  In coastal water systems, horizontal chaotic dispersion plays a significant
role in the distribution and fate of pollutants. Lagrangian Coherent Structures
(LCSs) provide useful tools to approach the problem of the transport of
pollutants and have only recently been applied to coastal waters. While the
fundamentals of the LCS approach using idealised analytical flow fields are
well established in the literature, there are limited studies on their
practical implementations in coastal waters where effects of boundaries and
bathymetry frequently become significant. Due to their complex bathymetry and
boundaries, unstructured grid systems are commonly used in modelling of coastal
waters. For convenient derivation of LCS diagnostics, structured grids are
commonly used. Here we examine the effect of mesh resolution, interpolation
schemes and additive random noise on the LCS diagnostics in relation to coastal
waters. Two kinematic model flows, the double gyre and the meandering jet, as
well as validated outputs of a hydrodynamic model of Moreton Bay, Australia, on
unstructured grids are used. The results show that LCSs are quite robust to the
errors from interpolation schemes used in the data conversion from unstructured
to structured grid. Attributed to the divergence in the underlying flow field,
the results show that random errors in the order of 1-10 % cause a break down
in the continuity of ridges of maximum finite time Lyapunov exponents and
closed orbit elliptic LCSs. The result has significant implications on the
suitability of applying LCS formulations based on a deterministic flow field to
diffusive coastal waters.
