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4
DROUGHT MANAGEMENT OPTIONS
Benedykt Dziegielewski
Department of Geography
Southern Illinois University
Carbondale, Illinois
Many municipal water systems face a risk of having
major disruptions in water supply during droughts. The
level of risk for any existing system can be assessed by
preparing a probabilistic forecast of potential water
supply deficits during a stated planning period. Such a
forecast is obtained by comparing the probability
distribution of the future availability of water in
supply sources with the long-term forecasts of water
requirements.
The systems facing a high level of risk can reduce
their vulnerability to shortages by expanding the
capacity of supply sources or implementing nonemergency
demand management programs. If the level of risk is low
or moderate, the best strategy may involve formulation
of drought contingency plans to cope with actual
emergencies.
This chapter summarizes the conceptual approaches to
planning for droughts and presents a method for
developing an optimal strategy for mitigation of water
deficits caused by droughts.
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. However, the
expected long-run drought damages are difficult to
estimate, since both the hydrologic variability of
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supply sources and the economic consequences of periodic
disruptions of water supply are not adequately defined.
Faced with inadequate data, water resource engineers
devised a compromise solution that balances the cost of
additions to supply capacity against the increments in
the reliability of Atwater system.
The term ''reliability" is related to the expectation
of water supply sources to sustain a stated level of
supply over time. Assuming that the hydrologic
variability can be described by a reasonably well known
probability distribution, reliability is defined as the
probability that a desired outcome (or level of supply)
will take place. In relation to droughts, the desired
outcome is usually defined as the "safe yield" which
determines the output of a supply project (or a
combination of projects) that can be maintained during a
severe drought, such as the worst drought in the
historic record.
In practice, the balancing of the cost of supply
additions against the increments of reliability is
reduced to the selection of a "design drought." In most
applications, either the worst drought on record or a
100-year drought is chosen as the basis for deciding on
the excess capacity of a water supply system. Since the
design drought implicitly sets the magnitude of the
economic losses that may be incurred, the selection of
the probability of such a drought (or its recurrence
interval) must assume that the incremental damages that
may result from recurrent shortages of water (caused by
droughts more severe than the design drought) 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. In recent years, however,
a number of unconventional alternatives have also been
considered. These may include the following:
-
1. more efficient utilization of existing water
supplies (e.g., pumped storage or reduction of losses),
2. use of ground-water aquifers for storage of excess
supply of surface water,
3. interbasin importation,
4. desalination of seawater or brackish ground water,
5. reclamation of waste water, and
6. implementation of cloud-seeding projects.
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Using the design drought approach, the optima1
combination of projects and the dates of their
completion are determined by minimizing the cost of
their implementation subject to the constraint that the
safe yield is at least equal to the requirements for
water at any time during a prescribed planning horizon.
While structural solutions to water supply planning
might have been efficient in the past, the cost of some
unconventional supply augmentation projects have made
this "fail-safe" approach to droughts prohibitively
expensive for many existing systems. As a result, water
resource planners have been forced to extend their
perspective to include nonstructural alternatives. A
combination of supply augmentation and long-term demand
management projects has the potential for affecting the
position of a water system, with respect to the risk of
recurrent water deficits, by not only increasing supply
but also by reducing future water use. The demand
management projects that can substantially reduce future
water use may include the following:
1. campaigns to educate the consumers on how to
modify water use habits to reduce water consumption,
2. promotion or a mandatory requirement of use of
water-saving devices and appliances,
3. promotion or a mandatory requirement of
low-water-using landscaping,
4. adoption of efficient marginal cost pricing, and
5. adoption of zoning and land use policies to
control the number of water users served by the system.
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. Also, the
reliance on demand management projects introduces two
additional sources of uncertainty that are associated
with the effectiveness (water savings) and the cost of
water conservation measures.
