Gold Coast Water is responsible for the management of the water, recycled water and wastewater assets of the City of the Gold Coast on Australia's east coast. Excess treated recycled water is released at the Gold Coast Seaway, a man-made channel connecting the Broadwater Estuary with the Pacific Ocean, on an outgoing tide in order for the recycled water to be dispersed before the tide changes and re-enters the Broadwater estuary. Rapid population growth has placed increasing demands on the city's recycled water release system and an investigation of the capacity of the Broadwater to assimilate a greater volume of recycled water over a longer release period was undertaken in 2007. As an outcome, Gold Coast Water was granted an extension of the existing release licence from 10.5 hours per day to 13.3 hours per day from the Coombabah wastewater treatment plant (WWTP). The Seaway SmartRelease Project has been designed to optimise the release of the recycled water from the Coombabah WWTP in order to minimise the impact to the receiving estuarine water quality and maximise the cost efficiency of pumping. In order achieve this; an optimisation study that involves intensive hydrodynamic and water quality monitoring, numerical modelling and a web-based decision support system is underway. An intensive monitoring campaign provided information on water levels, currents, winds, waves, nutrients and bacterial levels within the Broadwater. This data was then used to calibrate and verify numerical models using the MIKE by DHI suite of software. The Decision Support System will then collect continually measured data such as water levels, interact with the WWTP SCADA system, run the numerical models and provide the optimal time window to release the required amount of recycled water from the WWTP within the licence specifications.
Significant urban development surrounding the Gold Coast Broadwater and upper catchment has resulted in concerns about degrading water quality of the estuarine system. The Gold Coast Seaway plays an important role in the exchange of estuarine and oceanic waters influencing the intertidal waters of the region. Water quality within the Gold Coast Seaway and the immediately adjacent Broadwater was investigated three times at three sample depths at 13 sample locations. Conductivity, temperature, and depth casts, total (nitrogen and phosphorus) and dissolved inorganic (NO x and NH 4 +) nutrients, and fecal indicator bacteria were measured at hourly intervals to compare the water quality under different tidal conditions at each location. Hydrological data were also collected. From these measurements, the intratidal variability of the Seaway waters was determined. Observed current velocities ranged from 0.001 to 0.909 m s 21 and 0.018 to 1.8 m s 21 during neap and spring tide periods, respectively. Physical parameters and nutrient concentrations demonstrated typical cyclic variations, with the influence of tidal and diurnal cycles apparent. Near minimum and maximum concentrations were generally observed at high and low water, respectively, indicating the influence of oceanic water during flood tides and catchment waters during ebb tides. Significant correlations were observed between surface water salinity values and total nitrogen and phosphorus concentrations. Fecal coliforms and Enterococcus spp. concentrations were low (,60 colony-forming units per 100 mL 21), with no significant trends apparent between concentration and sample location, depth, or tidal phase.
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