Set Sprinkler Irrigation and Its Cost

Set Sprinkler Irrigation and Its Cost José Nicolás Ortiz Romero 1 ; Jesús Montero Martínez 2 ; Roberto Simón Martínez 3 ; and José María Tarjuelo Martín-Benito 4 Abstract: In this study, annual water application costs per unit area ha have been analyzed at the level of irrigation subunit in set sprinkler irrigation systems designed with pipes of different materials. In the cost, investment pumping, pipes, sprinklers, ditches, energy, labor, maintenance, and water costs have been considered. Four systems were studied: one with buried pipes, in a permanent solid-set system, using: a polyvinyl chloride with buried pipes PVCb, and three with pipes on the surface in surface solid-set systems, using b polyvinyl chloride pipes, c polyethylene pipes, and d aluminum pipes. The correct selection of the irrigation subunit size and shape can lead to a significant decrease in cost. The most economic irrigation subunits, among the four systems studied, were those formed by four laterals and a number of sprinklers per lateral of 10, 9, and 6 at 12 m 12 m, 12 m 18 m, and 18 m 18 m spacing, respectively. The most influential factor on the annual water application cost was spacing. Considering total annual cost, water cost was the most important, followed by investment and energy. Among the analyzed systems, the permanent system using PVCb produced the lowest annual water application cost per unit area. DOI: 10.1061/ ASCE 0733-9437 2006 132:5 445 CE Database subject headings: Cost control; Irrigation; Sprinkler irrigation; Water management. Introduction Sprinkler irrigation systems are used worldwide. In Spain, 24% of the 3.4 M ha of irrigated land use this system, with preference for two alternatives, center pivot and set systems MAPA 2003. In sprinkler irrigation, water is applied like rain, obtaining a uniform distribution with overlapping of several sprinklers. Water should be infiltrated in the point where it falls, without runoff or erosion. The water application in set systems depends mainly on: a the water distribution model of the sprinkler; b the layout and spacing between sprinklers; and c the wind mainly its speed. The water distribution model of the sprinkler depends on the type of sprinkler, the number, and design of the nozzles, and the working pressure Keller and Bliesner 1990. To obtain a high uniformity of water distribution, the sprinkler system must work in bloc Tarjuelo et al. 2000; Montero et al. 2001a; Ortega et al. 2004b. Consequently, solid-set systems 1 Professor, Agronomy Engineering, Univ. Centroccidental Lisandro Alvarado, Barquisimeto, Venezuela. E-mail: jortiz@ucla.edu.ve 2 Professor, Agronomy Engineering, Centro Regional de Estudios del Agua, Castilla-La Mancha Univ. Campus Universitario, s/n. E02071, Albacete, Spain. E-mail: Jesus.Montero@uclm.es 3 Researcher, Agronomy Engineering, Convenio Provincia de Rio Negro-INTA, CC153, 8500 Viedma, Argentina. E-mail: rsmartinez@ correo.inta.gov.ar 4 Professor, Agronomy Engineering, Centro Regional de Estudios del Agua, Castilla-La Mancha Univ. Campus Universitario, s/n. E02071, Albacete, Spain. E-mail: Jose.Tarjuelo@uclm.es Note. Discussion open until March 1, 2007. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on May 11, 2004; approved on October 29, 2004. This paper is part of the Journal of Irrigation and Drainage Engineering, Vol. 132, No. 5, October 1, 2006. ASCE, ISSN 0733-9437/2006/5-445 452/ $25.00. usually have a higher uniformity and efficiency than portable systems where the laterals are dispersed in the plot. Solid-set systems generally have a bigger investment cost but they need less labor. In permanent solid-set sprinkler irrigation systems, buried pipes assure the protection of the system. In surface solid-set systems, pipes are exposed to potential mechanical and environmental damage such as temperature, solar radiation, blows, etc. The advantage of these systems is the possibility of its use in other plots when the crop cycle is finished. In solid-set systems, aluminum Al, polyethylene PE, and polyvinyl chloride PVCs pipes on the surface can be used. Although each one has advantages and disadvantages and very different costs, all of them require more labor than a permanent system of polyvinyl chloride with buried pipes i.e., PVC buried PVCb. The water application cost with sprinkler irrigation includes investment