Rivers

Rivers

1. Landforms

   • Upper course
     • Waterfall - River flows over alternative types of rocks. River erodes soft rock faster creating a step. Further hydraulic action and abrasion form a plunge pool. Hard rock is above is undercut leaving cap rock which collapses providing more material for erosion. Waterfall retreats leaving steep sided gorge
   • Middle Course
     • Ox-bow lakes - Erosion of outer bank forms river cliff. Deposition inner bank forms slip off slope. Further hydraulic action and abrasion of outer banks, neck gets smaller. Erosion breaks through neck, so river takes the faster route, redirecting flow. Evaporation and deposition cuts off main channel leaving an oxbow lake.
   • Lower Course
     • Floodplains/levees - When a river floods, fine silt is deposited on the valley floor. Closer to the river's banks, the heavier materials build up to form natural levees.

2. River management schemes

   • Soft engineering
     • Afforestation - Plant trees to soak up rainwater, reduces flood risk
     • Demountable flood barriers - Put in place when warnings raised
     • Managed flooding - Naturally let areas flood, protect settlements
   • Hard engineering
     • Straightening channel - Increases velocity to remove flood water
     • Artificial levees - heightens river so flood water is contained
     • Deepening/widening - Increases the capacity for a flood

3. Hydrographs

   • Peak of discharge - discharge in a period of time
   • Lag time - delay between peak rainfall and peak discharge
   • Rising limb - increase in river discharge
   • Falling limb - decrease in river discharge to normal level

4. Causes of flooding

   • Physical
     • Prolong and heavy rainfall - Long periods rain causes the soil to become saturated leading to run off
     • Relief - Steep-sided valleys channels water to flow quickly into rivers causing greater discharge
   • Human
     • Land use - Tarmac and concrete are impermeable. Prevents infiltration and causes surface runoff