Characterization of saline groundwater in lower Karkheh river basin.

Groundwater salinization is a major limitation in irrigated farmlands that have shallow water table. It deteriorates soil resources, decreases land and water productivity and imposes cost, time and labor for construction of drainage water disposal facilities. Additionally, environmental impacts regarding to the outlet is another concern that should be considered. Dasht-e-Azadegan (DA) in southwest of Iran, is one of the areas where groundwater salinity has created similar constraints for its agriculture and ecosystem. To overcome to these problems, a management program that identifies interventions on farm, at system and policy levels should be planned and executed. The overall aim of the project is to define a range of suitable interventions that mitigate salinity, increase agricultural water productivity and improve livelihoods in the lower Karkheh. These interventions should eventually lead to sustainable irrigation in the area and contribute to maintain the health of the Hour al Azim swamp, into which the Karkheh River drains. For this purpose, as a preliminary research activity, a survey of lower KRB area for investigation of ground water depth and quality was accomplished. Maps of ground water depth and salinity were prepared and classified for delineation of hot spots in the region. Other relative useful information on the causes of ground water salinization, waterlogging problems and also interactions between ground water and soil were extracted through the project. Since existing literatures reveal that poor irrigation efficiency is a major cause for this situation, in this study, a GIS based overlay-index model, namely DRASTIC also was used to demonstrate the impact of different irrigation scenarios on salinization of DA groundwater. The hydro-geologic parameters of DRASTIC provide a systematic evaluation of the potential for groundwater contaminations and identify the areas that relatively need more considerations. Irrigation scenarios were defined as under irrigation (0.5ET, 0.7ET and 0.9ET), optimum irrigation (ET) and over irrigation (1.2ET, 1.5ET and 2ET), where ET is actual evapotranspiration demand of DA irrigated lands. For each scenario, DRASTIC model was separately run and its outputs were compared with present status of DA groundwater salinity. The results indicate that the model outputs for over-irrigation scenarios (especially 1.5ET) are more consistent with the current status of groundwater salinity. This means that DA groundwater salinity is mainly due to mismanagement of water at farm level. The result, however, is consistent with the evidence and reasons for groundwater salinization in this area that needs more considerations and improvements.