level rise. It is appropriate to incorporate this allowance given that the proposed breakwater structure has a design life of 25 years with a 0.3 metre sea level rise expected to have occurred by around the year 2042.

3.1.3 Water Levels for Assessment of Operational Performance

For the purposes of investigating the operational performance of the breakwater, more frequent events (at around one exceedance per year, and three to four exceedances per year) were required. This was in response to a request by TMR to analyse the breakwater effectiveness during less severe sea-state events, thereby offering insight into operational conditions on the boat ramp and the proposed pontoon.


4987

-01_

R01

v01

.doc

x

Since there are no long term tidal observations available for Thirsty Sound, an analysis was instead undertaken on statistical tidal data4 for the Standard Port of Mackay to provide an average 1-time tide level exceedance per year; and a tide level having on average around 3 to 4 exceedances per year. Tide levels at Mackay were used for this analysis since it is the closest location with observed data of reasonable length, having approximately 50 years of observed data available. The calculated water levels at Mackay were then scaled (based on the respective tidal plane differences between Mackay and Thirsty Sound) to provide corresponding water levels at the Stanage Bay site. The resulting ocean water levels are shown in Table 3-2.

Table 3-2 Tide levels used for assessment of operational performance (existing conditions)

Event Design Water Level (m MSL)

Average of 3 to 4 exceedances per year (approx.) +2.9

Average 1 exceedance per year (approx.) +4.0

3.2 Wind Climate The wind climate in the vicinity of the study area has been measured by the Bureau of Meteorology (BoM) at Middle Percy Island (Station 200001) located 58km northeast of the site and at Williamson (Station 033195) located 41km south of the site. A summary of the available data at each gauge is shown in Table 3-3.

Table 3-3 Summary of Available Wind Data

Wind Gauge Data Resolution Date Available

Middle Percy Island (200001) Continuous (Provided at 30 min intervals)

19/07/2004 – Present

(Received to 05/07/2017)

Williamson (033195) Continuous (Provided at 30 min intervals)

01/06/2005 – Present

(Received to 05/07/2017)

The data from the Middle Percy Island gauge is considered to be the most representative of the conditions which generate waves arriving at Stanage Bay. The Williamson gauge is located inland and wind measurements are likely to be affected by the topography of Normanby Range to its’ southeast. Normanby Range is likely to be blocking the dominant south-easterly trade winds that would otherwise be measured by the Williamson anemometer station.

As indicated in Table 3-3, data is available from Middle Percy Island between the years of 2004 and 2017, forming a complete time series over a 13-year period. The data was adjusted for measurement height and local terrain in accordance with the methods described in Resio et al (2003).

The wind climate representing the entire 13-year dataset is shown summarised in Figure 3-2. The wind climate is dominated by trade winds from the southeast. Wind speeds are generally below 6m/s with strongest winds occurring from the southeast.

4 File titled “054004A HILO Occurrence Table 1966 2016.pdf” provided by the tidal unit of Maritime Safety Queensland via email dated 13th June 2017.


4987

-01_

R01

v01

.doc

x

Figure 3-2 Middle Percy Island (2004 – 2017) Wind Rose

3.2.1 Design Wind Speeds

Design wind speeds have been established using Australian Standards AS/NZS 1170.2:2002 Structural Design Actions – Wind Actions. Extreme winds (100-year ARI event) were required for the generation of 100-year waves in the spectral wave model for breakwater design (as discussed in Section 3.4). More frequent events (1 exceedance per year; and 3 to 4 exceedances per year) were required to analyse the breakwater effectiveness during less severe sea states.

Table 3-4 Design Wind Speeds, Existing conditions

Event Design Wind Speed (m/s)

3 – 4 Exceedances Per Year 9

1 Exceedance Per Year 12

100 Year Annual Recurrence Interval 39


4987

-01_

R01

v01

.doc

x

3.3 Wave Climate The wave climate at the site consists of locally generated wind waves as well as “distant seas” generated by winds blowing across the open water fetches between the mainland and the Barrier Reef. Both wave components have been analysed to identify critical wave heights at the site. The following sub-sections describe the wave climate, whilst Section 3.4 discusses the spectral wave modelling used to transform generated waves to the site.

3.3.1 Offshore Wave Climate

Significant fetches are present offshore of Stanage Point. These long fetches result in the generation of large waves that are substantially attenuated by the offshore reefs before refracting to the proposed breakwater and pontoon site (as further discussed in Spectral Wave Modelling, Section 3.4).

Offshore wave characteristics have been determined based on measurements by the Queensland government’s offshore Waverider buoy off Emu Park (southeast of the site) which has similar offshore bathymetric features to Stanage Point.

The Emu Park Waverider buoy is operated by the Queensland Government and has collected approximately 20 years of data in 20m water depth. Analysis of data from this site shows offshore waves are largest from the north to southeast (through east), with the predominant large-wave direction from the southeast, as shown in Figure 3-4 (upper). This figure shows the wave direction of all waves in the record larger than 2m significant wave height. The period of these waves is shown in Figure 3-4 (lower), which typically varies from 5 to 7 seconds.

