ABSTRACT
Karst is very well-developed in Lebanon in thick, exposed, fractured and folded Jurassic, Cretaceous, and Eocene carbonates, as well as in localized, coastal Miocene limestones. This karstification not only results from the predominant calcareous lithology, but is also caused by the high, northerly trending ranges of the country, which cause abundant precipitation, as heavy rain and thick snow, to fall on Mt Lebanon, Habal Barouk, Habal Niha, and Mt Hermon, with lesser amounts falling on the Anti-Lebanon, Beqa’a Valley and the coastal hills of the country. Some 80% of precipitation falls from November through February. Five of these are first-magnitude springs (Ain ez Zarqa 1 1m3/sec, Ain Anjar (max. 10m3 /sec), Nabaa Ouazzani (max 6m3 /sec), Nabaa Arbaain (max. 3m3/sec) and Nabaa Barouk (max. 3m3/sec), plus hundreds of second-and third magnitude springs, and thousands of smaller springs. The large springs are all karstic and contribute to 13 perennial springs in the main Lebanese ranges, and 2 in the Anti-Lebanon. These include major rivers, such as the Nahr el Litani, Nahr el Assi (Orontes) and Nahr el Hasbani (upper Jordan River).
More than two-thirds of the area of Lebanon (i.e. 6900 km3) is karstified and includes surface karst features, such as poljes, uvalas, defines, blind valleys, natural bridges, and ponors, as well as smaller features, like karren and hoodoos. Subsurface karst features include many types of solutional shafts and galleries, grottoes, subsurface lakes and rivers and most types of speleothems.
There are at least 15 aquifers in Lebanon, of which 14 are in karstified carbonate atrata. The 1700 m limestone/dolomite core of the ranges and over 2000 m of flanking, or overlying. Cretaceous limestones provide the majority of these aquifers, while significant aquifers are also found in thick Eocene limestones.
High transmissivity values (T=or 1.83 x 10−1 m2) occur in these karstic aquifers, as is shown by the rapid decline in spring flow over the dry summer and autumn months, and their very quick recharge by winter and spring rains and heavy snow on the Lebanese ranges.
