Technical Assistance Consultant's Report Nauru: Sustainable And
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Technical Assistance Consultant’s Report Project Number: 48480 December 2017 Nauru: Sustainable and Climate-Resilient Connectivity Project Financed by the Asian Development Fund Prepared by Cardno Emerging Markets Fortitude Valley, QLD, Australia For Ministry of Finance Implementing agency This consultant’s report does not necessarily reflect the views of ADB or the Government concerned, and ADB and the Government cannot be held liable for its contents. (For project preparatory technical assistance: All the views expressed herein may not be incorporated into the proposed project’s design. TA-9009 NAU: Sustainable and Climate Resilient Connectivity in Nauru– PPTA Consultants (48480-001) MetOcean Design Criteria and dependent on a range of variables including the surface flow, the shape of the island and the depth of the surface layer. Figure 12 shows an example taken from Dong et al. (2007)17 Figure 12 Example of an island wake from modelling by Dong et al. (2007). Diagram shows vorticity due to eddies. 17 Dong, C., McWilliams, J.C. and Shchepetkin, F. (2007). Island Wakes in Deep Water. J. Phys. Oceanogr., 37, 962-981. DOI: 10.1175/JPO3047.1 TA-9009 NAU - MetOcean_Design_Critera_Revision 3.docx 24 July 2017 Page 28 of 37 TA-9009 NAU: Sustainable and Climate Resilient Connectivity in Nauru– PPTA Consultants (48480-001) MetOcean Design Criteria 46. As an initial investigation into this phenomenon, and to see whether it would explain the currents reported by the Pilot, the numerical modelling software Delft3D was used. A steady current from the east with a speed of 0.25 m/s (0.5 knots) was imposed. The bathymetry of Nauru was used in the model. In this somewhat idealized scenario, a wake was formed on the western side of the island with oscillating flow in the vicinity of the port. Figure 13 and 14 show the modelled flow at two times, 10 hours apart. The island of Nauru is the clear area in the center of the image. The reversing flow can be seen on the western side of the island. Figure 13 Modelled currents in an idealised steady westwards current showing southwards flow off the port. TA-9009 NAU - MetOcean_Design_Critera_Revision 3.docx 24 July 2017 Page 29 of 37 TA-9009 NAU: Sustainable and Climate Resilient Connectivity in Nauru– PPTA Consultants (48480-001) MetOcean Design Criteria Figure 14 Modelled currents in an idealised steady westwards current showing northwards flow off the port. 47. The oscillating flow from the model is shown in Figure 15 which is the northwards component of the flow at a point off the port site TA-9009 NAU - MetOcean_Design_Critera_Revision 3.docx 24 July 2017 Page 30 of 37 TA-9009 NAU: Sustainable and Climate Resilient Connectivity in Nauru– PPTA Consultants (48480-001) MetOcean Design Criteria Northwards current (m/s) current Northwards Figure 15 Modelled northwards current component for a location off the port site 48. The period of the oscillations in Figure 15 is just over one day, however this model is an idealised situation and does not include all the relevant phenomena. It is possible that the tidal currents, although small may interact with the eddy formation in the wake to produce a regime which resembles a tidal current although it is not the astronomical tide which is driving it. 49. The modelling is preliminary and idealized, but does demonstrate that with realistic inputs, it is likely that relatively strong currents will be experienced off the port site. The modelling shows that these currents are likely to be oscillating and therefore there will be relatively frequent times of low current speeds which can be used for berthing activities if required. It also suggests that real-time monitoring of the currents at the port location would be a very useful aid to the port operations. Such monitoring could be achieved by a horizontal looking ADCP mounted on or near the port infrastructure. It may also be possible to use one of the port vessels to check on the presence or absence of currents before berthing operations. Further modelling could be undertaken, but would require a field measurement program to generate data for model calibration and validation and this is beyond the scope of the present investigation. 