A Proposed Index of Water Quality Assessment for Irrigation


A water quality index in a simplified concept is a way for combining the complex water quality data into a single value or single statement. This study comprised the development of a new index called the ‘irrigation water quality index (IWQI)’. This index has advantages by reflecting the suitability of water for specific use,( e.g.irrigation water supply) and using a combination of many parameters that limits water suitability to soil characteristics or crop yield.. The New proposed index method utilizes five limitation groups that have been mentioned by Ayers and westcot (1985) with few modification in their classification categories for irrigation water qualityassessment . These limitation groups are: (a) salinity limitation, (b) infiltration and permeability limitation, (c) specific ion toxicity, (d) trace element toxicity; and, (e) miscellaneous impacts on sensitive crops . A linear combination of these groups is formulated to form the so-called IWQI, which is a technique that could be used to classify irrigation waters with respect to four suitability categories. The mathematical equations to transform the actual concentration values into rating values (quality sub indices) have been formulated. Weighted minimum operator method was proposed to obtain overall index scores based on individual index (sub-index) values. It is hoped that this proposed method has provided an index (IWQI) used as a simple tool foranalysis that serve decision-makers , non-technicians and/or farmers. This method has not been applied previously weighted and their current results look much better than the results of the un weighted minimum operator method , especially when there are sub indices of low values with low weights, along with indices of low values with high weights .The proposed technique was applied to assess the irrigation waterquality of Tigris , Euphrates and Shatt Al Arab rivers in Iraq based on observed water quality data. Data representing the monthly sampling of the three rivers were collected during 2008 and considered in this study. Results revealed that the overall quality of the surface water in Tigris river falls under the ‘suitable’ class and remainso until Kut city, and then ranged from moderately suitable to unsuitable until Qurna. In Euphrates river the suitability of water falls under suitable class from Saqlawiya until Kifil and then the quality ranges from moderately suitable to unsuitable untilQurna area. Water of Shatt Al Arab was not suitable through the year except in Jan, Feb, and Oct where the water was slightly suitable. On the other hand, water quality for Tigris and Euphrates was strongly affected by water returns resulted mostly by agricultural use and to a limited extent by domestic uses inside and outside of Iraqiterritories. This technique is hoped to help decision- makers in reporting the state of the water quality, as well as verification of the spatial and temporal variations.