longitudinal slope of brahmaputra
longitudinal slope of brahmaputra
longitudinal slope of brahmaputra
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1625 KM IN TIBET<br />
918 KM IN INDIA<br />
354 KM IN BANGLADESH
Aerial View<br />
AN AERIAL VIEW OF UPPER BASIN OF BRAHMAPUTRA<br />
5300m<br />
Total Drainage Basin<br />
580,000 sq.km<br />
Total river<br />
Length 2880 km<br />
Neuromorphic study <strong>of</strong> Longitudinal Pr<strong>of</strong>ile <strong>of</strong> the river Brahmaputra
BRAHMAPUTRA IN SPATE
Erosion near Kaniagaon, Majuli<br />
Erosion <strong>of</strong> tea garden in<br />
Dibrugarh area, 2002
Kanglung Kang<br />
Glacier<br />
LONGITUDINAL SLOPE OF BRAHMAPUTRA<br />
Dhubri
PROMINENT CHARACTERISTICS OF THE<br />
BRAHMAPUTRA<br />
FLUVIAL<br />
<br />
<br />
<br />
Large energy environment max.<br />
Large & highly variable discharge regime<br />
Heavy sediment load with fluctuating competence<br />
Av. annual sediment = 735 million tonne
MORPHOLOGICAL<br />
Highly braided plan form<br />
Few constricted nodal points<br />
Cycle <strong>of</strong> aggradation, bank erosion &<br />
channel widening<br />
Channel avulsion propensity at vulnerable<br />
points<br />
Large alluvial braid-plain <strong>of</strong> high instability
HYDROLOGICAL<br />
High precipitation on a relatively narrow valley<br />
High ratio between minimum to maximum discharges<br />
(3000 to 77000 m3/sec)<br />
Max. flood lift = 10.39 m<br />
Progressive degradation <strong>of</strong> watershed area
TECTONICS<br />
Presence <strong>of</strong> several active fault zones High<br />
seismicity<br />
Epicentres <strong>of</strong> two major earthquakes <strong>of</strong> 8.7<br />
magnitude on the richter scale<br />
Watershed areas comprise highly friable<br />
sedimentary deposits
TECTONIC FAULT ZONE MAP IN BRAHMAPUTRA REGION
MAJOR FLUVIAL HAZARDS IN THE<br />
BRAHMAPUTRA<br />
<br />
<br />
<br />
<br />
<br />
<br />
Occurrence <strong>of</strong> channel avulsion<br />
Stream bank erosion<br />
Occurrence <strong>of</strong> embankment breaches<br />
Occurrence <strong>of</strong> debilitating urban floods<br />
Occurrence <strong>of</strong> relentless streambed rise<br />
Encroachment <strong>of</strong> flood-plain, wetlands
G. Behera et al (2006), (Jalvigyan Sameeksha, Vol. 21)
G. Behera et al (2006), (Jalvigyan Sameeksha, Vol. 21)
Water<br />
Very High Vegetation<br />
High Vegetation<br />
Medium vegetation<br />
Low vegetation<br />
Sand/bars
Water<br />
Very High Vegetation<br />
High Vegetation<br />
Medium vegetation<br />
Low vegetation<br />
Sand/bars
ENCROACHMENTS ON FLOOD PLAIN &<br />
WETLANDS<br />
Rampant encroachments taking place over the<br />
flood – plains<br />
3,513 Wetlands are degenerated due to<br />
encroachments, bottom deposits, blockade <strong>of</strong><br />
feeder channels, pollution by industrial wastes.
