Executive Summary of Manas-Sankosh-Tista-Ganga

Introduction This report deals with the feasibility study of the Manas-Sankosh-Tista-Ganga link project which is one of the part of Himalayan Rivers Development Component of NPP. The objective of preparation of Feasibility Report is mainly to facilitate firming up of the proposals and for discussions among the concerned States/Countries for arriving at broad agreements on the quantum of diversions and utilizations of water, sharing of costs and benefits etc. The Manas-Sankosh-Tista-Ganga (MSTG) link project envisaging diversion of surplus water from tributaries of river Brahmaputra i.e. river Manas, Sankosh, Aie, Raidak, Torsa & Jaldhaka to the Ganga river and further towards South.

The prefeasibility report (PFR) of Manas-Sankosh-Tista-Ganga link project was prepared by NWDA in 1994 with proposed Manas dam on Rivers Manas 4 km u/s of Indo Nepal border, proposed Sankosh Dam on river Sankosh 12 km u/s of Indo Nepal border.

Surveys & Investigation The Survey & Investigation works Manas-Sankosh-Tista reach of this link project as was proposed in PFR was entrusted to Central Water Commission by Ministry of Water Resources while the Tista-Ganga reach to NWDA. A major part of link alignments was passing through Manas Tiger Reserve, Raidak RF, Buxa Tiger RF and Gabur Basra RF. The S&I works could not be completed in want permission for carrying out S&I works in reserved forest areas/wildlife sanctuaries. NWDA completed the S&I works of Tista- Ganga reach.

Keeping in view of above constraints, NWDA explored various alignments for this link avoiding reserved forest and wildlife sanctuaries. It was decided that alternative studies in MSTG link may be carried out avoiding forest and wild life sanctuaries in following three scenarios. i) Considering proposed Manas and Sankosh Dams (Alternative-I) when both Dams will come. ii) Without considering proposed Manas dam but with Sankosh Dam (Alternative- II) when only Sankosh Dam will come and having unregulated flow of . iii) Sankosh-Tista-Ganga link (Alternative-III) no contribution from Manas River and avoiding Manas-Sankosh link. Two barrages are proposed one each across Manas river and in downstream of proposed Manas dam and proposed Sankosh dam respectively in Indian territory. In Alternative I, the regulated flows of Manas dam and Sankosh dam will be received at Manas barrage and Sankosh barrage respectively and will be diverted into link canal from respective barrages. In Alternative-II, only natural flows of Manas river will be available at Manas barrage for diversion into link canal from Manas barrage and regulated flows of Sankosh dam will be received and diverted into link canal at Sankosh barrage. In Alternative-III, only regulated flows of Sankosh dam will be diverted into link canal from Sankosh barrage.

Alignment details Alternative-I & II:- To make the alignment completely forest free, a barrage is proposed across Manas river about 3 km below the Manas Tiger Reserved Forest boundary and 18 km downstream of Indo- border. The canal off takes from right

1 flank of the proposed barrage with FSL of 56.0 m. The top level and pond level of the barrage will be 58.60 m and 57.00 m respectively. Initially the canal traverses in South- West direction and crosses Aie river at RD 30.040 Km. A lift of 10m is proposed in this reach at RD 104.959 km. the link canal outfalls in Sankosh river at RD 109.850 km. A barrage is proposed across the Sankosh river with top level and pond level of 57.50 m and 56.50 m respectively. Total length of the link canal in this reach i.e. from Manas to Sankosh is 109.850 km.

The canal offtake from right flank of proposed Sankosh barrage with FSL 56.100m. The link canal runs towards west and North West direction and outfall into Tista barrage which is at higher elevation. In this reach 6 nos. of lifts are proposed at suitable locations to achieve the required level at Tista barrage. The link canal crosses Raidak, Torsa and Jaldhaka rivers at RD 117.600 km, 176.800 km and 230.600 km respectively, and the contribution from these rives is taken into the link canal by proposing level crossings across these rivers. The pond level of Tista barrage is 114.00 m. Total length of link canal in this reach i.e. Sankosh to Tista is 159.450 km.

