Ergene River Basin is a part of the Thracian Basin with its drainage area of 11300 km2. The Pliocene aged Sandy Complex aquifer (SCA), environing about half of the Ergene River basin, is a regional aquifer. It is tapped by several thousand wells, mainly for irrigation use. The eastern and western parts of the SCA is unconfined while the central part is confined. The saturated thickness of this spoon-shaped aquifer reaches the maximum value (350 m) in the central part. The Çorlu-Lüleburgaz fault interrupts the continuity of the SCA by acting as a barrier in the artesian area. SCA has experienced extreme declines in groundwater levels since the 1970s (70 m in the last 46 years). The persistent declines in groundwater levels in the SCA drew the attention of many researchers and a groundwater flow model was constructed to determine the safe and sustainable yields and the limits of utilization for the SCA (Ökten and Yazıcıgil, 2005). This model was first calibrated under steady-state and transient conditions and, eventually, tested a total of eight alternative groundwater pumping scenarios (from 2001 to 2030) to predict both groundwater level and reserve changes in the aquifer system along with the average base flow to streams. In one of these scenarios (A), Ökten and Yazıcıgil (2005) continued the pumpage conditions of the year 2000, for the rest of the scenarios, they decreased the annual pumping rates to be equal to 100%, 90%, 80%, 70%, 60% and 45% of the annual recharge rates, respectively. Eventually, they found out that the average decline in groundwater levels is between 28 m (Scenario A) and -3.9 m (Scenario G). This study is carried out to examine the current groundwater levels in the SCA by using five selected observation wells with limnigraphs. Accordingly, the groundwater levels obtained through 8 different scenarios are compared with the actual groundwater levels from January 2001 to September 2018. The results showed that the current pumping rates are greater than both the sustainable and safe yields of the system. In fact, in two wells, the groundwater levels are even below the levels estimated by Scenario A and in two of them, the levels are similar to the ones obtained as a result of Scenario B. These comparison efforts suggest that, sustainable groundwater management policies and plans have not been adopted in the area. The pumping rates over the past 18 years were significantly greater than the sustainable yield (168 hm3/year) and traditionally defined safe-yield in Turkey (about 70% of the annual recharge, 261 hm3/year), causing significant declines in groundwater levels and base flow of the streams.
References: Okten, S. & Yazicigil, H., 2005, Turkish Journal of Earth Sciences, Vol: 14, 209-226 p.