Coastal Risk Assessment: What You Need To Know

A coastal hazards assessment is a comprehensive evaluation of the potential hazards and risks that might affect a given coastal area. The assessment aims to identify, analyse and offer up mitigation measures for these hazards, to minimise the negative effects on coastal communities, infrastructure and ecosystems.

Coastal hazard assessments are usually commissioned by local councils and government authorities, but the resulting reports are used by a range of entities, including the private sector, research organisations and community groups.

Coastal risk assessments tend to feature a few key components and objectives:

Hazard identification

Coastal risk assessments identify both natural and human-induced hazards. Natural hazards include coastal erosion, storm surges, sea level rise, tsunamis and flooding caused by extreme weather events. Human-induced hazards include pollution, dredging, and coastal construction and development.

Exposure analysis

This is the process of evaluating the elements at risk within the specified coastal zone, including populations, ecosystems, buildings, infrastructure and economic assets. The geographic distribution of these elements is mapped to understand their spatial relationship with identified hazards.

Vulnerability assessment

Having identified both the hazards and the exposed elements, the next step is to understand how susceptible each element is to the potential damage or loss that the hazards could cause. The vulnerability assessment considers factors such as building materials, construction quality, coastal land use and socio-economic conditions. This assessment should place a particular focus on identifying vulnerable populations like low-income communities.

Risk analysis

At this point the task is to combine all of the information built up in the hazard, exposure and vulnerability assessments, to get a sense of the potential impacts of coastal hazards. Statistical analysis and modelling techniques might be used to predict the likelihood and potential extent of future hazards.

Impact assessment

How intense could the impact of the identified hazards be? This step of the coastal risk assessment is about evaluating the potential consequences if hazards or risks come to pass. Direct impacts could include damage to buildings, infrastructure and assets, social disruption and environmental degradation. There are also a range of indirect impacts, such as a hit to tourism revenue.

Mitigation/adaptation strategies

At this point the task turns to developing measures that mitigate identified risks and/or adapt to changing circumstances. Examples of such strategies include implementing zoning regulations, improving early warning systems and restoring natural coastal barriers like mangroves and dunes. Long-term risks like sea level rise demand adaptation planning like building seawalls and managing the retreat or elevation of structures.

Stakeholder engagement

Coastal risk assessments must consider and consult with a vast array of stakeholders, including communities, governments, businesses and local organisations, to ensure that the knowledge, needs and priorities of each are factored in. Engagement with these stakeholders is critical, and efforts may involve generating public awareness and education about the risks that a patch of coast faces, and the resilience measures that need to be enacted.

Monitoring and review

A coastal risk assessment offers a snapshot from a point in time. But it can - and should - be updated on a regular basis. Coastal conditions and hazard events should be monitored continuously along with the effectiveness of any mitigation/adaptation measures that have been implemented. A risk assessment needs to be updated regularly to reflect new data, changing conditions, and advancements in knowledge and technology.

What are the ultimate goals of a coastal hazard assessment? Objectives include:

Increasing safety: By actively identifying and mitigating coastal risks and hazards, residents, tourists and the general public are made safer, and injuries and fatalities can be significantly reduced.

Safeguarding assets: Risk mitigation can help to minimise damage to private property and public infrastructure.

Preserving ecosystems: Ultimately humans rely on Mother Nature, so by protecting and preserving marine ecosystems and coastal biodiversity, we protect ourselves.

Making communities more resilient: We must ensure that coastal development is resilient to hazards, and support communities to better control, prepare for, respond to, and recover from coastal hazards.

Furthering science: An important outcome of these assessments is the new knowledge we gain, which informs policy and planning by providing a scientific basis for coastal management and risk reduction strategies.

New Zealand is a unique country in a unique part of the world, so we unsurprisingly face a unique set of coastal hazards. A few of the key risks that the country's coastal communities must deal with, both now and into the future, include:

Sea-level rise: As the earth warms and the polar ice caps melt, sea levels will rise, placing low-lying coastal areas in danger. Christchurch City Council has created an accessible video breakdown of the risks of sea-level rise which you can check out here.

Erosion: Coastal erosion is a significant issue, particularly in sandy coastal areas hit by large swells. Sea level rise will also make erosion more intense.

Storm surges: Large waves, strong winds and low atmospheric pressures can combine to produce storm surges, which can lead to flooding and coastal erosion.

Tsunamis: Our spot on the Pacific Ring of Fire means that we're in a seismically active area, which makes us susceptible to tsunami events, which are notoriously unpredictable.

Other flooding: Along with sea-level rise, storm surges and tsunamis, coastal flooding can also be the result of heavy rainfall and high tides.

Saltwater intrusion: A long-lasting after-effect of flooding can be the infiltration of seawater into freshwater aquifers and low-lying groundwater systems, which can affect water quality, safety and availability.

Coastal landslides: Coastal cliffs and slopes may be prone to landslides, especially following heavy rainfall or during seismic activity, which can impact infrastructure and property.

Ultimately the mix of hazards faced by a particular patch of coast will depend on the topography, geological makeup, ecosystems and human development of the area.

There's no sugar-coating the fact that climate change will increase the number, regularity and intensity of coastal hazards. The main reason is sea-level rise, which will intensify the effects of erosion, storm surges, flooding and salt water intrusion. Climate change will also increase the intensity of storms, cyclones and rainfall events.

This makes coastal risk assessments all the more critical as we enter a warmer world.

Coastal hazard databases are maintained by a number of different government agencies, regions and councils. At a national level, NIWA studies coastal hazards as a broad subject, the Natural Hazards Portal compiles all relevant information into an easy-to-search database, and the Ministry for the Environment offers general coastal hazards and climate change guidance.

Regional agencies and local councils take a more detailed view. Most regions and some councils have their own dedicated coastal or natural hazard database, including:

• The Otago Natural Hazards Database
• BayHazards (Bay of Plenty)
• The Christchurch Coastal Hazards Online Portal
• Tasman District Council Coastal Risk Assessment

These databases and portals will often offer interactive maps that allow you to check the specific risks and hazards faced by your area, both now and into the future.

You also have the option of gaining access to curated information via the private sphere. That's where we come in.

At Eliot Sinclair we provide in-depth geographic information systems (GIS) that compile a wealth of data, including information from coastal risk assessments, into a digital map that visualises this information to make it easier to analyse and digest.

When combined with our geotechnical engineering expertise, our expert team is able to assess coastal conditions for a site both now and into the future, then provide technical guidance on your hazard mitigation requirements, to show how your project can be successfully completed in a way that ensures it stands the test of time.

Speak to our experts before starting your next coastal project.