Sedimentation Problems and Suggested Solutions of Istanbul’s Drinking Water Dams: A Case Study of Alibey Dam

Land misuse and natural balance impairing activities in dam watersheds are resulted in excessive sediment to enter the dam reservoirs and fill their dead storage prematurely; thus live storage begins to dwindle rapidly. such dams which are filled up their active volume by sedimentation earlier than their planned economic life become out of service in the context of construction purposes. in this study, sedimentation in alibey dam reservoir, which dried up to 70% of its area in the summer of 2007, was studied. during this dry season, it became possible to make the majority of its bathymetric map by terrestrial ground measurements. thus, it was intended that, by using the sediment deposited behind the dam wall, the sediment yield of the reservoir could better be estimated, comparing the newly produced bathymetric map with the one made by dsi in 1978. unfortunately, this estimation was not made possible due to the obvious fact that 1978 map inherited considerable amount of faults. during the field works carried out inside the dried dam reservoir, non-uniformity between earth layers in 33 soil profiles was observed up to 150-170 cm. since the bottom of the reservoir was heavily cultivated prior to dam construction, the 20-30-cm top layer determined in soil profiles could not be interpreted as the result of sedimentation. visual investigations revealed that one ruined bridge foot and a shallow concrete channel were still unburied. it was interpreted that comparison of measured drawing, old photographs, a historic gravure and photographs of mağlova aqueduct taken in 2007, sedimentation from middle of dam through crest siltation reached 10 cm.