Despite widespread recognition of the deteriorating health of our urban aquatic ecosystems and the need to conserve our precious water resources, there is only a slow rate of community adoption of ecologically sustainable development. To meet this challenge, the Upper Parramatta River Catchment Trust (UPRCT), in association with the NSW Stormwater Trust, is funding the creation of a landscape founded on the principles of ecological sustainability, including water-sensitive urban design (WSUD), at Homeworld 4, in Landcom’s Tallowood Hills residential development at Kellyville. They aim to demonstrate how and why WSUD can serve the needs of both humans and the ecosystem, and how these principles can contribute to a new garden aesthetic.

WSUD aims to protect and enhance our natural urban waterways by reducing nutrient and pollution runoff. Additionally, recycling water is an ecologically responsible and hopefully cost-effective use of a scarce resource. To this end, the UPRCT and the NSW Stormwater Trust are funding projects to demonstrate these principles, working at the catchment, subdivision and individual lot scale. All three scales are considered necessary to protect the receiving waters. The UPRCT engaged Pittendrigh Shinkfield Bruce (PSB) to produce a landscape design that integrates WSUD principles with an aesthetically pleasing landscape treatment at an individual lot scale. As a demonstration of WSUD, the site will encourage owners throughout the region to build with these principles in mind. Beyond environmental benefits, property owners had to experience the pleasures of living with WSUD. The design began with an analysis of soil conditions. Various tests, including permeability and salinity levels, informed an understanding of soil reactivity and the extent of water infiltration possible and indicated the type of soil modifications and structure protection needed. A peer review process by Tony Wong (for Landcom) had expressed concern that infiltration of rainwater into the soil could cause salinity – a justifiable worry in Australia. In, response, soil scientist Simon Leake analysed the soil and found that:

a) The rare salinity in this (Blacktown) soil type was due to scarce incised valley bottoms and not to a rising water table;
b) Urbanisation has reduced net infiltration across catchments; and
c) Infiltration promotes the downward flux of harmful salts away from the surface.

The analysis also informs other design features. First, perforated drainage piping is placed at the boundary of the A and less permeable B soil horizons to prevent ‘perching’ (settling) of water on the surface. Second, to prevent subsoil movement, moisture barriers are installed adjacent to walls.

Basic to the chosen design is the water filtration system and storage system. By slowing water flows from the site, the stormwater is polished of nutrients and sediment is captured. Water from the roof will flow in approximately equal proportion to rear and front sunken courtyards/water feature and a rainwater tank. In fact, all water falling on-site passes somehow into the soil, filtering through the remediated soil before either flowing into the conventional stormwater system or infiltrating the subsoil. Hence, the silty, compacted soil was ameliorated with gypsum, lime and compost to increase permeability, reduce erosion and accommodate plant growth.

At the house front, roof water flows into a sunken courtyard, creating an attractive detention basin around a water feature. During storms, water overflows into a conventional pit and is piped to the local stormwater system. Down the side driveway, water flows into a planted swale. It infiltrates a precisely calculated subgrade of recycled concrete; geofabric and 100mm perforated pipe, slowing, cleaning and ultimately either feeding the conventional stormwater system or infiltrating the soil. Overflow is captured in by-pass pits and piping that prevents water escaping towards the house or adjoining property.

Hydraulic engineers HughesTrueman modeled the effects of different tank sizes and the drawing of 35 to 100 per cent of roof runoff. They factored in data on rainfall, projected demand, evapotranspiration, runoff efficiency, soil water depth and the effect of automatic top-ups. Consequently, a five-kilolitre Aquaplate rainwater tank was selected – the maximum size allowed by council. A small (0.5 to 0.75hp) motor provides single-demand irrigation from the tank. When the tank runs dry, the irrigation system automatically switches to the Rouse Hill reticulated recycled water scheme. By combining recycled water and lot-level WSUD systems, the garden never uses precious potable water.

During heavy rainfall, the tank water overflows along a swale into the rear sunken garden, and finally under the rear timber deck. Retaining walls help detain and guide the water and together with the stepping stones across the courtyard and deck, provide opportunities for water play in the hours after rain. The water filters into treated soil before insects can breed.
While functionally coherent, the design of Homeworld 4’s landscape provides a transparent view into how urban society deals with natural systems like the water cycle. Innovative use of water feature, fountain, pond, stepping stones, deck and swale creates a playfully tactile living space, inviting engagement with the landscape. Given the pressing need to educate the public on how to apply WSUD principles at home, this Homeworld 4 initiative is timely and coherent in its aims and resolutions.
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