Location: Orewa Beach, New Zealand
Type of Project: Multi-Purpose Reef Design
Client: Orewa Beach Reef Charitable Trust
(Top Left) A summary of the natural and anthropogenic processes that have contributed to the erosion problem at Orewa Beach. (Top Right) Wave height attenuation caused by a set of offshore reefs. (Bottom) The complete beach solution including beach nourishment and four sets of offshore reefs.
Orewa’s long sandy beach is considered a major attraction and is a significant natural resource for the area. Since early last century a number of factors have dramatically reduced the width of the dry beach. Recently, beach nourishment has been used to increase the dry beach area and protect the back beach from further erosion; however this material does not stay in place over the long-term.
The study provided a design concept for a system of Multi-Purpose Reefs which would modify and dissipate incident wave energy resulting in a reduction of erosive alongshore currents and ultimately cause the formation of beach front salients which in turn will create a wider beach able to withstand the onslaught of typical storm events. The design study was based on sediment transport simulations driven by a calibrated inshore wave model. The Orewa site features additional complexities of a large tidal range and shallow sloping bathymetry which results in a wide surf-zone during storm events. Several reef and breakwater options were tested including shore parallel structures and more complex reef shapes. Ultimately, the "staircase" reef design was decide upon as it exhibited the best performance in terms of reducing alongshore currents and incident wave energy.« Download Project PDF