Effects of irrigation system management turnover on water table depth and salinity of groundwater

Abstract

In recent years, management of large, state owned irrigation projects in Turkey have been transferred to water users such as farmers cooperatives or associations in order to reduce the financial burden on the government and to increase irrigation efficiency and farmer participation. Water table depth and groundwater salinity are important factors in irrigation systems, not only for plant growth but for human health as well. The objective of this study was to determine the impact on water table depth and groundwater salinity for transferring management of the Mustafakemalpasa irrigation project (19, 370 ha) in north-western Turkey to local, farmer controlled irrigation districts. Maps of water table depth and groundwater salinity were created for the a month of July (averaged over several years), the month with the highest amount of applied irrigation water, based on measurements made in 200 wells in the project area before and after transfer of managerial control. Both depth of the water table and salinity decreased after transfer The area with average water table depth of 100-200 cm was 25.41% of total area before turnover and 79.45% after and the area with water table depth 200-300 cm was 73.4% before turnover and 20.50% after before turnover, the area with average groundwater salinity 1.5-2.0 dS/m was 26.16% of total area, and that with average salinity 2.0-2.5 dS/m was 61.73% of total area; after turnover, average groundwater salinity was 1.5-2.0 dS/m in over all areas. Both changes were the consequence of an increased amount of applied water after transfer of the control of irrigation management from the state to local irrigatior districts controlled by farmers. In the short run, the farmers will get benefit from increased irrigation. However, over the long term, if water table depth continues to decrease then secondary salinization could become a major hindrance to irrigation sustainability.