ATTEMPTS FOR MODELLING RIVER<br />
BRAHMAPUTRA<br />
Purpose: Flood Forecasting & Channel Improvements<br />
<br />
Hydrodynamic Modelling<br />
No distinct mathematical relationship for braided<br />
streams<br />
- Sediment discharge predictor<br />
- Flow resistance function<br />
<br />
ANN Modeling<br />
Making use <strong>of</strong> huge data base
Governing Equations<br />
Water continuity equation<br />
Momentum equation<br />
(...<br />
)2<br />
(...<br />
)2<br />
(...<br />
)2<br />
(...<br />
)2<br />
..........<br />
..........<br />
..........<br />
..........<br />
)<br />
.........<br />
)<br />
.........<br />
)<br />
.........<br />
)<br />
.........<br />
D<br />
S<br />
ρgA<br />
(<br />
S<br />
ρgA<br />
(<br />
S<br />
ρgA<br />
(<br />
S<br />
ρgA<br />
(<br />
S<br />
δX<br />
δX<br />
δX<br />
δX<br />
δρY<br />
δρY<br />
δρY<br />
δρY<br />
gA<br />
gA<br />
gA<br />
gA<br />
δX<br />
δX<br />
δX<br />
δX<br />
δρQV<br />
δρQV<br />
δρQV<br />
δρQV<br />
δt<br />
δt<br />
δt<br />
δt<br />
δρQ<br />
δρQ<br />
δρQ<br />
δρQ<br />
1<br />
f<br />
0 +<br />
−<br />
=<br />
+<br />
+<br />
(...<br />
)1<br />
(...<br />
)1<br />
(...<br />
)1<br />
(...<br />
)1<br />
..........<br />
..........<br />
..........<br />
.......... ..........<br />
..........<br />
..........<br />
.......... ..........<br />
..........<br />
..........<br />
.......... ..........<br />
..........<br />
..........<br />
0......... ..........<br />
0.........<br />
0.........<br />
0.........<br />
q<br />
δt<br />
δt<br />
δt<br />
δt<br />
δA<br />
δA<br />
δA<br />
δA<br />
δx<br />
δx<br />
δx<br />
δx<br />
δQ<br />
δQ<br />
δQ<br />
δQ<br />
`1<br />
`1<br />
`1<br />
`1 =<br />
−<br />
+<br />
(..<br />
)3<br />
(..<br />
)3<br />
(..<br />
)3<br />
(..<br />
)3<br />
..........<br />
..........<br />
..........<br />
....................<br />
..........<br />
..........<br />
....................<br />
..........<br />
..........<br />
....................<br />
..........<br />
..........<br />
0...................<br />
0.........<br />
0.........<br />
0.........<br />
q<br />
δt<br />
δt<br />
δt<br />
δt<br />
δA<br />
δA<br />
δA<br />
δA<br />
δt<br />
δt<br />
δt<br />
δt<br />
δA<br />
δA<br />
δA<br />
δA<br />
p<br />
δx<br />
δx<br />
δx<br />
δx<br />
δQs<br />
δQs<br />
δQs<br />
δQs<br />
s<br />
s<br />
c<br />
=<br />
−<br />
+<br />
+<br />
Sediment continuity equation<br />
THE MATHEMATICAL MODEL
Supplementary Relationships<br />
Aggradation Simulation<br />
To simulate aggradation or sediment deposition in<br />
the model, a simple but rational approach is<br />
formulated to distribute sediment deposition bed<br />
area sub-section wise in inverse proportion to<br />
conveyance as below.<br />
ΔA<br />
ΔA<br />
bk<br />
b<br />
=<br />
⎡<br />
⎢<br />
⎢<br />
⎢<br />
⎢<br />
⎣<br />
1<br />
−<br />
∑i<br />
=<br />
k<br />
1<br />
A<br />
k<br />
A<br />
k<br />
D<br />
2/3<br />
k<br />
.D.D<br />
2/3<br />
k<br />
⎤<br />
⎥<br />
⎥<br />
⎥<br />
⎥<br />
⎦
Degradation Simulation<br />
To simulate degradation or bed lowering, changes in<br />
bed area lowering is distributed sub-section wise in<br />
direct proportion to effective tractive force as below.<br />
⎡ τ τ<br />
Zs<br />
⎤<br />
0<br />
ocr<br />
⎢ − ΔAc<br />
= τ τ<br />
Δy<br />
⎥<br />
⎢ [ − ] ⎥<br />
⎢⎣<br />
∑<br />
0<br />
0cr<br />
W<br />
⎥⎦<br />
Channel width Adjustments<br />
Simplified search procedure <strong>of</strong> Chang satisfying<br />
minimum stream power criterion as given below is used<br />
subject to site constraints.<br />
S<br />
ΔX<br />
S ΔX<br />
S i 1 1 i 1 i<br />
i − 2 ΔX<br />
+<br />
+ ΔX<br />
−<br />
=<br />
i 1+<br />
( ) i<br />
−<br />
1
Stimulus<br />
Receptors<br />
(Dendrites)<br />
Neural<br />
net<br />
Effectors<br />
(Synapses)<br />
Response<br />
ILLUSTRATION OF BIOLOGICAL NEURON<br />
Input<br />
Hidden neurons<br />
Output<br />
ILLUSTRATION OF ARTIFICIAL NEURON<br />
x 1<br />
Weights<br />
w 1<br />
Summation Unit<br />
Sigmoidal unit<br />
x 2<br />
x n<br />
x 3<br />
w 2<br />
w 3<br />
w n<br />
Inputs<br />
(Simple structure <strong>of</strong> an ANN model)<br />
Output<br />
Sigmoidal function
0<br />
α 1 = a 1 /A<br />
0
Total Length<br />
The Study Length and Associated details<br />
640.07 km<br />
Kobo<br />
Xs-65<br />
Xs-2<br />
17.34 km<br />
tributaries<br />
442.7 km<br />
Guwahati<br />
Dhubri<br />
Ganga<br />
589,000<br />
MCM/yr+735 MT/yr<br />
Dhaka<br />
898.71 km<br />
The bay <strong>of</strong> Bangal<br />
1150 km<br />
Neuromorphic study <strong>of</strong> Longitudinal Pr<strong>of</strong>ile <strong>of</strong> the river Brahmaputra
RIVER AVULSION AND SHIFTING PROCESS AT<br />
CONFLUENCE ZONE OF MAINSTREAMS OF THE<br />
BRAHMAPUTRA NEAR SADIYA<br />
21.74 km<br />
SATELLITE IMAGERY OF YEAR 2002<br />
SATELLITE IMAGERY OF YEAR 1990
Kobo<br />
Noa Dihing<br />
Mesakimukh<br />
AVULSION<br />
15.77 km<br />
Avulsion <strong>of</strong> Brahmaputra near Saikhowa
16.88 km<br />
Saikhowa<br />
RF<br />
Oaklands<br />
Tea state<br />
Dinjangaon<br />
8.85 km<br />
Dibrugarh<br />
Mohanbari<br />
Chabua<br />
Barbari<br />
LISS III 2002
RADARSAT SATELLITE PLAN FORM OF MAJULI ISLAND 2002<br />
(Largest River Island in the World)<br />
Kherkutia<br />
Suti<br />
Haldibari<br />
Subansiri<br />
44.23 km<br />
Kamalabari<br />
20.13 km<br />
M A J U L I<br />
Dakhinpat<br />
Threat to<br />
JORHAT<br />
Serious<br />
erosion zone
EROSION OF MAJULI ISLAND AREA<br />
9.44%LOSS OF AREA<br />
DUE TO EROSION
Jia Bhareli<br />
Agnigarh Hills<br />
Gabharu<br />
Tezpur<br />
10.6 km<br />
2.7 km<br />
Koliabor Area<br />
Rock<br />
Outcrops<br />
1.2 km<br />
Silghat<br />
Kamakhya Hill<br />
Kaliabhomora<br />
Bridge<br />
Kolong<br />
21 km<br />
Radarsat satellite image near Tezpur, 2002
View <strong>of</strong> narrowest width 1.2 km <strong>of</strong> Bramhaputra at Guwahati
Barpeta<br />
Sualkuchi<br />
Nagarbera<br />
18.13 km<br />
Hatimura<br />
Hill<br />
1.20 km<br />
Chimpa<br />
Palasbari<br />
Dakhoa<br />
Hills<br />
Saraighat<br />
Bridge<br />
Gumi<br />
35.687 km<br />
IRS 1D LISS III satellite image D/S <strong>of</strong> Guwahati
Beki<br />
Manas<br />
15.67 km<br />
IRS 1D LISS III satellite image U/S Pancharatna
RADARSAT SATELLITE PLAN FORM NEAR DHUBRI 2002<br />
DHUBRI<br />
DHUBRI<br />
17.30 km<br />
PHULBARI<br />
Avulsion <strong>of</strong> Jinjiram<br />
Year 1990
RIVER CHANGES AT KEY POINTS FROM<br />
SATELLITE IMAGE (1990-2002)<br />
River flow area<br />
increased by<br />
Mean width change<br />
Overall migration<br />
Bank area lost to<br />
erosion<br />
12.10%<br />
7.99 km to 8.94<br />
km<br />
0.47(north)<br />
0.48 (south)<br />
20 sq.km/year
SOME COST EFFECTIVE SOLUTIONS<br />
<br />
Management & development <strong>of</strong> watershed<br />
areas to arrest soil erosion & reduce surface<br />
run-<strong>of</strong>f volume
PRESENT APPROACH OF RIVER<br />
MANAGEMENT<br />
Land spur Concept<br />
Efficacious in Dibrugarh,Gumi- Palasbari<br />
Fails in the event <strong>of</strong> frontal river attack as in Gumi<br />
Costly due to requirement <strong>of</strong> low Arc/Chord ratio<br />
