RANOBE MINE PROJECT, SOUTHWEST REGION, MADAGASCAR …

RANOBE MINE PROJECT, SOUTHWEST REGION, MADAGASCAR

VOLUME 15: SEDIMENT TRANSPORT ASSESSMENT

Prepared for:

Prepared by:

World Titanium Resources Ltd

15 Lovegrove Close, Mount Claremont Western Australia

6010

Prestedge Retief Dresner

Wijnberg (Pty) Ltd

Consulting Port and Coastal Engineers

5th Floor, Safmarine Quay, Clock Tower Precinct

Victoria & Alfred Waterfront 8002

Cape Town South Africa

January 2013

Sediment Transport Assessment – January 2013

Coastal & Environmental Services Ranobe Mine Project

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Ranobe Mine Project EIA Inputs – Sediment Transport Assessment

Document No. 483/43/01

Revision Date Author Checked Status Approved

00 September 2012 CS SAL Issue

01 October 2012 CS SAL Issue



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TABLE OF CONTENTS

1. Introduction .............................................................................................................................. 1

1.1. Background .............................................................................................................................. 1 1.2. Scope of Work .......................................................................................................................... 2 1.3. Study Methodology ................................................................................................................. 3

2. DATA ......................................................................................................................................... 4

2.1. Offshore Wave Climate ........................................................................................................... 4 2.2. Offshore Wind Climate ............................................................................................................ 4 2.3. Water Levels ............................................................................................................................. 5 2.4. Bathymetry ............................................................................................................................... 6

3. ASSESSMENT OF SEDIMENT TRANSPORT SYSTEM ......................................................... 7

3.1. Introduction .............................................................................................................................. 7 3.2. Sediment Sources and Sinks ................................................................................................. 8

3.2.1. The Fiherenana River as a Fluvial Sediment Source ................................................................ 8 3.2.2. Wind-Blown Sediment Sink ..................................................................................................... 10 3.2.3. Toliara Channel ....................................................................................................................... 10

3.3. Historic Shoreline Variations................................................................................................ 12

3.3.1. Large Scale Shoreline Variations ............................................................................................ 13 3.3.2. Local Shoreline Variations ....................................................................................................... 16

3.4. Interpretation of Sediment Transport Mechanics............................................................... 18 3.5. Future Shoreline Trends ....................................................................................................... 20 3.6. Numerical Modelling of Sediment Transport Regime ........................................................ 20

4. POTENTIAL IMPACT OF PROPOSED PORT DEVELOPMENT .......................................... 21

4.1. Introduction ............................................................................................................................ 21 4.2. Preferred Port Layout – Direct Loading Option .................................................................. 21 4.3. Barge Loading Option ........................................................................................................... 22

5. SEDIMENT TRANSPORT MONITORING PROGRAMME ..................................................... 23

5.1. Introduction ............................................................................................................................ 23 5.2. Beach Monitoring Programme ............................................................................................. 23 5.3. Grid Survey of Toliara Sand Spit ......................................................................................... 23

6. SUMMARY AND RECOMMENDATIONS ............................................................................... 24

6.1. Potential Impact of Proposed Port Facility on Sediment Transport Regime .................. 24 6.2. Additional Sediment Transport Modelling .......................................................................... 24 6.3. Shoreline Monitoring ............................................................................................................. 24

7. REFERENCES ........................................................................................................................ 25

8. APPENDIX............................................................................................................................... 26



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TABLES Table 2.1: Water Levels at the Port of Toliara ......................................................................................... 5 Table 3.1: Summary of Aerial Images .................................................................................................... 13

FIGURES

Figure 1.1: Location of Export Facility (Google Inc., 2010) ...................................................................... 1

Figure 1.2: Proposed Layout of Export Facility ........................................................................................ 2

Figure 2.1: Offshore NCEP Wave Climate (Lat: -24.00⁰, Long: 42.50⁰) .................................................. 4

Figure 2.2: Offshore NCEP Wind Climate (Lat: -24.00⁰, Long: 42.50⁰) ................................................... 5

Figure 2.3: Bathymetry in Toliara Channel Image: Google Earth 19th November 2010 (Google Inc., 2010) ................................................................................................................................................... 6

Figure 3.1: Extents of Sediment Transport System Image: Google Earth (Google Inc., 2010) ............... 7

Figure 3.2: Evidence of Fiherenana River Flood Channel (NASA Landsat Program, 2003) ................... 8

Figure 3.3: Dry Fiherenana River Bed – 14 June 2012 (Bok, 2012) ....................................................... 9

