شبیه‌سازی توسعه سیستم‌های مدرن آبیاری بر تعادل بخشی منابع آب زیرزمینی خراسان رضوی

Introduction Sustainable use of groundwater resources has been a concern of the past half century. Although a number of countries for many years have considered this issue, in Iran despite experts warning in the past two decades, recently has been highly regarded, especially by public officials. The use of modern irrigation systems by improving water distribution at the level of the farm and reduce the outflow of water from plant availability, improve irrigation efficiency but these systems increase evaporation and transpiration, and even in the event of a reduction of extraction water from wells, may not be effective in balance of the groundwater resources. The government of Islamic Republic of Iran, yearly pay a lot of subsidies (85% of total cost), to increase irrigation efficiency by equipping traditional culture to new irrigation systems. It may increase irrigation efficiency but may not improve balance of the groundwater resources. However, increasing irrigation efficiency in the process of conveyance, distribution, and application of water, improve groundwater balance, and reduce energy consumption, but costs, benefits and its impacts on balance of the groundwater resources are various in each step. so, technical and economic effects of each step and determining the priority of them, were the objectives of this study.
Materials and Methods In order to carry out this study, five cities include Mashhad, Sabzevar, Neyshabour, Torbat-e-jam and Torbat-e-heidarieh were selected. These areas are located in Khorasan Razavi in north east of Iran with average annual rain 200-250 millimeter. The mathematical relationships between extracted water from underground and surface resources and transfer it to farms as well as water influence to groundwater source and the rate of consumption in the fields and orchards were simulated in the excel spreadsheet. Data were collected by using questionnaires and interviews with farmers in the study area in the crop year 2012-2013. Additional data were collected from government documents in ministry of agriculture, energy and regional office. A multi scenario was simulated include 1-Increase the conveyance and distribution efficiency, CDE, to 95 % via transform dirty channel into the pipe. 2-Substitute pressurized irrigation systems instead of traditional system.3-Combining scenario one and two together. 4- Increasing irrigation application efficiency, IAE, to 75% in modern system in scenario three. 5-Increasing irrigation application efficiency, IAE, to 85% in modern systems in scenario three. 6- Execute scenario one and increasing area of irrigation modern systems to dual of initial forecast (only in Sabzevar until 1.5times). These scenarios also evaluated economically. In economic evaluation, increase of yield, between 10-40 percent as 4 scenarios separately, and reduce energy subsidies include increase power price to 2 times, and three kinds of cost price of power was considered.
Results and Discussion Average of CDE were obtained various between 57-78% in study area. The share of agricultural activity in reduce of groundwater source was 20% and most of area was encountered with low irrigation in warm seasons until to 50%. The most impact in creating balance in groundwater resources belonged to increase of CDE by first scenario and was quite economical. The most reduction on groundwater deficit can happen by scenario 5. However, in Torbat-e-jam and Torbat-e-heidarieh, groundwater deficit will continue unless the culture areas are reduced. Increasing IAE, is more effective than developing culture area of the pressurized irrigation systems, CAPIS, for example, in Sabzvar, increasing of IAE by 12% (scenario four), will reduce groundwater deficit 164% but increasing CAPIS, to 50%( scenario 6), will reduce groundwater deficit only 113%. Increasing CAPIS, with 30% increase in yield, make scenario three economical, but increase electrical energy and so, increase national cost by increasing subsidy of energy. First scenario, reduce consumption of electric power, so its benefit cost ratio will increase because reduce government cost but scenario two, increase consumed electrical energy. In the Sabzevar city power consumption in the first scenario was more than 176 million Kilowatt, which reduces farmers' spending by more than 23 billion IRR, But in the second scenario, energy consumption is rising by more than 25 million kilowatts. So, its benefit cost ratio will decrease if government reduce power subsidy. As a result, this scenario without increase of IAE and yield, will not be economical. In all city except Sabzevar with the increasing yield by 20 percent, all scenarios will be economical, also in all city, with omission of the power subsidy, scenario 2 will be uneconomical, so the government is forced to grant subsidies to expand new irrigation systems. The city of Sabzevar, which has the longest route for pipelines (about 42%), requires an initial investment of 695 billion rials, with investment of 1079 billion IRR needed to equip 15342 hectares of land to modern systems. Therefore, the first scenario, although having more economic benefits, requires a relatively small amount of investment as well. Regarding the energy cost of between 680 and 7300 Rls, a number of government payments with the implementation of the first scenario is reduced from 96 to 1263 billion rials yearly, while the total initial capital required to realization of the goal is 695 billion rials, which is estimated at 70 billion rials, annually.
Replacing the irrigation modern systems instead of traditional systems without reducing the gap between the current and potential IAE, had a little impact on the groundwater balance, and to consider energy subsidies, is in conflict to national benefits.
Conclusions Installation of volumetric meters and tubing for water transmission and distribution channels should be used in preference to increase the efficiency of irrigation, reduce energy consumption and water extraction from wells, protection of saving water, and prevention of increase in cultivation. In order to increase the water application efficiency and production, implementation of modern irrigation systems on farms and gardens should be accompanied by adequate supervision and training.