demand management
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refereed paper
THE IMPACT OF RESTRICTIONS ON REGIONAL URBAN DEMAND B Neal, C Meneses, D Hughes, T Wisener Abstract The water savings achieved under water restrictions in Victoria were previously estimated by a VicWater technical working group. This group estimated that a 14%, 44%, 67 % and 98% reduction in restrictable demand occurred at Stages 1 to 4 of restriction respectively. These figures were based on demand information collated for the Melbourne supply system prior to the 2006/07 drought and were recommended for application throughout Victoria. This paper presents information collated from a number of non-metropolitan urban wat er utilities to assess the water savings achieved under restrictions in recent drought years, including 2006/07, for comparison against the VicWater working group results. It also presents a simple but rigorous method for assessing the statistical significance of reductions in demand using two sample t-t ests on residuals of observed minus estimated unrestricted demand . Whilst there was generally a greater reduction in restrictable demand under Stage 1 restrictions than anticipated , the wide range of consumer response to restrictions meant that there was insufficient evidence to alter the previous VicWater recommendations. The ability to draw firmer conclusions from the analysis could be improved by adopting a consistent assessment method across all water utilities in Victoria and Australia in the future.
Introduction The demand reduction associated with the implementation of restrictions in most water resource models across Victoria is currently based on the outcomes of a VicWater technical working group paper from 2005 [rWGWSA, 2005). That paper recommended that the reduction in restrictable demand should be 14%, 44%, 67% and 98% at Stages 1 t o 4 respectively. Restrictable demand is that component of total demand which can be affected by restrictions. It typically includes non-essential activities such as garden wateri ng, and it typically excludes most in-house and industrial water use. Th ese figures from VicWater were based on a combi nation of analysis of demand
60 AUGUST 2010 water
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Figure 1. Many towns on restrictions and many on severe (Stage 4 of 4 stages) restrictions in 2006/07 (DSE, 2008).
data during periods of restriction, surveys of end user water use behaviours and market research during restriction periods. These figures were developed prior to the 2006/07 drought, in which severe restrictions were implemented across much of Victoria. Throughout Victoria each stage of restrictions was a standardised reg ime, limiting the tim ing and purposes of water use, such as garden wateri ng, but not affecting usage within the home or by industry. The drought conditions th roughout Victoria for some years had resulted in stream flows in 2006/07 being the lowest on record (DSE, 2008). In consequence many towns had been on restrictions, including many on severe (Stage 4) restrictions, as shown in Figure 1. This paper draws on actual data from three regional towns supplied by North East Water during 2006/07 when restrictions were imposed, compared with similar analyses undertaken by Goulburn Valley Water and Coliban Water. Th is project was commissioned by Goulburn Valley Water as part of its Drought Response Plan update.
Statistical analysis of data from country towns.
North East Water Data Analysis North East Water is an urban water utility wh ich supplies water to 38 towns, vi llages and cities in North East Victoria, serving an estimated population of 100,000 people (NEW, 2009). Most of North East Water's towns were on some form of water restriction in 2006/07. For this analysis, three of North East Water's larger supply systems were selected. These towns are Benalla, Bright and Wangaratta. It was considered that supply data from larger towns would be less susceptible to short-term variabil ity in losses or consumer behaviour than smaller towns. This allows the effect of restrictions to be more readily isolated.
Historical periods of restriction Bulk meter consumption data was provided for these three towns from July 2003 to June 2008. This period was selected to provide a period of analysis that included some restrictions . This period was considered short enough to be reasonably representative of current cond itions and relatively stationary, but long enough to allow inferences to be drawn from the data. The charts (Figures 2.3.4) indicat e that the first three years of data were unrestricted, with a range of restriction stages progressively put in place in the last two years of the data set.
technical features