Abstract
HF ocean surface radars routinely map ocean currents at a spatial resolution of the order of 1
km over a coastal area of some 1000 square kilometres with a repeat period of the order of 30
minutes and have become a routine oceanographic and engineering tool. The availability of such
spatial and temporal data allows us to calculate psuedo-Lagrangian tracks for surface particles. It
is now shown that this technology can be used to monitor the spreading of surface particles which
one would encounter in pollution events or dispersion of biological eggs and larvae. This calcula
tion is applied to HF radar data from Port Phillip Bay in Victoria, Australia, using the COSRAD
system. Two case studies are given: one is in an area with a high degree of bathymetric structure,
and the other is in an area with uniform shallow water. We find that the spreading cannot be
explained by eddy diffusion alone but requires the introduction of shears in the tidal flow.
