CentrePort Shipping Channel Deepening Project

Transcription

1 CentrePort Shipping Channel Deepening Project Dredging and Disposal Assessment 31 March 2016 Prepared for CentrePort Limited by Pro Dredging and Marine Consultants Pty Ltd DRAFT FOR PUBLIC CONSULTATION Assessment of Environmental Effects - Dredging and Disposal Assessment Page 1 of 65

2 Table of Contents 1 Executive Summary Glossary of Technical terms Introduction Experience and expertise Harbour Dredging Context Physical Characteristics of dredge and disposal areas Meteorological conditions and sea-state conditions Scope of Dredging Work Equipment selection and dredging methods Production of dredgers Environmental considerations Support vessels for the dredging operation...35 Appendices...36 Appendix 1: Project Description Shipping Channel Deepening Project - Project Description Introduction Project Aim Project Objectives Project Scope Core proposal for shipping channel deepening Consent duration Appendix 1 Figures Appendix 2: Location of samples and PSD results Appendix 2a: Locations of six sample from the 2003 SKM investigation Appendix 2b: Sample locations in the 2014 NIWA investigation Appendix 2c: PSD results from 2014 NIWA investigation Appendix 3: Wind and Wave Data Appendix 4: Revised design of Entrance Channel Appendix 5: Generic method statement for backhoe dredger Appendix 6: Trailing suction hopper dredgers in the 10,000 to 20,000 m 3 category Appendix 7: List of backhoe dredgers with more than 750kW installed power in the excavator Appendix 8: Curriculum Vitae Johan Pronk Appendix 9: Particulars of TSHD Volvox Asia Appendix 10: Particulars of TSHD Brage R Appendix 11: Particulars of TSHD Pelican Assessment of Environmental Effects - Dredging and Disposal Assessment Page 2 of 65

3 1 Executive Summary By international standards this project represents a straight forward activity of dredging granular materials in the environment of a shipping channel. Apart from the possible presence of hard materials the dredging activity does not present particular difficulties. Potential environmental effects The dredging of Wellington Entrance Channel will have minimal effects on the environment in view of dredging mostly medium sand which contain only a small percentage of fines. The dredge plume created by overflowing and propeller wash of the trailing suction hopper dredger (TSHD) is predicted in the MetOcean Summary Report to be negligible compared to natural conditions as a result of Hutt River flows and southerly storms and from shipping movements of container vessels. In addition noise from dredging operations is not expected to exceed the emission levels from a cargo ship sailing at a normal operating speed through the channel. Assessments undertaken Analysis of geotechnical conditions: Investigations in 2003 by SKM (see Appendix 2) and 2014 by NIWA (See Appendix 2) and T+T as referenced in Appendix 4 of the Sediment Characterisation Report have shown the dredged materials to consist of medium to coarse sands with a low percentage of fines. Only at the northern end of the channel the materials contain more fines. Further investigations near the elbow in the channel have revealed the presence of a "hard" area consisting of cobbles, boulders and gravel. The size of the cobbles is reported to be less than 300 mm in diameter and it is expected that large TSHDs are capable to dredge these materials. For the deepest option for 14.5m draught vessels there is a possibility that rock is present above the design depth of the channel in the "hard" area of the cobbles. The materials to be dredged in front of the Thorndon Container Wharf (TCW) are a mixture of muddy gravel, overlain by mixed sands, gravel and mud in various proportions. Analysis of sea-state conditions: The sea-state conditions in the Entrance to Wellington Harbour show in general a relatively calm wave climate for the period from September until March, which will result in minimal delays for large TSHDs. However, while this period provides the most settled weather period, dredging is still possible outside this period although with an increased occurrence of sea-state delay for the dredgers, especially for the smaller size of dredgers. Dredging methodology: The type of materials to be dredged (i.e. granular) and the sea-state conditions makes this project very suitable for execution by a TSHD. Moreover, the TSHD is highly flexible in its operation in combination with shipping traffic in the channel. Also alternative dredging methods have been considered. If rock is encountered above the design depth for the deepest design option of the channel, the employment of a backhoe dredger could be necessary. Equipment selection: TSHDs with hopper capacities of 10,000m 3 to 20,000m 3 are the preferred main dredging equipment for the project. These dredgers are widely available and a first selection identified 24 vessels in this category from four different international dredging contractors. Smaller TSHDs can execute the project as well and two further options of a 2,100m 3 TSHD and a 965 m 3 TSHD have been included in the production calculations. The project will take considerably longer (see below) when employing the smaller dredgers. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 3 of 65

4 In the event of the presence of rock in the "hard" area above design depth for the deepest option, a backhoe dredger with more than 1000 kw of power installed in the excavator will need to be employed on the project. Production calculations: The production has been calculated for all three sizes of dredgers considered in this study. There are a range of dredger sizes available. For the full 6.0M m³ excavation, the project involving a larger TSHD is estimated to take approximately 18 weeks, while a smaller option, such as a 2,100m 3 trailer dredge will take approximately 90 weeks. Production figures have also been calculated for staged dredging. Dredging to enable a 12.5m draught vessel (which would involve 2.4Mm 3 of sediment being dredged) would take 6 weeks for a 10,834m3 dredger, 35 weeks for a 2,100m3 dredger and 72 weeks for a 965m3 dredger. Disposal methods: All dredged materials from the harbour entrance will be transported by the TSHDs to the allocated disposal area in Fitzroy Bay. This disposal area is located in water-depths of 50m and the dredged materials will be discharged by bottom placement. If the backhoe dredger needs to be employed, the dredged materials will be transported to the disposal area by tug and barges and subsequently bottom placed. Environmental considerations: The use of a green valve on the TSHD will reduce the plume size when dredging in the Wellington Entrance channel. Other environmental issues are covered in the Tonkin and Taylor Sediment Characterisation report, being: the placement of the more contaminated surface layer at TCW at the bottom of the TCW disposal area so it is covered by the less contaminated deeper sediment; and the preferential placement of similar sized sediments to those presently existing at the Fitzroy Bay disposal site (with cobbles being buried). Assessment of Environmental Effects - Dredging and Disposal Assessment Page 4 of 65

5 2 Glossary of Technical terms Table 1 below sets out the technical terms and abbreviations used in this report. Term Abbreviation (if applicable) Meaning Backhoe dredger BHD A large excavator mounted on a fabricated pedestal located at one extremity of a spud-rigged pontoon. Capital Dredging The removal of large amounts of material from the sea bed to create larger navigation depths in order to serve larger ships Chart Datum CD Vertical datum, which is m below B.M. K80/1 (LINZ Code ABPB), a stainless steel pin set in concrete under iron cover, in Featherston Street at the intersection with Lambton Quay, Wellington Cutter Suction Dredger Dredge Disposal Area Maintenance Dredging Production Cycle Dredging Spread Significant wave height Significant wave period Thorndon Container Wharf Trailing Suction Hopper Dredger CSD FBDDA Hs Ts TCW TSHD A non-propelled or self-propelled vessel capable of excavating cohesive and hard materials from the seabed by way of a rotating cutter-head. The dredged materials are pumped through pipelines to designated reclamation areas ashore. Alternatively, dredged materials can be pumped into self-propelled hopper barges for transport to offshore disposal areas. The Dredge Disposal area off Fitzroy Bay The removal of sedimentation in shipping channels and harbour basins in order to restore original design depths The time for loading, transport, dumping and returning to dredging area Dredger plus ancillary craft required for its operation The average height of the highest 1/3 of all waves (sea and swell) passing a given point in a given time - it is not the maximum height which may be nearly double this height The significant wave period is the mean of the zero upcrossing periods associated with the highest one third of the waves The main container wharf in Wellington Harbour A sea-going self-propelled vessel able to dredge materials from the seabed, loading it into its hopper hold, transporting it to a designated disposal area and discharging it by various means Table 1: Technical terms and abbreviations Assessment of Environmental Effects - Dredging and Disposal Assessment Page 5 of 65

6 3 Introduction Project description and outline 3.1 CentrePort Limited ("CentrePort") is planning to deepen the Wellington Harbour entrance shipping channel and the approach to, and berth at, the Thorndon Container Wharf ("TCW") (together called the "Project"). The purpose of the Project is to enable larger ships to access CentrePort thereby maintaining CentrePort's existing container service and providing for its future growth. Globally, container ships are increasing in size and all major New Zealand ports are preparing for their potential arrival. 3.2 Wellington Harbour (Te Whanganui-a-Tara) is naturally deep. This has reduced the historical need to deepen the harbour and means that the scale of deepening works is significantly less than other ports in New Zealand. 3.3 CentrePort holds consents enabling the deepening of the harbour entrance to m Chart Datum (CD) and the TCW berth to -12.5m CD. However, the anticipated arrival of larger ships will require a greater depth than the present consent provides. 3.4 The Project scope is set out in Appendix 1, Project Description. It involves; A) The deepening of the harbour entrance shipping channel to the depths of -16.5m to m CD for the 14.5m draught design vessel. This includes allowances for 0.5m overdredge and 1.5m minimum under keel clearance. There are also options concerning deepening the channel in stages. The dredged profiles are shown below in Figure 1 together with the present seabed depths. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 6 of 65

