Chief Engineer.
Outline proposals are prepared for new water supply schemes for proposed development throughout the territory and also for revision of requirements in existing developments.
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The planning for and development of operational programmes for existing resources is carried out by the Supply Division, and includes the management of storage and supply by computerisation.
The Method
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The planning of resource development must begin with an estimate of the need in this case, the future demand for water. Crudely, this can be done by extrapolation of the past trend. This method, however, ignores possible changes in the community which may make the future increase in demand quite different from that in the past. A more sophisticated complementary analysis can be made by subdivision of demand into categories for example, industrial and various domestic categories and with all available knowledge of future growth rates of each category of consumer, gleaned from population estimates and building programmes, a picture of future demand can be built up from the estimates of its various parts. Estimates of this sort were prepared by the Water Resources Survey, and statistics to revise these are being gathered continuously by the Waterworks Supply Division.
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When demand is estimated, the possible resources can be matched to it, taking account of practical time-tables for the investigation, design and construction of large civil engineering works. This method showed the need to proceed with works to increase the capacity of the Plover Cove system, to construct the new reservoir at High Island, and to commence work on the building of a 40 million gallons a day desalting plant based on the multi-stage flash distillation principle.
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Planning of the supply facilities necessary to deliver water to the consumers involves assessment of the best physical sub-division into supply zones, limited in extent and level, calculation of probable demand in these zones, based on estimates of use, population, and unit demand rates and the selection of suitable sites for pumping stations, pipelines and service reservoirs. The process is the same in established but growing areas, with the added guidance of a record of demand growth. All of this planning is duplicated for salt water flushing supplies.
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Reservoir operational planning has historically depended on frequent adjustments of the supply zones of the various reservoirs so that the rate of draw-off from the individual reservoirs is changed. The object is to avoid overflow as far as is possible and to prevent some reservoirs emptying before others. The 'normal' complications of this work are the physical limitations on rate of draw-off from any particular source, the estimation of demand in the supply zone selected, and the rapid changes which can take place in the relative storage positions of the reservoirs due to uneven and unpredictable distribution of rainfall.
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