Pier 1 In-fill Development, Port of Durban: Modelling of potential environmental changes in the port marine environment

Pier 1 In-fill Development, Port of Durban: Modelling of potential environmental changes in the port marine environment October 2012

CSIR/NRE/CO/ER/2012/0068/B Pier 1 In-fill Development, Port of Durban: Modelling of potential environmental changes in the port marine environment Prepared for: Transnet Capital Projects Contact Person: Paris Forchand Prepared by: CSIR, Natural Resource and the Environment, October 2012

This report was compiled by: Roy van Ballegooyen Selwyn Bergman CSIR, Natural Resources and the Environment PO Box 320, Stellenbosch 7599, South Africa Tel: + 27 21 888 2572 Fax: + 27 21 888 2693 Email: rvballeg@csir.co.za CSIR, Natural Resources and the Environment Email: sbergman@csir.co.za Published and issued by: CSIR P O Box 320 STELLENBOSCH 7599 South Africa Tel: + 2721888-2400 Fax: + 2721888-2693 Email: rvballeg@csir.co.za The report should be cited as: van Ballegooyen, R.C. and S. Bergman (2012). Pier 1 In-fill Development: Modelling of potential environmental changes in the port marine environment. CSIR Report, CSIR/NRE/ECO/ER/2012/0068/B, 66pp.

Scope of Work Transnet Ports Authority has identified a need to expand (deepen, widen and lengthen) Berths 203 to 205 in order to improve the safety of the berths as well as to improve the efficiency of the Port of Durban. This will include the following: the westward expansion of Berth 205 by 170m; the eastward expansion of Berth 203 by 100m; the seaward expansion of Berths 203 to 205 quayside by 50m; the deepening of the berth channel, approach channel and vessel turning basin from the current -12.8m CDP to -16.5m CDP; the cutting into the central Sandbank by approximately 50m to 150 m. These activities will result in a potential change in the hydrodynamic functioning of the Port of Durban that may have a number of negative environmental effects within the port. These were identified in a screening study undertaken by the CSIR (CSIR, 2011) in which it was recommended that some of these potential impacts be assessed in greater detail. These included the identification and assessment of potential changes in the current and wave patterns in the Port and the consequences thereof for; the stability of the central sandbank and associated habitats; changes in water quality, and; potential effects on sensitive habitats such as the Little Lagoon. These potential changes and required mitigation measures have been predicted in a modelling study by Van Ballegooyen et al. (2012).and the consequences thereof assessed in CSIR (2012). A potential exists for a follow-on development, namely the Salisbury Island Pier 1 In-fill development. Here existing Berths 102 and 103 will be in-filled and new berths developed along the in-filled quays. Similar to the Berth 203 to 205 development there are potential impacts associated with the Pier 1 in-fill development. This modelling study provides a preliminary assessment of the likely hydrodynamic changes and associated potential environmental impacts, with a particular focus on wave effects. Reported here are the changes in hydrodynamic functioning and potential changes to sandbank stability (in any), water/sediment quality and waves conditions associated with an initial Pier 1 infill design provided by the WSP coastal engineering team. The assessment uses the proposed Berth 203 to 205 development Option 3G as a baseline and not the existing port layout. Roy van Ballegooyen Coastal Systems Research Group Natural Resources and the Environment CSIR Stellenbosch, South Africa October 2012 Page i

Table of Contents 1 INTRODUCTION... 1 1.1 BACKGROUND... 1 1.2 SCOPE OF WORK... 1 1.3 STRUCTURE OF THE REPORT... 2 2 ENVIRONMENTAL BASELINE DESCRIPTION... 3 2.1 WEATHER AND CLIMATE... 3 2.2 PORT LAYOUT AND BATHYMETRY... 6 2.3 HYDRODYNAMIC FUNCTIONING OF THE PORT... 8 3 PROJECT DESCRIPTION... 18 4 KEY ISSUES OF CONCERN... 22 5 APPROACH AND METHODS... 24 5.1 PROCESS OF RELEVANCE TO THE MODELLING STUDY... 24 5.1.1 Tidal forcing... 24 5.1.2 Wind-driven waves and currents... 25 5.1.3 Seiching in the Port of Durban... 28 5.1.4 Stratification... 28 5.2 ERODABILITY OF SANDBANKS... 29 6 MODEL SET-UPS AND CALIBRATION... 31 6.1 MODEL SET-UP... 31 6.2 MODEL CALIBRATION... 33 6.3 CONFIDENCE IN THE MODELLING RESULTS... 35 7 RESULTS... 37 7.1 CHANGES IN HYDRODYNAMIC FUNCTIONING IN THE PORT... 37 7.1.1 Changes in tidal and wind-driven flushing... 38 7.1.2 Potential exacerbation of existing seiching... 42 7.1.3 Changes in surface and near bottom flows... 50 7.1.4 Changes in bed shear stresses... 52 7.2 HABITAT CHANGE ON THE CENTRAL SANDBANK... 57 7.3 HABITAT CHANGE IN LITTLE LAGOON AND ITS SURROUNDS... 57 7.4 CHANGES IN WATER AND SEDIMENT QUALITY IN THE PORT... 57 7.5 CHANGE IN WAVE CONDITIONS IN THE PORT... 58 8 CONCLUSIONS AND RECOMMENDATIONS... 64 8.1 CONCLUSION... 64 8.2 RECOMMENDATIONS... 64 9 REFERENCES... 65 Page ii

1 INTRODUCTION 1.1 Background Transnet Ports Authority has identified a need to expand (deepen, widen and lengthen) berths 203 to 205 in order to improve the safety of the berths as well as to improve the efficiency of the Port of Durban. This will include: the westward expansion of Berth 205 by 170m; the eastward expansion of Berth 203 by 100m; the seaward expansion of Berths 203 to 205 quayside by 50m; the deepening of the berth channel, approach channel and vessel turning basin from the current -12.8m CDP to -16.5m CDP; the cutting into the central Sandbank by approximately 50m to 150 m. These activities will result in a potential change in the hydrodynamic functioning of the Port of Durban that may have a number of negative environmental effects within the port. These were identified in a screening study undertaken by the CSIR (CSIR, 2011) in which it was recommended that some of these potential impacts be assessed in greater detail. These have been assessed in van Ballegooyen et al., (2012) and CSIR (2012). A potential exists for a follow-on development, namely the Salisbury Island Pier 1 In-fill project. Here the existing Pier 1 Berths 102 and 103 will be in-filled and new berth developed along the in-filled quays. Similar to the Berth 203 to 205 development there are potential impacts associated with the Pier 1 in-fill development. This modelling study provides a preliminary assessment of the likely hydrodynamic changes and associated potential impacts, with a particular focus on wave effects. Reported here are the changes in hydrodynamic functioning and potential changes to sandbank stability (if any), water/sediment quality and waves conditions associated with an initial Pier 1 infill design provided by the WSP coastal engineering team. The assessment uses the proposed Berth 203 to 205 development Option 3G as a baseline for the assessment and not the existing port layout. 1.2 Scope of Work The scope of work for this study requires the identification and assessment of potential changes in the current and wave patterns in the Port over and above those likely to be experienced for the Berth 203 to 205 Container Berth development that have potential consequences for: the stability of the central sandbank and associated habitats; changes in water quality, and; potential effects on sensitive habitats such as the Little Lagoon. It is not anticipated that the hydrodynamic changes associated with the proposed Pier 1 In-fill development will have any consequences for the stability of the central sandbank and associated habitats or sensitive habitats such as the Little Lagoon. However, given the extent of the in-fill area it is possible that there will be changes in tidal prism in the outer port and possible water quality effects. Most likely Page 1

however are effects due to a changes in wave conditions associated with the re-orientation of the quaywall. It is the specific goal of this study to provide a preliminary assessment of potential impacts associated with changes in wave conditions in the port. It is not a requirement of this study that any mitigation measures be recommended or assessed. 1.3 Structure of the Report Chapter 1 contains the introduction, scope of work and the structure of the report. This is followed by a brief environmental baseline description in Chapter 2. An overview is given of the proposed development in Chapter 3, followed by a brief description of the key issues of concern in Chapter 4. Chapter 5 describes the methods used and the assessment approach taken in this study. The modelling set-up and calibration are described only briefly in Chapter 6 as this has been discussed in detail in a preceeding report (van Ballegooyen et al., 2012). The model results are discussed in Chapter 7, as is the relevance of the various model outcomes in terms of potential environmental impacts. Chapter 8 contains the conclusions and recommendations of this study. Page 2

2 ENVIRONMENTAL BASELINE DESCRIPTION 2.1 Weather and Climate Being located on the east coast of South Africa, the Port of Durban has a warm maritime climate. The area generally experiences hot summers with high humidity levels, and much cooler and dry winters (Figure 2.1 to 2.3). Majority of the rainfall is experienced during the summer months of October to March, mainly in the form of thunderstorms (De Villiers and Malan, 1985). This rainfall results in increased fresh water inflows into the port form the adjacent catchments and their corresponding canals during the hot summer months between October and March each year. 40 35 30 Temperature (⁰C) 25 20 15 10 5 0 1999-08-28 1999-12-06 2000-03-15 2000-06-23 2000-10-01 2001-01-09 2001-04-19 2001-07-28 2001-11-05 2002-02-13 2002-05-24 2002-09-01 2002-12-10 2003-03-20 2003-06-28 2003-10-06 2004-01-14 2004-04-23 2004-08-01 2004-11-09 2005-02-17 Min Temp Max Temp Mean Temp 2005-05-28 2005-09-05 2005-12-14 2006-03-24 2006-07-02 2006-10-10 2007-01-18 2007-04-28 2007-08-06 2007-11-14 2008-02-22 2008-06-01 2008-09-09 2008-12-18 2009-03-28 2009-07-06 2009-10-14 2010-01-22 2010-05-02 2010-08-10 2010-11-18 2011-02-26 2011-06-06 Figure 2.1: Daily air temperature measured at the old Durban International Airport (formerly thelouis Botha Airport) 100 80 60 Humidity (%) 40 20 0 1999-08-28 1999-12-06 2000-03-15 2000-06-23 2000-10-01 2001-01-09 2001-04-19 2001-07-28 2001-11-05 2002-02-13 2002-05-24 2002-09-01 2002-12-10 2003-03-20 2003-06-28 2003-10-06 2004-01-14 2004-04-23 2004-08-01 2004-11-09 2005-02-17 2005-05-28 2005-09-05 2005-12-14 2006-03-24 2006-07-02 2006-10-10 2007-01-18 2007-04-28 2007-08-06 2007-11-14 2008-02-22 2008-06-01 2008-09-09 2008-12-18 2009-03-28 2009-07-06 2009-10-14 2010-01-22 2010-05-02 2010-08-10 2010-11-18 2011-02-26 2011-06-06 Figure 2.2: Daily relative humidity measured at the old Durban International Airport (formerly the Louis Botha Airport) Page 3

