What is harbour and coastal erosion?
Harbour and coastal erosion happens when wind, waves and water wear away the shore line and contribute to land slips. It is a natural process that is also influenced by human activity.
The nature and rate of erosion along a coastline or harbour is affected by the type of land (e.g. rocky ‘hard’ or sandy ‘soft’ shores) and the energy of the sea (e.g. a ‘high energy’ surf beach or a ‘low energy’ sheltered estuary).
Why should we care?
We love to live by the sea, but erosion can be a big problem if houses are built on low-lying sandspits, dunes or coastal cliffs.
Many harbour and coastal residents think erosion is a distant issue and won't impact their wellbeing or lifestyle during their lifetime. The reality is that erosion can be very sudden and the on-going effects may never be able to be reversed, or, if they can be the solutions will be prohibitively expensive.
In addition to obvious safety issues, erosion can negatively impact property values, not only of the homes directly affected but also on neighbouring streets or the community.
It can result in decreasing opportunities to enjoy the harbour and coastal environment. Harbour and coastal erosion is also threatening sites of cultural importance e.g. urupa (cemeteries).
In some cases, infrastructure such as roads, marinas, and stormwater pipes can be affected or even lost.
There are a range of options that can be considered in addressing this issue - the costs of which vary widely. The financial impact on ratepayers will depend on the options chosen and how they are funded.
Why do we need a policy on erosion?
New Zealand’s sea level has risen about 18cm over the past 100 years. It has also been subjected to coastal storm inundation (flooding) that has been historically documented. This is expected to become more frequent in the future.
Coupled with a predicted further one metre sea level rise, what we currently consider to be an extreme ‘one in 100 year coastal event’ – will trend to becoming the norm.
In the next 20 to 30 years coastal hazard events may be manageable, but after that flooding risks will grow rapidly as the sea level rises.
Our communities need to consider all available options now to avoid committing to expensive and/or irreversible planning, investment and development decisions.
Today’s coastal properties may survive for the next 30 years but whether they will remain a viable investment for the 30 years after that is uncertain (see Section 3.1 of the policy).
The policy is intended to raise current and future coastal property owners’ awareness of sea level rise and potential approaches going forward (see Sections 4.2, 4.4 and 4.5).
What does this policy mean for private property owners?
Erosion protection works are incredibly expensive – $3000 per metre for rock revetment walls. The District’s inner harbour coastline alone – excluding the margins of Matakana, Rangiwaea and Motuhoa Island – is 140km. If the entire coastline was protected by hard structures the cost could be in excess of $420 million. These works would, in time, likely fail under predicted sea level rise too.
draft policy explicitly limits future Council funding to the protection of
Council owned land and strategic assets. It states public money will not be
spent on the protection of private property.
This may prove unpopular initially, but from a wider district and long term perspective it makes economic and intergenerational sense. Any public intervention to protect private property on the inner harbour or coast would be at a cost to all ratepayers and a gain only to individual property owners (see Section 3.3).
Please note there is nothing in the draft policy that prevents private property owners from undertaking protection works at their own cost, provided necessary consents have been obtained.
What does this policy cover?
The draft policy relates only to the future management of Council-owned coastal land and assets. It informs the community of our proposed consistent, precautionary approach to inner harbour and coastal erosion protection and to the future subdivision and intensification of these areas (see Section 4.1 for more information).
In a nutshell, it proposes we will undertake an assessment to determine the most appropriate erosion management option per case - out of ‘do nothing’, ‘adaptive approach’ or ‘hold the line’ (see Sections 5 and 6).
The policy also gives effect to Council’s statutory responsibilities (see Sections 1, 2.5, 7, 9 and 10).
What causes harbour and coastal erosion?
Erosion is a natural process that's been occurring for thousands of years. However, the process has increased through the presence of people and climate change.
Human activities (e.g. vehicles on dunes) and structures can have unintended consequences and worsen the problem. The increasing amount of hard surfaces (e.g. homes, driveways, footpaths, roads etc) due to increased development has resulted in an increase in stormwater run off, which also contributes to coastal and harbour erosion.
The release of water into the soil through septic tanks and storm water soak-away systems also leads to increased saturation of soils, which has triggered slips on vulnerable slopes along the shoreline.
Equally, climate change has resulted in increasing sea levels and extreme weather events, which increasingly contributes to erosion. Changes in ocean and atmospheric circulation in the Pacific Ocean (such as El Niño) cause long-term variations in New Zealand weather patterns. As changes in climatic conditions change the direction of onshore winds, there are episodes of increased erosion in some areas and a build up of sediment in other areas.
It is also important to take into account the combined effects of storm erosion and flooding. This is because the extent of flooding will be influenced by the amount of erosion.
What’s the nature of harbour and coastal erosion in the Western Bay?
Coastal settlements in the Western Bay are located on open coast dune areas (Pukehina/Waihi Beach), seacliffs (Maketu), estuary margins (Little Waihi) and the shoreline of the Tauranga Harbour (Omokoroa, Te Puna, Opureora).
Each area has a unique set of environmental factors including different rock types and land forms that affect the severity, timeframe and nature of erosion.
Because of the timeframes typically associated with shoreline erosion (measured over years and decades), there is little threat to public safety.
A different situation exists within the Tauranga Harbour. Many of the inner harbour islands and peninsular cliffs are subject to landslides.
Although these events are infrequent they can be relatively large scale and they can occur without warning.
In coastal areas roads and infrastructure will face increased risk.
Does this affect me if I don’t live by the harbour or coast?
It affects you if you use beaches, parks or roads by beaches and may also affect you if you pay rates e.g. if private property owners want Council to fund protection works for their properties, this will have to be funded through rates.
Some protection options can be very
expensive to construct, maintain and replace. The impact on ratepayers will depend on what options are agreed and
how these options are funded.
Does the policy require info on Land Information Memorandums (LIMs)?
This may be considered as part of the development of this policy. Read more about LIMs here.
Is there any direction from central and regional government on what should be done?
Council is legally obliged to comply with a range of requirements set by Government and the Bay of Plenty Regional Council.
The main legislation governing coastal management in New Zealand is the Resource Management Act 1991 which requires councils to preserve the natural character of the coastal environment and have particular regard to the effects of climate change.