FLOOD MANAGEMENT IN SUB-HIMALAYAN RIVERS

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MANAGEMENT OF KOSI FLOOD

Posted by gajananmishra on October 24, 2012 at 4:15 AM

Conceptual Suggestion by: RAI BAHADUR P C GHOSH, Ex Engineer, PWD, BIHAR (1941) in A Comprehensive Treatise on north Bihar flood problem:

“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 Diaphragms at their off-takes.’

‘If in this way the amount of flood water be controlled according to the capacity of the channels( which nay 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.” (page no. 120.)

                                                                 ACTION- PLAN

A. Treatment of Hill Tributaries of Kosi:

By making Weirs across Sunkosi, Tamorkosi and Arunkosi( all Himalayan hill tributaries of Kosi) as proposed and ardently demanded by Nepal, in

(i) Sunkosi- Kamla diversion scheme,

(ii) Mulghat Tamor kosi project,

(iii) Arun kosi I II III project.

As analysised by J N Nayak, Head, Civil Engineering Department, Tribhuban University, Nepal, and supported by A B Thapa, Ajay Dixit, Kanakmani Dixit, Dipak Gyawali- all WATER Expert in 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, the 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.

B. APPORTIONMENT OF KOSI:

At/Around CHATRA(Nepal)- Extensive Barrage to divide Kosi between WESTERN MAIN CHANNEL and EASTERN SURSAR.

Western Main Channel-

With the help of DIAPHRAGMS near Bhimnagar and further down, the Western Main channel can be apportioned among the following streams:

1. Haiyadhar- - flowing along Fatehpur, Pratapganj.

2. Parvane- flowing along Singheshwar.

3 Tilave- flowing along Ganpatganj, Baijnathpur.

4 Dhemura- flowing along Bhaptiahi, Supaul.

5 Kosi- flowing along Supaul, Nauhatta.

6 Tiljuga- flowing along Gopalpur, Bakunia.

This Apportionment of the Kosi will provide around 13 Lac acres 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 Ghongepur in west will be 50Km. 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 Ghongepur.

Sursar-

Sursar- enters through Nepal Tarai into India and Bihar around Bela-Ghurna-Pathraha-Nawabganj in Narpatganj block of Araria in west and Babiya- Narsinghtappu-Bhutaha- Ghuski-all in Sunsari district in Nepal in east and can be apportioned with the help of Diaphragms to be erected at suitable off-take points. Such apportionment of the Sursar will ensure its water flow through following Streams:

1. Sursar-Parman-Devni-Mahananda along Pathardeva, Dipol, Araria.

2. Sursar-Parman-Fulhar-Kalindi along Ekamba, Belgachia.

3. Sursar-Parman-Kamleshwari along Belgachia, Katakos.

4. Sursar-Kari Kosi-Saura along Hengna,Purneacity.

5. Sursar-Karikosi along Banbhag, Katihar.

6. Sursar-Karikosi-Livri/Barandi along Barari, Karhagola.

7. Sursar-Karikosi-Fariyani along Saifganj, Dhamdaha, Kursela.

8. Sursar-Lachchadhar along Anchra, Bhargama, Dhamdaha.

9. Sursar-Moglahadhar-Hiran along Khajuri, Birnagar.

10. Sursar-Moglaha/Saphadhar along Khajuri, Murliganj, Haripur, Puraini, Kursela.

11. Sursar- Hareli- along murliganj, Alamnagar.

12. Sursar-Mirchaiyadhar-Bharhi - along Mirganj, Goalpara.

13. Sursar-Mirchaiyadhar-Loren along Mirganj,Goalpara, Bargaon,Mainaghat.

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 16 lac acres in the districts of Purnea, Araria,Supaul, Madhepura, Saharsa and Katihar in Bihar;Maldah,North & South Dinajpur districts of the West Bengal and the Sunsari district of Nepal; the Latitudinal east west wide distance being more than 100 Km from Mirganj to Purnea town- Dengraha ghat and further south-east to Raiganj-Maldah.

C. 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; this eliminating the need of the Bhimnagar Barrage.

D. One of the channels shortest /suitable one can be used as NAVIGATION for Nepal to link with the Ganga, thereby meeting Nepal’s ardent demand.

WATERWAYS- IMPROVEMENT

E. In the Divisions of Saharsa and Purnea, following Main Road/Railways need more/better waterways:

Karjain-Balua Bazaar road, Simrahi-Pratapganj-Narpatganj-Farbisganj road,Bhaptiahi-Pratapganj-Narpatganj-Farbisganj railway, Supaul-Pipa-Triveniganj-Khajuri-Bhargama-Raniganj-Araria road, Mahisi-Saharsa-Madhepura-Murliganj-Purnea road, Saharsa-Madhepura-Murliganj-Purnea Railway, Koparia-Mansi railway, Kosi Dumri Bridge, Pasraha-Narayanpur road/railway, Kursela road/railway bridge.

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