TRANSPORTATION DEPOSITION in a Stream System Stream water

TRANSPORTATION & DEPOSITION in a Stream System

• Stream water flowing downhill has energy. This energy allows for the water to pick up and move loose sediments in the channel. • Eventually, the running water lays down and deposits these particles. • The transportation and deposition of earth particles gives

Transportation: The movement of the particles

• Streams can move particles because the running water has kinetic energy. • The energy with which the water flows is determined by three factors: 1) Velocity - distance water travels in a given amount of time (think: quickness) 2) Stream Gradient - steepness or slope of the land that makes the streambed 3) Discharge - volume of water that passes a certain point in a given time.

Factors affecting VELOCITY q The slope of the stream

Factors affecting VELOCITY q The contents and shape of the streambed

Factors affecting GRADIENT q The relief of the land that the stream flows downhill on.

Factors affecting DISCHARGE q How large the stream’s watershed is.

Factors affecting DISCHARGE q The amount of water flowing through the tributaries that feed the main stream.

PARTICLE vs. ENERGY �The amount of particles a stream can carry and the size of the particles a stream can carry are both based on how much energy the flowing stream has at any given time.

All of the mass that is being transported by a stream is called the load. • The stream’s load changes as the stream either gains or looses energy. •

A stream’s kinetic energy directly impacts the following 2 stream characteristics: q. Competence – a measure that describes the maximum size particles a stream can carry. q. Capacity – total amount of sediment a stream can carry.

�A stream’s competence can be measured by observing the sizes of the particles being transported in its load. �Different size particles move in different types of transportations.

�SOLUTION – smallest sizes, like clay particles, are dissolved in the stream’s water.

�SUSPENTION – Silt and small sands are floating and carried with the water.

�SALTATION - larger sizes (sand greater) can be bounced along the streambed.

�TRACTION -the largest (boulder) sizes are rolled along during heavy stream flow events.

Deposition: The laying down of the particles

• Differences in a stream’s energy cause the stream to not have the ability to carry sediments. • This decreases the capacity and competence. • When this happens, sediments are deposited, or laid down.

Areas where sediments are deposited become common features found along a stream system. §

• Alluvial Fans – When streams come out of mountain valleys, they lose a great deal of velocity and deposit massive amounts of larger sediments.

Sand Bars - Occur where stream currents deposit large amounts of sand-sized sediment in isolated areas.

• Braided Stream - A network of small channels separated by small temporary islands of sediment.

• Deposits happen along floodplains after heavy water events. • These sediments are removed materials from the stream channel

• Levee – build up of sediment on the banks of a stream channel that occurs after flooding.

�Delta - Area where sediments are deposited at the mouth of a river

Meanders: Erosion and Deposition Working Together

MEANDERING STREAMS q. Meandering streams wander side to side as they constantly seek out the lowest elevation. q. This constant motion creates a series of S-shaped “loops”. q Stream velocity varies from one side to the other side of the “S”, resulting in erosion in some places and deposition of sediments in others.

Inside & Outside Banks �Refer to a side of the curve of a meander Out side Ban k k n a B e d i Ins

�Cut-bank - forms on outside of curve of meandering streams or rivers due to higher water velocity, which causes erosion on outside of curves. �Point bars - form on inside of curves of meandering streams or rivers where velocity is less, causing sediments to be deposited.

Differences between Inside and Outside Banks of a Meander Curve: INSIDE CURVE Velocity Action Features Energy • Water moves slower. OUTSIDE CURVE • Water moves faster. • Deposition builds • Bank becomes up eroded • Area of deposition • Area of erosion is is called a point called a cut bank. bar. • ?

�The combination of erosion and deposition that occurs in meanders causes the formation of oxbow lakes and cutoffs.

�Cutoff – where stream erodes through a meander, reconnecting it and leaving an oxbow lake.

• Eventually, it takes too much energy to keep meandering, so rivers will cut off a bend, resulting in an oxbow lake.

Locate areas of erosion and deposition on the following slide of a stream system:

Alluvial Fan