pumping, pipes, sprinklers, ditches, energy, labor, maintenance, and water costs. The cost of the sprinkler irrigation system depends on the equipment and its design, materials, and automatization level. This cost is also influenced by other factors such as shape, layout, and size of the plot, distance from the water source to the plot, and pumping requirements Van der Gulik 2003. Some research Esquiroz and Puig 2001 shows the great influence of the number of sectors and their size in the investment cost. The wide variety of design alternatives makes it necessary to identify the lowest total cost, including investment and operation costs. Throughout sprinkler irrigation history, there has always been a concern about the system characteristics that lead to the cheapest results with irrigation Kumar et al. 1992. Also, numerous cost benefit analyses have been studied that look for optimal water use with different systems Khanjani and Busch 1982; Ortega et al. 2004b. In this work, annual water application costs were studied at the subunit level using different materials in set sprinkler irrigation systems. The subunit was formed by a submain pipe and several JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / SEPTEMBER/OCTOBER 2006 / 445

Table 1. Diameters Used in the Lateral and in the Manifold Lateral Material mm Manifold mm PVCb 50 0.62 63 0.79 90 1.59 110 2.30 125 2.99 140 3.73 160 4.84 180 6.14 200 7.55 PVCs 50 1.06 63 1.26 75 1.773 90 2.51 PE 50 1.41 63 2.03 75 2.99 90 6.62 110 7.80 Al 50 2.66 75 4.34 75 4.34 100 6.60 125 9.99 Note: For each diameter, the price in for linear meters is indicated in parentheses. laterals in permanent with all pipes buried and in surface solidset systems with submain and lateral pipes on the surface. The types of pipes used were PVCb or on surface PVCs, PE, and A1. The influence of the main factors on the annual water application cost per unit area, but assuring the correct hydraulic performance, has also been studied. This has been considered as the cost of the cubic meter of water applied to the soil and available for the crop Tarjuelo 1986; Montero et al. 2001b. Methodology To identify the optimum solid-set sprinkler irrigation subunit design, the annual water application cost, understood as the cost of cubic meter of water added to soil for crop use, has been calculated as the sum of investment, labor, maintenance, energy, and water cost, but always ensuring the correct hydraulic performance of the subunit. A subunit formed by one hydrant in the end of one submain and several laterals has been designed. It is assumed that this hydrant can provide water even for four subunits similar to this. In the subunit, the number of laterals per submain N l was varied among four and 12 and the number of sprinklers per lateral N s among three and 10. The spacing between laterals S l and between sprinklers S s were 12 m 12 m, 12 m 18 m, and 18 m 18 m. However, to highlight the differences, the results have mainly focused on the first and last one. The average working pressure in the sprinkler ranged from 250 to 450 kpa. To study the influence of size and shape on the subunit, the standard irrigation system was considered to have an average working pressure of 350 kpa, an application rate of 6.0 mm h 1, an application efficiency of 80%, a water cost of 0.06 m 3 and net crop annual irrigation water requirement N n of 6750 m 3 year 1 ha 1 representative data for maize cultivation in the region of Albacete, Spain. For subunit design, the criteria that the maximum pressure variation in the subunit should not exceed 20% of the average working pressure in the sprinklers was considered for correcting hydraulic performance of the subunit Keller and Bliesner 1990. First, friction head losses on the lateral were calculated, then, with the energy available to consume 20% of the pressure corresponding to the medium sprinklers, the submain size was selected. For process simplification, every pipe situated in horizontal ground has been considered. Pipes were calculated using the Veronesse Datei, Blassius, and Scobey formulas for PVC, PE, and Al, respectively. The diameters used in the lateral and submain, and the corresponding cost for different pipe types, are indicated in Table 1. Those diameters correspond to the most commonly used in this sort of irrigation system for an optimized design. In order to understand the influence of the main factors