Figure 3.4: The Fiherenana River during the Wet Season Containing Large Amounts of Suspended Sediments (MACCAFERRI, 2004) ........................................................................................................... 9

Figure 3.5: Direction of Wind-Blown Sediment Transport Image: Google Earth 19th November 2010 (Google Inc., 2010) ................................................................................................................................ 11

Figure 3.6: Wind-Blown Sediment Covering Infrastructure, Image: Google Earth 19th November 2010 (Google Inc., 2010) ................................................................................................................................ 12

Figure 3.7: Long-Term Shoreline Variability between Toliara and Ranobe Bay Image: Google Earth (Google Inc., 2010) ................................................................................................................................ 15

Figure 3.8: Long-Term Shoreline Variability near the Port Development Site, Image: Google Earth (Google Inc., 2010) ................................................................................................................................ 17

Figure 3.9: Distance from Causeway Root to Shoreline ........................................................................ 18

Figure 3.10: Wave Diffraction Pattern around Northern end of Grand Recif. Image: Google Earth (Google Inc., 2010) ................................................................................................................................ 19

Figure 4.1: Typical Impact of Groyne (Causeway) on Longshore Sediment Transport Based on (USACE, 2006) ...................................................................................................................................... 22



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1. INTRODUCTION

1.1. Background World Titanium Resources (WTR) has proposed to mine 400 000 tonnes per annum of ilmenite and 40 000 tonnes per annum of zircon/rutile from the Ranobe mineral deposit located north of the city of Toliara on the west coast of Madagascar. In June 2012, JFA BMT Consultants completed a pre-feasibility study of the proposed export facility, to be located in the lee of the Grand Recif (see Figure 1-1). This is a shallow water coral reef, acting as wave shelter for the area near the town of Toliara.

Figure 1.1: Location of Export Facility (Google Inc., 2010)

Location of proposed export facility

Grand Recif: Shallow coral reef

Port of Toliara



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As shown on Figure 1.2, the proposed export facility is made up of a 300 m by 300 m lay-down pad, as well as a 150 m long rubble mound causeway and 350 m long piled trestle structure. The berth is a 50 m by 25 m open piled structure.

Figure 1.2: Proposed Layout of Export Facility

1.2. Scope of Work

Prestedge Retief Dresner Wijnberg (PRDW) has been approached by Coastal & Environmental Services (CES) to perform a high-level desktop assessment and professional opinion on the potential implications of the causeway/trestle design on the local sediment transport regime. This is to be achieved through the following activities:

Undertake a desktop analysis and provide a professional opinion on the potential implications on sediment movement of the jetty designs prepared for the marine transport of product for the Ranobe Mine Project.

Review the concept designs presented in the BMT JFA consultants report entitled “Toliara Sands Project Marine Works: Pre-Feasibility Study”, dated June 2012 (reference R-246.02-1).

Provide a considered opinion as to whether a more detailed sediment analysis study is required, in light of the fact that concerns have been expressed that a jetty in this area will result in changes to sediment dynamics.

Develop a scope of work for a monitoring programme and the collection of sound baseline data to allow any shoreline changes due to the proposed jetty to be separated from natural or other non-project related changes.



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This report forms the deliverables of this study, which are described as follows:

A report describing how the jetty structure might influence sediment movement, and an assessment of how significant, if any, these changes might be.

A report detailing the scope of work for a sediment monitoring programme. 1.3. Study Methodology

Due to the lack of detailed site measurements, the Toliara Bay sediment transport assessment was carried out by a review of existing information, including aerial photography and oceanographic information, as well as reviewing past studies focussing on nearby coastal processes. Site data available during this investigation is limited to the hindcast wave and wind climate, as well as the predicted tidal levels for the Port of Toliara. Sediment transport regimes are usually assessed by first identifying the boundaries of the system, so as to identify the area which should be incorporated in the review. Following this, all environmental processes and other external factors which may have an impact on the system are assessed. Environmental processes which affect sediment transport systems may include the following:

Nearshore wave climate

Nearshore currents

Local wind fields

Sediment sources and sinks External factors may include the development of the shoreline, such as the construction of ports, groynes or other coastal structures.