Approximately 337 individual storms peaked with significant wave heights (Hs) greater than 2 metres during the record period. These were extracted from the database and ranked according to severity. An Extremal Significant Wave Height Analysis was then undertaken. This yielded the relationship between ARI and offshore significant wave heights shown in Figure 3-3. From which it can be seen that the 50-year ARI wave height to be used for the structural design of the breakwater is 4.04 metres.


4987

-01_

R01

v01

.doc

x

Figure 3-3 ARI of Offshore Wave Heights

Whilst these waves are large in offshore waters, spectral wave modelling (Section 3.4) suggests they are considerably attenuated as they propagate to the Stanage Bay boat ramp from almost all directions. As shown in Figure 3-5, the predominant wave direction (east to south-easterly offshore waves) are effectively blocked from reaching the boat ramp site by Stanage Point.

Quail Island also mostly blocks northerly waves. Therefore, the only significant offshore wave reaching the site is from the northeast wave direction. These northeast offshore waves have been included in the design wave estimation for breakwater design conditions. The northeast offshore wave was found to be not significant for the 1-year event and lower, and was therefore not included in the modelling for the smaller design events.

Figure 3-4 Wave Angle (Upper) and Period (Lower) for Large (>2.0m Hs) Waves at Emu Park Waverider Buoy


4987

-01_

R01

v01

.doc

x

Figure 3-5 Offshore wave fetches affecting the site


4987

-01_

R01

v01

.doc

x

3.3.2 Nearshore Wind Waves

Whilst the offshore generated waves are significantly attenuated before reaching the site, there is also a significant local fetch within Thirsty Sound. The wind waves generated in this local fetch are estimated in the spectral wave model using the design wind speeds generated in Section 3.2.

The local fetch within Thirsty Sound is largest to the west, with up to 3km of fetch. There is also an approximate 3km fetch to the north, with 1km to 2km fetches to the northeast and northwest (refer Figure 3-6). As discussed in Section 3.2, typically strong winds are from the southeast direction which has no local wind fetch, however it is also possible that strong winds could occur from the north or northeast. The generation of wind waves and results of the spectral wave modelling are discussed in Section 3.4.


4987

-01_

R01

v01

.doc

x

Figure 3-6 Local Wind Wave Fetch to Site


4987

-01_

R01

v01

.doc

x

3.4 Wave Modelling The design wave climate at the site and across the wider Thirsty Sound area was determined using DHI Software’s proprietary MIKE Spectral Wave (SW) model - a new generation wind-wave model based on unstructured meshes.

3.4.1 Bathymetry

To transform offshore wave conditions to the proposed breakwater location within Thirsty Sound, a spectral wave model of the area was established. The model domain was bounded by the shoals and offshore islands to the north, and the 20m depth contour to the east and southeast. This is the depth contour of the Emu Park Waverider buoy, so the offshore wave could be applied as a boundary condition.

Offshore bathymetric data was determined through a combination of the GeoScience Australia Australian 9-second DEM and Navigation Charts. The digital elevation model (DEM) of the model domain is presented in Figure 3-7.

Figure 3-7 DEM for wave modelling

The model is a flexible mesh model which allows for a varying grid resolution across the model domain. In the offshore area, the model resolution is of the order of 0.5 km2. The resolution is refined as proximity to the breakwater increases. The mesh resolution at the breakwater and boat ramp area is in the order of 50m2 – or a side length of 10m.

The mesh resolution around the proposed breakwater is illustrated in Figure 3-8.


4987

-01_

R01

v01

.doc

x

Figure 3-8 Mesh Resolution at the Breakwater

3.4.2 Model Input

The design water levels, wind conditions and wave conditions previously determined have been used as boundary conditions to the model. A range of combinations of design wave and water levels has been used to determine the critical wave height for the breakwater, and the effect of the breakwater on waves reaching the proposed pontoon in the lee of that structure.

Similarly, the wave directions have been varied to enable the peak wave direction at the breakwater to be established. Model parameters such as wave breaking and wave energy spectrum have been set to default model conditions due to the lack of specific local data for model calibration. These default model parameters have been tested in many situations globally and provide a good degree of reliability across a range of model simulations.

The spectral wave model was also run with representative wind speed, wind direction and water level conditions to establish a matrix relating wind climate to wave characteristics within the study area. The wind conditions measured at Middle Percy Island, and the predicted water levels at Thirsty Sound were then used with a wave correlation matrix to estimate a representative longshore sediment transport regime at the sites (as further discussed in Section 4.3).

3.4.3 Wave Model Scenarios

The wave model was run for a range of scenarios. These scenarios included:

existing conditions (i.e. with no breakwater in place);

the Concept 3 breakwater arrangement provided by TMR (refer Appendix A); and


4987

-01_

R01

v01

.doc

x

a modified concept design having a longer breakwater length and lower crest height (to allow for wave overtopping during sea conditions more severe than the 1-year ARI event - termed the WT Modified Concept). The arrangement was configured such that its intrusion beyond the Marine Park boundary of Mean Low Water was less than 1,000m2.

These various model scenarios are summarised in Table 3-5.

