Effects of sediment storage dams on suspended sediment transport: A case study for the Sera stream watershed (Trabzon, Turkey)

The Sera Lake Natural Park, which is one of the favorite tourist destinations, is in the Sera Stream Watershed (Trabzon, Turkey), where there was intensive suspension motion as well as bed load motion, particularly during flood times. Considering the sediment storage dams (SSDs) located upstream of the lake in the watershed, it was focused on temporal variation in the suspended sediment transport along with the main branch of the stream and the effects of the SSDs on this transport. The field studies, namely stream water sampling for total suspended solids (TSS, mg/L) on ten monitoring stations and stream water depth monitoring for discharge (Q, m3/s) on a gauging station, were conducted four times a month during a period of ten months (June 2019 – March 2020). As of September 2019, the adjacent stream watersheds, namely Değirmendere and Galanima, were included in the study to compare with each other for the transport. In the Sera Stream, where the average TSS values varied between 53 and 91 mg/L on a station basis, the values greater than 2,000 mg/L were monitored during flood times. It was observed that the SSDs, which could trap a part of TSS and all the bedload, were filled with sediment and lost their functions over time. The sediment was excavated and removed from the SSDs to make them functional, but the smaller ones were refilled with sediment due to repetitive floods. On the other hand, the stream having the highest TSS load was Değirmendere having Q values ranged from 0.685 to 30.600 m3/s and the average TSS values ranged from 47 to 236 mg/L. Finally, Pearson correlation analysis was performed between monitoring data of same variables but different streams and both same and different variables for same streams. On the one hand, the monitored streams had similar flow conditions considering the correlation coefficients varying between 0.871 and 0.887. On the other hand, the monitored streams had different sediment conditions considering the correlation coefficients varying between −0.178 and 0.129.