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2. DATA

2.1. Offshore Wave Climate

The offshore wave climate was obtained from the National Centre for Environmental Prediction (NCEP) online database for the period February 1997 to December 2010 at 3-hourly intervals (E Kalnay, 1996). The location at which this data was extracted is as follows:

Lattitude -24.00° Longitude +42.50°

Figure 2.1: Offshore NCEP Wave Climate (Lat: -24.00⁰, Long: 42.50⁰)

As shown on Figure 2.1, the offshore wave climate is dominated by a south-westerly swell component, with a small portion of the waves having a south-easterly direction. The latter component is locally generated wind waves, which are generally fairly small, and have short periods. Furthermore, considering that the project site is located along the south-western coast of Madagascar, the south-easterly waves are heading offshore, and therefore have no impact on the site under consideration during this investigation. The wave height histogram in Figure 2.1 shows that the offshore median significant wave height is 1.93 m, with 99% of all waves being smaller than 4.53 m. 2.2. Offshore Wind Climate

The offshore wind climate was obtained from the NCEP online database (E Kalnay, 1996), and was extracted at the same location as the offshore wave climate introduced in the previous section.



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As shown on Figure 2.2, the predominant wind direction is south-easterly, with the median wind speed being 6.4 m/s. The 99% non-exceedence wind speed is approximately 14.5 m/s. The south-easterly dominated wind field corroborates that the south-easterly wave component is generated by the local wind fields.

Figure 2.2: Offshore NCEP Wind Climate (Lat: -24.00⁰, Long: 42.50⁰)

2.3. Water Levels Time-based water level variations for the Port of Toliara were obtained from the MIKE C-MAP database (DHI, 2011). Results of a tidal analysis are shown in Table 2.1below. From this table it is clear that the water level variation is 2.61 m during a spring tidal cycle, whilst this is reduced to approximately 0.75 m during a neap tidal cycle. Table 2.1: Water Levels at the Port of Toliara

Description Acronym Level [m CD]

Highest Astronomical Tide HAT 3.71

Mean High Water Springs MHWS 3.41

Mean High Water Neaps MHWN 2.47

Mean Water Level ML 2.10

Mean Low Water Neaps MLWN 1.72

Mean Low Water Springs MLWS 0.80

Lowest Astronomical Tide LAT 0.55



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2.4. Bathymetry The bathymetry near the proposed project site is shown on Figure 2.3, obtained from the MIKE C-MAP database (DHI, 2011). This indicates that between the Toliara sand spit and the shallow offshore reef, the seabed dips sharply to a depth of approximately -12 m CD.

Figure 2.3: Bathymetry in Toliara Channel Image: Google Earth 19th November 2010 (Google Inc., 2010)



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3. ASSESSMENT OF SEDIMENT TRANSPORT SYSTEM

3.1. Introduction

The sediment transport system within which the proposed port development is located includes the northern section of the Bay of Toliara to the southern end of the Bay of Ranobe, a coastal length of approximately 17 km. The Fiherenana River feeds this system with significant volumes of sediment. The northern and southern ends of the system are sheltered by nearshore reefs, which significantly reduce the wave energy in those areas.

Figure 3.1: Extents of Sediment Transport System Image: Google Earth (Google Inc., 2010)

Sediment Transport System

Fiherenana River



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3.2. Sediment Sources and Sinks

Two sediment sources and sinks have been identified as being of importance, being the Fiherenana River adding sediment to the system, and wind-blown sediment transport removing material from the system.

3.2.1. The Fiherenana River as a Fluvial Sediment Source

The Fiherenana River flows for approximately 175 km before discharging via a wide sandy delta north of Toliara Bay. Like most rivers within the sub-arid region of south-west Madagascar, it often dries out during the dry winter months (April to November), as shown in Figure 3.1. As shown on Figure 3.2, the Fiherenana River has a second channel and delta, situated approximately 3.5 km south of the main delta. It is thought that the southern channel serves as a flood channel.

Figure 3.2: Evidence of Fiherenana River Flood Channel (NASA Landsat Program, 2003)



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Detailed information regarding river flows and corresponding sediment loads are not available at this stage. However, referring to Figure 3.4, it is clear that the Fiherenana River carries significant sediment loads during the wet season. A portion of this sediment is deposited in the nearshore environment, resulting in the formation of the river delta as can be identified on Figure 3.2.

