Phata Byung – assessment of a damaged hydropower project
Client: Lanco Mandakini Hydro Energy Pvt Ltd
Location: Uttarakhand, India
Date: August 2013 – December 2014
Assessing damages and investigating options for restoration of the headworks of a hydroelectric project to enable its completion and reduce future risks
Fierce flooding and landslides in the Indian Himalayas in June 2013 caused extensive damage to the 76 MW Phata-Byung hydroelectric project, which was under construction and 70% completed.
The diversion tunnel and sluice gate openings in the dam were completely blocked by logs and boulders, resulting in the entire reservoir area being filled with deposited material. The dam was overtopped by approximately 8 m and the loading on the upstream face of the dam was more than double the design load. As a result, a dam breach formed and extensive damage occurred to both the upper portion of the dam and the downstream walls and piers.
Entura was engaged to assess losses and damages to the project and investigate options for restoration, including a safety review of the dam structure, preliminary designs for the dam and headworks, construction schedule and preliminary cost estimate. Expertise was provided in structural engineering, geotechnical and hydraulic engineering, construction methodology, scheduling and cost estimating.
A flood damages assessment led to the development of a number of conceptual designs to re-establish the headworks. To reduce the risk of a similar event occurring in the future, the flood discharge was increased to 1850 m3/s, compared to the original discharge of 1100 m3/s, and a free-overflow spillway was included in the design to minimise the risk to the hydropower project. Risk reduction strategies were also adopted to improve the current design.
Entura’s assessment of the damage proposed a four-stage approach to restoring the Phata-Byung hydroelectric project by re-establishing the diversion tunnel, demolishing the upper portion of the dam through a staged process, removing the reservoir debris material by allowing the natural erosion process during the monsoon period, and reconstructing the upper portion of the modified dam.
Practical engineering solutions that are cost-effective and faster to implement will enable the project to be restored with confidence and reduce future risks.