Meandering Rivers are located on level terrain thatreduces the circulation speed ofwater, enabling the flow to curve or "meander". The bends in the river will migrate earlier and soon within the flow valley. There is adifferentiation in circulation speeds within a meandering river channel the produces locations of erosion and also deposition. There are unique sedimentary frameworks that an outcome from this process.

You are watching: At a bend in a river the main erosion is

Sediment Erosion/Deposition


Figure 1: Aerial picture of ameandering river. The allude bar, whereby sediment is deposited, have the right to be checked out in the inner bend of the river. There is a build up of gray colored sediment. The financial institution of the channel is where erosion occurs, and also is situated on the external bend of the river. Http://

When the water moves around a curve, the velocity the the water is highest possible along the outer component of the channel. This area is referred to as the bank of the channel, and it is wherein erosion the sediment occurs. Erosion is caused by the boost in flow velocity, which has actually the force to erode and also transportsediment indigenous the bank. Top top the inside bend that the river, known as the point bar,water velocity is slower due to the fact that it doesn"thave to take trip as much as the water on the external of the bend. This enables sediment to clear up out and also be deposited. Together this cycle of erosion and also deposition continues, the flow will migrate in it"sriver valley. This migration can lead come the production of one oxbow lake, i m sorry is defined further here:

Sedimentary Deposits/Structures

Due to the greater velocity in the middle and outside bendof the flow channel, coarser sediment will certainly be deposited in those areas. The coarser grains will be transported come these parts of the flow channel since thehigher velocity is able to transfer the heaver grains. This is concerned the ide of Reynolds Number,which steps whether sediment move of a specificgrainsize will be able to occurbased on the velocity of the water.

There aretwo distinct locations within the river channel that are characterized by various flow speeds and grain size, the external edge and also the inner bending of the channel. The various flow speeds will carry different size sediment grains, which willproduce a cross ar that is asymmetrical. The coarser grains will be current in the external edges that the channel, if finer sediment will be along the within of the channel. The different flow speeds in ~ the channel, together with the differentgrain sizes,will develop uniquesedimentary structures. The coarser grained areas that resultfrom a faster flow speed will have upper planar lamination or dune overcome stratification. The allude bar that the flow will develop current ripple lamination, because of the finer sediment and slower circulation speeds. As the flow migrates in the direction of the direction of the eroding bank, the present ripples that the suggest bar will come to be deposited on optimal of planar lamination/dune crossstratification that the bank.

Facies/Stratigraphic Column

Thetypical faciesthat occur within a meandering river environment include a scoured base of flow, which is brought about by the high circulation velocity inthe center of the channel the is able to pick up and also transport huge sediment particles. Over there would additionally be a lag deposit of mud rip-up clasts and the coarsest sediment in ~ the facies. A lag deposit is whereby physical procedures remove the finer sediment, leave behind the food grains.As we move upward in the stratigraphiccolumn, the grain size will become an ext fine. The frameworks you should uncover are trough cross stratification,rippled sands, and also finally sigmoidalcross stratificationresulting native the suggest bar migration.

Periodically, the river will flood, resulting in its floodplain come fill through fine-grained sediment. This is as result of the water flowvelocity decreasing as it flows away from the river channel. Much more information on floodplains deserve to be discovered on the previously linked page on Oxbow Lakes and Floodplains. The floodplain facieswill be incorporatedinto the usual meandering flow facies.

See more: How Much Is A Score Of Years Is 4 Score And 7 Years Ago? What Is Four Score In The Bible


Figure 2: A usual stratigraphic obelisk for a meandering river system with the lag deposits on the bottom, adhered to by trough cross stratification and also ripple cross lamination. This is overlain by a common floodplain facies that is composed of dirt cracks and also root traces in a fine grained sediment.

There space also vital differences in the facies because that a meandering river channel and also a braided river channel. Braided river networks will have actually coarser serial sizes due to their much faster flow speeds. Meanderingrivers carry lots of sediment in ~ suspension that will certainly be deposited in the frameworks associatedwith this environment, including point bars and also oxbow lakes. Lastly, the hike of meandering rivers is more uniform in direction than a braided river since it will always migrate towards the eroding bank. A braided channel will migrate in many directions at the same time.