FLOOD MANAGEMENT IN SUB-HIMALAYAN RIVERS

Econirvan-Bihar's Revival.

Flood Management in North Bihar

 

KOSI: DISASTER IN WAITING

The Kosi Project has now reached such a state where it is perceived as a perpetual threat rather than an effective protector in the context of its flood-prevention capacity. Because of one single factor-siltation within the Embanked area its water retaining capacity is alarmingly reduced. It is not that the Kosi planner had not anticipated the siltation problem; they had this apprehension and hence the mechanism of silt Ejector and Excluder was adopted to reduce and control the siltation problem to a safe limit. Now it is an accepted fact that this mechanism considerably failed to control the siltation problem. A central water commission report on Kosi in 1982 stated that after its completion in 1963, the barrage began inducing siltation; The rise and fall of the river was estimated over six stretches; in three reaches, the earlier phenomenon of river bed scouring changed to siltation after the barrage was built and in one stretch, the scouring rate was greatly reduced; over all the annual silt deposit over the river-bed between the embankments went-up from 16 m cum during the period 1955-62 to 84 m cum during 1963-74. what is more important is that siltation upstream the Barrage at Bhimnagar is very high.

The Center for Science and Environment in a report states- “The relief and rehabilitation commissioner in this report on this floods of 1987 has explicitly admitted that siltation has had a negative impact on the flood discharge capacity of river Kosi The Highest flood level(HFL) at Baltara (in 1987) exceeded the high flood level ever known, by one metre; this happened when the maximum flood discharge was slightly above 14,100 cumecs; whereas the flood discharge of the Kosi was as high as 24,200 cumecs in 1954 and 1968 respectively. This shows that heavy siltation has occurred.” Obviously the main cause is the Heavy siltation. The water retention capacity of the river has greatly reduced. It is a lay observation that the river-bed is up by about 10- 12 ft. The Kosi Barrage is now believed to be unable to with hold more than 5-6 lakh cusecs of discharge; what a contrast here is that the same Barrage was designed to withhold a discharge of 9.50 lakh cusecs and which actually withheld a discharge of 9.13 lakh cusecs in 1968, on 5th October though the Western embankment collapsed downstream near Jamalpur. But now much less discharge 4-5 lakh cusecs causes alarming bell; Kosi-Bandh collapse at Kusaha in Nepal- 12km upstream of Bhimnagar took place in 2008 when discharge recorded 2.36 lacs cusecs as maximum.

The Kosi Barrage and the Embankments is now seen by the people more as a DISASTER IN WAITING than as a SUCOUR.As per the Kosi Project Report the Annual SILT-DEPOSITION by the kosi is 87000 acre feet; of this, 16% is COARSE sediment, 28% - MEDIUM sediment and 56%-FINE sediment.

THE NOTORIOUS feature of the kosi is its SHIFTING tendency and the SHIFT is due to the fact that coarse sediment is deposited in the river-bed UPSTREAM of Bhimnagar; when there was no embankment, the kosi used to adopting and leaving one after another channel in its westward journey in the vicinity: from Dumraha-Inurva-Babia due east in Nepal to Birpur- Bhimnagar due west in India because coarse silt deposition used to cause silting up of flowing channel, forcing the kosi adopt adjoining channel and this phenomena of siltation related adoption and relinquishing happened in the vicinity of Bhimnagar during the first half of the 20th century. When the kosi was flowing in the realm of Purnea area before the 20th century, similar siltation related adoption and relinquishing of channel after channel took place in the neighbourhood of Balua Bazar-Pathraha-Nawabganj-Pathardeva-Babia-Dumaraha( later two in Nepal) the area immediately east of BIRPUR. Thus it is the area just east and west of Birpur where the perinigration of the kosi has taken place from one channel to another in its westward journey during the last three centuries. To tackle this coarse silt deposition and subsequent shifting tendency of the kosi, the BARRAGE was erected; this was one of the aims of the Barrage.