7 Figure 1: Shipping Channel Deepening Longitudinal Profiles Currently the shallowest parts of the harbour entrance shipping channel are -11.0m CD and -11.3m CD in the current shipping lane (i.e. along the line of the navigation leads). The harbour entrance deepening will potentially involve the removal of up to 6.0 million cubic metres of sediment over an area of 184 hectares. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 7 of 65

8 B) The deepening of the northern approach to TCW and the TCW berth to -15.2m CD. This will involve the removal of up to 270,000 cubic metres of sediment over an area of 30 hectares (refer to Appendix 1, Figure 4). C) The removed material will need to be disposed and disposal options and areas have been investigated. It is understood that the preferred option is disposal at sea in the vicinity of the presently consented Fitzroy Bay site in water depths of approximately 50m for material from the harbour entrance (refer to Appendix 1, Figures 1 and 3). For materials dredged in front of TCW and in the northern approach, proposed disposal is into an area with water depths in excess of 18m, which is adjacent and to the south east of the area to be deepened (refer to Appendix 1, Figure 4). The depths described above are sufficient to accommodate a 14.5m draught vessel (300m LOA and 48m beam) at a speed of 10 knots and include a 0.5m over dredge allowance and a minimum of 1.5m under keel clearance. 3.5 The depths of -16.5m CD to -17.2m CD (or -15.2m CD at TCW berth) include the 0.5m over dredge. It is expected that some dredged areas may need to be smoothed to achieve a consistent level. 3.6 A TSHD will be used to undertake at least the majority (if not all) of the deepening works. This commonly used dredging process involves a vessel moving across the area trailing a suction head and pipe which sucks the sediments off the seabed and subsequently loads the sediments into the hopper hold of the vessel. Immediately adjacent to the TCW wharf face or if hard material is encountered, a different type of method may be needed such as a back hoe dredger. The deepening may be done in one campaign or a number of campaigns staged over time or as a multi-year programme using a smaller size trailer dredger. Afterwards, target depths will be monitored and maintenance dredging may be required. Purpose of this report 3.7 This report: (a) (b) (c) (d) (e) Provides context for the proposed dredging and disposal works; Analyses the geotechnical parameters of the materials to be dredged; Identifies and assesses the alternative dredging and disposal methods and dredging equipment available for the deepening of the Entrance Channel and the approach to, and berth at, TCW; Describes the operational parameters for the preferred dredging and disposal option; and Provides production calculations, expected duration and indicative costing of the dredging works. 3.8 This report will be used by CentrePort in support for a resource consent application for the proposed deepening and the application will include an assessment of the effects on the environment from dredging and disposal. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 8 of 65

9 4 Experience and expertise 4.1 I have worked for more than 40 years in the dredging industry and have fulfilled various senior management positions as an international dredging contractor mainly in Australia and Asia. 4.2 I have firsthand experience with executing dredging projects in New Zealand as I was the managing director of New Zealand Dredging and General Works from 2002 till 2009 and, in that capacity, I was directly responsible for the maintenance dredging contracts in the ports of Tauranga, New Plymouth, Lyttelton and Timaru. 4.3 In 2009, I set up Pro Dredging and Marine Consultants. This company has provided consultancy services for dredging and reclamation projects to clients mostly located in Australia, such as major mining and resource companies, port authorities and large engineering consultants (Refer to Appendix 9 for the CV and experience record of Johan Pronk as principal of Pro Dredging and Marine Consultants). Preparation for this report 4.4 The following reports have been made available for the preparation of this report: Project Description for Shipping Channel Deepening Project, prepared by CentrePort. "Bathymetric and geophysical survey of Wellington Harbour Entrance Channel ref. WLG " dated July 2014, prepared by National Institute for Water and Atmospheric Ltd (NIWA). Report prepared by Tonkin & Taylor: Sediment Characterisation. Tonkin and Taylor Ltd letter dated 22 December 2015 titled Estimated Dredge Volume. CentrePort Wave and Wind statistics prepared by MetOcean Solutions Ltd (see section 7.4). MetOcean Solutions Ltd reports on numerical model studies of the wave, current and sediment dynamics. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 9 of 65

10 5 Harbour Dredging Context Global dredging operations 5.1 Dredging operations worldwide have responded well during the last 40 to 50 years to the ever increasing sizes of international shipping. Oil-tankers, bulk-carriers and container vessels have grown in size and consequently require larger navigation depths to enter ports and deeper harbour basins. The largest ports in the world require navigation depths in excess of 20m, requiring large quantities of materials to be dredged. This development is ongoing on all continents worldwide. 5.2 The dredging industry has responded to the above by increasing the size of their entire dredging fleets. All types of major dredging equipment, TSHD, BHD and Cutter Suction Dredge (CSD) have undergone major developments, and the modern dredgers are far more powerful and are considerably larger than the dredgers in the eighties. With regards to environmental performance of TSHDs significant improvements have been made by the construction of green valves in the overflow pipes of the TSHD (refer to paragraph 9.7 in chapter 9) and achieving a far more energy efficient operation of the dredger. 5.3 Best practice processes have gone hand in hand with the above developments and automation technology, different overflowing techniques, green valves, etc. have been developed for good environmental performance. New Zealand dredging operations 5.4 Maintenance dredging routinely takes place in various other ports on the New Zealand Coast. The main dredging activities are in Lyttelton, Port Chalmers, Timaru, Tauranga, Port Taranaki, Nelson and Napier. These are mainly maintenance dredging works carried out on a regular basis with a small trailing suction hopper dredger (TSHD). 5.5 Capital dredging works are executed occasionally and during the last twenty to twenty-five years capital dredging works have been executed in: Tauranga, 4.5 million m 3 dredged by TSHD to deepen channels and berths; Auckland, approximately 1 million m 3 dredged from Approach Channel by backhoe dredger; Port Taranaki, approx. 2 million m 3 excavated from harbour with backhoe dredger; and Marsden Point, approx. 1 million m 3 removed by small cutter suction dredger and small TSHD. 5.6 Recently, in anticipation of the arrival of larger container vessels visiting New Zealand a number of Ports have obtained consent to deepen their shipping channels, including Tauranga and Otago while Lyttelton and Napier are understood to be preparing consent applications. The dredging works at Tauranga and Otago are underway using medium to large TSHD and where applicable, areas of hard ground are proposed to be deepened by backhoe dredger. The dredged materials are being disposed of in offshore disposal areas. Wellington dredging operations 5.7 The harbour entrance channel has not been dredged since 1968 when 375,000 m 3 of material was dredged in the entrance channel and used for reclamation in the Thorndon Container Terminal. Since then only minor maintenance dredging of Seaview Wharf and the Thorndon Container Wharf has occurred. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 10 of 65

11 6 Physical Characteristics of dredge and disposal areas Materials to be dredged in Entrance Channel 6.1 A sampling program was carried out in 2003 by SKM for surface sediments in the entrance channel; the locations of the six samples are spread out over the length of the channel and are shown in Appendix 2a. Core lengths of 0.3m to 0.5m have been recovered and the materials have been described as fine dark sands with coarse shell grit and some soft grey clay. Table 2 provides three values on the grain-size distribution on each of the surface samples, including the D50, which is the average particle diameter by mass. E1 E2 E3 E4 E5 E6 D D D Table 2: PSD Data in microns for surface sediment samples in entrance channel (SKM 2003). The average D50 is approximately 165 microns. 6.2 The report "Bathymetric and geophysical survey of Wellington Harbour Entrance Channel ref. WLG " dated July 2014, which was prepared by National Institute for Water and Atmospheric Ltd (NIWA), provides additional information about the materials to be dredged following data from a high resolution seismic reflection (boomer) survey carried out in June/ July The data describe the characteristics of seafloor substrates as fine to medium sands overlaying coarse sand to fine pebble gravels. However the report also describes the presence of cobbles, boulders and gravels and a hard area in the elbow of the channel. Figure 2 shows the extent of the "hard area". The NIWA report describes that hard greywacke rock or very coarse gravelly materials and boulders could be expected in the top layer of the hard area. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 11 of 65

12 Fig.2: Location of hard area in the original alignment of the channel Assessment of Environmental Effects - Dredging and Disposal Assessment Page 12 of 65

