Impact of large-scale irrigation on a closed basin wetland: Water flow alterations and participatory irrigation management effects on the Sultan Marshes ecosystem in Turkey

Abstract

This dissertation analyzes alterations in a closed-basin wetland system resulting from the construction of a large-scale irrigation project in its catchment. The study was conducted at the Sultan Marshes ecosystem (Develi Basin, Turkey), which has been severely degraded within the last 20 years due to diversion of its major water sources for agricultural irrigation.

Spatial changes in the Sultan Marshes from 1980 to 2003 were analyzed using satellite remote sensing. Changes in the areal coverages of lakes, marshes, agricultural, and steppe areas determined by unsupervised classification of four Landsat images showed that both lakes and marshes became smaller after construction of the irrigation project. Steppe areas expanded onto wetlands. Significant portion of northern (Kepir) marshes were converted to agriculture.

Hydrologic changes in the Sultan Marshes were analyzed statistically and used to develop a dynamic hydrologic model of the system. Water levels dropped more than one meter in the lakes and marshes from 1993 to 2003, and decreases were observed in ground-water levels and spring flows, although precipitation and evaporation rates remained mostly stable. Simulations with the hydrologic model showed that even if surface water continues to be used for irrigation, reductions in appropriations from ground water and springs would restore and protect water levels in the marshes.

Agricultural and environmental changes in the Develi Basin were analyzed after the irrigation management was transferred from state to "irrigation associations" in 1994. The analyses showed that irrigated areas and water use in the Develi Basin showed significant fluctuations. The area allocated to production of high water-consuming plants increased. Water fee collection rates were lower than 100%. Although soil and water quality in the Develi Basin did not change significantly, ground-water levels, flow rates from springs and water levels in the Sultan Marshes all dropped. Four recommendations were developed that would help to resolve the conflict between agricultural and wetland water requirements: (1) a basin-wide approach water planning, (2) more realistic water pricing, (3) demand-based irrigation scheduling, and (4) rehabilitation of the irrigation system.

Economic costs and benefits associated with water diversions from agriculture to the wetlands were estimated, and the optimum or economically-efficient amount of water diversion was determined. When only direct-use values of the wetland (reed cutting, animal grazing and ecotourism) were included, the annual optimum amount of water diversion to the wetlands was found to be 5.2 million m 3 yr -1 (165 L s -1 ) compared to about 62 million m 3 yr -1 (1,957 L s -1 ) used in irrigation. Diversion of 5.2 million m 3 yr -1 water would be sufficient to restore the conditions in the marshes. The analysis showed that economically-efficient restoration of water levels in the Sultan Marshes is feasible with moderate amounts of water diversion.