|Posted by gajananmishra on January 16, 2014 at 10:00 PM|
KOSI-A MONSTROUS RIVER
: GAJANAN MISHRA
KOSI HAS TURNED INTO A MONSTROUS RIVER. THE DISTRICTS OF SUPAUL, SAHARSA, MADHEPURA, ARARIA, PURNIA, KATIHAR, KHAGARIA AND NAUGACHIA IN NORTH Bihar; SOUTH DINAJPUR AND MALDAH IN THE WEST BENGAL AS WELL AS NAWABGANJ AND RAJSHAHI IN THE BANGLA DESH BESIDES SUNSARI IN NEPAL ARE HEADING TO SUFFER THE EVER-WORST IMPENDING KOSI DISASTER.
THE 2008 KUSAHA FLOOD LOOKS LIKE A TRAILER AND IN ALL PROBABILITY WOULD PROVE TO BE A TIP OF THE ICEBERG BY COMPARISON WITH THE UPCOMING KOSI FLOOD DISASTER WHICH HAS A POTENTIAL OF DIRECTLY AFFECTING MORE THAN 30 MILLIONS OF THE PEOPLE IN AN AREA OF ABOUT 26000 SQ KM FROM KUSHESWARSTHAN TO MALDAH/NAWABGANJ AND DELINKING THE NORTH-EASTERN PART OF INDIA FROM REST OF THE COUNTRY BESIDES USUAL FLOOD DAMAGES. IT WOULD UNLEASH A MULTI-NATION INTERNATIONAL ISSUE. AS HIGH SILT, HIGH DISCHARGE, HIGH SPEED- THE THREE FUNDAMENTAL FEATURES OF KOSI ARE DISREGARDED BY THE BARRAGE AND BUNDS, HENCE THE MONSTROSITY OF THE KOSI. IMPLICITLY A NEW PARADIGM OF FLOOD MANAGEMENT IS URGENTLY REQUIRED.
KOSI ON THE VERGE OF FORGING TO EAST
We might be very close to the time when the OVERFLOWING Kosi would permanently leave its present course and be freely rampaging the vast eastern flood plain from KUSHERSWARSTHAN in DARBHANGA district in west to RAYGANJ/MALDAH in the WEST BENGAL in east. This 180km long east-west stretch would be crisscrossed by more than a dozen channels of Kosi during high flood. As the geographical contour runs down towards south-east, the area most favourable to be the location of its stable course would be ARARIA-PURNIA-KATIHAR and this course would confluence with the GANGA/PADMA from MANIHARI in Katihar to NAWABGANJ in Bangla Desh.
KOSI MEGAFAN OF DAMAGE
Kosi is flowing well above the countryside, more particularly upstream of the Barrage at Bhimnagar. Similarly perched river was the YELLOW river in CHINA which when burst down its embankments in 1887,the death toll as reported on Internet was 9.00 to 20.00 lakh; in 1931, it was 8.50 to 40.00lakh and in 1938, 5.00 to 9.00 lakh. The Yellow river used to burst periodically its embankments in course of high floods. The present Kosi is akin to the Yellow river.
The probable MEGAFAN of KOSI AFFLICTION would include the administrative divisions of Kosi (SAHARSA) and PURNIA (minus KISHANGANJ), the districts of KHAGARIA and NAUGACHIA in the NORTH Bihar, much of SUNSARI and a QUARTER OF MORUNG DISTRICTS in NEPAL, SOUTH DINAJPUR and MALDAH in the WEST BENGAL as well as NAWABGANJ and RAJSHAHI in the BANGLA DESH. This Area inhabits more than 3.00 crore of the people.
The Kosi in high flood would cross the 4-LANE HIGHWAY between Bhaptiahi in Supaul and Farbisganj in Araria; downward it would intercept Purnia-Siliguri NATIONAL HIGHWAY between Purnia and Dalkola. Further down its course might pass through BARSOI where the Railway Link to NewJalpaiguri/North-Eastern States of India is located. All these locations might be in jeopardy during high Kosi flood.