13 6.4 Investigations (refer Sediment Characterisation Report) in the Entrance Channel have been carried out between September and December 2014: vibro-cores were taken at 8 locations along the proposed channel and also 10 piston samples were taken (refer to Appendix 2b). Samples were collected and laboratory testing to establish particle size dimensions (PSDs) on representative samples were carried out (refer to Appendix 2c). 6.5 The investigations show the material to be dredged from the harbour entrance channel comprises fine sands (north end), cobbles (elbow), and sands and gravel. Finer materials are present at the north end of the channel, where the channel widens into the harbour. Thirty sediment samples within the dredge area were tested for particle size distribution. The average D 50 of all samples is 327 m (microns), (laser method; 312 m using the wet sieve method). D 50 is the particle size where 50% of the particles are larger than the D 50 particle size and 50% greater. Based on the test results and NIWA's plan showing seismic survey classes: In the central and southern zones (backscatter classes 1 and 4; refer Figure 4), there is almost no fine fraction present. Of the 10 samples tested, 9 had 0% less than 63 m, and 1 had 1.2% less than 63 m. Coarse sands are present in the southern zone (D 50 ranging from 210 to 370m in the 5 samples from backscatter class 4), with even coarser material in the central zone (D 50 ranging from 850 to 1000 m (5 samples)). In the northern section, coarse sands grade to finer materials as the channel widens into the harbour. In the area defined by NIWA backscatter classes 5 and 6 (lower North Channel), there are very few fines: the percentage less than 63m ranges from 0.01% to 14%, with a median of 0.21% for the 17 samples tested. The D 50 in the area defined as backscatter classes 5 and 6 ranges from 120 to 260 m, with most samples around 140 m. Class 2 in the northern part of the channel contains finer sand (D m with 41% less than 63 m), and the backscatter results indicate muds are present at the very northern fringe of the dredge area (or the option of 14.5 m draught vessel only). Assessment of Environmental Effects - Dredging and Disposal Assessment Page 13 of 65

14 Figure 3: results of NIWA's backscatter (seismic) survey (source: Figure 4-7, NIWA 2014) 6.6 At the outer "elbow" of the harbour entrance channel, NIWA's geophysical survey identified a dense material within the proposed dredge depth. NIWA's survey could not distinguish between rock and dense gravels. After optimising the channel lay-out and alignment of the channel, the area and volume of "hard" material within the proposed dredge zone is as follows (provided by Tonkin &Taylor): 12.0 m vessel draught: 0.15 ha and 160 m m vessel draught: 0.72 ha and 2,500 m m vessel draught: 3.4 ha and 26,000 m m vessel draught: 6.4 ha and 80,000 m 3 Assessment of Environmental Effects - Dredging and Disposal Assessment Page 14 of 65

15 6.7 Diver investigations at 3 locations within this zone showed large cobbles, generally smaller than 250 mm and with a maximum dimension of 300 mm in diameter underlying approximately 1 m of coarse sand and gravel. The cobbles were excavated by diver to approximately 2 m below the existing seabed. Although investigations by diver only encountered cobbles in this area, and no rock, it cannot rule out the possibility that rock may be present in isolated areas, or at greater depth, within this zone. Elsewhere in the harbour entrance channel, NIWA's survey shows that the hard material drops away steeply to below the target dredge zone Fitzroy Bay particle size 6.8 The surface sediment at the Fitzroy Bay disposal area comprises coarse sands, with a grading from southeast to northwest of coarser to finer material. Six samples of surface sediment were tested from within the disposal area. The D 50 (laser method) ranged from 232 m at the southeast part of the disposal area down to 130 m at the northwest end of the disposal area. The fraction less than 63 m ranged from 4% at the southeast end to 26% in the northwest part of the zone. The samples were within the disposal zone but did not describe the entire extent of the disposal area. As explained in the Sediment Characterisation Report, based on the video tows carried out as part of the ecological investigations, there appears to be a continuum of coarser sediment in the southeast part of the zone and finer sediment in the northwest part. Materials to be dredged in front of TCW 6.9 Previous investigations have indicated that the sediments are muddy gravel, overlain by mixed sands, gravels and mud in varying proportions. The depth of rock is found at depths greater than -50m CD The Sediment Characterisation Report describes that the TCW dredge area comprises a mix of silty, sandy gravelly surface sediment, underlain by lenses of silty gravel and sandy silt. Within the TCW dredge area: Surface sediment: 10 surface sediment samples were tested. There was significant variation across the dredge area, which is consistent with this area being subject to disturbance from propeller wash. The D 50 in the surface sediment of the dredge area ranged from 8 m to 920 m. The percentage of fine material (less than 63 m) ranged from 10% to 98%; and In the deeper layers to be dredged, finer sediments are present at the southern end of the dredge area, with coarser material present in lenses in the northern part of the dredge area. The D 50 for the deeper sediments at the northern end of the dredge area (6 samples) ranged from 230 m to 780 m, with only 7% to 31% finer than 63 m. In the southern part of the dredge area, siltier materials are present, with D 50 of 8 m to 14 m and 88% to 100% finer than 63 m. TCW disposal area particle size 6.11 The TCW disposal area comprises fine sands and muds, with little variability across the disposal zone. The 6 samples of surface sediment tested had D 50 ranging from 8.8 to 9.9 m (laser method), and the percentage less than 63 m ranged from 92 to 95%. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 15 of 65

16 7 Meteorological conditions and sea-state conditions 7.1 The climate in Wellington can be described as mild in temperature but very windy. Tides Both northerly and southerly winds regularly reach strengths of 40 to 50 knots. Consequently, the entrance channel is subject to a vigorous wind and sea climate with the southerlies causing the larger waves. 7.2 Water levels at Wellington are influenced on a daily basis by semidiurnal tidal variation. The tidal levels for Wellington are shown in Tables 2 and 2a of the Navigation Report Sea-state conditions 7.3 During and following southerly winds large swells are entering the entrance channel and create rough sea conditions. 7.4 Monthly summaries of wind and wave data have been provided by Metconnect for the period June 2012 till July 2013 and for the four-month period January April The data was collected at the location of the Front Lead Beacon in the entrance channel (refer Appendix 1). The data provide detailed daily measurements on mean wind speed and maximum wind gusts in knots and for significant wave heights (Hs) in metres and significant wave periods (Ts) in seconds. 7.5 From the recorded data it can be concluded that the period from August till March appears to provide the calmest weather with limited exceedance of a mean significant wave height of 2.0m. This time period would reduce delay time for the dredgers as a result of unfavourable sea-state conditions. However, while it provides the most settled weather period, dredging is still possible outside this period although with an increased occurrence of sea-state delay for the dredgers. 7.6 Further data on observations and analyses over a 20-year period have been made available by MetOcean Solutions (refer to Appendix 3) for a location to the west of the proposed disposal area in Fitzroy Bay. The data from observations between 1979 and 2012 show little variance over the years with all mean wave height statistics falling within a band of plus or minus 10%. It shows over the 23 years that the period from September till March as the period with lowest average wave heights both for mean and maximum wave heights. 7.7 The observations also provide data on the direction where the waves are coming from and this is mainly from a southerly direction. 7.8 The results of both analyses show a relatively calm wave climate from September till March which will result in minimal delay time for the large size trailer dredger. In addition, by choosing a calm period the wave climate should limit the downtime for other type of dredgers, like the backhoe dredger and smaller trailers (please refer to the two smaller trailer dredgers reviewed in chapter 10). However, while it provides the most settled weather period, dredging is still possible outside this period although with an increased occurrence of sea-state delay for the dredgers. The exceedance percentages during the relatively calm period between September and March have been estimated for the purpose of dredger efficiency: for Hs =2.75m as approximately 5%; for Hs = 2.0m as 10%; and for Hs = 1.5m as 20%. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 16 of 65

17 Currents and flows 7.9 Currents in the entrance channel are mainly caused by tidal variation. The MetOcean Summary Report describes a 50cm/sec spring tide through the constricted harbour entrance Such currents do not have an effect on the efficiency of the dredging operations and are immaterial for the various options being considered. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 17 of 65

18 8 Scope of Dredging Work General 8.1 The proposed dredging works for the Entrance Channel involves the deepening of the existing channel to accommodate larger container vessels. The dredging area in the present channel is approximately 6.5 km long and has a shallowest depth of -11.0m CD. The channel design has been revised as a result of an extensive optimisation exercise. The revised design will ensure maximum channel operability, except in extreme wave climate or swell events. The width in the southern section of the entrance channel is 217m, widening for the bend area to 270m at the central elbow (course alteration point) and from the bend in the channel the width decreases to 217m at the end of the entrance channel (refer to Appendix 4) 8.2 Dredging is targeted to achieve design depths (including a 0.5m overdredge) sloping down from respectively -16.5m to -17.2m CD, descending to the south along a longitudinal profile. Dredging for the approach to and Berth 1 of TCW, which at present has a depth of -11.6m CD, are targeted for the design depth of -15.1m CD. 8.3 The following maximum depths (including 0.5m over dredge allowance) are shown in Table 3 and will apply to the four vessel scenarios (staging of construction) considered by CentrePort: Vessel draught scenario Northern section Southern section 12.0m draught 14.0m 14.7m 12.5m draught 14.5m 15.2m 13.5m draught 15.5m 16.2m 14.5m draught 16.5m 17.2m Table 3: maximum depths for the three scenarios 8.4 A summary of gross dredging quantities has been provided for the four vessel draught scenarios in table 4 by Tonkin &Taylor, calculated from bathymetric survey data, collected by Discovery Marine Ltd (DML). Vessel draught scenario Total dredge volume (m3) Area of disturbance (ha) 12.0m draught 1,600, m draught 2,400, m draught 4,000, m draught 6,000, Table 4: Estimated dredging volumes Entrance Channel The above quantities allow for 1:5 batter slopes in the northern section and for 1:9 batter slopes in the southern section of the channel. The quantities also allow for a contingency of 10%. 8.5 For the northern approach to TCW and for TCW berth the dredging quantities are summarised in Table 5: Vessel draught scenario Total dredge volume (m3) Area of disturbance (ha) 12.0m draught 20, m draught 50, m draught 140, m draught 270, Table 5: Estimated volumes for Thorndon Container Wharf Assessment of Environmental Effects - Dredging and Disposal Assessment Page 18 of 65

