Présentations Colloques

Session 8.05: Karst aquifers
Doummar (orateur)
Assessment of vulnerability in karst aquifers using a quantitative integrated numerical model- catchment characterization and high resolution monitoring - Application to semi-arid regions- Lebanon.
Karst aquifers are highly heterogeneous and characterized by a duality of recharge and a duality of flow which directly influences groundwater flow and spring responses. Given this heterogeneity in flow and infiltration, the assessment of their vulnerability reveals to be challenging. Studies have shown that vulnerability of aquifers is highly governed by recharge to groundwater. On the other hand specific parameters appear to play a major role in the spatial and temporal distribution of infiltration on a karst system, thus greatly influencing the discharge rates observed at a karst spring, and consequently the vulnerability of a spring. This heterogeneity can only be depicted using an integrated numerical model to quantify recharge spatially and assess the spatial and temporal vulnerability of a catchment for contamination. **In the framework of a PEER NSF USAID funded project, the vulnerability of a karst catchment in Lebanon is assessed quantitatively using a numerical approach. The aim of the project is also to refine actual evapotranspiration rates and spatial recharge distribution in a semi arid environment. For this purpose, a monitoring network was installed since July 2014 on a pilot karst catchment to collect high resolution data to be used in an integrated catchment numerical model with MIKE SHE, DHI including climate, unsaturated zone, and saturated zone. Catchment characterization essential for the model included geological mapping and karst features (e.g., dolines) survey as they contribute to fast flow. Tracer experiments were performed under different flow conditions (snow melt and low flow) to delineate the catchment area and reveal groundwater velocities. A series of laboratory tests were performed to acquire physical values used as a benchmark for model parameterization, such as soil hydraulic parameters. Time series used for input or calibration were collected from continuous high resolution monitoring of climatic data, moisture variation in the soil, and discharge at the investigated spring. This similar model approach used on a catchment site in Germany is validated on a karst catchments governed by semi-arid climatic conditions. **