Figure 3.3: Dry Fiherenana River Bed – 14 June 2012 (Bok, 2012)

Figure 3.4: The Fiherenana River during the Wet Season Containing Large Amounts of Suspended Sediments (MACCAFERRI, 2004)



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Over the past five decades, the south-western region of Madagascar has undergone severe deforestation (Casse, et al., 2002). This has the effect of increasing the sediment load of the rivers whose catchments are located in the deforested areas. This is because vegetation generally increases the cohesion of surface sediments. Although the sediment loads as such cannot be quantified at this stage, it can be argued that due to the increased deforestation, the sediment load of the Fiherenana River has increased recently, thereby delivering an increased volume of sediment to the littoral zone between Toliara and Ranobe Bay. 3.2.2. Wind-Blown Sediment Sink

Although details of the nearshore wind climate are not available at this stage, it is expected that these have a similar direction but lower speed relative to the offshore climate presented in Section 2.2. It will be recalled that this climate showed a south-easterly dominated wind field. An initial review of aerial photography indicates that significant volumes of wind-blown sediment transport occurs near the project site. This can be identified through the formation of crescentic sand dunes, as well as by the wind-blown sand tracks north of the project site. Both of these observations can be identified on Figure 3.5 and Figure 3.6. The wind-blown sediment transport is seemingly occurring in a north-easterly direction, which can be identified through the orientation of both the crescentic dunes and the direction of the wind-blown sand tracks. Referring to Figure 3.6, it is clear that wind-blown sediment has recently covered existing infrastructure, which could have occurred due to one of two reasons. Either, the infrastructure was developed following a period of low wind-blown sediment transport, resulting in this area no longer being covered by sand, or, the magnitude of wind-blown sediment transport has recently increased. Regardless of the cause, it is clear that this area is subject to a variable magnitude of wind-blown sediment transport, and is therefore considered to be highly dynamic. The significance of a variable wind-blown sediment transport rate is that this can directly influence the nearby shoreline position. An increase in the volume of wind-blown sediment being transport at the site currently under investigation means that more sediment is removed from the active littoral zone. This could result in shoreline recession.

3.2.3. Toliara Channel

The bathymetry of the entrance to Toliara Bay has been introduced in Section 2.4, indicating that between the sand spit and the shallow offshore reef, the seabed dips sharply to approximately -12 m CD. This sharp dip may result in sediment being deposited in the channel, thereby functioning as a sediment sink to the system. The magnitude of this sink would have to be determined through two-dimensional sediment transport modelling, and cannot be quantified at this stage.



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Figure 3.5: Direction of Wind-Blown Sediment Transport Image: Google Earth 19th November 2010 (Google Inc., 2010)



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Figure 3.6: Wind-Blown Sediment Covering Infrastructure, Image: Google Earth 19th November 2010 (Google Inc., 2010) 3.3. Historic Shoreline Variations

As previously mentioned, historic aerial imagery was used to assess the shoreline variations near the proposed project site. Aerial images were obtained from Google Earth (Google Inc., 2010) and the online LANDSAT database (NASA Landsat Program, 2003). The LANDSAT images are of fairly low resolution, with one pixel covering an area of approximately 30 m by 30 m. As such, a detailed shoreline assessment cannot be performed using these images. However, they remain useful to identify large scale shoreline variations. The following table summarizes the aerial images used during the desktop assessment.

Crescentic

dunes

Covered road

Covered saltpans



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Table 3.1: Summary of Aerial Images