19 8.6 It is to be noted that no over-dredging has been applied to the volumes in the batter slope, but as the present estimate allows for 10% contingency and the fact that the assumption for the batter slope is a conservative one (1 in 9), it is expected that quantities for the final design of the batter slope including over-dredging will not exceed the above quantities. 8.7 The above quantities are used as target quantities in this report for production calculations and indicative costings. Dredge Disposal Areas 8.8 The dredged materials from the Entrance channel will be transported to the Dredge Disposal Area off Fitzroy Bay (FBDA), which is shown in Appendix 1, Figures 1 and 3. The FBDDA is located approximately 2.5 nm to the south of Pencarrow Head and is in approximately 50 to 55m m deep water. It has a rectangular shape and the size is approximately 140 ha. 8.9 The dredged materials from TCW1 will be transported to the Dredge Disposal Area, which is located approximately 400m off TCW in 18m water depth (refer to Appendix 1, Figure 4). Assessment of Environmental Effects - Dredging and Disposal Assessment Page 19 of 65

20 9 Equipment selection and dredging methods 9.1 The choice for dredging equipment to be utilized on a dredging project usually depends on the following factors: Materials to be dredged; Meteorological and sea-state conditions; Design depth for the areas to be dredged; Accessibility of the dredging areas and disposal area; Sailing distance to the disposal area; Availability in the market; Existing Marine traffic in the shipping channel; Project schedule; and Environmental Regulations, Constraints and Guidelines. Trailing Suction Hopper Dredger 9.2 Taking the above factors into consideration and in particular in view of the fact that mainly granular materials are required to be dredged in the entrance channel, a TSHD has been identified as the preferred major dredging equipment for the project, since it is: Flexible in its operation in combination with shipping traffic in the channel; Can work in varying offshore wave climates; Can transport the dredged materials to the offshore Disposal Area, and High production capacity. In these circumstances the trailer dredger is the obvious choice for the execution of the project, in which no other dredging equipment can perform as well and efficiently. The trailer dredger can work in conjunction with the other shipping traffic, like ferries and container vessels, without affecting each other's operation. Figure 4: 10,800m 3 TSHD "Volvox Asia" (Van Oord, Netherlands) 9.3 The present channel is sufficiently wide (> 300m) and has a declared depth of -11.0m CD. This has a limiting effect on the size of trailing suction hopper dredgers to be used for the project, and makes this project not suitable for the Jumbo trailers with hopper capacities well in excess of 20,000m 3. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 20 of 65

21 9.4 A large sized TSHD with a hopper capacity of 10,000m 3 to 20,000m 3 and a loaded draft of approximately 10m is ideally suited for the execution of the works (refer to figure 5). The short sailing distance of on average 8 to 11km to the FBDA will provide a commercially attractive solution. If a larger dredger is chosen, for instance a 30,000m 3 trailer with a loaded draft of 12.5 to 13.0m, draft restrictions and reduced loads would need to be applied. The preferred (large) category of trailer dredgers is widely available within the dredging industry and in Appendix 6, 24 trailer dredgers have been identified worldwide in the category of hopper capacities ranging from 10,000m 3 to 20,000m 3. By international standards this project represents a straight forward dredging project, dredging granular materials in the environment of a shipping channel and which apart from the possible presence of hard materials does not present particular difficulties. The trailer dredge with a hopper capacity of 10,800m 3 trailer (example "Volvox Asia" of Van Oord, Netherlands, refer to fig 5) is an example of the above category and is one of the three sizes of trailer dredgers considered for this project. General working principle of a trailing suction hopper dredger General description 9.5 A TSHD is a sea-going self-propelled vessel equipped with one or two suction pipes, designed to trail along the side of the vessel when on the seabed. At the lower end of the suction pipe, a drag-head is attached. Suction is provided by a pump mounted inside the vessel in a purpose built pump room. The suction created by this pump is sufficient to dislodge and then transport a mixture of seabed materials and water through the drag-head and suction pipe. In principle the main parts of the dredge are: Figure 5: Trailing suction hopper dredger. Hull, containing the engines, propulsion, pump(s), the crew quarters, the bridge with the navigation control etc; Hopper well where the pumped mixture of soil and water is pumped and the dredged material is allowed to settle down and the water is discharged through an overflow system; Suction pipe through which the mixture is transported to the pump; and Drag-head, attached to the end of the suction pipe, which liquefies the sea bottom with the aid of a water jet system. Different types of drag-heads can be fitted depending on soil conditions. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 21 of 65

22 9.6 A trailing suction hopper dredger is a non-stationary dredger. During dredging operations, the vessel is required to sail. When the dredger approaches the borrow area, it reduces speed and lowers the suction pipes overboard. The suction heads at the end of the suction pipes will be kept above the seabed until the scheduled dredging area has been reached. The dredge pumps are started and the sea water is taken in until the suction heads touch the sea-bed. The drag-heads (see Figure 6) are able, if necessary, to erode and liquefy material for retrieval. They do this using a water-jet system. When touching the seabed, the dredge pumps can suck up the sand and water mixture through the drag-head, suction pipe and pumps into the hopper. The density of the pumped mixture will be measured with a density meter, which is installed near the dredge pump. The dredge operator will divert the mixture in to the hopper by closing the pumpoverboard valve, if mixture density is acceptable. Once in the hopper, the material settles in the hopper well and water is discharged through an adjustable overflow system. Figure 6: Typical drag-head. During dredging, the vessel will sail with a speed of 1-3 knots, depending on the dredge location, the surrounding marine activities, sea condition and soil parameters. The material to be dredged will be stripped in layers over the full width of the dredging area. The position and depth of the drag-heads can be checked by using the measurements of the angles of the separate sections of the suction pipes in combination with the draught and trim of the vessel. Alternatively, the depth can be determined by using the pressure readings from sensors on the different parts of the suction pipe and drag-heads. Dredge cycle 9.7 A production cycle consists of four consecutive operations: 1. Loading 2. Sailing with a full load 3. Unloading 4. Sailing empty after discharge. Sailing time - both full and empty - depends on a number of factors including sailing distance, currents, tides, weather conditions, shipping traffic and speed limits. The time spent on loading and unloading the vessel depends mainly on soil characteristics. Vessel operations are assumed to continue 24 hours a day, seven days a week for the larger dredgers. Operating times for the smallest dredger is less as specified below. 1. Loading: The time required to fill the hopper and the volume of soil in the hopper will depend mainly on soil parameters and dredging depths. Each TSHD has a certain load capacity. This load is either limited by volume or by weight, depending on the vessel s technical specifications. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 22 of 65

23 The load could also be the result of an optimisation to determine the most economical loading time or alternatively it could also be restricted by navigational depth. Depending on the available trail-length the trailer dredge will normally be required to make a 180 degrees turn within the dredging area while continuing to dredge. Optimisation of the dredging cycle sometimes makes it necessary to work with overflow. This means that the TSHD will continue dredging with excess water flowing out of the hopper back into the sea. This will continue until the density of the material inside the hopper is optimised for the overall cycle production. A conventional hopper overflow will entrain air during the overflow process. The overflow system consists of a cylindrical weir with an adjustable height to control the required level of the liquid in the hopper. The air is trapped in the overflowing mixture and carries particles of material to the surface when it rises in the form of bubbles. Air can be prevented from entering by a regulating valve. This so-called 'environmental valve' or 'green valve' (see figure 8) controls the level of the overflowing water column in the lower vertical pipe of the overflow system. Because the overflowing mixture has a higher density than the surrounding water, it will behave like a column of water of higher density, which falls to the bottom of the dredging site. This is called a 'dynamic plume'. In other words, when the green valve is used, the suspended sediment settles towards the seabed, staying closer to the dredging area and reducing the amount of turbidity in the surrounding environment. Figure 7: Green valve in overflow pipe. When the hopper is fully loaded, the suction mouth is raised and the pumping system is shut off. The suction pipes will be hoisted and secured on board. Hopper volume will be measured and calculated on board. 2. Sailing with a full load: When loading of the vessel is complete, the vessel will proceed to the disposal area where its load will be deposited. During sailing, the watertight bottom doors of the hopper remain closed. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 23 of 65

