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Scenario:

450 m² lot; 200m² roof area; 3 person household; 65% impervious area (including roof); in Brisbane, Melbourne and Sydney. These are important factors in urban planning.

Options analysed included business-as-usual (BAU), 5kL rainwater tank, and WaterCell technology (64 kL). BAU is the traditional centralised approach (i.e. dams, pumps and pipes), the 5kL rainwater tank option simulated an above-ground rainwater tank, and the WaterCell design incorporates 64kL of rainwater storage (in the floor plan design during construction. 

Note:

Water demand data and climate files were different for each location. Water demand and rainfall are major variables dictating yield from a rainwater storage of any size. The table below summarises input data to the Probabilistic Rainfall and Wastewater Reuse Simulator (PURRS - Coombes, 2002). 

Coombes, P. J. (2002). Rainwater Tanks Revisited: New Opportunities for Urban Water Cycle Management. PhD Thesis, School of Engineering, University of Newcastle, NSW, Australia. http://www.eng.newcastle.edu.au/~cegak/Coombes/ 

 

PURRS is currently used as a research tool, however the creator (Peter Coombes) and the model are very well known in the water industry (government, water authorities and consultants). The Figures below summarise mains water savings (MWS%) and stormwater runoff (volumes) reduction (SWR%) at the household scale (when compared to BAU). 

The Figures (on the following page) show the impact of WaterCell technology in reducing peak stormwater discharges (in m³/s) from the allotment.

 

The reduction in peak stormwater discharge (m³/s from the allotment) is shown for a range of annual recurrence intervals (i.e. 1 in 10 year event, 1 in 50 year event, etc). Significant reductions in peak discharge can be seen when WaterCells are incorporated into the house design. This has potential for offsetting infrastructure costs when considering investment for “downstream” stormwater management strategies.