COMPARISON OF SAFE AND SUSTAINA0BLE YIELDS: A CASE STUDY OF AN OVEREXPLOITED AQUIFER IN WESTERN TURKEY

Groundwater serves as an important source of fresh water throughout the world, supplying water for domestic, industrial and agricultural use. The proportion of groundwater use to total water use has been rising significantly in recent decades. It must be kept in mind that the groundwater resources are, although replenishable, not inexhaustable. Shortages of groundwater in areas where excessive withdrawal have occurred emphasize the need for accurate estimates of the available groundwater reserves and the importance of proper planning to ensure the continued availability of groundwater resources. The Küçük Menderes River basin aquifer system located in western Turkey is one of such areas where excessive groundwater withdrawals for irrigated agriculture have caused rapid declines in groundwater levels during the past two decades.

This study compares the safe and sustainable yields of the Küçük Menderes River Basin aquifer system. Geological, hydrogeological, and geophysical data are used conjunctively to define various hydrogeological units and their geometry. Distributions of hydraulic parameters and recharge are estimated by geostatistical methods and hydrologic simulations, respectively. A finite-difference groundwater flow model are used to represent the unconfined flow in the aquifer system. The model has been calibrated under steady-state and transient conditions. The resulting model was used to test seven management scenarios for a planning period of 21 years to determine the safe and sustainable yields of the aquifer system and to investigate the potential impacts of four planned surface water reservoirs on groundwater resources in the basin. The results demonstrate that the continuation of the present pumping rates exceed both the safe and the sustainable yields of the aquifer system. Consequently, the growing need for irrigation water should be met by the construction of the planned surface water reservoirs and the implementation of efficient water management policies and plans.