Assessment of Changes in Channel Morphology in a Mountain River Regulated Using Grade Control Structures

Abstract

Grade control structures (GCSs) serve as some of the most frequently used forms of river channel regulation in the Polish Carpathians. The main purpose of such structures is to reduce the gradient of the channel and strike a balance between erosion and deposition. Despite the widespread use of GCSs, not much is known about their functioning over the long term. The aim of the study was to examine a host of changes in channel morphology in a mountain river regulated using such structures. The object of the research was the lower stretch of Biały Dunajeca Carpathian river that follows a high mountain regime. The studied river stretch was regulated 33 years ago. The history of regulation and state of the channel immediately following regulation work were assessed using available regulation documents as well as a document on the post-construction period for the studied structures. The presentday morphology of the studied river channel was investigated via a geomorphologic survey and assessment of 22 channel cross sections. Gradual changes in morphology were analyzed using orthophotomaps from different years. Research has shown that the studied river channel is shaped by all fluvial processes. In the longitudinal profile, distinct channel zones characterized by stable tendencies were identified. The upstream zone is dominated by deposition, where the channel is flooded with debris after each high water stage, and GCSs cease to function as barriers to material transport. In the middle zone, lateral erosion plays a greater role, while in the downstream zone it is downcutting and lateral erosion. The river cuts alternately into both banks, thus damaging its regulated pathway. The role of deposition increases once again in the mouth zone of the river. The studied channel is not stable, and its morphology has changed many times over the years due to discharges much lower than design discharge. The Biały Dunajec did not conform to the parameters of its regulated pathway and aims to increase its width and sinuosity. The studied channel stretch requires ongoing financial expenditures to cover repair work.

Mountain Streambed Roughness and Flood Extent Estimation from Imagery Using the Segment Anything Model (SAM)

“…These tasks can be automated using the presented method for predefined gravel riverbed material (d50, d65, d75, d84 and d94). Changes in fluvial forms and cover within the riverbed can also be examined using aerial photos or photos from unmanned aerial vehicles [29]. For some locations, these methods may prove to be the most economically effective.…”

A proposed quantitative method for assessing the impact of river regulation on its hydromorphological status

“…If a river hydrological regime does not undergo significant changes, then after some time the river will restore parameters of a stable channel. On the other hand, contemporary permanent changes of morphological river channel parameters are mainly influenced by anthropogenic factors, such as: -climatic changes (Marchi et al, 2010;Macklin, Lewin and Woodward, 2012); -changes in river catchment management, which change the characteristics of water outflow and sediment transport from the catchment (change in hydrological regime of river) (Mosley and Jowett, 1999;Overeem, Kettner and Syvitski, 2013;Recking et al, 2016); -river regulation (Djekovic et al, 2013;Salit et al, 2015;Korpak, 2020); -construction of flood banks in river valleys (Bujakowski and Falkowski, 2019); -hydrotechnical development of rivers (retention reservoirs, damming structures), which result in the loss of dynamic stability of a riverbed. It also changes local conditions for water flow and transport of bedload and suspended load (Liaghat, Adib and Gafouri, 2017;Biswas and Pani, 2021).…”