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While Lebanon is in a relatively favourable position as far as rainfall and water resources are concerned, constraints for development consist in the limited availability of water during the seven dry summer months due to the very low water storage capacity, the difficulty of capturing the water close to the sea, and the shortcomings of the existing water delivery systems and networks. The total length of streams in Lebanon is 730 km, mainly on the western side of the mountains, which have steep slopes. Annual internal renewable water resources are estimated at about 4.8 km3. Annual surface runoff is around 4.1 km3 and groundwater recharge 3.2 km3, of which 2.5 km3 constitutes the base flow of the rivers. About 1 km3 of this flow comes from over 2 000 springs with an average unit yield of about 10–15 l/s, sustaining a perennial flow for 17 of the total of 40 major streams in the country.
The annual net exploitable surface water and groundwater resources, water that Lebanon can technically and economically recover during average rainfall years, are estimated at 2.080 km3, consisting of 1.580 km3 of surface water and 0.500 km3 of groundwater.
In total, there are about 40 major streams in Lebanon and, based on the hydrographic system, the country can be divided into five regions:
- the Asi-Orontes Basin in the north; the Asi-Orontes River flows into the Syrian Arab Republic in the northeast of the country;
- the Hasbani Basin in the southeast; the Hasbani River, which flows into Israel in the southeast of the country, is a tributary of the Jordan river;
- the Litani Basin in the east and south; the Litani River reaches the sea in the southwest of the country;
- all the remaining major coastal river basins; the northern El Kebir River Basin is shared with the Syrian Arab Republic, the river itself forming part of the border between the two countries before flowing into the sea;
- all the small, scattered and isolated sub-catchments remaining in-between, with no noticeable surface stream flow, such as the endorheic catchments and isolated coastal pockets.
The first three river basins cover about 45 percent of the country. The Asi-Orontes and Hasbani rivers are transboundary rivers, while the Litani River flows entirely within Lebanon. With a total length of 170 km it is the longest river in Lebanon. Its catchment area is about 2 180 km2, equal to some 20 percent of the total area of the country. Average annual water flowing in the Litani River is 475 million m3. In the coastal regions, there are about 12 perennial rivers originating in the western slopes of the mountain ranges and flowing from east to west to the sea. The coastal rivers have relatively small catchments (200 km2 on average) and small courses (< 50 km). The major replenishment of rivers in Lebanon comes from precipitation, as well as from snowmelt and springs. However, a drastic decrease in the river flow has been recorded in the last three decades.
There are eight major aquifers, with a total estimated volume of 1 360 million m3. Exploitable groundwater ranges from 400 to 1 000 million m3 (Samad, 2003). The presence of fissures and fractures encourages snowmelt and rainwater to percolate and infiltrate deep into the ground and feed these aquifers. Water may reappear at lower elevations as springs that flow into rivers. Springs are commonly found in Lebanon because of the highly fractured geologic rocks, and because of the existing inter-bed rock formation of differing permeability, which is a feature of the whole country. In total, there are about 2 000 major springs and many other minor springs in Lebanon, generating an estimated flow of 1 150 million m3/year. Other springs are commonly found along the coast or in the submarine area. They are also called “non-conventional” springs because it is more or less impossible to capture their water before it flows into the sea.
Since Lebanon is at a higher elevation than its neighbours it has practically no incoming surface water flow. The flow of 76 million m3/year of the El Kebir River on the border between Lebanon and the Syrian Arab Republic is thought to be generated by the 707 km2 bordering Syrian catchment areas. There might also be some groundwater inflow from these areas, but no figures on quantities are available.
Total surface water outflow is estimated at 735 million m3/year, of which 160 million m3 to the sea. Surface water outflow to the Syrian Arab Republic is estimated at 415 million m3 through the Asi-Orontes River. Surface water flow into northern Israel from the Hasbani/Wazani complex is estimated at 160 million m3/year.
The transboundary Mount Hermon aquifer contributes to the discharges of the Banias springs in the Golan and the Dan springs in Israel. The total groundwater outflow is estimated at about 1 020 million m3/year. Of this total, 740 million m3 is estimated to flow to the sea, 150 million m3 to Israel (Hulah Lake) and 130 million m3 to the Syrian Arab Republic (Dan Springs).
The geological conditions make construction of storage dams difficult. The largest artificial lake in Lebanon is located in the southern part of the fertile Bekaa Valley on the Upper Litani River, known as the Qaraoun Reservoir. Constructed in the 1960s, it has a total capacity of about 220 million m3 and effective storage of 160 million m3 (60 million as the inter-annual reserve). It supplies in turn three hydroelectric plants generating about 7 to 10 percent (about 190 MW) of Lebanon’s total annual power needs. Moreover, the Qaraoun Reservoir potentially provides every year a total of 140 million m3 for irrigation purposes (110 for South Lebanon and 30 for Bekaa), and 20 million m3 for domestic purposes to the South. On the other hand, the Green Plan, which is a public authority established in 1963 for the development of water reservoirs, and the private sector and NGOs have already developed hundreds of small earth and concrete storage ponds, with a maximum capacity per unit of 0.2 million m3. During the period 1964–1992 the Green Plan led to a total of 3.5 million m3 of earth pounds and 0.35 million m3 of concrete pounds. The Litani River Authority implemented three hillside stock ponds in the early 1970s, for a total storage capacity of about 1.8 million m3. The Bisri Dam on the Awali River is currently in the final design stage; it will have a storage capacity of 128 million m3 and is intended mainly for supplying water to Greater Beirut. The Khardaleh Dam on the middle reach of the Litani River, with the same planned storage capacity of 128 million m3, has been put on hold at the preliminary design stage because of the prevailing adverse security situation in the southern border region. In 2007, a new artificial reservoir and dam, named Shabrouh, was inaugurated with a storage capacity of 8 million m3. It is located near the ski resort town of Faraya and provides water for domestic and irrigation purposes. The project will help alleviate water shortages in the Qadaa Kesrouan and parts of the Metn regions.
Lebanon generates an estimated 310 million m3 of wastewater per year (Table 2), of which 249 million m3 is produced by the domestic sector with a total BOD load of 99 960 tonnes and an estimated 61 million m3 by industry. This represents an increase of 88 percent compared with 1991 when 165 million m3 was generated. In 2006, treated wastewater was only 4 million m3, of which 2 million m3 was destined for agricultural purposes, and the rest disposed of in the marine environment by direct diversion to the rivers, or it was infiltrated by deep seepage to groundwater. The potential for reuse of domestic wastewater is estimated at around 100 million m3/year. Some illicit irrigation from untreated wastewater is practised. Another source of non-conventional water is desalinated sea water, which is estimated to be 47.3 million m3 (Mdalal, 2006).