Layout

Structures of the Kohala Hydropower Project can be separated into three categories; headworks, waterway system for power generation, and powerhouse. The headworks will mainly include the dam, ecological flow hydropower station and permanent camp at the dam sitedam site. The waterway system for power generation includes the water intake, headrace tunnel, surge shaft, penstock and associated structures. The powerhouse system includes the surface powerhouse, tailrace, switchyard, permanent camps at the powerhouse area and associated infrastructure.

The dam will be a curved concrete gravity dam, with a crest elevation of 910m, a maximum height of 69m and a top length of 270m.

The water inlets will be bank-tower independent inlets, consisting of two independent intake tower sections arranged side by side. Their invert and top elevations will be 882.00 m and 911.20 m respectively resulting in an intake height of 32.7 m.

The two headrace tunnels will be parallel to each other with a 45 m distance between centers; each tunnel will have an 8.5 m diameter, 17.4 km length and 425 m3/s total design diversion flow.

The main powerhouse will be 144 m long, 31.5 m wide at upper part, and 49.5 m wide at lower part; the turbine setting elevation will be 573.5 m. The auxiliary powerhouse, which will be a 4-story frame structure, will be located at left side of the main powerhouse.  The tailrace will be 53.9 m long and 96 m wide at its base, and its invert elevation will be 578.5 m at the outlet.

The booster station is located upstream of the main powerhouse and is a three-story frame structure, with a length of 144m and a width of 17m. The first story is for the main transformer chamber where 4 main transformers are furnished; the second story is for GIS pipes and the third story is for the GIS equipment. Outgoing line equipment will be arranged on the artificially excavated platform upstream of the main powerhouse. The platform elevation will be 617.5m. The outgoing line platform will be a "convex" shape. The plane dimension of the downstream rectangular site will be 196.0 m x 22.25 m and that of the upstream rectangular site will be 87.0 m x 29.25 m.

The permanent camp at the powerhouse area will be located on the hilly terrace on the right bank of the north gully.

With 1100 MW of installed capacity, the main hydropower station will be equipped with 4 vertical Francis turbine generator units, each with a capacity of 275 MW, a rated head of 292 m and a diversion discharge of 106.25 m3/s. Its annual output will be 5.079 billion kWh. The installed capacity of the ecological flow hydropower station will be 18 MW (2 x 9 MW), the diversion discharge of each unit will be 22.5 m3/s, and the average annual energy generation for the station will be 95 million kWh.

There will be a total installed capacity of 1118 MW and total annual power generation of 5.174 billion kWh by this project.