Assessing the impacts of dam construction on river morphology by applying a new automated method on remote sensing images

Abstract

Spatiotemporal morphological impacts of river regulation owing to the construction of hydraulic structures on Kor River, Fars Province, Iran has been quantified using Remote Sensing images during 1993–2017. The river morphology has been studied before and after the construction of the Mollasadra Dam in 2006. MATLAB programming was utilized to extract the waterline in order to reduce the errors derived from manual extraction of the river path. Several characteristics of river morphology, such as the temporal thalweg movements and spatiotemporal Sinuosity Index (SI) have been calculated. Through this work, the Absolute and Rate of Thalweg Movement (ATM and RTM), and spatial movement of meander centroids were proposed as new indices to show morphological changes in the river. The results indicate that thalweg has moved towards to the southwest by an average movement of 40 cm, to the northeast by 20 cm and to the southwest by an average of 40 cm per year during 1993–2003 (pre-impact), 2003–2011, and 2011–2017 (post-impact), respectively. In spatial scale, changes in the morphology of the river is increased from upstream to downstream and this was particularly evident in the last 10% of the river length. The results of SI values show that despite a 5% mutation in the straight class of sinuosity in the pre-impact period, there is a decrease of 18 % in the same class during the post-impact period and river tends to meander after the construction of Mollasadra Dam. Considering the spatial movement of meander centroid, temporal change in major meanders was assessed.