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  1. 1. Rivers, floods and management Rivers, floods and management
  2. 2. Rivers, floods and management The drainage basin hydrological cycle
  3. 3. Rivers, floods and managementRiver discharge The storm hydrograph
  4. 4. Rivers, floods and managementRiver dischargeWhat factors might result in a ‘flashy’ hydrograph? • short-lived but intense rainfall • impermeable underlying rock such as granite • steep relief • urban area, where water is channelled through drains to the stream • small round drainage basin
  5. 5. Rivers, floods and managementRiver dischargeWhat factors might create a hydrograph like this? • dense woodland vegetation • high infiltration capacity of soil • permeable underlying rock, such as limestone • elongated drainage basin
  6. 6. Rivers, floods and management The long profile
  7. 7. Rivers, floods and management The Hjülstrom curve
  8. 8. Rivers, floods and management An upper course channel Amanda Barker
  9. 9. Rivers, floods and management A middle course channel Amanda Barker
  10. 10. Rivers, floods and management A lowland channel in flood Amanda Barker
  11. 11. Rivers, floods and management High Force waterfall• vertical erosion (by hydraulic action and corrasion) below the waterfall deepens the plunge pool• undercutting of the softer rock leads to eventual collapse of the resistant Whin John Pallister Sill and results in headward erosion
  12. 12. Rivers, floods and management The development of an oxbow lake
  13. 13. Rivers, floods and management Reasons for formation of a delta• the sediment load carried by the river is substantial• the river has a large drainage basin• the mouth of the river is located on a coastline where ocean currents and tides are weak so the rate of deposition exceeds the rate of sediment removal
  14. 14. Rivers, floods and management Features related to rejuvenation• knick points, rapids and waterfalls• river terraces• incised meanders, both entrenched and ingrown AerofilmsThe city of Durham is built insidean entrenched meander
  15. 15. Rivers, floods and managementFlooding Physical causes of flooding• excessive precipitation over • the nature of the drainage a long period of time basin• intensive precipitation over • relief a short period of time • rock and soil type• snowmelt • natural vegetation• climatic hazards such as hurricanes
  16. 16. Rivers, floods and managementFlooding Influence of human activities on flooding• Urbanisation creates impermeable surfaces so reducing infiltration. Surface water is therefore transported more rapidly through drains to the river.• Deforestation reduces interception and increases runoff.• Some methods of river management, such as channelisation, increase flood risk downstream.• Global warming leads to more extreme rainfall events.
  17. 17. Rivers, floods and managementFlooding Areas of high flood risk in England and Wales
  18. 18. Rivers, floods and managementFlooding Responses to floodingShort-term responses: Long-term responses:• media broadcasts of information • government and/or foreign aid• emergency relief, rescue, shelter, • disaster planning for the future food • flood management programmes• armed services for evacuation and building emergency defences
  19. 19. Rivers, floods and managementFlooding Examples of hard engineering• channelisation, to raise, straighten or strengthen banks• dams and weirs• diversion channels• dredging• retention basins and balancing lakes• artificially raising the height of the floodplain
  20. 20. Rivers, floods and managementFlooding Examples of soft engineering• afforestation• floodplain zoning• land-use management, e.g. contour ploughing• wetland and riverbank conservation• river restoration• improved forecasting and warning