on the annual water application cost, the layout and spacing, number of laterals and sprinklers per lateral in the irrigation subunit, working pressure, average application rate of the system, and efficiency, were considered. For solid-set systems with PVCs, PE, and Al pipes, the possible advantage of the possibility of plot change has not been considered in relation to the option of permanent PVCb. Since we only tried to understand the subunit irrigation design of the lowest annual water application costs, we started with available water in the hydrant placed at the beginning of the subunit, at necessary pressure and flow conditions in each case. From this approach, the possible effect of the pumping station and the main pipes until reaching the hydrant on the different subunit designs under the suggested conditions had not been considered. Investment Cost To evaluate the investment cost C i,in, every element necessary for subunit installation, such as pipes, sprinkler, tees, bends, risers, reduction sleeves, etc., and assembly cost has been considered. In addition, for the permanent sprinkler irrigation system, the opening and closing of ditches has been included. Installers from the Albacete area Spain were asked to give price estimates for materials, machinery, and labor. The investment annuity A, year 1 was calculated by multiplying the initial investment by the capital recovery factor CRF. The CRF was calculated using Eq. 1, assuming an interest rate i of 6% and a useful life n depending on the pipe material, and whether the pipe was buried or on the surface. For pressurized systems, Scherer and Weigel 1993, recommended a useful life n of 15 20 years. In this study, 20 years was assumed for permanent PVCb pipes, 15 years for PE and Al on the surface, and 8 years for PVCs on the surface CRF = i 1+i n 1+i n 1 1 To establish comparisons, the unitary cost of investment C a,in year 1 ha 1 was determined using Eq. 2 C a = A S = CRF C i S where S irrigated area in the subunit in ha. Energy Cost The annual energy cost per unit of irrigated surface C e, in year 1 ha 1 has been calculated by taking into account the net power P, inkw necessary for the water application in the sub- 2 446 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / SEPTEMBER/OCTOBER 2006

Fig. 1. Influence of the number of sprinklers and pipe material on the water application cost for a spacing of 12 m 18 m and four laterals unit, the operating hours per year of the system n h, the price of the energy rate P e in kw 1 h 1, and the subunit irrigated area S, inha, using Eq. 3 C e = P n h P e 3 S The net power consumed for irrigation water application in the subunit P has been calculated according to the pressure H 0,in m and discharge Q 0,inm 3 s 1 necessary in the hydrant P = 9,81 Q 0 H 0 4 H 0 and Q 0 were determined considering the necessary sprinkler pressure and discharge, as well as friction losses in the lateral and submain, for the different pipe size combinations. The number of operating hours per year n h has been calculated as the ratio between the gross water requirement per year N b,inmm and the average application rate in the system A r,in mm h 1. The gross requirement has been obtained as the ratio between the net crop annual irrigation water requirement N n and the general application efficiency E a n h = N b = 5 A r E a A r The general application efficiency E a for a defined percentage a of adequately irrigated area can be calculated as Keller and Bliesner 1990 N n E a =ED a P ef where ED a distribution efficiency ratio between net crop requirement, N n, and the gross water average depth that reach the soil surface, D rs ; and P ef the effective proportion of water emitted by the sprinklers that reach the soil surface, P ef =D rs /N b. Supposing the water distribution through the irrigation system has a normal distribution, the ED a value can be easily deduced as a function of the irrigation uniformity coefficient and the percentage of adequately irrigated area a. In order to study the effect of the irrigation efficiency on the water application cost, several efficiencies were considered: 60 and 70% example of inadequate irrigation design and management, 80% adequate management, and 90% excellent management. The lowest irrigation efficiency supposes higher water consumption, but it is considered that it has no influence on the crop since the same N n value