Factors Affecting the Discharge Rate of the Streams – Case Study; Damour River Basin, Lebanon

The distribution of precipitation on runoff, evapotranspiration and groundwater recharge and the change of this distribution in response to human activities plays rather important role in the availability of water resources, especially in areas of Mediterranean climate. This study used data on the discharge obtained from six gauging stations along the Damour River and its tributaries, and rates of precipitation obtained from rain gauges located in Beirut belonging to LMS. The study used these data to evaluate the relationship between the precipitation and streams discharge, and to assess the ratios of runoff, evapotranspiration and infiltration. The study came up with the following conclusions: The rates of runoff and groundwater discharge for the whole Damour river basin could reach 70%, and the remaining 30% go mostly to evapotranspiration and submarine springs fed from this basin. The lag time between maximum rainfall and peak discharge of streams ranges between one and three month(s), and the longest lag time is exhibited by es Safa spring discharge. High relief areas play a major role in shortening the lag time between maximum rainfall and peak discharge. The timing factor of precipitation events is rather significant and causes great differences in the ratios of discharge throughout the wet season. Finally, the runoff ratio is affected by the following factors: Underlying rocks, snow cover, steepness of the slope, vegetation cover, and timing of precipitation.