The Banora Point Drainage Scheme is an open channel stormwater drainage system that extends from Lochlomond Drive in the south and discharges into Trutes Bay at its west and Shallow Bay at its east. This system was constructed to enable the development of Banora Point west of Darlington Drive.
Apart from Lake Kimberley which has a limited amount of tidal flushing, the open channels and lakes within the Scheme consist of fresh water. This water regime maintains the natural fresh water habitat zones in Vintage Lakes and surrounds for fauna, particularly the Comb-crested Jacana bird that is listed as Vulnerable under the NSW Threatened Species Conservation Act, 1995
. However, fresh water systems present challenges for aquatic weed control, and over the last decade the Scheme has been increasingly infested by declared noxious weeds such as “salvinia molesta
” and “cabomba caroliniana
”. Other aquatic plants present in large quantities include the commonly known Parrot’s Feather and Wandering Jew that grow across shallows, and also desirables such as Waterlilies and Red Azolla (or Water Fern). Waterlillies provide nesting and foraging areas for Comb-crested Jacana birds, and they cannot be disturbed during the Jacana nesting period of November to August.
Of the abovementioned aquatic plants, Council’s primary focus is controlling the growth of salvinia
. This plant floats on the top surface of a waterbody and in the warmer months can double its mass in 2 to 3 days. Methods used to control this weed include:
- Removal by mechanical harvester. This method is used in the larger ponds of Vintage Lakes and channels in the Banora Waters areas. The weed is removed from site and can be used as a fertiliser. Care must be taken when harvesting that waterlilies are not damaged during operations and that the underwater cabomba weed is not accidently propagated by disturbance.
- Biological control using the ant-sized non-native weevil Cyrtobagous salviniae. This method is used in the Club Banora Golf Course moat where the weevil effectively kills the weed by feeding on the tips of the leaf and tunnelling through the plant stems. The plant noticeably changes colour from a bright green to a dark brown when the weevil activity is strong. The main constraint to this method is that shaded and cooler areas limit the weevil population and activity.
- elective herbicide spraying (undertaken by Far North Coast Weeds on behalf of Council)
Unfortunately, at this point in time there is no effective method of controlling the underwater cabomba weed. Council is aware of trials being conducted by research organisations such as the CSIRO and Department of Primary Industries, and will be guided by their recommendations when a method is found.
The Vintage Lakes ponds often have growth periods of the Red Azolla plant. This plant is in fact a native aquatic fern is not targeted for removal from the waterways unless salvinia is also present and requires removal. This plant can assist in preventing algae blooms by competing with algae for nutrients in the water such as nitrogen and phosphorous.