Journal of Environmental Quality 30:1150-1153 (2001)
© 2001 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
TECHNICAL REPORT
Ecological Risk Assessment
Analysis of Irrigation Systems Using Sustainability-Related Criteria
Odysseus G. Manoliadis*
Department of Geotechnology and Environmental Engineering, Technological Education Institute of Western Macedonia, Gr-50100 Kozani, Greece
* Corresponding author (omano{at}tee.gr)
Received for publication March 24, 2000.
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ABSTRACT
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Sustainable agricultural development as a desired goal in irrigation management is a result of recent public awareness of the scarcity of water for food production. In order to incorporate sustainability-related criteria in the analysis of irrigation systems, the present study aims at introducing environmental indices that represent irrigation water conservation and satisfactory production and income for farmers under stress conditions. An experiment was conducted in Chania, Greece, during the irrigation periods of 1989 and 1990. The irrigation water delivered to 40 experimental plots and the relevant soil moisture content at the root zone were recorded. The data, collected in real time, were used for the calculation of the corresponding environmental indices. The variation of indices in time and space was high, and demonstrated that up to 13% of water was delivered to crops, 82% was yield loss, and 84% was economic return. The study indicated that environmental indices could be easily computed by means of routinely collected data, and could also be incorporated into decision-making approaches, such as compromise programming, in order to develop policies for irrigation water allocation.
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INTRODUCTION
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RECENT public awareness of the scarcity of water for food production has prompted sustainable agricultural development issues in irrigation water management (Conway, 1975). Under conditions of scarcity and conflicts concerning irrigation water use and management, it is required that water be distributed as efficiently as possible, to ensure satisfactory production and low cost. For the incorporation of the corresponding environmental indices in the decision-making process, the definition and trade-offs between the criteria examined must be clearly established.
In the past, several studies addressed analysis of irrigation system performance in terms of social and economic criteria. Oad and Levine (1985) and Oad and Podmore (1989) addressed seasonal reliability in water deliveries by introducing the term relative water demand, defined as the ratio of supply (irrigation plus rainfall) to demand (evaporation plus seepage and percolation losses), to express adequacy. Molden and Gates (1990) used equability (defined as the standard deviation to mean quantity of water applied to crops) to analyze water distribution. Jensen (1967) used yield production to evaluate irrigation efficiency. Anderson and Mass (1971)(p. 23–34) evaluated irrigation performance using the economic return of irrigation as a production function.
Despite the fact, however, that numerous studies have examined social and economic criteria in relation to performance, no effort appears to have been made to evaluate the performance of irrigation projects in terms of effect on the environment. In effect, disregarding these issues has led to poor performance of irrigation schemes. Needless to say, the processes that irrigation management imposes, such as water movement and storage in the soil, are considered of major importance for sustainable development, and cannot be overlooked in environmental impact studies of irrigation projects. The specific processes are of particular significance in relation to the hydrologic cycle, plant growth and crop production, and the movement of chemicals in the environment. In addition, these processes have a major influence on overland flow and ground water recharge. In the present study, an attempt was made to combine indices with the above environmental issues, aiming at evaluating the performance of existing and planned irrigation projects according to sustainability issues.
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ENVIRONMENTAL INDICES
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Sustainability, according to Conway (1975), is the ability of a system to withstand collapse while maintaining satisfactory production. In Conway's terms, except for equability, agricultural systems should be assessed according to productivity, stability, and sustainability in association with yield and income distribution. Recommendations about how to include sustainability issues into project appraisal are found in the work of Mergos (1991). Thus, in an attempt to define the above issues in practice, the following environmental indices are introduced:- Efficiency: Defined as the goal of conserving water resources via system management. Resource conservation plays an important role because it reduces overland flow and ground water recharge. Saving water may also reduce expenditures required for infrastructure and can possibly fulfill other water requirements. The environmental index, ei1, is defined as:
 | [1] |
where wij is the amount of water delivered to crop i at decision step j.
- Sustainability: Defined as the socially desirable objective of the system to maintain productivity and withstand collapses when subject to stress. The environmental index, ei2 (measured in kilograms), is expressed by the total yield loss:
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where LAL is the lower allowable limit of soil moisture content, sij is the soil moisture content measured of crop i at decision step j, and 
ij = 0 if sij > LAL or ij = lij (yield loss coefficient; Doorembos and Kassam, 1979, p. 5–8).
- Relative cost: Defined as the cost of recovery, that is, the yield loss as a result of saving a volume of water wij. The environmental index, ei3, is defined as:
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where cij is the cost of yield loss of crop i at decision step j.
