The sediment transport rate is a function of these seven variables, as well as the size-shape-density distribution often assumed as a standard deviation of the particle diameter of the suspended particles In addition, the largest river discharge does not automatically mean that a river will have the largest sediment load.
The quantity and material of the sediment particles, as well as the geography of the local terrain will still play a contributing role in the sediment load The sediment load itself is calculated as a depth-integrated sediment mass above a unit area It is variable for multiple reasons, but can be estimated with a time-average collected sediment concentration While it is dependent on flow to initiate and continue transport, it is not calculated from flow rates, as the main variables in sediment load come from environment factors.
Sediment transport relies on water flow to move a load downstream. Water flow is variable, affected not only by the local terrain e. Most changes in water level are due to weather events such as rainfall Precipitation causes water levels to initially rise, and then return to previous levels base flow over the course of hours or days.
Rainfall, whether slight or heavy can affect water flow and sediment transport. The extent to which a weather event will influence sediment transport is dependent on the amount of sediment available. Snowmelt in a glaciated area will result in a high sediment load due to glacial silt Heavy rainfall over an area of loose soil and minimal vegetation will create runoff, carrying loose particles into the waterway. Likewise, flooding will also pick up sediment from the local area.
Increased water level creates additional volume in a channel, and increases the hydraulic radius cross-sectional area of a waterway. The increased hydraulic radius increases the discharge rate, regardless of whether or not flow is uniform or non-uniform Increased flow will increase the stress on the bed, making it more likely for water flow to initiate sediment transport.
The higher velocity also increases erosion rates as flow overcomes the shear stress of sediment Seasonal effects are also responsible for changes in water level and flow Most seasonal changes are due to precipitation levels and events such as snowmelt. During low precipitation and low flow periods, sediment transport falls. During the peak of snowmelt, the sediment load can increase by a factor of 15 or more Climate change can also play a role in sediment transport, as it affects both the timing and magnitude of floods and other weather events Anthropogenic factors, such as dams and altered land use will affect both the sediment load and sediment transport rate Dams affect the water flow through complete detention or restricted channels A sediment-starved river will not be able to provide habitats for benthic organisms or spawning fish The highly silted reservoir behind the dam may face issues of too much sediment, including changes in aquatic life and the potential for algal blooms.
On the other side of the spectrum, when a dam release occurs, the flow rate downstream can dramatically increase. If the release is controlled, it can refresh the bed material, building bars and other habitat areas. An uncontrolled release or dam removal can result in flooding, carrying the released sediment further downstream than is needed Human land use, such as urban areas, agricultural farms and construction sites will affect the sediment load, but not the transport rate These effects are indirect, as they require heavy rainfall or flooding to carry their sediment into the waterway.
However, anthropogenic land use is one of the leading contributors to excessive sedimentation due to erosion and runoff This loose soil is then easily carried into a nearby river or stream by rainfall and runoff. While sediment is needed to build aquatic habitats and reintroduce nutrients for submerged vegetation, too much or too little sediment can easily cause ecosystem and safety issues.
Whether the concerns are caused by scour, erosion, build up, or simply excessive turbidity, the sediment transport rate is an important environmental factor In addition to the problems cause by load quantity, sediment can easily introduce pollution and other contaminants into a waterway, spreading the pollutants downstream Large sediment loads are the most common issue seen with sediment transport rates.
Too much sediment can cause poor water quality, algal blooms, and deposition build-up. For aquatic life, excessive suspended sediment can disrupt natural aquatic migrations, as well damage gills and other organs 8, Diminished water quality occurs with unusually high sediment transport rates.
Turbidity can cause water temperatures to rise sediment absorbs more solar heat than water does 1. Rising water temperatures will cause dissolved oxygen levels to drop, as warm water cannot hold as much oxygen as cold water Suspended sediment can block sunlight from reaching submerged plants, decreasing photosynthesis rates and lowering dissolved oxygen levels still further If the increase in the sediment load is due to agricultural and urban runoff, algal blooms can occur from the increased nutrient load carried into the water body Regular sediment deposition can build bars for aquatic habitats, but increased sedimentation can destroy more habitats than it creates.
Siltation, the name for fine sediment deposition, occurs when water flow rates decrease dramatically. This fine sediment can then smother insect larvae, fish eggs and other benthic organisms as it settles out of the water column 1, Sediment deposition is responsible for creating alluvial fans and deltas, but excessive accumulation of sediment can build up channel plugs and levees.
These deposits then block the river from reaching other stream threads or floodplains Increased sedimentation is considered one of the primary causes of habitat degradation Depending on the local geology and terrain, sediment build-up can damage aquatic ecosystems not only in downstream sites, but in upstream headwaters as the deposits grow Sediment deposition is considered extreme when it exceeds the recommended or established total maximum daily load TMDL.
A TMDL establishes a limit for measurable pollutants and parameters for a body of water That means that TMDLs can be created for several different elements of the sediment load, including total suspended solids, nutrient impairment, pathogens and siltation When developing a TMDL report, it is important to consider whether or not the waterway itself is generating the sediment load naturally, as an unstable stream channel Though too much sediment is the more common concern, a lack of sediment transport will also cause environmental issues.
Sediment starvation is often caused by man-made structures such as dams, though natural barriers can also limit sediment transport 8. This can be when a river enters a shallow area this coud be when it floods and comes into contact with the flood plain or towards its mouth where it meets another body of water.
Rivers flood on a regular basis. The area over which they flood is known as the floodplain and this often coincides with regions where meanders form. Meanders support the formation of flood plains through lateral erosion. Adopt ClearIAS smart work approach! Online Classes with a difference! Get our newsletter Don't miss our email updates! We write simple, easy to understand articles, but always ensure high standards of quality. Comments Trully helpful for me to understand n Crete a coordination with tough geographical termology.
Damn good and easy to understand. Just love it. Thank you so much this is everything am looking for. Outstanding… Love it….. I wanna ask that river act as agent of erosion in upper course give reason. Deposition is likely to occur when: waves enter an area of shallow water; waves enter a sheltered area, eg a cove or bay ; there is little wind; a river or estuary flows into the sea reducing wave energy; there is a good supply of material and the amount of material being transported is greater than the wave energy can transport.
Related Topics Use the images below to explore related GeoTopics. Landforms of Coastal Deposition. Salt Marsh. Sand Dunes. Please Support Internet Geography If you've found the resources on this site useful please consider making a secure donation via PayPal to support the development of the site.
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