Date Extents Source

17th May 1985 125 km north of Toliara to 80 km south of Toliara LANDSAT

6th March 1988 125 km north of Toliara to 80 km south of Toliara LANDSAT

21st April 1990 125 km north of Toliara to 80 km south of Toliara LANDSAT

24th April 1991 125 km north of Toliara to 80 km south of Toliara LANDSAT

23rd September 1994 125 km north of Toliara to 80 km south of Toliara LANDSAT

2nd December 1999 125 km north of Toliara to 80 km south of Toliara LANDSAT

16th July 2001 125 km north of Toliara to 80 km south of Toliara LANDSAT

29th September 2003 125 km north of Toliara to 80 km south of Toliara LANDSAT

15th February 2003 Sand spit near project site Google Earth

13th December 2003 125 km north of Toliara to 80 km south of Toliara LANDSAT

25th April 2004 Sand spit near project site Google Earth

18th March 2006 Sand spit near project site to north of Fiherenana River delta

Google Earth

27th March 2007 125 km north of Toliara to 80 km south of Toliara LANDSAT

26th August 2009 Sand spit near project site Google Earth

19th November 2010 Southern end of Ranobe Bay to northern end of Toliara Bay

Google Earth

9th November 2011 125 km north of Toliara to 80 km south of Toliara LANDSAT

3.3.1. Large Scale Shoreline Variations

Large scale shoreline variations, including the coast of the entire sediment transport system from the southern end of the Bay of Ranobe to the northern end of Toliara Bay, was analysed using the LANDSAT set of images. These images covered a twenty year timeframe, from 1983 to 2003. Results of this analysis are summarized in Figure 3.7. Referring to Figure 3.7, the shoreline position at the northern end of the study area, i.e. at the southern end of the Bay of Ranobe, has undergone considerable changes between 1983 and 2003. Since the first available aerial image taken in 1983, the shoreline at the northern end of the study area has accreted approximately 500 m in a cross-shore direction, over an alongshore distance of approximately 1.5 km. It is clear that since 2003, this trend has continued. The shoreline between the southern Fiherenana River delta and the area discussed above, the shoreline has remained fairly stable, with variations presumably due to seasonal variations in the nearshore wave climate. No long-term shoreline morphological changes are therefore expected in this area. Significant shoreline variations are visible at the southern Fiherenana river delta, to the extent of up to 300 m in a cross-shore direction. These changes are caused by the variability of the volume of sediment being delivered to this area from the Fiherenana River. In addition it is thought that the shoreline position has a strong seasonal variability. It is expected that during the dry winter months, when little to no water flows through the river’s flood channel,



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the southern delta is eroded since the longshore sediment transport capacity is larger than the supply of sediment to this area. Conversely, during the wet summer months, the sediment load of the river exceeds the transport capacity, resulting in shoreline accretion. Furthermore, by reviewing the dates of the respective shoreline positions, no long-term trend can be identified. It is therefore expected that, although significant shoreline variability is expected to continue in this area, it is unlikely that this variability will result in a net change in shoreline position.



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Figure 3.7: Long-Term Shoreline Variability between Toliara and Ranobe Bay Image: Google Earth (Google Inc., 2010)

1.5 km alongshore distance

500 m accretion in cross-shore direction



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3.3.2. Local Shoreline Variations Local shoreline variations were investigated using a combination of LANDSAT and Google Earth aerial imagery, covering a period from 1983 to 2010. Results of this assessment are summarized on Figure 3.8. From this figure, the significant short-term variability of the local shoreline position becomes evident. At the location of the proposed port development, the shoreline has receded approximately 150 m between 2003 and 2010, at a rate of approximately 20 m/year. Analysing the results shown on Figure 3.8 further, it could be argued that, although there is significant temporal variability, the historic shoreline position at the location of the proposed port development is approximately 150 m further seaward than currently (February 2010). This is shown on Figure 3.9, on which the drastic shoreline erosion of approximately 150 m can be identified after 2000. However, the shoreline position pre-2000 also shows significant temporal variability, to the extent of approximately 50 m. It could further be argued that the sediment which is removed from the western side is deposited on the southern end of the sand spit. This means that sediment is transported further into Toliara Bay. In addition to this, the observed shoreline variations are seemingly occurring as sudden bursts, presumably due to episodic events. At the proposed port development site, the shoreline has receded in two distinct movements, the first being between the 25th April 2004 and the 18th March 2006, and the second movement having occurred between the 26th August 2009 and 19th November 2010. This however needs to be confirmed through the analysis of historic weather patterns, which does not form part of the scope of the current investigation.



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Figure 3.8: Long-Term Shoreline Variability near the Port Development Site, Image: Google Earth (Google Inc., 2010)



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Figure 3.9: Distance from Causeway Root to Shoreline

3.4. Interpretation of Sediment Transport Mechanics

By comparing the dominant south-westerly swell direction to the shoreline orientation near Toliara, the net longshore sediment transport direction is expected to be northwards. This means that, in general, sediment that is delivered to the system by the Fiherenana River is transported north towards Ranobe Bay. The net northern longshore sediment transport is the cause for the accelerated shoreline accretion in the southern end of Ranobe Bay, compared to the northern end of Toliara Bay. Furthermore, the deforestation which may recently have increased the sediment loads of the Fiherenana River may also be a cause for the significant sediment accretion to the north of the river. Wave diffraction occurs around the northern end of the Grand Recif, as can be identified on Figure 3.10. This causes a clockwise rotation of the mean wave direction in the lee of the reef, which causes a reversal of the otherwise northern net longshore sediment transport direction. In addition to the wave rotation, the shelter of the reef also causes a reduction in wave height in the area shown on Figure 3.10. This generates a differential wave height distribution along this piece of coastline. Due to the larger wave heights to the north of the reef’s shelter, the mean water level is higher in this area compared to that in the area of reduced wave heights. This water level variation generates a southern longshore current, as shown on Figure 3.10. It is therefore expected that, due to the combined effect of wave rotation and the generation of a longshore current due to water level variations, the net longshore transport direction south of the southern Fiherenana River delta is southwards, towards Toliara Bay. Considering this, it can be argued that shoreline variations near the proposed port development site are influenced primarily by sediment being deposited in the southern



