The effects of dams on river channel morphology: a case study at the historical carsamba Bridge on the Yesilirmak River in northern Turkey

Dams are structures that are built to store river water; however, in doing so, they also cause many alterations to the geomorphic and hydrological characteristics of the river and can even alter the climate of the river basin. These dams store not only water in their reservoirs but the sediments that come with the water as it flows into the reservoir. The water is then released without its sediment load to downstream areas with a new and increased potential energy, which induces changes to the geometry of the riverbed. In this study, we investigated the vertical traces of clean-water erosion of the riverbed at the historical carsamba Bridge in the Yesilirmak River, Turkey, after the construction and operation of dams. Cross-sections at the historical carsamba Bridge for 1980, 1989, 1996 and 2019, 14 km north of the Suat Ugurlu Dam, were investigated. Using long-term flow rate regimes and suspended sediment data, changes were determined in the riverbed before and after the dams were present. After construction of the dams, a decrease in the differences of monthly flow rates was observed. With the newly acquired potential energy resulting from the release of water from the dam reservoir, we found that the river flow eroded the riverbed up to 5.9 m in a vertical direction over the 39-year period between 1980 and 2019. This illustrated that according to these measurements, the river flow scoured the riverbed at a rate of 15 cm/year. The results of this study indicated that river degradation is a major environmental problem at the historical carsamba Bridge and also along the riverbed of the Yesilirmak River after dam construction.

Automated summary

The construction and operation of dams have significant impacts on river geomorphology and hydrology, leading to riverbed erosion and potential environmental issues.