Présentations Colloques

Oral Presentation
Session 8.02: Groundwater Development and Protection in Coastal and Volcanic Environments with Complex Geological Structures
Wilske Cornelia
A pilot study to use the 36Cl bomb peak as a tracer for groundwater flow velocities in the Western Dead Sea catchment
The aquifer system of the western Dead Sea catchment is stressed by semi-arid to arid climate conditions, limited groundwater recharge rates and increasing water abstractions for human water needs. The groundwater flow system is dominated by two main Cretaceous limestone aquifers with karst characteristics and discharging in springs in the Lower Jordan Valley and Dead Sea region. The karst properties give reason to assume parts of the flow system having high transmissivities and groundwater flow velocities, respectively. For estimating recharge rates and rain water infiltration time periods, 36Cl and 3H were used, with the anthropogenic bomb peaks as input functions. **The chloride content in groundwater of the limestone aquifers enriches after contact with the saline Quaternary sediments and groundwater in the Lower Jordan Valley. The 36Cl Cl ratios in groundwater were found to be up to 1E-12 in the recharge area and decrease to 1E-14 in the discharge area. Groundwaters in the recharge area show partly 36Cl Cl ratios comparable to those in recent precipitation. The wide range of 36Cl Cl in the recharge area indicates different stages of chlorine isotope and elemental mixing within the recharge area or aquifer system. This may be due to varying Cl input (dependent on altitude and coastal proximity), varying 36Cl input (regional variation in fallout) or both. Together with 3H analyses it is possible to evaluate the recent rain water component in the springs emerging from the uppermost part of the Cretaceous aquifers.**Our results show that a combination of the 36Cl Cl and 3H measurements in groundwater and a correlation to the atmospheric input curves of 36Cl Cl and 3H allow estimating the admixture of post-bomb recharge in groundwater.**