Identifying material repelling areas in coastal water systems through Lagrangian coherent structures

Lagrangian coherent Structures (LCS) are useful to investigate material transport and have only recently been applied to coastal waters. Identification of material lines by LCS in a chaotic flow can assist in highlighting areas of strong spreading of floating materials in waterways. Here we investigate the persistent areas of potential strong spreading of floating materials in a semi-enclosed tidal embayment using LCS. The analysis is performed on the output of a hydrodynamic model of Moreton Bay, a semi-enclosed subtropical embayment on the east coast of Australia. The forward finite time Lyapunov exponent (FTLE) is used as diagnostic for repelling material lines which signals areas of strong spreading. The work presents the tidal asymmetry results for the investigation of strong repelling of floating pollution and contaminants. The results indicate that in the spring and ebb tides, persistence of repelling material is more prominent than neap and flood tides.