Kaligandaki Tinau Diversion Multipurpose Project

10 months ago

Kaligandaki Tinau Diversion Multipurpose Project, located in Palpa, Syangja and Rupandehi districts, is a multipurpose project with primary aim of irrigating the cultivated areas of Rupandehi and Kapilvastu Districts in Lumbini Province by diverting water from Kaligandaki River into Tinau River. The hydropower development along the diversion route is a secondary product of this project.

Location of Project area

The command area is classified as Eastern and Western Command Area taking Tinau River as reference. The proposed project boundary is located between latitude and longitude of 27° 41’ 33”to 27° 54’ 28” N and 83° 25’ 54'' to 83° 39’ 35” E respectively. A barrage 2200m downstream from the existing Ramdi Bridge and intake on the right bank of Kaligandaki River along with surface settling basin was proposed in DFSR. From the settling basin a 22.5 km long and 9 m dia. Inverted D HRT was proposed upto the surge shaft in Dovan Gaun. The diameter of the proposed surge shaft was 20 m and the height of surge shaft was 65 m. After the surge shaft a 450 m long penstock pipe of 6.4 m dia steel was proposed upto the Powerhouse. Two sets of surface Powerhouses were proposed with the tailrace tapping option. The first Powerhouse was proposed on the left bank of Dovan Khola in Dovan Gaun whereas the second Powerhouse was proposed in Belbas. The two Powerhouse options also enabled the supply of irrigation water to the Eastern Command Area and Western Command Area from Powerhouse-1 and Powerhouse-2.

Hydrology and Sedimentology

Kaligandaki River is one of the major catchments of Narayani River basin. The catchment area at the barrage axis in Ramdi is 10,486 km2. About 20% of this catchment lies above 5000 masl, which is considered to be in permanent snow line. Similarly, the catchment area of Tinau River in Dovan is 164.6 km2, all of which lies below 3000 masl. Kaligandaki River is a gauged catchment, hence the discharge in the intake area at Ramdi was derived using CAR with Kaligandaki Gauging station in Ansing. The 1000 years flood flow at intake was found to be 10,347.5 m3/s. 10% of the minimum monthly flow (8.06 m3/s) will be released as the downstream flow as per the Environmental Regulation Guideline of Nepal from the barrage area in Ramdi. The Kaligandaki River has a religious value at Devghat. The downstream release from the barrage axis and the intermediate catchment discharge between Ramdi and Devghat will be 18.54 m3/s in the driest month in March. For the rest of the year, the Discharge available in Devghat will be more than 18.54 m3/s. Further need of the downstream release requirement and the sufficiency of the proposed release should be confirmed with an EIA study in the next stage of study.

The maximum sediment concentration in the intake site is 82,399 ppm, which indicates huge sediment deposition in monsoon months in the Barrage area. The mineralogical analysis shows the maximum amount of quartz in the sediment. Hence, settling basins in the headworks is inevitable for reducing the wear and tear in turbines and also to reduce the sediment deposition in the irrigation canal.

Impacts Downstream of KTDMP Intake

1.Local Irrigation: 10 m3/s is constantly released for local irrigation in the downstream stretches

Assumption:

Local settlements along the Kaligandaki banks are already provided with water supply services

Irrigation demand is not as high as in Terai settlements due to terrace-farming and availability of less farming area

Private or community constructed canals are rare due to flat nature of Kaligandaki river, as canals will have relatively longer lengths to convey water from upstream

Hence, 10 m3/s flow may suffice for local irrigation

2.Religious Values: Additional 10 m3/s is constantly released as religious demand for Devghat in non-peaking hours.

3.Ecological Demand: 20 m3/s is constantly allowed in the downstream from KTDMP intake. Minimum ecological demand governed by policies is 8.06 m3/s. Ecological flow demand will always be met if 20 m3/s will be released downstream all year round.

