EffluentReuse: Land and Wet Weather Storage Requirements

ReportNo WSAA 80

July 1994

SYNOPSIS

Thisproject, jointly funded by the Urban Water Research Association of Australiaand NSW Public Works, determines the extent that effluent reuse for irrigationof land is a feasible proposition and provides basic design data.

Thework was undertaken by computer model studies of the operating behaviour ofsystems using climatic data and recorded effluent flows for a sample of town invarious locations in NSW.

Adaily simulation model of effluent reuse was developed to monitor storage,runoff and overflow volumes for a given system with general applicability toany locality. The model was used to size works and produce basic regionaldesign charts relating effluent flow rate, land area and storage volume.

Theregional design charts vary according to differences in evaporation andprecipitation and the rainfall distribution and intensity for the region. Thecharts show that in general for a given land area higher effluent applicationrates are attainable for inland regions where evaporation greatly exceedsprecipitation as opposed to coastal regions. Consequently the wet weatherstorage volume requirements for zero discharge will be less for inland areas.

Theachievement of 100% reuse and the condition of zero discharge for wet weatherstorage are generally costly due to the large land area and storagerequirements. A more practical approach would involve partial reuse and theallowance of overflows from the wet weather storage volume at some reasonablefrequency such as a 1 in 10 year event.

Theincrease in sewage flow due to infiltration and inflow to the sewer systemduring high rainfall events significantly increases the storage requirementsfor reuse schemes. Effluent reuse schemes should be accompanied by a seweragesystem improvement program to reduce wet weather flows thereby improving theperformance and reducing the cost of the reuse scheme.

Theregional charts provide a more rigorous solution in comparison to othertechniques in the sizing of works in a reuse scheme. Compared to other methodsthe regional charts provide a simple, quick but rigorous initial method forsizing an effluent reuse scheme taking account of daily data, site runoff andwet weather inflows.

Forfinal design of effluent reuse systems, a daily simulation model should be usedto assess system performance taking account of local climatic data, wet weatherinflows and the irrigation and drainage characteristics of the irrigation site.

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