6.2 Climate Change 50. There are no detailed predictions on the impact of climate change on the ocean currents in the vicinity on Nauru. In part this is due to the lack of detailed understanding of the mechanism of generation of the currents. However, given that the foregoing background discussion suggests that it is regional currents which drive the local currents adjacent to the port, some inferences can be drawn. The equatorial current which is observed in the TAO mooring data and which appears to drive the local currents, is in turn driven by the trade winds and changes in water temperature between the east and west Pacific Ocean. Specific changes in the trade winds are not included in climate forecasts for Nauru, however the effects of changes in the TA-9009 NAU - MetOcean_Design_Critera_Revision 3.docx 24 July 2017 Page 31 of 37 TA-9009 NAU: Sustainable and Climate Resilient Connectivity in Nauru– PPTA Consultants (48480-001) MetOcean Design Criteria winds are reflected in changes in the wave climate and these are forecast to be small. Changes in the water temperature are a function of ENSO (El Nino/La Niña) and the future behavior of ENSO is “unclear”18. These results suggest that there will not be any major change in the current system around Nauru due to climate change, however there is significant uncertainty in this conclusion. This means that the selected option for the port for Nauru must be as resilient as possible with regard to ocean currents. The ship simulations reported in the following section show that Options 2 and 3 are better able to cope with ocean currents and are therefore more resilient in this area. 7 CLIMATE CHANGE RESILIENCE 7.1 Background 51. There is significant uncertainty regarding the impacts of climate change on the Nauru port. There will undoubtedly be impacts from sea-level rise and this is the most reliably predicted impact. However the limiting factor for port operations, particularly the existing port facilities, is the wave climate. The present day operations are subject to downtime resulting from wave activity form the westerly sector. There is limited information available concerning downtime due to weather in port operations. The most complete data comes from JICA (2014)19 and indicates the number of days of operation lost through heavy weather (Table 3-4 of the JICA report). The table is reproduced as Table 6. Table 6 Number of days of port operation lost to heavy weather (JICA, 2014) Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 2001 0 1 0 0 3 5 1 4 0 2 3 23 42 2002 8 10 0 3 2 4 14 8 19 20 8 18 114 2003 15 5 0 3 3 5 2 1 0 2 1 1 38 2004 21 3 7 5 0 7 4 8 0 0 0 11 66 2005 - - - - - - - - - - - - No data 2006 - - - 5 0 1 6 12 2 27 13 5 71in 9M 2007 - 5 4 0 2 0 0 0 0 0 4 5 20 2008 - - - - - - - - - - - - No data 2009 - - - - - - - - - - - - No data 2010 - - - - - - - - - - - - No data 2011 2 0 1 0 1 0 0 1 1 - - - 6 in 9M Total 46 24 12 16 11 22 27 34 22 51 29 63 52. The data in Table 6 shows that 2002 was an exceptional year for downtime, particularly the second half of the year. It is noted that Figure 2 and Figure 5 indicate that 2002 is as a year 18 PACCSAP. (2015) Current and future climate of Nauru. Pacific-Australia Climate Change Science and Adaptation Planning Program 19 JICA (2014). The Preparatory Study on the project of Constructing Reef-edge Quaywall and Causeway at Aiwo Harbour. Japan International Cooperation Agency. TA-9009 NAU - MetOcean_Design_Critera_Revision 3.docx 24 July 2017 Page 32 of 37 TA-9009 NAU: Sustainable and Climate Resilient Connectivity in Nauru– PPTA Consultants (48480-001) MetOcean Design Criteria of exceptional wave occurrence from the west and with larger waves than normal. The year 2006 also shows as having more downtime than other years and this year has a higher frequency of westerly winds and waves than many other years, but less than 2002. 53. It was noted in commentary on Figure 2 and Figure 5 that the years 1997, 2002 and 2015 had stronger winds and waves from the west than other years. Using the hindcast wave data, the operability (see Figure 6) for these years was compared with the average over all hindcast years. The results for the percentage of time with Hs above 1.0 m for varying durations is shown in Figure 16. Figure 16 Port operability for a threshold of Hs = 1.0 m for varying durations 54. Figure 16 shows that both 1997 and 2002 have significantly more time with significant wave height above 1 m compared with the average, 39%, 32% respectively compared with 16% on average. It can also be seen that these exceedances occurred in longer durations with multiple periods between 240 and 360 hours (10 – 15 days) in 1997 and between 360 and 720 hours (15 – 30 days) in 2002. These are significant periods of interruption to the supply chain of essential supplies for Nauru. 55. The identified years were therefore investigated in more detail to examine the characteristics of the climate in those years. The following are extracts from “Climate Assessment” and “State of the Climate” reports from the Bulletin of the American Meteorological Society (note MJO refers to the Madden-Julian Oscillation and is discussed further below): The global climate during 1997 was affected by both extremes of the El Niño–Southern Oscillation (ENSO), with weak Pacific cold episode conditions prevailing