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River erosion

River Bank erosion and some control measures

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River erosion

  1. 1. M. Tech, 1st Semester, WATER RESOURCE ENGG.
  2. 2. WATER IS THE MOST IMPORTANT NATURAL RESOURCES FOR PLANET EARTH THE PROSPERITY OF A NATION DEPENDS PRIMARILY UPON THE EXPLOITATION OF THIS RESOURCES. THUS IT CAN BE STATED THAT THE PRIMARY WEALTH OF A NATION IS WATER, WHICH FLOWS IN THE RIVER OR STREAMS.
  3. 3. AN IMAGE OF A RIVER
  4. 4. AS A RIVER FLOWS, THE FORCE OF ITS MOVING WATER WASHES AWAY LOOSE SOIL & PIECES OF ROCKS. IN THIS WAY THE RIVER CUTS ITS OWN CHANNEL IN THE GROUND. THIS PROCESS IS CALLED EROSION
  5. 5. HYDRAULIC ACTION ABRASION ATTRITION SOLUTION
  6. 6. The force of water wears away the river bank from underneath. The pressure of water breaks the rock particles. Water force hits river banks and pushes water into cracks. Thus the pressure expands the cracks and breaks the rocks into fragments.
  7. 7. Image showing Hydraul i c Ac t ion
  8. 8.  The sediments carried by the river scours the bed and banks.  Where depression exist in the channel floor the river can cause Pebbles to spin around and turn hollows into potholes.
  9. 9. An image potholes c reated by abras ion
  10. 10. What i s At t r i t ion ? Rocks being carried by the rivers smash together and break into smaller particles. Overtime, they become smaller and eventually reduced t fine particles called silt.
  11. 11. CO2 dissolves in the river to form a weak acid. This dissolves rock by chemical processes. This process is common where carbonate rocks such as limestone & chalk are evident in the channel.
  12. 12. A typical drawing of four types of River Erosion Process
  13. 13. To prevent the river from changing its coarse & to avoid outflanking of structures like bridges, weirs etc. To prevent flooding of the surrounding areas by providing a safe passage for the flood waters without overtopping the banks. To protect the river banks by deflecting the river away from the attacked banks. To ensure effective disposal of sediment load.
  14. 14. Marginal embankment or Levees Guide banks Groynes or Spurs
  15. 15. Levees are generally earthen embankments, running parallel to the river. These embankment-wall retain the river water to carry the bank soil with the water.
  16. 16. AN IMAGE OF LEVEES AT THE RIVER BANK
  17. 17. The guide banks are generally provided across a river as to ensure not only a safe and expeditious disposal of flood water but also to ensure a permanent reasonable width of the waterway for the river flow. Symmetrical and parallel guide banks are usually adopted.
  18. 18. A DRAWING OF A GUIDE BANK
  19. 19. GU I D E B A N K
  20. 20. Groynes are the embankment type structures, constructed transverse to the river flow to protect the bank by deflecting the current away from the bank. As the water is unable to take a sharp embayment, the bank gets protected.
  21. 21. A N I M A G E O F A G R O Y N E
  22. 22. Ordinary or normal Groynes Repelling Groynes Attracting Groynes
  23. 23. G R O Y N E
  24. 24. River controlling methods mainly depends upon the type of the river, its regime and the flow characteristics of the river. So the methods to control the river erosion varies from place to place. Hence, no particular method of river controlling can be stated to be the best. A comprehensive planning and model testing is necessary before any measure are undertaken to control the river.

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