Study of stable isotopes in the Kouris catchment (Cyprus) for the description of the regional groundwater flow

The stable isotopes of oxygen and hydrogen in groundwater and precipitation were integrated for the description of groundwater flow in the Kouris catchment (Cyprus). The catchment consists of an ophiolitic complex in the North and sediments in the South. It is characterized by strong heterogeneity of the underground media and steep slopes of the topography. The regression line, constructed from the data of 70 rainfall samples, is described by the equation: δD=6.6δ18O+10.9, which shows evaporation during precipitation. The altitude gradients in the precipitation were estimated to be −1.7‰/100 m for δD and —0.27/100 m for δ18O. The stable isotope analysis of 234 groundwater samples reflected fractionation due to evaporation. The origin of groundwaters in the catchment was described based on the regression equation between surface elevations and δD contents for 33 selected springs of the ophiolitic complex. It was found that the groundwaters in the ophiolitic aquifer and in the consolidated sediments originated from local recharge at high and low altitudes, respectively. On the contrary, the groundwater in the alluvium aquifer originates from the high altitudes in the ophiolitic complex. Additionally, δD data were used for the calibration of the recharge rates for a steady state groundwater flow and transport model. The resulting calibrated total steady state recharge rate was 100–130 mm per year.