Brisbane City Council is currently in the midst of a $1.1 million investment into the implementation of long-term solutions to address the issues and improve the health of Forest Lake, as part of an overall Forest Lake management plan.
Stage One : Desilting & Reducing the Nutrient Load
The Forest Lake Management Plan provides an evidence-based solution in two stages. Stage One involves strategic desilting at both of the lake’s inlet areas of the lake, aiming to reduce nutrient loads where the nutrient and sediment levels are highest. This will ensure control and management of algal blooms across the lake.
Algal Blooms
Over the summer months, both heat and rainfall have contributed to some significant changes in Forest Lake.
Council has cleaned up debris from lake inlets and from various stormwater quality improvement device units, after storm events in late 2019 and early 2020. Rainfall has resulted in a runoff, introducing additional nutrients into the lake.
Increased water temperature due to the summer weather, coupled with the runoff, constitute ideal conditions for the growth of blue-green and green algae, leading to an observable decrease in water clarity in the lake, and the musty odour that residents and visitors have characteristically observed.
As a result, Council has been extracting pockets of algal build-up in the pockets near Santorini Place and Freshwater Circuit. Likewise, suction trucks are on standby to remove algal blooms as they occur in accessible areas of the lake.
Harvesting Salvinia growth
Salvinia, an invasive plant, has continued to grow at Forest Lake. This growth has actually been helping to minimise blue-green algal blooms at the lake by reducing the nutrient levels in the water.
To prevent Salvinia, overgrowth, Council has been conducting regular monitoring and harvesting. A trial harvest was done in March 2020, using a small machine which was deemed inadequate. Larger equipment has been allocated and harvesting has been planned to ensure that over half of the current Salvinia growth remains in the lake, to make sure that nutrients are kept at a level that does not encourage algal growth.
Drainage Maintenance
As part of Council’s drainage and creek rehabilitation maintenance program, drainage maintenance works have been performed from Jindabyne Circuit to Illawarra Close, along the table drain that leads into Forest Lake at Seabrook Crescent, Forest Lake.
Ongoing maintenance works include desilting of existing sediment ponds, removal of undesirable tree species, clearing of existing drainage infrastructure, channel reinstatement, and stabilisation of the lake’s banks to reduce bed scour and erosion. Maintenance are expected to be completed by mid-2020.
Routine inspection and maintenance procedures are in place to ensure collection of litter, clearing of traps, treatment of weeds, testing of the lake water and monitoring the overall health of the lake.
Management of the Ibis Population
In February 2020, 42 ibises were observed to be roosting at Forest Lake. Waste droppings from the ibis population on the lake has led to excess nutrients which also contributed to algal bloom in the past. The 2020 population is already a significant decline from over 400 ibises observed in 2018.
Wildlife consultants have recommended egg and nest movement, along with vegetation management to further manage the ibis population and prevent it from increasing again.
Vegetation management will ensure that reeds and rushes where ibises roost will be replaced with something less suitable for them to inhabit. Council has announced that the planting of alternate vegetation will be determined by the cattle egret bird breeding season, from September to March.
Stage Two : Replanting Program
Stage Two involves introducing 70,000 new plants in the desilted areas of the lake and also, more broadly around it to further reduce the nutrient levels in the lake. Activities for the first half of 2020 include sourcing of seeds and soil, plus beginning to grow the plants for the lake, according to their life cycles.
Overall Solution
Overall, the Forest Lake Expert Working Group has divided its lake management options into four categories:
- reducing nutrient levels by controlling contributing factors entering the lake and within it;
- managing light availability;
- recreating a more ‘plant-based’ lake system; and
- potentially increasing water movement in the lake to reduce stagnation.
Schedule
BCC has announced a general methodology and schedule which will be updated over time. Below is a copy from the BCC site.
| Action | Date |
|---|---|
| Final strategic management plan | Complete July 2019 |
| Planning and design | Complete August 2019 |
| Approvals, permits, procurement and tendering | August 2019-March 2020 |
| Desilting and replanting | April 2020-late 2020 |