24 3. Unloading: The TSHD entering the disposal area reduces speed and manoeuvres itself to the allocated area where the load can be bottom dumped. When the vessel is exactly in location using the vessel s propulsion and bow-thrusters, the dredge-master opens the bottom doors or conical valves and the sand and/or gravel starts to drop out of the hopper. In the meantime the dredge master keeps the vessel in position above the allocated area until all the sand and/or gravel has left the hopper. 4. Sailing empty: When the hopper is empty, the dredge-master closes the bottom doors. The vessel then sails back to the dredging area and the dredging cycle starts all over again. 9.8 In addition to utilising the trailer dredger, a dredging contractor may decide to use a bed-leveller for levelling out high spots and ridges within the dredged areas. Backhoe Dredger 9.9 In the event that hard materials are encountered in the elbow of the channel above the selected design depth and if these materials could not be removed by the TSHD, alternative equipment will need to be mobilized. In view of the small quantities involved, a backhoe dredge has been selected as the dredger for dredging these materials, which could consist of hard gravels, boulders or weathered rock. Pro Dredging recommends that in order to be successful in removing the hard materials, the backhoe dredger needs to have a minimum installed power of 1000kW for the excavator (refer to fig. 10). Usage of a rock breaker (refer to Figure 8) could be necessary to pre-treat the rock and break the rock up in lumps. Figure 8: Rock-breaker (Rohde Nielsen, Denmark) 9.10 The backhoe dredger will be able to work in the wave climate of the entrance channel, but the calmer season will need to be selected as explained above. Backhoe dredgers can lift their pontoon out of the water for approximately 0.5m and are able to continue dredging up to a significant wave height Hs of approx. 0.75m with periods Ts of 8 seconds. The non-propelled bottom disposal barges towed by tugs or self-propelled split hopper barges are able to continue operating up to sea-conditions of approximately Hs of 2m. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 24 of 65

25 Figure 9: Backhoe Dredger "Machiavelli" loading into bottom dump barges (Heron Construction) The backhoe dredger will be supported by either non-propelled bottom dump barges towed by tugs or self-propelled split hopper barges for the transportation of the dredged materials to the FBDA. A more detailed description of the work method of the backhoe dredger and its operation is provided in Appendix 5. Barges with a hopper capacity of nominal 1,000m 3 are commonly used with this size of backhoe dredger. Alternative dredging equipment 9.12 Alternative equipment has been considered for the execution of the dredging project, like for instance cutter suction dredgers and grabs dredgers. In the circumstances of the entrance channel the trailer dredger is the obvious choice for the reasons described in section 9.2. A cutter suction dredger is normally used in conjunction with reclaiming the dredged materials, but is not an economic option here. The work can be completed much more quickly and economically using a TSHD. A backhoe dredger will be used for any hard rock areas. A cutter suction dredger would cause considerable hindrance to the shipping traffic in the entrance channel and its operation is affected by sea conditions when the significant wave height Hs in excess of 1 m. The TSHD would also be suitable for transferring material to the Wellington International Airport runway extension reclamation. A grab dredger is a poor alternative for the backhoe dredger; it cannot remove hard rock and if the materials are already broken up in lumps and boulders it can remove these materials and load it into bottom dump barges. Output is very low and in order to utilize a decent size grab dredger, mobilization and demobilization from and to South East Asia will be involved, which is very expensive. Availability of equipment 9.13 TSHDs with hopper capacities of 10,000m 3 to 20,000m 3 are the preferred main dredging equipment for the total scope of this project. These dredgers are widely available and a first selection identified 24 vessels in this category from four different international dredging contractors. The trailer dredgers are listed in Appendix 6. Individual hopper capacities together with details on installed horse-power are recorded in the Appendix. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 25 of 65

26 It is expected that if a larger trailer dredger is chosen, it will need to be mobilised from outside New Zealand as there are limited opportunities for employing this category of dredgers in New Zealand. An opportunity may arise around the present harbour deepening project in Tauranga which would provide considerable savings on mobilisation costs. The project in Tauranga is presently (March 2016) utilising a trailer dredger with hopper capacity of 6,000 m 3. Two smaller dredgers have been considered in this report as well under chapter 10 and 11 in view of their presence in New Zealand and/or the East Coast of Australia For the backhoe dredgers a choice can be made between different sizes of backhoe dredgers, and a list of potential 18 backhoe dredgers is enclosed as Appendix 7. During the last few years a number of backhoe dredgers have been working on large dredging projects in Australia but these projects have been completed last year. All the equipment has been de-mobilised to South East Asia and other areas. There is normally only one backhoe dredger operating on the New Zealand market, the BHD "Machiavelli" of Heron Construction. It has a Liebherr excavator with 840 kw installed engine power, but it is committed to the Webb Dock project in Melbourne, Australia until late Assessment of Environmental Effects - Dredging and Disposal Assessment Page 26 of 65

27 10 Production of dredgers Production of the TSHD 10.1 The production cycle of a TSHD consists in general of the following parameters: 1. Sailing empty from the FBDA: during this trip the hopper will be pumped dry; 2. Dredging to the overflow; 3. Dredging with overflowing till maximum load is reached; 4. Turning within dredging area during the dredging operation; 5. Sailing with full load; and 6. Disposal of the dredged materials at FBDA For the calculation of the sailing distances to the existing FDBA, sailing distances of respectively 8km and 11km have been used from the centre point of both the southern and northern dredging area Three different sizes of dredgers have been considered on the request of Centre Port (technical details have been provided in Appendices 11-13): o o o TSHD Volvox Asia with a hopper capacity of 10,834 m 3 (Van Oord, Netherlands) (Appendix 9); TSHD Brage R with a hopper capacity of 2,100 m 3 (Rohde Nielsen, Denmark) operating mainly in the Australian / New Zealand region (Appendix 10); and TSHD Pelican with a hopper capacity of 965 m 3 (long term maintenance contracts NZDGW, New Zealand) (Appendix 11). 10,834 m 3 trailing suction hopper dredger 10.4 The following input data have been used for the production calculation of the TSHD, category 10,000m 3 : Two dredge pipes with a diameter of 1,100 mm; Suction velocity in dredge pipe 5 m/sec; Flow in the dredge pipe: 4.75 m 3 /sec or 9.50 m 3 /sec for two pipes; Loading time to overflow: 10,834/9.50 = 1,140 sec or 19 minutes; Total dredging time: 75 minutes in view of presence of some fine materials; Turning of the dredger in dredging area: 5 minutes; Duration of placement of materials within FBDA: 10 minutes; Trailing speed of the dredger: aver. 1.5 knots; Average hopper load: 7,500m 3 (in situ); Allowance for delays as a result of rough sea- conditions (5%); and 86.3% efficiency resulting in 145 operational hours per week. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 27 of 65

28 10.5 Based on the above factors an average dredging cycle is built up as follows: Dredging: 75 min Turning: 5 min Sailing full: 25 min Disposal: 10 min Sailing empty: 25 min Miscellaneous: 5 min Total cycle: 145 min 10.6 Number of trips per week: 145 x 60 / 145 = 60 trips per week (i.e in the order of 9 trips per 24 hours). Based on the above the average weekly production of 60 trips at 7,500m 3 / trip = 450,000m 3 is able to be dredged each week No specific production calculation has been made for the possible hard area in the elbow of the entrance channel; if the materials are loose gravel then this material will be dredged by the trailer dredge in conjunction with dredging the granular materials. However, if the materials are hard an attempt can first be made with using a ripper drag head on the trailer dredge and see whether the materials can be broken up with the trailer. As the quantity is relatively small (up to 80,000m 3 ), an allowance has been made for an additional two days dredging for the deepest option. It is to be noted that not all trailer dredgers in the 10,000 to 18,000 m 3 category have ripper capability. 2,100 m 3 trailing suction hopper dredger 10.8 Similar production calculations have been made for the 2,100 m 3 trailer dredger, and the following input data have been used for the production calculation of this TSHD: One dredge pipes with a diameter of 700 mm; Suction velocity in dredge pipe 5 m/sec; Flow in the dredge pipe: 1.9 m 3 /sec; Loading time to overflow: 2,100 / 1.9 = 1,105 sec or 19 minutes; Total dredging time: 85 minutes in view of presence of some fine materials; Turning of the dredger in dredging area: 5 minutes; Duration of placement of materials within FBDA: 10 minutes; Trailing speed of the dredger: aver. 1.5 knots; Average hopper load: 1,400m 3 (in situ); Allowance for delays as a result of rough sea- conditions (10%); and 81.5% efficiency resulting in 137 operational hours per week Based on the above factors an average dredging cycle is built up as follows: Dredging: 85 min Turning: 5 min Sailing full: 30 min Disposing: 10 min Sailing empty: 30 min Miscellaneous: 5 min Total cycle: 165 min Assessment of Environmental Effects - Dredging and Disposal Assessment Page 28 of 65

