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

Korpak Joanna

Journal of Ecological Engineering

2020

Vol. 21, nr 8

163--176

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 Dunajec – a 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.

Influence of Extreme Discharge on Restoration Works In Mountain River – A Case Study of the Krzczonówka River (Southern Poland)

Lenar-Matyas A., Korpak J., Mączałowski A.

Journal of Ecological Engineering

2015

Vol. 16, nr 3

83--96

The research was conducted on the Krzczonówka River channel, one of the gravel-bedded, regulated mountain river in Polish Carpathians. The main morphological and ecological problem of the river was lack of sediment and channel down cutting. The area is currently associated with an on-going project called “the Upper Raba River Spawning Grounds”. Lowering of an existing debris dam on Krzczonówka River is a part of the project. In 2013 twelve artificial riffles have been created by heaping up stones at points within the segment of the river channel below the debris dam. The riffles are to introduce variety to the longitudinal profile of the river and to reduce the river’s slope. Consequently, these are to decrease sediment transport and to prevent further deepening of the river channel. Post-project monitoring of river restoration works is conducted to determine channel changes and development. In May, 2014, extreme flooding occurred, which caused unexpected changes in channel development. This paper describes maintenance work performed in the riverbed of the Krzczonówka River. Observations and calculations concerning changes in conditions of water flow and sediment transport are also presented. The main purpose is to characterize the influence of an extreme flow event on morphology and functioning of the recently restored gravel-bed river.