Overall, the long-term adjustments to droughts can
effectively reduce the magnitude and the frequency of
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potential water deficits; however j the criterion of the
design drought with arbitrarily established levels of
acceptable severity and unknown economic consequences is
inadequate for developing optimal drought mitigation
plans. Due to the rising costs of supply augmentation
projects, the use of the design drought approach is very
likely to lead to suboptimal plans in which the
incremental cost of system reliability considerably
exceeds the actual cost of shortages.
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. Since the
severity (or recurrence interval) of an ongoing drought
cannot be determined with a reasonable degree of
certainty, to be on the safe side the manager is very
likely to assume that the ongoing drought is more severe
than the design drought. To keep the risk of running
out of water reasonably low, the manager will always try
to adjust the demand for water by imposing increasingly
severe water use restrictions to forestall more severe
cutbacks that may be required if the perceived shortage
of water materializes at later stages of the drought.
Past drought experiences show that the actions of
water managers can greatly influence the magnitude of
the monetary and nonmonetary losses from the drought.
Although the manager apparently has little choice but to
pass (or create) water shortage to the customers, the
drought literature documents a great variety of drought
emergency measures undertaken in response to anticipated
shortages of water. Generally, these measures fall into
three broad categories:
~ a, v
demand reduction measures,
1.
2. improvements in efficiency in water supply and
distribution systems, and
3. emergency water supplies.
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Table 4-1 classifies specific drought management options
according to these three categories.
Each urban area has considerable potential for
temporary reduction of "normal" water consumption during
drought emergency without significant costs or
inconvenience to consumers. However, when the emergency
actions are undertaken as uncoordinated ad hoc responses
to changing storage conditions, the cost of these
actions may be substantial. For example, high cutbacks
in water delivery may very rapidly increase the losses
suffered by local economies, especially when industrial
output must be reduced. Therefore planning for water
deficits in the long run should begin with the
minimization of the cost of short-term deficit
The central question is how
management programs.
potential water shortages can be averted at minimum cost
to the supplier or, alternately, to the region served by
the water utility.
The information that would aid the most water managers
in coping with water deficits during an actual drought
is the following:
1. the level of deficit most likely to result from an
ongoing drought if no action is taken,
2. the effectiveness of specific drought management
measures (i.e., the quantity of water saved or obtained
due to the implementation of the measure), and
3. the total cost of individual measures including
the economic losses resulting from cutbacks in water
delivery.
Given this information, the manager would be able to
devise a drought emergency program that would alleviate
the expected deficit at the minimum cost.
An important consideration in the formulation of
minimumrcost drought emergency plans is that it is not
likely that one emergency program can be optimal for all
droughts that may occur during the planning period. 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. Alternately, separate plans may be formulated
for coping with deficits of increasing magnitudes, for
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TABLE 4-1 A Typology of Drought Management Options
I. Demand Reduction Measures
1. 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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TABLE 4-1 (Continued)
6. Rationing programs:
6.1 Per capita allocation of residential use
6.2 Per household allocation of residential
use
6.3 Prior use allocation of residential use
6.4 Percent reduction of commercial and
institutional use
6.5 Percent reduction of industrial use
6.6 Complete closedown of industries and
commercial establishments with heavy uses
of water
II. System Improvements
Raw water sources:
1.1 Reservoir/lake evaporation suppression
1.2 Reduction of dam leaks
1.3 Transfer of surplus water between
reservoirs
1.4 Pumped reservoir storage
Water treatment plant:
2.1 Recirculation of washwater
2.2 Blending impaired quality water
3. Distribution system:
3.1 Reduction of system pressure to minimum
possible levels
3.2 Implementation of a leak detection and
repair program
3.3 Discontinuing hydrant and main flushing
III. 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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TABLE 4-1 (Continued)
,
Cross-purpose diversions:
2.1 Reduction of reservoir releases for
hydropower production
2.2 Reduction of reservoir releases for flood
control .
2.3 Diversion of water from recreation water
bodies
2.4 Relaxation of minimum streamflow
requirements .
