Streams Water flowing through a channel ranging from a large river to a narrow creek.

The velocity of a stream or river determines The size of the sediment it can carry Example: What velocity would be required to transport a small cobble (6.4 cm.) ? The following chart shows how to get the answer

Intersects Graph here Answer= 175cm/sec

What is the largest size particle that could be transported by a stream with a velocity of 400 cm/sec?

Answer = boulders

Particles that are 1.5 cm. In diameter would be which type of particle?

Answer = pebbles

The volume rate of water flow through a point in the stream Stream Discharge The volume rate of water flow through a point in the stream

As the gradient of a river becomes less, the river enters the mature stage of it’s life Yellowstone River

The river may start to braid and deposit sediment in the mature stage Sand bar The river may start to braid and deposit sediment in the mature stage

As the river becomes old, it develops meanders

Large meander

Old meandering stream in Colorado

As a result: Erosion here As the stream curves It slows on the inside And speeds up on the outside, Deposition here As a result: Sand bar

High velocity large sediment carried Low velocity larger sediment deposited

Red line shows the fastest velocity Deposition here Erosion here Where the stream runs straight, the fastest velocity is in the center just below the surface

Meander bend on the River Conwy Explain why there is more deposition at ‘A’ rather than at ‘B’.

In the process an oxbow lake is formed Streams that develop very sharp meanders may actually undergo cutoff a new channel is formed as shown

Oxbow lake New channel

Sand bar Oxbow lake Flood plane

Profile of an old age river

When old age rivers reach the ocean or a lake, a delta is formed as the river drops most of it’s remaining sediment Young delta Mature delta Old delta

New Orleans river Gulf of Mexico Mississippi delta as seen from space shuttle Gulf of Mexico

Nile River Delta Nile River Mediterranean Sea

As a river enters a still body of water (lake, or ocean) it’s velocity slows to zero. As it does, it deposits the sediment load according to size. This is known as horizontal sorting Lake Largest first Medium next Finest last

smallest largest

Which particle would settle the fastest in still water? Which particle would settle the slowest in still water?

It should also be noted that sediment A most likely settled more quickly than sediment B Sediment A and B are both round, and of the same size. How can you account for the fact that sediment A has settled mostly on the bottom? Answer: Sediment A is denser than sediment B

Summary of deposition factors: Size: larger sediment particles settle faster than smaller particles Shape: rounder sediment particles settle faster that flat particles Density: denser sediment particles settle faster than lower density particles