EXPERIMENTAL STUDY ON CHARACTERISTICS OF BRAIDED STREAMS

Abstract

Alluvial river channels are 'self-formed' as they flow over the alluvial lands having sandy-silty-clay materials. Their morphology results from the entrainment, transportation and deposition of the unconsolidated sedimentary materials of the valley fill and flood plain deposits across which they flow (Richards, 1982). Alluvial channels are generally categorized as straight, meandering, anastomosing and braided patterns (Fig.1.1). Braided streams are associated with high stream power and unstable braid bars formed of sediments, which are often unvegetated. Braiding is the division of a single channel into two or more anastomosing channel ways. Braided rivers may be envisaged as a series of channel segments, which divide and rejoin around bars in a regular or repeatable pattern as can be seen from the satellite image of the Brahmaputra river in Bangladesh vide Plate 1.1 (a,b). Generally, braiding is favoured by high-energy fluvial environments with steep valley gradients, large and variable discharges, dominant bed load transport, and non-cohesive banks lacking stabilisation by vegetation. Lane (1957) stated that a braided stream is characterised by 'having a number of alluvial channels with bars or islands between meeting and dividing again, and presenting from the air the intertwining effect of a braid'. Schumm (1963) expressed the braided channels as single