The project also seeks to manage and mitigate any environmental effects and to enhance the environment where possible. This includes measures to mitigate effects to the coastal edge (for birds, plants and ocean life) as well as for recreational impacts eg. by including areas of beach nourishment to respond to loss of valued beach space in key locations.
Throughout the option consideration and design process, our approach has been to avoid potential adverse effects. Where avoidance isn't possible, the approach has been to remedy or mitigate actual or potential adverse effects associated with the construction stage and the operation of the project.
The design has been through a series of iterations that were considered against the parameters of the natural environment to achieve an optimum design. These include coastal processes and ecologically sensitive areas (intertidal and subtidal areas). It balances the need for resilience with all the other matters that need to be considered (biodiversity, natural character, amenity etc). The design will be further developed during the detailed design stage once consents have been granted.
Little penguins are found in the Project area with an estimated 42 breeding sites (six of these are inland of Marine Drive). The main habitat of the existing breeding sites is artificial rock. Many of these are less than one metre above sea level and are at current risk of inundation by storms. With storms predicted to increase there is an increasing risk and threat to penguins in general.
The project includes plans to develop alternative safe breeding sites for penguins to offset the effects of the Shared Path on their habitats. The Seaview Marina breakwater has been identified as a suitable breeding area for both penguins and shoreline foraging birds. This proposal will be developed further with input from the community.
In October 2017, Conservation Dog Handler Alastair Judkins and his Penguin Detection Dog Mena conducted a little blue penguin survey along the eastern bays of the Wellington harbour. This was completed in collaboration with the Lower Hutt City Council and the Eastern Bays Penguin Group.
The Shared Path provides a basis for future opportunities to protect the resilience of the road and underground services by upgrading the supporting seawalls. Marine Drive provides the only road access to the Eastern Bay suburbs and is therefore a key transport route for the region. Key infrastructure services, including the main outfall sewer pipeline, are located within the road corridor. These services are regionally significant infrastructure, and along with the road access are important lifeline utilities for the wider community.
The proposal includes replacing seawalls to provide improved protection from storm events for Marine Drive and other infrastructure contained within the Marine Drive road corridor. The replacement seawalls will reduce overtopping and debris on the road and develop a consistent seawall design that can be added to in the future. The Shared Path will sit on top of the new seawall.
Climate change and sea level rise
The project will also provide the first step in enabling the Marine Drive road corridor to respond to the challenges of sea level rise. The road is vulnerable to closure and reduced operation because of wave overtopping caused by heavy storms. The existing seawall is vulnerable to failure in places, and does not provide effective storm mitigation.
Over time sea levels will rise, aggravating the situation. Ministry for the Environment's (MfE) 2017 projections forecast a 16cm sea level rise by 2030-2040 (depending on global emissions). Further sea level rise will increase the frequency of all coastal inundation along the Eastern Bays.
The project recognises the ongoing processes of managing coastal values in the face of climate change and sea level rise, however it is not a solution to all of the effects of sea level rise. The project is a first step in a potential series of upgrades that would assist in protecting the road and underground services. It is an adaptation option in addressing the effects of sea level rise along this section of the coast.
The design has a strong focus on resilience, demonstrated by the design principles adopted (set out in the application) and the whole environment approach. The design doesn't prevent future options, and allows extra protection to be added onto the top of it in the future if considered appropriate. It will 'buy time' until council has developed a Climate Change and Resilience Strategy with the community.
Sea level rise scenarios
We have assessed the sea levels for the project and have included a series of nine cross sections showing the periods of sea level rise at 0.5 meter and 1 meter. 2017 MfE guidance provides four scenarios of sea-level rise for NZ to assess against project plans.
For this project, sea level rise values have been used to evaluate the proposed seawalls by 2070 (50-year design life), and to stress test designs with sea level rise in 2120 (100-year assessment in the New Zealand Coastal Policy Statement). The stress-test assesses the long term effects of wave overtopping hazards and storm-tide (tidal elevation and storm surge).