![]() ![]() Meanders are formed after cutting up of the banks as already described. The process of meandering depends upon the following factors: Unequal erosion of the banks may deviate the flow from its axis to form meanders. If the equilibrium condition (stable condition) of the river is somehow disturbed and if the bed is not degradable, the banks get eroded. Consequently the river flow may be deviated from its axis and meanders are formed.Ģ. If the banks are not resistant to erosion, increased velocity may erode the banks. ![]() When there is heavy sediment load in the river water, which is more than that required for stability, river tends to build up a steeper slope by depositing the sediment load on the bed. The main causes of meandering may be summarised as follows:ġ. In years of time the river develops well defined meanders as progressive scouring of one bank and silting of the other bank takes place. 14.2 clearly explains how the sinuous path is followed by the river. Consequently a shoal is created along the other bank as shown in Fig. When the river flow turns away from its axis and flows along one bank, silting of other bank takes place. The ratio M b/M a is called the meander ratio.Ī crossover is a portion of meandering river joining two meanders.Īt this stage it is clear that the river meanders when the river flow departs from its uniform axial path due to some reason. It is the distance between the outer edges of clockwise and anticlockwise loops. It is the distance measured at right angles to the axis of the river. It is a ratio of actual length to meander length. Tortuosity or sinuosity of a river is nothing but a measure of winding course adopted by the river. It is the tangential distance between the corresponding points of meander. 14.1 M a is the axial length of one meander. Various meander parameters are defined below: The length of this stage of river depends on: A river reach in which this periodic change in water level occurs due to the tides is called a tidal stage of river. The ocean water enters the river during flood tide and recedes during ebb tide irrespective of the main flow in the river channel. When river joins sea it may receive water from the tidal waves of the ocean. The delta and tidal stage of the river comes almost simultaneously. Because of flat slope and consequent low velocities the channel gets silted up and when the water level rises the water may spill over the banks to form new channels. The slope of bed is very flat and may range from 1 in 5000 to 1 in 10,000. This interwoven structure of the river branches is called a delta. When the river is about to end its course by joining the sea it may split up into number of channels or branches. But it is always true that even this type of river migrates within its khadir. When there is no scouring or silting in a river bed that is when the river carries down only that load which it receives, it is called a stable type of river thus there is no appreciable change in the alignment and slope of the channel from year to year. This water picks up sediment from river bed. The reason being that the sediment load in the flow gets deposited in the reservoir and clear water discharges over or through the dam. The river becomes degrading river generally below a dam. If the river bed is getting scoured from year to year it is called degrading type of river. The rivers in this stage generally meander. The sediment load which the river carries is similar is character to that of the river bed and the banks. During floods the river inundates very large areas causing considerable damage. The slope of the bed is still flatter and ranges from 1 in 1000 to 1 in 2000. It forms new land by depositing its excess load during the flood season. ![]() ![]() This stage of river is also known as river in flood plain or alluvial river because in this region. Thus shifting braided and interlaced channels are formed in the river course. The water flows round the heaps and the river flow is bifurcated. Rivers in this stage have straighter courses with wide bed and non-submersible banks.ĭuring flood period the coarse material comes in the river channel together with the high velocity flow and when the flood subsides these heavy and material piles up in heaps. As the bed material is very pervious there exists good amount of subsoil water flow. In this stage the bed is made up of a mixture of sand, shingle, gravel and boulders. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |