About a month ago Jamie (who’s a builder) called me and asked if we wanted some sandstone blocks delivered on site. A mate of his was doing some excavating.
I couldn’t let that opportunity pass – we’ll work out what to do with it later!
A few days later I was looking at a small mountain on site.
For a while I had been thinking about the possibility of building a ‘swale’ on the lower part of the site. A swale is a water sensitive urban design (WSUD) feature that in this case, will take stormwater from the neighbouring road, detain and filter it, allow part to permeate, with the treated water returned to the gutters. The location and topography of the site allows this feature to be incorporated into the site simply and efficiently, with minimal works.
It involves excavating a shallow trench, with one end running to a gap that will be cut into the gutter. Sandstone blocks can be used to create short retaining walls and weirs to detail and slow down water flow. Other areas would be planted with appropriate local plants from the Cooks River/Castlereagh Iron bark species lists, mainly grasses, sedges etc (eg Themeda australis, Juncus usitatus, Persicaria decipiens) to be obtained from the Marrickville Community Nursery at Addison Road.
(a) The swale would receive stormwater run-off from approximately 300sqm of road surface, remove almost all suspended solids (including heavy metals, oil and grease, hydrocarbons), 85% of the phosphorus and 45% the nitrogen which is currently dumped into the Cooks River.
(b) During heavy rain, there is currently an issue with water ponding on the road at the base of the hill on which the Bushpocket site is located. This creates a hazard to be negotiated by road users. It is envisaged that by detaining and slowing down stormwater run-off this hazard will be reduced or eliminated.
(c) This could be a showcase example of a community initiated WSUD project, implemented with minimal cost or delay, with potential to be replicated in other parts of Marrickville making a significant contribution to improving the condition of the Cooks River, and involving the community in this process.
(d) The feature would enhance the existing Bushpockets site, adding visual interest and increasing biodiversity and habitat. This is an opportunity to replicate part of the freshwater swamp habitat which (according to the book Missing Jigsaw Pieces: The Bushplants of the Cooks River Valley (1999, Benson, Ondinea, Bear) would have originally existed at this location.
The next step was to develop a plan. Time was of the essence, as the sandstone was subject to ongoing pilfering (although this has decreased since Marrickville Council fenced the pile off for us).
The next piece of good fortune was to hook up with local residents David Knights and Alexa McAuley, who both also happen to be environmental engineers working with one of the firms that is leading the way with this work Equatica. Equatica are water professionals providing innovative and sustainable water management solutions in the urban environment. They’ve worked on other projects around Marrickville and Sydney (including some fantastic rain gardens in the new promenade at Sydney University).
We spent a Saturday morning surveying the site – then David and Alexa produced a detailed plan:
As if waiving their fees for this work was not enough – David has also lined up funding for the project from the Sydney Metropolitan Catchment Management Authority.
We are currently finalising these arrangements, and working through the implementation details with Wal Petschler, the Manager of Engineering at Marrickvile Council (who has been very supportive).
Our current plans are to construct the swale over the period 20 – 21 November.