مديريت و برنامه ريزي منابع آب با استفاده از مدل برنامه ريزي خطي

Water resources management using linear program model

جهت درنظر گرفتن ابعاد و پيچيدگي هاي سيستم هاي منابع آب، امروزه مديران و برنامه ريزان براي رسيدن به تصميمات بهينه، به استفاده از مدلهاي بهينه سازي به عنوان ابزاري كارآمد روي آورده اند. در پژوهش حاضر براي بررسي الگوي كشت موجود در دشت همدان بهار و تدوين سناريوهاي مديريت منابع آب در بخش كشاورزي، از مدل برنامه ريزي خطي و نرم افزار لينگو استفاده شد. اين مدل با هدف تعيين الگوي كشت بهينه، تعيين ميزان تخصيص بهينه از منابع آب سطحي و زيرزميني و حداكثر كردن سود حاصل از كشت محصولات تدوين شد و با توجه به قيود و محدوديت ها به اجرا درآمد. به منظور بررسي گزينه هاي مديريتي، سه شيوه ي بهينه سازي الگوي كشت در وضع موجود، بهينه سازي الگوي كشت با اعمال محدوديت برداشت از منابع زيرزميني، بهينه سازي الگوي كشت با تغيير در شيوه آبياري تدوين و با استفاده از مدل اجرا شد. نتايج به دست آمده از اجراي مدل، حاكي از برتري تغيير شيوه آبياري نسبت به دو شيوه ي ديگر است؛ به گونه اي كه ميزان آب مصرفي الگوي كشت 8 /23 درصد كاهش و ميزان توليد، سطح قابل كشت و سود به دست آمده به ترتيب 1 /13 درصد، 7 /12 درصد و 8 /15 درصد نسبت به الگوي موجود افزايش نشان مي دهد.

Considering the complexity of water resource systems، nowadays managers have widely applied optimization models as efficient tools to reach useful decisions on this issue. The existing optimization models provide new opportunities for better decision making in field of water resources development and planning. Using optimization methods allows decision makers to make the most appropriate decisions among the solutions available for water and soil resources. Optimization is a method by which the best possible answer for a problem is determined according to the target and the existing conjugations، which are specified by functions and mathematical relations. The optimal problem has a target function and several constraints. Math planning is suggested as a useful and efficient way to solve resource allocation problems especially when decision variables، constraints and various parameters are examined. Linear programming is one of the simplest and most practical optimization models. This type of planning can be used for issues with simple relationships such as direct resource allocation to complex operational and management issues. Since all the mathematical relations contained in this model are of the first order type، it is called the linear model. Hamedan-Bahar plain has faced many problems such as lack of surface water resources، decline of underground water resources and the negative balance of groundwater in the recent years، one part of agricultural land in Hamadan-Bahar Basin is located in Bahar city and the other part in Hamedan city. The water needed for agricultural sector in Bahar city is completely extracted from underground resources while in Hamedan city، about 80% is extracted from underground resources and the rest is supplied by the surface resources. In this region، the first priority is the allocation of water resources for drinking and the second priority belongs to the industrial sector، and agricultural sector is in the third priority. Due to this allocation priority as well as lack of water resources in the region، the water need of crops is not fully ensured according to irrigation scheduling and pattern of cultivation. This research has been tried to compare the different methods of planning، with considering the priorities of water resources allocation and percentage of water supply needs in agricultural sector. Therefore، a linear programming model was created with the goal of 1- determining the optimal cultivation pattern، 2- determining the optimal allocation of surface water and underground water sources، and 3- maximizing the benefit from crop production. This model، based on available water resources and also with considering limitations، determines the cultivation pattern of crops and the amount of water allocated، so the most benefit from crop production will be obtained. Studying the cultivation pattern on this plain and water resources management scenarios، linear program and LINGO software were used. Objective of this model was maximizing of benefit and optimizing allocation of water and cultivation pattern. Evaluating three Scenarios of optimization of cultivation pattern in current situation، optimization of cultivation pattern in changing irrigation method and optimization of cultivation pattern by limiting of groundwater utilization، showed that، the optimization of cultivation pattern in changing irrigation method is better than two others and have more benefits. In this scenario، water consumption of cultivation pattern showed 23.8 % decrease; also، production، area of cultivation and advantage showed 13.1%، 12.7% and 15.8% increase، receptively. The results of this research revealed the necessity of changing the pattern of water consumption in agriculture as an optimal solution to overcome the problems of dehydration and shrinkage of aquifers. Meanwhile، providing social and cultural backgrounds for modifying the pattern of crops by replacing less-water-based products with more economic costs، instead of high-water requirements products، can reduce water use and improve conditions to sustainable use of water resources in the region. Due to the proper allocation of water، demand management and water consumption patterns، especially in the agricultural sector، can create a better and more stable economic situation. Finally، it can be claimed that with the help of planning and optimization models، examining and comparing different methods، making the best decision in the field of water resources management is possible. Eventually، examining other models such as nonlinear planning and applying more limitations and scenarios، especially changes in cultivation pattern، and comparing with the results of this study is suggested.