Irrigation Studies 

The command area has been taken as the land area below 170 masl in Rupandehi and Kapilvastu districts. The command area covers 12 Municipalities and RMs in Rupandehi and 10 Municipalities and RMs in Kapilvastu district. The Gross Command Area of Rupandehi and Kapilvastu Districts are 89,150 ha and 87,044 ha respectively. The Eastern Command Area lies completely in Rupandehi District, East of Tinau River in Butwal and also covers 3 kms West of Tinau River. The Western Command Area covers Rupandehi and Kapilvastu District, 3 kms west of Tinau River. The net command area is 24,191 ha and 13,534 ha in dry season and wet season for Eastern Command Area. Similarly, the net command area is 74,410 ha and 61,834 ha in dry season and wet season for Western Command Area respectively. The water in the Eastern Command Area will be facilitated through Tinau River. During the high flow in Tinau, water will be drawn directly from Tinau River. During the low flow in Tinau River, the discharge required for irrigation will be released from tailwater in Dovan. The remaining discharge will be conveyed to Western Command Area from Powerhouse-1. Main food crops are paddy, maize and wheat for the cropping pattern for both of the command areas. Main cash crops are potato and vegetables due to higher return of yield and less water requirement respectively.The optimum design discharge for the diversion has been calculated as 82 m3/s considering the water availability in Kaligandaki and Tinau River. The project has been designed to withdraw an additional 10% discharge from Kaligandaki River by operating the turbine at COL if there is insufficient discharge in the Western Command Area.

Geology 

The Project area lies partly in the rocks of the Lesser Himalaya and partly in the rocks of the Siwaliks, Central-West Nepal. The area is mainly composed of intercalation of phyllite, quartzite, diamictite, slate, conglomerate and dolomite of the Lesser Himalayan rocks, sandstone, mudstone and conglomerates of the Siwaliks.

The project area crosses the major thrust of the Himalaya like the Central Churia Thrust (CCT), Main Boundary Thrust (MBT), and other thrust like the Klippe Thrust (KT) as well as Ramdi Fault from south to north direction.

The proposed barrage axis is located 2.2 km downstream from the Ramdi Bridge along the Siddhartha Highway at Ramdighat Bazaar (Pipaldanda). Geologically, the barrage, intake and settling basin is located on northern limb of the Anticline formed on the fine-grained, grey to milky white, thin bedded quartzite intercalated with the greenish grey shale rocks of the Saidi Khola Formation of the Kaligandaki Supergroup. Geo-physical investigation done on both banks of the river shows bedrock on the left bank and sand dominant alluvium on the right bank whereas, the settling basin lies on the alluvium cultivated river terrace which consist of gravel and cobble of slate and quartzite. 

HRT-1 passes through the rock of Kaligandaki Supergroup Formation which are (Saidi Khola Formation, Ramdighat Formation, Chappani Formation, Khoraidi Formation), and through Tansen Group Formations which are (Sisne Formation, Taltung Fromation and Amile Formation) and again repetition of Tansen Group and Kaligandaki Supergroup Formation as Kerabari and finally passes out through Siwalik Group Formation which are Middle Siwalik and Lower Siwalik Formation. The repetition of the formations is due to the Tansen Synclorium. Along this headrace tunnel, Shale, Slate, Quartzite, Dolomite, Limestone, Phyllite, Mudstone and Sandstone rock are encountered in the tunnel. Few weak zones such as Ramdighat Thrust, Klippe Thrust (KT), Tansen Synclorium and Main Boundary Thrust (MBT) are encountered along the tunnel alignment. Similarly, HRT-2 passes through the rock of Siwalik Group Formation which are Middle Siwalik and Lower Siwalik Formation. Along this headrace tunnel, Mudstone and Sandstone rock are encountered in the tunnel. 

The surge shaft-1 area lies geologically on the rocks of the Middle Siwalik, Siwalik Group. But, superficially thin to thick layers colluvial and alluvial deposits have covered the proposed surgeshaft-1 area. The shaft area shows the presence of Central Churia Thrust (CCT) near the outlet portal where the older fine grained middle siwalik rock lies structurally above the younger pebbly sandstone rock of the middle siwalik rock, whereas, surge shaft-2 lies in the rocks of the Lower Siwalik Formation, Siwalik Group on the gentle slope surface at Prabas. 

