[<< wikibooks] HKDSE Geography/M2a/Fluvial Processes
The three fluvial processes are erosion, transportation and deposition.

Erosion is the process in which materials are removed by an agent.
Transportation is the process in which eroded materials are carried away.
Deposition is the process in which materials are 'dumped'.


== Erosion ==
There are three directions and four processes. Remember the names and what they mean (but don't memorise the definitions).


=== Three Directions ===


=== Four Processes ===
Four processes:

Hydraulic action: Water exerts pressure on the river bank and undercuts it. Cracks are widened.
Corrosion/Solution (Solvent action): Water dissolves soluble minerals from the bed or bank, e.g. calcium in limestone. It is a form of chemical erosion.
Abrasion (Corrasion): River load acts as a tool to wear away the bed or bank, e.g. large, angular boulders downcut the bed.
Attrition: Load knocks against each other, the bed or the bank. They break down into smaller pieces and get smaller and smaller.


=== Factors ===
These factors affect erosion:

Nature of load:
Load weight ↑ → Erosion ↑
Load angularity ↑ → Erosion ↑
Amount of load: Load amount ↑ → Erosion ↑
Discharge and velocity:
Discharge ↑/Velocity ↑ → Energy ↑  → Erosion ↑
Geology of rocks: Joints ↑ → Erosion ↑
Additional factors for corrosion:
Water acidity ↑ (pH value ↓) → Erosion ↑
Hot and humid climate → Erosion ↑
Rocks composed of soluble minerals → Erosion ↑


== Transportation ==
The materials carried by transportation are load.


=== Four Processes ===


=== Factors ===
Energy ↑ → Velocity ↑ → More, heavier load
Fluvial Erosion ↑ → Load ↑
Soil Erosion ↑ → Load ↑
Deposition ↑ → Load ↓


== Deposition ==


=== One Process ===
One process occurs in deposition: Sorting. The heaviest load is deposited first. Cobbles are deposited, then pebbles, then sand, then silt, and finally clay. Thus deposited materials are deposited in layers.


=== Factors ===
Input of water ↓ / Output of water ↑
Drought, dry season, high evaporation rate → Amount of water (discharge) ↓ → river energy ↓ → Deposition ↓Velocity ↓
Inland flow of seawater →  Velocity ↓ → Deposition ↑
Load ↑ → Internal friction ↑ →  Velocity ↓ → Deposition ↑
Examples: Siltation, landslide
Channel friction ↑ → Deposition ↑
Examples: entering a channel with long wetted perimeter
Gradient ↓ →  Velocity ↓ → Deposition ↑
e.g. waterfall, entering a flood plain
Water enters a large body of water
shallow lake, shallow sea
At inner banks (will be discussed later)


== Impact of Velocity on Fluvial Process Occurrence ==


== Downstream Variation ==