The effects of the dam construction process on downstream river geomorphology

Abstract

This study aims to describe how the construction process of a reservoir dam affects and changes in river morphology such as cross-section changes and total sediment movement in different annual and seasonal scales. Cross-sectional and profile changes, and spatial distribution of differences (degradation and aggradation areas) between topographic measurements and bend variations are also discussed. For this purpose, a field measurement campaign was carried out on Büyükkumla stream, where Büyükkumla dam is built, from the spillway of the dam to the Marmara Sea. Topographic measurements were taken every six months from the beginning of the dam’s construction until the body is completed. Precise measurements were made across the entire stream, including the thalweg of the mainstream bed, up to 25 m on the right and left bank at 20-m intervals, and at the intermediate points where the required cross-sectional changes were found. The aggradation and degradation volumes were determined as much as the number of cross-sections available for each region at different time periods. Besides, the reasons for these aggradations and degradation were investigated considering the construction activities and meteorological conditions. Finally, our results show that there is a correlation between dam construction activities and downstream geomorphology changes. It is also observed that excavation activities in dam construction have a significant impact and regulate downstream and the changes in annual and semi-annual periods differ.