Spatial variation of river-ice thickness in a meandering river

Earth Surf Processes Landf

Tarsa

Kämäri

et al. 2019

Self Cite

To be able to understand year‐round river channel evolution both at present and in the future, the spatial variation of the flow characteristics and their sediment transport capabilities under ice cover need to be detected. As the measurements done through cross‐sectional drill holes cover only a small portion of the river channel area, the numerical simulations give insight into the wider spatial horizontal variation of the flow characteristics. Therefore, we simulate the ice‐covered flow with a hydrodynamic two‐dimensional (2D) model in a meandering subarctic river (Pulmanki River, Finland) in mid‐winter conditions and compare them to the pre‐winter open‐channel low flow situation. Based on the simulations, which are calibrated with reference measurements, we aim to detect (1) how ice‐covered mid‐winter flow characteristics vary spatially and (2) the erosion and sedimentation potential of the ice‐covered flow compared to open‐channel conditions. The 2D hydrodynamic model replicated the observed flow characteristics in both open‐channel and ice‐covered conditions. During both seasons, the greatest erosional forces locate in the shallow sections. The narrow, freely flowing channel area found in mid‐winter cause the main differences in the spatial flow variation between seasons. Despite the causes of the horizontal recirculating flow structures being similar in both seasons, the structures formed in different locations depended on whether the river was open or ice covered. The critical thresholds for particle entrainment are exceeded more often in open‐channel conditions than during ice‐covered flow. The results indicate spatially extensive sediment transport in open‐channel conditions, but that the spatial variability and differences in depositional and erosional locations increase in ice‐covered conditions. Asymmetrical bends and straight reaches erode throughout the year, whereas symmetrical, smaller bends mainly erode in open‐channel conditions and are prone to deposition in winter. The long ice‐covered season can greatly affect the annual morphology of the submerged channel. © 2019 John Wiley & Sons, Ltd.

Section: Study Areamentioning

confidence: 99%

“…Kämäri et al . () estimated that skim ice formed on the Pulmanki River when the cumulative number of freezing air temperature degree‐days was 22 (e.g. on 21 October 2013).…”

Section: Study Areamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Spatial variation of flow characteristics in a subarctic meandering river in ice‐covered and open‐channel conditions: A 2D hydrodynamic modelling approach

Earth Surf Processes Landf

Tarsa

Kämäri

et al. 2019

Self Cite

“…The channel morphodynamics of subarctic rivers are influenced throughout the year by several key variables in addition to discharge from the contributing catchment. These key variables include: 1) hydro‐climatic variations over both annual and seasonal timescales; 2) sub‐zero temperatures and the duration of river ice cover; 3) the extent of inundated floodplain as dictated by channel flow and channel‐floodplain ice conditions; and, 4) the geotechnical characteristics of river banks, which will be affected by sub‐aerial processes (Vandenberghe, ; Turcotte et al, ; Lewis et al, ; Kämäri et al, ; Lotsari et al, 2017). Each season exerts different controls on the channel flows, sediment transport, and morphology and these controls may differ also between regions, i.e., at varying temporal and spatial scales, with differing hydro‐climatic conditions and varying magnitudes of the season specific processes (Tananaev, ).…”

Section: Introductionmentioning

confidence: 99%

Sub‐arctic river bank dynamics and driving processes during the open‐channel flow period

Earth Surf Processes Landf

Hackney

Salmela

et al. 2020

There is growing concern that rapidly changing climate in high latitudes may generate significant geomorphological changes that could mobilise floodplain sediments and carbon; however detailed investigations into the bank erosion process regimes of high latitude rivers remain lacking. Here we employ a combination of thermal and RGB colour time‐lapse photos in concert with water level, flow characteristics, bank sediment moisture and temperature, and topographical data to analyse river bank dynamics during the open‐channel flow period (the period from the rise of the spring snowmelt flood until the autumn low flow period) for a subarctic river in northern Finland (Pulmanki River). We show how variations of bank sediment temperature and moisture affect bank erosion rates and locations, how bank collapses relate to fluvial processes, and elucidate the seasonal variations and interlinkages between the different driving processes. We find that areas with high levels of groundwater content and loose sand layers were the most prone areas for bank erosion. Groundwater seeping caused continuous erosion throughout the study period, whereas erosion by flowing river water occurred during the peak of snowmelt flood. However, erosion also occurred during the falling phase of the spring flood, mainly due to mass failures. The rising phase of the spring flood therefore did not affect the river bank as much as its peak or receding phases. This is explained because the bank is resistant to erosion due to the prevalence of still frozen and drier sediments at the beginning of the spring flood. Overall, most bank erosion and deposition occurrences were observed during the low flow period after the spring flood. This highlights that spring melt, while often delivering the highest discharges, may not be the main driver of bank erosion in sub‐arctic meandering rivers. © 2019 John Wiley & Sons, Ltd.

Impacts of rising, peak and receding phases of discharge events on erosion potential of a boreal meandering river

Kärkkäinen

2022

Hydrological Processes

Self Cite

Flow features of a meandering river can vary seasonally and widely in the boreal zone, as seasonal variation in discharges affect the properties of meander bends and the spatial location of flow magnitudes. However, a better understanding of the impacts of consecutive high‐discharge events in the boreal zone requires further analyses. Thus, the impacts of the fluvial processes and their magnitudes on different types of meander bends (e.g., sinuosity, symmetricity) were analysed throughout an open‐channel flow period, using accurate flow measurements and hydrodynamic (two‐dimensional) modelling. In particular, the research compared the impacts of different discharge events in magnitude and length of river evolution, and whether there is a difference in the erosion forces of the rising and falling phases of discharge hydrographs, and which of the phases has the greatest relevance to erosion forces. A case study was carried out in a middle boreal zone meandering river (Koitajoki in eastern Finland) during the 2020 open water season from May to October. Five different types of meander bends were considered in the study area. Flow magnitudes and shear forces were at their strongest during the spring flood peak, which is normally considered as the highest flow event during the hydrological year. Exceptionally, the largest summer discharge event reached a level that was close to the spring floods' maximum erosional capabilities. Bed shear stress values indicated the falling phases of the flood hydrographs are more important to river evolution than during the ascent stage, as the long duration of the flood downstage contributes more strongly to meander bend erosion and development. The smaller the curvature and larger the sinuosity of the bends, the more variation in erosional forces occurs between discharge stages. The study provides new insights into seasonal fluvial processes in boreal river meander bends as well as reinforces results from earlier river studies.