But with the construction of the Barrage, entire coarse-silt and portions of Medium and Fine silt is deposited upstream of the Barrage which is now over 45 yeas old; during this period, the total coarse silt deposited is estimated to be that which must be sufficient to raise the level within the both Afflux Bandhs Considerably. As per lay observation and the informal information from the Concerned Engineers, the silt deposition upstream of the Barrage is more than 10-12 feet. The Barrage was originally designed to discharge over 9.00lac cusecs of water; but much of the detention space has been silted up; in 1954, the maximum discharge was 8.55lac cusecs, in 1968- it was 9.13lac cusecs and in 1987-it was 5.27 lac cusecs; in 1927, it is reported to be over 7.00 lac cusecs; in 1987, there was a catastrophic damage; in 1968, the damage was much milder because the maximum discharge was on 5th October when the Ganga was quite normal; this conjecture is not without reasoning that had a discharge of 9.13 lac cusecs been in the months of July-August-September in 1968, the Damage-scenario might have been totally different. Now if such high discharge takes place in the rainy season or as the Engineers informally confess, if a discharge of over 6.00 lac cusecs takes place, the Barrage and/ or Eastern Afflux Bund is likely to succumb. Here we are reminded by the Kosi Technical Committee Report, 1975 also. This report mentions that due to siltaton upstream the Barrage in 1956 when the Barrage was not constructed, the Bed-slope of the Kosi was 3.22ft per mile within 6 Km upstream of Bhimnagar i e the barrage site; but in 1969- 6 years after the construction of the Barrage- the Bed-slope reduced to 2.22ft per mile; this reduction in the Bed-slope of the Kosi upstream of the Barrage was due to Siltation mainly by Coarse Silt; the report considered a maximum 5ft rise in the Bed-level to be the limit to which the Barrage and the Eastern Afflux Bund could withstand; meaning thereby that beyond this limit in the rise of Bed-level, these Hydraulic structures might collapse. By now, the Siltation is decidedly much more than 5ft.( Kosi Technical Committee Report, 1975, page-12,13).By now, the Bed-slope must have been reduced to minimum.

As mentioned above, siltation is most conspicuous and the highest UPSTREAM of the Barrage. Downward Chatra in Nepal, around Rajabas- upstream of the barrage by the eastern side of the eastern Afflux bandh, there is a Channel of water through which the Main Kosi used to flow until a century ago which lower down is locally called SURSAR flowing down by east of Birpur to make a network of channels uniting here and separating there in the present districts of Araria, Purnea, Katihar, Supaul, Madhepura and Saharsa; the conspicuous channels of such network still flowing are seen from west to east onward at Mirganj, Murliganj, Dheema ghat( Banmankhi), Chunapur-Banbhag, Purnea city. The channel passing by Murliganj is called upstream as HAHA dhar; one passing by Banmankhi is known locally as FARIYANI dhar; Banbhag dhar is the KARI-KOSI and Purnea city channel is the SAURA dhar. The Kosi in case of collapse of the Eastern Afflux Bund around Chatra Chakraghatti/Rajabas might occupy the Sursar to flow through the districts of Araria,Purnea, KatiharSupaul, Madhepura and Saharsa; here it must be mentioned that the length of the channel flowing by Chatra, Anchra ghat, Bhargama, Dhamdaha, Pothia-Falka and Kursela is the shortest of all the channels of the kosi. The kosi is likely to adopt one or many channel in the districts of Araria and Purnea. If the Eastern Afflux Bund or the Barrage collapses near Bhimnagar, the Kosi is likely to occupy one or many of the channels still flowing in the districts of Supaul, Saharsa and Madhepura and through which it used to flow in the first half of the 20th century; such channels from west to east onward are Dhemura, Tilave, Parvane and Sursar. The northern openings of these cannels are in the vicinity of Bhimnagar. Presently One going eastward by road from Mahisi near Eastern Kosi Embankment in Saharsa finds Dhemura at Mahisi, Tilave at Baijnathpur, Parvane at Madhepura and Sursar at Rampur-Mirganj. The contour lines are from north-west to south-east in the kosi basin area. In case of collapse of the Bund or the Barrage, the adoption by the Kosi of one or many of the channels- Dhemura, Tilave, Parvane, Sursar in the Administrative division of Saharsa and Haha dhar, Faryani kosi, Kari kosi and Saura dhar in the districts of Araria, Purnea and Katihar- is likely to happen in ONE-GO. Moreover, the Sursar with the link channel of- what is locally called in SUNSARI DISTRICT OF Nepal- BURHI DHAR spills over to the eastern most stream of PARMAN flowing down by PATHARDEWA near Jogbani in Araria district and the Parman with the link channel of Devni offtaking at Ekamba/Araria gets into the Mahananda around Amour/Dengrahaghat(Baisi) in Purnea. And the Mahananda may strike at Maldah through its length and breadth. Here it must be pointed out that PERINIGRATION of the kosi used to happen in the area between Bhimnagar and Birpur during the first half of the 20th century and during the 17th 18th and 19th century, such PERINIGRATION took place in the area around Bela-Basmatia- BaluaBazar- Anchara ghat and Dumaraha-Babia-Pathraha-Nawabganj-Pathardewa. Needless to mention, such adoption by the kosi in one go is bound to be CATASTROPHIC of Unprecedented scale.

