A water crisis is looming for Lebanon. Economic growth, natural population growth and the inflow of refugees from Syria cause an increased water demand in Lebanon. In the meanwhile, the precipitation rates of Lebanon are decreasing. An important water source of Lebanon is the Litani river, which is totally located within the borders of Lebanon. The water of this river is used for agricultural purposes, production of hydropower and supply of domestic water. At the moment, domestic water supply is only a small user of the water of the Litani river. However, water supply from the Litani river to the capital of Lebanon, Beirut is proposed. The Litani already nearly dries up each year and therefore the water allocation of the Litani river has to be optimised. This research aims to optimise the water allocation of Lebanon, in order to protect the country against the looming water crisis. Since the Litani is the most important river of Lebanon, the research focuses only on this basin: the Litani River Basin (LRB).
Optimal water allocation is achieved when the social benefits gained from the deviation of water are at a maximum. The social benefits are described by three principles: economic efficiency, social equity and sustainability. Since the Litani river is an important source for the Lebanese economy, the economic efficiency principle is assumed to be the most important principle in optimising the water allocation.This means that the optimal water allocation is achieved when the profits from the deviation of water are maximised. In order to optimise the water allocation in the LRB, the current water allocation is needed. In this research project, first the current water allocation will be described. Afterwards,
scenarios will be applied to see what the effect is on the current water allocation. The research ends with the implementation of measures in order to see their effect on the water allocation.
The current water allocation is based on hydrological data of the area and the assumption that in the current water allocation everyone tries to maximise the total income of the LRB.

The water of the Litani river is used by three different sectors: agriculture, energy and supply of domestic water. In most of these sectors, water does not directly generate a profit. For example the agricultural sector: yields are increased by the availability of water and these yields will be sold. Formulas of the Food and Agricultural Organisation (FAO) are used in order to determine the actual yields. The actual yield depends on reference evapotranspiration, actual evapotranspiration and crop characteristics. 훼 is added to the equation in order
to model the current situation. 훼 describes the current power of the agricultural sector. This value is based on the current amount of water flowing to this sector and the profits that are generated within this sector. The value of this objective function is limited by the hydrological conditions of the area. The current power of the agricultural sector is 0.445. Therefore, the power of the hydropower sector is 0.555. When water is used for the production of hydropower, it can be used for other purposes afterwards. A part of the water that is used for the production of hydropower is used for the supply of domestic water afterwards, therefore the domestic water sector is not included in the objective function.

In the current water allocation 71.7% of the water is used in the agricultural sector. The other 28.3% is used to produce hydropower. Of this water 23.4% is afterwards supplied as domestic water to the inhabitants of the LRB. The agricultural water use is mainly high in the subbasins with a high marginal
value. If one extra unit of water is flowing to these subbasins, the increase in the profits will be significant. The model is based on the assumption that all individuals try to maximise the total income of the Litani River Basin and therefore the water will be used in the subbasins with the highest marginal
value.

Two scenarios are applied to see the effect on the current water allocation: a water supply to Beirut and a flow to the downstream subbasins. Water supply to Beirut is a proposed solution in order to provide the inhabitants of Beirut with enough domestic water. The water that will be supplied to Beirut, first will be used to produce hydropower. Therefore, the minimum flow to the hydropower stations will be 93 million 푚3/year. In order to reach this amount of water, less water will be used for agriculture. This causes a decrease in the profits generated within the area. Furthermore, the Qaraoun Lake is over-exploited. In the end of the season in which hydropower is produced, the Qaraoun Lake is almost empty. In the first years, 93 million 푚3/year can be delivered to Beirut. However, the Lake has to be over-exploited to reach this amount and therefore the water could not be supplied in the last years.The demand of Beirut is too high to be supplied by the LRB.
The supply of water to the downstream basins will only take place during the dry months. In the current water allocation the water level is high during these months, since the water is not used for the production of hydropower in these months. During the dry period, the demand of the agriculture in the downstream subbasins is high. During these months 10% of the water stored in the Qaraoun Lake will flow downstream. The profit will remain more or less constant, however the flow to the hydropower stations will decrease. The amount flowing from the Qaraoun Lake to the downstream subbasins is small compared to the area of the downstream subbasins and therefore the effect will not be significant.

Measures are proposed to see how the water allocation could be optimised. Replacing water sensitive crops by water insensitive crops is the best way to optimise the water allocation within the LRB. There are two reasons why this measure is the most effective one. The first reason has to do with the yield
response factor. Water insensitive crops have a lower yield response factor and therefore the decrease in yield will be less significant when a water-deficit occurs. Furthermore, the water insensitive seasonal crops are groundnut and tobacco. These crops are profitable crops and this will positively affect the water allocation within the LRB as well. The other principles of optimising the water allocation are social equity and sustainability. It is difficult to give a conclusion about the sustainability, since the exact water levels in the Litani are unknown. However, the system is not sustainable when it has to supply water to Beirut. In order to reachthis demand, the water of the lake has to be over-exploited. A conclusion can be drawn about thesocial equity principle, agricultural water is available within the entire LRB and the agricultural profits generated per hectare are equally divided over the area. Since there is enough water available for the inhabitants of the LRB and agricultural water is available over the entire basin, the water allocation is optimal according to the social equity principle. However, when Beirut is included in this social equity principle, the water allocation will be optimal when water is supplied to Beirut as well.