29 10.10 Number of trips per week: 137 x 60 / 165 = 49.8 trips per week (i.e 7 to 8 trips per 24 hours). Based on the above, the average weekly production of 50 trips at 1,400m 3 / trip = 70,000m 3 is able to be dredged each week No specific production calculation has been made for the possible hard area in the elbow of the entrance channel; if the materials are loose gravel then these materials will be dredged by the trailer dredge in conjunction with dredging the granular materials. If, however the materials are rock this category of trailer dredgers are not capable to remove the hard materials. 965m 3 trailing suction hopper dredger Technical information has been provided about this trailer dredger Pelican in Appendix The following input data have been used for the production calculation of the TSHD Pelican for dredging in granular materials during continuous operation: One dredge pipe with a diameter of 500 mm; Suction velocity in dredge pipe 5 m/sec; Flow in the dredge pipe: 0.9 m 3 /sec; Loading time to overflow: 965/0.9 = 1070 sec or 18 minutes; Total dredging time: 70 minutes in view of presence of submerged pump; Turning of the dredger in dredging area: 5 minutes; Duration of placement of materials within FBDA: 5 minutes; Trailing speed of the dredger: aver. 1.5 knots; Average hopper load: 650m 3 (in situ); Allowance for delays as a result of rough sea- conditions (15%); and 77.4% efficiency resulting in 130 operational hours per week Based on the above factors an average dredging cycle is built up as follows: Dredging: 70 min Turning: 5 min Sailing full: 35 min Disposing: 5 min Sailing empty: 30 min Miscellaneous: 5 min Total cycle: 150 min Number of trips per week: 130 x 60 / 150 = 52 trips per week (i.e. on average 8 trips per day). Based on the above, the average weekly production of 52 trips at 650m 3 / trip = 34,000m 3 is able to be dredged each week. No specific production calculation has been made for the possible hard area in the entrance channel as the dredger will have difficulty removing the cobbles and the dredger will not be able to dredge hard material. Note: Allowing for 1 day per week standby time as a result of unfavourable sea-state conditions can only be achieved in the season with calm weather, mainly during the months December till March. Staged dredging works is an option for CentrePort. If CentrePort was to stage the dredging to different depths over time the period for each individual dredge stage would reduce. For example, dredging to enable a 12.5m draught vessel (which would involve 2.4Mm 3 of sediment Assessment of Environmental Effects - Dredging and Disposal Assessment Page 29 of 65

30 being dredged) would take 6 weeks for a 10,834m3 dredger, 35 weeks for a 2,100m3 dredger and 72 weeks for a 965m3 dredger. Production of the backhoe dredger The production of a backhoe dredge is dependent on many factors: Type of materials to be dredged; Size of bucket (for instance 4m 3 bucket in hard clay/ rock); Thickness of layer to be removed; Lowering and hoisting speed of the excavator; Swing speeds; Experience of the crew Barge change times Weather conditions for barge changing The production for a backhoe with excavator-engine of 1000kW engine will be very low if hard rock is encountered with an estimated output of less than 100 m3/ hour In general backhoe dredgers have efficiencies between 60 and 65%, without weather delay, and therefore 100 operational hours per week is a good assumption for the dredging hours. If an allowance is made for a quantity of 25,000m3 that needs to be removed in the hard area by the backhoe dredger, a prudent estimate of 2.5 weeks work for the duration of the backhoe dredging can be made. Expected duration of dredging works The dredging works is split up between a trailer dredger and a backhoe dredger. Trailer dredger spread Based on the production calculations in 10.5 and 10.6 above, the 10,800 m 3 trailer dredger is expected to take approximately 15 weeks to complete the scope of approximately 6,000,000m 3 of dredging in the entrance channel. Total execution time: 16 weeks including allowance for dredging of hard area (0.3 weeks) and 0.5 weeks for TCW1. The whole duration for the complete scope of the project can be accommodated within a period of calm weather (September till December) Based on the production calculations in 10.9 and above, the 2,100 m 3 trailer dredger is expected to take approximately 86 weeks to complete the scope of approximately 6,000,000m 3 of dredging in the entrance channel. Total execution time: 90 weeks including allowance for dredging of hard area (1.5 weeks) and 2.5 weeks for TCW1. The whole duration for the complete scope of the project cannot be accommodated within the season of calmer weather (September till March). If the calmer period is strictly adhered to then it will take more than 3 seasons to complete the project, but this will result in additional mobilisation costs. Alternatively, if dredging will be executed continuously the project will take close to two months longer as substantial sea-state delays will be experienced during the period March up to and including August (15 to 20% weather delay) Based on scheduling the smallest dredger during a six months period in the calm season the TSHD Pelican can produce a quantity of approximately 800,000m 3 during the five to six months with the most favourable weather. In consultation with CentrePort, full year operation of the small trailer dredger has not been taken into consideration. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 30 of 65

31 Backhoe dredger spread As described in chapter above, an allowance is to be made for 2.5 weeks dredging in the calm season if rock is encountered in the hard area in the elbow of the entrance channel and if the trailer dredger has not been able to remove the hard materials. Note: the above durations are actual dredging times exclusive of mobilisation and demobilisation time. Based on the volumes calculated, the dredging work and durations set out above and the costs of obtaining the services of a dredger (including mobilisation), dredging to enable a 14.5m draught vessel to enter Wellington at any tide would cost approximately $37-44m. This variation reflects the various sized dredgers that could undertake the work. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 31 of 65

32 11 Environmental considerations Percentage of fines 11.1 Notice should be taken that the top layer of fine sands and some clay will contain a percentage of fines (please refer to samples SKM 2003 in table 2). Detailed PSDs are not available from the SKM sampling, but it is noted that it provided D25 readings in the order of 120 to 140 microns. With regards to the materials to be dredged underneath the top layer the NIWA report indicates that the materials are becoming coarser with fewer fines than in the top-layer. The recent 2014 investigations provided more information about the grain sizes and detailed PSDs have been made from the samples taken. The fine fraction results in the Entrance Channel from the recent 2014 investigation are summarised in Table 6: Section Number samples NIWA backscatter class Min (% <63m) Median (% <63m) Northern fringe Northern 18 5, Central Southern 6 4, 2, Table 6: Fine fractions in Entrance Channel Max (% <63m) 11.2 Segregation of the fines will take place during the loading process of the hopper well and mixtures overflowing from the hopper dredge will create dredge plumes. In this respect the percentage of fines < 63 microns is important to provide an indication for the dredge plumes. From the recent investigations explained in the Sediment Characterisation Report it can be concluded that only the northern fringe contains higher percentages of fines The MetOcean Summary Report indicates minimal plumes are expected to be generated during dredging in the harbour entrance, which is consistent with rapid settling (sands). However, if plumes are more pronounced than expected, then a possible mitigation measure would be to dredge each load from north to south, so that the finer materials are dredged before the TSHD starts to overflow. Overflowing and Dredge cycles 11.4 The hopper well is quite large (depending on the size of the trailer 60 to 100m long and having hopper capacities between 10,000 and 20,000m 3 ) and this provides an opportunity for the fines to settle in the hopper well. After approximately 20 minutes of loading the hopper starts to overflow and a mixture of water and fines will be discharged through the adjustable overflow pipe. This continues for 55 minutes and towards the end of the loading process the concentration of fines going overboard increases slightly as there is little room left in the hopper for the fines to settle. This process is more or less continuous, and only stops when the dredger reaches its full load. Consequently, the overflowing process would continue for approximately 55 hours per week. Green valve 11.5 The dredge pump sucks up the soil and water mixture through the drag-head and suction pipe and pumps the mixture into the hopper-well. The solids will settle in the hopper-well and the water is discharged through an adjustable overflow system. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 32 of 65

33 Noise Almost all dredgers are nowadays fitted with a green valve in the overflow pipes, which enables air trapped in the mixture to escape and hence reduces the turbidity of the water flowing out of the dredger (see Figure 7 above) Figure 10 provides an overview of the underwater noise generated by a TSHD. In general there are three categories of sound sources during trailer dredging operations: Excavation (drag-head); Operation of the vessel (engines, propeller, pumps, winches, thruster, etc.); and Dumping of dredged materials. Because the TSHD departs the dredging site for the disposal site on a regular cycle, exposure to such sounds would be limited to the period of active excavation. Sound production is strongly influenced by the properties of the materials to be dredged. Unfortunately, few research data and published characterizations of dredging induced sound levels exist. Figure 10: sources of underwater noise TSHD (CEDA) In a position paper (November 2011) of the Central Dredging Association (CEDA) a table has been produced which amongst others compares the sound produced by dredgers with normal shipping and other construction vessels. It found that sound levels emitted by hopper dredgers are generally in line with those expected for a cargo ship travelling at a speed between 8-16 knots. Background conditions in Lambton Harbour and in the entrance channel to Wellington 11.9 Pro Dredging understands that the Hutt River discharges considerable amounts of fines into Wellington Harbour during periods of increased flow of the river. Especially during windy conditions it is noticeable that fines are stirred up, creating discolouration of the bay and the sea. Against this back-ground it is expected that the amount of turbidity created by dredgers will be negligible compared with what happens under natural conditions. In particular, MetOcean's comments are noted (MSL 2016 CentrePort Harbour Deepening Project - Summary of Physical Effects): "The temporary and localised plumes caused by dredging need to considered in the context of the natural variability in suspended sediment at this location. Notably, the storm flows from the Hutt River periodically discharge high sediment loads directly into the harbour, Assessment of Environmental Effects - Dredging and Disposal Assessment Page 33 of 65

34 causing highly turbid conditions. Also, during southerly storm conditions there is evidence that the seabed sediments in the entrance area are regularly mobilised, which gives rise to elevated levels of suspended sediments in the water column, persisting for many days. Accordingly, it is considered that any plume created by dredging activities will have effects that are negligible in comparison to the effect of a typical southerly storm or the Hutt River flows after a high rainfall event." Assessment of Environmental Effects - Dredging and Disposal Assessment Page 34 of 65