Furthermore the Kosi would meet the GANGA at Manihari or downstream. The heavy Kosi discharge, reinforcing the Ganga just upstream of Farakka might lead to a situation where the Ganga already sedimented may forge its way, across the embankment bursting towards Maldah and adopting the channel of Kalindri/Pagla to confluence with the Padma at Godagarighat in the Bangla Desh, altogether bypassing the Bhagirathi channel.
ROLE OF COARSE SILT
Monstrosity of the Kosi is due to a considerable rise in its bed. Kosi flows down through Triveni- 5km upstream of Varahkshetra in the Mahabharat range of the Middle Himalaya to debouch at Chatra in Nepal Tarai; at Triveni, its three Major Hill Tributaries: SUNKOSI, TAMOR Kosi and ARUN Kosi- receive the load of water and sediments from the far-flung Kanchenjunga in east to Mt Everest and Makalu to Gosaithan in west. Kosi carries not only high discharge of water, but more importantly, a high load of Sediments as well. Sediments being of three sizes- Coarse, Medium and Fine-Coarse sediments is not transported by the river beyond Bhimnagar-Ghurna-Pathardeva stretch: 35-45km down of Chatra. This hydrological limitation of Kosi was before the Barrage also; now after the Barrage, some of Medium silt is also naturally supposed to being trapped upstream, besides the Barrage prompting more coarse silt deposition. It is the coarse silt sedimentation that has resulted in its Avulsion, shifting its channels from Purnia in east to Kusheswarsthan in west- a distance of 125km- in several stages during the last 4 centuries.
ALARMING RISE IN BED LEVEL ABOVE BARRAGE
The table below: CUBATURE Analysis quite clearly shows the ALARMING SEDIMENTATION above the Barrage.
CUBATURE Analysis of Kosi Embankments (1955-74)
River-Stretch Change in River-bed Levels Volume change in River Bed Remarks
Cross Section No Pre-Barrage 1955-62 mm/year Post-Barrage 1963-74 mm/year Pre-Barrage 1955-62 million cum/year (MCM) Post-Barrage 1963-74 million cum/year
Upstream of Barrage
1-19 I Chatra to Jalpapur
27km -17.6 +123.4 -4.046 +28.304 Scouring induced Siltation.
20-32 II Jalpapur to Bhimnagar
15km -165.6 +107.0 -16.058 +10.436 As above
Downstream of Barrage
33-49 III Bhimnagar to Dagmara
26km -35.6 -08.3 -5.082 -1.181 Scouring has reduced
50-70 IV Dagmara to Supaul
34km -03.8 +18.6 -2.081 10.228 Scouring induced Siltation.
71-90 V Supaul to Mahishi
40km +95.6 +63.5 +42.90 +20.949 Rate of siltation reduced
91-98 VI Mahishi to Koparia
25km NA +120.3 NA +15.730 -
Total:- +15.633 +84.466
(Comprehensive Plan of Kosi prepared by GFCC 1986 presented in Bihar Second Irrigation Commission Report vol V part II)
The table unequivocally reflects that after the Barrage, there is a pronounced and Quantitative increase in sedimentation above the Barrage. In the light of the table, it has been calculated that the average annual rate of sedimentation above the Barrage is about 5cm. Then it implies that within the last 50 years after the commissioning of the Barrage, a 2.50 metre thick layer of sediments might have already deposited on the river bed.
The Kosi Barrage was designed for a Maximum flood discharge of 9.50 lakh cusecs. But now, with high sedimentation upstream, the capacity of the Barrage to hold and discharge safely must have severely reduced. Dr A B THAPA (former Executive Secretary, Water and Energy Commission, Nepal) - an expert on Kosi calculates that the present maximum flood discharge capacity of Barrage is only up to 5.00 lakh cusecs. Then with more than 5.00lakh cusecs discharge flowing in Kosi, coupled with high monsoon rainfall in the plain catchment area and the swelling Ganga, the Barrage and the Eastern Afflux Bund might be seriously ENDANGERED.
WRONG THINKING OF EMBANKMENTS
THE ENGINEERING ASSUMPTION behind the Kosi embankment was that constraining the river would increase the velocity, leading to a scouring of the river-bed and thereby providing to it an extra space to accommodate flood. But what has actually happened is just the reverse. Because of the siltation, the river now has the less space for flood accommodation. Moreover the embankments cause severe and rampant waterlogging on both sides and even flood in the protected areas.
