Integrated urban water management: Woden Valley, ACT

The reliability of surface water resources in Australia is increasingly coming under scrutiny. To help maintain system reliability, the ACT Government has identified three main goals for the Canberra system.

The reliability of surface water resources in Australia is increasingly coming under scrutiny under the weight of population growth, natural climate variability and the potentially lower rainfalls and higher temperatures expected under climate change.

To help maintain system reliability, the ACT Government has identified three main goals for the Canberra system - reductions in potable water demand, reductions in overall water consumption, and maximising the quality of runoff entering waterways. At the same time, the Government is determined to minimise overall costs.

In a recent case study, researchers used Urban Developer to predict the impact of installing rainwater tanks on 39 houses in Collier Street, Curtin. Using data from the current rainwater tank rebate scheme, the researchers determined and applied a distribution of tank sizes to Collier Street, with all houses installing a rainwater tank connected to existing internal plumbing.

ABS census data was used to determine a distribution of household occupancy, applied across the model, in order to most accurately represent the typical household occupancy in the model. And since the roof area of the house has a considerable impact on the runoff that can be collected, roof areas were measured from satellite images using GIS software.

When determining water usage, the researchers separated consumption into indoor and outdoor usage, with outdoor usage assumed to be consistent from household to household, and indoor usage considered as being consistent from person to person. Water consumption was assumed to vary dependent upon the number of people present in the house. Indoor uses connected to the tank were assumed to be toilet, laundry and dishwasher.

Based on the above information, Urban Developer predicted the total mains water savings from the rainwater tanks in the 39 Collier Street houses to be 2890kL over the year of the simulation. This indicates that installation of rainwater tanks which are connected to internal plumbing can lead to considerable mains water savings by substitution with rain water.

To achieve these goals, the ACT Government is weighing up several options including the provision of rainwater tanks and water saving appliances, and development of several stormwater ponds for irrigation purposes. Before selecting the best options, the Government needs to fully assess their impact. An important part of this assessment requires detailed computer simulation.

Urban Developer, a new integrated urban water management tool from the eWater CRC, was used to analyse the impact of installing rainwater tanks in a single street in the Woden Valley Catchment. The results from this study will subsequently assist in determining the optimal operating strategy for the Canberra water system at the cluster scale.

Urban Developer delivers modelling at a household scale that accounts for the fact that rainwater tank provision will affect each household differently, depending on such variables as tank size, the size of the connected roof area and household water usage. Urban Developer can also operate at the cluster scale to predict the overall water saving.