Table 3-5 Model Scenarios

Event Scenario Purpose

100 Year ARI

100 Year ARI Water Level with 100 Year ARI Wind

Existing Conditions (no breakwater)

DTMR Concept 3 Breakwater

Update Breakwater design for critical overtopping and rock sizing. Discussed in

Section 4.

1 Exceedance Per Year (EPY)

1 EY Water level with 3-4 EPY Wind/Wave

3-4 EY Water Level with 1 EPY Wind/Wave


DTMR Concept 3 Breakwater

WT Modified Concept

Assess benefits of updated breakwater on Pontoon during more frequent events. Discussed in

Section 3.4.4.

Matrix allowing for interpolated 1-year of wave data


WT Modified Concept

Assess sediment transport implications at beach.

Discussed in Section 4.3.

3.4.4 Model Results

3.4.4.1 Assessment of Operational Performance

Whilst the model results are used for determining design conditions for the breakwater, it has also been used for assessing the effectiveness of the breakwater during more frequent storm events. As discussed in Section 2.3, the following scenarios have been considered as potentially constituting the 1-year ARI event, and to then consider the one having the most adverse effect on the performance of the breakwater:

Scenario 1: 1-year ARI tide level occurring simultaneously with wave characteristics that could be expected on average 3 to 4 times in any year; or

Scenario 2: 1-year ARI wave condition occurring simultaneously with a high ocean water level that could be expected to occur at Stanage Bay on average 3 to 4 times in any year.

Results were extracted from offshore of the site and at five points along the proposed pontoon in the lee of the breakwater (shown in Figure 3-9) for each of the 1-year ARI scenarios.

The wave height is at a maximum when the wind direction is coming from the northeast. The critical scenario for the 1-year ARI event is typically Scenario 2, namely the 1-year wave with the water level having 3-4 exceedances per year. This scenario produces a northeast wave of approximately 0.4m height in waters offshore of the boat ramp site. For Scenario 1 the offshore wave height is smaller, being approximately 0.25m.

The results of the wave modelling for the determination of wave conditions in the lee of the breakwater are summarised in Figure 3-10.


4987

-01_

R01

v01

.doc

x

Figure 3-9 Model Extraction Locations

Figure 3-10 Model results – wave heights along pontoon for 1-year ARI


4987

-01_

R01

v01

.doc

x

Without a breakwater in place, wave heights of between 0.3m and 0.34m occur at the proposed pontoon site. When the breakwater is included in the modelling, the sheltering effect is evident through the wave shadow behind it (refer Figure 3-11) resulting in waves at the pontoon being smaller. The TMR Concept 3 arrangement attenuates north-easterly waves to be less than 0.17m in height (i.e. 50% reduction in wave height).

The WT Modified Concept further reduces the wave height to between 0.07m and 0.11m along the pontoon, suggesting a 68% reduction in wave height. The extracted wave heights are shown in the table of Figure 3-10.

Figure 3-11 Wave Shadow from Breakwater

Following consideration of the results of the above assessment of operational performance, TMR confirmed that the preferred breakwater arrangement remained as Concept 3 (refer to the concept drawing enclosed as Appendix A).

3.4.4.2 Conditions for Breakwater Design

The spectral wave model was also run for the design conditions discussed earlier, namely a storm tide level of RL+5.12m AHD (refer Section 3.1.2) and 50-year ARI offshore wave conditions of 4.04m height and 8.5 second wave period. The resulting inshore wave conditions were extracted from the model for locations just in front of the proposed breakwater alignment. These conditions were then used for the structural design of the breakwater. The design parameters are presented in Table 3-6.

Table 3-6 Design Conditions

Design Parameter Value

Storm Tide Level RL+5.12m AHD

Wave Height 2.2 metres

Peak Period 8.5 seconds

Pontoon


4987

-01_

R01

v01

.doc

x

4 BREAKWATER DESIGN

4.1 Design Methodology A requirement of TMR’s Concept 3 arrangement for the breakwater is to have the crest level at around RL+5.0m AHD. this ensures that the structure integrates appropriately with existing foreshore levels. Given that the Design Storm Tide Level is RL+5.12m AHD, it is evident that the breakwater will act as a low-crested structure during design conditions. Such structures are defined as being those which can be overtopped by waves because their crest level is around the still water level.

This definition includes those scenarios where the crest level may be above the prevailing still water line during some storm events, but below it for other somewhat more severe events. There are several design methodologies that can be applied to determine the armouring requirements for low-crested structures. However, not all methods yield the same results. Typically, breakwater designers adopt the most conservative of the available design methods.

This has been the approach applied for the design of the proposed breakwater. The algorithms and stability formulae found to be best applied to the design of low-crested breakwaters include those of Vidal et al (1995), Burger (1995), Kramer and Burcharth (2004). An informative summary of the various technical strengths and shortcomings of these methodologies, along with recommendations as to suitability of each to particular circumstances is offered in CIRIA, CUA, CETMEF (2007).

4.2 Required Armour Characteristics The design approach has been to consider the proposed breakwater alongside the Stanage Bay boat ramp as a statically stable structure – that is, one which does not deform when subjected to the design conditions. Following consideration of the various technical approaches for low-crested breakwater design, it was determined that the technical methodology attributable to Kramer and Burcharth (2004) was the most conservative for the Stanage Bay scenario.