At stake is there the entire kosi basin area: Sunsari and south-west corner of Morang districts in Nepal and Supaul, Saharsa, khagaria, Madhepura, Araria, Purnia, Katihar and Naugachia districts in Bihar and Maldah as well as South and North Dinajpur districts in the West Bengal in India and Rajshahi/ Nawabganj districts in Bangla Desh. The road-link of India with the North-eastern states via Purnia at Dalkola ghat and the railway-link via Katihar at Barsoi are likely to collapse. And the Ganga being reinforced by the Kosi -discharge around Manihari-Kantakos-Kaliachak may occupy the Kalindri channel to reach Maldah and Nawabganj and ultimately joining the PADMA near Lalgolaghat, completely bypassing the Farakka Barrage. The people inhabiting these areas and likely to be affected amount to around 9.00lac in Sunsari/Morang in Nepal, 167 lac in Saharsa and Purnia divisions of North Bihar and 51 lac in South Dinajpur and Maldah districts of the West Bengal in India and 10 lacs in Rajshahi and Nawabganj districts in Bangla Desh i.e a total of around 237 lac.

A Trailor of Such Catastrophe happened in 2008. On August 18 2008, the Eastern Afflux embankment along the kosi at Kusaha (12.04 RD) in Sunsari district of Nepal caved in and most of its water along with sediment load bagan flowing over the area hitherto flood-secure since the kosi-project. The flowing-water adopted the course of Sursar to run down, causing disastrous damage in Sunsarri district of Nepal and Araria, Supaul,Madhepura, Saharsa, Purnia and Khagaria districts of India, numbering 50000 and 30 lacs people respectively. It was the worst-ever flood-damage in India. This Kusaha- Breach took place when the river-discharge at Chatra was 1.80 lac cusec per second only as against its August-average of 4729 cumec/second. The Breach and consequent flood was not the result of any heavy downpour and cannot be attributed to climatic causes. If the discharge of the river at Varahkshetra on the day or thereafter had been anywhere more than 5.00 lac cusecs/sec, the scale of the damage would have been much much more davastatating. The kosi had already recorded discharge of 9.13lac cusecs/sec,8.54 lac cusecs/sec and 5.27 lac cusecs/sec in 1968,1954 and 1987 respectively. During the early days of Kusaha Breach, some of flood water had reached through the Parman to south-east of Farbisganj; had the kosi –discharge at Chatra been more on August18,2008, the Parman and through it the Mahananda also might have been in focus. Through the Mahananda, the flood water is in all likelihood to affect first the Katihar district and then downstream West Dinajpur and Maldah districts in the West Bengal. Because of the discharge in 2008 being much less than the average,the Kusaha Breach could affect only around 3 million people while the Kosi with its recorded- discharge has the potential of affecting more than 20 million people at present. Hence the Kusaha Breach in Kosi Bandh in 2008 should at best be taken as Trailor.

In 1984 also, the Kosi had breached at Nauhatta in Saharsa district when the discharge was around 4.00 lac cusecs; 4.00 lac people were affected mainly in Saharsa and some in Khagaria districts. In comparison to the Kusaha breach in 2008, the damage in 1984 was much much less although the discharge then was almost double; mainly because the Breach in 1984 was far downstream. The Conclusion thus emerged is that the lower the breach, the less is the Damage; the Higher the breach, the more the Damage. And now probably vulnerable points caused mainly by sedimentation lie mostly upstream of the Barrage at Bhimnagar : Rajabas, Madhuban.

Hence the big Concern!