The canal offtake from right flank of existing Tista barrage with FSL of 113.600 m. It is proposed that existing Tista-Mahananda feeder canal will be utilized afte remodeling. The FSL at outfall into is 110.740 m. pond level of Mahananda barrage is 107.290 m. The total length of link canal in this reach i.e. Tista to Mahananda is 25.700 km.

Downstream of the Mahananda barrage, Mahananda river forms the Indo-Bangladesh boundary. To avoid the Indo-Bangladesh boundary, it is proposed to off-take the link canal from the Mahananda barrage at Fulbari village upto the aqueduct at Dongapara village parallel to existing Mahananda canal and out-fall into Mahananda river. The length of link canal in this part is 20.44 km. from Dongapara Bagdob barrage and then divert the water from Mahananda river to join its original alighment upto Ganga. The off-take level at Mahananda barrage is 107.00 m. The pond level of proposed Bagdob barrage is 35.00 m. The river training works are to be carried out to Mahananda river wherever required to accommodate link discharge together with self-discharge. Total length of Mahananda to Bagdob reach is 135.800 km and FSL at Bagdob barrage is 36.698 m. The pond level of Bagdob barrage is 35.00 m.

The link canal offtake from Bagdob barrage with FSL of 34.600 m and follow the South- West path upto a length of 8 km to join the original MSTG link alignment. From this point the link alignment traverse in North-South direction upto its outfall into Ganga river near village Katakosh, 4 km downstream of Manihari Ghat and 60 km upstream of Farakka barrage. The total length of this reach i.e. bagdob to Ganga and FSL at outfall point is 53.875 km and 30.858 m respectively. The total length of the link canal is 484.675 km out of which 112.400 km lies in , 191.400 km in West Bengal and 180.875 km in Bihar state.

Alternative-III:- The Sankosh-Tista-Ganga link is conceived if construction of Manas dam does not materialize. Thus link canal of 109.850 km between Manas to Sankosh river and considering Sankosh dam wrt above two alternatives. The Sankosh-Tista-Ganga link canal is proposed to offtake from the right flank of proposed barrage across Sankosh river, about 28 km downstream of Indo-Bhutan border. The link canal diverting water

2 from Sankosh river along with the contribution from intermediate major stream i.e. Raidak, Torsa and Jaldhaka. The alignment follows the route as mentioned in Alternative- I & II from Sankosh barrage to its out-fall into Ganga. The total length of link canal in Alternative-III is 374.825 km.

Topographical Surveys The topographical survey of the link canal alignment between Manas to Tista reach for alternative-I, II & III as applicable has been carried out by NWDA through outside agency and Tista to Ganga reach departmentally by NWDA. Other investigations by outside agencies viz. Geological Survey by GSI, Borrow area and construction material survey for canal and various CD structures by National Test House, Kolkata and drilling works for Geo-technical investigations carried by Pioneer Surveyors, Kolkata. The socio- economic and environmental & ecological impact assessment carried out by IRG Systems South Asia Pvt. Ltd. New Delhi.

Cross Drainage structures The link canal crosses a number of streams, roads, railway lines etc. on its way. Suitable structures are proposed at these crossings. Level crossings (Barrages) are proposed at Raidai, Torsa and . The total numbers of cross drainage structures in Alternative-I, Alternative-II and Alternative-III are 205, 205 and 136 respectively.

Hydrology Water availability and Diversion at Manas Barrage The catchment area of the Manas sub-basin up to the proposed Manas barrage is 30049 sq km. The yield at proposed Manas barrage is computed considering the observed flow data of Mathanguri G&D site (Catchment Area 29424 sq km) are available for the period from 1955-56 to 1989-90, and observed flow data available at NH crossing (Manas + Beki) for period 1989-90 to 2015-16. The catchment area upto NH crossing is 31924 sq km. After considering the availability, import, export, regeneration and water needs in the basin the surface water balance at 75% and 50% dependabilities assessed to 24343 MCM and 27326 MCM respectively. Due to limitations of monthwise availability of water, it is proposed to divert 17513 MCM and 9970 MCM water to MSTG link in Alternative-I and Alternative-II respectively.

