Scotts Peak Dam Upstream Geomembrane Seismic Upgrade
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Project Objective

Scotts Peak Dam is located on the Huon River in Tasmania, Australia and impounds Lake Pedder, one of a series of lakes and dams supporting the Gordon Power Station owned and operated by Hydro Tasmania. The main section of the dam is 43m high and was completed in 1973 as an asphalt-concrete-faced rockfill dam with a downstream slope that is reinforced near the toe. Together with two adjoining saddle dams, each less than 20m high, the dam has a crest length of just over 1,000m and provides a reservoir storage capacity of 2,960x106 cubic meters. A tall parapet wall retains the upper part of the dam and crest and provides additional freeboard. A silty gravel blanket was placed above the bottom third of the upstream bituminous face as a leakage protection measure, shortly after initial filling of the reservoir.

The owner is undertaking a project to evaluate concepts and implement a preferred alternative to improve the reliability of the dam under potential seismic loading. One of these alternatives consists of lining the upstream dam face with an impervious geomembrane system and sealing the geomembrane to the plinth and parapet wall. The entire geomembrane system is to be installed underwater while the reservoir remains at normal levels and is designed to minimize leakage during construction, support post-construction leakage monitoring, and withstand future seismic deformations.

Geosyntec’s Scope of Services

Geosyntec is providing technical design support and review of the upstream geomembrane alternative for seismic upgrading of the dam to Damwatch Engineering, the owner’s design engineer. Geosyntec’s scope of work includes evaluating the upstream geomembrane design concept and developing protocols and recommendations for testing and validation of the geomembrane system. Notably, Geosyntec is: (a) performing a study to assess the seismic performance of the proposed geomembrane alternative; (b) participating in design, construction, and associated risk assessment activities, meetings and workshops with the project team; (c) reviewing and synthesizing the anticipated dam performance during the design earthquake as necessary to evaluate the design requirements for the geomembrane anchoring system; (d) reviewing the geomembrane design details and materials to evaluate design requirements for the anchoring system based on known field conditions and anticipated seismic deformations; and (e) developing laboratory geomembrane testing and validation requirements for the geomembrane system. Additionally, Geosyntec is providing peer review and consultation on the numerical 2-dimensional dynamic response and deformation analyses performed with FLAC as part of the seismic deformation assessment.

Notable Accomplishments

As specialists in the engineering of geosynthetics and dams, Geosyntec is lending its extensive expertise in support of the project and providing liaison between the client and the geosynthetics manufacturer/designer to validate the geomembrane system design for possible future implementation and upgrade of the dam.