Lyall Bay coastal remediation

Abstract

An investigation has been undertaken at Lyall Bay in Wellington to propose options with regard to protecting the natural and built coastal infrastructure and reinstating a functional dune. Lyall Bay is an important recreational asset for Wellington as it is popular with the community for many activities both in the water and on the beach, as well as scenic drives, visiting cafes, and plane watching with the nearby airport. The project has specifically included investigating options for:

1) dune restoration to maximize their effectiveness in absorbing wave energy and protecting natural and built infrastructure

2) protect the rocky shoreline, grassed area and trees on the western side of the bay

3) the shifting of sand around the bay and dealing with current infrastructure within the beach environment.

Lyall Bay is a highly modified beach environment that has been developed since early last century, leading to a number of constraints and changes when coastal processes are considered. The dune field has been replaced with people/houses/buildings; the bay has been contained within walls, roads and parking; stormwater discharges into the bay through 20 different outfalls; the eastern third of the bay has been reclaimed for the airport, and a further 350m of reclamation is proposed in the near future. These constraints prevent the beach from responding naturally to extreme events and mean it requires on-going management and maintenance. The main driver of beach change in Lyall Bay is wave-energy with refraction aligning the waves to the seabed contours, resulting in very little alongshore sediment transport. Bay-wide remediation options have been proposed and consultation undertaken with the community and stakeholders to seek input to the best options. The beach has been divided into 4 zones and specific intervention and management options have been designed for each, however the entire beach requires holistic management for long-term outcomes.