Présentations Colloques

A successful example of managed aquifer recharge (MAR) into karst is the Wala reservoir in Jordan, where storm water is captured and infiltrates naturally into the carbonate aquifer and supplies a wellfield 7 km downstream. Sedimentation in the reservoir successively clogged the infiltration path and reduced the storage capacity. To predict the impact of sedimentation on the recharge rate and to characterize the hydraulic properties of the underground, a numerical assessment was conducted using the finite element approach with specific adaptation for karst aquifers. The 3D model domain was projected onto a 2D vertical cross-section. An independent calibration of the recharge and abstraction processes was achieved by dividing the cross-sectional model into a recharge model and an abstraction model. To account for the heterogeneity and anisotropy of the aquifer, both models were subdivided into horizontal zones of different permeability. The simulation of groundwater table fluctuations, as a result of the karst characteristic flow pattern of fast flow and slow depletion, were achieved with the fitting of high permeability zones and with a large anisotropy of permeability. Strong water level fluctuations at the wellfield could be assigned to changes in the abstraction depth. Climate scenarios for a dry period of low reservoir inflow and a wet period of high reservoir inflow, each 10 years (2013-2023), predict a lowering of the average groundwater table of around 2.7 m downstream the reservoir as a consequence of sedimentation in the reservoir. An average groundwater table decrease of 2.7 m and 6.3 m at the wellfield was computed when two different abstraction depths were applied to the wet scenario. Stronger influences of 9.0 m and 12.0 m, respectively, were calculated for the dry scenario. Flow quantities and water balance were not examined with this modeling approach. The numerical model can support the management of the reservoir and the wellfield and demonstrate an approach how MAR can be evaluated in karst regions with similar hydrogeological conditions.< p>