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

shortage trigger and shortage criteria for irrigation uses. The purpose of the latter
output will be explained in the following section.
ECONOMICS MODEL
The Economics model consists of three sectors corresponding to the water uses
identified above - irrigation, M&I, and instream flow. The methodologies for estimating
marginal benefits within each sector vary in complexity, ranging from a detailed
optimization framework for the irrigation sector to a single- valued avoided cost
technique for M&I.
Irrigation component
The net benefit of alternative reservoir operation plans for the irrigation sector is the
change in net farm income resulting from a proposed plan minus net farm income from
a baseline plan. Net farm income is defined as gross revenue from irrigated crop
production minus production expenses. In years when simulated project deliveries are
100 percent of normal, cropping patterns are assumed to generally follow historical
acreages. During low flow periods, when water deliveries to irrigation uses are reduced,
irrigators are assumed to adjust their cropping patterns and water application rates in a
manner which minimizes the economic damages of the low flows. This is accomplished
with a mathematical programming model which maximizes net farm income subject to
water and other resource availability.
Figure 2 describes the irrigation component of the economics model in terms of a
flowchart. Eight boxes stacked vertically summarize its input. The two top boxes
contain economic information necessary to compute net farm income. Crop prices and
yields, along with irrigated acreage, are used to calculate gross income. Production costs
can then be subtracted from this to arrive at net farm income.
The remaining boxes contain additional information used by the mathematical
programming model to estimate income maximizing levels of crop production. The
crop/water production function describes the relationship between water application and
crop yield. When faced with a shortage, an irrigator will typically face the decision of
whether to reduce irrigated acreage and maintain a normal water application rate, or
maintain normal acreage and reduce water application rates. Critical to this decision is
information on how crop yields relate to water application, or alteratively stated, how
tolerant the crops are to drought.
Crop irrigation requirements, the fourth box, report the crops' consumptive water use
requirements, net of rainfall, on a month by month basis. Availability of other water
sources in addition to project water, such as groundwater, is the fifth box. Other water
sources are of obvious importance because they can help mitigate the adverse impacts of
reduced project deliveries. The sixth box contain water costs from project and non-
project sources. Water costs may include pumping costs, ditch assessments, and other
related costs. Non-water irrigation costs, such as labor and equipment are included as
production expenses in the first box.
The reservoir operations model provides information in the final two boxes. As
previously mentioned, in addition to monthly water deliveries the operations model
provides the irrigation component with periodic reservoir contents, the shortage trigger,
and the shortage criteria. The latter parameters are used in the irrigation component to