Powerhouse-1 area lies on the rocks of the Middle Siwalik. Superficially, thick old alluvial and residual soil deposits have covered the flat river terrace on the bedrocks and thick colluvial and alluvial deposits are seen on the slope also. Huge Excavation is required to reach the foundation level of the Powerhouse on the river alluvium terrace which required well slope stability measures. Powerhouse-2 lies on the rocks of the Lower Siwalik. Superficially, thin old alluvial and residual soil deposits have covered the stream terrace on the bedrocks and thin colluvial and alluvial deposits are seen on the slope. 

Project Layout 

The project is designed as a RoR project with tailrace tapping modality. The diversion discharge from Kaligandaki in Ramdi will be carried for power generation up to Powerhouse-1 in Dovan. From Powerhouse-1, all the discharge will be diverted to Powerhouse-2, given that there are no irrigation demands in Eastern Command Area.  

The first powerplant consists of the barrage across Ramdi, side intake, surface settling basin, power culvert, inlet portal, HRT-1, surgeshaft-1 and horizontal chamber, outlet portal, valvehouse-1, penstock and anchor block, Powerhouse-1, tailwater collection pond and tailrace culvert-1. 

Similarly, the second powerplant consists of headpond and spillway, river crossing culvert, inlet portal, HRT-2, surgeshaft-2, outlet portal, valvehouse-2, penstock and anchor block-2, Powerhouse-2, tailwater collection pond-2 and tailrace canal-2. 

The headworks consists of 6 number of side intakes designed on the right bank of Kaligandaki River for diverting design discharge 82 m3/s plus 25% additional discharge for flushing. Of the 25% additional discharge, 15% will be used for flushing of settling basin and 10% will be used to operate the plant in Continuous overloading (COL) for irrigation purposes as per the requirement of irrigation and availability of water in the river. The intake sill is located 2 m below the Minimum Operation Level (MOL 393.00 masl) for submergence and to prevent the entry of floating particles and debris. 6 number of surface settling basins bays with two hoppers each with 130 m length and 15 m width have been designed on the right bank of Kaligandaki River in Ramdi.

From the settling basin the discharge will be conveyed through power culvert and then HRT-1. The HRT-1 is 26.603 km long concrete lined circular tunnel with 6.5 m finished diameter. At the design discharge, the velocity in HRT-1 will be 2.47 m/s however, during the COL, the velocity in the tunnel will be 2.72 m/s. The tunneling in HRT-1 is proposed to be carried out by using a TBM. Surge shaft-1 is provided to arrest the excessive surge generated during the sudden opening and closing of turbine units in Dovan. The proposed surge shaft is a simple surge shaft with 26 m diameter and 93.59m height. The discharge is conveyed from surge shaft-1 via 5.2 m dia doubly bifurcated and buried penstock pipe to Powerhouse-1. The valve house-1 lies along the penstock alignment.

Powerhouse-1 is designed as a surface Powerhouse and lies on the alluvial plain on the left bank of Dovan Khola and consists of 3 units of vertical axis Francis turbines with a positive setting of 0.37 m. Powerhouse-1 is 55 m long, 19.5 m wide and 40.2 m high. The turbine axis level is at 287.44 masl and the tailwater level at the draft tube outlet is 290.00 masl at design discharge. The discharge from Powerhouse-1 is collected to the tailwater collection pond to release either via tailrace culvert-1 or headpond. If there is irrigation demand in the Eastern Command Area, the water will be released via tailrace culvert. However, if there is no demand on the Eastern Command Area, all the discharge available in the tailwater collection pond will be diverted to the Powerhouse-2 via a headpond, river crossing culvert, HRT-2 and surface penstock. A side spillway is provided at the left wall of the headpond.  