High maintenance
EMBANKMENT SYSTEM<br />
Efficacious as palliative measure<br />
Progressive morphological changes requires<br />
recurring raising <strong>of</strong> embankment height<br />
Regular occurrence <strong>of</strong> breaches<br />
High maintenance<br />
Porcupine<br />
Very effective in relatively shallower channels<br />
to induce siltation
Porcupine<br />
Porcupine
Bank Revetment<br />
Efficacious but very costly<br />
Difficulties in apron laying in deeper channels<br />
<br />
<br />
Emergency Temporary Measures<br />
Bamboo Crib<br />
Leat Fencing<br />
Catalyst for channel closure
BANDALLING<br />
For navigation during low flows from<br />
December to April – Limited temporary use<br />
CHANNELISATION BY ATTEMPTING<br />
SUBSIDIARY CHANNEL CLOSURE<br />
Bottom Panels :<br />
Deployed in the 1969 –72 period with the<br />
help <strong>of</strong> French experts through ECAFE<br />
(ESCAP)<br />
Out <strong>of</strong> five sites, fairly good results at two<br />
sites reported
DREDGING<br />
Tried out at Gumi site during 1973-75 period by<br />
Assam Flood Control Deptt.<br />
Results not satisfactory due to quick<br />
redeposits
TRIALS ON EXPERIMENTAL METHODS<br />
Submerged Vane<br />
<br />
Board –fencing
SUBMERGED VANE TECHNIQUE
Sediment deposited on vanes after floods in river
Trapezoidal vanes with and without collar<br />
installed in river
BOARD-FENCING
Ecological Responses to Environmental Changes:
(Ref: Dr. Sanchita Boruah & Pr<strong>of</strong>. S. P. Biswas)<br />
Distribution <strong>of</strong> dolphins in relation to the depth <strong>of</strong><br />
the river Brahmaputra<br />
Percentage<br />
45<br />
40<br />
35<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
0<br />
7m<br />
River depth<br />
Percentage<br />
composition <strong>of</strong><br />
dolphins
Status <strong>of</strong> aquatic habitat<br />
* Extreme fluctuation <strong>of</strong> water level
Status <strong>of</strong> aquatic habitat<br />
* Extreme fluctuation <strong>of</strong> water level
Status <strong>of</strong> aquatic habitat<br />
* Extreme fluctuation <strong>of</strong> water level
* Water cover and aquatic biota<br />
Dolphin
Siltation
Erosion
Erosion
* Raised river beds
* Braided channels
* Siltation <strong>of</strong> channel mouths
* Shrinkage <strong>of</strong> wetlands
(Ref: Post Doctoral Study By Dr. Sanchita Boruah)
(Ref: Post Doctoral Study By Dr. Sanchita Boruah)
(Ref: Post Doctoral Study By Dr. Sanchita Boruah)
(Ref: Post Doctoral Study By Dr. Sanchita Boruah)
Some Salient Findings<br />
Unabated channel widening along with aggradation process <strong>of</strong> the<br />
Brahmaputra river due to bank erosion has gradually reduced the lean<br />
period water depth.<br />
Reduced water depth has deprived the mega fauna like Dolphin, turtle,<br />
etc. <strong>of</strong> the required water cover for sustenance, causing their habitat<br />
shrinkage.<br />
Sporadic bed sedimentation has disturbed the organic matter at the bed<br />
and sides which is part <strong>of</strong> food chain <strong>of</strong> fish.<br />
Intermittent radical channel changes like avulsion has caused higher<br />
velocities with reduced transparency detrimental to aquatic biota.<br />
Blockage <strong>of</strong> feeder channels <strong>of</strong> wetlands due to silting has inhibited<br />
conducive spawing activities <strong>of</strong> fish.<br />
More interdisciplinary research required to evolve solutions to preserve<br />
ecosystem vis-à-vis morphology changes.
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