Mauritius

Ocean Pollution Bulletin on the Wakashio oil spill accident - Mauritius (22 Aug 2020)

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Situation Report
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DISCLAIMER - The information and views set out in this Bulletin are those of the authors (CMCC Foundation and cmcc srl) and do not necessarily reflect the official opinion of the governments of the area. CMCC Foundation and cmcc srl do not guarantee the accuracy of the data included in this study. Neither the CMCC Foundation, cmcc srl nor any person acting on the author's behalf may be held responsible for the use which may be made of the information contained therein.

Contact point: Giovanni Coppini; email giovanni.coppini@cmcc.it; phone: +39 3923857919

Foreword

On the 25/07/2020, the Japanese bulk carrier Wakashio ran aground on a reef in Mauritius leaking between 800 and 1,200 tonnes of fuel oil. Remaining oil has been pumped out by salvage experts. Oil leakage was observed on the 06/08/2020 (Figure 1a) and ESA Sentinel 1,2 imagery for the 10/08/2020 (Figure 1b) indicates that the leakage persisted for at least two days.

The grounding event took place in an area of complex coast morphology and bathymetry (Figure 2). Meteo-oceanographic conditions inside the reef are expected to differ from those found offshore. Extensive satellite monitoring of the spill event indicates that most of the leaked oil ended up in the coastal portion of the coral reef.

The oil spill trajectory and fate were simulated using the MEDSLIK-II oil spill model coupled with Copernicus Marine Service (CMEMS) oceanographic and ECMWF (provided by Aeronautica Militare Italiana) meteorological products. ESA Sentinel-1 SAR imagery for the 10/08/2020 01:37 (Figure 1b) was used to define MEDSLIK-II initial spill conditions (i.e. position and shape). Despite salvaging efforts, fuel oil leakage continued for days after the spill detection. Up-to-date press information indicates that 30m3 of oil are still in the ship.

Given the complexity of the spill scenario, i.e. shipwreck on the reef, and also given the fact that CMEMS Global current fields do not cover the area inside the reef lagoon it has been chosen to simulate the oil spill within the lagoon only with the wind forcing. Oil spill simulation for areas outside the reef lagoon did rely on CMEMS fields.

The spill evolution was simulated with MEDSLIK-II for the period between 10/08/2020 02:00 and the 23/08/2020 23:00 as a composition of three different sources:

  • satellite-detected oil spill (10/08/2020 01:37 UTC)

  • two continuous spills originated at the vessel position representing the spill trajectory inside and outside the reef