HRT-2 is about 7,264 m long and 6.5 m dia circular tunnel. Tunnelling in HRT-2 will also be carried out by TBM due to the restrictions for construction of Adit tunnel. The tunnel will be lined by C35 concrete segments and the velocity of water in the tunnel will be 2.47 m/s at design discharge.

Surge shaft-2 is designed as a simple surge shaft with 25 m diameter and 96 m height with invert level at 246.59 masl on the gentle slope at Prabas to arrest the excessive surge generated during the sudden opening and closing of the units.

Powerhouse-2 is located just below a small hill on Belbas near the existing water tank on the hill side of the road connecting to the water tank from Belbas. The Powerhouse-2 consists of 3 units of vertical axis Francis turbines with a positive setting of 1.50 m. Powerhouse-2 is 57 m long, 19.5 m wide and 38.5 m high. The turbine axis level is at 177.28 masl and the tailwater level at the draft tube outlet is 179.80 masl at design discharge. Tailwater collection pond is provided at the downstream of Powerhouse-2 from where the discharge required by the Western Command Area will be supplied via Tailrace Canal-2. The excess discharge will be released to the nearby Dano River which will drain down to Tinau River in Butwal. 

Total power generated 

The installed capacity of Powerhouse-1 and Powerhouse-2 is 59.26 MW and 72.93 MW respectively. The total dry and wet season energy for Powerhouse-1 is 242.369 GWh and 243.317 GWh per year respectively. Total energy production from this Powerhouse-1 in Dovan is 485.686 GWh. Similarly, Powerhouse-2 has the total energy production of 599.449 GWh annually of which the dry season energy is 295.044 GWh and wet season energy is 304.406 GWh respectively. The total installed capacity of the project is 132.19 MW and the total annual energy generation is 1,084.11 GWh of which 537.41 GWh accounts for dry season energy and 546.70 GWh accounts for wet season energy. 

Power Evacuation

The generated power will be evacuated via a 5 km long 220 kV single circuit transmission line from both Powerhouse-1 and Powerhouse-2. This 5 km long transmission line from each powerhouse will combine at Sidhhababa. From Siddhababa the combined power will be evacuated via 26 km long double circuit 220 kV transmission line to New Butwal substation at Ramnagar. 

 Construction schedule

The project is scheduled to be completed in 10 years. Tunnelling in HRT-1 is the critical activity of the project. All the other construction activities are dependent on the construction of HRT-1. The tunnelling in HRT-1 and HRT-2 shall be accomplished by TBM. Same TBM can be used for both the tunnels to save the time and cost of the project. Similarly, the ancillaries required by both the tunnels could be shared to reduce the cost. 

After completing the tunnelling in HRT-1 and partly completing the tunneling in HRT-2, all the other civil works will begin. The civil works in headworks are planned to be completed in 4 seasons. River diversion will be carried out by constructing a diversion canal and a cofferdam for the first two seasons and by constructing a cofferdam in the third and fourth season. Similarly, the river diversion in Dovan will be carried out for one season only.

Cost of the Project 

The total cost of hydropower development including VAT and Tax is NPR 70,565,869,708. Of this cost, the civil work constitutes 60.40%, EM, HM and Transmission line constitutes 12.34% and other costs such as infrastructure development cost, general works, engineering management costs, tax and contingencies constitute the remaining 27% of the cost. The total cost of irrigation system development including VAT and TAX is NPR 74,009,565,484. Hence the collective cost of the project including Hydropower and Irrigation Development is 144,575 Million NPR.

Feasibility of the Project 

From the economic analysis, the BC ratio and IRR of the project was calculated as 2.12, 15.05%. 

From the financial analysis, the BC ratio and IRR of the project was calculated as 1.21, 12.60%. Similarly, the BC ratio and IRR on equity is 1.05 and 13.28%.

Due to the stronger economic indicators it is suggested that the water be diverted to the irrigation development in both Eastern and Western command area as far as possible.