is guaranteed. Likewise, the system application rate varied from 3 to 10 mm h 1. Water Cost Water as a production factor has a cost and, therefore, it should have an assigned price. A first approximation to the irrigation water price is the cost of obtaining it Caballer and Guadalajara 1998. The assigned price corresponds to the water found at the hydrant, with enough pressure and flow for suitable operation of the irrigation subunit. The annual investment pumping station, main pipes, and other regulation and control elements, maintenance, labor, etc., have also been included within the price. To analyze the effect of the cost of a cubic meter of water, four prices P w have been considered: 0.03, 0.06, 0.09, and 0.12 m 3 Ortega et al. 2004a. Thus, the cost of the irrigation water C w, year 1 ha 1 is C w = N n P w 6 E a For comparison, the total cost per unit of water applied C ta,in m 3 has been calculated as the ratio between total cost C t, sum of the three previous costs, and the net water applied per hectare and year N n. So, the effect of the irrigation efficiency can be spotlighted Ca + Ce + Cw C ta = N n = C t N n For the subunit design, bearing in mind the large number of combinations proposed, laterals have been calculated with diameters of 50 and 63 mm for PVCb, PVCs, and PE, and 50 and 75 mm for Al. In this way, the subunit design combination lateral submain can be selected so that the water application cost is the lowest possible. 7 JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / SEPTEMBER/OCTOBER 2006 / 447

Fig. 2. Influence of the number of laterals and pipe material on the water application cost for a spacing of 12 m 12 m and seven sprinklers per lateral Other Cost At surface solid-set sprinkler irrigation systems, the labor for system installation and dismantling before and after cropping and the additional maintenance cost over the permanent solid-set system have been estimated as 5% of the investment cost. Results Influence of Subunit Design The results show that the most inexpensive subunit for the four irrigation systems are those formed by four laterals and a variable number of sprinklers per lateral depending on the spacing. These have 10 sprinklers for a spacing of 12 m 12 m, nine sprinklers for 12 m 18 m, and six for 18 m 18 m. Fig. 1, for 12 m 18 m spacing, shows how the water application cost decreases until nine sprinklers and afterwards it increases. A bigger number of sprinklers per lateral would increase the necessary pipe diameter, increasing the cost. The higher number of sprinklers per lateral in smaller spacing corresponds to the lower sprinkler discharge for obtaining the same application rate. Using PVCb, PVCs, or PE, the diameters that produce lower cost are 50 mm for laterals and 90 mm for submains. For Al pipes, diameters must be of 50 and 75 mm in laterals and submains, respectively. In the four systems studied, for specific lateral and sprinkler spacing and equal number of sprinklers per lateral, a bigger number of laterals increase the water application cost Fig. 2. The reason is the requirement of a bigger diameter in the submain. Fig. 2 shows that the cost of a subunit composed of 12 laterals and seven sprinklers per lateral is very similar for PVCs and PE systems due to the influence of the useful life in this situation and the fact that the lateral diameter increases from 50 to 63 mm for PVCs system. As the number of laterals increases from four to 12, the water application cost increases by 2.4, 9.5, 3, and 6%, in PVCb, PVCs, PE, and Al pipes, respectively. Since those percentages are considered low, the most practical installation for a Fig. 3. Influence of the spacing and type of material on the water application cost for a disposition of four laterals and seven sprinklers per lateral 448 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / SEPTEMBER/OCTOBER 2006

