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An embankment is an artificial barrier thattypically is used to hold back water or tosupport a roadway, railway, or canal.It is a ridge to prevent water from passingbeyond desirable limits.These man-made mounds mainly consist ofstones, rocks, and earth.Most have sloping sides, much like small hills.Generally, embankments are longer than theyare in height.
The Place Embankment along the Neva River inSaint Petersburg, Russia
The Embankment along the DEE River in NorthWales, England
Eagle eye view: The Place Embankmentalong the Neva River in Saint Petersburg,Russia
To hold back water in order to preventflooding from seas, lakes, or rivers ontoadjacent land.Typically strong barriers provideprotection to lower-lying grounds byacting as a levee, as well.Helps to confine the movement ofwater by allowing it to flow faster andhigher without overflowing.
(CONTD.) A transportation embankment usually isused to support a roadway, canal orrailway by keeping land flat or straight anduninterrupted.It also may be used to support lowlands,such as valleys, that may need to becrossed.Most embankments are built so as to beimmune to surface erosion.
An embankment may be eitherearth-filledOr,rock-filled.An earth-filled barrier usually is thesimpler of the two, consisting mainlyof earth and natural materials.
(CONTD.)A rock-filled barrier generally ismade up of more granularcomponents, consisting mostly oflarge varieties of rocks, stones, andother fragmented particles.Rock-filled mounds usually are moreideal to cover wider areas.
Fig: The river bank of the Brahmaputra river in a village in the Kamarjani Union
Components of an embankment: (Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain )
CONSTRUCTION OF EMBANKMENTS: EARTH CUTTING
BREACHING OF EMBANKMENTS
EMBANKMENT UNDER CONSTRUCTION
Displacement of cc blockEmbankment condition after rainy season.
Map Showingexistingembankmentsin Bangladesh
Notable Embankments at a glance:Brahmaputra Right Bank EmbankmentGumti River EmbankmentKhowai River Embankment
Brahmaputra Right Bank Embankment: Brahmaputra right bank embankment Brahmaputra view from satellite
Brahmaputra Right Bank Embankment:One of the first embankments constructed in 1960s to provide flood protection to about 230,000 ha lying on the western side of the Brahmaputra- Jamuna and Tista rivers.It is 217 km long and extends from Kaunia in Rangpur at the northern end up to Bera upazila in Sirajganj district at the southern end.
Brahmaputra Right Bank Embankment:Construction of the embankment started in 1963 and was completed in 1968 at a cost of about Tk. 80 million.The average height is 4.5m, crest width 6m and side slope 1:3 on both sides.The embankment has been under constant threat of erosion by the Jamuna river and needs relocation further away from the riverbank.
Gomti River Embankment Gomti River Embankment
Gumti River Embankment: located in Comilla districtComprises 67 km of embankment on the left bank of the river Gumti from Katak Bazar and 64 km on the right bank from Golabari up to Gauripur of Daudkandi.
Khowai River Embankment Khowai River Embankment
Khowai River Embankment:Lies in HABIGANJ district andProvides flood protection to 25,790 ha of land.This 40 km embankment on the right bank of the river Khowai extends from Habiganj to CHUNARUGHAT and 47 km on the left bank up to Rajabazar.
DND PROJECTLocated between the cities of Dhaka andNarayanganj and bounded by the Buriganga andthe Shitalakshya river.It was started in 1964 and completed in 1968at a cost of Tk. 22.9 million. A dual purpose pumping station is located atShim rail having a total capacity of 4.2 cusec. Theproject provides flood control for 4,860 ha,irrigation for 6,070 ha, pumped drainage for4,860 ha and gravity drainage for 2,470 ha ofland.
HAZARDS CAUSED BY DND PROJECT• But as the project is located close to Dhaka city, urbanization is taking place rapidly. So the initial objective has been distorted.• The area gets clogged in the rainy season.
HAZARDS CAUSED BY DND PROJECTNearly two million people havebecome marooned as unplannedurbanization left the rainwater trappedinside the Dhaka-Narayanganj-DemraProtection Embankment.The urbanization, which is takingplace rapidly in the DND irrigationproject, posed a severe threat to theproject as well as to the people in thearea.
The Coastal Embankment Project (CEP) BACKGROUND: CEP Covers the coastal districts of Bangladeshand includes Coxs Bazar, Chittagong, Feni,Noakhali, Lakshmipur, Bhola, Barisal,Patuakhali, Jhalokati, Barguna,Pirojpur, Khulna,Satkhira and Bagerhat districts.The project was implemented between1961 and 1978 by the Bangladesh waterdevelopment board in twophases.
