module 1 the fluvial environment n.
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Module 1 : The Fluvial Environment. Fluvial: Relating to or occurring in a river. Possible source?. Jobs carried out by a river. CORRASION Load rubs bed and banks – abrasion – like sandpaper Most effective in flood Vertical and horizontal erosion

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module 1 the fluvial environment

Module 1 : The Fluvial Environment

Fluvial: Relating to or occurring in a river

erosion
CORRASION

Load rubs bed and banks – abrasion – like sandpaper

Most effective in flood

Vertical and horizontal erosion

Pebbles caught in hollows swirl to form potholes

ATTRITION

Bedload collides and is broken in to smaller pieces

Rocks become increasingly rounded downstream

EROSION
erosion 2
HYDRAULIC ACTION

Sheer force on outside of bend – water pushed into cracks – air compressed- pressure causes collapse

Captivation –bubbles of air collapse -shock waves weaken banks

Slowest and least effective form of erosion

SOLUTION OR CORROSION

Happens continuously

The concentration of carbonic acid and humic acid in the water enables it to dissolve material from bed, bank and load.

Humic acid derived from humus

EROSION 2
transportation 1
Uses energy remaining after friction

Increases with

Discharge (amount)

Velocity (speed)

Turbulence (rough flow)

Up to bankfull stage / flood levels

In flood large wetted perimeter friction deposition

SUSPENSION

Fine particles clay and silt

Amount + size of suspended load increases velocity and turbulence.

Increases towards mouth (brown water)

Greatest part of river’s load

TRANSPORTATION 1
transportation 2
SOLUTION

Precipitation

carbonic acid

limestone.

Normally dissolved or solution load is small proportion of total load (except in limestone areas)

SALTATION

Large bedload is lifted and bounced

TRACTION

Largest bedload rolls or slides along bed

Proportion of bedload may be small if river not at flood level

Difficult to measure

TRANSPORTATION 2
summary
Load =

- suspended load

- dissolved or solution load

- bedload

Where does it come from?

Material worn from bed and banks

Material from weathering on valley sides

River Tyne (annual)

57% suspended

35% solution

8% bedload

10 tonne every 20mins

River Amazon

40 tonnes every minute

Summary
hjulstrom curve 1935
HJULSTROM CURVE (1935)
  • Shows relationship between particle size (competence) and velocity
  • Mean or critical erosion velocity curve = velocity needed to pick up (entrainment) and transport particles in suspension
  • Mean fall or settling velocity curve = velocity at which particles fall out of suspension and are deposited
  • Note:
  • Sand (1) is easier to pick up than finer particles (2), clay has more cohesive properties
  • Velocity needed to maintain particles in suspension is less than that needed to pick them up, especially true for finer particles – compare (2) & (4)
homework
HOMEWORK
  • Read ‘An Integrated Approach’ p.71-74
  • - read it carefully and study all the diagrams
  • - make notes on anything you missed in class
  • Define the terms COMPETENCE and CAPACITY
  • Answer questions on Hjulstrom curve