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<br />REUSE OF AGRICULTURAL DRAINAGE
<br />
<br />107
<br />
<br />For simplicity, all projects along the river were assumed to be identical in
<br />terms of resources, cropping patterns,technology, and cost. The differences
<br />resulting from Strategies 1.11, and III implied in table 4 are assumed to be the
<br />only ones that distinguish lhe farms along the river.
<br />The economic evaluation was based on lhe following functions which
<br />describe the long-term profit associated with the i-th farm activity under
<br />strategy Ie,
<br />
<br />[3] ",', =
<br />
<br />J
<br />i {[I_R',].y ,'(P.-H ).C-F ,'p.,w',,-p"r',,-p"d'..},
<br />y I IJ J J 'J IJ IJ IJ IJ
<br />j
<br />
<br />[4] 11' = :r",', - S(v.c),
<br />
<br />where Jt',and 11' are the farm and regional profits, respectively; J, is lheset of
<br />crops grown on farm i; f3', is the yield loss (fraction) for crop j due to salt
<br />concentration in the applied irrigation water; y'j is the maximum yield level
<br />available when crop j is irrigated with fresh water; Pj and Hj are crop yield price
<br />and harvest cost associated with crop j, respectively; C'jand Fijare. respectively,
<br />nonwater variable cost and fixed COSt for crop j; and p', p', and p' are,
<br />respectively, water price, drainage disposal cost, and water reuse cost. The
<br />lauer two water costs represent, respectively, additional costs associated with
<br />the disposal ofthe drainage water (such as treatment, evaporation ponds, etc.).
<br />and associated with reuse (such as cost of pumping, ponds for intermediate
<br />storage, and monitoring). Note that all social costs tllat migllt result Crom
<br />drainage disposal are included in the variable p'. The variables w'.., d'.., r'.., are
<br />IJ IJ ,
<br />volume of applied freshwater, volume of disposed drainage water. and vOlume
<br />of drainage applied for reuse, respectively. Note that the total amount oC
<br />applied irrigation water on crop j in farm i under strategy k is w',- + r',.. The
<br />variableS(v,c) is the regional (social) cost associated with the vOlJme olwater
<br />, remaining in the river (v) and its salinity (c). Obviously, S is a decreasing
<br />function ofv and an increasing function ofc. This topic falls beyond the scOpe
<br />of the current analysis and will not be considered here. .
<br />potential yield and crop yield prices used in the economic analysis are
<br />presented in table 5 [or the [our crops. In ordcr to dctermine e[[ccts o[ the
<br />different variables on single project and tOlal regional profit, a sensitivilY
<br />analysiswasper[ormed with respect to these variables. RangcsoCvalues Cor p.,
<br />p', and p' were used to account fore[[ects of changes in water prices, drainage
<br />disposal costs, and water reuse costs on the profitability of the three strategies.
<br />For example, a zero value for p' was used where drainage disposal was not
<br />considered to cause a problem to society; and high levels of p' wcre uscd to
<br />account for the additional costs to make drainage disposal safe (pumping,
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