Water availability and Diversion at Sankosh Barrage The catchment area of the Sankosh sub-basin up to the proposed barrage where MSTG link crosses is 9775 sq km. The yield of the sub-basin upto the MSTG link crossing is computed considering the observed flow data of Srirampur G&D site (Catchment Area 9925 sq km) available for the period from 1956-57 to 1991-92 and the observed flow data of LRP G&D site (Catchment Area 8230 sq km) available for period 1992-93 to 2015-16. After considering the availability, import, export, regeneration and water needs in the basin the surface water balance at 75% and 50% dependabilities assessed to 12798 MCM and 14497 MCM respectively.

As per simulation study carried out in DPR of Sankosh HEP-2012 by THDC, a quantum of 13405 MCM water is available as regulated releases and spills from Sankosh dam. This study has been considered for firming up the water diversion to MSTG link from Sankosh barrage. After considering 2224 MCM as environmental and ecological needs, 11181 MCM of water is available for diversion through the MSTG link as per the link requirement.

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Contribution from Intermediate rivers i) Aie river: The catchment area of the Aie sub-basin up to the MSTG link crossing is 1753 sq km. The yields of the sub-basin upto the MSTG link crossing is computed considering the observed flow data of Railway Bridge crossing G&D site (Catchment Area 1831 sq km) are available for the period from 1973-74 to 2005-06. After considering the availability, import, export, regeneration and water needs in the basin the surface water balance at 75% and 50% dependabilities assessed to 2495 MCM and 3151 MCM respectively out of which 1448 MCM and 1446 MCM water is proposed to be contributed to link canal in Alternative-I & Alternative-II respectively. No contribution in Alternative-III is possible as Aie river crosses in Manas-Sankosh reach. ii) Raidak River: The catchment area of the Raidak sub-basin up to the MSTG link crossing is 4836 sq km and the G&D site. The yields of the sub-basin upto the MSTG link crossing is computed considering the observed flow data of Railway Bridge crossing G&D site at Barabisa available for the period from 1978-79 to 2007-08. After considering the availability, import, export, regeneration and water needs in the basin the surface water balance at 75% and 50% dependabilities assessed to 3866 MCM and 4650 MCM respectively. 3866 MCM is proposed as contribution to MSTG link project. iii) The catchment area of the Torsa sub-basin upto the MSTG link crossing is 4005 sq km. The yields of the sub-basin upto the MSTG link crossing is computed considering the observed flow data of Torsa river at Hasimara G&D site (Catchment Area 3920 sq km) available for the period of 1978-79 to 20105-16. After considering the availability, import, export, regeneration and water needs in the basin the surface water balance at 75% and 50% dependabilities assessed to 4679 MCM and 5306 MCM respectively, 4679 MCM is proposed as contribution to MSTG link project. iv) Jaldhaka river The catchment area of the Jaldhaka sub-basin up to the MSTG link crossing is 1501 sq km. The yields of the sub-basin upto the MSTG link corssing is computed considering the observed flow data of the at NH 31 crossing G&D site (Catchment Area 1530 sqkm) are available for the period from 1978-79 to 2015-16. After considering the availability, import, export, regeneration and water needs in the absin the surface water balance at 75% and 50% dependabilities assessed to 4041 MCM and 4775 MCM respectively. 4041 MCM is proposed as contribution to MSTG link project.

The monthwise water dieversion is proposed keepkgn in view of monthwise water availability and monthwise proposed demands. The link project is proposed to meet enroute demands of link and balance water will cater demands of dependent link ie Farakka-Sunderban link, Ganga (Farakka)-Damodar-Subarnarekha link and Subarnarekha-Mahanadi link. After meeting demands of these dependent links, balance water if any will be diverted to southward through Mahanadi-Godavari link to meet water demands in water scarce areas in southern .

