What is Sediment Transport and Deposition?
Sediment transport is the movement of organic and inorganic particles by water. In general, the greater the flow, the more sediment that will be conveyed. Water flow can be strong enough to suspend particles in the water column as they move downstream, or simply push them along the bottom of a waterway. Transported sediment may include sand, silt, clay, and organic material. Sediment deposition occurs when suspended particles settle down to the bottom of a body of water. This settling often occurs when the river flow slows down (such as when a stream bends) or stops (when there are obstacles such as large boulders blocking the water flow). Sediment deposition can be found anywhere in a water system, from high mountain streams to rivers, lakes, deltas, and floodplains. Rivers that run through soft soil typically have a higher sediment transport load than rivers exposed to bedrock, as much of the sediment load is taken from the sides and bottom of the channel. In addition to non-erodible bedrock terrains, highly vegetated areas are less subject to runoff erosion during flood events, as the roots of the plants hold the soil in place.
Figure 1: Sediment deposition occurring on the side of a bent river.
What is a Beach?
A beach is a landform alongside a body of water that consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, and pebbles. Freshwater beaches differ significantly from their saltwater counterparts. Freshwater beaches vary greatly depending on what type of water body they are found on. Beaches on lakes are often quite narrow and sandy. Due to the smaller tides found on lakes, their beaches tend to be more static as longshore drift does not occur as dramatically. Riverside beaches tend to be wide and can have huge piles of sediment. These beaches change a lot depending on localized flooding and erosion. Where marine beaches are influenced by tides and sediment getting brought onto shore, freshwater beaches are more often created from materials found along the shore or deposited along the way.
Figure 2: A beach
All of these logging tasks can be observed from the GZ.
- Observe the beach across the stream. Recall that “riverside beaches tend to be wide and can have huge piles of sediment. These beaches change a lot depending on localized flooding and erosion.” Does this beach at the viewpoint hold up to these characteristics of a riverside beach? Name specific signs at the GZ (how large is the beach, is there a noticeable sediment build-up, etc).
- Calculate the stream’s speed. You can do this by counting how far water moves (in feet) down the stream for 5 seconds.
For example, if the water moved 25 feet in a span of 5 seconds, the speed of the stream would be 25 feet / 5 seconds or 5 ft/sec.
- Based on your calculated speed of the stream and what you know about sediment deposition in the description, do you think that the stream is able to carry large amounts of sediment that could be deposited to the riverbank?
- Do you notice any vegetation present near the bank of the stream? If so, name specific types. How does vegetation increase or decrease streambank erosion?
- As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
https://www.fondriest.com/environmental-measurements/parameters/hydrology/sediment-transport-deposition/#:~:text=This%20settling%20often%20occurs%20when,%2C%20lakes%2C%20deltas%20and%20floodplains.
https://en.wikipedia.org/wiki/Beach
https://www.theswimguide.org/2018/03/29/different-beaches-guide/#:~:text=Freshwater%20Beaches,-Found%20in%20the&text=Not%20completely%20free%20of%20salt,often%20quite%20narrow%20and%20sandy.
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