CASE STUDY: ASLANCIK HYDROELECTRIC PROJECT, GIRESUN, TURKEY, MINIMUM FLOW STUDY FOR THE MAINTENANCE OF WATER QUALITY AND BIOLOGICAL RESOURCES

The objective of the study was to determine the minimum flow required to maintain the water quality and the aquatic biological resources in the 18-kilometer reach of the Harsit River to be bypassed by the proposed Aslancik Dam and Hydroelectric Power Plant Project (Giresun, Turkey). The study focused on the three fish species identified in the project area that are listed in Annex 3 of the Bern Convention, to which Turkey is a signatory. The lowest average flow for seven consecutive days that statistically occurs once every ten years was recommended as the minimum flow to maintain existing water quality. The minimum flow to maintain aquatic biological resources in the bypass reach was determined by hydraulic simulation modeling using the Riverine Habitat Simulation (RHABSIM) system. The required inputs (depth, velocity and type of substrate) were collected by field studies conducted during biologically sensitive periods (the low flow period and the spawning period). Based on RHABSIM analysis, separate minimum flows were defined for the bypass reach to maintain spawning habitat and to maintain habitat for feeding and growth. The higher of the flows required to maintain water quality or to maintain the biological resource was recommended as the minimum flow for the bypass reach. The minimum release from the Aslancik Dam required to maintain these minimum flows were calculated by subtracting the flow from the tributaries. Based on published information, this was the first time that such a minimum flow study was conducted and reported in Turkey.