Water circulation within Beachmere Lake.
- Inlet valve
Operation sensitive to lake water level.
Critical for optimal operation of lake tidal exchange.
These flaps allow excess stormwater to drain into the swamp area but prevents flows from the swamp entering the lake system.
The water intake from the sea is located along Kunde Street (indicated by the yellow line). The sea water only enters the lake through this pipe system when the tide level is 0.5m above mean sea level.
The combination of the size of the inlet pipes together with activation on the top part of the tide is designed to ensure the water entering the lake is sufficient to allow flushing, however is not so much that it causes the level of the lake to rise and impact on nearby homes.
The outflow from the lake is located at the northern end of the lake and is controlled by a weir system. This system allows water to flow back to the sea via underground pipes (indicated by the purple line) for the period when the tide levels are below 0.5m.
The intake and out-take pipes operate continuously, responding to each high tide. Minor fluctuations in water level within the lake occur in response to tidal cycles (typically 100-150mm rise and fall per tide).
Stormwater overflow weir
Stormwater drains (for example curb side gutters) in the surrounding residential areas also flow into the lake.
To cater for stormwater input into the lake during and after rainfall events, a stormwater overflow weir is provided at the southern end of the lake. If, due to rainfall events, lake levels exceed 0.8m, excess stormwater is discharged via this overflow. The overflow weir has been specifically designed to prevent high tide water entering the lake from the mangrove area south of Kunde Street. If water was to enter the lake from this location, impacts to homes may occur.
Tidal exchange system
The existing tidal exchange system was designed to control lake inflows and outflows. The pipework carrying the tidal water has been inspected and cleaned to remove the build-up of growth and restore the hydraulic efficiency of the system. The following images illustrate the pipe condition before and after cleaning.
Additionally, Council officers have identified a number of upgrades to the pipe network that will improve maintenance access and ensure the long term efficiency of the system.
These upgrades are currently being designed and will be included as part of the scope of works during the revetment wall renewal.
A survey of the lake bed has been completed and compared with survey information from 2013. The comparison showed areas of accumulated silt and sediment at the southern end of the lake covering approximately 250 square meters. This sediment has come from the ocean via the tidal inlet.
The desilting work at Beachmere lake is now completed and the park has been reinstated with new turf.