2019 – Waimea Community Dam: Design of a resilient CFRD in a Highly Seismic Environment

D. A. Fletcher, J.O. Grimston, M.C.N. Taylor, D. J. Andrews, H. J. Bowen, P. Cazalis de Fondouce, E. Guilleminot, I. G. Walsh

The Waimea Community Dam will be the largest multipurpose concrete face rockfill dam (CFRD) to be constructed in New Zealand. This 53 m high CFRD will impound a reservoir of 13 Mm3 and is essential to securing the future water needs of the community and environment of the Waimea Plains and wider Tasman/Nelson region.
The design of this unique large dam in the New Zealand context was a long-term collaboration of local dam design expertise and international experience that took the ‘historic precedent based design approach’ for CFRD’s and supplemented this with modern embankment design techniques for the highly seismic environment at the dam site. Design of this High Potential Impact Category dam presented a range of technical challenges for the designers and wider project team, which required new and innovative design solutions and approaches.
The dam features a number of unique arrangements in the New Zealand context including:

• A 4 m high parapet wall with horizontal movement joint connection to the concrete face and designed to accommodate displacements and embankment deformation due to seismic induced crest accelerations of up to 1.9g.
• A twin barrel diversion culvert through the dam designed for the high seismic loads and with geometry to accommodate construction diversion floods and following closure, installation of two pressure pipe conduits within the culvert that consider future maintenance and accessibility requirements.
• A mass concrete starter dam at the upstream toe to provide regular geometry for the plinth and concrete face above the diversion culvert.

The project had its origins in the early 2000’s. Detailed design commenced in 2010, and was externally peer reviewed. The detailed design stage was undertaken in an Early Contractor Involvement (ECI) process which was completed in February 2019.

This paper covers the important seismic design aspects for this large dam, including understanding and designing for the potential range of displacements and embankment deformations to inform the crest parapet wall and diversion culvert designs, and understand how differing rockfill properties might affect the dam performance. Quantifying the range of potential dam performance enabled a more resilient dam design.