The Erathna Mini Hydro Power Project is one of the run of river mini hydro power projects in Sri Lanka which has the install capacity of 10 MW. The project is located on the Kuru Ganga, a tributary of the Kalu Ganga (Black River).
Introduction
The developer of the project is Vallibel Power Erathna PLC and the project is developed on a build, own and operate basis. The intention of the company is to generate 40 GWh of green energy annually and to export it to the national electricity grid of the Ceylon Electricity Board which is the only authorised Institute for electricity transmission in Sri Lanka, controlling the all major functions of electricity generation, transmission, distribution and retailing in the country.
The project consists of weir, intake, headrace channel, sedimentation tank, forebay, penstock, powerhouse and transmission system.
Location
The catchment of this project is 14.5 km2 and the design flow is 2.7 m3/s. The catchment falls within the peak wilds and is considered a natural reserve. Topography surveys of the project area are available in sheet 68 – Nuwara Eliya which is on a scale of 1:50,000 by the Survey Department of Sri Lanka. Sheet 61/16, 1:10,000 is also used for the initial conceptual development of the project. The Geo Coordinates of the project activity is 6° 49’36” N, 80° 26’ 29” E.
Kuru Ganga leaves the peak wilderness sanctuary at an elevation of 1030 m AMSL and flows steeply westwards until it reaches the village of Adavikanda at an elevation of 400 m AMSL. Close to the pilgrim's rest called “Maha Ambalama” forms the “Manna-Kethi” falls from elevation 860 m to 840 m. Thereafter flows on steeply exposed bedrock to an elevation of 600 m. The riverbed below this level is covered with large boulders and banks with thick vegetation.
Project implementation
The project is owned and operated by Vallibel Power Erathna PLC, which is the largest public quoted mini hydropower company in Sri Lanka. 5 MW hydropower potential was identified at the aforesaid location at Erathna and a feasibility studying process was initiated under the name of Zyrex Power Company Erathna Limited. Then the ownership of the company was changed to Vallibel Group of Companies. Then the project capacity was enhanced up to 10 MW with the identification of the higher hydropower potential by the Vallibel Group. Later, the name of the company changed to Vallibel Power Erathna PLC.
The project developer, Vallibel Power Erathna PLC itself carried out the construction work. Some of the contracts were awarded to third parties on the basis of labour contracts. Project Management was done by the Vallibel group.
Construction of the power plant commenced in September 2001 with the traditional groundbreaking ceremony.
Access road
In order to facilitate the project and the other operational and maintenance purposes, a 3.5 km-long new access road was built from the powerhouse location to the forebay location. The access road starts from Adavikanda where the powerhouse is built-up. The endpoint is Warangala; the forebay location. By the construction of the access road, the requirement of accessing the weir, penstock path, forebay and channel was fulfilled. Since the path is along the part of a highland complex of the country and 3.5 km long path climbs an elevation of 460 m, it consists of steep valleys, rock cliffs, boulders and boulder trains. And also slope directions and slope angles vary considerably from place to place due to the inherent nature of the area. Therefore, it was a hard task to complete the access road and the construction took a period of 8 months.
With the access road implementation, nearby existing roads were rehabilitated by the company for upgrading the community's wellbeing. Although the construction work is done, the company managed to make less environmental impact. Because instead of removing vegetation within the construction site, a lot of trees were planted by carrying out continuous tree planting programs.
Weir
To optimise the plant design, the actual flow measurements should have been taken immediately. Therefore, the weir construction was started parallel to the construction of the access road and constructed weir was used to measure the river flow.
Since motorable access was not available at that time, labourers climbed with all materials such as sand, metal, cement, steel etc. for a 460 m elevation from the powerhouse location to the weir location.