Three microcomputer based irrigation design programs were built using the BASIC
language. The design models used agronomic, meteorological, economic, and
environmental variables to design an irrigation system. Next, the design models
computed the variable and fixed cost associated with a portable pipe, fixed big gun,
traveling gun, and center pivot irrigation systems.
The more economically important variables impacting fixed and variable irrigation
costs were randomized in a uniform and independent distribution using the random
number generator in the BASIC language. The design models were simulated using these
uniform distributions to build a database representing 3000 observations for each
irrigation system for a total of 12,000 observations. Each of these 12,000 observations
encompassed the variable cost, fixed cost, parameters of the irrigation system, and the
number of drought days the system would be operating.
This database was analyzed to determine the relationships between cost and each
of the variables. This analysis showed that all variables were linearly related to cost,
except for field size. Further analysis showed that field size could be linearly
transformed by using its inverse.
The database and ordinary least squares were used to build econometric equations
which summarized the design models' information. These econometric equations were
used in an example to show how these models could be used in a benefit-cost analysis.
Since the benefit-cost analysis was relatively simple, further refinement of the models to
include income taxes, inflation, and risk assessment is recommended.
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