Gold Coast Broadwater Assimilative Capacity Study

Transcription

1 Gold Coast Broadwater Assimilative Capacity Study A Journey Toward a Smart Environmental Release Sayed Khan Gold Coast Water 12 Th International RiverSymposium, Brisbane 23 September 2009

2 Presentation Overview Gold Coast Snapshot Coombabah Recycled Water Journey Broadwater Assimilative Capacity Study Seaway SmartRelease Initiative

3 The Gold Coast Population to grow from 0.5 to 1.2 m Growth of 14,000 persons/year 10.3 million tourists/year 1,402 km2 and 70 km of beaches Extensive river systems, beautiful coast line and Broadwater estuarine system are part of Gold Coast lifestyle Community expectations and awareness

4 Recycled Water Release System 4 Wastewater Treatment Plants Current combined capacity of 130 ML/day RW usage ~ 18 ML/day 112 ML/day excess recycled water released to the Seaway Two release diffusers at the Seaway (Coombabah and Benowa system) EPA licence controls environmental release In 50 years time recycled water volume to grow 3 folds (350 ML/day)

5 Coombabah Catchment Existing Capacity Catchment

6 The Challenges.. Capacity of release system is 65 ML/day. Actual flow was nearing the above capacity An immediate short-term solution was required Licence allowed for discharge 10.5 hours per day Existing Capacity 10.5 hours Council was developing a draft Recycled Water Strategy to develop long-term solutions An interim solution was required

7 The Journey Began.. In 2004, the Coombabah Waterfuture Committee was formed They investigated 12 short-term options over a period of 2 years In February 2006, the Committee recommended storage ponds at South Stradbroke Island

8 Back to the Drawing Board.. A new Advisory Committee was set up in May 2006 This committee re-assessed all the short-listed options again and recommended the duplication of existing release pipe The cost of pipe duplication was estimated as $60.5 Million In Nov 2007, GCW completed the Assimilative Capacity Study and lodged licence application to EPA Council s approval of the pipe duplication was subject to the pending EPA decision

9 Broadwater Assimilative Capacity Study Utilised GEMS HD model developed jointly by Council and Griffith Centre for Coastal Management Assimilative Capacity Model (Mike21) - ~50m grid - flux boundaries from the GEMS model Detailed 3D fine scale model - investigate near-field mixing - fine scale with Seaway only (~5m) - 10 vertical layers (~1m near outlets) HD model upgraded to Advection Dispersion model Dye testing to calibrate the AD model

10 Low to High Water fluxes Flushing Characteristics 36 GL Spring Tide 20 GL Neap Tide 21 GL Between High and Low tide 11 GL Between High and Low tide 65 GL 35 GL 8 GL 4 GL Highly flushed system - up to 100 GL tidal exchange a day 100 ML/d of recycled water with 100 GL/d of sea water - 1 in 1000 mixing ratio!

11 Release Scenarios Simulated Release scenarios from hrs/day

12 Plume Re-entering Phenomenon

13 Mixing Zone Dynamics

14 Key Findings Phase Lag 1.6 hrs Phase-lag phenomenon observed (average of 1.6 hrs) between the tide level and flow reversal was observed Existing release practice with respect to tide level was not optimal

15 Key Findings Flushing Cycle

16 Summary of Study Findings The Broadwater is very well-flushed Concentration within Broadwater is influenced by the re-entering of released recycled water No long term accumulation occurs within Broadwater as the system is completely flushed over a 5 day period The extended release showed potential marginal increase in the ambient concentration however receiving water could support extending the release times without any measurable adverse effects on water quality or marine habitat The Water Quality Objectives for Broadwater could still be achieved EPA approved a new licence extending the release window by 2.8 hours (13.3 hours/day) The new licence required further optimisation of release window

17 Seaway SmartRelease Project Seaway Monitoring Intensive water quality and current speed measurement 3D Numerical Modelling Further calibration of the AD model and SW model DSS Intelligent Decision Support System for optimal release window

18 Water Quality Monitoring Real-time tide level recording (via telemetry to Coombabah) Boat mounted and permanent ADCPs to record current speed and direction 5 transects, 3 depths, 4 boats, 15 crew members, dawn to dusk sampling Pilot day + 3 intensive monitoring days Extensive WQ sampling (approx 920) collected over February April 2009 TN, TP, NOx and NH 3 enterococci, and faecal coliforms are analysed in Griffith University laboratory Caffeine samples were collected but lab test proved difficult

19 Model Update Further calibration of the HD Model using the intensive WQ monitoring data Further enhancement of HD Model via a Spectral Wave (SW) model including environmental forcing (wind and waves) Wind data from BOM FTP site. Wave constituencies from DHI global wave model Provide computational engine for real time modelling

20 Decision Support System Packaging up of multi-layer information Central database of plant and tidal information Intelligent decision minimising environmental impacts based on: - lagoon level - plant inflow - tide level and current flow - power usage and tariff cost - plume extent in the Seaway Real-time plume animation Project to be completed in Dec 2009