35 12 Support vessels for the dredging operation 12.1 The dredging spreads will be supported by the following ancillary craft: a) One survey vessel working in day-shift only to execute hydro-graphic survey works, initially a couple of times a week increasing to almost on a daily basis during the final stages of the project. Various types of vessels can be suitable for this type of work, but normally a fast moving launch of minimum 15m length and capable of sailing at a speed of 18 to 20 knots will be employed; b) One crew-boat to transfer crew members and project staff between dredgers and shore. The length of this vessel is usually around 15m as well. This vessel may also be used by the client s representative for visits to the dredgers; Note: the contractor may decide to take care of both functions with one vessel. c) In the event of employing a backhoe dredger, one ocean going tug with minimum 1200kW propulsion power and 15-ton bollard pull for towing the bottom dump barges between the backhoe dredger and the FBDA and vice versa The intensity of the vessel movements will vary daily, but is estimated to be as follows: Survey vessel: daily travelling between Wellington harbour and the dredging area and returning and executing survey work in the dredging areas and also sometimes in the FBDA; Crew-boat: assume on average 4 to 5 trips per day between Wellington harbour and dredging area and returning; For the tug it is estimated that it will make on average two trips a day to the FBDA. All the support vessels will in general sail within the shipping channel, but in view of their limited draught they can go outside the channel, when shipping traffic so demands In addition to mobilising dredging spreads a dredging contractor may decide to mobilise a bedleveller for levelling out high spots in the channel (refer chapter 9.8). This is an alternative that the contractor may consider compared to dredging for a longer period of time with the trailer dredger. The bed leveller is a tug which can lower a sweep-bar down to sea-bed level via a winch and an A- frame at the stern of the vessel. The depth of the sweep-bar can be adjusted for tidal variations and the size of this tug would be: a minimum length of 25m and approximately 2000kW propulsion power installed. Figure 12: Animation of bed leveller with tug Assessment of Environmental Effects - Dredging and Disposal Assessment Page 35 of 65

36 Appendices Assessment of Environmental Effects - Dredging and Disposal Assessment Page 36 of 65

37 Appendix 1: Project Description Introduction Shipping Channel Deepening Project - Project Description As an international port, CentrePort is critical to the economy of central New Zealand. 1 As Central New Zealand contributes 26.3% of national GDP it is important to New Zealand's growth to maintain and enhance its strong international connections. To enable Central New Zealand to flourish requires strong transport connections. Nearly all of New Zealand's exports and imports are transported via sea. CentrePort needs to be able to effectively and safely meet the needs of its customers, including importers/exporters and international shipping operators. Those needs are changing. The global demand for more efficient freight movement is driving demand for larger ships, in turn requiring deeper shipping channels. The largest container ships regularly visiting Wellington can carry approximately 4,300 containers. Ships carrying around 6,500 containers are anticipated in New Zealand by the end of 2016 and even larger ships of 8000 plus containers, and with draughts of up to 14.5m, are expected in New Zealand within 10 years. All major NZ ports are preparing for this change and the Port of Tauranga and Port Otago have commenced dredging to enable larger ships. The first stage of these deepening programmes will be complete in late Wellington Harbour is a naturally deep water harbour. However, the current harbour entrance shipping channel, berth and berth approach depths restrict ships with draughts over 11.6m. While CentrePort has consents in place (since 2003 and 2005) to deepen shipping channels they are to insufficient depths and volumes to meet future needs. New consents are therefore required and it is important to CentrePort that future consents are sufficiently flexible to enable channel deepening to occur when required, to the optimum depths required and in the most economic manner. Project Aim The overall Project Aim is to enable CentrePort to deepen the shipping channel in the Wellington harbour in order to meet the long term needs of its customers. Project Objectives Economic: to support and enhance the economic growth and competitiveness of central New Zealand through enabling the region to maintain and grow direct international freight transport connections by ensuring CentrePort can accommodate larger ships. Commercial: to enhance the long term commercial competitiveness of CentrePort as a container freight port by providing certainty for the needs of shipping customers through long term, flexible, resource consents. Navigational safety and compliance: to enable larger ships to access Wellington Harbour and CentrePort's container berth in compliance with relevant international guidance for navigational safety. Sustainability: to identify and sustainably manage environmental, economic, social and cultural effects of deepening shipping channels including placement of material. 1 Central New Zealand includes the Taranaki, Hawke's Bay, Manawatu/Wanganui, Wellington, Tasman, Nelson and Marlborough regions. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 37 of 65

38 Project Scope Shipping channel deepening requires a 3 stage process: Phase 1 - Investigation and Design; Phase 2 - Consenting; Phase 3 - Construction. The scope of this Project is limited to Phases 1 and 2 only. Phase 1: Investigation of alternatives, feasibility and potential impacts of the core shipping channel deepening concept (refer below). Consultation with iwi, stakeholders and regulators, and preparation of resource consent applications. Phase 2: Lodgement and determination of a resource consent application for the core shipping channel deepening proposal (subject to Phase 1 findings and consultation). Core proposal for shipping channel deepening Design vessel dimensions 14.5m laden draught 300m LOA 48m beam Transit speed 10 knots Estimated maximum cargo capacity 9500TEU Harbour Entrance Channel Channel design has been revised as a result of an extensive optimisation exercise. The revised design will ensure maximum channel operability (or unrestricted design vessel access), except in extreme wave climate or swell events. Location and coordinates Refer Appendix 1 (Figures 1 and 2) Dimensions Refer Appendix 1 (Figure 2) Channel widths (in accordance with PIANC Guidelines, 2014), excluding batter slopes: Depth 217m at north and south ends 270m at central elbow (course alteration point) Maximum depths are 16.5m to 17.2m (below Chart Datum, based on a sloped channel descending to the south along a longitudinal profile) 2 Maximum depths include a 0.5m overdredge allowance Maximum depths include provision for 1.5m under keel clearance at all times Depths do not include allowance for tide (i.e. any depth of water due to tide is additional) To achieve the above maximum depths the maximum dredge depth below current seabed is 5.5m. The following maximum depths apply to the four vessel draught scenarios (construction staging) outlined below 2 Reference: MetOcean Solutions Ltd, CentrePort Channel Deepening Project, Optimised Depth Profiles, Report P , Rev O, Figure 3.1, 98% operability profile, October Assessment of Environmental Effects - Dredging and Disposal Assessment Page 38 of 65

39 Vessel draught scenario Depth (mcd) incl. 0.5m overdredge Coordinates of ends of sloped section North section South section North (WGS 84) South (WGS 84) 12.0m draught m draught m draught m draught Estimated disposal volume and areas of disturbance Maximum disposal volume 6.0M m 3 The following total cumulative dredge volumes apply to the four draught scenarios Vessel draught scenario Total dredge volume (million m 3 ) Area of disturbance (ha) 12.0m draught m draught m draught m draught Includes batter slopes of: 1:5 for north section of channel 1:9 for central and south sections of channel Includes 10% contingency Based on a sloped channel descending to the south along a longitudinal profile Disposal Area for Harbour Entrance Disposal location, depth and dimensions Primary disposal option is at Fitzroy Bay (refer Appendix 1 Figure 3). This is a previously consented disposal area. Depth: 50-55mCD Area: approximately 140ha Thorndon Container Wharf (TCW) Location Refer Appendix 1 (Figure 4) Dimensions Refer Appendix 1 (Figure 4) Depth (berth and approach channel) Maximum depth of 15.2m (below Chart Datum) The following maximum depths apply to the four draught scenarios (construction staging) outlined below: Assessment of Environmental Effects - Dredging and Disposal Assessment Page 39 of 65

40 Vessel draught scenario Depth including overdredge (mcd) Max dredge depth (m below current seabed surface) 12.0m draught m draught m draught m draught Depth includes: 0.5m overdredge allowance 0.6m minimum under keel clearance Provision for Wellington spring tidal range of 1.34m Estimated disposal volume and areas of disturbance Maximum disposal volume 270,000 m 3 The following total cumulative dredge volumes apply to the three draught scenarios Vessel draught scenario Total dredge volume (m 3 ) Area of disturbance (ha) 12.0m draught 20, m draught 50, m draught 140, m draught 270, Includes 1:5 batter slopes 10% contingency Disposal Area for TCW Disposal location, depth and dimensions Primary disposal option is off TCW (refer Appendix 1 Figure 4). Depth: mCD Area: approximately 30ha Construction (Phase 3) scenarios The following construction scenarios need to be considered for the Harbour Entrance Channel. Scenario 1 staged. The following indicative stages are proposed (actual staging and associated depths and volumes may be more or less than that indicated). Stage 1 up to 12.0m draught vessel Depth 14.0m 14.7m (below Chart Datum) Up to 1.6 M m 3 Stage 2 up to 12.5m draught vessel Depth 14.5m m (below Chart Datum) Up to 2.4 M m 3 Stage 3 up to 13.5m draught vessel Depth 15.5m m (below Chart Datum) Assessment of Environmental Effects - Dredging and Disposal Assessment Page 40 of 65

