WaterSubject

Urban development and its constructed hydraulic systems cause profound changes to the natural water cycle. The area of impervious surfaces is increased whilst natural watercourses are replaced with hydraulically efficient pipes and channels. Water demand resulting from urban development is typically met by importing large volumes of treated water, across large distances and at considerable cost, from neighbouring catchments. At the same time similar volumes of stormwater from roofs are discharged unused from urban developments via expensive stormwater systems.

Water sensitive urban development (WSUD) source controls include reuse of rainwater, stormwater and wastewater. Research into WSUD from the urban water cycle management perspective shows that significant economic, social and environmental benefits to the community may be derived from more efficient use of water resources and infrastructure. However, a major impediment to the use of the WSUD approach is a perception that it is expensive to implement and has limited economic benefits.

This study evaluates the economic benefits arising from the use of rainwater stored in tanks to supplement domestic indoor and outdoor water use. It assesses these benefits in the context of two very different case studies in the Lower Hunter and Central Coast regions of New South Wales, Australia.

The Lower Hunter and Central Coast regions, chosen for this study, have contrasting socio-economic and water resource characteristics. The Central Coast region has a smaller population size, a larger annual growth rate and a domestic consumption that is a greater portion of total mains water demand than the Lower Hunter region. The Central Coast region relies primarily on extraction from streams whereas the Lower Hunter region is more reliant on large surface and subsurface storages. These contrasting characteristics will lead to substantially different economic and environmental outcomes.

This paper is organized as follows: A simulation model of household water demand, satisfied in part from rainfall and in part from mains water, is developed. This model provides input to a water supply headworks simulation model that is used to evaluate drought security and water supply augmentation options. Several scenarios involving different source control and traditional allotment water management options are investigated. For each scenario, the augmentation schedule for the headworks system is determined using established drought security criteria and a comparative economic analysis is performed to evaluate the benefits.

2. Demographic and housing stock data

The approach taken to evaluate household water demand at the regional scale involves two steps:

Develop a simulation model of indoor and outdoor water demand representative of the individual household in a particular urban zone; and

Scale household demand up to the regional scale taking into account the population, housing stock and socio-economic characteristics of the zones that constitute the region.

In this section the demographic and housing stock data for the two case studies are reviewed.

2.1. Lower Hunter region

The Lower Hunter region has a population of 455,000 people with an overall annual growth rate of 0.9%. Domestic water demand accounts for approximately 43% of total water use. The region spans five local government areas, namely Newcastle, Lake Macquarie, Maitland, Cessnock and Port Stephens. The region has been divided into nine zones to facilitate water supply modelling. The provides annual population growth and annual dwelling growth data for these zones. The dwellings in the five local government areas were categorized as either a detached house or a housing unit that includes flats and apartments. All dwellings in the five areas were also categorized by number of occupants This enabled water use modelling for different numbers of occupants and different dwelling types.