water Article Grain Size Distribution of Bedload Transport in a Glaciated Catchment (Baranowski Glacier, King George Island, Western Antarctica) Joanna Sziło 1,* and Robert Józef Bialik 2 1 Institute of Geophysics, Polish Academy of Sciences, 01-452 Warsaw, Poland 2 Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 02-106 Warsaw, Poland; [email protected] * Correspondence: [email protected]; Tel.: +48-504-595-266 Received: 20 February 2018; Accepted: 20 March 2018; Published: 23 March 2018 Abstract: The relationships among grain size distribution (GSD), water discharge, and GSD parameters are investigated to identify regularities in the evolution of two gravel-bed proglacial troughs: Fosa Creek and Siodło Creek. In addition, the potential application of certain parameters obtained from the GSD analysis for the assessment of the formation stage of both creeks is comprehensively discussed. To achieve these goals, River Bedload Traps (RBTs) were used to collect the bedload, and a sieving method for dry material was applied to obtain the GSDs. Statistical comparisons between both streams showed significant differences in flow velocity; however, the lack of significant differences in bedload transport clearly indicated that meteorological conditions are among the most important factors in the erosive process for this catchment. In particular, the instability of flow conditions during high water discharge resulted in an increase in the proportion of medium and coarse gravels. The poorly sorted fine and very fine gravels observed in Siodło Creek suggest that this trough is more susceptible to erosion and less stabilized than Fosa Creek. The results suggest that GSD analyses can be used to define the stage of development of riverbeds relative to that of other riverbeds in polar regions. Keywords: GSD; proglacial channels; bedload transport; field measurements; fluvial erosion 1. Introduction One of the most important challenges in studies of bedload transport is investigating the differences between mobile and bottom particle sizes and taking these relations into account in new transport models [1–4]. This problem is mostly based on the lack of complex datasets for flow velocity, transport, and grain size distribution (GSD) of the bedload and bottom particles [2]. The lack of sufficient field observations and datasets collected during high flows when active transport is observed [5,6] is not the only problem associated with model development and geomorphological process assessments in Arctic or Antarctic catchments. The limited application of current models to natural gravel-bed rivers [7], and methods of predicting the sediment flux to the global ocean from small rivers [8] represent other problems that remain to be resolved. Bedload transport is one of the main factors associated with changes in the morphology of troughs [9–14], and the difficulty describing the relationships among water flow conditions, GSD, and deposition processes was identified decades ago (e.g., [15–18]). Although a substantial amount of progress has been made in this field because of research conducted in laboratory channels (e.g., [19–21])and field studies (e.g., [22–26]) and with the use of bedload transport models (e.g., [1,2,27–30]), the relationships among the factors associated with bedload transport are poorly understood in natural gravel-bed channels in general and in those located in polar regions in particular [31]. Water 2018, 10, 360; doi:10.3390/w10040360 www.mdpi.com/journal/water Water 2018, 10, 360 2 of 15 GhoshalWater 2018, et 10, al. x FOR [32 PEER] claimed REVIEW that the bedload has a large influence on the GSD and determines2 of 15 the concentration of each size fraction of noncohesive particles under changing hydrological conditions. GSD analyses30]), the relationships have frequently amongbeen the factors used associated as indicators with bedload of the threshold transport are for poorly the initiation understood of in particle motion,natural and sheargravel- stressbed channels dictates in general the specific and in role those of located particles in polar in this regions process in particular [10,33–37 [31].]