Temporal variation of braided intensity and morphodynamic changes in a
regulated braided river using 2D modeling and satellite images
Abstract
The river morphology of a braided-type river is rather complex. High
sediment transport rates and frequently changing discharges are the
cause of dynamic planform evolution. Over the past few decades,
scientific attention has been directed toward understanding the
coexistence of alternating bars and the consequent emergence of
confluences and divergences, all of which interact intricately with the
process of bank erosion. It is still rather challenging to estimate or
predict the total sediment transport rate in such type of rivers,
especially by considering various hydrologic data and climate effects.
This study is focused on a reach of the Devoll River in Albania, located
upstream of the Banja dam. Understanding the morphodynamic of this river
reach holds significance due to the expanding delta upstream of the dam
reservoir. The objectives of the two-dimensional (2D) depth-averaged
approach of the present study are to investigate the temporal variation
of braided intensity of Devoll River due to using a discharge hydrograph
from hydrologic data compared to the regulated one from the upstream dam
on the morphodynamic of the river, and estimate the sediment transport
rate of this complex braided river. After evaluating various parameters
such as 11 different sediment transport functions, the best results were
reached for a cell size of 5×5 m 2, Manning roughness
coefficient of 0.03, Meyer-Peter and Müller’s sediment function, Hayashi
et al. (1980) hiding function, and Van Rijn bed roughness predictor in
this study. In addition, the results of comparing satellite images and
modeling the river from 2019 to 2023 show that the braided index (BI)
decreased, and this can be due to the fact that the real scenario of the
river has a regulated discharge (scenario A) compared to the
non-regulated discharge of hydrologic data (scenario B), in the
mentioned period. Moreover, the study also estimates sediment transport
rates, with scenario A showing higher values for total bed load rate
(35.93 kg/s/m) and suspended load concentration (652.48 mg/l) compared
to scenario B (16.32 kg/s/m and 152.39 mg/l). This research highlights
the impact of regulated discharge on sediment transport in a complex
braided river.