طراحی آبیاری سطحی نواری و تعیین متغیرها با استفاده از بهینه سازی چند هدفه

Surface border irrigation design and variables determination using multi-objective optimization



M. Saleki , M.R. Nouri , H.R. Salemi , R. Fatahi





Abstract

Design of surface border irrigation systems is usually performed based on empirical relations presented in the literature or through simulation results in various models. These methods do not allow investigating the impact of all design variables on different irrigation indices.

Designing based on minimizing the volume of water input along with maximizing indices such as application efficiency, distribution uniformity, and irrigation adequacy is a new approach that can provide the best results through multi-objective optimization. The best choice for design variables, including length, width, slope, inflow rate, and cut-off time in a field, can be obtained using this method to achieve optimal indices.

In this research, by measuring the water advance in sample plots in a field in Isfahan and simulating water movement in the border strips, the soil infiltration coefficients were obtained. Based on this, for a net irrigation depth of 75 mm and a roughness coefficient of 0.15, 56700 closed-end border irrigation events were simulated using WinSRFR 5.1 software. Among the obtained results, using the constrained objective function multi-objective optimization method, with the aim of minimizing the volume of water input and application efficiency higher than 90%, distribution uniformity and irrigation adequacy more than 0.8, 515 optimal options for designing the irrigation border strips were determined, and among them, some options were presented for the optimal design of the irrigation border strips in this field and similar fields.

The results show that the volume of water input in the optimized options is between 712.8 and 757.3 cubic meters per hectare, which is significantly different from the measured values in the field. The method presented in this research can be used as a new approach for designing surface border irrigation systems and increasing water productivity in agriculture.



Introduction:

Due to the global population growth, there is an escalating demand for food, necessitating maximized utilization of available freshwater resources for food production (Foley et al., 2011; Brauman et al., 2013). Surface irrigation holds the predominant position among irrigation techniques. Enhancing irrigation efficiency and reducing water consumption in surface irrigation not only decreases water usage per unit area but also facilitates the expansion of cultivated land, preservation of water reservoirs, and allocation of water resources to other sectors such as drinking and industrial use.

The solution to reducing water consumption volume and enhancing irrigation indicators, such as water use efficiency, distribution uniformity, and irrigation adequacy, lies in the proper design of various variables. These variables include the dimensions of the farm (length, width, and slope) as well as the flow rate and timing of water application. Improving these indicators results in decreased water wastage and increased yield, ultimately boosting water productivity in agriculture (Bastiaanssen and Steduto., 2017; Zwarta. et al., 2010).

In Border Irrigation, the design of irrigation strips has traditionally relied on empirical relations and tables outlined in references, occasionally optimizing one or two variables in papers (Wynn R. Walker, Gaylord V. Skogerboe. 1987; Chen et al., 2013; Smith et al., 2016). However, the maximization of irrigation indicators often involves conflicting objectives, where enhancing one indicator may diminish another. Consequently, employing multi-objective optimization methods becomes imperative. Additionally, irrigation simulation models and software are essential for assessing various options effectively. Since 2007, WinSRFR software has been utilized for modeling, simulating, and analyzing irrigation events, as well as designing surface irrigation systems. (Alavi et al., 2022; Mazarei et al., 2020; Fadul et al., 2020; Salahou et al., 2018; Heydari and Abbasi, 2016)

Multiple studies have confirmed the attainment of indicators exceeding 90% in border irrigation (Liu et al., 2020). However, the simultaneous consideration of all variables and irrigation indicators in border irrigation design has been largely overlooked. Furthermore, previous studies have not explored the impact of indicators and variables on minimizing water consumption in surface irrigation.

Hence, adopting the innovative approach of this research, employing multi-objective optimization to attain optimal designs for surface irrigation systems, emerges as a novel and indispensable method. This approach yields substantial reductions in agricultural water consumption while simultaneously enhancing water productivity.



Methods:

For this research, experiments were conducted and data were collected on a 180-hectare farm located in the western region of Isfahan city, Iran. The experiments were conducted across six plots of winter wheat fields, each with distinct geometrical dimensions. The soil on the farm is homogeneous and classified as loam-clay. The research process proceeded as follows:

Field data, including water movement along the strips, dimensional characteristics, and input flow to the closed-end irrigation strips, were gathered.

The measurement results were inputted into the Analysis section of WinSRFR 5.1 Software, and through irrigation simulations, the values of soil water infiltration coefficients in the Kostiakov relation were obtained.

The range of design variables for the irrigation strip, including length, width, slope, inflow rate, and flow cutoff time, was established.

Information for 56,700 potential design options was entered into the Simulation section of WinSRFR software, yielding irrigation indicators and the volume of incoming water for each option.

Optimization steps were executed using Bounded Objective Function multi-objective optimization method to determine the optimal cases.

From the optimal choices, the best design for the surface irrigation strip was selected for the designated farm.

The results of field measurements were compared with those derived from the design optimization method.



Results:

In this research, 56,700 potential design options for border irrigation on the farm were evaluated. Among these, 515 optimal choices were identified, characterized by maximal irrigation indicators and minimal water volume entering the strip. These optimal options exhibit application efficiencies exceeding 90%, alongside irrigation adequacy and water distribution uniformity in the strip of over 0.8.

In general, employing this optimization method for fields with loam-clay soil and penetration coefficients of K=110 mm/h^a and a=0.735, for a required irrigation depth of 75 mm, the following can be observed:

The optimal slope of irrigation strips falls within the range of 0.004 to 0.007 m/m.

The optimal inflow cutoff time correlates with the length of the strips. For strips up to 70 meters long, cutting off water flow is optimal when water reaches the strip's end (RCD=1). For strip lengths of 80 to 90 meters, cutoff is advisable when the water front reaches 0.9 of the strip length (RCD=0.9), and for strip lengths of 100 to 120 meters, it's recommended at 0.8 of the lengths (RCD=0.8). (RCD = Relative Cutoff Distance)

The optimal flow rate and the width of the strip vary based on the slope and length. These parameters can be chosen from optimal options according to the designer's discretion. Moreover, as the strip length increases, the optimal flow rate per unit of width also increases.

In conclusion: Employing the Surface (Border) Irrigation design method based on multi-objective optimization is recommended as a novel approach for surface irrigation design, aiming to achieve maximal irrigation indicators and minimal water application volumes. Through the advancement of this method, it becomes feasible to aid in reducing water consumption and enhancing water productivity in agriculture, all at minimal costs.





Keywords: Border irrigation, Multi-objective optimization, Surface irrigation design, Water productivity

Citation: Saleki M. Nouri M.R. Salemi H.R. Fatahi R. Surface border irrigation design and variables determination using multi-objective optimization. Iranian Water Research Journal