The practicalities of rock supply are such that all rocks in a breakwater are not the same size - it is inevitable that there will be a range in sizes. So, when considering the issue of rock size, it is necessary to nominate a representative weight. This is typically the average weight of all armour rocks. Or in other words, it is the weight that 50% of the total number of rocks in the structure exceed.

The design calculations result in the following requirement for primary armour size:

M50 = 3.0 tonnes

where M50 is the mass for which 50 % of the armour matrix is higher.

The recommended cross-section of the breakwater is presented in Appendix B.

When specifying the average rock size required for a breakwater, limits on the minimum and maximum rock sizes are necessary - to ensure that interlocking of the completed rock matrix is not compromised. If there is a wide range either side of the average, then the interlocking of the preferred size can be compromised. The large number of smaller rocks in a widely graded armour can get in-between and inhibit the firm contact between the larger rock sizes that are required to withstand the wave forces. They may also fill the voids within the armour layer, thereby significantly compromising the ’s ability to dissipate incoming wave energy.

Similarly, individual very large rocks within a widely graded armour can inhibit effective interlocking by reducing the number of contact points that adjacent rocks might otherwise have with each other - meaning that those rocks aren’t as well held within the overall rock matrix because of the presence of the very large rock.


4987

-01_

R01

v01

.doc

x

Internationally accepted design guidelines regarding rock gradings have been developed for this purpose. Construction specifications for rock-armoured marine structures also frequently incorporate strong and clear requirements for individual rocks to be placed in firm contact with at least three others in the same layer.

Rock shape is also an important consideration in ensuring adequate interlocking within an armour layer. Rocks that are tabular in shape (i.e. excessively flat), quite long, and/or cylindrical will not interlock as effectively as cubic or spherical shaped rocks - although very round rocks are not as effective as cubic rocks. Consequently, breakwater designers will frequently place limits on the shape of rocks (for example, by specifying the maximum allowable ratio of any rock’s longest dimension to its shortest dimension).

The specific requirements for the rock armouring of the proposed breakwater alongside the Stanage Bay boat ramp have been incorporated into a Technical Specification. That specification is included as Appendix C to this report, and is a fundamental part of the Engineering Design of the structure. The Technical Specification ensures that vital aspects relied upon during the design process are incorporated into construction.

4.3 Potential Impacts on Adjacent Foreshores Constructing a breakwater at the site has the potential to interrupt local longshore sediment transport regime - which can lead to impacts on adjacent foreshores.

Whilst detailed numerical modelling of sediment transport processes was beyond the scope of the design commission, potential impacts to long-shore sediment transport was investigated using the results from the wave model discussed in Section 3.4 in conjunction with desk-top analytical techniques.

A matrix of modelled wind and water level conditions was applied to both the measured wind records at Middle Percy Island and the predicted water level at Mackay, to generate a synthetic year of wave data. As noted previously, there are no observed or predicted tides available for Thirsty Sound, so the tidal characteristics of the nearby Standard Port of Mackay has been used – with appropriate scaling to subsequently account for the differences in tidal planes of the two sites.

Following analysis of the wind records, the year 2009 was been selected as being representative of the Middle Percy Island wind records in terms of both typical wind speed and direction. So, the synthetic dataset represents an approximately indicative year in terms of sediment transport.

Wave conditions from the synthetic dataset were extracted at several locations along the project’s foreshore for simulations with and without the breakwater in place (refer to Figure 4-1 for locations). Two points each side of the structure were selected, with typically 60 metres between the breakwater and adjacent points. All points are located 50m offshore. The enhanced Kamphuis formula (Kampuis, 1991; van Rijn, 2001) was then applied to predict the potential longshore transport at each location.

The method uses wave energy in the breaker zone to assess the potential sediment transport. The technical approach is based on there being an unlimited supply of sand available across the inshore profile which can be moved by the incident waves. However, being a perched beach / reef system, the study foreshore does not have an unlimited supply of sediment. Consequently, the quantities of sediment transported calculated by the Kamphuis technique will be a substantial over-estimate of actual quantities. Nevertheless, the approach still provides a reliable indication of the relative magnitudes and directions of longshore sediment transport in the area.

The Kamphuis technique of calculating longshore sediment transport is based on the incident wave height; and the angle between the breaking wave and the shoreline. It accounts for the influence of bed slope and sediment grain size. The original formula has been further enhanced to include the influence of the peak wave period (van Rijn, 2001).


4987

-01_

R01

v01

.doc

x

Figure 4-1 Longshore transport assessment points

The formula for calculating the longshore sand transport is:

2.33 ,. . . . 2

where: Q = onshore sediment transport rate (immersed mass) in kg/s Hs,br = significant wave height at breaker line (m) Tp = wave peak period (s) br = wave angle at breaker line d50 = median particle size in surf zone (m) m = beach slope

The bed slope was determined using the wave model bathymetry in the area surrounding the output locations; being some 50m offshore of the beach. The sediment is assumed to be a fine sand size having a d50 characteristic of 0.2mm.

