Beachmere Lake

Beachmere Lake is a constructed lake which plays an important role in stormwater and flood mitigation for the Beachmere community.  The lake also provides significant visual amenity for the surrounding residential properties and is connected to the ocean via a tidal exchange system, which assists in maintaining good water quality within an estuarine environment.

Council will be carrying out a number of improvements to Beachmere Lake to improve functionality.

Updates on the project will be provided regularly. Current information published June 2020.

Location

Kunde and Biggs Avenue, Beachmere 4510  View map

Google Map

The current lake revetment wall is made of timber and shows signs of failure in a number of sections.

Renewal of the lake wall was proposed to occur during 2019, however, these works were delayed following the fish kill that occurred in March 2019 and the subsequent water circulation system maintenance inspections.

Council officers have recently reviewed the scope of works and have revised the areas of lake wall that will be upgraded.

The design is currently underway and on-ground work is likely to commence June 2020 weather permitting and will include the complete replacement of the timber wall with a vinyl sheet pile solution as well as replacing sections of the tidal exchange system to improve function and maintenance access. An overview of the revetment renewal is planned as illustrated.

Beachmere Lake revetment wall replacement
  1. Revement walls to be replaced.
  2. No change to existing concrete wall.
  3. Additional wall section to be constructed.
  4. No change to vegetated banks.
  5. No change to existing overflow drain.

Water circulation within Beachmere Lake.

Beachmere Lake water circulation

 

  1. Inlet valve

    Operation sensitive to lake water level.

  2. Outlet weir
    Critical for optimal operation of lake tidal exchange.

  3. Tidal flaps
    These flaps allow excess stormwater to drain into the swamp area but prevents flows from the swamp entering the lake system.

Inflow

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.

Outflow

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.

Beachmere Lake - Overflow weir


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.

Sediment removal

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.

A water quality buoy is located within the lake. This buoy sends information on the quality of the water electronically to Council, such as water levels, dissolved oxygen concentration, pH and temperature. In addition, an alarm system has been set up to alert Council to conditions that could potentially result in poor water quality.

Three aerators (bubblers) are installed in the lake to assist with water circulation and the mixing of salt and fresh water. Typically, freshwater will sit above salt water in an estuarine environment. The aerators assist by mixing the freshwater and salt water, reducing the risk of poor water quality conditions. The compressor that provides air to the aerators has been upgraded to a quieter and more efficient unit.

In March 2019 the water quality of the lake was impacted causing fish in the lake to perish. An assessment of the lake’s circulation system was conducted and testing of water quality and algae also occurred.

The analysis of these tests indicates that several factors contributed to the fish kill, including:

  • a significant rainfall event following a period of dry weather, resulting in the influx of nutrient-rich stormwater into the lake
  • blockages and non-performance of the stormwater overflow system
  • partial blockages within the tidal exchange system.

Collectively, these factors resulted in the lake containing nutrient-rich stormwater for an extended period which lead to an algal bloom. The algal bloom affected dissolved oxygen concentrations in the lake, contributing to the fish kill.

In response to this situation several initiatives have been completed, including:

  • inspecting (via closed circuit camera) all the pipework and circulation system components as outlined in Water circulation system maintenance.
  • reviewing the functionality of the stormwater overflow weir
  • assessing the tidal exchange system and investigating options to supplement the system.

This information has been used to guide the design upgrades that will be implemented in the upgrades to the system.

Council have engaged a specialist fisheries consultant to assist in identifying the most suitable process for managing adult fish populations in the lake into the future. Options could include a program of regular catch and release from the lake to the Caboolture River, or a fish passage device designed to allow the movement of fish without impacting on the tidal exchange system or reducing the stormwater and flood mitigation function of the lake. This project has now commenced and is due for completion late 2020 with outcomes of the strategy to be implemented as soon as practical. Council is seeking advice from specialist fisheries experts to assist in identifying the most suitable process for managing adult fish populations in the lake into the future. Options could include a program of regular catch and release from the lake to the Caboolture River, or a fish passage device designed to allow the movement of fish without impacting on the tidal exchange system or reducing the stormwater and flood mitigation function of the lake. 

The aerator system is also under investigation and will be upgraded due to the increased maintenance issues and inability to access parts to repair when necessary. The installation of the new system previously scheduled for June 2020 will be delayed to later in the year due to interruption in supply of new equipment due to COVID associated impacts.