Module 1 : The Fluvial Environment Fluvial: Relating to or occurring in a river

Possible source? Source: Where a river begins Lake (or reservoir) e.g. Nile and Lake Victoria Springs e.g. River Thames in the Cotswolds Glaciers or snow melt e.g. The Rhone in the Alps Areas of very heavy rainfall e.g. mountains or rainforests - Amazon

Jobs carried out by a river Transportation Deposition 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

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

Processes of Transportation

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

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

DEPOSITION 1 Load is dropped when: Discharge is reduced after period of low precipitation Velocity low on entering sea or lake Shallow water on inside meander River overflows banks velocity outside channel is reduced Load suddenly increased eg debris from landslide

Deposition 2 Heaviest load dropped first e.g. boulders in mountain streams Gravel, sand + silt (bedload or suspension) dropped on floodplain or in channel as it nears mouth Silt + clay suspended load deposited where river meets sea e.g. delta Dissolved load carried out to sea, helps Maintain saltiness of the oceans

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 Read ‘An Integrated Approach’ p 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