Belgeo (Sep 2023)
Le fonctionnement hydrodynamique et géochimique des aquifères jurassique et crétacé dans le bassin versant du Nahr El-Bared (Liban Nord)
Abstract
This study exposes the complexity of the hydrological functioning of the two Jurassic and Cretaceous karstic systems in the El-Bared watershed. It qualifies geochemistry as an indicator of this functioning. Our study is based on two approaches (hydrodynamic, hydrogeochemical) in order to study the water characteristics and the flow mode in the watershed.The methodology applied is based on the study of the natural responses of the main outlet of the karstic aquifer, considered here as a black box. Time series analysis and recession curve analysis are applied in studying the outflow from the aquifer. The monthly physico-chemical variations of springs water are also taken into account.The layout of the recession curve leads to the estimation of a significant water reserve of approximately 1282 Mm3 in Mechmeche aquifer and 1528 Mm3 downstream.The physico-chemical analysis of the waters of the sources of Nabaa Es-Soukkar and El-Qseim at high altitudes shows that the temperature of the water is influenced by the melting of the snow. It decreases during the spring and summer period unlike the atmospheric temperature. In addition, the temperature is affected by the thickness of layers traversed. The salinity of Jurassic springs (Nabaa Ez Zahlane and Ain Ech Chqaiq) increases significantly during the period of recession (September-October).A significant increase in pH was recorded during the recession period in the Cretaceous springs (Nabaa El-Soukkar and Nabaa El-Qseim), as opposed to the Jurassic springs, which recorded a drop in pH during this period in due to the increase in biological activity which increases the level of CO2 in the water. The Cretaceous springs are characterized by a high calcium content and a reduction in the magnesium content, while the Jurassic springs show a higher calcium and magnesium content due to the extension of the period of the residence of water in these last.
Keywords
