SimultaneousPeak Flows for Medium Density Residential Areas

ReportNo WSAA 91

February 1995

SUMMARY

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

Theresults indicate that the ratio of peak instantaneous demand and 24 hour demandis similar for both duplexes and strata units. Duplexes and strata units werefound to use approximately 67% of a small block residence.

Theestimates of peak instantaneous demand and peak 24 hour demand relative to astandard residential service indicate that the 24 hour demand of small blocksis similar to a standard single residence while the peak instantaneous demandis 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 relieson correlation of results from successive summers. It is possible that thisresult may be due to the differences observed in the 24 hour demand patternsfor different service types, however this requires further investigation.

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

Otherfindings of the study include:

Boreshave 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 somewhatless, reducing it to 40%.

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

Analysisof the effect of other physical characteristics which affect the pressure at aparticular property boundary such as short or long service, block slope, andlocation on the block, indicate pressure alone is not a determining factor inpeak use.

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

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

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