Equilibrium theory states that meandering is the process by which a river adjusts its gradient (length along the course divided by the drop in elevation) so that there is an equilibrium between the erodibility of the terrain and the erosive power of the stream. Stochastic theory ascribes random fluctuations in the flow velocity due to some obstacle or disturbance to affect velocity distribution across the section, for the formation of meanders. Surprisingly, Einstein’s contribution to river engineering has not been acknowledged in the literature. This result in formation of tortuous water course called meandering. The secondary currents cause the flow to proceed in the direction towards eroded portion until redistribution of velocity reverses the process. This can generate erosion on one bank and deposition of sediment on the opposite bank. Even where there is no bend, Coriolis force caused by the earth’s rotation can cause a small imbalance in velocity distribution such that velocity on one bank is higher than on the other. Since then understanding of the process has traversed from simple physics to stochastic, equilibrium and geomorphic theories on one hand and from empiricism to complex mathematical modeling on the other, and yet without a final word as to-why and how rivers meander!Īccording to Einstein, a slight change in the velocity of flow between the banks of a river (due to a bend in the river) would give rise to secondary circular currents in the plane perpendicular to the direction of the flow. No less an intellectual luminary than Albert Einstein postulated in 1926 a theory explaining the process of meandering on the basis of simple physical laws. Meandering river has been one of the most explored and investigated topics in hydraulic engineering. Crooked rivers with lazy loops and bends have been favorites of artists and photographers. A meandering river originating form a valley formed by two mountains and a rising sun is the most likely sketch that a beginner in a drawing class would attempt. It is believed that the river Sabarmati (meandering all along its course) in western India, has derived its name from a poetical expression- ( saa bhramati) meaning- she (the river) is wandering. Continuous erosion on the outer bank and deposition on the inner bank forms a meander in the river, which will migrate downstream and change shape over time.Central Water and Power Research Station, Pune, IndiaĮ mail: rivers have fascinated all sections of viewers laymen, students, artists, poets, and scientists alike.Water moves slowly on the inside of the bend and the river deposits some load, forming a gently sloping river beach (also called a slip-off slope).The river erodes the outside bends through hydraulic action, corrasion and corrosion.This occurs on the outside of the bend and forms a river cliff. Water moving faster has more energy to erode.A corkscrew-like flow of water called Helicoidal Flow moves material from the outside of one meander bend and deposits it on the inside of the next bend.Once pools and riffles have developed, the river flows from side-to-side in a winding course.Riffles are areas of shallow water created by deposition of coarse sediment. Pools are areas of deep water and greater erosion (energy build-up due to less friction).This results in areas of slower and faster water movement.
In a straight river channel pools and riffles will develop as water twists and turns around obstructions such as large boulders.
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