EMBANKMENTS INCREASING VULNERABILITY
In the absence of a firm scientific and historical understanding of the geomorphologic processes at work in the Kosi delta, the flooding in its basin continues to be denigrated as ‘Disaster’, one that needs to be controlled by structural measures. Because of the monsoon, the discharge in the Himalayan Rivers are temporally skewed and cannot be accommodated within the shallow cross sectional areas of the riverbed in the plains. The artificial reduction in the cross sectional area of the Rivers of North Bihar- created by the embankments- only causes increasing vulnerability. HENCE EMBANKMENTS ARE NO REMEDY. One way or the other, the silt laden flood waters have to be allowed to spill out in the Paleo-channels. THIS IS the CONTROLLED FLOODING.
In 1954 the Kosi discharge at Varahkshetra was 8.53 lakh cusecs; in 1968, it was 9.13 lakh cusecs; in 1987, it was 5.36 lakh cusecs; in 1924, the discharge is reported to be 7.00 lakh cusecs. After 1987, the discharge has never exceeded 4.00 lakh cusecs. Can the higher discharge or the discharge close to the record be ruled out?
EASTERN ALIGNMENT OF KOSI
During the 1950s when Kosi was embanked, it was flowing along the western embankment. But since 1980s it has been flowing along the eastern alignment, close to the eastern afflux bund from Chakarghatti downward, by Rajabas, Prakashpur, Madhuban, Kusaha and Bhimnagar.
EASTERN AFFLUX BUND UNDER STRAIN
The heavy sedimentation upstream of the barrage and consequent rise in the bed-level as reflected by the cubature analysis, coupled with the eastern alignment of the flow of river and existence of the Sursar network of channels countryside adjoining the eastern afflux bund creates a geographical firmament where the Kosi in case of high discharge might forge its way across the bund to adopt the Sursar network to reach the Ganga through the districts of Sunsari in Nepal; Supaul,Madhepura, Saharsa, Araria, Purnia, Katihar, khagaria and Naugachia in Bihar. This Avulsion in Kosi would be in one-go and would result in unprecedented damage and disaster. The Trailer of such disaster is already seen in 2008 Kusaha flood. Dr A B THAPA rightly states “it is frightening even to think of the horrors if the Kosi would suddenly burst the embankment at a time when the flood discharge is close to nine lakh cusecs. There would be a total devastation of almost the whole north-east Bihar and a large area of Nepal’s Sunsari district if we failed to take in time adequate preventive measures”.
CONCEPT OF CONTROLLED FLOODING
Controlled flooding can be a method for tackling the discharge and silt problem of Kosi. The old and abandoned dhars of Kosi can be revived to receive a portion of diverted flood and thereby the flood intensity in the main river can be reduced. Since quantity of silt increases with increase in flood discharge, diversion of flood to old dhars during high floods would also carry silt along with. The excess water as well as excess silt of Kosi has to be transported to the old and abandoned dhars and adjoining low waterlogged areas with the help of the Sursar network of channels in the geographical space from Kusheswarsthan to Maldah. The Bihar second irrigation commission report (Vol V part II) also states-“the idea of flood diversion in old Kosi dhar, in the opinion of this commission, appears to be best first hand solutions for saving the suffering mass of population from vagaries of Kosi during high floods.”
Prof Kalyan Rudra (former member of National Flood Management Core Group) writes-“the only sustainable option for the Kosi challenge is to divert these flood waters into convenient outlets. The only technical solution seems to be to channel the flood waters through the old courses. Utilising the old channels would be less expensive and provide a more realistic solution to the recurrent disasters. The option would also manage the floods better than would the proposed High Dam in Nepal”.
Management of Kosi problem through the controlled flooding is conceptualised by Rai Bahadur Prafulla Chandra Ghosh, executive Engineer in 1941 when he advises its flood- diversion through the Sursar network of channels in the plain area. His suggestions can be made the foundation of an Action – Plan for Apportionment of Kosi-Flood into its various old/abandoned channels so as to manage its flood problems with its agronomic utilisation.