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Fiherenana River delta. No mechanisms have been identified which could transport sediment from the main river delta southwards into Toliara Bay. Referring specifically to the sand spit on which the proposed lay-down pad is to be located, a mild southern sediment transport regime is expected. This is because, although wave heights along this shoreline are relatively small, the relative angle between the wave crests and shoreline is fairly large. It is further expected that, because of this net southern transport direction, sediment is gradually displaced from the western side of the sand spit to the southern end. Shoreline erosion at the western side of the Toliara sand spit is thought to be linked to periods of minimal or no sediment being deposited at the southern Fiherenana River delta. During these periods, the system which transports sediment southwards from the western to the southern side of the sand spit is not fed with additional sediment, which means that there is a net deficit in sediment volume along the western side, resulting in shoreline erosion in this area.

Figure 3.10: Wave Diffraction Pattern around Northern end of Grand Recif. Image: Google Earth (Google Inc., 2010)

Conversely, shoreline accretion along the western side of the sand spit is expected when large volumes of sediment are deposited at the southern Fiherenana River delta. In addition to the coastal processes described during the previous paragraphs, the mechanism of wind-blown sediment transport, discussed in Section 3.2.2, is thought to continuously remove sediment from the sand spit. This results in a net loss of sediment, resulting in shoreline erosion along the western side of the sand spit.

Un-diffracted wave direction

Diffracted wave direction

Area of reduced wave height

Longshore current



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3.5. Future Shoreline Trends

It has been shown that recently, the shoreline on the western side of the Toliara sand spit is receding at a rate of approximately 20 m/year. However, this trend is not evident in the long-term. Although significant temporal variation of the shoreline position near the proposed port development has been identified, no clear trend of accretion or erosion has been observed. It can therefore be argued that the Toliara sand spit is in a state of dynamic equilibrium, being controlled through episodic flooding events of the southern arm of the Fiherenana River. Although it could be argued that the most recent shoreline position (February 2010) is a conservative one, in the sense that it is situated the furthest landward of all the observed shoreline positions, it is not clear whether the short-term erosion on the western side of the sand spit will continue. It is therefore possible that, in the absence of a significant volume of sediment being delivered to the longshore sediment transport by the southern Fiherenana River delta, shoreline erosion of the western side of the sand spit is likely to continue. 3.6. Numerical Modelling of Sediment Transport Regime

One of the objectives of this study was to provide a professional opinion on whether additional sediment transport modelling should be performed to better understand the local sediment transport regime. Sediment transport modelling can broadly be described by shoreline modelling and two- and three-dimensional sediment transport modelling. Shoreline models would not be accurate for the current application, since the coastal processes occurring near the Toliara sand spit are dominated by complex coastal processes, including diffraction and the generation of a longshore current due to a differential mean water level. These processes are not adequately incorporated in shoreline models. As such, shoreline modelling is not considered to be a feasible option of furthering the sediment transport assessment. Two-dimensional sediment transport modelling, including waves, currents and the corresponding coastal processes is a viable option to better understand to sediment transport characteristics at the proposed port development site. However, significant amounts of additional site data would be required for this modelling work to be of value. Since the shoreline behaviour at the proposed port development site is directly linked to the volume of sediment being delivered by the Fiherenana River, the following site data would be required:

Detailed description of Fiherenana flow volumes, split into the northern and southern channels

Detailed description of the volume of sediment delivered by the river, split into the northern and southern channels

Detailed characterization of sediment properties being delivered by the Fiherenana River Until such a time as this data is available, two-dimensional sediment transport modelling is not expected to supplement the current understanding of the local sediment transport characteristics.



