Drought Management and Its Impact on Public Water Systems Report on a Colloquium Sponsored by the Water Science and Technology Board (1986) / Chapter Skim
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4. Drought Management Options
4. Drought Management Options
Pages 65-77
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From page 65... ...
THE "DESIGN DROUGHT" APPROACH The traditional approaches to water supply planning treat the question of droughts as a part of the capacity expansion problem. Theoretically, the capacity expansion problem should be solved by balancing the cost of water supply augmentation projects against the expected damages that may result from recurrent shortages of water caused by droughts.
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From page 66... ...
during the planning horizon are balanced with the incremental costs of the additions to supply capacity. Typical capacity expansion projects usually involve the construction of new facilities for water storage, treatment, and transmission.
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From page 67... ...
Although the inclusion of demand management projects may reduce the overall cost of the long-term adjustments to droughts, it does not eliminate the problems associated with the arbitrary selection of the design drought. This is true in cases where the minimum-cost combination of the supply augmentation and nonemergency demand management projects is determined subject to the constraint that the safe yield is at least equal to the anticipated future water requirements with conservation at any time during the planning period.
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From page 68... ...
DROUGHT EMERGENCY PROGRAMS The formulation of the canacitv expansion Droblem ~ r -- -—-a -- -rid described in the previous section assumes that the costs of water shortage are prohibitively high and the situations in which the capacity falls below requirements are not permitted except for droughts more severe than the design drought. During an actual emergency, the knowledge of the system's safe yield is of limited value to the water manager.
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From page 69... ...
The "best package" of various drought management measures may be different for different sizes of water deficits. Therefore in order to carry out a complete evaluation of drought management alternatives, it is necessary to develop a probabilistic forecast of future water supply deficits.
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From page 70... ...
Public education campaign coupled with appeals for voluntary conservation Free distribution and/or installation of particular water saving devices: 2.1 Low-flow showerheads 2.2 Shower flow restrictors 2.3 Toilet dams 2.4 Displacement devices 2.5 Pressure-reducing valves Restrictions on nonessential uses: 3.1 Filling of swimming pools 3.2 Car washing 3.3 Lawn sprinkling 3.4 Pavement hosing 3.5 Water-cooled air conditioning without recirculation 3.6 Street flushing 3.7 Public fountains 3.8 Park irrigation 3.9 Irrigation of golf courses 4. Prohibition of selected commercial and institutional uses: 4.1 Car washes 4.2 School showers Drought emergency pricing: 5.1 Drought surcharge on total water bill 5.2 Summer use charge 5.3 Excess use charge 5.4 Drought rate (special design)
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From page 71... ...
Emergency Water Supplies 1. Interdistrict transfers: 1.1 Emergency interconnections 1.2 Importation of water by trucks 1.3 Importation of water by railroad cars
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From page 72... ...
3.4 Reactivation of abandoned wells 3.5 Drilling of new wells 3.6 Cloud seeding example: 10, 20, 30, or 50 percent of unrestricted water requirements in any year of the planning period. The critical point in the formulation of drought emergency plans is the evaluation of specific emer~enev actions such as those listed in Table 4-1.
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From page 73... ...
The descriptive data on individual drought management options produced through these steps allow the manager to formulate optimal (minimum cost) drought emergency plans corresponding to deficits of varying magnitudes occurring in different points in time during the planning period.
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From page 74... ...
Provided with a cumulative probability distribution of water deficits that may be caused by the ongoing drought, the manager may either choose the expected deficit (expected value) or a volume of deficit with a "sufficiently" low probability of occurrence and match it with the corresponding minimum-cost shortage mitigation plan defined during the drought preparation stage.
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From page 75... ...
The expected value of the long-term costs to cope with emergencies in the supply of water allows water planners to examine the trade-offs between the short-term and the long-term adjustments to droughts. Any combination of the long-term supply augmentation and demand management projects will affect the probability distribution of supply deficits in each future year thus resulting in the new expected value of the long-term cost of coping with emergencies.
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From page 76... ...
Although further refinement of forecasting methods can considerably improve the planning for water deficits, the most critical research needs are related to the measurement of the effectiveness and costs of various emergency actionse A complete evaluation of short-term drought management measures will allow water utility managers to make more informed decisions during crisis situations and will also result in more efficient long-term water supply planning. REFERENCES Crews, J
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From page 77... ...
1979. Water deficit planning, Proceedings Paper _ Southeast Regional Conference on Water Conservation and Alternative Water Supplies, Georgia Institute of Technology.
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