Dr A B Thapa writes-‘At present the capacity of the present Kosi river channel to hold back big floods is greatly reduced. It would not anymore be possible to confine always the river within the boundaries of the embankments to prevent the rerun of the last disaster. However, the loss of life and property can be greatly reduced by preventing the Kosi to roam freely to rampage its vast floodplain. For this purpose one of the relegated old Kosi channels must be developed as a buffer channel for the diversion of the high flood water in excess of the carrying capacity of the present Kosi course. A spillway must be provided to discharge safely the flood water across the embankment into the buffer channel, which could also help to hold back the sediments already accumulated on the river bed.’
EXISTENCE OF SURSAR NETWORK OF CHANNELS
DOWNWARD Chatra there is a channel of water east of the eastern afflux bund through which the main Kosi used to flow until a century ago; this channel lower down is called SURSAR. It flows down by Dumraha, Inurva, Babia and Ghuski- all in Sunsari district of Nepal and enters into Bihar east of Birpur around Basmati-Ghurna-Manikpur in Narpatganj block of Araria district. This Sursar makes a network of channels, uniting here and separating there in the districts of Araria, Supaul, Madhepura, Purnia, Saharsa, Katihar; the conspicuous channels of this network can still be seen flowing at Rampur Mirganj and Murliganj in Madhepura; Dhimaghat (Banmankhi), Chunapur-Banbhag and Purnia city in Purnia district; all these channels are linked one way or the other in upstream with the Sursar.
Sursar below Inurva-Babia in Nepal sends down an emissary locally called Budhi dhar which runs down to Pathardeva/Sonapur near Farbisganj in Araria district where it joins the Parman River. And Parman, with the link channel of Devani dhar off taking at Araria/Ekamba gets into the Mahananda River around Amour/Dengaraha ghat (Baisi) near Dalkola in Purnia district. And Mahananda through the Jhaua/Lava channel and the Barsoi/Raiganj/Maldah confluences with the Ganga and the Padma respectively.
CHANNEL NETWORK AROUND BHIMNAGAR
The present Kosi emanates on its eastern side near Bhimnagar a channel that lower down gives rise to what is called Parvane dhar at Madhepura; Tilave dhar at Baidyanathpur and Dhemura dhar at Mahishi/Bangaon: later two places being in Saharsa district. Near Bhimnagar on to its western side, the Kosi sends down a channel that lower down is linked to Tiljuga dhar which flows by Nirmali/Ghonghepur/kusheswarsthan and through which the Kosi was flowing during 1950s.
IMMENSE AGRONOMIC BENEFITS
Controlled flooding has immense Agronomic benefits. Along with spilling water, silt is also carried to crop lands as a result of which they get heavy deposits of silt that has a fertility of very high degree. Hence the inundated areas harvest bumper crops. Agricultural bounty of Kamla and Bagmati is beyond doubt. Kosi is also no exception; otherwise the Kosi belt would not be producing record Maize and jute, abundant fishery and lush green Grasses. This is such an important factor that cultivators rather welcome the inundation on his fields by the rivers. The general opinion of the cultivators is that it would be better if the duration and depth of inundation is less- normally less than 2.00 ft. except in low-lying areas. To limit the DEPTH and DURATION of Inundation is what the Controlled Flooding aims at.
IRRIGATION FROM REVIVED CHANNELS
Old and abandoned dhars, when revived under a controlled flooding system- measure about 1000 miles in length within the Kosi catchment of the districts of Saharsa and Purnia divisions as well as Khagaria and Naugachia districts. They can irrigate more than 7.00 lakh acres. Almost similar area is available in the form of wetlands and lowlands within the catchment which is self-irrigated. Besides, underground water table normally within 15-20 ft. from the surface would be copiously and regularly recharged. A super rich Aquifer below at a close distance can easily be harnessed for Artificial IRRIGATION when required in exigency with the application of appropriate technology and available vast Man/Drought power. Suitable modification in the existing Agronomic norms and practices would need to be planned and executed.