The predicted annual potential sediment transport volumes are presented in Table 4-5 for each of the output points for both ‘with’ and ‘without’ the breakwater. Positive transport indicates sediment transport is to the northeast (from the boat ramp towards the Air-Sea Rescue facility); negative transport signifies sand being transported in the opposite direction.

The results reflect the observation from aerial imagery, that net sediment transport is to the southwest. Despite over-estimating actual sediment transport volumes, predicted magnitudes are very small. The local bathymetry is such that water depths are shallower to the northeast of the boat ramp than to the southwest. Wave energy in the deeper water will be greater, thus the magnitude of the transport will be slightly greater on the southwestern side of the breakwater.

Overall, the model results indicate that some sand build-up is likely to occur against the northeast side of the proposed breakwater. This is because the structure intercepts the south-westerly transport of sand coming off the sandy foreshore of the open space to the northeast of the site. When seasonal sea and weather conditions change so as to induce a northeasterly sediment transport, the sand in the now leeward side of the breakwater is “trapped” since it cannot be moved back onto the foreshore from which it was previously moved. Over time, this will result in recession of the foreshore further to the northeast.


4987

-01_

R01

v01

.doc

x

This accumulation of sand against the north-eastern side of the breakwater (in front of the Air Sea Rescue facility) will be slow since sand transport rates are very low. Nevertheless, since it will be accompanied by the associated recession of the foreshore to the northeast, it may be necessary to undertake sand back-passing from time to time.

This entails simply relocating some of the trapped sand back onto the eroded foreshore. Due to the low volumes predicted, this can potentially be undertaken by excavator and truck – and would only be required on average every few years.

Table 4-1 Indicative longshore sediment transport

Scenario Gross Northeasterly Transport

(+ve tonnes/year)

Gross Southwesterly Transport

(-ve tonnes/year)

Net Transport

(tonnes/year)

W1 W2 E1 E2 W1 W2 E1 E2 W1 W2 E1 E2

No Breakwater +30 +16 +22 +23 -389 -162 -201 -85 -359 -146 -180 -62

With Breakwater +30 +13 +5 +12 -303 -219 -192 -77 -273 -197 -187 -64

Difference 0 -2 -16 10 -86 48 -9 -8 -86 +50 +7 +2


4987

-01_

R01

v01

.doc

x

5 REFERENCES

Burger, G. (1995). Stability of low-crested breakwaters: stability of front, crest and rear. Influence of rock shape and gradation. Report H1878/H2415, WL | Delft Hydraulics, Delft; also MSc thesis, Delft University of Technology, Delft, The Netherlands.

CIRIA, CUR, CETMEF, (2007). The Rock Manual. The use of rock in hydraulic engineering (2nd edition). Published C683, CIRIA, London..

Department of Transport and Main Roads, (2016). Queensland Tide Tables – Standard Port Tide Times 2017. Prepared by Maritime Safety Queensland, Department of Transport and Main Roads. Published online at: http://www.msq.qld.gov.au/Tides/Tide-tables.

James Cook University, (2004). Queensland Climate Change and Community Vulnerability to Tropical Cyclones, Oceans Hazards Assessment – Ocean Hazards Assessment – Stage 3. The Frequency of Surge Plus Tide During Tropical Cyclones for Selected Open Coast Locations Along the Queensland East Coast and Tropical Cyclone-Induced Water Levels and Waves: Harvey Bay and Sunshine Coast. July 2004.

Kamphuis, J.W. (1991) "Alongshore sediment transport rate." Journal of Waterway, Port, Coastal, and Ocean Engineering 117.6, 1991: pp 624-640.

Kramer, M. and Burcharth, H.F. (2004). “Stability of low-crested reakwaters in shallow water short crested waves”. In: J.A. Melby (ed), Proc 4th coastal structures conference, Portland, OR, 26-30, August 2003. ASCE, Reston, VA.

Resio, D.T., Bratos, S.M. and Thompson E.F. (2003). Coastal Engineering Manual: Chapter II-2 - Meteorology and Wave Climate. US Army Corps of Engineers, Report No: EM 1110-2-1100 (Part II).

van Rijn, L.C. (2001). Longshore Sediment Transport, Report Z3054. Delft, The Netherlands: Delft Hydraulics

Vidal, C., Losada, M.A. and Mansard E.P.D. (1995). “Stability of low-crested rubble-mound breakwater heads” Journal of Waterway, Port, Coastal, and Ocean Engineering, vol 121, no. 2, Mar/Apr, pp 114-122.


4987

-01_

R01

v01

.doc

x

APPENDIX A TMR’S CONCEPT 3 BREAKWATER ARRANGEMENT


4987

-01_

R01

v01

.doc

x

Page 32

APPENDIX B TYPICAL CROSS-SECTION OF BREAKWATER

TYPE CROSS SECTION

1.5

1

SE

TO

UT

LIN

E

RL +5.00

GEOTEXTILEPlaced under rock,

'ELCOMAX 600R' or

equvialent

TYPE A ROCKTwo layers on side

slopes and crest

TYPE B ROCKTwo Layers as filter

under Type A

Breakwater foundation level notionally

SURFACE LEVEL

CORE MATERIAL

1.5

1

0.2 to 0.7 metres below existing surface. See Note 5.

0.84

0

1.92

5

REVISIONS

REV. DESCRIPTION DATE INIT.

CLIENT: Water Technology Pty LtdCCONSULTANT:

ABN: 60 093 377 283

Melbourne T +61 3 8526 0800

Water Technology Pty Ltd

APPROVED

CHECKED RJD

PLO

PLODESIGN

CHECKED PLO

DRAWN RJD

Rev No.

Drawing No.

A3

4987-01_D01V01_001

STANAGE BAY BOAT RAMP BREAKWATER

JOB NO. J4987-01SHEET 1 of 2

1:75SCALE:

V01

TYPE CROSS SECTIONPROJEX PARTNERS

NOTES:

1. These drawings are to be read in conjunction with the Technical Specification.

2. Dimensions are in metres unless noted otherwise.

3. Dimensioned layer thicknesses are an indication of minimum thickness only; and generally reflect that required to

achieve the number of specified armour layers.

4. The nature and extent of the transitioning of the breakwater and armouring works into the existing foreshore is to be

defined on site by the Works Supervisor.

5. Geotechnical investigations indicate the likely presence of a very dense clayey layer underlying a 0.2m to 0.7m

layer of soft, shallow alluvium along the alignment of the proposed breakwater. The breakwater can be founded on

the underlying dense stratum.

6. Seawall Design Parameters:

• • • • Design Event = 50-year Average Recurrence Internal storm event (ie. 2% Annual Exceedance Probability)

• • • • Ocean storm tide level (inc wave setup) = RL+5.12m AHD.

• • • • Design wave parameters (at toe of seawall)

− − − − Hs = 2.2 metres

− Tp = 8.5 Seconds

• • • • Duration of joint storm tide and waves = 2 hours

TYPE A ROCK - PRIMARY ARMOUR

•••• Nominal size is 3 tonnes.

•••• Allowable range in size is 0.75 to 6 tonnes, and 50% of rocks (by

number) must be greater than 3 tonnes.

•••• Minimum of 2 layers placed as primary armour.

•••• Notional thickness of primary armour is 1.925m.

TYPE B ROCK - FILTER ARMOUR

•••• Nominal size is 250 kg

•••• Allowable range in size is 100kg to 0.75 tonne, and 50% of rocks

(by number) must be greater than 250 kg.

•••• Minimum of 2 layers placed directly beneath TYPE A ROCK.

•••• Notional thickness of filter armour is 0.840m.

BR

EA

KW

ATE

R S

OL

PROPOSED BOAT RAMP AND JETTY FOOTPRINT

2m

OFFSET

REVISIONS

REV. DESCRIPTION DATE INIT.

CLIENT: Water Technology Pty LtdCCONSULTANT:

ABN: 60 093 377 283

Melbourne T +61 3 8526 0800

Water Technology Pty Ltd

APPROVED

CHECKED RJD

PLO

PLODESIGN

CHECKED PLO

DRAWN RJD

Rev No.

Drawing No.

A3

4987-01_D01V01_002

STANAGE BAY BOAT RAMP BREAKWATER

JOB NO. J4987-01SHEET 2 of 2

1:50SCALE:

V01

FOOTPRINTPROJEX PARTNERS


4987

-01_

R01

v01

.doc

x

Page 33

APPENDIX C TECHNICAL SPECIFICATION FOR BREAKWATER WORKS

[Stanage Bay Boat Ramp - Proposed Breakwater Works – Technical Specification | 21 July 2017 Page 1

MEMORANDUM To Projex Partners

From Paul O’Brien, Water Technology

Date 21 July 2017

Subject Stanage Bay Boat Ramp - Proposed Breakwater Works – Technical Specification

1 GENERAL

The breakwater works are to be completed to the lines and levels shown on the Drawings. The material to be

placed must be of uniform quality and characteristics in accordance with this Specification.

2 MATERIALS

2.1 Rock Armour

All rock used in the construction of the breakwater is considered and referred to herein as rock armour. The

Contractor is responsible for the sourcing, extraction, transportation, handling and placement of all rock armour

required for the Works.

All such armour must be of volcanic or metamorphic origin; and be angular or sub-angular in nature. All rock

armour shall be well graded, clean, free from overburden, spoil, shale and organic matter.

Individual rocks shall be slightly weathered to fresh; durable; sound; and suitable for use as armour in a marine

environment. All rock armour must be free of any defects which would result in breakdown of individual stones

in the environment of the Works. Rocks displaying cleavage planes and weak seams shall not be used.

All rock armour shall have a Specific Gravity of at least 2.65. The Contractor shall carry out tests to confirm

the Specific Gravity of rock armour being used in the works prior to the use of such rocks in the Works.

In this Specification of rock armour, the following definition of terms applies:

𝑙 = maximum axial length; given by the maximum distance between two points on the rock.

𝑑 = minimum axial breadth; given by the minimum distance between two parallel straight lines between

which the rock can just pass.

