7021

• UCREFRP Catalog Number: 7021
• Author: Oamek, G., et al.
• Title: Methodology For Analyzing Alternative Reservoir Shortage and Operating Criteria.
• USFW Year: n.d.
• USFW - Doc Type: \
• Copyright Material: YES

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model which incorporates hydrologic data, water demands, priorities in use, shortage
criteria, and other information, and an economic model to estimate the economic V
benefits of alternative combinations of the above variables. The operations model drives
the system by computing water deliveries for three groups of users over a period of
record. Irrigation, municipal and industrial (M&I), and instream flows are the water
uses considered. The modeling system is sufficiently flexible to be applied to a range of
geographic areas, hydrologic conditions, and project uses.
The following sections describe the models and their application to two case studies.
RESERVOIR OPERATIONS MODEL
A spreadsheet-based model of reservoir operations simulates annual and monthly
deliveries to project uses considered. Based on a water balance concept, it uses a
homogeneous hydrologic sequence (adjusted for historical use) to construct a monthly
time series of reservoir inflows. Using this, and data regarding the physical
characteristics of the reservoir site, including area-capacity, rainfall, and pan evaporation,
a monthly time series of deliveries to each sector is constructed for each reservoir
operation strategy considered. Operating criteria concerning priority of use and
shortage criteria for each user group are explicitly considered, and can be altered to
consider a range of criteria.
During a drought period, the operations model assumes the reservoir operator, whether
it be the Bureau or a private agency, has two variables to consider for allocating
available water. One is the shortage trigger, which defines the beginning of drought
period operations. Defining a shortage, or drought condition, within the operations
model requires the user to specify a reservoir level at which reduced deliveries are
initiated. In the first case study, for example, deliveries to irrigators are reduced when
the volume of water in the reservoir falls below 90,000 acre-feet. This level is referred
to as the "trigger" level because it initiates reduced deliveries to one or more groups of
water users. The model assumes each group of water users has a unique shortage
trigger. Priority of use in times of shortages is directly related to the trigger since the
lower the trigger is set, the higher priority for water the user has.
The second variable, shortage criteria, is defined as the reduction in deliveries imposed
when the reservoir falls below the trigger level. Shortage criteria is expressed in
percentage terms. For the case study example, the baseline shortage criteria for
irrigation uses is 50 percent. Therefore, when the reservoir volume falls below 90,000
acre-feet, deliveries to irrigators are reduced 50 percent of normal.
Figure 1 contains a flowchart of the reservoir operations model. The data input
requirements, shown on the left side of the figure, illustrate the flexibility of the
modeling system. Any of the listed data parameters can be varied to observe their
effect on economic benefits. 'Of interest is the priority of use, shortage trigger, and
shortage criteria for each water use classification. However, the second box, identifying
reservoir and conveyance capacities, has been of interest in past studies regarding
reservoir sizing or enlargement. As can be seen in Figure 1:, other variables such as
alternative periods of record, flood pool requirements, and intra-season demand
distribution can be examined within this methodology.
The output of the operations model mainly consists of deliveries to the water user
groups. Additional output includes reservoir contents at user-specified intervals, and the