Precipitation (mm) 180 160 140 120 100 80 60 40 20 0 2011-06-06 2011-02-26 2010-11-18 2010-08-10 2010-05-02 2010-01-22 2009-10-14 2009-07-06 2009-03-28 2008-12-18 2008-09-09 2008-06-01 2008-02-22 2007-11-14 2007-08-06 2007-04-28 2007-01-18 2006-10-10 2006-07-02 2006-03-24 2005-12-14 2005-09-05 2005-05-28 2005-02-17 2004-11-09 2004-08-01 2004-04-23 2004-01-14 2003-10-06 2003-06-28 2003-03-20 2002-12-10 2002-09-01 2002-05-24 2002-02-13 2001-11-05 2001-07-28 2001-04-19 2001-01-09 2000-10-01 2000-06-23 2000-03-15 1999-12-06 1999-08-28 Figure 2.3: Daily rainfall as measured at the old Durban International Airport (formerly the Louis Botha Airport) The source of the data presented in Figure 2.1 to 2.3 above and Figure 2.4 is the web-site http://www.tutiempo.net/en/climate/durban_louis_botha. The prevailing winds in the region are predominantly SW and NNE, the strongest winds occurring during spring and summer. 100 90 80 70 60 Wind (km/h) 50 40 30 20 10 0 2011-06-06 2011-02-26 2010-11-18 2010-08-10 2010-05-02 2010-01-22 2009-10-14 2009-07-06 2009-03-28 2008-12-18 2008-09-09 2008-06-01 2008-02-22 2007-11-14 2007-08-06 2007-04-28 2007-01-18 2006-10-10 2006-07-02 2006-03-24 2005-12-14 2005-09-05 2005-05-28 2005-02-17 2004-11-09 2004-08-01 2004-04-23 2004-01-14 2003-10-06 2003-06-28 2003-03-20 2002-12-10 2002-09-01 2002-05-24 2002-02-13 2001-11-05 2001-07-28 2001-04-19 2001-01-09 2000-10-01 2000-06-23 2000-03-15 1999-12-06 1999-08-28 Max Sustained Wind Speed Max Wind Gust Mean Wind Speed Figure 2.4: Daily winds as measured at the old Durban International Airport (formerly the Louis Botha Airport) Page 4

The winds inside the port are significantly less than those measured at Port Control and on the eastern breakwater. Within the port, the Salisbury Island area is sheltered from the SW to SSW winds that predominate in winter (Figures 2.5 and 2.6). To a lesser extent the same observation can be made for the container terminal, however wind measured on the northern side of the port between the yacht basin and the T-jetty do not show such sheltering effects. All sites seemingly are fully exposed to the NNE and NNE winds that predominate in spring and summer, the strongest NNE/NE winds within the Port of Durban being observed at Salisbury Island. Port Control 2 Eastern Breakwater Durmar Building Container Terminal Pier 2 SA Navy Base (Salisbury Island) Figure 2.5: Annual wind roses for various locations in the Port of Durban for the period May 2010 to October 2011 Page 5

Figure 2.6: Seasonal wind roses for Port Control (left panel) and the Container Terminal (right panel) for the period May 2010 to October 2011 2.2 Port Layout and Bathymetry The bathymetry datasets used in the modelling were obtained from various sources. Individual bathymetry surveys were received from ZLA (undertaken for this project), EMS, EPRC, PRDW and Transnet Capital Projects (Table 2.1). Bathymetry data coverages from earlier CSIR Projects were also used. The datasets were merged using a mosaicing process (see Figure 2.6). The oldest coverages provided the starting point for this process. Where more recent coverages existed these were then used to replace the older data sets. Two final datasets were produced, one for the Offshore area and a second for the Port Area. The Port Area dataset encompasses data for the Port of Durban as well as the Entrance Channel. The offshore data set, encompasses all areas outside of the Port Area domain (i.e. the bathymetry over the adjacent shelf as well as surveys of the offshore dredge spoil disposal site). Only the Port Area data were used in this study. Page 6

Table 2.1: Bathymetric data sets used in the modelling # Filename Date of survey Comment 1 100 S1 0920090823.asc 2009/08/23 Area just off Berth 100 2 101_10220120210.asc 2012/02/10 Area just off Berths 101 and 102 3 105,6,7 S2 05-01-2011.asc 2011/01/05 Area just off berths 105, 106 and 107 4 108,9 S1 08-01-2011.asc 2011/01/08 Area just off berths 108 and 109 5 20320111011.asc 2011/10/11 Area just off berth 203 6 204-20520110302.asc 2011/03/02 Area off berths 204 and 205. There existed depth differences up to 0.6m from the other berth 204 survey. The survey date is about the same, perhaps some maintenance dredging 7 A-B 20120110.asc 2012/01/10 Area just off Sheds A and B 8 Bas D S2 1120120221.asc 2012/02/21 Region between T Jetty and Berth 104 9 Bas E S2 1120120202.asc 2012/02/02 The diagonal from Cross Berth (108& 109) to Tug Jetty, Shed B and Shed O. There are some points in this dataset that are not in the area at all 10 Bas F S2 1120120216.asc 2012/02/16 The region between the Container berths and south of the sandbank. 11 Bluff Bsin.asc Unspecified Region west of Coaling berths, south of A, B and C Berths, and North of berths N11, N12, N14 and N15 12 C S3 1120120110...asc 2012/01/10 Multi purpose terminal berth C 13 D,E,F 20120106.asc 2012/01/06 Berths D, E, and F along the Multi Purpose terminal 14 Point Basin 20110509 dtm.asc 2011/05/09 Area between Multi purpose Terminal and T Jetty (in the north) and Salisbury Island and Pier 1 (in the South) 15 MW T S4 1120120106..asc 2012/01/06 Turning basin between the sugar terminal and the Congella sandbank 16 20120314104.asc 2012/03/14 area just off berth 104 17 20120314200_202.asc 2012/03/14 Berths 200, 201, 202 18 20120314 IV1.asc 2012/03/14 Bulk shipping terminal 1 19 20120314 IV6.asc 2012/03/14 Island view wharf 6 20 20120315 Silt N.asc 2012/03/15 North Silt Channel 21 20120315 Silt S.asc 2012/03/15 South Silt Channel 22 20120316 IV chan_bas.asc 2012/03/16 Island view channel 23 AC_100503_PO.pts 2010/04/29 From the entrance channel (outside the harbour), around the curve and ending at T Jetty 24 Dormac20110825.asc 2011/08/25 Bayhead Ship Repair Jetty 25 2010_WGS84_Lo31_CDP.txt Oct Nov 2010 Sandbanks in harbour 26 EPRC_Harbour_Sand_Banks_XYZ_Data_CDP_WG31.txt late 2006/early 2007 Used as the initial bathymetric coverage 27 EPRC_MB_WG31_CDP_5m_complete late 2006/early 2007 To use as a starting point 28 Dbn Hbr Orig SOW Pts 0.5x0.5.txt 2012/04/04 Provided to CSIR by ZLA 29 Dbn Hbr Extra SOW pts 0.5x0.5.txt 2012/04/06 Provided to CSIR by ZLA 30 Spoil Area rev 10x10 Pts.txt 2012/04/08 Outside the port. Page 7

Figure 2.6: The mosaic of bathymetry data used in the modelling study. 2.3 Hydrodynamic functioning of the Port The water circulation in Durban Bay is largely tidally driven, with more localised effects due to windforcing of the surface waters and inflows of freshwater in the upper reaches of the port. Shorter term fluctuations are observed in the port (PRDW, 2009) as resonant seiches with periods of approximately 1 hour and 10 minutes, respectively. Water level variation in the Bay comprises predominantly a semi-diurnal tide with a period of approximately 12.4 hours and a range of 0.4 m at neap tide, increasing to 2.3 m at maximum spring tide. These tidal water level variations drive near-surface tidal flows of up to 0.3 to 0.4 m/s mid-channel in the entrance channel, with surface flows exceeding 0.55 m/s in shallow waters on either side of the channel (PRDW 2009). Tidal flows in the entrance channel during neap tides are significantly less, approximately 0.1 m/s near-bottom and 0.15 m/s near the surface (PRDW 2009). Strong tidal flows are observed over shallows adjacent to Victoria Embankment and over the Central Sandbank between Pier 2 and the Maydon Wharf Channel. Measurements made by the CSIR in the entrance channel in early summer 2001 (CSIR unpublished data) and in 2005 (PRDW, 2009) indicate that near-bottom flows are not much less than those near the surface. Page 8

