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

Abstract

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.

The evolution of meandering and anabranching rivers in postglacial and loess landscapes of Europe

“…Kasvi et al, 2013), and interactions between sediments frozen in winter period, influence of high-flow events caused by snowmelt, rain events and related mass failures, and groundwater seeping (cf. Lotsari et al, 2020).…”

Where will widening occur in an outwash braidplain? A new approach to detecting controls on fluvial lateral erosion in a glacierized catchment (north‐western Spitsbergen, Svalbard)

“…F I G U R E 4 Downstream variation in braidplain slope (after Weckwerth et al, 2017 and width of proximal, middle and distal parts of the Waldemar River outwash (a) and transverse profiles in its proximal (b), middle (c) and distal (d) parts (see profile location in Figures 2 and 10D) Changes in air temperature and precipitation totals affect the mass balance of the glaciers, which leads to changes in river discharge, influencing fluvial activity in the forefields of contemporary glaciers (Costard et al, 2003;Lotsari et al, 2019;Strzelecki et al, 2018). Many years' worth of research in the catchment of the Waldemar River provides an important contribution to the understanding of fluvial processes (including lateral erosion) taking place in the river catchment (Sobota, 2005(Sobota, , 2014.…”

“…Active and passive controls on braidplain widening in the Arctic region are conditioned by mutual relationships between the discharge of F I G U R E 1 0 Distributary channel patterns and changes in the Waldemar River outwash feeding system: (a-c) active both northern (red arrow) and southern (yellow arrow) feeder channels and distributary streams active in northern and southern parts of the braidplain; (d) active southern (yellow arrow) feeder channel and distributary streams active in the southern part of the braidplain (for details see Figure 11). An aerial photograph taken in 1966 was not included in investigations on braidplain widening rate due to low image resolution [Colour figure can be viewed at wileyonlinelibrary.com] meltwater, braidplain morphology, sediment spatial distribution (Lotsari et al, 2019;Turowski et al, 2008). In terms of the lateral erosion of proglacial streams, its modelling was based usually on processes recognized over the course of a single melt season or as the result of short-term investigations (Fenn & Gurnell, 1987;Kociuba et al, 2014;Kociuba et al, 2019;Warburton, 1994).…”

Geomorphological impacts of a glacier lake outburst flood in the high arctic Zackenberg River, NE Greenland

“…However, the warming air temperatures could also have thawed permafrost and destabilised river banks, enabling more geomorphic work to be accomplished than if the ground remained frozen (c.f. Lotsari et al, 2020). Furthermore, it might be considered that the majority of Greenland deltas are aggrading (Bendixen et al 2017) due to enhanced meltwater generation and sediment mobilisation.…”