The Coastal Embankment Project (CEP)BACKGROUND: (CONTD.)Phase I comprises some 92 poldersproviding protection to one million ha of landPhase II consists of 16 polders coveringanother 0.40 million ha. Polder is a Dutchword meaning an area enclosed by dikes.Within the CEP more than 4,000 km ofembankment and 1,039 drainage sluiceshave been constructed.
The Coastal Embankment Project (CEP)Main Purposes:The CEP comprises a complex network ofdikes and drainage sluices and was the firstcomprehensive plan for providing protectionagainst flood andTo prevent saline water intrusion in thecoastal area.
The Coastal Embankment Project (CEP)Within the CEP more than 4,000 km ofembankment and 1,039 drainage sluiceshave been constructed. Such as_ Sea dike embankment Interior dike embankment Marginal dike embankment
The Coastal Embankment Project (CEP) Typical dimensions of three types ofembankments are as follows: Embankment Side slope Crest Freebo Set type width ard (m) back (m) distanc e (m) Country Sea side side Sea dike 2:1 7:1 4.2 1.5 75 Interior dike 2:1 3:1 4.2 0.9 50 Marginal dike 2:1 2:1 2.4 0.9 40
The portion of Bangladesh mapshowing Coastal Embankment protected area The Coastal Embankment Protected Area
The Coastal Embankment Project (CEP)More than 4,000 km ofembankment and 1,039 drainagesluices have been constructed in theCoastal area.providing protection against floodand saline water intrusion in thecoastal area
The Coastal Embankment Project (CEP) (CONTD.)oThese embankments are intended to protectland from tidal inundation but cannot preventovertopping and damage from cyclonic surgesand tidal bores.oIn addition to increased agriculturalproduction, these embankments have providedgood road communication and contributedtowards improvement of the overall socio-economic condition in the coastal zone.
Embankment ErosionThe instability in river regime coupled withhuge discharge and sediment load causeerosion, scouring and also deposition, andthus a chain action proceeds. This is almost arecurring phenomenon. As per the latestinformation available from BWDB, it is foundthat 441 projects/sub-projects are either fullyor partially damaged due to the severe floodsof 1998. The total estimated cost of therehabilitation works is about US$143.17million.
Collapse ofEmbankment Embankment
Main areas of erosion in Bangladesh8 River No. of location of Length of erosion bank/embankment (km) erosionBrahmaputra- 41 162.50JamunaGanges-Padma 26 94.0Meghna 8 72.0Teesta 11 34.90Minor river 112 92.30Flashy river 75 23.0Tidal river 32 85.80Total 305 565.10
Rainfall impact (from both the regularmonsoon rains and torrential rains)
CAUSES OF EROSION (Contd.)Wave action (daily/periodic andcreated by constant wind): Tidal waves cause damage to theembankments located too near to thesea.A severe hydraulic load is steadilyexerted on the toes and slopes andcauseserosion.
Cyclonic storms in the coastal zone(occurring repeatedly) act upon thewater surface, causing it to advancetowards the shore with enormoushydraulic loads.The waves thus formed eventually hitthe embankment toe and slopes.
Turbulent water currents (mainly inrivers and at coastlines):·
The high velocity flow of waterassociated with vortex motion in riversand estuaries often causes erosion ofthe banks by undermining, and theeventual collapse of the embankmentthreatens unless protective measuresare taken.Source: Bangladesh Meteorological Department
The presence of continuous borrow-pits on a river:
· The presence of continuous borrow-pits on a river or seaside inducesundercutting of the embankment toesand slopes due to complete inundation ofthe riverbank or seashore during themonsoon. The borrow-pits and adjoininglowlands thus inundated induce a parallelwater current to flow along very near theembankment toes and slopes, therebyeroding the surfaces rapidly.
Human Interference:The human interference responsiblefor major embankment erosion isquite diverse in nature and oftenvaries according to the lifestyle andmanner of using the embankments ofthe inhabitants of different areas.
Human Interference: REMOVAL OF EMBANKMENT STONES BY IGNORANT PEOPLE
Excessive grazing: Excessive grazing also make the embankment vulnerable.
At different locations protectivemeasures are taken by any of thefollowing methods:· Mattressing along the bank line· Revetments either by boulders or byconcrete/brick boulders· Permeable spurs· Groynes· Guide bundle
Rehabilitation of Embankments
· Artificial loop cut· Porcupines· Retards (palisade fences)· Gravel drains· Bandals· Biological treatment eg.afforestation in the foreshore andembankment.