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4. POTENTIAL IMPACT OF PROPOSED PORT DEVELOPMENT

4.1. Introduction

Referring to the high-level desktop assessment of the sediment transport characteristics near the proposed port development site discussed in the previous section, it can be concluded that the site is located within the active sediment transport zone. As such, the port structures are expected to have an effect on the local sediment transport characteristics, the extent of which will be discussed in the following paragraphs. 4.2. Preferred Port Layout – Direct Loading Option

The preferred port option, being the direct loading option shown in Appendix A, is made up of a piled berth structure, with dimensions of 50 m by 25 m. The berth is connected to the shore by a 351 m long piled access trestle and 150 m rubble mound causeway. The seaward end of the rubble mound causeway is approximately located at the current shoreline position. The rubble mound causeway connects to an armoured laydown pad, with dimensions of 300 m by 300 m. The berth structure and access trestle are not expected to have an impact on the sediment transport characteristics. Waves, currents and the resulting sediment transport regime are permitted to pass through the open structure, thereby retaining the natural coastal processes. The solid rubble mound structure on the other hand, being an impermeable structure, blocks off waves and currents, and therefore has the potential to disrupt the natural sediment transport characteristics. As mentioned previously, the rubble mound causeway extends to the current shoreline position (February 2010). If the shoreline remains in this position, or accretes, the proposed port development is not expected to have an impact on the local sediment transport characteristics. However, considering the initial shoreline position in 1991 shown on Figure 3.8, which represents the most seaward shoreline position of the available aerial images, it is possible that significant shoreline accretion could result in the siltation of the proposed berth, reducing the navigable depth of the facility. Cognisance of this risk should be taken when deciding on the length of the proposed access trestle. As discussed in Section 3.5, it is uncertain whether the current rate of shoreline erosion of approximately 20 m/year is likely to continue, or whether the current shoreline represents the landward-most position of the coast. It is however clear that if the shoreline does continue to erode the rubble mound causeway would have an impact on the sediment transport characteristics. This impact would occur in the form of the blockage of southward moving sediment. Figure 4.1 shows the typical impact of such a blockage. In the figure, the net longshore sediment transport direction is from left to right, with a groyne (or causeway) structure interrupting this transport. Shoreline accretion occurs to the left of the structure, whilst shoreline erosion occurs to the right of the structure. For the situation currently under investigation, the shoreline would accrete on the northern side of the causeway, whilst shoreline erosion would occur to the south.



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Figure 4.1: Typical Impact of Groyne (Causeway) on Longshore Sediment Transport Based on (USACE, 2006)

With this being said, the shoreline to the north of the groyne is not expected to erode landward of the seaward end of the causeway, since sediment is effectively trapped on the northern side of the structure. As such, the causeway would fix the landward-most shoreline position in this area.

This fixing of the northern coastline would however come at the cost of exacerbating shoreline erosion to the south of the proposed development. The extent of this erosion depends on the volume of sediment which is fed to the system by the Fiherenana River. If a sufficient volume of sediment is provided, this is likely to be transported past the head of the causeway to the southern side, thereby minimizing erosion in this area. However, during periods when little sediment is provided, such as the period from February 2003 to November2010, severe shoreline erosion can be expected to the south of the proposed port development.

It should be noted that, considering that between February 2003 and November 2010 the shoreline receded approximately 120 m, and the length of the rubble mound causeway is 150 m, it is possible that the accelerated erosion to the south of the development could result in the shoreline reaching the lay-down pad in this area. This could have severe secondary effects, such as undermining the armoured revetment surrounding the lay-down pad.

Further to the potential impact of the facility on the longshore sediment transport along the coast, the facility is also likely to have an impact on the characteristics of the wind-blown sediment transport. Considering the SSW wind direction, it is likely that wind-blown sand will accumulate on the southern side of the rubble mound causeway structure, thereby interrupting the natural movement of sand from the coast to the hinterland.

4.3. Barge Loading Option

The difference between the preferred direct loading option, shown in Appendix A, and the barge loading option is that the access trestle of the latter option is shorter. As discussed in the previous section, the open piled access trestle and berth structure are not expected to have a noticeable effect on the sediment transport characteristics. As such, the impact of the proposed port layout for the barge loading option is expected to be similar to that of the preferred direct loading option.



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5. SEDIMENT TRANSPORT MONITORING PROGRAMME

5.1. Introduction

It is recommended that a comprehensive monitoring programme be implemented, to obtain sound baseline data to determine that natural variability of the local coastline. This monitoring programme should include beach surveys, covering the coastline between the proposed port development site and the main Fiherenana River delta, as well as a grid survey programme, to determine the morphology of the Toliara sand spit. These programmes are explained in more detail in the following sections. 5.2. Beach Monitoring Programme

