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 Manas river. 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 Sankosh river 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-Bhutan 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 Mahananda river 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 Assam, 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 Jaldhaka river. 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.