. Johnson [38] Ghoshal et al. [32] claimed that the bedload has a large influence on the GSD and determines the suggested that the geomorphology of the bed as well as the sediment transport rate should be concentration of each size fraction of noncohesive particles under changing hydrological conditions. considered because of their relationship with grain size and shape. Moreover, the distribution of GSD analyses have frequently been used as indicators of the threshold for the initiation of particle particlesmotion, also and depends shear stress on the dictates mechanism the specific of fluvial role of transportparticles in and this canprocess be used[10,33 to–37] define. Johnson the [38] influence of flowsuggested conditions that onthe thegeomorphology geomorphology of the of bed the as channel, well as the as statedsediment by transport Kociuba rate and should Janicki be [ 31] or Lisle [23considered]. Although because the coarserof their fractionrelationship is entrained with grain with size greaterand shape. discharge Moreover, [39 ],the because distribution of protrusion of and hidingparticles effects, also depends particles on larger the mechanism than the mean of fluvial grain transport size are and easier can tobe moveused to than define smaller the influence ones [40 –42]. The above-mentionedof flow conditions on situation the geomorphology may be understood of the channel by using, as stated the by GSD Kociuba for the and analysis Janicki [31] of selectiveor bedloadLisle transport [23]. Although in natural the gravel-bedcoarser fraction channels is entrained [43] or with by performinggreater discharge a direct [39], analysis because of of certain protrusion and hiding effects, particles larger than the mean grain size are easier to move than smaller parameters, such as the mean grain size, sorting, or skewness, which can be used to predict the ones [40–42]. The above-mentioned situation may be understood by using the GSD for the analysis directionof selective of sediment bedload transport transport [in27 natural,44]. These gravel parameters-bed channels allow [43] or us by to performing obtain information a direct analysis about the predominantof certain size parameters, of the transported such as the mean particles, grain theirsize, sorting dispersal, or skewness, during this which process, can be andused their to pre symmetrydict or preferentialthe direction dispersal of sediment to one transport side of[27,44]. theaverage. These parameters Ashworth allow et us al. to [ 45obtain] concluded information that about sediment sortingthe can predominant occur during size entrainment,of the transported transport, particles, or deposition.their dispersal In during this research, this process, sediment and their sorting is calculatedsymmetry based or on preferential the sediment dispersal caught to one in trapsside of during the average. bedload Ashworth transport. et al. [45] concluded that Thesediment objective sorting of thiscan studyoccur during is to answer entrainment, the following transport questions:, or deposition. (1) HowIn this is research, GSD modified sediment during sorting is calculated based on the sediment caught in traps during bedload transport. the times of peak discharge in a polar catchment? (2) What is the relationship between the GSD The objective of this study is to answer the following questions: (1) How is GSD modified during and GSDthe times parameters of peak discharge and the in amount a polar catchment? of transported (2) What material is the relationship in gravel-bed between rivers? the GSD (3) and Does the modificationGSD parameters of GSDs and during the efficientamount of bedload transported transport material events in gravel allow-bed for rivers? the identification (3) Does the of the developmentmodification stage of ofGSDs river during troughs efficient during bedload changing transport meteorological events allow conditions? for the identification of the Todevelopment answer these stage questions, of river troughs insightful during measurements changing meteorological have been conditions? performed in Fosa and Siodło creeks, twoTo proglacialanswer these gravel-bed questions, insightful channels measurements located on the have forefield been performed of the Baranowskiin Fosa and Siodło Glacier on King Georgecreeks, two Island proglacial in Western gravel Antarctica-bed channels (Figure located1). on This the forefield study is of a the continuation Baranowski andGlacier development on King of George Island in Western Antarctica (Figure 1). This study is a continuation and development of the the results presented by Sziło and Bialik [46], who identified the relationship between bedload transport results presented by Sziło and Bialik [46], who identified the relationship between bedload transport and rapidand rapid outflow outflow and and high high water water discharge discharge in in thethe form of of eight eight-loop-loop hysteresis hysteresis for these for these creeks. creeks. Figure 1. Location of the study site: (a) King George Island; (b) Baranowski Glacier catchment; (c) Figureforefield 1. Location of the glacier of the and study measurement site:( sites.a) King Reference George system: Island; WGS 1984, (b) Baranowski UTM zone 21S, Glacier geoid EGM96. catchment; (c ) forefield of the glacier and measurement sites. Reference system: WGS 1984, UTM zone 21S, geoid EGM96. Water