N. Nur Ozyurt
Investigation of the groundwater residence time distribution in the Aladag (Kayseri-Adana, Turkey) karstic aquifer
PhD Thesis, Hacettepe University, Department of Geological Engineering, Hydrogeological Engineering Division
The Aladağ karstic aquifer of Eastern Taurids Range extends between 400m and 3750m elevations and, covers an area of 1900 km2 within Adana-Kayseri-Niğde provinces. The study covers the Kapuzbaşı, Göksu shallow circulation and Yerköprü 1, Yerköprü 2 and Yerköprü 3 deep circulation springs that extend from recharge area to the Zamanti river.
The system is fed by precipitation of Mediterranean origin and total precipitation input, evapo-transpiration, net recharge and its volumetric equivalent are found to be 1113 mm, 451 mm, 879 mm and 939 106 m3. Mean annual discharges of Yerköprü 3, Yerköprü 1 and 2, Göksu and, Kapuzbaşı and Barazama springs are 449 106 m3, 82 106 m3, 299 106 m3 and 146 106 m3. Noble gas ( 20Ne, 40Ar, 84Kr) and 18O isotopes suggest recharge area elevation and temperature ranges of 1700-2100m and 2-6 oC. The helium (He) content of groundwater increases with increasing circulation depth. Year round biweekly-monthly samples’ electrical conductivity, tritium ( 3H) and 18O content reveal that Kapuzbaşı and Göksu springs and, Yerköprü 1 and Yerköprü 2 springs behave similarly among themselves.
The “CFC model ages” of the springs where, chlorofluorocarbon (CFC) contents increased from 1997 to 2002, range between 10 to 20 years and 20 to 30 years in the shallow and deep circulation parts, respectively. The 3H/3He* absolute age of groundwater from springs is around 20 +/- 2.5 years. In the computer code LUMPEDUS that was developed for unsteady state lumped parameter modeling applications, 3H, tritiogenic helium-3 ( 3He*), CFC-11, CFC-12, CFC-113, and 18O were used as environmental tracers. Serially connected plug-exponential flow model applied to all springs. All models were calibrated for observed outflux and their forecasted 3H, 3He* and 18O time series were found to be in good agreement with the observations. Mean residence times found by models are in agreement with 3H/3He* ages. According to residence time distribution suggested by models, most of the discharges comprise recharges that occurred within last 20 to 30 years. Sixty per cent of discharge comprises recharges of the last 3 to 4 years. The active reservoir volumes of Yerköprü 1-2, Kapuzbaşı, Göksu and Yerköprü 3 springs are found to be 1604 106 m3, 2808 106 m3, 5728 106 m3 and 8609 106 m3 , respectively. According to well established linear relationship between reservoir volumes and discharge elevations, an active volume increases 50 106 m3 per 1m decrease in elevation. Cumulative active reservoir volume is found to be 18749 106 m3 at 450 m elevation where Yerköprü 3 spring is located. Uppermost elevation of active reservoir is located at 836m. Groundwater’s velocity ranges from 2.09 m/day to 5.57 m/day and the corresponding hydraulic conductivities for different reservoirs are between 41.8 m/day and 212.2 m/day. The ordering of hydraulic conductivity among springs (  >  >  >  ) seems to be related to their time of formation. Based on an assumption of 1500m of maximum hydraulic head at the recharge area, the effective porosity of the system is estimated to be 0.86 per cent.
Keywords : groundwater, residence time, lumped model, unsteady flow, noble gas, tritium, tritiogenic helium-3, stable isotopes, chlorofluorocarbon, karst, Aladağlar.
Advisor: Prof. Dr. Serdar Bayari, Hacettepe University, Department of Geological Engineering, Hydrogeological Engineering Division |
