Bank ErosionBank Erosion

SARADA MANDALSARADA MANDAL

Associate Professor in GeographyAssociate Professor in Geography

Teacher-in-ChargeTeacher-in-ChargePRABHU JAGATBANDHU COLLEGEPRABHU JAGATBANDHU COLLEGE

ANDUL, HOWRAHANDUL, HOWRAH

Hydraulic GeometryHydraulic Geometry Formula given by Leopold and Moddack in Formula given by Leopold and Moddack in

1953 : Q = WDV1953 : Q = WDV Q= Quantity of waterQ= Quantity of water W= Width of the channelW= Width of the channel D= Depth of the flow D= Depth of the flow V= Velocity of waterV= Velocity of water

Factors of Bank ErosionFactors of Bank Erosion

Fluctuation in quantity and volume of waterFluctuation in quantity and volume of water Sediment loadSediment load Characteristics of bank materialCharacteristics of bank material Distortion of equilibrium in soil waterDistortion of equilibrium in soil water Meandering of channelMeandering of channel Nature of the drainage basin (e.g. underlying Nature of the drainage basin (e.g. underlying

structure, nature of rainfall, nature of weathering etc.)structure, nature of rainfall, nature of weathering etc.) Braiding of channelBraiding of channel Characteristics of soil profileCharacteristics of soil profile Human actionHuman action

Damage in West Bengal due to Bank ErosionDamage in West Bengal due to Bank Erosion

MaldahaMaldaha yearyear Land erosion in Land erosion in hectarehectare

1931-781931-78 1433514335

19791979 6060

19801980 104104

19811981 259259

19821982 6565

19831983 9292

19841984 6868

19851985 9191

19861986 106106

19871987 240240

19881988 7272

Damage in West Bengal due to Bank ErosionDamage in West Bengal due to Bank Erosion

MaldahaMaldahayearyear Land erosion in Land erosion in

hectarehectare

19891989 152152

19901990 160160

19911991 167167

19921992 130130

19931993 145145

19941994 160160

19951995 145145

19961996 310310

19971997 450450

19981998 395395

19991999 480480

Damage in West Bengal due to Bank ErosionDamage in West Bengal due to Bank ErosionMurshidabadMurshidabad

YearYear Land erosion in Land erosion in hectarehectare

Affected peopleAffected people No. of affected No. of affected buildingsbuildings

1931-781931-78 28,28928,289 ---- 5600056000

19791979 100.00100.00 900900 180180

19801980 100.91100.91 12711271 318318

19811981 79.2879.28 990990 200200

19821982 88.2088.20 11231123 280280

19831983 103.44103.44 12031203 300300

19841984 635.63635.63 80068006 20002000

19851985 242.95242.95 30213021 600600

19861986 178.41178.41 21472147 502502

19871987 106.39106.39 13401340 270270

19881988 253.50253.50 30933093 618618

Damage in West Bengal due to Bank ErosionDamage in West Bengal due to Bank ErosionMurshidabadMurshidabad

YearYear Land erosion in Land erosion in hectarehectare

Affected peopleAffected people No. of affected No. of affected buildingsbuildings

19891989 173.20173.20 21822182 543543

19901990 121.80121.80 14001400 280280

19911991 116.70116.70 14701470 360360

19921992 114.30114.30 13401340 270270

19931993 271.00271.00 35133513 702702

19941994 2585.002585.00 32,55932,559 65126512

19951995 272.00272.00 20622062 515515

19961996 465.22465.22 58605860 11721172

19971997 415.00415.00 40504050 10101010

19981998 395.00395.00 56105610 11251125

19991999 480.00480.00 50055005 10241024

Mapping of Bank ErosionMapping of Bank Erosion

1) Superimposition of the same channel-section for two 1) Superimposition of the same channel-section for two separate time-period separate time-period

a) Identification of locations of area of erosion and a) Identification of locations of area of erosion and deposition along the left bank and right bankdeposition along the left bank and right bank

b) Calculation of length of erosionb) Calculation of length of erosionc) Calculation of area of erosionc) Calculation of area of erosiond) Calculation of volume of erosiond) Calculation of volume of erosione) Calculation of rate of erosion per yeare) Calculation of rate of erosion per year

Mapping of Bank ErosionMapping of Bank Erosion

2) Mapping from cadastral map2) Mapping from cadastral map3) Mapping from topographical sheet3) Mapping from topographical sheet4) Mapping by Prismatic Compass Survey4) Mapping by Prismatic Compass Survey5) Thematic map by showing loss and damages5) Thematic map by showing loss and damages6) Mapping by showing bank-material, process 6) Mapping by showing bank-material, process

of erosion and level of erosionof erosion and level of erosion