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• Board Meeting Date: 11/14/2007
• Description: CF Section - En-bloc Non-Reimbursable Investments - Colorado River Water Availability Study
• Board Meetings - Doc Type: Memo

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"How much water from the Colorado River Basin System is available to meet
Colorado's current and future water needs?"
Colorado River Water Availability Study Goal
The answer to that question will take into consideration the following factors.
Hydrology varies in time, location and amount. Agreement on how to consider these factors in a water
availability study will be important to gain greater understanding and acceptance of the study conclusion. As
described later in this scope the initial study phase will focus on issues in a period of known hydrology and a
period extended from known hydrology.
Water Availability -will include both legal and physical supply considerations. Initially legal availability will
consider current demands.
Water Use -water use consideration (also referred to as demands) should include existing absolute water rights.
Water uses will also include existing transmountain diversions. Water use can be measured in terms of
consumptive use, gross diversions or total deliveries. Categories of water use include municipal (domestic and
commercial), industrial, agricultural, water rights for instream environmental flows and water rights for
recreational in-channel diversions. To fully answer the above question it will be important to examine the
interplay between future consumptive and non-consumptive uses in the context of the Colorado River Compact.
At various locations within the state initial water availability will be evaluated using the following formula:
Water Availability Physical Supply -Current Water Use (includes downstream demands)
The above factors can be modified using various assumptions and techniques. It is the application of these
assumptions and techniques which dramatically increases the complexity of the analysis. In addition,
assumptions/techniques in considering the following factors also affect the precisions and accuracy of the
analysis:
• methods for determining consumptive use
• legal interpretations which may constrain supply
characterization of shortages to current demands
characterization of current demand patterns/project operations
time steps (instantaneous, daily, monthly, yearly, multiyear) associated with demands
• reliability considerations in meeting a set or sets of demands (risk)
• assumptions regarding temperature and the impacts of temperature changes on the timing and amount of
consumptive uses and return flows
~ assumptions regarding precipitation (timing, amount, form)
The scope of work being developed includes assumptions regarding how some of the above factors will be
considered and evaluated (in some case it may be overly speculative to make assumptions). It is important to
note that there is no single right or wrong answer. In addition, how an individual views the risks associated
with future use will in large part correlate with the extent to which that individual current use is met (i.e., those
users whose current needs are not being met may take on considerably more risk then those whose current needs
Flood Protection • Water Project Planning and Finance • Stream and Lake Protection
Water Supply Protection • Conservation Planning