COSEM - COntaminant Spread in the Eastern Mediterranean

Case study: documented event of intense garbage transport

Introduction

As a case study, we focused on a dramatic event that took place during November 2010, where large amounts of waste have washed up the shores of Israel [1]. Some of the trash had labels indicating that the origin of the waste is a dump near the city of Tyre, Lebanon [2]. This incident has been taken as a test case for the combined SELIPS and LAgrangian Manifolds and Trajectories Analyser (LAMTA) package to see if it is possible to simulate the transport of pollution. For this purpose a script was written to simulate the emission of tracers continuously from a point. In the simulation that was run, several points in the vicinity of Tyre released tracers to the flow throughout the period of September to November.

Picture from of the waste arriving to the Israeli coast (courtesy of Alex Axelrod).

The flow field used in the simulation consists of forecasted flow fields produced by SELIPS in a configuration which consists of 7 days of hindcast with SST nudging followed by a 5 day forecast. The 5 day time average of the currents at 5 m depth is used in the tracer analysis.

orbits of continuously released tracer particles

Location of tracers (red dots) released continuously from 25/Sep/2010. Blue lines represent the FSLE from SELIPS averaged flow forecast.

Results

The results of the simulation reveals that the simulation correctly transported the tracers south during the second half of October. Finite size Lyaponov exponent analysis shows that the flow field is characterized by an unstable manifold separating the deep water from the coastal region and blocking the deposition of tracers to the shore .

Conclusions

The simulation could not deposit the tracers on the shore. This deficiency in the system requires further investigation as the deposition of pollution on the shore is likely to be of great interest to decision makers in pollution and search and rescue (SAR) events. Several possible processes which may account for this drawback are: wind stress acting on the tracers; wave induced currents which are unmodeled in SELIPS; diurnal or high frequency changes in the current which are averaged out; inaccuracies in the forecasted current field near the shore.