Jakub Ondruch

Seasonal hydrological and suspended sediment transport dynamics in proglacial streams, James Ross Island, Antarctica

ABSTRACT Rapid warming of the Antarctic Peninsula is producing accelerated glacier mass loss and can be expected to have significant impacts on meltwater runoff regimes and proglacial fluvial activity. This study presents analysis of the hydrology and suspended sediment dynamics of two proglacial streams on James Ross Island, Antarctic Peninsula. Mean water discharge during 8 January 2015 to 18 February 2015 reached 0.19 m3 s−1 and 0.06 m3 s−1 for Bohemian Stream and Algal Stream, respectively, equivalent to specific runoff of 76 and 60 mm month−1. The daily discharge regime strongly correlated with air and ground temperatures. The effect of global radiation on proglacial water discharge was found low to negligible. Suspended sediment concentrations of Bohemian Stream were very high (up to 2927 mg L−1) due to aeolian supply and due to the high erodibility of local rocks. Total sediment yield (186 t km−2 yr−1) was high for (nearly) deglaciated catchments, but relatively low in comparison with streams draining more glaciated alpine and arctic catchments. The sediment provenance was mostly local Cretaceous marine and aeolian sediments; volcanic rocks are not an important source for suspended load. High Rb/Sr ratios for some samples suggested chemical weathering. Overall, this monitoring of proglacial hydrological and suspended sediment dynamics contributes to the dearth of such data from Antarctic environments and offers an insight to the nature of the proglacial fluvial activity, which is likely to be in a transient state with ongoing climate change.

Active layer monitoring at CALM-S site near J.G.Mendel Station, James Ross Island, eastern Antarctic Peninsula

The Circumpolar Active Layer Monitoring - South (CALM-S) site was established in February 2014 on James Ross Island as the first CALM-S site in the eastern Antarctic Peninsula region. The site, located near Johann Gregor Mendel Station, is labelled CALM-S JGM. The grid area is gently sloped (<3°) and has an elevation of between 8 and 11ma.s.l. The lithology of the site consists of the muddy sediments of Holocene marine terrace and clayey-sandy Cretaceous sedimentary rocks, which significantly affect the texture, moisture content, and physical parameters of the ground within the grid. Our objective was to study seasonal and interannual variability of the active layer depth and thermal regime at the CALM-S site, and at two ground temperature measurement profiles, AWS-JGM and AWS-CALM, located in the grid. The mean air temperature in the period March 2013 to February 2016 reached -7.2°C. The mean ground temperature decreased with depth from -5.3°C to -5.4°C at 5cm, to -5.5°C to -5.9°C at 200cm. Active layer thickness was significantly higher at AWS-CALM and ranged between 86cm (2014/15) and 87cm (2015/16), while at AWS-JGM it reached only 51cm (2013/14) to 65cm (2015/16). The mean probed active layer depth increased from 66.4cm in 2013/14 to 78.0cm in 2014/15. Large differences were observed when comparing the minimum (51cm to 59cm) and maximum (100cm to 113cm) probed depths. The distribution of the active layer depth and differences in the thermal regime of the uppermost layer of permafrost at CALM-S JGM clearly show the effect of different lithological properties on the two lithologically distinct parts of the grid.

Response of channel dynamics to recent meander neck cut-off in a lowland meandering river with artificial training history: the Morava River, Czech Republic

ABSTRACT One-decade-long observations of post-cut-off channel development and oxbow lake formation are presented to offer insight into the morphological response of the Morava River to neck cut-off. The main objectives were: calculation of the amount of sediment released to the channel by collapse of the meander neck; comparison of floodplain erosion and deposition rates before and after cut-off; and description of the rate and pattern of oxbow lake sedimentation. The amount of sediment released due to cut-off (~35 000 m3) equalled 2–5 years of sediment input by lateral erosion averaged for the past six decades. Bank erosion rates substantially exceeded long-term averages (0.63–6.21 m year−1, post cut-off). Despite a low entrance angle, alluvial plugs in a newly formed oxbow lake were established within a few months. Between 2006 and 2016, sedimentation of the alluvial plugs proceeded at an average rate of 0.55 m year−1, reflecting the time since cut-off and the frequency of overbank flows.

Response of lateral channel dynamics of a lowland meanderingriver to engineering-derived adjustments - an example of theMorava River (Czech Republic)

Abstract Freely meandering (quasi)natural reaches of lowland rivers represent a rare phenomenon in Central Europe. Increasing attention is currently being paid to the dynamics of quasi-natural (artificially influenced) meandering rivers as this attention represents the basic prerequisite for the development of appropriate restoration strategies on regulated rivers. This study focused on a 5.5 km long reach of the Morava River in the Strážnické Pomoraví region, Czech Republic that is characterised by quasi-natural evolution after substantial engineering adjustments were made in the first decades of the twentieth century. Based on Geographic Information Systems (GIS) analysis of aerial photographs, the spatio-temporal dynamics of bank erosion and accretion rates were quantitatively described and variables that control channel migration rates were identified. High rates of lateral shifts were localised in high sinuosity segments (sinuosity 1.17-2.37), whereas segments with very low rates were straight or formed into slightly curved bends (sinuosity 1.05-1.18). As a key factor, engineering works that influenced local river bed slope and induced a dramatic increase in bank erosion rates were identified. River engineering works induced a dramatic increase in bank erosion rate (2.19 m/year for 1938-53 and 1.47 m/year for 1953-63). An interval of approximately 25 years was needed before the erosion rates dropped back to values documented before river regulation (0.35-1.09 m/year for 1841-1938). Other important controlling variables included radius of curvature, frequency and magnitude of floods and, locally, river bank material properties and floodplain land cover.