Planning for Drought May 2000

• Title: Planning for Drought
• Date: 5/1/2000
• Description: Draft Planning for Drought document
• Basin: Statewide
• Drought Mitigation - Doc Type: Drought Planning Document

Few communities have done any serious drought
planning. The CWCB recently contacted water
providers that produce 2,000 acre-feet or more of Water Management Tools
treated water per year to determine the extent and
level of drought planning in Colorado. We asked if Master Water Supply Plan-a projection of future
they had a master water supply plan, a hydrology demand for water in a specific service area under various
study that considered the risk of drought, a drought development scenarios and an analysis of the technical,
financial,and economic feasibility of various alternative
response plan, a water conservation plan, and if they options to develop a reliable supply of water to meet the
had adopted an ordinance that prescribes water long-term demand.
conservation in times of drought. The results from •
67 municipalities showed that less than half (49%) Hydrology Study-an analysis of the firm supply of water
had done some form of drought planning. 53% had to a system that considers the physical availability of
a master water supply plan, 22% had a hydrology water, including the risk of severe,sustained drought,and
the relative priority of the legal water rights to divert water
study considering drought, 22% had a drought for beneficial use.
response plan, 74% had a water conservation plan,
and 36% had a water conservation ordinance. In Drought Response Plan—a document that describes an
reviewing the hydrology studies, only about 4% agreed upon process to assess periodically water supply
included a robust, risk based drought analysis. conditions and the options for responding to emerging
drought based on pre-defined deficiencies or triggers.
Many water utilities appear to have designed their
water systems assuming an average year supply. Water Conservation Plan-a formal plan to encourage
all customers to use water more efficiently by
systematically considering a wide range of specific
ID Master Water Supply Plan water-saving measures.
El Drought Hydrology Study
❑Drought Response Plan Water Conservation Ordinance-a regulatory measure
❑Water Conservation Plan adopted by local governments designed to encourage
in Water Conservation Ordinance water use efficiency.
•y• 80%/ A true risk based drought analysis of surface water
`1) 70°i °Io supplies requires the use of sophisticated
PP q P
°- 60% mathematical techniques to define stream flow
• 50% characteristics during low-flow periods. This
40% o F analysis is possible now due to recent advances in
30% / V : j computers. Drought severity is a function of
a 20% / duration (in months or years) and the magnitude of
10% the deficits. A deficit is the difference or shortage
0%- in volume between the demand and total available
Municipalities supply, including storage, for a given increment of
time (typically a month). The design drought is a
planning tool to describe a monthly or annual series
of low flows. It can be based on the recorded .
The CWCB is developing new design drought historic drought experienced in the region, but it is
parameters based on risk analysis. What is difficult to determine the level of risk due to the
needed are estimates of drought characteristics, limited length of recorded data. A better technique
such as duration and percent of average is to estimate drought characteristics from a
precipitation or stream flow, by major river basin or statistical analysis of available stream flow or
climatic region. With such information, planners precipitation records with long term "synthetic"
would have a better idea about what is needed to stream flow histories using stochastic models. The
survive a drought, and current attitudes disputing synthetic stream flow histories maintain the
the need for reservoir storage might change. monthly, seasonal, and annual characteristics of the
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