The resonant seiches of an approximately 1 hour period (first resonant mode of the Bay) occurring in the bay have a water level range of approximately 0.1 to 0.2 m and result in short-term fluctuations in currents of approximately 0.1 to 0.15 m/s. Resonant seiches with an approximate 10 minute period are also present but are somewhat smaller in amplitude, ranging approximately between 0.05 and 0.1 m. Wind-driven influences on circulation in the Bay include large-scale wind-driven flows over the adjacent shelf that affect conditions and the nature of flows in the entrance channel and the temperature of waters entering into the Bay (see Section 2.1). More immediate wind influences result in modifications to surface flows and wind waves in the port. These influences vary around the Bay, due to the local variations in the wind field. Winds inside the Bay are significantly less than those measured at the Port Control tower and on the eastern breakwater. Within the Bay, the Salisbury Island area is sheltered from the SW to SSW winds that predominate in winter. To a lesser extent the same observation can be made for the container terminal. However, winds measured on the northern part of the Bay between the yacht basin and the T-jetty do not show similar sheltering effects with respect to SW to SSW winds. All sites seemingly are fully exposed to the NNE and NE winds that predominate in spring and summer, the strongest NNE/NE winds being observed at Salisbury Island. The water column within the Bay is not strongly stratified. Measurements within the Bay confirm that although episodic stratification events may occur, temperature stratification is limited. Thermistor chain measurements in the entrance channel (obtained in November to December 2001, that is, prior to widening of the entrance channel conducted between May 2007 and February 2010) indicate a mean difference between the surface and bottom sensors of 0.4 C, with a maximum difference of 2.5 C (PRDW 2009). Recent surveys of water quality at 15 stations across the Bay (Figure 2.7) in the summer and winter of 2011 undertaken by the CSIR for Transnet National Ports Authority (CSIR 2011) and research on long-term (23 surveys over 18 months) trends in water quality at the same stations in 2009 and 2010 (CSIR unpublished data) confirm that vertical temperature gradients generally do not exceed one or two degrees Celsius (Figures 2.8 and 2.9). Where such temperature stratification does occur, it generally is confined to the upper metre of the water column. Freshwater inflows result in salinity-driven stratification events in the upper part of the Bay (see Figures 2.8 and 2.10). This stratification is generally limited to the upper part of the water column, often resulting in lower salinity water being confined to the upper tens of centimetres of the water column. The magnitude and depth of the halocline depends on the magnitude of these freshwater inflows, which peak in summer. The nature of flushing in the Bay (tidal near the entrance channel and flushing by freshwater inflows in the upper reaches) results in a strong gradient in flushing potential. At the entrance channel there is strong flushing due to tidal flows. With recent widening of the entrance channel this flushing has increased. However, in the upper reaches, where the influence of tidal flushing is limited, flushing rates and residence times have remained largely the same as those that existed prior to the entrance channel widening. The fact that the freshwater inflows are generally confined to surface layers of the water column means that the surface water may be relatively well-flushed in the upper reaches of the port. However the deeper waters remain largely insulated from these flushing effects unless there are very large freshwater inflows, i.e. flushing of these deeper waters is mainly tidal and to a lesser extent winddriven. Page 9

Figure 2.7: Stations where water quality was monitored in Durban Bay, January and July 2011. Aerial view reproduced from Google Earth. Temperature ( o C) Salinity 25.0 24.5 24.0 23.5 23.0 22.5 22.0 21.5 21.0 36 32 28 24 20 16 12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Station Figure 2.8: Average water temperature and salinity in surface and bottom water at 15 stations across Durban Bay between October 2008 and March 2010. The vertical bars represent the 99% confidence interval of the mean for 23 surveys. Symbols are offset for display purposes. Page 10

Temperature difference ( o C) 4 3 2 1 0 Station 1 Station 2 Station 3 4 4 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Sep 09 Oct 09 Jun 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 4 3 2 1 0 Station 4 Station 5 Station 6 4 4 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) Temperature difference ( o C) 4 3 2 1 0 Oct 08 Nov 08 4 3 2 1 0 Station 7 Station 8 Station 9 4 4 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Station 10 Station 11 Station 12 4 4 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Feb 09 Mar 09 Apr 09 May 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Sep 09 Oct 09 Nov 09 Dec 09 Nov 09 Dec 09 Jan 10 Feb 10 Jan 10 Feb 10 Mar 10 Mar 10 Temperature difference ( o C) Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Dec 08 Jan 09 Feb 09 Mar 09 Feb 09 Mar 09 Apr 09 May 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Dec 09 Jan 10 Feb 10 Mar 10 Feb 10 Mar 10 Temperature difference ( o C) 4 3 2 1 0 Station 13 Station 14 Station 15 4 4 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Temperature difference ( o C) 3 2 1 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 Figure 2.9: Temperature differences between surface and bottom waters at 15 stations across Durban Bay between October 2008 and March 2010. Page 11

Salinity difference Salinity difference Station 1 Station 2 Station 3 35 35 35 30 25 20 15 10 5 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 Salinity difference 30 25 20 15 10 5 0 Oct 08 Nov 08 Dec 08 Jan 09 Station 4 Station 5 Station 6 35 30 25 20 15 10 5 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 Salinity difference 30 20 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Station 7 Station 8 Station 9 Feb 09 Mar 09 Feb 09 Mar 09 Apr 09 May 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Sep 09 Oct 09 Nov 09 Dec 09 Nov 09 Dec 09 Jan 10 Feb 10 Jan 10 Feb 10 Mar 10 Mar 10 Salinity difference Salinity difference 30 25 20 15 10 5 0 30 20 10 Oct 08 Nov 08 0 Oct 08 Nov 08 Dec 08 Jan 09 Dec 08 Jan 09 Feb 09 Mar 09 Feb 09 Mar 09 Apr 09 May 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Dec 09 Jan 10 Feb 10 Mar 10 Feb 10 Mar 10 Salinity difference 30 20 10 Salinity difference 30 20 10 Salinity difference 30 20 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 Station 10 Station 11 Station 12 Salinity difference 30 20 10 Salinity difference 30 20 10 Salinity difference 30 20 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 Station 13 Station 14 Station 15 Salinity difference 30 20 10 Salinity difference 30 20 10 Salinity difference 30 20 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 0 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jul 09 Aug 09 Jun 09 Oct 09 Nov 09 Sep 09 Dec 09 Jan 10 Feb 10 Mar 10 Figure 2.10: Salinity differences between surface and bottom waters at 15 stations across Durban Bay between October 2008 and March 2010. Page 12

Model simulations of maximum current speeds in Durban Bay prior to the entrance channel widening show that the mean current speeds in the entrance channel have changed significantly with its widening. Model predictions suggest that mean current speeds in the entrance channel over a tidal cycle will have reduced from 0.25 m/s to 0.12 m/s and the maximum current speed from 0.55 m/s to 0.30 m/s. Conversely, the maximum current speed over the Central Sandbank during spring tides is predicted to have increased from 0.40 m/s to 0.55 m/s with the widening of the entrance channel. The mean current speed during spring tides is predicted to remain largely unchanged. The maximum current speeds are also predicted to have increased on the southern end of the tidal mud flats in the vicinity of the Yacht Basin. These increases have been attributed to the widened entrance channel allowing more long period energy (near the resonant oscillation period of approximately 1 hour) to enter the Bay (PRDW, 2007). Concern that changes in water levels and flows due to the wider entrance channel could lead to changes in the sandbanks and reported bottoming out problems at the Yacht Basin were investigated in 2009. The results of the study (PRDW 2009) indicated that the widening of the entrance channel has not affected the range of semi-diurnal tides but had resulted in an amplification of the one hour resonant seiches from typically 0.1 m to 0.2 m and the 10 minute seiches from 0.05 m to approximately 0.1 m. Amplification of these seiches seemed to be greatest in the upper reaches of the Bay. The study was not able to conclude the extent to which this amplification (doubling of the amplitude) of the seiches was implicated in the reported scour of sandbanks and problems at the Yacht Basin. Surveys of the sandbanks in Durban Bay did indeed indicate changes between 2007 and 2010 but it is uncertain whether these changes could be ascribed to the effects of channel widening or were merely the result of seasonal re-distribution of sediment (EMS 2010). Possibly of greater concern is the fact that in some cases dredging operations have encroached on the toe of some of the sandbanks, resulting in localised progradation and slumping (CSIR 2010). While there is not significant penetration of wave energy into the port in the areas inland of the T-jetty, there is some penetration of wave energy into the outer port area. The penetration of such wave energy is a potential concern for the Pier 1 In-fill development as the proposed development involves a substantial re-orientation of existing quaywalls. Reflection of wave energy from the newly re-orientated quaywall, to the extent that waves penetrate the port and such reflection occurs, could result in wave energy reaching locations not subject to such wave energy previously. This could lead to changed mooring conditions or possible even infrastructure damage if the changes prove to be of sufficient magnitude. For this reason we provide a brief overview of offshore wave conditions that may influence the outer port area, particularly the Pier 1 quays and surrounds. The best representation of the wave climate near the port entrance is that obtained from wave times series measured just south of the port entrance in an approximate water depth of -30m CD (Figure 2.11). The annual and seasonal wave roses are presented in Figure 2.12 while the occurrence of wave height versus wave direction are reported in Tables 2.2 and 2.3, the occurrence wave height versus wave period in Tables 2.4 and 2.5 and the occurrence of wave period versus wave direction in Tables 2.6 and 2.7. The expected worst case wave conditions impacting upon Pier 1 are offshore waves (swell) from the NNE to ENE sector together with locally generated seas under persistent and strong NNE to ENE winds. These conditions are expected during spring when strong E and NE winds occur. Consequently only the annual and spring season wave occurrence data are reported here. Page 13

Figure 2.11: Location of the wave buoy measuring the offshore wave climate. Table 2.2: Annual occurrences of significant wave height versus wave direction Hmo (m) Wave Direction (degrees TN) N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW Total 0.0-0.5 0.00 0.5-1.0 0.00 0.05 0.23 0.65 1.00 1.69 0.24 0.00 3.87 1.0-1.5 0.00 0.17 1.64 2.86 7.14 7.95 14.94 2.43 0.15 0.00 37.29 1.5-2.0 0.00 0.31 3.58 5.01 5.88 6.03 12.81 2.55 0.57 0.01 36.75 2.0-2.5 0.15 2.04 2.38 2.19 2.41 4.81 1.16 0.31 0.01 15.46 2.5-3.0 0.01 0.46 0.91 0.82 0.73 1.62 0.36 0.07 0.00 4.97 3.0-3.5 0.03 0.12 0.29 0.29 0.43 0.07 0.00 1.23 3.5-4.0 0.08 0.12 0.06 0.02 0.28 4.0-4.5 0.00 0.05 0.02 0.07 4.5-5.0 0.00 0.04 0.00 0.04 5.0-5.5 0.02 0.02 0.04 5.5-6.0 0.00 0.00 Total 0.00 0.01 0.64 7.81 11.52 17.08 18.63 36.37 6.83 1.10 0.02 0.00 0.00 0.00 0.00 0.00 100. Table 2.3: Occurrences of significant wave height versus wave direction during spring Hmo (m) Wave Direction (degrees TN) N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW Total 0.0-0.5 0.00 0.5-1.0 0.01 0.09 0.10 0.31 0.72 0.92 0.18 2.33 1.0-1.5 0.10 1.25 2.22 5.76 6.99 12.10 2.76 0.14 31.33 1.5-2.0 0.01 0.33 3.83 6.17 5.75 5.82 13.39 3.01 0.59 0.01 38.90 2.0-2.5 0.11 3.04 4.94 2.16 2.98 5.25 1.62 0.34 0.03 20.48 2.5-3.0 0.02 0.88 1.81 0.64 0.54 1.35 0.48 0.05 5.76 3.0-3.5 0.02 0.16 0.38 0.05 0.30 0.06 0.01 0.97 3.5-4.0 0.18 0.01 0.04 0.23 4.0-4.5 0.01 0.01 4.5-5.0 0.00 5.0-5.5 0.00 5.5-6.0 0.00 Total 0.00 0.01 0.56 9.10 15.41 15.19 17.12 33.30 8.14 1.13 0.04 0.00 0.00 0.00 0.00 0.00 100. Page 14