KOSI PAVING WAY FOR KAMLA/BAGMATI FLOOD MITIGATION
Around Kusheswarsthan/Tilkeshwarsthan, Kosi receives Kamla-Balan and Bagmati rivers to drain them out. Higher Volume and Velocity in Kosi here impedes drainage in Kamla-Balan and Bagmati, resulting in their surging back and flooding in the districts of Sitamadhi, Shivhar, Muzaffarpur, Madhubani, Darbhanga and Samastipur.This flood-locking in Kamla-Balan and Bagmati is the main cause of damages in the above districts. To remove this flood-locking, Kosi discharge in high floods needs to be diverted appropriately into the Sursar network of channels. Kosi Management would not only resolve flood problem in around 18000 sq. km of its basin area from Kusheswarsthan to Barsoi but also would pave way for flood mitigation in 9000 sq. km of Kamla-Balan and Bagmati Basins in the districts of Sitamadhi, Shivhar, Muzaffarpur, Darbhanga, Madhubani and Samastipur.
MIRAGE OF HIGH DAM
The solution of the Kosi problem is being sought in the Varahkshetra high Dam since decades. But Sedimentation, Seismic effect, displacement of people and arable lands, danger of flash flood, unclear local benefits, extreme expenditure, limited flood moderation, upland-lowland riparian rights, danger of international diplomacy etc are the CONCERNS the experts point out, ascribing them to be potent enough to make this project DOUBTFUL in efficacy, integrity and practicability.
No wonder therefore that many experts- Dipak Gyawali, AB Thapa, Ajay Dixit, JN Nayak, Buddhi Narayan Shreshtha, Hari Man Shreshtha, Kanak Mani Dixit etc from Nepal and Dinesh kumar Mishra, Rameswar R Aiyer, Gopal Krishna, Sudhirendra Shrma, Kalyan Rudra, Rajiv Sinha etc from India question the High Dam. In the present firmament, it appears to be at best a remote possibility. But Kosi reaching the ‘threshold of Do or Die’ urgently needs an alternative plan, instead of inching towards Mirage of High Dam.
CULPABILITY OF FARAKKA BARRAGE
Kosi outfalls into the Ganga at Kursela. Ganga is intercepted by a Barrage at Farakka. Huge sedimentation and declining slope of the channel is reported upstream of Farakka. The bed of the Ganga is reported to be rising all along in Bihar and even higher. With the construction of Farakka barrage in 1971, there has ensued a stage of higher flood in Bihar. Serious sedimentation in Kosi is said to owe a lot to rising bed level in Ganga due to the Farakka Barrage. Hence in the interest of rivers in Bihar, Ganga needs to be free of Drainage-constraints.
The problem of Kosi is HIGH SILT, HIGH DISCHARGE and HIGH SPEED. Hence its MANAGEMENT requires these to be well addressed. A conceptual framework to manage the Kosi in an Eco-Friendly manner is provided by RAI BAHADUR PRAFULLA CHANDRA GHOSH, EXECUTIVE ENGINEER, PWD, Bihar (1941) in his “Comprehensive Treatise on north Bihar flood problem”. In the light of his Suggestions, an ACTION-PLAN for KOSI MANAGEMENT has been formulated.
GHOSH suggests “the main problem in training the Kosi is its high discharge, high velocity and the vast amount of boulders, pebbles, silt etc. which it brings down. Of the above three factors, the last one is the most important. The whole safety of any project for training of the Kosi would lie in the scientific disposal of the high percentage of silt which the Kosi carries. The easterly and the westerly peregrination of the Kosi which is the most dreadful feature in the destruction of the area is solely due to the raising up the country level of the area over which She flows by yearly deposit of silt and finally adopting another channel in the west after raising the bed of its own channel.’
‘To regulate the percentage of the Kosi silt would be entirely difficult. It can be done partly by stopping Deforestation and Surface soil Erosion due to cattle grazing in the hill area where from the silt is gathered by the river. Also the high velocity of the Kosi in the Sub-mountainous region has got a wearing action on the soft sand stone. This accumulation of sand by the Kosi water can only be checked if the velocity can be reduced to a safer limit so that the wearing action may be lessened.’
