Abstract
Despite several decades of intensive study of the morphological changes in meandering rivers, less attention has been paid to confined meanders. This paper studies the hydro-morphodynamics of two adjacent sub-reaches of a meandering creek, located in the City of Ottawa, Canada. Both of these sub-reaches are meandering channels with cohesive bed and banks, but one is confined by a railway embankment. Field reconnaissance revealed distinct differences in the morphological characteristics of the sub-reaches. To further study this, channel migration and morphological changes of the channel banks along each of these sub-reaches were analyzed by comparing the historical aerial photography (2004, 2014), light detection and ranging (LIDAR) data (2006), bathymetric data obtained from a total station survey (2014), and field examination. Moreover, two different spatially intensive acoustic Doppler current profiler (ADCP) surveys were conducted in the study area to find the linkage between the hydrodynamics and morphological changes in the two different sub-reaches. The unconfined sub-reach is shown to have a typical channel migration pattern with deposition on the inner bank and erosion on the outer bank of the meander bend. The confined sub-reach, on the other hand, experienced greater bank instabilities than the unconfined sub-reach. The average rate of bank retreat was 0.2 m/year in the confined sub-reach whereas it was lower (0.08 m/year) in the unconfined sampling reach. In the confined sub-reach, an irregular meandering pattern occurred by the evolution of a concave-bank bench, which was caused by reverse flow eddies. The sinuosity of the confined sub-reach decreased from 1.55 to 1.49 in the 10-year study period. The results of the present study demonstrate the physical mechanisms by which meander confinement can change the meandering pattern and morphological characteristics of a cohesive clay bed creek.
Highlights
Channel migration and morphological changes of the channel banks along each of these sub-reaches are analyzed by comparing historical aerial photography, light detection and ranging (LIDAR) data and bathymetric data obtained from a total station survey
The present study examined the meandering behavior of a cohesive clay bed river over a
The results showed an evolution of the concave-bank bench on the upstream limb of the outer banks of the sharp menders in the confined reach, whereas bank instability was observed downstream of the bend apices
Summary
Many river scientists and engineers have studied meandering rivers over the past few centuries (e.g., [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]). It is known that river meandering is associated with the bank erosion mechanism and can be influenced by the spatial progression of bars [17]. Bank instability and erosion are intrinsic characteristics of meandering rivers [18]. 8. Channel margin migration along Earth the M3 sampling. Channel geometry of each sub-reaches of (m) the study samplingTable reaches
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