Table 2.4: Annual occurrences of significant wave height versus wave period Period (Tp) (s) Hmo (m) 0-2 2-4 4-6 6-8 8-10 10-12 12-14 14-16 16-18 18-20 20-22 22-24 24-26 26-28 28-30 30-32 Total 0.0-0.5 0.00 0.5-1.0 0.08 0.46 0.84 1.84 0.54 0.09 0.01 0.02 3.87 1.0-1.5 0.02 2.42 6.86 6.46 13.16 5.40 2.58 0.27 0.07 0.03 0.01 37.29 1.5-2.0 3.20 8.75 5.68 10.83 5.05 2.77 0.41 0.05 36.75 2.0-2.5 0.66 4.70 2.02 4.60 2.04 1.27 0.13 0.04 15.46 2.5-3.0 0.05 1.21 0.69 1.45 0.75 0.68 0.11 0.04 4.97 3.0-3.5 0.10 0.10 0.38 0.28 0.30 0.07 1.23 3.5-4.0 0.01 0.03 0.14 0.04 0.05 0.01 0.28 4.0-4.5 0.00 0.05 0.00 0.01 0.07 4.5-5.0 0.04 0.04 5.0-5.5 0.04 0.04 5.5-6.0 0.00 0.00 Total 0.00 0.02 6.41 22.09 15.83 32.52 14.10 7.76 1.02 0.22 0.03 0.01 0.00 0.00 0.00 0.00 100 Table 2.5: Occurrences of significant wave height versus wave period during spring Period (Tp) (s) Hmo (m) 0-2 2-4 4-6 6-8 8-10 10-12 12-14 14-16 16-18 18-20 20-22 22-24 24-26 26-28 28-30 30-32 Total 0.0-0.5 0.00 0.5-1.0 0.05 0.31 0.67 1.08 0.13 0.10 2.33 1.0-1.5 0.03 1.67 6.49 6.95 10.09 4.26 1.67 0.14 0.01 31.32 1.5-2.0 3.68 10.13 7.55 9.89 5.22 2.33 0.10 38.90 2.0-2.5 1.01 8.50 3.70 4.39 1.61 1.12 0.14 0.01 20.48 2.5-3.0 0.10 2.24 1.45 1.00 0.36 0.41 0.17 0.02 5.76 3.0-3.5 0.11 0.20 0.17 0.06 0.30 0.13 0.97 3.5-4.0 0.02 0.12 0.05 0.04 0.01 0.23 4.0-4.5 0.01 0.01 4.5-5.0 0.00 5.0-5.5 0.00 5.5-6.0 0.00 Total 0.00 0.03 6.51 27.80 20.65 26.67 11.64 5.96 0.69 0.04 0.00 0.00 0.00 0.00 0.00 0.00 100. Page 15

Table 2.6: Annual occurrences of wave period versus wave direction Tp (s) Wave Direction (degrees TN) N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW Total 0-2 0.00 2-4 0.01 0.00 0.00 0.01 0.02 0.04 4-6 0.01 0.43 2.69 1.06 0.17 0.24 0.19 0.80 0.80 0.02 6.40 6-8 0.21 4.88 6.46 3.75 3.06 2.14 1.26 0.29 0.00 22.04 8-10 0.21 3.37 8.23 6.38 5.23 0.78 0.01 24.22 10-12 0.00 0.56 3.66 6.00 11.73 2.22 24.17 12-14 0.00 0.05 0.97 2.20 9.71 1.19 14.12 14-16 0.00 0.00 0.26 0.68 6.22 0.58 7.74 16-18 0.01 0.06 0.91 0.04 1.01 18-20 0.02 0.22 0.01 0.24 20-22 0.00 22-24 0.01 0.01 Total 0.00 0.01 0.65 7.79 11.51 17.05 18.63 36.35 6.88 1.11 0.02 0.00 0.00 0.00 0.00 0.00 100. Table 2.7: Occurrences of wave period versus wave direction during spring Tp (s) Wave Direction (degrees TN) N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW Total 0-2 0.00 2-4 0.02 0.04 0.06 4-6 0.01 0.45 2.58 1.01 0.14 0.20 0.22 0.96 0.87 0.04 6.49 6-8 0.10 6.09 9.24 3.89 3.59 3.07 1.59 0.22 27.80 8-10 0.42 4.61 9.15 7.58 5.77 0.85 28.38 10-12 0.49 1.43 3.78 10.67 2.58 18.95 12-14 0.06 0.24 1.63 8.22 1.48 11.64 14-16 0.29 0.32 4.71 0.64 5.96 16-18 0.05 0.02 0.60 0.02 0.69 18-20 0.04 0.04 20-22 0.00 22-24 0.00 Total 0.00 0.01 0.56 9.09 15.41 15.19 17.12 33.31 8.14 1.13 0.04 0.00 0.00 0.00 0.00 0.00 100. Page 16

Period 2007-08-01 to 2012-02-29 Station DURB BLUFF Position 29.884 S, 31.07067 E Instrument Depth 0 m Water Depth 30 m Instrument Type All Instruments Records 71355 Figure 2.12: Annual and seasonal wave roses for waves measured just south of the port entrance in an approximate water depth of -30m CD. Page 17

3 PROJECT DESCRIPTION Transnet Ports Authority has identified a need to expand (deepen, widen and lengthen) berths 203 to 205 in order to improve the safety of the berths as well as to improve the efficiency of the Port of Durban. This will include: the westward expansion of Berth 205 by 170m; the eastward expansion of Berth 203 by 100m; the seaward expansion of Berths 203 to 205 quayside by 50m; the deepening of the berth channel, approach channel and vessel turning basin from the current -12.8m CDP to -16.5m CDP; the cutting into the central Sandbank by approximately 50m to 150 m. These activities will result in a potential change in the hydrodynamic functioning of the Port of Durban that may have a number of negative environmental effects within the port. These were identified in a screening study undertaken by the CSIR (CSIR, 2011) in which it was recommended that some of these potential impacts be assessed in greater detail. These have been assessed in van Ballegooyen et al., (2012) and CSIR (2012). A potential exists for a follow-on development, namely the Salisbury Island Pier 1 In-fill project. Here the existing Pier 1 Berths 102 and 103 will be in-filled and new berth developed along the in-filled quays. Similar to the Berth 203 to 205 development there are potential impacts associated with the Pier 1 in-fill development. This modelling study provides a preliminary assessment of the likely hydrodynamic changes and associated potential impacts due to the Pier 1 infill, with a particular focus on wave effects. Figure 3.1 contains the existing port layout while Figure 3.2 contains the latest design (Option 3G) for the proposed Berth 203 to 205 development. The baseline in this study is not the existing port layout but rather the layout after the proposed Berth 203 to 205 development, i.e. the Option 3G layout as indicated in Figure 3.2. As the development Option 3G was not yet available when this study was commenced, layout Option 3F (Figure 3.3) has been used as the baseline in place of Options 3G. This will not change the model results as the changes between Option 3G and 3F the changes are so small as not to be resolvable by the modelling study (where typically a computational grid resolution of less than 10 m was achieved in the areas of interest). The only change between Option 3F and 3G is an approximate 2m expansion of the Central Sandbank into the basin opposite Berths 203 to 205 that extends from opposite Berth 205 to opposite Berth 104. Any reference to Option 3F and any associated finding can therefore be considered to be a reference to Option 3G and the findings reported for Option 3F being equally valid for Option 3G. Figure 3.4 contains the proposed post-construction Pier 1 in-fill development layout. The only changes to the Berth 203 to 205 final design are the in-fill of existing Pier 1 berths 102 and 103 as well as the a deepening of the approaches to the new Pier 1 berths, i.e. the area between the main channel and the Pier 1 quaywalls. Page 18

Figure 3.1: Existing port layout Figure 3.2: Development Option 3G Page 19

Figure 3.3: Development Option 3G Figure 3.4: Development Option 3F together with the proposed Pier 1 In-fill. Page 20

Table 3.1 provides estimates of the volume and surface water area of the Port of Durban at various water levels. Here the port is considered to extend to a line extending across the entrance channel perpendicularly from the outermost extremity of the northern breakwater at the port entrance. The pier 1 development results in an approximate 2.3 % reduction in the water volume of the port an approximate reduction in surface water area of the Port of Durban ranging between 2.3% and 2.8%, depending on the assumed tidal water level. In making these calculations the changes pre- and post-construction water depths have been taken into account. Table 3.1: Estimated changes in water volume and surface water area within the Port of Durban associated with the proposed Pier 1 in-fill development. MLWS +0.21 m CD Berth 203 to 205 development Option 3F/G MLWN +0.87 m CD MSL (LLD) 0.913 m CD MHWN +1.36 m CD MHWS +2.01 m CD) Volume (million m 3 ) 82.8 87.5 87.9 91.5 96.8 Area below MSL (million m 2 )* 6.80 7.95 8.00 9.19 8.22 Post-construction (Option 3f/G + Pier-1 infill) Volume (million m 3 ) 80.9 85.5 85.8 89.4 94.6 Area below MSL (million m 2 )* 6.61 7.76 7.81 8.00 8.03 % change from pre- to post construction of Pier 1 in-fill development Volume (million m 3 ) -2.27 % -2.29 % -2.29 % -2.30 % -2.30 % Area below MSL (million m 2 )* -2.82 % -2.41 % -2.39 % -2.34 % -2.33 % * MSL here is assumed to be equivalent to Land Levelling Datum (LLD) Page 21

