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Sea Cage Aquaculture
The physics of Conn Creek
Understanding the movement of water in the vicinity of the farm is
crucial to understanding ecosystem processes, as well as to estimate the
physical removal of wastes. To understand the physics of Conn Creek, AIMS
scientists first described the physical structure of the water and
monitored diurnal change in physical variables. They then developed a
two-dimensional model of water movement in Conn Creek, and validated this
by direct measurement of currents.
A two-dimensional numerical hydrodynamic model was
applied to describe the movement of water in the vicinity of the farm. The
numerical model computed water surface elevations and horizontal velocity
components on a computational domain that covered the majority of Conn
Creek and surrounding mangrove catchment. The model was validated against
observed current velocities within the creek. The flushing characteristics
of Conn Creek were simulated by releasing a virtual passive tracer into
the model from within a sub-region of Conn Creek that included the area of
the farm. The tracer was initialised within the sub-region with a
concentration of 100mg L-1 and zero elsewhere. Predicted tidal forcing was
applied to the domain and the advection/diffusion of the tracer was
simulated using the computed hydrodynamics during both spring and neap
tide.
In the following animations, the predicted concentration
of the plume of virtual passive tracer is given by the accompanying
colourbar, with the maximum concentration (100mg L-1) shown as red,
changing to yellow for 5mg L-1. The simulated plume becomes transparent
when concentration approaches background levels.
These animations show the modelled dispersion of this
passive tracer in Conn Creek.
Neap mangroves flush
shows the behaviour of the tracer during a neap tide cycle.
Spring mangroves flush
shows the behaviour of the
tracer during a spring tide cycle.
These models indicate the tidal flushing times in Conn Creek are rapid.
Tidal exchange removes 60% of the water within Conn Creek within 12h
during spring tides and within 24h on neap tides. This is an effective
mechanism for the removal of suspended and dissolved wastes from Conn
Creek.
