Overview
An intensive bi-hourly water monitoring program was undertaken to collect data to assist with the calibration of the computational models. This snap shot of water quality data was collected throughout three tidal cycles in February, March and April, in addition to the deployment of Acoustic Doppler Current Profilers (ADCP) to assess the flow dynamics of the Seaway channel.
Design
Water quality samples were collected during a semidiurnal tidal cycle on each of the intensive monitoring days, reflecting the timing of the release of the recycled water under the new DA requirements. Samples were collected at one hour before the release (approximately one hour before the predicted high tide), one, two, three, five, seven, nine and ten hours after start of the release, resulting in 12 hours of sampling. Thirteen samples sites within the Seaway channel and surrounding waters were selected along with sampling directly from the recycled water trunk mains.
Up to 850 individual samples were collected and analysed for the study and were used to investigate water quality dynamics throughout a tidal cycle.
Given the nature of recycled water, water samples were analysed for a range of nutrients and micro-bacteria. The following parameters were measured:
- Total nitrogen (TN)
- Total phosphorous (TP)
- Nitrate/nitrite (NOX)
- Ammonia (NH3)
- Faecal coliforms
- Enterococci
In addition Conductivity, Temperature and Depth casts (CTD) were undertaken to assess changes with the vertical water column and limits of stratification.
Sampling conditions
Example of challenging weather conditions in Seaway
Sampling in such a dynamic environment created its own set of challenges ranging from strong surge force due to the tidal current, wave run-up along the Seaway walls, length of the sampling period and the logistics associated with such a large number of samples collected. IFurther challenges included coordinating four boats, a team of sixteen staff and graduate students, competing activities within the Broadwater (particularly the Seaway channel) and variable weather conditions. Sampling days were postponed on two occasions due to extensive rainfall in February and the impact of Cyclone Hamish in March. Sampling dates were also rescheduled in April and May to avoid dredging activities in the Broadwater that were being undertaken as part of the Broadwater Parkland redevelopment project. However, despite these challenges a safe sampling program was achieved and meaningful data collected.
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