4 KEY ISSUES OF CONCERN The proposed changes associated with the expansion of Berths 203 to 205 may result in changes in the hydrodynamic functioning of the Port of Durban that, in turn, may have a number of negative ecological consequences. As noted previously these were identified in an initial environmental screening study undertaken by the CSIR (CSIR, 2011) and have been assessed in a prior assessment (van Ballegooyen et al., 2012). Here we focus on potential additional changes in the hydrodynamic functioning of Port of Durban associated with the Pier 1 infill. While the scope of work for the assessment only require that changes in wave conditions be assessed in the vicinity of the Pier 1 development, the assessment undertaken here follows the same format of that for the Berth 203 to 205 development and includes potential changes in the current and wave patterns in the Port and the possible consequences thereof for; the stability of the central sandbank and associated habitats changes in water quality, and; potential effects on sensitive habitats such as the Little Lagoon. The above additional assessments are undertaken mainly for the purposes of due diligence as the only changes of significance expected to be associated with the Pier 1 in-fill are a possible reduction in the tidal prism in the port seaward of the T-Jetty, changes in waves conditions in the same area and possibly changes in seiching behaviour in the port. The following issues have been assessed: Potential change in tidal flushing associated with changes in the tidal prism due to the changed layout of the port. There will be a significantly reduction in surface water area in the port due to the Pier 1 in-fill that is expected to affect the tidal prism in at least the port area seawards of the T-Jetty. Changes in flows in the port could also occur due to changes in wind or wave driven flows. These changes in currents, if significant, can lead to: o o o o exacerbation of water quality issues in the port; potential localised scour issues, including destabilisation of the Central Sandbank (unlikely), should flows increase due to the Pier 1 infill; negative ecological effects in Little Lagoon although this considered highly unlikely as no clear vector exists for such an impact; potential changes in sediment deposition patterns should tidal flushing decrease that could ultimately lead to the exacerbation of existing sediment and/or water quality concerns; Potential exacerbation of one hour and/or 10 minute oscillations due to changes in port layout that, in turn, could: o o o play a role in destabilising the Central Sandbank; have potential negative consequences for mooring conditions in the Yacht Basin; result in potential changes in mixing dynamics and flushing in the port; Wave patterns in the Bay could be altered by the change in layout and re-orientation of the Pier 1 quaywalls with potential effects on mooring conditions and, in a worst case scenario, possible infrastructure damage. Page 22

In simulating the changes in in hydrodynamic functioning and associated potential habitat changes, we have focussed on the following: Change in Wave Conditions in the port. Changes in the tidal prism and consequent potential changes in Water and Sediment Quality in the port; Changes in seiching behaviour Considered to be of secondary importance is the assessment of: Habitat change on the Central Sandbank; Habitat change in Little Lagoon and its surrounds; as it is highly unlikely that the Pier 1 in-fill development will have any impact on these areas. Also identified are possible changes in long-wave energy in the port that could lead to mooring problems. These concerns, however, are not addressed here as they are deemed to be an engineering design issue. Page 23

5 APPROACH AND METHODS The approach to the study has been to set-up a hydrodynamic model that simulates all of the processes relevant to making the above assessments. This requires that appropriate data sets be collated that both describe these processes and that can be used to undertake the modelling. Specifically the modelling study requires datasets prescribing the forcing in the model (e.g. wind, waves, tidal water levels, etc) and that can be used for calibration purposes. 5.1 Process of Relevance to the Modelling Study The processes of relevance to the modelling study are: tidal forcing; offshore swell; wind-driven waves and currents within the port; seiching behaviour within the port. The effect of offshore swell entering the port presently were not considered in the Berth 203 to 205 development as the effect of these swells is minimal in the Berth 203 to 205 and sandbank areas in the port. However the Pier 1 in-fill development is located nearer the port entrance and may be influenced by wave (swell) energy penetrating into the port.. For this reason the influence of offshore waves need to be included in the study. For consistency with the Berth 203 to 205 assessment (van Ballegooyen et al., 2012), an initial assessment is undertaken without considering the effect of offshore waves entering the port through the harbour entrance. This is followed by an assessment that includes offshore wave effects in the port. Stratification effects again have been excluded from the modelling study as thermal stratification in the bay is fairly limited in all but the upper reaches of the port. Salinity stratification, where it exists due to catchment inflows to the port is generally constrained to the upper few metres of the water column and, where significant, is generally of limited duration. The exclusion of these effects will not significantly affect the metrics used in the modelling study to assess potential environmental impacts of concern, particularly not the metrics used to characterise potential changes in wave conditions within the port.. 5.1.1 Tidal forcing The tidal characteristics for the Port of Durban are summarised in Table 5.1 below. Table 5.1: Tidal characteristics for the Port of Durban Tidal Levels Lowest Astronomical Tide (LAT) Mean Low Water Springs (MLWS) Mean Low Water Neaps (MLWN) ML (Mean Level) Land Levelling Datum (LLD) Mean High Water Neaps (MHWN) Mean High Water Springs (MHWS) Highest Astronomical Tide (HAT) 0.000 m 0.210 m 0.870 m 1.110 m 0.913 m 1.360 m 2.010 m 2,300 m Page 24

The tidal forcing used in the model is the predicted tide based on the tidal constituents (see Table 5.2) reported by Rosenthal and Grant (1989). Table 5.2: Tidal characteristics for the Port of Durban Tidal Constituent Amplitude (m) Phase (deg) Z0 1.1100 - M2 0.5594 99.720 S2 0.3130 133.620 N2 0.0999 91.290 K2 0.0885 128.620 K1 0.0519 175.880 P1 0.0150 180.230 μ2 0.0161 102.340 O1 0.0176 319.750 The predicted tides used to force the model are presented in Figures 5.1 to 5.3. 5.1.2 Wind-driven waves and currents Wind-driven waves are likely to be a major determinant of bed shear stress over the shallow Central Sandbank, however in the context of the Pier 1 in-fill development, offshore wave effects also are likely to be significant. For this reason the modelling includes simultaneous forcing of wave conditions in the port by both offshore waves penetrating into the port through the entrance channel and local wind-driven waves within the port. Tidal currents resulting from tidal forcing at the model boundary are also a major determinant of flows and bed shear stresses in the model. Wind-forced currents are likely to be equally important in the model, particularly in the shallow areas of the port. These wind-driven flows have been included in the modelling for a representative range of environmental conditions. Also included in the modelling are wind-driven set-ups over the adjacent continental shelf that can result in synoptic-scale water level changes of up to 20 cm in the port (van Ballegooyen, 1996). To ensure that a representative range of environmental conditions are simulated we have considered three periods for simulation in the model: winter conditions (Figure 5.1) where SW wind conditions are common and south-westerly busters can occur (July 2010); late summer conditions (Figure 5.2) when the persistence of the E/NE wind conditions is greatest (Feb 2010), and; spring conditions (Figure 5.3) when strong E and NE winds occur (Oct 2010). In terms of assessing worst case conditions only those of winter and spring are of relevance. Consequently model simulations have only been undertaken and reported upon for the winter and spring periods. Page 25

Figure 5.1: Wind and water level conditions used for the winter modelling scenario (July 2010). Figure 5.2: Wave conditions used for the winter summer modelling scenario (October 2010). Page 26

Figure 5.3: Wind and water level conditions used for the spring modelling scenario (October 2010). Figure 5.4: Wave conditions used for the spring modelling scenario (October 2010). The red portion of the time series indicates the original times series prior to modification to include worst case conditions. Page 27

To ensure that worst case offshore wave conditions are included in the study, the offshore wave conditions on 18 October 2011 were modified to include the maximum swell heights (~ 3.5 m) observed for the ENE/NE sector. A worst case offshore wave condition (H mo = 3.5 m and wave direction ~ 38 degree TN) was assumed for 15:00B and 18:00B on 18 October 2010. This coincides with wind speeds of between 15 and 18 m/s from a direction of 20 to 50 degrees TN. These conditions represent an approximately 99% exceedance conditions for wave heights from a NNE / NE sector and approximately 95% exceedance conditions for wind speed from a NNE / NE sector. 5.1.3 Seiching in the Port of Durban Water level variability due to the seiching reported to occur in the Port of Durban (PRDW, 2009) has two major components: a resonant seiche with a period of approximately 1 hour and a range of approximately 0.1 to 0.2 m. a resonant seiche with a period of approximately 10 minutes and a range of approximately 0.05 m to 0.1 m. The widening of the Port entrance, while it did not affect the semi-diurnal tides, is reported to have increased the range of the 1 hour seiche from approximately 0.1 to 0.2 m, and increased the range of the 10 minute seiche from approximately 0.05 to 0.1 m. The ranges of these seiches differ at various sites in the harbour with the highest amplitudes being observed in the Silt Canal area. It is postulated that the widened entrance either i) allows additional infra-gravity energy to enter the harbour from offshore or, ii) shifts the resonant modes inside the harbour (PRDW, 2009). To simulate the seiching, which is clearly evident in all the available current and water level measurements inside the port, the approach taken is that used by PRDW (2009). This entails adding a white noise signal with a period range from 10 minutes to 6 hours and a standard deviation of 0.017 m to the predicted tide applied on the offshore model boundary. Here the white noise comprised 36 equal amplitude frequency components distributed linearly across the relevant frequency range, i.e. 1.7 x 10-3 to 4.6 x 10-5 Hz. 5.1.4 Stratification Stratification in the Port of Durban is of such a nature that it is not deemed necessary to include these processes in the modelling study. The existence of stratification will influence vertical velocity shear in regions where it is significant, however these effects are only expected in the upper reaches of the harbour. In the lower and middle reaches the vertical velocity shear are largely determined by frictional effects due to the strong wind-driven and tidal flows. The model is three dimension (i.e. has 8 layers) but does not include baroclinic effects (i.e. flow modifications due to vertical changes in the density fields) as a compromise was needed between the need for high spatial (horizontal) resolution simulations to estimate potential morphological change and the need to resolve the secondary effect of vertical changes in velocity due to density effects. The fact that density stratification is not included in the model has a very limited influence on the morphological predictions and only a minor effect on the manner in which we have characterised potential changes in currents (and consequently flushing potential) in the bay. Page 28

