Creek care and maintenance
Channel erosion and deposition is a natural process for creeks of all sizes. However in many urban areas land use change and continued development have continued to impart extra pressure on the areas creeks. There are a number of general rules that you can follow to help maintain a natural balance of erosion and deposition.
Maintain Riparian Vegetation
The plants that grow on the banks and in the channel are very important for stability of a channel. It is best to ensure that ground covers, mid-storey and canopy species are present. At a minimum there must be a stable, established ground cover covering the banks.
Avoid removing woody debris and plants
Where a plant is growing or branches fall and accumulate in a creek, try to avoid removal. These features slow down water flow and decrease its power causing erosion. However in some circumstances they are a flood hazard, or cause localised scour that threaten infrastructure or assets. If this is the case the debris may need to be removed.
Use "soft engineering" to stabilise channels
In certain circumstances it may be necessary to stabilise an eroding channel through re-grading the banks, adding vegetation and/or strategically placing natural features such as logs. However any works such as this should be designed and constructed by appropriately qualified professionals and be carried out under a development application.
Use "hard engineering" to stabilise channels
"Hard engineering" such as rock lining, channel re-alignment and/or other significant work is required to stabilise a channel. These works should be designed and constructed by appropriately qualified professionals and be carried out under a development application.
Any significant work within a channel must be in accordance with Council's DCP 47 (Water Management). Major works within a creek channel are a controlled activity and must be considered during the planning program.
Sound engineering design requires additional protection at all pipe and culvert inlets and outlets. This should be designed by a qualified engineer using suitably sized natural materials and constructed in a manner that complements the receiving environment. Further information can be found in the fact sheet guidelines for controlled activities - outlet structures from the Department of Water and Energy.
Riparian vegetation and weeds
We have compiled an aquatic and riparian vegetation weed list for Ku-ring-gai.
Riparian Vegetation List (pdf. 1MB)
Natural channel design
It is important to keep as much of a river network as natural as possible to ensure that the catchment and river condition can be maintained. In Ku-ring-gai much of the urban development is concentrated along the interfluve areas with the lower parts of the catchments being dominated by protected areas such as national parks and significant estuaries. Maintaining natural channel design wherever possible allows ecological, geomorphic and hydrological processes to be maintained, and minimises the degree of negative impact on the downstream valuable areas.
Many different species live in the creeks and riparian areas around Ku-ring-gai. Some of the most common native species include:
Eastern Water Dragon
Striped Marsh Frog
Long finned eel
Whirligig water beetle
Long neck turtle
The introduced species commonly found in creeks and riparian areas include:
Snails (from NZ)
What is it?
If you have noticed a slimy brown/orange residue in your local waterway or drain, it may be iron bacteria, a naturally occurring micro-organism. Iron bacteria is a natural part of the ecosystem and while the visual impacts of iron bacteria are unsightly there is no evidence that suggests the presence of iron bacteria is harmful to our personal health, or the health of our waterways.
Why does it happen?
The presence of iron bacteria in our waterways is associated with the amount of dissolved iron present in the water. Iron bacteria may become evident after heavy rain when iron leaches from the soil into runoff which flows to our waterways. Also, iron becomes more soluble in water where there is little or no oxygen, such as groundwater, so iron bacteria may also be evident during drier times in waterways that receive sub-surface and groundwater flows. When oxygen, water and iron combine they create the right environment for bacteria to bloom. Iron bacteria need to oxidise iron to give them energy. A chemical process occurs, which involves changing ferrous iron (Fe2+) into ferric iron (Fe3+). This process makes the iron insoluble and produces the slimy brown/orange residue you may have noticed in our waterways.
Is it iron bacteria?
There are two quick and simple tests to help you assess that you're looking at iron bacteria and not a pollution incident.
Surface test - Poke a stick into the material that looks like an oily film on top of the water. If the surface fractures like ice and does not join back together, it is most likely to be related to iron bacteria. However if the substance clings to your stick and joins back together after breaking the surface, then it could be oil.
Smell test - If the odour smells like decaying matter, this is OK - the odour is most likely caused from the bacteria dying. However, the substance should not smell toxic like sewage, chemicals, petrol or oil.