Cross-shore beach profile surveys should be performed at 250 m alongshore intervals along the coastline between the proposed port development site and the main Fiherenana River Delta. These 25 survey stations should be surveyed on a three-monthly basis, to incorporate the seasonal variability of the shoreline position. The location of the 25 survey locations should be kept constant, so as to allow a direct comparison of surveyed data. Each cross-sectional survey should extend from a position landward of the primary dune, to the seaward end of the profile. Survey points should be chosen at the discretion of the surveyor, so as to accurately replicate to cross-shore profile. Surveys should be performed to coincide with the low water level of the spring tidal cycle, as this allows a greater coverage of the lower beach profile to at least 1 m below LAT. 5.3. Grid Survey of Toliara Sand Spit

To be able to comment on the three-dimensional behaviour of the sand spit at the proposed port development site, a grid surveying approach is recommended. Here, spot heights should be surveyed in a grid format at intervals of 50 m, or at changes in gradients. Similarly to the beach surveys, the grid survey should be repeated on a three-monthly basis, so as to incorporate the seasonal variability of the sand spit.



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6. SUMMARY AND RECOMMENDATIONS

6.1. Potential Impact of Proposed Port Facility on Sediment Transport Regime The potential impact of the proposed port development has been discussed. This has shown that the open piled berth and access trestle structures are not expected to have a noticeable impact on the sediment transport mechanics. The rubble mound causeway structure however has the potential of interrupting the natural southward longshore transport, which could result in shoreline accretion to the north of the structure and shoreline erosion to the south. The extent of the shoreline erosion is dependent on the volume of sediment being delivered via the southern Fiherenana River channel. Furthermore, the rubble mound causeway is likely to interrupt the northward moving wind-blown sediment, resulting in the accumulation against the southern side of the structure. The proposed causeway and laydown area are located close to a highly dynamic shoreline which is currently eroding at 20 m/year. It is recommended that the laydown area and causeway be moved further inland which will reduce their potential impact on the sediment dynamics and avoid the potential failure of these structures due to shoreline erosion. To further minimize the impact of the rubble mound causeway, its length should be minimized, whilst the length of the piled access trestle should be maximized. 6.2. Additional Sediment Transport Modelling

The viability of performed detailed sediment transport modelling has been discussed. Two-dimensional sediment transport modelling has been identified as the only modelling approach which could aid the understanding of the nearby sediment transport mechanics. Performing this modelling work would however require significant amounts of additional site data, including a detailed description of the flow volume and sediment load of the Fiherenana River. 6.3. Shoreline Monitoring

A shoreline monitoring programme has been recommended, which included beach profile surveyed spaced at a 250 m alongshore interval, performed on a three-monthly basis. In addition to this, a grid survey of the Toliara sand spit should be performed, with spot heights taken at 50 m intervals. This survey should also be repeated on a three-monthly basis.



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7. REFERENCES

BJC, 2012. Toliara Sands Project - Marine Works: Pre-Feasibility Study (Ref No R-246.02-1), Australia: BMT JFA Consultants.

Bok, A., 2012. Draft Fish Report, Port Elizabeth: Anton Bok.

Casse, T., Milhoj, A., Ranaivoson, S. & Randriamanarivo, J. R., 2002. Causes of deforestation in southwestern Madagascar: What do we know?, s.l.: Elsevier Science B.V.

CES, 2012. Toliara Sands Project - Ranobe (TSP-R), Draft Scoping Report, Grahamstown, South Africa: Coastal and Environmental Services.

DHI, 2011. MIKE C-MAP, Extraction of World Wide Bahymetry Data and Tidal Information, User Guide, Copenhagen, Denmark: Danish Hydraulics Institute.

E Kalnay, e. a., 1996. The NCEP/NCAR Reanalysis 40-Year Project. Bulletin of the American Meterological Society, I(1), pp. 437-471.

Google Inc., 2010. Google Earth (Version 6) [Computer Program], Washington, USA: Google Inc.

MACCAFERRI, 2004. The Flood Protection of the Tulear - Hydraulic and Erosion Control, South Africa: Construction World.

NASA Landsat Program, 2003. Landsat ETM+ scene LE7161076, Sioux falls: USGS.

Reef Doctor, 2008. Physical and Chemical Analysis of the Bay of Ranobe - Field and analytical procedures for the study of sedimentation and phydical, chemical aspects effecting coral reef growth in the Bay of Ranobe, s.l.: Reef Doctor.

USACE, 2006. Coastal Engineering Manual, Part V, Chapter 3 - Shore Protection Projects, Washington, USA: United States Army Corps of Engineers.



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8. APPENDIX

APPENDIX A – CONCEPT PORT DEVELOPMENT LAYOUTS

(BJC, 2012)

Documents

RANOBE MINE PROJECT, SOUTHWEST REGION, MADAGASCAR …