Rivers

Rivers

1. River Processes

   • Upper Course
     • Steep sided valleys
     • Water travels slow due to high friction
     • Stony river bed
     • Interlocking spurs
     • Rapids and Waterfalls
   • Lower Course
     • Flood Plain
     • Oxbow lake
     • Deeper river channels
     • Fast water flowing
     • Water is full of sediment
   • Middle Course
     • Meanders
     • Flatter floored valleys
     • More sediment in the water
     • Gradient reduces
     • Less friction, smoother river bed

2. Floods

   • Short lag time
     • Impermeable rocks
       • Clay and granite
     • Steep slopes
     • Grasslands and thin soil
     • Short period of rain
       • Heavy rainfall
     • Ground saturated from previous rainfall
   • Long lag time
     • Permeable rocks
       • Sandstone
     • Gentle slopes
     • Forests with deep soil
     • Long periods of light rainfall
     • Previously dry
       • Ground can absorb the rain

3. Erosion

   • Hydralic Action
     • Water builds up pressure in rocks
     • Rocks "explode" from pressure
     • Mainly occurs in waterfalls
   • Abrasion
     • Rocks and particles dragged along the river bed
     • "Thrown" against the banks of the river and wears the rocks away
     • Mainly occurs in the middle course of the river
   • Attrition
     • Rocks and particles are worn away and brocken down
   • Corrision
     • The water dissolves the the permeable rocks
       • Limestone

4. Transportation of loads

   • Traction
     • Rocks and other particles are dragged along the river bed
   • Suspension
     • Small particles are kept in the water itself until it stops moving
     • Solution
       • Material is dissolved in water
         • E.G Salts and Bicarbonates

5. The Bradshaw model

   • Channel Depth
     • It will increase further down the river
       • This is due to erosion
   • Occupied channel width
     • This increases the further down the river
       • Its because of lateral erosion
       • Its also due to the joining of tributaries
   • Mean velocity
     • This is to increase the further down river
       • Its because of the amount/volume of the water
   • Discharge
     • This is to increase the further down the river
       • Its because of the tributaries joining to the river
   • Volume of load
     • This is to increase the further down the river
       • This is because the river has more energy
   • Load particle size
     • This is supposed to decrease the further down the river
       • This is because of the erosion, making the rocks sizes smaller
   • Channel bed roughness
     • This is to decrease the further down the river
       • Its due to attrition smoothing the bed of the river
   • Gradient
     • This is to decrease the further down the river
       • This is due to lateral erosion