5.2 Erodability of Sandbanks It was anticipated at the start of the Berth 203 to 205 development study (van Ballegooyen et al., 2012) that additional field measurements may be required both for the calibration of the model and to better characterise critical bed shear stresses for erosion of the sandbank. It is known that the erodability of the seabed can vary substantially depending on the ration of sand to mud in the sediments (Ahmad et al., 2011). For example, the critical shear stress for erosion increases when mud is added to sand and also when sand is added to mud. The addition of up to 50% sand to a mud bed typically increases the critical erosion shear stress by a factor of 2. Conversely, the addition of 30% mud to a sand bed can increase the critical shear stress by a factor of 10 (Mitchener and Torfs, 1996). Furthermore, factors such as organic content and consolidation can dramatically increase the critical shear stress for erosion. A brief review of anticipated critical shear stresses for erosion of the seabed (Van Rijn, 1993; Mitchener and Torfs, 1996; Basaniak and Verhoeven, 2006; Ahmad et al., 2011, Jacobs et al., 2011) provided clear indication that it would be difficult to define confidently a critical shear stress for erosion to be used in a numerical model. Basaniak and Verhoeven (2006) report very low rates of erosion for some mud samples at erosion shear stresses of up to 3 Pa, while Mitchener and Torfs (1996) report erosion shear stresses ranging between 0.05 Pa and 1.9 Pa for naturally occurring sandy, consolidated beds. For artificially mixed beds with a sand content above 80%, critical shear stresses of between 1 and 3 Pa were reported by Mitchener and Torfs (1996). Theoretical calculations, using the distribution of measured sand to mud ratios in sediments (sampled for the Berth 203 to 205 development modelling study) in the formulae presented by Ahmed et al. ( 2011), results in predicted critical shear stresses of erosion that range between 0.14 to 0.21 Pa. Based on i) model predictions of shear stresses that on occasion reached up to 4 Pa and ii) the high critical shear stresses reported in the literature for consolidated beds containing a sand-mud mixture, it became clear that it would not be possible to rely on the calculated theoretical critical shear stress for erosion for use in that study (van Ballegooyen et al., 2012) or the present study. If one was to use these theoretical critical bed shear stresses (generally as determined mainly in flumes) to estimate erosion of the sandbanks, the Central Sandbank theroretically would be subject to substantial erosion under present day hydrodynamic conditions in the Port of Durban. A review of historical imagery from GoogleEarth indicates that very little change in the morphology of the sandbank has occurred over the past 10 years. Limited changes have been observed in the shallow sediments on the eastern extremity of the sandbank subsequent to widening of the port entrance. Similarly, a detailed assessment based on surveys of the morphology of sandbanks within the port, have indicated little change (EMS, 2010; CSIR, 2011). Where such changes have occurred they have been ascribed to disturbances other than changes in the hydrodynamic functioning of the port (e.g. maintenance dredging). To resolve uncertainties in determining the critical bed shear stresses for the sandbanks in the Port of Durban, the approach taken in the previous Berth 203 to 205 development modelling study and in the present study to determine potential changes in the sandbanks within the port, is to assume that a potential for erosion or scour only exists if the post construction model simulations indicate an increase in bed shear stresses compared to model simulations for the existing port layout. One only needs to consider the upper range of bed shear stresses as it is only these higher bed shear stresses that will result in erosion and/or movement of sediments. Page 29

In summary, the approach used to estimate potential long-term changes in the Central Sandbank in this and the previous study (van Ballegooyen et al., 2012) is based on the assumption that should the bed shear stresses in the post development scenario exceed those for the existing port layout, the region(s) where this occurs will be susceptible to erosion. Whether the bed shear stresses on these occasions will actually exceed the critical shear stress of erosion for the sediments under consideration, is uncertain. Consequently, we have decided to take a worst case approach by assuming that should the bed shear stresses in the post development scenarios exceed those for the existing port layout, erosion will occur wherever this is found to be the case. Such an approach has precedent in that it has been used in a similar erosion prediction exercise in an erosional estuary (Brennan et al., 2007) Figure 5.4: GoogleEarth image of the sandbank showing the complexity of bed forms in the area between Berth 205 and the Little Lagoon where the modelled bed shear stresses are high. The complexity of the bedforms (channels, rivulets, etc) on the Central Sandbank in the regions where the model predicts high bed shear stress (i.e. the sandbank in the area between Berth 205 and Little Lagoon), suggest that the bed shear stresses in these regions approach the critical shear stress of erosion for these sediments. This provides support for the approach taken to predict potential erosion of the sandbanks in the port in both this and the previous Berth 203 to 205 development modelling study. Page 30

6 MODEL SET-UPS AND CALIBRATION The model set-up and calibration are described below. Particular attention has been given to the selection of appropriate critical bed shear stresses for erosion used to predict likely changes in the bathymetry of the Central Sandbank and other sandbanks within the harbour. 6.1 Model set-up The model comprises a three dimension coupled wave and hydrodynamic simulation of representative environmental scenarios for the Port of Durban. The software used is the Deltares Delft3D-Wave and Delft3D-FLOW software (Deltares, 2011a,b). As noted earlier, density effects have not been included in the modelling. The hydrodynamic grid used in the modelling (Figure 6.1) is a fairly high resolution grid that has been refined in the areas of interest. Figure 6.1: The model grid for the pre-pier 1 in-fill development scenario, i.e. the Berth 203 to 205 development Option 3G layout For the wave modelling four categories of reflective surface were defined, sand, mangrove, breakwater and vertical quayside or walls (Figure 6.2). A reflection co-efficient of 0.4 was assumed for the breakwaters and 1.0 for the non-porous vertical walls that are considered to be totally reflective. These reflection co-efficient were based on values found in literature (e.g. Al-Nassar et al., 2007; GHKSAR, 2003; Chadwick et al., 2004). Page 31

Figure 6.2: The model grid for the post-pier 1 in-fill development scenario Figure 6.3: Obstacles in the wave model for the pre-pier 1 in-fill development scenario, i.e. Berth 203 to 205 development Option 3G. The black outline represents breakwaters of various sorts and the brown outline represents vertical walls. Other areas not outlined in black or brown represent either sand or mangroves, both having an assumed wave reflection co-efficient of zero.). Page 32

Figure 6.4: Obstacles in the wave model for the post-pier 1 in-fill development scenario. The black outline represents breakwaters of various sorts and the brown outline represents vertical walls. Other areas not outlined in black or brown represent either sand or mangroves, both having an assumed wave reflection co-efficient of zero.). In the modelling undertaken here both the offshore waves entering through the port entrance and locally wind-driven waves are included in the model. The offshore wave times series used in the modelling is that measured at a site just southeast of the port entrance in an approximate water depth of -30 m CD (see Figure 2.11). The hydrodynamic model is forced by applying predicted water levels at the offshore boundary. These predicted water levels comprise the predicted tide, a predicted wind-driven set-up component and a white noise signal with a period range from 10 minutes to 6 hours and an amplitude having a standard deviation of 0.017 m. The winds used to force the model are those measured at Port Control. Given the height and topography of this measurement location, these wind speeds are likely to be somewhat greater in magnitude that those actually occurring within the harbour. While this is a potential source of error in the modelling, any such error introduced into the modelling, if anything, is likely to provide a more conservative result in terms of potential environmental impacts. The results are in any case comparative so such errors are of minor concern. 6.2 Model Calibration Considerable effort was expended in collation of potential calibration data for the model, however only limited data exist for the post entrance-widening period. These data comprise limited duration wave data measured in the vicinity of Salisbury Island. Unfortunately, the offshore wave buoy was Page 33

not functional during the period that these data were measured. Consequently these data cannot be used to calibrate the models for the penetration of offshore waves into the port. The only current / flow data that exist are those measured prior to the widening of the port entrance. Thus the only significant data that presently exists for the post entrance-widening period are: water levels measured by the Hydrographic Office of the South African Navy, and; the water quality profiling and sediment quality data measured by the CSIR. However, as part of this project, wave and current data are being measured at a number of locations within the harbour (see Figure 6.3). These will become available in due course and, if necessary, the calibration of the models will be verified using these data. Figure 6.3: Wave and current field measurement sites for the proposed Pier 2, Container Berth development. The modelled water levels and 3 minute resolution measured water levels measured by the SA Navy are presented in Figure 6.4. The upper panel represents a neap tide period when the seiching and other oscillations within the harbour are generally at a maximum. The lower panel represents a spring tide period when the seiching and other oscillations are often less noticeable possibly due to frictional effects associated with the stronger tidal flows. The model predictions of water level closely match those measured both in tidal amplitude and the nature and amplitude of higher frequency oscillations (seiching). The offset in water levels in the upper panel are most probably due to some unresolved water level variability associated with larger-scale current variability over the adjacent continental shelf (e.g. Agulhas Current variability). Page 34

Figure 6.4: Modelled versus measured water levels within the Port of Durban. 6.3 Confidence in the modelling results The hydrodynamic model set-up to assess potential changes in the port marine environment associated with the proposed development includes all of the major processes of relevance, i.e.the influence of offshore waves, tides, wind driven waves and flows and seiching behaviour in the port). Stratification has been excluded as thermal stratification in the bay is fairly limited in all but the upper reaches of the port. Salinity stratification, where it exists due to catchment inflows to the port is generally constrained to the upper few metres of the water column and is generally of limited duration. No data other than sea level is available for calibrating the model as all calibration data that exist were measured prior to the widening of the port entrance. Despite this there is confidence in the modelling results as the hydrodynamics within the port are primarily determined by bathymetry, winds and tides, all of which have been accurately measured for the Port of Durban. The seiching behaviour has been assessed against measured data. The approach used to estimate potential long-term changes in the Central sandbank is based on the assumption that should the post development bed shear stresses exceed those for the existing port layout, the region where this occurs will be susceptible to erosion. Whether the bed shear stresses Page 35

actually exceed the critical shear stress of erosion for the sediments being under consideration is uncertain. In this study as well as in the Berth 203 to 205 development studies, we have taken a worst case approach by assuming that should the bed shear stresses post development exceed those for the existing port layout, erosion will occur where this is the case. Such an approach has precedent in that it has been used in a similar erosion prediction exercise in an erosional estuary (Brennan et al., 2007) It is not possible to simultaneously consider both wave diffraction and wave reflection effects in the SWAN wave model that was used in this study. Furthermore the wave diffraction processes included in the SWAN model are not as robust as would be the case in a Boussinesq wave model. For this reason we have not attempted to model wave diffraction effects in the wave modelling. The absence of wave diffraction effects will reduce the wave energy entering the Port of Durban should the offshore waves arrive at the port entrance from any direction other than in direct alignment with the port entrance channel. The extent of the underestimation of the wave energy entering the port will increase with increasing deviation of the offshore wave direction from that of the port entrance channel orientation. In the modelling study we have artificially included offshore wave conditions that represent extreme wave conditions that are aligned with the port entrance channel and therefore have modelled what are considered worst case conditions in terms of potential penetration of wave energy into the Port of Durban. For such wave conditions, the errors introduced by exclusion of diffraction effects from the wave modelling are insignificant in terms of the conclusions to be drawn from this study. Page 36

