Determination of suspended sediment distribution and water quality parameters in the borçka dam lake basin

In this study, surface water quality was investigated monthly between December 2010 and November 2011 at 12 monitoring stations selected in the Borçka Dam Lake, which is located in the Lower Çoruh River Basin and planned for flood protection and hydroelectric power generation, the Çoruh River and Murgul Stream. Within the scope of the study, in-situ (temperature, pH, water depth, dissolved oxygen, specific conductance, chlorophyll-a, turbidity, and Secchi disk depth) measurements and laboratory (suspended sediment, total nitrogen, total phosphate phosphorus, and chemical oxygen demand) analyzes were carried out. In addition, remote sensing data and synchronous in-situ data were used together to determine suspended sediment (SS), turbidity (T) and chlorophyll-a (Chl-a) parameters of the water mass in the Borçka Dam Lake. The Borçka Dam Lake was classified as oligotrophic in terms of Chl-a, mesotrophic in terms of total nitrogen (TN), and eutrophic in terms of total phosphate phosphorus (TP), with reference to the Surface Water Quality Regulation (SWQR). The measurement results reveal that the Çoruh River and the Murgul Stream have high-quality water, considering TN and chemical oxygen demand (COD), but slightly polluted water regarding TP. Considering the decrease in the annual average values of TN and COD, it is concluded that the Borçka Dam Lake had a positive effect on the surface water quality in the Lower Çoruh River Basin. Based on the annual average of 41 mg/L for SS and 46 NTU for T, it was concluded that the Borçka Dam Lake could trap a large portion of the SS and could reduce turbidity considerably because of its long hydraulic residence time, and thus reduce possible silting in the downstream reservoir. Within the scope of the study, the use of Canadian water quality index, weighted arithmetic water quality index, and trophic state index was also targeted, and it was observed that the seasonal evaluation and the quality classes obtained were compatible with the material movement and pollution load in the study area.