The 75% dependable yield and proposed water diversion at able diversion sites is summarized below:

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Sl. Diversion site/river 75% dep. Proposed Water Diversion (MCM) No. yield (MCM) Alt-I Alt-II Alt-III 1 Manas 29850 17513 9970 0 2 Sankosh 15489 10421 10422 10497 3 Aie 3131 1448 1446 0 4 Raidak 4907 3866 3866 3866 5 Torsa 5853 4679 4679 4679 6 Jaldhaka 5093 4041 4041 4041 Total 41968 34424 23083

Ground Water A wide diversity in ground water conditions in the project area has been noticed. The districtwise assessment of ground water potential in the

Sl. State / Total replenishable Total draft Balance ground water No. District ground water available for exploitation (ham) A Assam 1 Barpeta 13610 3066 10544 2 89942 32758 57184 3 Kokarajhar 33637 1941 31697 4 Dhubri 66493 27735 38758 B West Bengal 1 Kooch Bihar 67023 13228 53795 2 Jalpaigrui 23735 382 22753 C Bihar 1 Katihar 16891 10139 6752

Irrigation & water use The MSTG link canal will provide enroute irrigation to an area of 3,40,519 h utilizing 3133 MCM water for Alternative – I & II and 1,47,125 ha utilizing 1327 MCM for Alternative –III. Considering 100% irrigation intensity lying in the districts of Bongaigaon, Dhubri, , Barpeta of Assam, Koch Bihar, Jalpaiguri of West Bengal and Katihar of Bihar State. Also a major indirect benefit of the project is to save Kokata port by providing water through Farakka-Sunderban link. The transmission losses worked out to 922 MCM, 725 MCM and 443 MCM for Alternative-I, Alternative-II and Alternative- III respectively.

Power Requirement 7 lifts in Alternative-I & II and 6 lifts in Alternative-III are proposed at different locations to lift the water to higher elevation in order to out fall into the existing Tista barrage which is at higher elevation than the off-take point at Manas river. Details are given in table below:

Sl. R.D. Lift Alternative-I Alternative-II Alternative-III No. (km) (m) Installed Annual Installed Annual Installed Annual capacity energy capacity energy capacity energy (MW) req.(MU) (MW) req.(MU) (MW) req.(MU) 1 104.950 10 217 914 119 558 - - 2 171.900 12 302 1717 301 1288 213 790 5

3 199.800 22 597 3275 595 2569 497 1689 4 229.100 13 381 2092 379 1638 319 1079 5 249.850 12 427 2188 425 1761 360 1242 6 259.850 7 286 1464 284 1177 242 835 7 269.300 6 258 1321 256 1061 219 754 Total 12971 10052 6389

Construction schedule: The schedule for construction of the link project is planned for a period of 8 years.

Cost Estimate The total cost of the link canal project for all three Alternative at 2019-20 price level are given in table below:

Cost (Rs. Crore) Alternative-I Alternative-II Alternative-III Head works 984.58 984.58 545.54 Canal 36998.84 33306.51 24056.92 Lifts 21239.53 20405.52 15878.16 Total 59222.95 54696.61 40480.62

Cost Proportioning to the MSTG link & B.C. Ratio The cost for all three Alternative works out in proportion of utilization of water in Manas- Sankosh-Tista-Ganga link and augmentation to Ganga. The benefit cost ratio and Internal rate of return of the project is worked out on the basis of apportioned cost benefits. The details are furnished in table below:-

Sl. Particulars Alternative-I Alternative-II Alternative-III No. 1 Proposed Water use in MCM 3133 3133 1327 2 Transmission losses in MCM 70 67 26 Total water use in MCM 3203 3200 1353 3 Augmentation to Ganga including TL 38765 31224 21730 in MCM 4 Total water diversion in MCM 41968 34424 23083 5 Total cost of project (Rs. Crore) 73072.24 58101.80 43885.82 (including 20% cost of Manas & Sankosh dam) 6 Share of cost of MSTG link according 5576.88 5401.06 2572.29 water use (Rs. Crore) 7 Annual benefits (Rs. Crore) 2787 2787 1216 8 Annual cost (Rs. Crore) 1378 1338 593 9 Benefit-Cost ratio 2.02 2.08 2.05 10 Internal rate of return 15.28% 15.60 14.70

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MANAS-SANKOSH-TISTA-GANGA LINK PROJECT INDEX MAP

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