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DATA CALCULATION OF ENVIRONMENTAL INDICES
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The data required for the calculation of environmental indices were collected on a real-time control basis. As can be seen in Eq. [1–3], the quantity of the water and the soil moisture content in each crop and decision step are the necessary data for the calculation of the environmental indices ei1, ei2, and ei3. For the program of measurement, volumetric meters and tensiometers were used on each farm. The volumetric meters measure the volume of water on each farm on a real-time control basis. The tensiometers (one at each farm) were used to estimate the soil moisture in specific spots of the farms. Soil moisture was measured in a depth typical for soil conditions and root zone, and ranged from 30 to 60 cm.
The data recorded for the quantity of water used for irrigation of the crops for the three successive periods (3 wk) are presented in Table 1. In Table 2, the corresponding soil moisture content measurements are tabulated. The calculation of the environmental indices based on these data is as follows:
- Environmental index ei1 (efficiency):
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where, for when n = 40, k = 3, and wij are listed in Table 1, ei1 = 2979.9 m3. For a period of 3 wk the amount of excess water supplied to olive trees is 771.02 m3, or 771.02 m3/60000/2 m2 = 25.70 mm, or 2221.24 m3/160000/2 m2 = 27.76 mm.
- Environmental index ei2 (sustainability):
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where, for when ij for the 3 wk is equal to 0.07, 0.10, and 0.10 (Table 2), ei2 = 0.07 or 7% yield loss for both crops (45 kg for olive 153 kg for orange trees).
- Environmental index ei3 (relative cost): the cost of economizing on water in terms of yield loss is then estimated, assuming 150 drs (monetary unit) kg-1 for orange and 200 drs kg-1 for olives. Therefore, the resulting relative cost is:
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For olives, relative cost = 45 x 200/771 = 11.67 drs m-3. For oranges, relative cost = 153 x 150/2221 = 10.33 drs m-3.
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CASE STUDY
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The alternative management option assessment was based on irrigation policies proposed during the irrigation periods of 1989–1990 in 40 experimental plots in Chania, Greece. The specific irrigation networks were supplied with water from service reservoirs and pump stations. The type of irrigation system on the farm was trickle irrigation. The data and methodology are reported in Tsakiris and Manoliadis (1994). Farming in the area has changed since 1989. On a percentage basis, orange trees have increased from 30 to 50% while olive trees have been reduced from 65 to 50%. The competing use of water resulted in poor irrigation scheme performance operation.
Management Alternatives
A discrete set of eight different management alternatives is introduced, resulting from two different crops with different relative water demands and durations between applications. Table 3 lists the important attributes of each alternative.
Environmental Indices and Compromise Programming Structure
The compromise structure (Zeleny, 1982, p. 10–35) is formulated so that indices could lead to trade-off between available water conservation and yield or conservation of water and economic return. Formulation of the case study is presented for illustrative purposes only. The case study employed five basic indicators. The first index, ei1, refers to the amount of water delivered to crops; the second and third indices, ei2or and ei2ol, refer to the yield loss for each of the crops (olive trees and orange trees, respectively); and the fourth and fifth indices, ei3or and ei3ol, refer to the relative cost. Thus, the total number of indices is five.
An illustration of the composite programming tree structure is presented in Fig. 1. The preferred management option is then identified among the specific alternatives by locating the system nearest to the ideal point in terms of the compromise distance (Fig. 2). For the comparison of environmental indices, because these are measured in different units, a normalized distance, R(x), for each of the basic indicators, and for each management alternative, x, is used:
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where R is the index value and R(w) and R(i) are the worst and ideal values, respectively. To clarify, if we calculate the normalized distance of alternative I for the environmental index ei1, the index value is 885 mm while the ideal and worst values are 845 and 971 mm, respectively. Therefore, the impact relationship value of alternative I is calculated as:
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Analysis of Management Options
The selection of a preferred option is determined by considering which system is robust with respect to variation of the criteria that measure system performance. The specific preferences may be expressed by means of various scenarios. The following scenarios were investigated individually within the context of the multiple criteria decision making:
(i) Express a strong concern for limiting water consumption.
(ii) Express a strong concern for a sustainable yield.
(iii) Stress the importance of minimum relative cost.
Preference weights that emphasise each of the objectives are given in Table 4.
