River channel proccesses

Hello everyone

this is the summary for what we have learnt so far about the river channel processes.

I have organized it into a clearer manner for us to easily catch the idea

Basic ideas:

· High velocity results in high kinetic energy which allows the sediment being disturbed and the larger the quantity and the size of particles that can be transported

· Low velocity will result in the opposite way

Erosion	Transportation	Deposition
It is the picking up and removal of material · Corrosion: particles of rock carried by the river at the bed · Hydraulic action: high speed water at waterfall or flood produce air bubbles which may burst and send out shockwaves which increases erosion · Solution: carbon dioxide increases erosion by reacting with limestone	Types of material transported · Dissolved: invisible chemical dissolved in the water · Suspended: sediment that is whisked up by the water · Bed load: material is too heavy to be suspended, bounced and rolled along the river bed	When the speed of flow drops, particles deposit. Usually at river banks or where the river enters the sea due to great friction

The main factor controls transportation, erosion and deposition is the speed of the river. The relationship between the velocity and the size of the particles are shown in the Hjulstrom curve

1. Critical erosion velocity is the velocity required to pick up a particle of a give size (entrainment). The larger the particle, the greater the velocity needed to pick it up. One exception is the fine clay-size particles which require surprisingly high velocities because they have a tendency to stick to together. The particles requiring the lowest velocity to move are sand-sized particles. Erosion is above this point

2. Conversely, critical deposition velocity is the velocities where the small particles are dropped. It is more logical as the velocity falls, successively smaller particles are dropped. The area below this line indicates when deposition will occur.

3. The gap in between shows the ability to hold and suspend particles even if the velocity falls below that which is required to pick them up in the first place. It represents the process of transportation.

ANH(22)