Spatial and temporal variability in grain sizes of Alaknanda River

Abstract

Recent studies have probed grain size analysis to understand the transport energy, deposition, source of the sediments in rivers.Sediment size also relates to the geochemical composition of the sediment and for predicting the response of climate and anthropogenic activities on watersheds.Following the approach of Folk and Ward, 1957 grain size characteristics were evaluated for the channel sediment sampled from river Alaknanda during different time periods.River Alaknanda is one of the major tributary of River Ganga flowing in Garhwal Himalayas.The erosion rate in the Alaknanda basin is very high, almost double the world's average; a large number of landslides occur in the entire watershed which are caused naturally due to steep slopes and lithology and nowadays promoted by increased anthropogenic disturbances and thus in this case grain size becomes the fundamental character to understand the river processes.Grain size was evaluated by using a particle size analyzer.The different time period data highlights the spatial and temporal variation in the statistical parameters of grain sizes.The values of mean size, sorting, skewness and kurtosis varies considerably.It was found that sand dominates in most of the samples.Well sorted to poorly sorted nature of the sediment was observed.The skewness and kurtosis values show the heterogeneous nature of grain sizes.An approach has also been followed to discriminate the grain size distribution of two different intervals by using the ANOVA test.A one way ANOVA test was performed to estimate the remarkable difference in the mean values of grain size parameters of two samples.ANOVA results confirm that significant differences exist between the samples.The outcome of the study demonstrates the influence of discharge, river energy, erosion rate and seasonal variability in determining the sediment size.