3. Auxiliary emergency sources:
3.1 Utilization of untapped creeks, ponds,
and quarries
3.2 Utilization of dead reservoir storage
3.3 Construction of a temporary pipeline to
an abundant source of water (major river)
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.
~ — ,
~ . _ The purpose
of the evaluation of individual measures is to prepare
an array of applicable, technically feasible, and
socially acceptable conservation practices together with
the information on quantities of water saved and the
expenditures and monetary losses associated with their
implementation.
The specific steps in the evaluation of demand
reduction measures must include the following:
1. determination of technical feasibility, i.e., the
capability of a given measure to produce a reduction in
water use upon implementation,
2. determination of social acceptability to predict
the probable response to the measure of various sectors
of the community,
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3. analysis of implementation conditions to identify
the agencies responsible for implementation and to
define the temporal and sectoral coverage of each
measure,
4 e determination of effectiveness, i.e., the
reduction in water use that can be attributed to the
implementation of each measure,
5. determination of the utility's expenditures on
implementing the measures, and
6. dete~-~uination of the economic losses resulting
from cutbacks in water delivery borne by the customers
in various sectors of local economy.
The identification and evaluation of emergency water
supplies must follow similar steps; however, the
information sought is of different character and it
includes the following:
1. availability and quality of water in potential
emergency sources during persisting dry weather
conditions,
2. adequacy of existing treatment facilities to
produce finished water of acceptable quality when
emergency supplies make up some fraction of raw water
supply,
3. lead time required to construct necessary water
transmission and Pretreatment facilities (if required).
4.
construction and operation-maintenance costs
required to bring emergency sources on line,
5. forgone benefits associated with cross-purpose
diversions of water from alternative uses, and
6. potential legal and institutional considerations
involving permits, rights to water, or easements for
transferral systems.
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.
The selection of an emergency plan for implementation
during an actual water crisis should be preceded by the
determination of the expected magnitude of supply
deficit. Preliminary actions of the water manager are
contingent upon some indication of potential water
shortage. When a shortage alert is in effect, the
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manager should initiate the analysis to assess the
likelihood of water deficit. A probabilistic forecast
of supply deficits can be developed by comparing the
probable levels of supply in the short-term with
short-term forecasts of unrestricted water demand.
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. If after the implementation of the selected plan
it becomes apparent that the volume of deficit will be
different than predicted, the appropriate adjustments
are made based on revised estimates of the supply
deficit.
An alternative approach to managing of actual drought
emergencies involves a sequential implementation of
increasingly
~ . .
severe shortage mitigation measures as the
supply conditions become more critical. Although this
approach eliminates the need to assess the risk of
shortage at the onset of a drought, the overall cost of
coping with emergency may be higher, since the measures
capable of providing substantial increases in supply (or
water savings) at relatively low cost are not likely to
be used during the critical period of the drought. When
the drought emergency decisions are geared to the
expected magnitude of supply deficits, the most
effective measures are likely to be used at the earlier
stares of the drought. and the decision as to when in
the course of a drought to introduce and terminate
-
emergency measures becomes less critical.
MINIMIZING THE LONG-RUN COST OF COPING WITH DROUGHTS
The use of the minimum-cost plans during actual
emergencies does not imply a simultaneous minimization
of the long-term cost of coping with shortages. It is
reasonable to expect that a system that has to resort to
emergency measures every year or even every five years
can deal with supply deficits more effectively by
expanding the capacity of supply sources and/or
implementing nonemergency water conservation programs.
