Those bends and turns manage the energy of water, as it moves through and over channel terrain, by increasing resistance and reducing channel gradient. The geometry of the meander minimizes the amount of work, or energy expended, while using that same energy uniformly.
Streams meander to maintain equilibrium — a dynamically stable form and function. Remember, streams are transport machines, moving water and sediment from their watersheds relentlessly downslope. Meanders are produced when water in the stream channel erodes the sediments of an outer bend of a streambank and deposits this and other sediment on subsequent inner bends downstream.
This process reinforces the riffle-pool structure of a stream. As every angler knows, deep pools form on the outer bends of meanders, with low sloping point bars of accumulated gravel or cobble on the inside bends. In these pool and bend sections, one side of the channel is significantly deeper. Further downstream, moving out of the bend, the channel straightens, and the channel cross-section becomes more uniform through the riffle. Support our Natural Stream Restoration efforts to recreate stable channels based on the hydrology and hydraulics that shape natural channels.
Charlton, F. INT, Hydraulics Res. Chang, H. Church, M. Ferguson, R. Area 5: 38— In:6—29 Google Scholar. British rivers ed. Henderson, F. Kellerhals, R. Lane, E. Leopold, L. Neill, C. National Res. Therefore, in addition to growing laterally, the bends also gradually migrate down the valley. Explore This Park. Fluvial Features—Meandering Stream. Oxbow lake formation in a meandering stream Phil Reiker, NPS Geologic Resources Division A meandering stream has a single channel that winds snakelike through its valley, so that the distance 'as the stream flows' is greater than 'as the crow flies.
If we look at a channel in cross section, it is asymmetric, representing the sites of erosion and deposition. Variation in flow speed also produce different sedimentary structures. Upper planar lamination and dune cross stratification are common where Re is highest, and ripple cross lamination is common where Re is lower.
The main parts of the channel include eroding bank, the thalweg the deepest point of the flow and the point bar on the inside of the bend where most sediment is accumulating. As the channel migrates due to erosion and deposition, a distinctive suite of sedimentary structures accumulate.
The deepest part is coarser and has upper planar lamination or dune cross stratification. This is overlain by finer sediment with current ripple lamination. As meandering rivers migrate, the meanders tend to increase. Eventually, the channel forms almost a circle, and the meander gets cut off, often during a flood. This straightens the channel temporarily and produces an ox bow lake in the abandoned meander.
The lake accumulates mud and organic matter. It slows down very quickly and the water becomes shallower, both of which cause a decrease in Re. Thus, the water can not transport as much sediment on the floodplain as it does in the channel. Thus, finer sands that may be in suspension during a flood are transported as bedload or rapidly deposited once the river tops its banks.
This produces levees. The finer silts and especially clays remain in suspension much longer and settle out on the floodplain as the flood waters dry up. Thus, the channel bottom can aggrade fill in until the bottom of the channel is as high or higher than the floodplain. When the next flood comes along, the river avulses and does not go back into its old channel which is higher than a new one on the floodplain.
This results in the downstream part of the channel being completely abandoned. Transport Capacity Erosion by water occurs when water is flowing across a surface and the flow is capable of transporting more sediment than is currently moving as bedload. Rivers Rivers are responsible for most sediment transport from mountains to lowlands and the oceans.
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