represent the direct impacts of the biological control of giant reed. Environmental and
recreational values are not included, nor are benefits accruing to the Department of Homeland
Security and the Border Patrol.
Value to the Rio Grande Valley
Associated with the control of Arundo is an expected increase in irrigated acres that are
converted from dryland production in the defined study area. Such acreage conversion suggests
increased yields and higher values of production. The initial estimate of the value of Arundo
control is based on the increase in returns to water (based on crop prices received and costs paid
by farmers). This net value is estimated annually 2009-2058, as control becomes more effective
and extensive through time. Using capital budgeting techniques, the present value of annual
returns, as well as the present value of total water saved, is calculated for the 50-year (2009-
2058) planning horizon.
Water Valuation
Since municipalities have a legal priority for water and receive sufficient water to meet
their needs, any increase in water is logically used for irrigation (Griffin 2006); i.e., agriculture is
the residual beneficiary of any increases in real water supplies.1 To determine the direct impact
of the saved water from the control of Arundo donax, the value of irrigated water is used as the
appropriate measure of benefits. This is accomplished by developing a composite acre for
dryland crops, and also for irrigated crops. A composite acre is a representative acre consisting
1 The valuation of water for use on irrigated crops is based on the criteria that municipalities in the area have a
priority for water supply and are already receiving the amount they need, i.e., they receive first priority and there
are sufficient supplies to handle their needs. As a result, all additional water realized through the mitigation of
Arundo donax is assumed used in agriculture and adds value to crops. Some acreage of some crops currently
being farmed as dryland acres are converted to irrigated acres. Irrigation crops typically leads to higher yields,
resulting in positive returns to water (Lacewell 2008).