Hydrology and Fluvial Geomorphology: River channel processes and landforms

Question 1

What is hydraulic action?

Answer 1

Sheer power/force due to the water’s velocity which allows joints and cracks to be exploited, leading to the fragmentation of the rock and the dislodging of particles (may also contribute to cavitation)

Question 2

Cavitation

Answer 2

The force of air exploding. As fluids accelerate, pressure drops and air bubbles may form. Cavitation is the implosion of these trapped air bubbles, a process which evicts tiny jets of water with velocities of up to 130 km/h, which can weaken solid rock.

Question 3

Attrition

Answer 3

Load particles knock against each other and are worn away, becoming smaller and rounder.

Question 4

Corrosion/solution

Answer 4

A chemical action which dissolves chemical ions in carbonate rocks such as limestone.

Question 5

Abrasion/corrasion

Answer 5

The erosion/wearing away of the channel banks and bed by coarse and angular fragments of hard rock carried within the river’s lad. These particles are thrown against the bed and banks by fast-flowing river flow and are used as a mechanical tool for grinding them. This may produce pot holes where pebbles become trapped in the bed and are whirled around by the current. It is assisted by turbulent flow where the speed of the water is continuously undergoing changes in magnitude and direction

Question 6

Traction

Answer 6

Larger, coarser load ar rolled along the stream bed by the river current

Question 7

Saltation

Answer 7

The hopping or bouncing motion of medium-sized particles along the bed of the river as a result of sufficient river energy

Question 8

Suspension

Answer 8

Light sediments are suspended above the bed by the current and moved within the body of the water

Question 9

Solution

Answer 9

The transport of soluble material dissolved in the river water

Question 10

Competence

Answer 10

Maximum particle size that a river can transport

Question 11

Capacity

Answer 11

Maximum load that a river can transport

Question 12

Which factors affect rate of erosion? (9)

Answer 12

Discharge, human impacts, velocity, competence, type of rock, pH, load, vegetation, relief

Question 13

When do river deposit their load?

Answer 13

When they slow down. When gradient becomes more shallow. When volume decreases. When friction increases.

Question 14

Deposition

Answer 14

When the river loses its energy so it is forced to drop its load (heaviest first)

Question 15

Sedimentation

Answer 15

The deposition of sediment

Question 16

Important features of the Hjulstrom curve (3)

Answer 16

1. Smallest and largest particles require high velocities to lift them - clay resists entrainment due to its cohesion
2. Higher velocities are required for entrainment than for transport
3. When velocity falls below a certain level, those particles are deposited

Question 17

Three types of flow

Answer 17

Laminar, turbulent, helicoidal

Question 18

Three channel types

Answer 18

Straight, braiding, meandering

Question 19

Thalweg

Answer 19

Path of quickest flow