CHAPTER 7 • The Implications of Oceanographic Chaos for Coastal Management
137
mum concentration, and the duration of these high concentration events are predicted
to be highly variable temporally and spatially. A mean and a standard deviation at target points are insufficient to characterize the impact because essentially the situation
is chaotic.
7.7
River Plumes
River plumes are often very patchy, especially when the coast is rugged and the freshwater discharge unsteady. An example is the Burdekin river, Queensland, Australia. The
plume is extremely patchy (Fig. 19). Oceanographers are able to successfully model this
plume (King et al. 1998). The results, shown in Anim. 32, show the plume forming as
the riwr discharge increases. It turns left at the mouth, a result of the Coriolis force,
and flows northward along a rugged coast around numerous headlands and islands.
The model suggests that the patches are due to the unsteadiness of the wind and to the
freshwater discharge, and to the complex currents at the headlands. The patchiness in
the salinity field was also enhanced by discharges from neighbouring rivers and by
tidal interactions with headlands along the coast. The model underestimates by a factor of about 2 the observed patchiness at the reef (Wolanski 1994), patchiness in this
case being the amplitude of the salinity variability at times scales of 2-5 days.
The main influences on the size of the river plume, and thus on which reefs are
impacted, are the discharge volume of the river and the local wind forcing. These vary
annually, so one would expect different reefs to be impacted differently each year. Given
that the fate of the plume is highly variable and patchy, a risk assessment analysis from
a hindcast of the floods for the last couple of decades is needed to quantify the impact
of river floods on the Great Barrier Reef. This is achieved by simulating many years of
floods and by quantifying the recurrence and duration of freshwater impact on given
reefs.
This modelling capability provides a tool to assess physical impacts to reefs from
riverine material (e.g. fine sediment and nutrients) produced as a result of various land
management policies in the catchment area. Although the physical impact is chaotic,
it can be quantified statistically although the model underestimates the patchiness. The
resulting ecological impact probably cannot be predicted yet. Research on the biological response of reefs to such transient forcing clearly is warranted because riverine
material affects the biology of coastal waters and its quality and quantity are both
greatly affected by human land use.
7.8
Discussions
Topographically complex environments include rugged coastlines comprising headlands and islands, coral reefs and mangrove-fringed coastal waters. While our examples refer to tropical environments, the conclusions probably apply also to temperate
systems with a rugged coast with headlands, shoals and salt marshes. Such environments are common in the world, yet they have been little studied compared to
topographically simple systems such as the North Sea, where there are continental
shelves with comparatively straight coastlines. Physical, biological and chemical data
137
mum concentration, and the duration of these high concentration events are predicted
to be highly variable temporally and spatially. A mean and a standard deviation at target points are insufficient to characterize the impact because essentially the situation
is chaotic.
7.7
River Plumes
River plumes are often very patchy, especially when the coast is rugged and the freshwater discharge unsteady. An example is the Burdekin river, Queensland, Australia. The
plume is extremely patchy (Fig. 19). Oceanographers are able to successfully model this
plume (King et al. 1998). The results, shown in Anim. 32, show the plume forming as
the riwr discharge increases. It turns left at the mouth, a result of the Coriolis force,
and flows northward along a rugged coast around numerous headlands and islands.
The model suggests that the patches are due to the unsteadiness of the wind and to the
freshwater discharge, and to the complex currents at the headlands. The patchiness in
the salinity field was also enhanced by discharges from neighbouring rivers and by
tidal interactions with headlands along the coast. The model underestimates by a factor of about 2 the observed patchiness at the reef (Wolanski 1994), patchiness in this
case being the amplitude of the salinity variability at times scales of 2-5 days.
The main influences on the size of the river plume, and thus on which reefs are
impacted, are the discharge volume of the river and the local wind forcing. These vary
annually, so one would expect different reefs to be impacted differently each year. Given
that the fate of the plume is highly variable and patchy, a risk assessment analysis from
a hindcast of the floods for the last couple of decades is needed to quantify the impact
of river floods on the Great Barrier Reef. This is achieved by simulating many years of
floods and by quantifying the recurrence and duration of freshwater impact on given
reefs.
This modelling capability provides a tool to assess physical impacts to reefs from
riverine material (e.g. fine sediment and nutrients) produced as a result of various land
management policies in the catchment area. Although the physical impact is chaotic,
it can be quantified statistically although the model underestimates the patchiness. The
resulting ecological impact probably cannot be predicted yet. Research on the biological response of reefs to such transient forcing clearly is warranted because riverine
material affects the biology of coastal waters and its quality and quantity are both
greatly affected by human land use.
7.8
Discussions
Topographically complex environments include rugged coastlines comprising headlands and islands, coral reefs and mangrove-fringed coastal waters. While our examples refer to tropical environments, the conclusions probably apply also to temperate
systems with a rugged coast with headlands, shoals and salt marshes. Such environments are common in the world, yet they have been little studied compared to
topographically simple systems such as the North Sea, where there are continental
shelves with comparatively straight coastlines. Physical, biological and chemical data