Project Location and Accessibility

Jomori hydropower project (HPP) is a pure run-off the river scheme planned across Jomori, and it is planned and designed as standalone project. The Jomori HPP lies in extreme South-East of Bhutan and is spread over two Gewogs under Jomotsangkha Dungkhag under Samdrup Jongkhar Dzongkhag. The dam complex falls in Lauri Gewog and the powerhouse complex under Serthi Gewog.

Field Investigations

The topographical map and river cross sections of the project area of requisite scale had been prepared to enable proper planning, engineering and design works. Total of 12 ground control points had been established to facilitate survey works. The topographical survey covering the whole project area in a scale of 1:5,000 with 5 m control interval and 1:1,000 scale with 1 m contour interval for major project components had been prepared. The longitudinal profiling and cross section survey of the river in requisite scale had been surveyed and drawings prepared.

Project Layout & Features

The project layout has been proposed on the left bank of Jomori. It envisages a design discharge of 28.66 cumecs, net head of 359 m and corresponding installed capacity of 90 MW. 

The civil structure includes, the temporary river diversion arrangement which includes a 6.0 m x 6.0 m D-shaped, 330 m long diversion tunnel and cofferdams, 15 m and 9 m high, upstream and downstream. A 45 m high concrete gravity dam with a 79.9 m crest length features 3 overflow and 3 non-overflow blocks. It has three radial spillway gates (8 m x 11 m) to discharge 3,099 cumecs, and a high-level spillway (8 m x 7 m) for debris. The design includes two power intakes with trash racks and a cleaning machine. Feeder tunnels (3.5 m diameter, 148 m long) connect to two underground desilting chambers (138 m long, 8 m wide) to filter sediment over 0.20 mm. The headrace tunnel (HRT) has a 4.1 m diameter and 6,355 m length, aided by construction adits. A 10 m diameter, 68.9 m high surge shaft connects to a steel-lined pressure shaft (2.8 m diameter) leading to two-unit penstocks. The surface powerhouse measures 42.0 m x 25.5 m x 27.0 m, and tail race channels (3.0 m x 2.5 m, 35 m long) discharge at elevation 772.6 m. 

The hydro-mechanical components includes a fixed wheel gate (6.0 m x 6.0 m) at the inlet of each diversion tunnel and three radial spillway gates (8.0 m x 11.0 m) with hydraulic hoists for the main spillway. A high-level spillway is equipped with a vertical lift gate (8.0 m x 7.0 m) and a hydraulic hoist. The dam's main spillways have five-panel slide-type stoplogs (8.0 m x 11.0 m) operated by an electrically powered gantry crane. Each intake structure has four trash rack bays (2.5 m x 5.0 m) with a trash rack cleaning machine. Two intake emergency gates and two intake service gates (3.5 m x 3.5 m) are equipped with hydraulic hoists, as is the fixed wheel gate (3.5 m x 3.5 m) at the desilting chamber outlet. The silt flushing duct has four bonnet-type slide gates (1.0 m x 1.5 m), while two slide gates (3.0 m x 3.5 m) with monorail hoists are installed for the unit tail race channel. A hinge-type gate (3.0 m x 3.0 m) is also provided for Adit 1 for inspection and future use. 

The powerhouse has been designed to house two vertical shaft Pelton turbines having rated output of 2x45 MW under a design head of 359 m at 375 rpm synchronous speed. Each turbine shall be provided with spherical type main inlet valve. The generators shall be synchronous and of the vertical shaft type of 53 MVA rated power at 0.9 power factor and 50 Hz frequency. The generators shall have a speed of 375 rpm and generator voltage of 11 kV. With an installed capacity of 90 MW, it is expected to generate 367.33 GWh of energy annually which will provide stable back-up power supply system to facilitate self-contained supply flexibility for Samdrup Jongkhar Dzongkhag and also to create economic activities at grass-roots level and help generate employment and engagement of the people.

Project Contract

The access road construction, Site-I (Phokchiri to Zamtari) & Site III (Tshanglari to Woongthi) was awarded to M/s Chimi RD on October 18, 2023.

The access road construction, Site-II (Zamtari to Tshanglari) was awarded to M/s Rigsar  Construction Private Limited on October 18, 2023.