Fig. 4. Influence of the spacing and working pressure on the water application cost for a disposition of four laterals and seven sprinklers per lateral subunit is one that irrigates a large area. In Fig. 2 the steps observed in the graphic match the changes in pipe diameter for correct hydraulic performance of the subunit. Influence of the Sprinklers and Lateral Spacing For the four systems studied, the water application cost was lower when the spacing was larger Fig. 3. The reason is that although the necessary diameter is bigger the total length of the pipes is smaller. Fig. 3 shows that the lowest cost system is permanent PVCb pipes, although differences in cost are smaller when spacing is larger. An exception is the PVCs system, where the cost of 12 m 18 m spacing was practically the same as 18 m 18 m when using the same pipe size for correcting hydraulic performance of the subunit. The water application cost for the spacing 12 m 12 m as compared to 18 m 18 m is increased by 12, 12, 21, and 19% for PVCb, PVCs, PE, and Al pipes, respectively. Therefore, it seems logical that the design of those systems should use larger spacing. Since small spacing presents better uniformity and efficiency Keller and Bliesner 1990; Tarjuelo et al. 1999a,b, the influence of irrigation efficiency has also been considered in this cost. For 12 m 12 m, 12 m 18 m, and 18 m 18 m spacing, efficiencies of 84, 82, and 80% have been considered for the most favorable situations, respectively. Lower irrigation efficiency entails higher water consumption, but it is considered that it has no re- Fig. 5. Breakdown of the water application costs comparing different working pressures and type of pipes JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / SEPTEMBER/OCTOBER 2006 / 449

Fig. 6. Effect of the application rate and the spacing on the water application cost for a disposition of four laterals and seven sprinklers per lateral percussion on the crop since the same N n value is guaranteed. For the spacing 12 m 12 m, the difference in cost with regard to an efficiency of 80% was smaller than 3%. Influence of Mean Working Pressure The working pressure has a clear effect on the energy cost. In addition, it can also have an influence on the investment cost, depending on the need of a change in the pipe diameter to fulfill the maximum difference in pressure in the subunit to the 20% of the pressure corresponding to the medium sprinkler Figs. 4 and 5. Sprinkler pressure variation can cause a little variation in irrigation uniformity. In this case, as it is expected to check the influence of only one factor in the total water application cost, it has been considered of 80% efficiency, and the possible irrigation uniformity variations have not been considered when pressure varies. Fig. 4 shows the influence of the sprinkler and lateral spacing and the working pressure on the water application cost for a subunit of four laterals and seven sprinklers per lateral. In Fig. 5, the breakdown of the water application costs for different pressures and material is shown for the spacing 18 m 18 m in a subunit of four laterals and seven sprinklers per lateral. For the same working pressure, the difference in total cost C t is only due to the annual investment cost C a since water cost C w and energy cost C e are the same since water applied is also the same. The aluminum system is the more expensive and the PVCb the cheaper, since the PVCs and PE systems have similar total cost. In Fig. 5, it can also be observed that in the breakdown of the total annual cost the most important factor is the water cost at the inlet of the subunit, followed by investment and energy used to produce the necessary pressure. For the spacing 12 m 12 m Fig. 4, the water application cost increases when the average working pressure increases. In this case, not shown in the paper, the annual investment cost is constant because the pipe diameter does not vary in the subunit, increasing only the energy cost. The situation is not the same in the 18 m 18 m spacing Fig. 4, because it is possible to use a Fig. 7. Effect of the application efficiency and the price of a cubic meter of water 0.06 or 0.12 m 3 on the water application cost 450 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / SEPTEMBER/OCTOBER 2006