The need for expanding supply capacity of an existing
system can be assessed by using the expected value of
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the cost of coping with drought emergencies during the
planning period. The expected value of the coping cost
is a common metric for comparing the alternative
long-term adjustments to drought. For any given water
supply system, the expected value of the cost of coping
with emergencies can be determined on the basis of the
probabilistic forecast of supply deficits and the cost
of drought emergency plans. For each future year,
minimums drought emergency plans are determined for
a range of possible supply deficits. The probability of
occurrence of these deficits is assigned to the cost of
the corresponding emergency plans so that higher costs
associated with large volumes of deficit have lower
probability. The expected value of the coping cost in
each year is found by summing the products of the costs
and their respective probabilities. For a specified
planning period, the expected values of annual costs are
reduced to a single number by finding the sum of the
present worths of the expected values of coping costs in
each future year. This number represents the expected
value of the cost of coping with water deficits in the
long run.
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.
Theoretically, the optimal strategy for dealing with
droughts would be determined by balancing the
incremental cost of the long-term adjustments with the
decrements of the cost to cope with emergencies.
However, the optimal solution selected in this manner
would be based on the comparison of the relatively
certain costs of system expansion with uncertain
expenditures and economic losses during droughts. A
more appropriate approach would be to compensate for the
differences in uncertainty by assigning subjective
weights to each of the two cost categories.
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AVAILABILITY OF ANALYTICAL TOOLS
A more complete elaboration of the drought planning
approach outlined in this discussion is given in
Dziegielewski et al. (1983a,b). This approach follows
the concepts and decision criteria formulated by Russell
et al. (1970), Young et al. (1972), and Russell (1979~.
The practical application of this method largely depends
on the availability of analytical tools for forecasting
the water supply and demand. There exists a large body
of literature on forecasting water supply. The methods
most relevant to drought planning are described by Stall
and Neill (1963), Lampe and Smith (1982), and Sheer
(1980~. The methods for forecasting water demands are
also available. A computerized water use forecasting
system known as IWR-MAIN (Crews and Miller, 1983) is
most useful for the evaluation of drought management
alternatives, since it estimates water use at a highly
disaggregate level based on demographic and
socioeconomic characteristics of the water service area.
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. E., and M. A. Miller. 1983. Forecasting
Municipal and Industrial Water Use: IWR-MAIN System
User's Guide for Interactive Processing and User's
Manual. Contract Rep. 83-R-3. U.S. Army Corps of
Engineers, Institute for Water Resources.
Dziegielewski, B., D. D. Baumann, and J. J. Boland.
1983a. Evaluation of Drought Management Measures for
Municipal and Industrial Water Supply. Contract Rep.
83-C-3. U.S. Army Corps of Engineers, Institute for
Water Resources.
Dziegielewski, B., D. D. Baumann, and J. J. Boland.
1983b. Prototypal Application of a Drought Management
Optimization Procedure to an Urban Water Supply
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System. Contract Rep. 83-C-4. U.S. Army Corps of
Engineers, Institute for Water Resources.
Lampe, L. K., and R. L. Smith. 1982. A Drought
Contingency Manual for Kansas Public Water Supplies.
Prepared for the Kansas Department of Health and
Environment by the Center for Research, Inc.,
University of Kansas.
Russell, C. S. 1979. Water deficit planning, Proceedings
Paper _ Southeast Regional Conference on Water
Conservation and Alternative Water Supplies, Georgia
Institute of Technology. Pp. 209-219.
Russell, C. S., D. G. Arey, and R. W. Kates. 1970.
Drought and Water Supply. The Johns Hopkins
University Press, Baltimore, Md.
Sheer, D. P. 1980. Analyzing the Risk of Drought:
Occoquan Experience. Journal of American Water Works
Association, 72:246-253.
Stall, J. B., and J. C. Neill. 1963. Calculated risks of
impounding reservoir yield. Journal of Hydraulics
Division, ASCE, 89(HY1~.
Young, G. K., R. S. Taylor, and J. J. Hanks. 1972. A
Methodology for Assessing Economic Risk of Water
Supply Shortages. Contract Rep. 72-4. U.S. Army
Corps of Engineers, Institute for Water Resources
Representative terms from entire chapter:
drought emergency