To illustrate, we calculate the compromise distance from the ideal solution of alternative I that scores at each evaluation criterion as follows, using the normalized values (ei1 = 0.68, ei2or = 0.65, ei2ol = 0.61, ei3or = 0.60, ei3ol = 0.38). The composite distance from the ideal point (0.00, 0.00, 0.00) is:
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RESULTS
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Data collected from real-time control measurements of two successive years were analyzed. The statistical analysis of the quantities of water delivered to crops has resulted in an equability factor (standard deviation divided by mean value) of 3.7%. The calculation of environmental indices (in terms of the their recorded units and normalized values from 0 to 1) for two successive irrigation periods is presented in Table 5. Environmental index, ei1, representing efficiency, ranged from 845 to 971 mm with a variation of 13%. The corresponding environmental indices for sustainability, ei2ol and ei2or, ranged from 35.89 to 61.88% yield loss for olive trees and from 10.55 to 58.15% for orange trees, and resulted in a variation of 42% for olive trees and 82% for orange trees. Finally, the relative cost indices, ei3ol and ei3or, ranged from 0.43 to 2.72 drs m-3 for olive trees and from 0.33 to 0.65 drs m-3, and the variation calculated was 84 and 49%, respectively. Examining the results in terms of the first management option (i.e., express a strong concern for limiting water consumption; environmental index ei1), Alternative IV (distance from the ideal point 0.00) ranked first. In terms of the second management option (i.e., concern for a sustainable yield; environmental indices ei2or and ei2ol), Alternatives VII (distance from the ideal point 0.00, 0.00) and IV (distance from the ideal point 0.03, 0.00) ranked first, whereas the third management option (i.e., minimum relative cost of water; environmental indices ei3or and ei3or), demonstrated that Alternatives VII (distance from the ideal point 0.00, 0.00) and III (distance from the ideal point 0.01, 0.00) ranked first.
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Table 5. Environmental indices and normalized environmental indices for the irrigation period (1989–1990) of the case study.
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The score of each alternative, computed as the relative distance of the ideal point (0.00, 0.00, 0.00) and assuming equal weight assigned to each index, is as follows: I (0.85), II (0.96), III (0.90), IV (0.82), V (1.28), VI (0.98), VII (0.67), VIII (1.12).
Therefore, the option that was demonstrated to rank better among all management options (or the best solution) is Alternative VII, because it is closest to the ideal.
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DISCUSSION
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It has been shown that environmental indices expressing sustainability-related criteria during irrigation management under sustainable development can be obtained during irrigation monitoring from randomly collected data. The study indicated that environmental indices could also be incorporated to select alternative irrigation policies for irrigation water allocation. A case study was presented to demonstrate the use of environmental indices combined with compromise programming. The approach used to select the final management alternative aimed at determining a system that is robust with respect to different management options and system objectives expressed as scenarios. In conclusion, the final decision involves a trade-off analysis between conservation of water and desired system sustainability in terms of yield and income distribution. The structure of environmental indices can be modified to include other project features (i.e., soil types, crops, irrigation systems, etc.). It should be noted that the methodology could be implemented to any type of additional environmental measure according to project features. Furthermore, it can be used in several cases of irrigation management (assessment of existing projects, assessment of planned irrigation projects management, selection of alternative management options). These features combined with the increasing awareness of the scarcity of water for irrigation management warrant further investigation into environmental index studies and multiple criteria decision-making approaches.
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REFERENCES
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- Anderson, R.L., and A. Mass. 1971. A simulation of irrigation systems. Tech. Bull. 1431. USDA Economic Res. Serv., Washington, DC.
- Conway, G.R. 1975. The properties of agroecosystems. Agric. Syst. 24:95–98.
- Doorembos, J., and A.H. Kassam. 1979. Yield response to water, irrigation and drainage. FAO, Rome.
- Jensen, M.E. 1967. Evaluating irrigation efficiency. J. Irrig. Drain. Div. Am. Soc. Civil Eng. 93:83–98.
- Mergos, G.J. 1991. Sustainability issues and technology choice in irrigation investment. Water Resour. Manage. 5:244–251.
- Molden, J., and T. Gates. 1990. Performance measurements for evaluation of irrigation delivery systems. J. Irrig. Drain. Eng. Am. Soc. Civil Eng. 116:804–823.
- Oad, R., and G. Levine. 1985. Distribution of water in Indonesian irrigation systems. Trans. ASAE 28:1185–1191.
- Oad, R., and T.H. Podmore. 1989. Irrigation management in rice-based agriculture: Concept of relative water. Int. Council Irrig. Drain. Bull. Suppl. 38:1–10.
- Tsakiris, G., and O. Manoliadis. 1994. Stochastic modelling of the operation of hydrants in an irrigation network. p. 252. In New uncertainty concepts in hydrology and water resources. Int. Hydrol. Ser. 2(6). Cambridge Univ. Press, Cambridge, UK.
- Zeleny, M., 1982. Multiple criteria decision making. McGraw–Hill, New York.
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ABSTRACT
INTRODUCTION
