Physical and chemical properties of recently deposited sediments in the reservoir of the Borçka Dam in Artvin, Turkey

Authors: BÜLENT TURGUT, MEHMET ÖZALP, BAHTİYAR KÖSE

Abstract: Large dams produce important changes in flow regime and sediment deposition and distribution in rivers. When inundation starts with the building of dams, water surface area increases, flow rate decreases, and sediment carried by the river is deposited in the reservoir. However, there is a lack of research on the physical and chemical properties of recently deposited sediment in reservoirs of large dams. We aimed to fill this gap in the literature by providing valuable data on the initial formation of sediment deposition areas in reservoirs. Therefore, the aim of this study conducted within the Borçka Dam reservoir was to estimate some physical and chemical properties of deposited sediment, including grain size distribution, penetration resistance, water-stable aggregate, moisture content, organic matter content, and pH at two depths (0-10 cm and 10-20 cm). Another objective was to analyze the distribution of these properties across the sampling site. For this purpose, one of the aforementioned sediment deposition areas, approximately 3.6 ha, was designated as the study site; the study site was further divided into intersecting transects of 10 × 50 m. The penetration resistance values were determined in the field and 182 sediment samples were taken at 91 intersection points of transects, both from the surface (0-10 cm) and subsurface (10-20 cm) layers for laboratory analysis. Data gathered were evaluated using descriptive statistics and ANOVA, while geostatistical analyses were used for calculating spatial variability in the data. Results indicated that the most common texture classes were loam in the surface layer and silty loam in the subsurface layer. Moreover, the penetration resistance values, sand content, and water-stable aggregate values in the surface layer were significantly (P < 0.01) higher than in the subsurface layer, and moisture content, clay and silt content, pH, and organic matter were significantly (P < 0.01) higher in the subsurface layer than in the surface layer. Geostatistical analyses showed that all properties were described by the isotropic variogram and the ranges were lower in the subsurface layer than in the surface layer. This study revealed that the analyzed physical and chemical properties of the recently deposited sediments showed significant differences between the layers.

Keywords: Dam reservoir, geostatistics, recently deposited sediment, sediment properties

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