‘Reduction of velocity may be done by constructing a number of Weirs across the tributaries of the Kosi above the Varahkshetra in their mountainous region. Such weirs may also help in reducing the flood height in British India as the Reservoirs so formed will act as retarding basins at the time of floods. The catchment area of such retarding basin can well be expected to be pretty large. Detailed survey of these valleys is recommended to be made in order to know the feasibility of such a scheme.’
‘Also the flood disaster due to the Kosi may be reduced by redistributing the Kosi discharge into Two channels, viz. the Kosi and the Sursar at Chatra by erecting extensive Barrage works at the point of bifurcation. The discharges thus brought down by the Sursar and the main Kosi channel further lower down may be distributed into various dead channels by making pucca Diaphragms at their off-takes.’
‘If in this way the amount of flood water be controlled according to the capacity of the channels( which may have to be kept of proper section by constant dredging operation) the area over which such channels flow would be built up uniformly and thus there will be lesser chance of the Kosi, shifting from one to the other.” (Comprehensive Treatise on north Bihar flood problem…..page no. 120.)
Treatment of Hill Tributaries of Kosi:
By making Weirs across Sunkosi, Tamorkosi and Arunkosi (all Himalayan hill tributaries of Kosi) to create Detention Basins by executing the following proposed schemes-
(i) Sunkosi- Kamla diversion scheme,
(ii) Mulghat Tamor Kosi project,
(iii) Arun Kosi I II III project.
As analysed by Prof J N Nayak, Head, Civil Engineering Department, Tribhuban University, Nepal- Sunkosi-Kamla diversion project will trap 50% of the Sediments and 40% of Discharge; Tamor Kosi project : 20% of sediments and 20% of discharge; altogether 70% of sediments and 60% of discharge being trapped, thus two main factors: high silt and high discharge can thus be managed. The third main factor: high speed is also inherently managed by these projects.
APPORTIONMENT OF KOSI:
At/Around CHATRA (Nepal) - Extensive Barrage to divide Kosi between The EASTERN SURSAR CHANNEL and The WESTERN MAIN CHANNEL
Sursar- enters through Nepal Tarai into India and Bihar around Bela-Ghurna-Pathraha-Nawabganj in Narpatganj block of Araria in west and Babia- Narsinghtappu-Bhutaha- Ghuski-all in Sunsari district in Nepal in east and may be linked with the help of Diaphragms/FLOW REGULATORY STRUCTURE to be erected at suitable off-take points with its abandoned channels (locally called with different names at different locations along the course) and such channels out-falling into the Ganga at different points. Such LINKAGE of the Sursar will ensure its water flow through the following NATURAL COURSES:
1. Sursar-Budhi-Parman-Devani-Mahananda along Inurva, Babia, Pathardeva, Dipol, Araria/ Ekamba, Dengaraha ghat, Raiganj, Maldah, Nawabganj. (185km in length)
2. Sursar-Budhi-Parman-Fulhar-Kalindri/Pagla along Araria/Ekamba, Belgachia,Kadwa, Amadabad, Ratua, Kaliachak.(160km)
3. Sursar-Budhi-Parman-Kamleshwari along Belgachia, Katakos.(135km)
4. Sursar-Chakradaha/Gorobhagar-KariKosi-Saura along Inurva, Bhutaha, Kaptanganj, Badhepara, Hengna, Mohini, Purnia city, , Lalganj.(135km)
