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sca-bluewater-physics


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 flushshows the behaviour of the tracer during a neap tide cycle.

Spring mangroves flushshows 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.