41 Up to 4.0 M m 3 Stage 4 up to 14.5m draught vessel (consented maximum depths and volumes) Depth 16.5m to 17.2m (below Chart Datum) Up to 6.0 M m 3 Scenario 2 multi year programme Multi year dredging programme using a low volume (<1000m 3 ) dredge vessel Assumes dredging up to 6 days week for 50 weeks/year, daylight hours only (subject to limitations such as weather and sea state, mechanical downtime etc). Scenario 3 single event Dredging and disposal to consented maximum depths and volumes (refer above depths of m; volume up to 6.0M m 3 ) Estimated duration weeks. Given the lower volumes involved, construction scenarios at TCW are unlikely to include Scenario 2 (i.e. design depths will be achieved by a single event or in stages). Maintenance dredging Maintenance dredging to approved depths is to be provided. Consent duration CentrePort will seek resource consents for a term of 35 years. Appendix 1 Figures Figure 1: Site location map Figure 2: Harbour entrance channel deepening area (update to include 12m scenario) Figure 3: Fitzroy Bay placement area Figure 4: Thorndon Container Wharf northern approach deepening area and placement area Figure 5 Shipping Channel Deepening Longitudinal Profiles Assessment of Environmental Effects - Dredging and Disposal Assessment Page 41 of 65

42 Figure 1: Site location map Assessment of Environmental Effects - Dredging and Disposal Assessment Page 42 of 65

43 Figure 2: Harbour entrance channel deepening area Assessment of Environmental Effects - Dredging and Disposal Assessment Page 43 of 65

44 Figure 3: Fitzroy Bay placement area Assessment of Environmental Effects - Dredging and Disposal Assessment Page 44 of 65

45 Figure 4: Thorndon Container Wharf northern approach deepening area and placement area Assessment of Environmental Effects - Dredging and Disposal Assessment Page 45 of 65

46 Figure 5: Shipping Channel Deepening Longitudinal Profiles Assessment of Environmental Effects - Dredging and Disposal Assessment Page 46 of 65

47 Appendix 2: Location of samples and PSD results. Appendix 2a Locations of six sample from the 2003 SKM investigation Appendix 2b Sample locations in the 2014 NIWA investigation Appendix 2c PSD results from 2014 NIWA investigation Assessment of Environmental Effects - Dredging and Disposal Assessment Page 47 of 65

48 Appendix 2a: Locations of six sample from the 2003 SKM investigation Assessment of Environmental Effects - Dredging and Disposal Assessment Page 48 of 65

49 Appendix 2b: Sample locations in the 2014 NIWA investigation Assessment of Environmental Effects - Dredging and Disposal Assessment Page 49 of 65

50 Appendix 2c: PSD results from 2014 NIWA investigation Assessment of Environmental Effects - Dredging and Disposal Assessment Page 50 of 65

51 Assessment of Environmental Effects - Dredging and Disposal Assessment Page 51 of 65

52 Appendix 3: Wind and Wave Data Assessment of Environmental Effects - Dredging and Disposal Assessment Page 52 of 65

53 Appendix 4: Revised design of Entrance Channel Assessment of Environmental Effects - Dredging and Disposal Assessment Page 53 of 65

54 Appendix 5: Generic method statement for backhoe dredger General working method of a backhoe dredger The backhoe dredger has evolved from the common land-based backhoe excavator. Whereas the landbased machine is normally mounted on a tracked or wheeled undercarriage, the dedicated dredging machine is mounted on a fabricated pedestal located at one extremity of a spud-rigged pontoon. The spud location of the pontoon is necessary to provide a positive reaction to the hydraulic digging action, particularly when dredging in difficult ground. The single digging bucket is located at the extremity of a pin-jointed arm. Between the bucket and the main structure of the machine are three points of rotation, all in the same plane. High pressure hydraulic cylinders control the movement of each section relative to the other. Typical backhoe dredger (side view) For backhoe dredging operations the dredging area will be divided into cuts of a certain width, depending on the depth and the reach of the dredger. The backhoe dredger will complete dredging a cut in circular segments, before being relocated to the next cut. The dredger will be positioned backwards (approximately 6 m) after completion of each circular segment. This is achieved by using the spud carrier. The bucket will be positioned on the seabed to fix the heading of the pontoon. The two forward spuds will be lifted and by moving the aft spud in the carrier a step can be made. After it is verified that the pontoon is level and that it has the correct heading, dredging in the new area can commence. Dredging operations Prior to the start of the dredging works a pre-dredge survey will be carried out of the entire working area. These in-survey data will be presented visually on board all vessels equipped with positioning equipment, i.e. the backhoe dredger and the survey vessel. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 54 of 65

55 Once the dredger has been made operational and all the required survey equipment, i.e. the (horizontal) positioning equipment (DGPS system) and the (vertical) dredging support equipment (tidal data receiver), has been properly set up, the backhoe dredger will be towed to the dredging area by the tug boat. The backhoe dredger will be positioned at an appropriate location inside the dredging area. This dredging area will be divided into cuts of a certain width, depending on the depth and the reach of the dredger. Once the dredger is in the correct position the spuds will be lowered and dredging can commence. Upon completion of each cut across the face and before the pontoon is moved, a sweep across the face should be made with the bucket held at the target finish level to check for high spots and to level any minor peaks For discharging of the excavated material, a hopper barge is moored alongside the pontoon of the backhoe. The backhoe will excavate the material from the trench with the bucket and dump the dredged material into the hopper barges. After the barge is fully loaded, a tugboat will be positioned either in front or after the barge, the barge will be disconnected from the backhoe dredger and the tug will tow or push the barge to the designated offshore spoil ground where the material will be dumped by opening the hopper of the barge. After discharging the load, the barge will sail back to the backhoe dredger to be loaded again. The cycle can be optimised to dredge continuously with the backhoe dredger, by using more than one barge. Dredging control To control the dredging operation, use is made of a monitor on board the dredger, displaying the geometry of the trench and an outline of the vessel. Inputs for this system are generated by data from angle and displacement measurement devices derived from a DGPS receiver, in combination with the gyrocompass. As a back-up a line laser onshore might be used to aid positioning. The dredge computer has two screens. Each screen is a graphical representation of the crane while in operation. One screen provides a top view of the entire crane and dredged area. The second screen provides a cross section of the entire crane including the desired trench bottom. The progress of the dredging operations with the backhoe dredger will be monitored by executing intermediate surveys with the survey vessel at regular intervals. The dredged volumes, the dredged profile, any possible sedimentation or eventual over-dredging can be determined from the results of these surveys. Dredging tolerances Generally, tolerances to be taken into account for backhoe dredging will be: Vertical: 0.5 m; and Horizontal: 1.0 m. Assessment of Environmental Effects - Dredging and Disposal Assessment Page 55 of 65

56 Appendix 6: Trailing suction hopper dredgers in the 10,000 to 20,000 m 3 category 10,000-14,000 m 3 category Name Owner Hopper capacity in m 3 Power in kw Lelystad Van Oord 10,327 15,930 Volvox Asia Van Oord 10,834 21,453 Ham 310 Van Oord 13,500 11,810 Gateway Boskalis 11,000 14,033 Willem van Oranje Boskalis 11,000 13,870 Seaway Boskalis 13,256 12,819 Breydel Dredging International 11,296 11,037 Brabo Dredging International 11,650 11,037 Breughel Dredging International 11,650 11,037 Vlaanderen 18 Dredging International 11,927 13,547 Uilenspiegel Dredging International 13,914 13,860 Lange Wapper Dredging International 13,914 13,860 Francis Beaufort Jan De Nul 11,363 11,363 Filippo Brunelleschi Jan De Nul 11,363 11,363 James Cook Jan De Nul 11,870 14,180 16,000-20,000 m 3 category Name Owner Hopper capacity in m 3 Power in kw Utrecht Van Oord 18,292 23,807 Terranova Van Oord 20,015 Rotterdam Van Oord 21,800 27,470 Prins Der Nederlanden Boskalis 15,961 19,500 Oranje Boskalis 15,961 19,500 Nile River Dredging International 17,000 19,998 Kaishuu Jan De Nul 16,500 17,918 Juan Sebastian de Elcano Jan De Nul 16,500 17,918 Gerardus Mercator Jan De Nul 18,876 21,992 Assessment of Environmental Effects - Dredging and Disposal Assessment Page 56 of 65

57 Appendix 7: List of backhoe dredgers with more than 750kW installed power in the excavator Assessment of Environmental Effects - Dredging and Disposal Assessment Page 57 of 65

58 Appendix 8: Curriculum Vitae Johan Pronk Assessment of Environmental Effects - Dredging and Disposal Assessment Page 58 of 65

59 Assessment of Environmental Effects - Dredging and Disposal Assessment Page 59 of 65

60 Appendix 9: Particulars of TSHD Volvox Asia Assessment of Environmental Effects - Dredging and Disposal Assessment Page 60 of 65

61 Assessment of Environmental Effects - Dredging and Disposal Assessment Page 61 of 65

62 Appendix 10: Particulars of TSHD Brage R Assessment of Environmental Effects - Dredging and Disposal Assessment Page 62 of 65

63 Assessment of Environmental Effects - Dredging and Disposal Assessment Page 63 of 65

64 Appendix 11: Particulars of TSHD Pelican Assessment of Environmental Effects - Dredging and Disposal Assessment Page 64 of 65

65 Assessment of Environmental Effects - Dredging and Disposal Assessment Page 65 of 65