Analysis of size, shape and textural maturity of sands from the Kaligandaki River

Abstract

The Gandaki River System is one of the major river basin of the Himalaya originating from China and flows through Nepal and eventually mixes with the Ganga River in India. The study aims at analyzing the textural properties (size and shape) and maturity of the Kaligandaki River sands, and their downstream variation. Sand samples were collected along the river from the Tethys Himalayan region up to the Indo-Gangetic Plain of Nepal. The sands are classified as slightly muddy sand, in which mean and median sizes and sorting increase with respect to the distance downstream from the provenance. The results indicate that coarsely skewed and platy to mesokurtic sands become nearly symmetrical to finely skewed and leptokurtic suggesting increase in fine-grained sands and enhancement of sorting downstream. The percent of fines (mud) ranges from 0 to 5% and shows no distinct downstream variation trend. Mean roundness of quartz is generally sub-angular (2 to 3 p), and downstream variation does not reflect change in roundness category. However, there occurs slight diminish of roundness with distance downstream. Inclusive graphic standard deviation (Cj) varies from 0.30 to 1.38j. After 100 km downstream, Gj decreases reflecting improvement of sorting. Sediments are immature to mature, and are sub-mature in upstream and midstream segments except for few sites where they are immature not due to flux, but probably due to local contribution of fines. Due to increased downstream distance, sediments tend to be more mature owing to enhancement of sorting