Assessing past and present recharge using radiocarbon: case study of the Saharan aquifers
Abstract
In this study, we developed two-dimensional hydrodynamic age expressions for the free-surface aquifer problem required for radiocarbon data interpretation in terms of recharge. Time-varying recharge over the last 40 ky are accounted for in fully transient or pseudo-steady state alternative analytical expressions applying to weakly or highly hydraulically reactive unconfined aquifers. These expressions extending a previous model based on a constant recharge represent a convenient alternative approach to the more complex numerical resolution of a particle tracking problem considering climate variability. An application of the developed models was carried out to assess past and present recharge rates for the North Western Saharan Aquifers System (NWSAS) and the Djeffara plain aquifer (Tunisia-Libya). Using the available 14C data at different outcrops, we obtained local recharge values ranging from 1.27 to 8.92 mm yr-1 for the NWSAS, and 6.25 mm yr-1 for the Djeffara. A linear relation between the present recharge and the average annual rainfall was obtained then used to produce a regional distribution of the recharge as well as domain-averaged values. Global values of 1.08 km3 yr-1 for the NWSAS and 0.3 km3 yr-1 for the Djeffara are in excellent agreement with the values obtained by hydrogeological models and using Satellite gravity data. The relation between recharge and rainfall obtained here can be used as a first-order estimate for hydrogeological modeling or water management analysis in the Saharan area.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH163.0008C
- Keywords:
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- 1807 Climate impacts;
- HYDROLOGY;
- 1829 Groundwater hydrology;
- HYDROLOGY;
- 1832 Groundwater transport;
- HYDROLOGY;
- 1875 Vadose zone;
- HYDROLOGY