Table 2. Water Cost Increase % for Different Water Price, Water Application Efficiencies and Annual Water Net Necessities 6,750 m 3 ha 1 Water price m 3 Efficiency % Gross requirement m 3 0.03 0.06 0.09 0.12 60 11,259.0 337.5 675.0 1,012.5 1,350.0 70 9,642.9 289.3 578.6 867.9 1,157.1 80 8,437.5 253.1 506.3 759.4 1,012.5 90 7,500.0 225.0 450.0 675.0 900.0 Increase= a b /b * 100 50.0 50.0 50.0 50.0 smaller diameter when increasing the working pressure, satisfying the design condition of the difference in pressure between two sprinklers in the subunit less than the 20% of the pressure corresponding to the medium sprinkler. Fig. 4 shows that for both types of spacing with the available diameters for the PVCs system Table 1, it is not possible to satisfy the design condition for the average pressure in sprinklers lower than 300 kpa. Influence of Application Rate To carry out this analysis, an application rate ranging between 3 and 10 mm h 1 has been selected, which would be admissible for most sprinkler irrigated soils. There is an increment in the total water application cost when the application rate is increased from 3 to 10 mm h 1. For 12 m 12 m spacing, this increase has little effect on the total water application cost Fig. 6. On the contrary, for 18 m 18 m spacing, when the application rate is higher than 5 or 6mmh 1 the water application cost is increased in the four studied systems, with the Al system standing out Fig. 6. This is due to the need for a bigger diameter in the lateral or in the submain to transport the higher discharge generated by the increased application rate. For 18 m 18 m spacing in PVCb, PE, and Al pipes systems the increment in the total water application cost is 3, 8, and 15%, respectively, when the application rate increases from 3 to 10 mm h 1. In the PVC system, the available diameters do not allow application rates higher than 7 mm h 1 for 18 m 18 m spacing. In this case, when there is a change from 3 to 7 mm h 1, the total water application cost is increased by 4%. Higher application rates, apart from the difference in the total cost, can also lead to problems on the soil surface when its structure is weak and/or there is a risk of runoff in soils with low infiltration capacity. To study the effect of the application rate, it could also be taken into account that when the application rate is increased, there is a reduction in the necessary irrigation time. This can cause important variations in the size of the subunit. For example, if using an application rate of 5 mm h 1, a subunit of 1 ha should be irrigated in 8 h, then using an application rate of 10 mm h 1, two subunits of 0.5 ha could be irrigated in 4 h. That can cause small variations in the investment cost if the 0.5 ha subunits could use a smaller pipe diameter than the 1 ha subunits. However, this possible effect was not taken into account in Fig. 6. Influence of Application Efficiency and Water Price As in the previous cases, in this section the influence of only one factor irrigation efficiency on the total water application cost is analyzed. Lower irrigation efficiency entails higher water consumption, but it is considered that it has no repercussion on crop production and quality since the same N n value is guaranteed. In Fig. 7, the effect of the water application efficiency and the price of a water cubic meter on the total water application cost is shown. For a water price of 0.06 m 3, increasing the efficiency from 60 to 90%, the total water application cost decreases by 44, 42, 39, and 37% for PVCb, PVC, PE, and Al systems, respectively. If the water price was 0.12 m 3 for the same systems, the total water application cost would decrease by 46, 45, 43, and 42%, respectively. The economic saving is more important when the water price increases, as well as when the water cost represents a bigger percentage of the total water application cost. For this reason, a bigger economic saving is produced when the system uses buried PVC pipes, followed by PVC, PE, and Al. The water cost is increased by 50% when efficiency decreases from 90 to 60%. That is independent of the water price and the type of material of the pipe used in the irrigation system, since it only depends on the total water volume used Table 2. Conclusions Irrigation subunits with the lowest total water application cost are those composed of four laterals and 10, nine, and six sprinklers per lateral for 12 m 12 m, 12 m 18 m, and 18 m 18 m spacings, respectively, for the four systems studied PVCb, PVC, PE, and Al. In solid-set sprinkler irrigation, sprinklers and lateral spacing are the most influential factors on the total water application cost. With PVCb, PVC, PE, and Al pipes, for 12 m 12 m spacing the total water application costs are 12, 12, 21, and 19% higher, respectively, in comparison to the 18 m 18 m spacing. Application rates higher than 6 mm h 1 can lead to a significant increase in the total water application cost for wide spacing, such as 18 m 18 m, due to the need for large pipe diameters. The water cost increases by 50% when the application efficiency decreases from 90 to 60%, independent of the water price and type of pipe used. The reason is the important increase of water applied. In the breakdown of the total water application cost, the most important component is water cost, followed by annualized investment and energy costs. Comparing the four analyzed systems, the most inexpensive is the permanent set system with buried PVC pipes. JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / SEPTEMBER/OCTOBER 2006 / 451

