7020

• UCREFRP Catalog Number: 7020
• Author: Oamek, G. and S. R. Johnson.
• Title: Economic and Environmental Impacts of a Large Scale Water Transfer in the Colorado River Basin.
• USFW Year: n.d.
• USFW - Doc Type: \
• Copyright Material: YES

water supplies is the sum of the consumptive use requirements for the crops times their
base year acreages.
The models assume irrigators are price takers through fixed output prices. Land use,
output prices, and input costs are based at 1983 levels, the most recent year for which
full information is available. Each assumes a fixed technology in the sense that there is
no opportunity to move down the production function by practicing deficit irrigation to
conserve water. On-tarm irrigation application efficiencies are also assumed fixed at
approximately 50 percent for each PA. The value of irrigation water implied by the
models would have to be considered on the high side in light of the lack of
technological substitution possiblities.
Preliminary baseline results indicated implausible specialization in certain profitable
crops and virtually no acreage of other crops. As an alternative to the traditional
cropland flexibility constraints, the models then incorporated Positive Quadratic
Programming (PQP), as put forth by Howitt and dean (9). This technique avoids
flexibility constraints by first calibrating the models with land use constraints intact, and
then using the dual values associated with them to derive a quadratic cost term to add
to the objective function value of the crop production activities. This quadratic term
accounts for the unmeasurable costs of risk, seasonal machinery and labor availability,
qualitative differences in soil types, and other unobservable factors inherent in
agricultual production.
Although convenient in implementing and defendable in short run applications, PQP has
the obvious shortcoming of distorting the objective function in order to achieve a given
base level of land use. The objective function value then becomes a poor indicator of
net regional income. For example, one PA had a value of 5835,000 when constrained to
base year acreage levels. Adding the PQP term increased the objective to S13.6 mil.
The impact of this undesirable characteristic of PQP was much less noticeable on the
dual value of irrigation water, having minimal impact until water became severely
constrained.
Offsite environmental impacts were assessed with the Bureau of Reclamation's Colorado
River Simulation System (CRSS) (10), adapted for this research. The model is
particularly well suited for this analysis due to its regional delineation along sub-basins
and the ability to easily alter its institutional constraints.
Historical river and tributary flows are the hydrological inputs to the CRSS which can
be varied by the user to thatch any historical record desired For this study, a 30 year
period of record was used incorporating the flow pattern of 1922 through 1951.
Sectoral water demands, return flows, institutional constraints, and river operation
criteria are exogenous input to CRSS. The bureau supplied necessary information for
the their-1986 baseline values.
Linking the two modeling frameworks was a straight forward process. Output from t
he
CRSS model regarding irrigation water delivery to each sub-basin for each year of
record was aggregated to the PA level. The annual variation in these deiveries was then
used to adjust the surface water constraint in the PQP models. The latter are then
solved for each year of record.