IWRA Proceedings

AbstractChekka karst submarine springs in Lebanon are considered as the most productive ones in the Mediterranean Sea. This fresh water could represent an interesting water resource in a region that has to face both water scarcity and an increasing demand. But their potential exploitation is only an option among others to fill the current or future gap between water supply and demand. In order to support Lebanese water authorities in their way toward sustainable water management of the Chekka Bay area, tools and guidelines are being elaborated within the MEDITATE European project. The project has adopted an integrated approach relying on a hydrogeological study of the submarine spring catchment, a social and economical survey at a larger scale and the integration of all these information and knowledge in a numerical model. The study area covers 1200 km2 of the North Lebanon district. It includes three rivers (Abou Ali, Asfour and Jawz) and their watershed. Jurassic and cenomanian limestones form the two main aquifers of the area. The most important water consumption is for irrigation then for domestic use with a population of nearly 1 million persons in the study area. A model has been developed with the WEAP software to simulate the dynamical links of water resource and water demand in this case study, and to explore the system behaviour according to different management options and evolution scenarios. After calibration, the model was run for a reference year. Effective rainfall is estimated to almost 500 million cubic meters/year on the three watersheds, and 750 million cubic meters/year on the overall study area. It appears that almost 80% of this water are infiltrated. But this amount of water input is clearly underestimated in the Abou Ali watershed as shown by the comparison of simulated and observed river flowrates. The discrepancies can be explained both by the inaccuracy of available time series data (especially an under-evaluation of snowy precipitations) and by the poor knowledge of aquifer recharge areas. Actually, the hydrogeological catchment from which recharge should be calculated is probably much wider than the topographic one used in the model. This water resource has to be compared to the total water demand estimated around 215 million cubic meters in 2005, and which could increase up to 70 % by the year 2030 in a “business as usual” scenario. The significant contribution of the WEAP model to this study is that it can evaluate at the same time water resource and water demand at a monthly time step. It will be shortly applied to simulate the different scenarios of water management that were defined after two Water Vision Workshops that have been organised with the local stakeholders. At the same time, a cost-effectiveness analysis (CEA) of different measures that could bring new resources to the area or could allow decreasing or stabilising the water demand has been performed. The combined results of the WEAP model and of the CEA will allow providing informed guidelines to Lebanese water authorities.