Table of Contents 1. INTRODUCTION Tinekhu Khola Small Hydropower Project (TKSHP) with an Installed Capacity of 990 kW utilizes flow from Tinekhu Khola which is located at Suri and Jhyaku VDC’s of Dolakha District, Janakpur zone in Eastern Development Region of Nepal. Tinekhu Khola Small Hydropower Project (The Project) is Run off River (ROR) type with its headworks located in Tinekhu River at some 3 km upstream from the confluence of Tamakoshi River and Tinekhu River. The distance to the intake site from Singati Bazaar is about 6 km north-east.
The powerhouse is located along the left bank of Tamakoshi River, ome 100 m upstream from the confluence of Tamakoshi River with Tinekhu River. There is a bridge over Tamakoshi River near powerhouse and a seasonal road up to the forebay area. The entire project area (headworks to powerhouse) is located in Suri and Jhakhu VDC’s of Dolakha District along the right bank of Tinekhu River. Geographically, the project area is located between the longitudes 86010’45″E to 86012’06″E and latitude 27044’07″N to 27045’1 5″N.
Physio-graphically, the project area belongs to the Middle Mountain Zone and elevation ranges from 980 meter above mean sea level (amsl) to 1400 m amsl along the upper catchment boundary. According to the hydrological study, the design discharge of 0. 35 m3/s is about 57% exceedence river flow. Thus with a gross head of 412 m and net head of 392. 01 m and 0. 35 m3/s design flow at 74. 5% efficiency the installed capacity will be 990 KW. The net annual energy generation at delivery point (i. e. , substation at Singati) is expected to be about 6. 60 GWh. The dry season energy is 1. 71 GWh and wet season energy is 4. 890 GWh.
The total project development cost is 193 Million NPR including Interest During Construction (‘DC) and the construction period is estimated to be 23 months. Power Purchase Agreement (PPA) has been made on 8th Aswin 2069. The land acquisition on the project site has already been completed. 2. General arrangement and description 2. 1 General arrangement of the Project The general arrangement of the project includes headworks, water conveyance arrangement and powerhouse on the left bank of the Tamakoshi River. The major headworks structures are the over-flow diversion weir, a side intake, gravel trap and settling basin.
A gravel excluding arrangement is provisioned to flush-out the bed- load that would enter through the intake orifices during the high flow seasons. From the gravel trap, water is diverted into a settling basin where the suspended an internal diameter of 400mm conveys the flow from the settling basin to the forebay. Then a 759. 54 m long and 450 mm diameter steel penstock pipe conveys the design discharge to generating units inside the powerhouse. The tailwater will be discharged to Tamakoshi River through a 54. 35 m tailrace culvert. The generated power will be evacuated through 11 kV,3 km long transmission line to the substation at Singati.
Figure : General Project Layout 2. 2 Headworks The headworks of the TKSHP comprise of 2. 6 m high and 17. 0 m long free flow permanent weir. A side intake is provided adjacent to the diversion weir along the right bank. The intake is furnished with two orifices opening sufficient to abstract design discharge of 350 Ips along with the flushing discharge required for gravel trap and settling basin. The intake canal conveys the diverted flow into the gravel trap where the bed load that entered through the intake orifice opening will be settled and flushed back to the River downstream through gravel flushing.
The approach canal of size 0. 8 m wide and 0. 8 m high conveys the flow from gravel trap to the ettling basin. Two chambered settling basin is proposed to settle the particle size up to 0. 2 mm. The flow from the settling basin will then be conveyed to the forebay through 2046. 0m headrace pipe. The detail description of components is explained hereunder. Weir An overflow diversion weir of length 17. 5 m is proposed across the River. The proposed weir comprises of permanent structure constructed with concrete. The crest level of the weir is fixed at an elevation of 1398. 60 meter above mean sea level (amsl).
At the upstream and downstream of the weir, numerous big boulders are ested which can also be utilised as an upstream and downstream apron with plum concrete infill. Intake A side intake is proposed along the right bank of Tinekhu Khola adjacent to the proposed weir. The intake is furnished with two orifice openings each 0. 80 m wide and 1. 35 m high. The invert and sill level of the openings are fixed at an elevation 1397. 90 m amsl and 1399. 25 m amsl respectively. Two orifice openings towards the diversion weir are furnished with manually operated gate and operational.
These two openings are sufficient to withdrawal design discharge with the required flushing discharge. In order to provide impervious floor at the front of the intake, filling of plum concrete in the existing boulders is provisioned. This will also prevent scouring and seepage at the intake area. Intake canal and Gravel trap A 14. 10 m long, 0. 8 m wide and 0. 8 m high intake canal conveys the flow to the gravel trap. The gravel trap is designed as a single chamber with hopper bottom. The gravel trap is 3. 0 m long, 1. 5 m wide and 2. 8 m high.
