The projected costs and benefits of water diversion from and to the Sultan Marshes (Turkey)

The Sultan Marshes in the Develi Basin, Anatolia, one of twelve internationally important wetlands of Turkey, have been severely affected by the construction of an irrigation project in 1988. Intensive use of surface and ground water in irrigation has caused more than a 1 m decline in water levels and has affected the wetlands' ecological characteristics. Previous studies indicate that Sultan Marshes will need more water to restore viable ecological conditions. In this study, we analyze how economic benefits from agriculture and wetlands would be affected if moderate amounts of water were diverted from agriculture back to wetlands in the Develi Basin. By estimating total and marginal costs and benefits associated with water diversions, we determined the optimum or economically-efficient amount of water diversion. When only direct-use values of the wetland (animal grazing, plant harvesting, and ecotourism) were included in the analysis, the optimum amount of water diversion to the wetlands was found to be 5.2 million m³ year^{- 1} (165 L sec^{- 1}), which compares to about 62 million m³ year^{- 1} (1,957 L sec^{- 1}) used in irrigation. When wastewater treatment benefits (an indirect-use value) were added, the optimum amount rose to 7 million m³ year^{- 1}. Overall, the analysis showed that water diversion from agriculture to the Sultan Marshes is economically preferable.