Simultaneous Peak Flows for Medium Density Residential Areas

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Report no. UWRAA 32

February 1995

Synopsis

An analysis of peak water demands for medium density residential services in Perth during the summer of 1992-93 has established estimates of the relative demands of different types of services. As well as peak instantaneous demand, peak 24hour consumption was also studied. These are key to the design of water supply systems so that provision can be made for adequate capacity.

The results indicate that the ratio of peak instantaneous demand and 24 hour demand is similar for both duplexes and strata units. Duplexes and strata units were found to use approximately 67% of a small block residence.

The estimates of peak instantaneous demand and peak 24 hour demand relative to a standard residential service indicate that the 24 hour demand of small blocks is similar to a standard single residence while the peak instantaneous demand is somewhat less. A similar relative trend was found for duplex and strata units. This result is contrary to initial belief and has some uncertainty as it relies on correlation of results from successive summers. It is possible that this result may be due to the differences observed in the 24 hour demand patterns for different service types, however this requires further investigation.

Nevertheless, in general terms, the results are very similar to those ratios currently used in Perth in the design process, which were previously derived using total annual consumptions and limited field testings in the 1970’s.

Other findings of the study include:

Bores have a substantial effect on peak instantaneous demand, reducing it to just 28%of what it would otherwise be. The effect on peak 24 hour demand is somewhat less, reducing it to 40%.

The effect of variables which relate to reticulation pressure proved difficult to quantify. There is evidence to suggest low pressure areas use substantially less water than high and medium pressure at peak times. This conflicted with the findings of the 1991/92 study. In addition the effect of reticulation pressure was inconsistent, with ‘high’ pressure areas using less than ‘medium’ pressure areas.

Analysis of the effect of other physical characteristics which affect the pressure at a particular property boundary such as short or long service, block slope, and location on the block, indicate pressure alone is not a determining factor in peak use.

Morning instantaneous demand appears to be as important as evening instantaneous demand when considering the duplex and strata title unit services.

This study targeted differences between small single residential blocks, duplexes and strata title units. The sample did not include any standard residential services making the comparison with these dependent upon the relationship with the data collected in the previous year resulting in a lowered accuracy in the comparison. It is recommended that further work directly compare these small services with the standard residential service.

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