Notation The following symbols are used in this paper: A investment annuity year 1 ; A r average application rate mm h 1 ; CFR capital recovery factor; C a total investment annual cost year 1 ha 1 ; C e energy cost year 1 ha 1 ; C i investment cost ; C t total cost of water application year 1 ha 1 ; C ta total cost per unit of water applied m 3 year 1 ; C w cost of the irrigation water year 1 ha 1 ; D rs gross water average depth that reach the soil surface decimal ; ED a distribution efficiency decimal ; E a application efficiency decimal ; H 0 pressure in the hydrant m ; i interest rate decimal ; N b gross water requirement m 3 ha 1 ; n useful life years ; n h number of operating hours h year 1 ; n n net water requirement m 3 ha 1 ; P net power kw ; P e price of the energy unit kw 1 h 1 ; P w price cubic meter of water m 3 ; Q 0 discharge in the hydrant m 3 s 1 ; and S irrigated area per subunit ha. References Caballer, V., and Guadalajara, N. 1998. Valoración económica del agua de riego, Mundi, Madrid, Spain in Spanish. Esquiroz, O., and Puig, J. 2001. Optimización económica de instalaciones de riego en parcela. Proc., XIX Congreso Nacional de Riegos, Asociacion Española de Riegos Y Drenajes, Zaragoza, Spain in Spanish. Keller, J., and Bliesner, R. D. 1990. Sprinkle and trickle irrigation, Van Nostrand Reinhold, New York. Khanjani, M. J., and Busch, J. R. 1982. Optimal irrigation water use from probability and cost benefit analyses. Trans. ASAE, 25 4, 961 965. Kumar, D., Heatwole, C. D., Ross, B. B., and Taylor, B. 1992. Cost models for preliminary economic evaluation of sprinkler irrigation systems. J. Irrig. Drain. Eng., 118 5, 757 775. Ministerio de Agricultura Pesca y Alimentación. MAPA. 2003. Plan nacional de regadio Horizonte 2008. http://www.mapya.es/ desarrollo/pags/pnr/rega.htm Nov. 18, 2003. Montero, J., Tarjuelo, J., and Carrión, P. 2001a. SIRIAS: A simulation model for sprinkler irrigation. Part II: Calibration and validation of the model. Irrig. Sci., 20 2, 85 98. Montero, J., Tarjuelo, J. M., and Martínez, R. 2001b. Análisis de los costes en una subunidad de riego por aspersión en cobertura total. Proc., 1st Congreso Nacional de Ingeniería para la Agricultura y el Medio Rural, Valencia, Spain in Spanish. Ortega, J. F., de Juan, J. A., and Tarjuelo, J. M. 2004a. Evaluation of the water cost effect on water resource management. Application to typical crops in a semiarid region. Agric. Water Manage., 66 2, 125 144. Ortega, J. F., Tarjuelo, J. M., de Juan, J. A., and Carrion, P. 2004b. Uniformity distribution and its economic effects on irrigation management in semiarid zones. J. Irrig. Drain. Eng., 130 4, 257 268. Scherer, T., and Weigel, J. 1993. Planning to irrigate ¼ A checklist. NDSU Extension Service, North Dakota State Univ., Fargo, N.D. http://www.ext.nodak.edu/extpubs/ageng/-irrigate/ae91w.htm March 21, 2003. Tarjuelo, J. M. 1986. Estimación del coste de aplicación de agua con riego por aspersion en la llanura norte de la Provincia de Albacete. Albacete, Spain in Spanish. Tarjuelo, J. M., Montero, J., Honrubia, F. T., Ortiz, J. J., and Ortega, J. F. 1999a. Analysis of uniformity of sprinkle irrigation in a semiarid area. Agric. Water Manage., 40 2 3, 315 331. Tarjuelo, J. M., Montero, J., Carrión, P., Honrubia, F. T., and Calvo, M. A. 1999b. Irrigation uniformity with medium size sprinklers. Part II: Influence of wind and other factors on water distribution. Trans. ASAE, 42 3, 677 689. Tarjuelo, J. M., Ortega, J. F., Montero, J., and de Juan, J. A. 2000. Modeling evaporation and drift losses in irrigation with medium size impact sprinklers under semi-arid conditions. Agric. Water Manage., 43 3, 263 284. Van Der Gulik, T. 2003. Irrigation equipment cost, Ministry of Agricultural and Food, Abbotsford, B.C., Canada. 452 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / SEPTEMBER/OCTOBER 2006