Bank Erosion

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Bank Erosion

• SARADA MANDAL
• Associate Professor in Geography
• Teacher-in-Charge
• PRABHU JAGATBANDHU COLLEGE
• ANDUL, HOWRAH

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Hydraulic Geometry

• Formula given by Leopold and Moddack in 1953 Q
  WDV
• Q Quantity of water
• W Width of the channel
• D Depth of the flow
• V Velocity of water

3
Factors of Bank Erosion

• Fluctuation in quantity and volume of water
• Sediment load
• Characteristics of bank material
• Distortion of equilibrium in soil water
• Meandering of channel
• Nature of the drainage basin (e.g. underlying
  structure, nature of rainfall, nature of
  weathering etc.)
• Braiding of channel
• Characteristics of soil profile
• Human action

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Damage in West Bengal due to Bank Erosion

• Maldaha

year Land erosion in hectare
1931-78 14335
1979 60
1980 104
1981 259
1982 65
1983 92
1984 68
1985 91
1986 106
1987 240
1988 72
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Damage in West Bengal due to Bank Erosion
year Land erosion in hectare
1989 152
1990 160
1991 167
1992 130
1993 145
1994 160
1995 145
1996 310
1997 450
1998 395
1999 480

• Maldaha

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Damage in West Bengal due to Bank
ErosionMurshidabad
Year Land erosion in hectare Affected people No. of affected buildings
1931-78 28,289 -- 56000
1979 100.00 900 180
1980 100.91 1271 318
1981 79.28 990 200
1982 88.20 1123 280
1983 103.44 1203 300
1984 635.63 8006 2000
1985 242.95 3021 600
1986 178.41 2147 502
1987 106.39 1340 270
1988 253.50 3093 618
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Damage in West Bengal due to Bank
ErosionMurshidabad
Year Land erosion in hectare Affected people No. of affected buildings
1989 173.20 2182 543
1990 121.80 1400 280
1991 116.70 1470 360
1992 114.30 1340 270
1993 271.00 3513 702
1994 2585.00 32,559 6512
1995 272.00 2062 515
1996 465.22 5860 1172
1997 415.00 4050 1010
1998 395.00 5610 1125
1999 480.00 5005 1024

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Mapping of Bank Erosion

• 1) Superimposition of the same channel-section
  for two separate time-period
• a) Identification of locations of area of
  erosion and deposition along the left bank and
  right bank
• b) Calculation of length of erosion
• c) Calculation of area of erosion
• d) Calculation of volume of erosion
• e) Calculation of rate of erosion per year

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Mapping of Bank Erosion

• 2) Mapping from cadastral map
• 3) Mapping from topographical sheet
• 4) Mapping by Prismatic Compass Survey
• 5) Thematic map by showing loss and damages
• 6) Mapping by showing bank-material, process of
  erosion and level of erosion

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