Meeting with Stockland & Covey Associates – 12 Nov 2025

Twin Waters West

Meeting with Stockland & Covey Associates

Meeting Notes 12/11/2025

On 12 November the Development subcommittee met with Stockland to discuss a variety of questions related to the TWW lake design & operation around concerns expressed by Twin Waters residents.  The design consultants presented a comprehensive review of the design, the results of modelling and answered numerous follow-up questions from our committee.  Below are the key take-aways from the meeting.

1. Lake
   1. It was clarified that the water level in the TWW lake will only average 20-40cm above the existing TW lake. Our current understanding is that, because of the difference of tidal impacts on the two lakes average low tides will see the existing lake being approximately 750mm below the new lake and at high tides the existing lake will be approximately 150mm above the new lake
   2. The TWW lake will be fed in two manners with tidal flow from the river at high tides and intermittent pumped flow from the TW lake. The pumped supply from the TW lake will be controlled automatically based on salinity monitors at both ends of the lake in order to maintain the proper salinity levels for the ecosystem in the new lake since rain events will dilute the salinity of the lake thus threatening the lake ecosystem if not managed.  The pumps will also cycle on every 3 days regardless of salinity.
   3. Design & modelling data was reviewed which demonstrated that the nominal volume of water to be drawn from the existing TW lake will have no impact on flow velocities in the TW lake and therefore pose no threat to the revetments in the current lake due to the volume of the existing lake and the cross section of the feeder canal to the intake pumps
   4. The river end of the lake will discharge into an area along the riverbank which will be planted with mangrove trees as a revegetation area and from there will be connected to the river via 2 pipes which will allow bidirectional flow providing for tidal flow into the TWW lake similar to the existing lake.
   5. Various types of revetments will be used along different sections of the new TWW lake. Sheet pile will predominantly be used in the area of the lake discharge and the side of the lake nearest the Sunshine Coast Motorway.  Both of these areas are several hundred metres from existing TW residents and therefore the ground vibrations from the drivers should not impact on any residents. A coffer dam will also be built to enable construction of the intake system, which will be installed below the waterline around the northern weir. The coffer dam will also need to be sheet piled. The northern weir will also require a sheet pile to its length. However, these will be small scale, temporary works, excepting the weir sheet piling, which is permanent. Vibration monitoring will be undertaken by the contractor, who will notify surrounding residents in advance of the works.
2. Intake
   1. There will be an intake structure, suction / discharge pipe and underwater pump.
   2. The structure design and pumps will be similar to other developments on the Sunshine Coast with the pump being submerged which results in negligible noise above ground.
   3. The intake pipe and suction box will be fully submerged and will be covered with a screen to meet Queensland requirements (3mm) which will preclude capture of marine fauna.
3. Discharge
   1. The discharge end of the lake, nearest the river, will be a structure similar to a dam spillway which is flooded at most times. This spillway will connect to an outfall pit which will be connected to the river via 2 underground pipes.
   2. The combination of the spillway and design of the outfall pit/piping are designed to maintain a wet area for the regeneration of a mangrove field between the lake and the river. Stockland will plan new mangrove trees to accommodate regeneration of this area.
   3. The two pipes will allow bi-directional flow between the lake/spillway and the river in much the same way as the pipes in the existing TW weir functions but at much reduced volumes.
   4. During low tides (approximately 2-3 hrs, twice per day) water will drain from the lake into the discharge pit which is approximately 1m deep with a sloping bottom to minimize the sound generated by the falling water. The resultant sound will be significantly less than that generated by the water topping the weir and gabion barriers at the existing TW weir.  This combined with the distance to the nearest existing residence and the vegetation which will surround the pit should provide for minimal, if any noticeable noise in existing Twin Waters residences.