The gravel deposited in the gravel trap is discharged back to the River through the flushing culvert of 5. 60 m long with settle the particle size of 5 mm. The longitudinal slope of 1 in 40 is provided in the gravel flushing canal. The base and certain height of the gravel trap are lined with dressed hard stone masonry to prevent from wear and tear due to the bed load and the inner side walls are lined with 16mm thick steel plate. The flushing canal is furnished with a stoplog and a manually operated gate to ease the flow regulation during operation of the plant and to flush out the excess the bed load entered into the gravel trap.
During the time of maintenance of gate, Stoplog will be used.. A coarse trash rack of 1. 5 m wide and 1. 0 m high with 1:6 (H:V) slope is provided at the ntrance of the approach canal to prevent the passing of floating debris into the settling basin. The gravel trap is provided with 5. 0 m long spillway at the River side wall to spill the excess water that enters into the intake during high flow season. The crest level of spillway is fixed at 1398. 60 m amsl. The normal water level at the gravel trap for the designed discharge will be 1398. 85 m amsl and the adopted wall level is 1399. 75 m amsl.
Approach Canal and Settling Basin A 23. 30 m long, 0. 8 m wide and 0. 8 m high approach canal conveys the gravel free water into the settling basin. At the end of approach canal or at the entrance of the settling basin a spillway is provided and is 2. 0 m long which controls the flow (allow to enter allocated flow into the basin) that entered into the basin. The crest level of the spillway is fixed at elevation of 1398. 40 m amsl. At the entrance, one manually operated gate is also provided for the repair and maintenance of the basin. The settling basin is designed to settle a particle of 0. 0 mm size with 90% efficiency. The basin is divided into two chambers each 1. 5 metre wide. The length of inlet transition is 7. 56 metre. The transition is in the slope of 1:5. (100 ) from the channel. The effective length of the basin is 16. 0 m and the average height 2. 96 m. Two flushing culvert of size 0. 50 m wide and 0. 50 m height is provided at the end of basin for flushing purpose. Each flushing contains two nos. of gate (a stoplog and a manually operated gate) for operation and repair purpose. Backfilling at certain height is done at the hillside wall of the basin for structural safety.
Surface and sub-surface drainage is also provided in the hill side backfilling of the basin. Conveyance Tank The tank is designed to store the discharge and to convey the flow to the headrace ipe with sufficient submergence. A spillway of length 3. 0 m with the elevation fixed at 1398. 77 m amsl will discharge back the excess flow back to the River. A 2. 0 m long, 3. 5 m wide and 2. 32 m high canal conveys the flow to the forebay. Headrace Pipe Two number of 2058. 73 m long, 400 mm diameter High Density Polyethylene Pipe (HDPE) along the right bank has been proposed to convey the flow from the conveyance tank to the forebay.
The fine trash rack has been placed at the entrance of headrace pipe to prevent from entering of trashes into the forebay. The pipe is buried at minimum of 1. m from the ground throughout the section. Altogether 43 numbers of anchor blocks are provisioned at the bends of the headrace pipe. At Kholsi and gulley crossings, concrete casing and drainage system has been provisioned to protect the pipe from washed away and erosion. C25 with 40% plum concrete has been recommended for anchor blocks and Cl 5 concrete for blinding at At the end of the headrace pipe, forebay is provisioned and is located on cultivated land with an elevation of 1384. 4 m amsl. The forebay is 4. 0 m long, 3. 5 m wide and 4. 0 m high, sufficient to provide required submergence to the penstock pipe. The top of the forebay is closed by concrete slab and a manhole is provided at the top. It is also furnished with a 52. 85 m long surge pipe (steel pipe) to receive the excess water during up-surge and also the air vent has been provided to outflow the entrapped air inside the forebay. A fine trash rack is provided at the entrance of the penstock pipe to prevent from entering of trash. Penstock pipe and anchor blocks A 759. 4 m long and 450 mm internal diameter steel pipe conveys the flow from the forebay to the generating units inside the powerhouse. Thickness of the pipe varies from 8 mm to 32 mm. At 759. 4 m, the pipe bifurcates into two from where flow is distributed. Each bifurcated pipe is 320 mm in diameter, 25 mm thick and 13. 68 m in length. Altogether 16 number of anchor blocks are provisioned throughout the pipe alignment at various bends (horizontal, vertical and combined bends) along with 107 numbers of intermediate saddle support. Saddle support is placed at the spacing of 7 m interval.
