evaluation of the best irrigation system by using Analytical Hierarchy Process (Case study: Plain izeh)

Multi-criteria decision making (MCDM) and Geographic Information System (GIS) for accurate decision making about the evaluation parameters used in natural sciences. This selection is influenced by different factors such as production and irrigation system expenses, water availability and quality, soil characteristics, climate conditions, labor skills, and cultural acceptability. The present study was conducted over an area of approximately 11081 ha in the Izeh plain Khuzestan province, south west Iran during 2015-2016. Results of the comparison (for each factors pair) were described in term of integer values from 1 (equal value) to 9 (extreme different) where higher number means the chosen factor is considered more important in greater degree than other factor being compared with. Analytic Hierarchy Process (AHP) is one of Multi Criteria decision making method that was originally developed by Prof. Thomas L. Saaty. In short, it is a method to derive ratio scales from paired comparisons.. The AHP was used for optimization.Spatial analysis to identify susceptible regions for pressurized irrigation systems starts with representing each selected physical sub-criterion by a thematic layer in which each point takes a value (1 to 9) which the samples have been gathered in a laboratory or a qualification according to that criterion. In order to layer all the criteria, data are gathered from satellite images and official sources at different available forms (digital and hard copy maps, tables and charts). Then, they are analyzed and treated using GIS and geostatistical tools. Each layer is obtained in raster data model. Spatial data on water characteristics, topography and climate (temperature map) are obtained from “water and power authority’’ of Khuzestan district, which is the Iranian official source of agricultural spatial database. Data are already available in digital format with 1/150,000 scale.

Major advantage of AHP is to formalize and renders systematic what is largely a subjective decision process and as a result facilitates ‘accurate’ judgments, that weights of criteria are also provided to decision maker, and that sensitivity analysis is easy to conduct by using computer. The weights of each criterion were computed by using the geometric mean to obtain the weight values. After that the weights should be aggregated and each weight divides on aggregated weights in order to normalize the weights. The normalized weights determine the priority of criteria. The sum of all normalized weights in each Table is equal to unity. The AHP methodology says that prioritizing and weighting the criterions should be done firstly. According to fundamental Saaty 's scale for the comparative judgments and by performing pair - wise comparisons of criteria with respect to the object, here the comparison and calculation of criteria in 1st , 2nd and 3rd levels in general for Localize irrigation system as an example. Most large drip irrigation systems employ some type of filter to prevent clogging of the small emitter flow path by small waterborne particles. New technologies are now being offered that minimize clogging. Considering conditions of water used for irrigation in the study region, suspended materials (W sm) and biological materials (W bm) were seen in the water according to laboratory experiments. Filters were employed in the farm and the water is available in the farm by pumping it from wells, but filters need to be changed after a while so possibility of clogging in the drippers still exists, therefore, these two alternatives have higher weight than available water. The amount of Sodium concentration (W na) was low and has less importance than other criteria except available water. Localized irrigation systems designed for no leaching fraction. High electrical conductivity (EC) and salts applied with the irrigation water may build up in the root zone but EC of the study region is almost low. Alkaline water (refers to pH) could make sediments in the drippers

In this study surface irrigation system found to be the best systems for this region. The comparisons expose that the results from the proposed model are in good agreements with results from the field investigations. An additional benefit of the model is that the decision-maker can perform a more exhaustive conceptual comparison of the different decision components. Causing that an extensive set of factors involved in selecting an irrigation system has been included in the proposed model, it can be claimed to be a comprehensive and practical model that can be used in selecting the irrigation methods for various agricultural sites, thereby improving soil and water resources exploitation and productivity.