7 RESULTS Here the modelled changes in hydrodynamic functioning within the port are characterised in a manner that supports the assessment of potential ecological impacts of the proposed Pier 1 in-fill development. Initially, an overview is given of the potential changes in hydrodynamic functioning, followed by specific assessments related to the ecological issues of concern. 7.1 Changes in Hydrodynamic Functioning in the Port Here we focus on potential additional changes in the hydrodynamic functioning of Port of Durban associated with the Pier 1 infill. The scope of work for this study only requires that changes in wave conditions be assessed in the vicinity of the Pier 1 development, however the assessment undertaken here follows the same format of that for the Berth 203 to 205 development and includes potential changes in the current and wave patterns in the Port and the possible consequences thereof for; the stability of the central sandbank and associated habitats changes in water quality, and; potential effects on sensitive habitats such as the Little Lagoon. The above additional assessments are undertaken mainly for the purposes of due diligence as the only changes of significance expected to be associated with the Pier 1 in-fill are a possible reduction in the tidal prism in the port seaward of the T-Jetty, changes in waves conditions in the same area and possibly changes in seiching behaviour in the port. As noted previously, the changes in hydrodynamic functioning of concern are potential changes in: Potential change in tidal flushing associated with changes in the tidal prism due to the changed layout of the port. There will be a significantly reduction in surface water area in the port due to the Pier 1 in-fill that is expected to affect the tidal prism in at least the port area seawards of the T-Jetty. Changes in flows in the port could also occur due to changes in wind or wave driven flows. These changes in currents, if significant, can lead to: o o o o exacerbation of water quality issues in the port; potential localised scour issues, including destabilisation of the Central Sandbank (unlikely), should flows increase due to the Pier 1 infill; negative ecological effects in Little Lagoon although this considered highly unlikely as no clear vector exists for such an impact; potential changes in sediment deposition patterns should tidal flushing decrease that could ultimately lead to the exacerbation of existing sediment and/or water quality concerns; Potential exacerbation of one hour and/or 10 minute oscillations due to changes in port layout that, in turn, could: o o o play a role in destabilising the Central Sandbank; have potential negative consequences for mooring conditions in the Yacht Basin; result in potential changes in mixing dynamics and flushing in the port; Wave patterns in the Bay could be altered by the change in layout and re-orientation of the Pier 1 quaywalls with potential effects on mooring conditions and, in a worst case scenario, possible infrastructure damage. Page 37

In simulating the changes in in hydrodynamic functioning and associated potential habitat changes, we have focussed on the following: Change in Wave Conditions in the port. Changes in the tidal prism and consequent potential changes in Water and Sediment Quality in the port; Changes in seiching behaviour Considered to be of secondary importance is the assessment of: Habitat change on the Central Sandbank; Habitat change in Little Lagoon and its surrounds; as it is highly unlikely that the Pier 1 in-fill development will have any impact on these areas. Also identified are possible changes in long-wave energy in the port that could lead to mooring problems. These concerns, however, are not addressed here as they are deemed to be an engineering design issue. 7.1.1 Changes in tidal and wind-driven flushing The changes in tidally and wind-driven flushing in the port have been assessed by plotting instantaneous fluxes and cumulative fluxes through critical cross-sections in the port (see Figure 7.1). The instantaneous fluxes provide an indication short term changes in flows through these cross-sections while the cumulative fluxes provide a much better indication of changes in the flushing through these cross sections. The relative magnitude of the fluxes across the various cross-sections, as expected, decreases dramatically as on moves deeper into the port (see Figure 7.2). This means that, the deeper into the port are the changes in layout, the less their potential to influence tidal flows. The changes between the pre- and post-construction Pier 1 in-fill layouts have been assessed for winter and spring conditions (i.e. July 2010 and October 2010). A positive flux indicates an outflow from the port while a negative flux indicates incoming flows. As the effects of offshore waves on tidal and wind-driven flushing is expected to be limited, only the results for the model simulations excluding offshore wave effects are reported here. Assessed here are flows through cross sections at: the port entrance; the entrance to the Island View Basin the channel at the T Jetty; the channel in the vicinity of the Little Lagoon, as well as flows across the Central Sand Bank and also the Western end of the sandbank. Changes in flows across the port entrance provide an indication of likely changes in the outer port area, while changes in the cross-section at the T-Jetty provide an indication of the likely changes in flushing landwards of this location. The cross-section at Little Lagoon allows the any changes in flushing potential of the Congella Basin to be assessed. Finally, the cross-section across the Central and Western sandbank are used to assess the shift in flows across the sandbank. As the Pier 1 in-fill development area lies seawards of the T-jetty, it is expected that changes in the tidal prism, if observable, will only be seen in the cross-section across the port entrance where a reduced tidal prism is expected to be observed. The effect however is likely to be very small as the tidal prism is roughly proportional to the surface water area in the port and this is indicated to change by < 2.8% at the worst. In reality the model predicted changes in tidal prism seems to be significantly less than suggested by the change in surface water area. Page 38

Figure 7.1: Cross-section across which the fluxes have been assessed. Figure 7.2: Fluxes through the port entrance, the channel opposite the T-Jetty and the channel opposite Little Lagoon. The changes in water fluxes in and out of the port are surprisingly limited and are universally smaller that those predicted for the Berth 203 to 205 development. The only observable change is in the cross section across the port entrance (Figures 7.3 and 7.4) but even these are negligible. It is therefore not expected that the changes in flushing potential due to the Pier 1 in-fill development will be of significance. There may well be more localised and short-term changes in currents in the vicinity of the Pier 1 in-fill but these will not have an impact on the system water quality beyond the immediate surrounds of Pier 1. Page 39

Figure 7.3: Accumulated fluxes (upper panel) and instantaneous fluxes (lower panel) through the port entrance for the winter scenario (July 2010). Page 40

Figure 7.4: Accumulated fluxes (upper panel) and instantaneous fluxes (lower panel) through the port entrance for the spring scenario (October 2010). Page 41

7.1.2 Potential exacerbation of existing seiching There exists significant energy at frequencies of 60 to 70 minutes and 10 minutes in the Port of Durban due to seiching. The concern is that potential increases in this seiching may: play a role in destabilising the Central Sandbank have potential negative consequences for mooring conditions (e.g. the outer port area, the Yacht Basin); result in potential changes in mixing dynamics and flushing in the port These latter two effects will only be observed should there be a substantial change in the seiching behaviour within the port. It is not expected that the Pier 1 in-fill development will change seiching behaviour in areas other than the outer port area lying seawards of the T-Jetty. The locations chosen for assessing changes in seiching behaviour are indicated in Figure 7.5 below. Yacht Basin Eastern Central Sandbank T-Jetty Central Sandbank opposite Berth 205 Pier 1 Channel 4 Channel 1 Little Lagoon Channel 3 Channel 2 Silt Canal Figure 7.5: Location at which water level and currents have been plotted to assess potential changes in seiching behaviour. Plots of time series of water level and surface and bottom currents at Pier 1 (Figure 7.6), the T-Jetty (Figure 7.7), Channel 4 (Figure 7.8), Channel 2 (Figure 7.9) and at the Yacht Basin (Figure 7.10) show that there is no significant change in seiching behaviour at any of these sites. Similar plots for the other locations indicated in Figure 7.5) (not presented here) confirm that the seiching behaviour does not change at these other locations. The changes in particularly the surface currents at Pier 1 (Figure 7.6) and to a lesser extent at the T-Jetty site (Figure 7.7) and the Channel 4 location (Figure(7.8) are due to larger scale changes in wind-driven flows that occurs during and after strong N to NE wind episodes. These changes are localised and are associated with the changed layout of Pier 1 after the in-fill. The exact nature of these changes are indicated in Figures 7.11 and 7.12 where the changes typically are confined to the area demarcated by the dashed red line. Page 42

Figure 7.7: Comparison between the surface and bottom currents at the Pier 1 location for pre- (red line) and post-construction layouts (dashed black line) associated with the Pier 1 in-fill development for winter (July 2010) and spring (October 2010) periods. Page 43

Figure 7.7: Comparison between the surface and bottom currents at the T-Jetty location for pre- (red line) and post-construction layouts (dashed black line) associated with the Pier 1 in-fill development for winter (July 2010) and spring (October 2010) periods. Page 44

Figure 7.8: Comparison between the surface and bottom currents at the Channel 4 location for pre- (red line) and post-construction layouts (dashed black line) associated with the Pier 1 in-fill development for winter (July 2010) and spring (October 2010) periods. Page 45

Figure 7.9: Comparison between the surface and bottom currents at the Channel 2 location for pre- (red line) and post-construction layouts (dashed black line) associated with the Pier 1 in-fill development for winter (July 2010) and spring (October 2010) periods. Page 46

Figure 7.10: Comparison between the surface and bottom currents at the Yacht Basin for pre- (red line) and post-construction layouts (dashed black line) associated with the Pier 1 in-fill development for winter (July 2010) and spring (October 2010) periods. Page 47

Figure 7.11: Surface currents for pre- (upper panel) and post-construction layouts (lower panel) associated with the Pier 1 in-fill development during a period of strong N to NE winds. Page 48

Figure 7.12: Near-bottom currents for pre- (upper panel) and post-construction layouts (lower panel) associated with the Pier 1 in-fill development during a period of strong N to NE winds. Page 49

