2022 – A Pacific Island case study of a multipurpose dam

Richard Herweynen – Entura, Hydro Tasmania

Multipurpose dams can achieve a number of development goals simultaneously and can be designed to readily adapt to future changes. The Alaoa Multi-Purpose Dam, planned for Samoa and funded by the Asian Development Bank, is a fitting example.

Samoa is a small tropical island country in the Pacific, and has been heavily affected by severe tropical storms. In 2012, Cyclone Evan caused extensive flooding and damage to the Apia region, the capital, where most of the population and economic activity is located. With such storms predicted to increase in frequency and severity as the climate changes, the Government of Samoa has adopted a programmatic approach to address climate-change-induced flooding. This includes the new Alaoa Multi-Purpose Dam, sized and designed with long-term climate scenarios in mind and potential to provide multiple functions. It aims to increase flood protection, improve the seasonal reliability of the current water supply system, and provide additional hydropower via the installation of a small hydro facility.

In the planning and early design phase of a new dam, it is possible to modify the design to: (1) achieve multiple purposes and increased benefits; (2) increase operational flexibility to allow the dam to adapt to future changes and demands; (3) improve the use of scarce water resources for all needs, including the environment; and (4) increase the climate change resilience of the dam project. In the case of the Alaoa Multi-Purpose Dam, the design considered multipurpose functions and climate change risks. It included small modifications to provide better outcomes in terms of climate change resilience, environmental sustainability and dam safety. It recognised the importance of reservoir operation in achieving the various functions, providing flexibility for future adaptive modification of the operation to align with the changing demands of the reservoir. This paper will use the Alaoa Multi-Purpose Dam as a case study on how these
elements can be considered and built into future dam projects.

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