Mars Creek Rehabilitation
2012 saw the first stage of work commenced under an ambitious environmental plan for the University’s major water course Mars Creek.
Mars Creek drains from the suburb of Marsfield and flows for over a kilometre through Macquarie University and directly into the Lane Cove National Park. The valley of Mars Creek comprises the largest area of open green space in the University, and has considerable potential for innovative environmental management.
Urban creeks are beset with a variety of impairments to their long term integrity as habitats. Researchers have dubbed these challenges collectively as the ‘urban stream syndrome’.
Effects of this syndrome can be reduced, and habitat value allowed to recover, if measures are put in place to help the creek environment ride out the extremes that urban runoff imposes. These artificial extremes include:
- Increased erosion energy from the peak flows entering the creek from roads, roofs and drains during storms
- High sediment and elevated nutrient carried in from the urban catchment
- Reduced contribution of clean groundwater to the creek’s flow during dry weather, risking stagnation and drying out
- Lack of shading, poor habitat complexity and associated food chains where native vegetation is absent along the creek edge
Using natural and biodegradable materials,the first 200 metres of Mars Creek have been re-shaped from an ‘erosion ditch’ into a sinuous pattern of pools and riffles. The gently sloping banks are now softened by dense plantings of native sedges and grasses. A vegetated buffer zone extends along both sides of the rehabilitated creek.
Improved Water Quality and Reduced Flooding
Water filtration and reduction of peak inflows occurs through an onsite ‘Treatment Train’. Storm flows are firstly routed through a 30,000 litre underground pollutant trap, leaving behind most of their litter and sediment.
Downstream of this unit is a 200 square metre reed-bed wetland. The diverted water is slowly released back into the creek environment over many hours. Water leaving our treatment train re-enters the creek having been through significant natural filtration for removal of urban pollutants and sediments.
Vegetation ‘swales’ intercept several smaller storm water pipes, to improve these sources before they reach the creek.
Stream Watch analysis at points along the creek reveals an improvement in many of the attributes of water quality as water testing progresses downstream through the rehabilitated section. Water re-entering the creek from the treatment wetland is in particularly good shape in terms of its salinity, turbidity (mud content) urban nutrient levels, and dissolved oxygen values.
A second basin - the back swamp - provides temporary flood storage and a sedge-land habitat, attractive to frogs and other wildlife.
A mesh-deck footbridge across the creek connects with existing footpaths.
The Bigger Picture
This work forms part of a catchment-scale environmental plan, produced under Property's Sustainability Projects in 2011 for Mars Creek.