The armour rock to be supplied, delivered and placed shall comprise of the following types.

2.1.1 Type A - Primary Armour

Type A armour is the primary armour forming the outer layers of rock on the breakwater. It has a nominal

weight of 3 tonne (with an allowable range between 0.75 tonne and 6 tonne). The primary rock armour is to

comply with the following dimensional criteria:

Dimensional ratio of 𝑙

𝑑< 2.5

Least minimal breadth of any rock is 500mm (ie. 𝑑 > 500mm)


Maximum axial length of any rock is 2400mm (ie. 𝑙 < 2400mm)

Rocks larger than the maximum specified range may be placed as armour in the Works only with the prior

approval of the Superintendent, who will specify the location for such rocks. Approval for these larger rocks is

likely to be forthcoming only where such rocks can be placed in the lower part of the breakwater.

2.1.2 Type B - Filter Armour

Type B armour forms the underlayer beneath the primary armour on the breakwater. It has a nominal weight

of 250 kg (with an allowable range between 100kg and 750kg). Type B rock armour is to comply with the

following dimensional criteria:

Dimensional ratio of 𝑙

𝑑< 2.5

Least minimal breadth of any rock is 250mm (ie. 𝑑 > 250mm)

Maximum axial length of any rock is 1200mm (ie. 𝑙 < 1200mm)

In addition to the size and weight requirements Types A and B armour rocks shall have the following properties:

TABLE 2-1 REQUIREMENTS OF ARMOUR

Aspect Requirement

Petrography Fresh, interlocking crystalline, with few pores, no clay

minerals, and no soluble minerals - as determined by a

petrographic analysis of representative specimens of rock

undertaken by a Petrographer.

Assessment of the insitu rock mass at the proposed rock

source by a specialised Geologist or Geotechnical Engineer

to confirm the absence of any defects/joints/fractures (within

individual armour stones extracted from the insitu source)

having the potential for adverse weathering and/or

breakdown of supplied rocks over time if placed in an

exposed marine environment.

Apparent Particle Density Greater than or equal to 2.65

Absorption Less than 1.2 percent

Sulphate Soundness Less than 2% loss in seven cycles

Los Angeles Abrasion Less than 25% loss

Wet/Dry strength variation 35%

Petrographic assessments and analyses are to be undertaken by appropriately qualified and experienced

Petrographer, Geologist and/or Geotechnical Engineer. Reports on these assessments and analyses are to

be provided to the Superintendent prior to the commencement of any Works. The reports must clearly state

whether the proposed rock armour units are suitable for use as armour in the local marine environment of the

site. It will only be with such project-specific endorsement that the Superintendent will approve the proposed

rock source for the supply of armour for the works.

Other tests as listed above are to be undertaken by NATA endorsed testing facilities, with the results reported

on NATA endorsed test certificates. The certificates shall not be dated more than six months prior to the date

of their submission for approval by the Superintendent. Additional NATA certificates shall be submitted if the

supply source; or if in the opinion of the Superintendent the physical characteristics of supplied rocks change.


2.2 Core Material

Core material shall be approved angular or sub-angular igneous or metamorphic rock, and shall be:

free from vegetation, roots, clay and organic matter.

moderately weathered to fresh; up to 25% by weight may be moderately weathered subject to being

at least medium strength and compliance with other criteria.

sound, angular and suitable for use as core in the marine environment as determined by petrographic

examination (as per requirements for such examination and reporting outlined above in Table 2-1)

reasonably free of appreciable silt and clay particles to minimise turbidity when placed in water.

Apparent Particle Density - not less than 2.5 tonnes per cubic metre.

Wet Strength - not less than 110kN on the fresh to slightly weathered rock component.

2.3 Geotextile

Geotextile shall be Elcomax 600R. Equivalent non-woven geotextile may be offered for approval by the

Superintendent as an alternative.

2.4 Placement of Material

2.4.1 General

The techniques used in the handling, transportation and placement of all material in the breakwater shall be

such as to minimise any breakdown and production of fines. The placement method shall be such that there

is minimal segregation of material within each particular type/classification.

The construction activity shall be appropriately planned and executed to ensure that the placement of the core

material and placement of the geotextile proceeds at the same rate of advancement along the breakwater as

the primary and filter armouring. The preparation and geotextile placement should not be so far advanced of

subsequent armouring operations to expose it unnecessarily to risk of damage by inclement weather and/or

wave conditions. The degree of acceptable risk will be determined by seasonal conditions; nevertheless the

filter layer shall at no time be more than 15m in advance of the placement of primary armour.

2.4.2 Placement of Geotextile

Where geotextile is used in the breakwater, it shall be carefully placed to ensure that it is not punctured or torn.

Any areas where the geotextile is punctured or torn shall be removed or repaired to the satisfaction of the

Superintendent and in accordance with the manufacturer’s instructions.

All lap joints between adjoining sheets shall be no less than 500mm, or alternatively sheets are to be

mechanically joined in accordance with the manufacturers recommendations.

If laps are used then the planning and placement is to be such that only vertical laps are utilised on the front

slope of the breakwater. No horizontal laps are allowed on the front slope – that is, entire geotextile sheets

are to be placed on the full height of the prepared embankment slope.

