TRANSPORTATION & DEPOSITION in a Stream System

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 1) Velocity - distance water travels in a given amount of time (think: quickness) 2) Stream Gradient 2) Stream Gradient - steepness or slope of the land that makes the streambed 3) Discharge 3) Discharge - volume of water that passes a certain point in a given time.

Factors affecting VELOCITY  The slope of the stream

Factors affecting VELOCITY  The contents and shape of the streambed

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

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

Factors affecting DISCHARGE  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:  Competence size  Competence – a measure that describes the maximum size particles a stream can carry.  Capacity amount  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 SOLUTION – smallest sizes, like clay particles, are dissolved in the stream’s water.

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

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

TRACTION 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: Meanders: Erosion and Deposition Working Together

MEANDERING STREAMS  Meandering streams wander side to side as they constantly seek out the lowest elevation.  This constant motion creates a series of S-shaped “loops”.  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 Outside Bank   Inside Bank

Cut-bank 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 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 OUTSIDE CURVE Velocity Water moves slower. Water moves faster. Action Deposition builds up Bank becomes eroded Features Area of deposition is called a point bar. Area of erosion is called a cut bank. Energy ? ?

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.

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

Alluvial Fan