7.1.3 Changes in surface and near bottom flows Potential changes in the surface and bottom flows need to be considered as they constitute and important habitat variable, particularly in more sheltered areas such as the Little Lagoon. The changes in the surface and bottom flows for the various development options have been characterised statistically in terms of percentiles and the median current speeds. The changes in the median surface and bottom current speeds are negligible. The changes are greatest for the Spring period when currents are the strongest, consequently only the predicted changes for the spring period are presented here. The 99 percentile surface and bottom current speeds for post-construction Pier 1 in-fill development layout for the spring scenario are presented in Figures 7.13 and 7.14, respectively. The magnitude of the change in 99 percentile surface and bottom current speeds between the pre- and post-construction Pier 1 in-fill development are presented in Figures 7.15 and 7.16, respectively. These changes are generally negligible except for along the new Pier 1 quaywall where increases exceeding 0.2 m/s are observed for both the surface and near bottom currents. The increase in surface currents are concentrated in the vicinity of existing berths 103 and 104 and the channel between Pier 1 and the T-Jetty. The increase in bottom currents is focussed towards the southern end of the Pier 1 quaywall (i.e. in the vicinity of existing berths 101 and 102). These changes are highly localised and will only affect benthic habitats in the already disturbed areas around the new Pier 1 berths. There may also be a slight coarsening of the benthic sediments in the shipping channel between Pier 1 and the T-Jetty, however these changes will be limited in extent. The Pier 1 in-fill development has no direct influence on the Central Sandbank of other habitats deeper inside the port (e.g. Little Lagoon). Figure 7.13: Magnitude of the 99 percentile surface currents for the post-construction Pier 1 in-fill development layout. Page 50

Figure 7.14: Magnitude of the 99 percentile bottom currents for the post-construction Pier 1 in-fill development layout. Figure 7.15: Magnitude of the changes in the 99 percentile surface currents between the pre-and postconstruction Pier 1 in-fill development layouts. Page 51

Figure 7.16: Magnitude of the changes in the 99 percentile bottom currents between the pre-and postconstruction Pier 1 in-fill development layouts. 7.1.4 Changes in bed shear stresses The changes in port layout have the potential to result in changes in bed shear stresses. This is important to assess as these changes may lead to long term changes in the morphology of the seabed within the port. It is not anticipated that the Pier 1 in-fill development will result in modification of the morphology of the Central Sandbank as the changes in wave and currents associated with changed layout do not seem to extend that far into the port. To assess these potential changes, model simulations have been undertaken for both the pre- and postconstruction Pier 1 in-fill development layouts. These model simulations have been processed to provide the 99 and 95 and percentile bed shear stresses (in Pa) as well as the median bottom shear stresses. The most important bed shear stresses are those with a magnitude that is likely to mobilise the sediments within the port. As noted in Section 5.2 of this report, these critical bed shear stresses are difficult to determine with confidence, particularly where there a various ratios of mud and sand in the sediments and where there the sediments under consideration are consolidated sediments such as those constituting the Central Sandbank in the Port of Durban. The approach taken here to determine potential changes in the sandbanks within the port therefore is to assume that the potential for erosion or scour only exists if the post construction simulations indicate an increase in bed shear stresses compared to simulations for the pre-construction port layout. Furthermore, one only needs to consider the upper range of bed shear stresses as it is only these greater magnitude bed shear stresses that will result in erosion and movement of sediments. Page 52

For this reason we have undertaken a comparative assessment of the 99 percentile bed shear stresses for the pre-construction and post-construction port layouts. As the hydrodynamic conditions can change significantly under various wind, wave and tidal conditions, the assessment has been made for the following two of the three representative environmental scenarios proposed for this study: winter conditions where SW wind conditions are common and south-westerly busters can occur (July 2010); spring conditions when strong E and NE winds occur (Oct 2010), and; The third late summer condition when the persistence of the E/NE wind conditions is greatest (Feb 2010) has not been modelled as the worst case E/NE conditions are covered by the spring scenario (Oct 2010). Of the two scenarios modelled, the worst case scenario in terms of potential changes in morphology is the spring scenario as the highest bed shear stresses are observed during this period (October 2010). During this month high bed shear stresses are observed over the whole of the Central Sandbank while during the other simulation period (July) high bed shear stresses are confined mainly to the region between the westward extension of berth 205 and Little Lagoon. The 99 percentile bed shear stress contours for the pre- and post-construction are presented in Figure 7.17 for the winter scenario (July 2010) and in Figure 7.18 for the spring scenario (Oct 2010). Differences in the 99 percentile bed shear stress contours between simulations of the pre- and postconstruction layouts are presented in Figure 7.19 for the winter scenario and Figure 7.20 for the spring scenario. The model results clearly indicate that the Pier 1 in-fill development will have negligible (if any) influence on the sandbanks within the port. The only observable changes are in the immediate vicinity of the Pier 1 in-fill where locally accelerated bottom flows (most noticeable for the spring scenario) occur. These changes are very small and at best may result in some coarsening of the sediments at the new Pier 1 berths. The effects will be negligible compared to the effects due to shipping movements at these locations. Page 53

Figure 7.17: 99 percentile bed stress contours for winter (July 2010) for the pre-construction (upper panel) and post-construction (lower panel) Pier 1 in-fill development layouts. Page 54

Figure 7.18: 99 percentile bed stress contours for spring (October 2010) for the pre-construction (upper panel) and post-construction (lower panel) Pier 1 in-fill development layouts. Page 55

Figure 7.19: Difference 99 percentile bed stress contours for winter (July 2010) for the pre-construction (upper panel) and post-construction (lower panel) Pier 1 in-fill development layouts. Page 56

Figure 7.20: Difference 99 percentile bed stress contours for spring (October 2010) for the preconstruction (upper panel) and post-construction (lower panel) Pier 1 in-fill development layouts. 7.2 Habitat change on the Central Sandbank The potential changes to habitat on the Central Sandbank of concern are mostly related to a concern that the changes in hydrodynamic functioning in the port will result in long term changes associated with erosion of sandbank habitats. However, the model predictions indicate that the Pier 1 in-fill development will not influence conditions on the Central Sandbank or any other sandbanks within the port. Whilst a possibility exists for locally accelerated bottom flows in the vicinity of the new Pier 1 berths, any resultant changes (i.e. coarsening the bottom sediments) will be negligible compared to the effects due to shipping movements at these locations. 7.3 Habitat change in Little Lagoon and its surrounds Any changes in the hydrodynamics of the prot due to the Pier 1 in-fill development are sufficiently remote to have no effects on the Little Lagoon area and other habitats landwards of the T-Jetty. 7.4 Changes in Water and Sediment Quality in the port Should there be changes in water and sediment quality due to changes in hydrodynamic functioning in the port, this could be of concern. For example, a decrease in tidal or wind-driven flushing may exacerbate existing water quality concerns in the port. Similarly, decreases in bottom flows could lead to increased deposition of fine material that typically is a good proxy for trace metal contamination in the sediments. Page 57

Initially it was intended to simulate the transport and fate of a conservative tracer and to determine flushing times for the existing and various post-development options. This approach while valid would not however provide the precision required to assess in detail changes in the various habitats as it would be comparing flushing times in terms of renewal of the waters in the port by either inflow waters from the adjacent shelf or from river inputs. Thus to assess the potential changes in water and sediment quality in the port we have adopted the following metrics: Predicted changes in both surface and bottom currents. Predicted changes in both surface and bottom shear stresses. Changes in both these metrics are limited and highly localised (see Figures 7.11, 7.12 and 7.17 to 7.20) suggesting negligible changes in sediment and water quality. The changes in fluxes across critical cross-sections in the port also indicate negligible changes (little change (see Section 7.1.1). From this it can be concluded that the changes to flushing potential in the port will be minimally affected and any such changes will be extremely localised. 7.5 Change in Wave conditions in the port The changes in wind-driven wave conditions in the port due to the proposed Pier 1 in-fill development, while they do occur, are limited to the immediate vicinity of Pier 1. These changes in wave conditions are not of the scale and magnitude that they would be of concern to other users in the port or of a nature that is likely to result in infrastructural damage due to increase wave exposure. The changes in wind-driven wave conditions are presented in Figures 7.21 and 7.22 where the 99 percentile significant wave heights have been plotted. The changes a very small and localised for both the winter and spring periods (i.e. changes in wave are < 0.1m and extend only into the shipping channel too the E and NE of Pier 1). Similar plot of the 99 percentile significant wave height for the situation where offshore wave are included in the model simulations are presented in Figures 7.23 and 7.24. The changes in significant wave again are localised (i.e. extend only into the shipping channel too the E and NE of Pier 1) and while, limited in magnitude are somewhat larger (< 0.2m) than those experienced for wind driven waves alone. The implication is that there is there is some swell energy that enters the port and is reflected off the post-construction Pier 1 quaywall, however the exten and magnitude of these changes is limited. The worst case wave conditions (i.e. offshore swells entering the port entrance channel along its alighnment) are plotted in Figure 7.25, the upper panel representing the wave conditions for the preconstruction layout and the lower panel representing the wave conditions for the post-construction layout. At the scales plotted there is almost no discernable change in wave heights. It is interesting however to note that the wave energy is focussed on the bulk shipping terminal where wave damage is known to have occurred subsequent to the widening of the port entrance. Page 58

Figure 7.21: Contours of 99 percentile significant wave heights of locally wind-driven waves for winter (July) for the pre-construction (upper panel) and post-construction (lower panel) Pier 1 in-fill layouts. Page 59

Figure 7.22: Contours of 99 percentile significant wave heights of locally wind-driven waves for spring (October) for the pre-construction (upper panel) and post-construction (lower panel) Pier 1 in-fill layouts. Page 60

Figure 7.23: Contours of 99 percentile significant wave heights of both locally wind-driven waves and swell entering the port for winter (July) for the pre-construction (upper panel) and postconstruction (lower panel) Pier 1 in-fill layouts. Page 61

Figure 7.24: Contours of 99 percentile significant wave heights of both locally wind-driven waves and swell entering the port for spring (October) for the pre-construction (upper panel) and postconstruction (lower panel) Pier 1 in-fill layouts. Page 62

Figure 7.25: Contours of significant wave heights of both locally wind-driven waves and swell entering the port under assumed worst case conditions in terms of offshore swell entering the port (Hm0 = 3.5 m, Tp = 9s and wave direction = 38 degrees TN) for the pre-construction (upper panel) and post-construction (lower panel) Pier 1 in-fill layouts. Page 63