The handling and storage of all geotextile prior to installation shall be in accordance with the manufacturer’s

recommendations and to the satisfaction of the Superintendent.


2.4.3 Placement of Primary Armour

The Drawings require that a minimum of two (2) rock layers are to be placed on the front face and crest of the

breakwater. This is an important structural requirement and will not be relaxed at any location nor under any

circumstances.

Where layer thicknesses are shown on the Drawings, these are to give an indication of minimum thicknesses

only and generally reflect that required for the number of specified layers.

Small rocks must not be placed so as to fill the voids and spaces between armour rocks thereby giving a

smooth appearance to the finished structure. This infilling reduces the effectiveness of the rock slopes when

dissipating wave energy and can result in increased overtopping and damage by storm waves.

Armour rocks shall be firmly bedded on the underlying rocks. Each rock shall be in firm contact with at least

three other stones of the same layer to form a tightly interlocked placement. This is an important structural

requirement (including for Type B filter armour) and will not be relaxed at any location nor under any

circumstances.

Consequently, all rocks on the finished face of the armoured structure shall be placed in a stable attitude

whereby they do not create a hazard and cannot be readily displaced or rocked from side-to-side by manual

means.

This Technical Specification allows for a range of rock sizes within a specific armour classification (refer Clause

2.1). The design intent is to have all sizes within the allowable range distributed uniformly throughout the

relevant armour layers. Consequently, the supply and placement of all rock shall be such as to avoid large

areas of the armoured slope constructed of rocks near the limits of the specified range. The Superintendent

reserves the right to direct at his absolute discretion, that an area where the armouring on any layer consists

of too great a coverage of either smaller rocks or larger rocks (despite being within the allowable range) be

replaced by more uniformly distributed sizes at no additional cost to the Principal.

The nominated finished gradient shall be adhered to over the full height of the armoured slope. Placement

shall commence at the toe of the slope and material shall be placed to its final thickness proceeding up the

bank slope.

The method for placement of armour rock shall minimise breakdown during handling and the production of

fines. Any rocks damaged during placement which results in their not complying with the requirements of this

Specification shall be removed and replaced at the Contractors expense.

The placement of armour rocks shall at all times be carried out in such a manner as to cause minimum

disturbance or dislodgment of the underlying material, particularly any geotextile material placed in the Works.

Any such damage shall be repaired at the Contractor’s expense.

3 TOLERANCES

Unless directed by the Superintendent, the crest position of the breakwater shall be within 0.3 metres of the

plan position shown on the Drawings. The crest level shall be as shown on the Drawings within the tolerances

of +0.3 metres, -0.0 metres; and shall not vary by more than 0.3 metres when measured over any 5.0 metre

length of section. The toe of any armoured slope shall not be above the level shown on the Drawings.

The side slopes shall be within +0.15, -0.0 of the nominated gradient (i.e. for the nominated gradient of 1 : 1.5

the tolerance is between 1 : 1.65 and 1 : 1.5).

Nowhere on the breakwater shall the thickness of rock armour be less than that shown on the Drawings.


4 SURVEY OF THE WORKS

Prior to the commencement of the Works, the Contractor shall set such line and level pegs as are necessary

for the adequate control of the construction of the Works. The Contractor must have satisfactory survey

equipment assigned to the worksite and shall employ on the Works a person approved by the Superintendent

capable of exercising control of line and level.

The Contractor shall make available as and when required by the Superintendent such chainmen and staffmen

as may be required by the Superintendent for checking of line and level of all Works, and for the measuring

up and recording by the Superintendent of all works.

The Contractor shall give written agreement to the information supplied on the Drawings regarding existing

surface levels within fourteen (14) days of the Date of the Letter of Acceptance. If no such notification is

received by the Superintendent, the information supplied on the Drawings regarding existing surface levels

shall be taken as final and not subject to negotiation.

Furthermore, no subsequent claim for any variation to a Lump Sum Contract for alleged base survey

inaccuracies shall be entertained.

At the completion of the Works and prior to the Practical Completion Certificate being granted, the Contractor

shall carry out a detailed completion survey over the entire area of the Works - to demonstrate that the required

construction lines and levels have been achieved.

Upon completion of this survey, the Contractor shall prepare and submit "As Constructed" Drawings. The

survey shall locate the position to an approved Azimuth Datum and the level relative to Australian Height

Datum (AHD) of the finished crest and the toe of the breakwater side slopes - at 5m spacings along the

alignment of the breakwater.


4987

-01_

R01

v01

.doc

x

Page 34

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

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

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

Perth PO Box 362 Subiaco WA 6904 Telephone 0438 347 968

Geelong PO Box 436 Geelong VIC 3220 Telephone 0458 015 664

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

Wimmera PO Box 584 Stawell VIC 3380 Telephone 0438 510 240

www.watertech.com.au

[email protected]

Stanage Bay Boat Ramp - Department of Transport and Main …Breakwater Design Report...

Documents

Transcript of Stanage Bay Boat Ramp - Department of Transport and Main …Breakwater Design Report...