Powerhouse / Tailrace Powerhouse is located on the left bank of Tamakoshi River some 100 m upstream from the confluence of Tinekhu Khola and Tamakoshi River. Powerhouse comprises two horizontal axis pelton turbine units. Two sets of Generators will be installed with the same horizontal axis of the turbine inside the powerhouse. Other electromechanical accessories such as unit control panel and excitation panel will be placed on the side the generator. The centre line of Pelton wheel is set at the elevation 985. 61 m amsl. The preliminary sizing of the powerhouse is 16. 5 m long, 8. metre wide and 12 metre height from foundation level. Control room area, maintenance room are suitably arranged inside the powerhouse. The flows from the generating units are discharged to the Tamakoshi through 54. 35 m m long, 0. 8 m wide and 0. m high tailrace. The longitudinal slope of the tailrace is fixed at 1 in 100. The powerhouse and the tailrace canal are suitable located to prevent from flash flood. Furthermore, boulder lining and gabion boxes are also provided along the left bank of Tamakoshi in the powerhouse and tailrace area. The sill level of the tailrace at the outlet is fixed at the elevation of 982. 9 m amsl. Transmission Line The nearest connection point of TKSHP will be at the Singati substation which is under construction by NEA. The length of the transmission line is approximately 3 km. 3. Project Evaluation 3. 1 Cost and energy The total project development cost is 193 Million NPR including Interest During Construction (‘DC) and the construction period is estimated to be 23 months. The estimated construction period is adequate for this size of project. The total project cost includes all costs including physical contingencies and engineering management and project administration cost.
The installed capacity of the Project is 990 KW. The net annual energy generation at delivery point (i. e. , substation at Singati) is expected to be about 6. 60 GWh. The dry season energy is 1. 71 GWh and wet season energy is 4. 890 GWh. 3. 2 Financial Evaluation The financial evaluation has been performed using the discounting techniques and Discount rate Evaluation period 30 years Long term average annual inflation 5% Debt/Equity ratio 70:30 Interest on Bank loan p. a. Loan tenure/repayment 12 years/10 years from operation Energy tariff 8. 40 NPR/kWh for dry season energy and 4. 0/ NPR/kWh for wet season energy The base case analysis has been performed for the total capital costs including financing costs (IDC at the rate of 12 % interest on Bank loan during the construction period). The 10 years (ten years from commercial operation) repayment period is considered in this base case analysis. The base case analysis shows that the plant yields a Net Present Value of around 113 Million NPR, an internal rate of return of 17. 27%, return on equity 23. 27% and benefit cost ratio 1. 53 which can be seen in Error: Reference source not found.
Table : Results of base case analysis Total Capital Equity Investment NPV IRR B/C-rati0 ROE 113 17. 27% 1. 53 23. 27% 1. 1 Sensitivity test Sensitivity test has been performed to foresee the bottom line investment of the project with respect to increase in costs and decrease in generation. The test has been performed for the different variations of the cost and energy generation to redict the viability of the project. The most likely combination of the sensitivity parameters has been considered as follows: Energy generation 95% and costs cost variation (increase) by 10%. The results of this analysis have been presented in Table 2.
Table : Results of most likely case evaluation 75 14. 56% 1. 32 64. 97 19. 20% It can be seen from the Table 2 above that the return on equity (FIRR) is 19. 2% and the IRR of the total investment is 14. 56%. This demonstrates that the Project is financially very attractive. 4. CONCLUSIONS AND RECOMMENDATIONS 1. 2 Conclusions The following conclusions are made based on the detail study: 1 . Tinekhu Khola Small Hydropower Project is technically and financially feasible if connected to the INPS system under a PPA with NEA at standard buy back rates for small hydropower plants. 2.
Installed capacity and energy: The installed capacity of the plant is 990 KW (2 x 495 KW) with a design discharge of 0. 35 m3/s and gross head of 412 m. The gross energy production is 7. 48 GWh (Dry Season energy 1. 71 GWh and wet Season energy 4. 89 GWh or 6. 60 GWh/annum net energy at delivery point). The overall plant factor is expected to be around 76%. 3. Financial viability: Both base case and most likely case nalysis have been performed for this project. Base case analysis has been performed for the total capital cost including IDC with the interest of 12 % and 10 years repayment period.
This result into a rate of return of 17. 61% on total capital with a return on equity of 22. 76%. The most likely case analysis has been performed assuming 10 % increase in capital cost and revenue loss by 5%. The results of this analysis still possesses good parameters for investment, i. e. return on equity of around 19. 2% (higher that the expected return of 16%) and the return on total capital as high as 14. 56%. 4. The Initial Environmental Examination (IEE) is not mandatory by law for this 990 kW TKSHP however, preliminary assessment shows that the environmental and social impacts are low as other low flow run-of-River projects. . The headworks diversion structures are designed for 100 year flood with 95% confidence limit with some free board. Minor damages are expected during these floods but the structures are expected to be intact. 6. Tinekhu River is an ungauge river, hence no flow data are available. Therefore, flow measurement at the proposed intake should be carried out in the dry seasons to refine the flow hydrology. 7. About km long, 11 W transmission line will be required from the project powerhouse to the Singati Sub-station for connection to the INPS. . A construction period of 23 months has been considered. 1. 3 Recommendations Based on the findings of this detail study, the project is recommended for implementation. a. i. l . The proposed settling basin and the powerhouse will be founded on the alluvial deposit, hence the bearing capacity of the soil in these areas need to be confirmed prior to the construction. a. i. 2. Tinekhu River being an increase the confidence level in the hydrological study and energy generation estimates. Appendix-I