5. Sursar-Gorobhagar-Karikosi along Badhepara, Swaldaha, Raniganj, Banbhag, Lalganj Katihar, Manihari.(130km)
6. Sursar-Gorobhagar-Karikosi-Livari/Barandi along Raniganj, Sarsi, Rangpura, Barari, Karhagola.(130km)
7. Sursar-Gorobhagar-Karikosi-Fariyani along Raniganj, Dhamdaha, Kursela.(130km)
8. Sursar-Lachchadhar along Bhutaha, Ghurna, Anchara, Narpatganj, Fatehpur, Bhargama, Dhamdaha, Kursela.(130km)
9. Sursar-Moglahadhar-Hiran along Narpatganj, Khajuri, Birnagar-Bisharia, Dharhara, Bhavanipur, Kursela.(130 km)
10. Sursar-Moglahadhar/Sapahadhar along Khajuri, Murliganj, Haripur, Bihariganj,Puraini, Chausa, Pachrasi.( 135 km)
11. Sursar-Hareli- along Murliganj, Uda- Kishanganj Alamnagar, Phulaut.(140 km)
12. Sursar-Mirchaiyadhar-Bharahi – along Anchara, Bhimpur, Chatapur, Raisri, Mirganj, Goalpara, Muraut,. (150 km.)
13. Sursar-Mirchaiyadhar-Loren along Mirganj,Goalpara, Bargaon, Mainaghat (Sonbarsa), Chautham, Muraut, Phulaut, Pachrasi, Kursela.(160km)
This apportionment of the Eastern channel of the Kosi through Sursar into above mentioned channels will spread over flood water in an area more than 7000 sq. km in the districts of Purnia, Araria, Supaul, Madhepura, Saharsa and Katihar in Bihar; Maldah, North & South Dinajpur districts of the West Bengal; Sunsari district of Nepal and Nawabganj district of the Bangla Desh; the Latitudinal east- west wide distance being more than 140 Km from Mirganj to Purnia town- Dengaraha ghat and further south-east to Raiganj-Maldah in the West Bengal and still further south to Nawabganj/Godagari in the Bangla Desh.
Western Main Channel-
With the help of DIAPHRAGMS/FLOW REGULATORY STRUCTURE around Bhimnagar, the Western Main channel can be apportioned among the following streams:
14 Haiya/Belhi dhar- - flowing along Sripur/Haripur, Fatehpur, Pratapganj, Madhepura, Kamp, Lagma, Chautham.( 170 km long)
15 Parvane- flowing along Bhimnagar, Shivnagar, Raghopur, Dinapatti, Singheshwarsthan, Mathahi, Lagma, Chautham. (180 km long)
16 Tilave- flowing along Bhimnagar, Shivnagar, Ganpatganj, Bavani- Bhelva, Baijnathpur, Patuaha, Sonbarsa, Chautham. (200 km)
17 Dhemura- flowing along Bhimnagar, Binania, Bhaptiahi, Supaul, Mahishi, Koparia, Chautham.(210km)
18 Kosi- flowing along Bhimnagar, Baisa, Supaul, Nauhatta, Hati, Baluahaghat, Rajanpur, Dhamahara, Chautham, Kursela. (220km)
19 Tiljuga- flowing along Bhimnagar, Dagmara, Gopalpur, Bakunia, Ghonghepur, Tilkeshwarsthan, Dhamahara, Chautham.( 230 km)
This Apportionment of the Kosi will provide around 5300 sq. km of area for flood water to spread over the districts of Saharsa, Madhepura and Supaul; the East-west latitudinal distance between Madhepura in east and Kusheswarsthan/Ghonghepur in west will be 60Km. Thus the Kosi flood, instead of being confined within 10-12 Km wide embankments as it is today, will spread over within an area 60Km wide between Madhepura and Ghonghepur.
CHATRA BARRAGE may be used to cross over the Kosi to be linked by road via Bharaul, Baklauri and Pakali at Mahendra Rajmarg in east and via Thoksila, Tapeshwari, Fatehpur and Kanchanpur at Mahendra Rajmarg in west; thus eliminating the need of the Bhimnagar Barrage.
One of the channels shortest /suitable one can be used as NAVIGATION TRUNK for Chatra to be linked with the Ganga.
In the Divisions of Saharsa and Purnia, following Main Road/Railways need adequate waterways for facilitating smooth drainage:
Karjain-Balua Bazaar road, Simarahi-Pratapganj-Narpatganj-Farbisganj road, Bhaptiahi-Pratapganj-Narpatganj-Farbisganj railway, Supaul-Pipra-Triveniganj-Khajuri-Bhargama-Raniganj-Araria road, Mahishi-Saharsa-Madhepura-Murliganj-Purnia road, Saharsa-Madhepura-Murliganj-Purnia Railway, Koparia-Mansi railway, Kosi Dumari Bridge, Pasraha-Narayanpur road/railway, Kursela road/railway bridge, Katihar-Barsoi railway, Katihar-Maldah railway etc.