Assessing risk from natural hazards at visitor sites

Visitor risk management background

We manage sites with a variety of risk levels. These accommodate different outdoor activities and risk tolerances.

Our management is scaled. Highly accessible sites are managed to have low risk, while remote sites have higher risk and less management.

Visitors should choose experiences that match their skills and risk tolerance.

Our responsibilities:

• Compliance: Ensuring structures and facilities meet standards and regulations.
• Hazard identification: Identifying and assessing risks at visitor sites and informing visitors.
• Site management: Managing sites to appropriate risk levels for the main visitor group.

Our standardised method

We have developed a standard method that we call “the methodology” for experts to assess risk from landslides, tsunamis, and volcanic and geothermal hazards on public conservation lands and waters. This helps determine the level of risk these hazards pose to visitors.

The method is set out in six GNS Science reports:

Part 1 – Methodology overview (PDF, 1,429K)

Part 2 – Framework for landslides (PDF, 2,370K)

Part 3 – Guideline on landslides for point and linear features (PDF, 2,674K)

Part 4 – Commentary on landslides for point and linear features (PDF, 10,445K)

Part 5 – Framework for tsunamis (PDF, 959K)

Part 6 – Framework for volcanoes (PDF, 2,346K)

We commissioned GNS Science to create the risk analysis methodology to help us make sound decisions about natural hazard management. It enables us to assess if the risk level is acceptable for visitors and if it can be reduced.

It is mainly used to assess landslides and rockfalls as these are the most common natural hazards that affect our visitor sites. The landslide methodology also covers debris flows and volcano flank collapse.

The methodology helps determine:

• the risk level at a site
• if the risk is changing over time
• if the risk is acceptable for the visitor experience
• if the risk can be reduced to an acceptable level
• if risk reduction is feasible and cost-effective.

The methodology is used for:

• new site developments or significant investments
• significant changes in site use or hazard levels
• ongoing landslide/rockfall risks
• understanding if the risk exceeds our risk thresholds for visitor sites.

Three levels of landslide risk analysis

1. Preliminary Assessment: A screening tool to identify landslide hazards and decide if further assessment is needed. It classifies the hazard level (1-4) and guides the next steps.
2. Basic Assessment: Quantifies risk at a basic level for tracks, roads, huts, carparks, etc. It checks if the risk is within our risk thresholds for visitor sites. Recommendations for risk mitigation are provided.
3. Advanced Assessment: A detailed risk analysis requiring more time, data, and resources, including peer review of the risk calculations.

Risk assessment review and decisions

Once we get a natural hazard risk assessment, an expert panel reviews it.

The panel includes:

• the report’s author
• a geotechnical expert
• a Visitor Safety Team member
• the Operations Manager
• the Senior Ranger, and other relevant staff.

They help the Operations Manager decide how to manage the risk at the site.

Natural hazard risk thresholds

We use quantitative (numerical data) thresholds to manage natural hazard risks for visitors. GNS Science Te Pū Ao and TTAC Ltd experts developed these thresholds by analysing accident data and international risk management systems. They provided us with recommendations in two reports.

Risk Comparisons for DOC Visitors and Workers (PDF, 3,439K)

Guidelines for DOC on dealing with Natural Hazard Risk (PDF, 2,882K)

Our staff provided feedback on the proposed approach and then the thresholds were approved by our senior leadership.

Lower, medium and higher-risk tolerance sites

The thresholds are categorized into lower, medium and higher-risk tolerance sites

Lower-risk tolerance visitor sites

These are visitor experiences where the visitor has no intention of taking life-threatening risks. The risks at these sites are comparable to activities with minimal or no threat to life. For example, playing tennis or the safer end of driving (an experienced driver driving to the road rules in a modern car).

Medium-risk tolerance visitor sites

These are visitor experiences where the visitor is not expecting much risk but knows that accidents can happen. These risks are comparable to activities where occasional fatalities occur but are not thought of as high-risk. For example, swimming or riding a bike.

Higher-risk tolerance visitor sites

These are visitor experiences where the visitor is prepared to accept a higher level of risk. At the high end of these risks, they are comparable to the death rate of climbing or remote tramping (with unbridged rivers and rock scrambling). When compared with driving, the risk is comparable to the fatality risk of an inexperienced driver in an older vehicle.

Our response

After a risk assessment, the findings are compared to the applicable risk threshold for the visitor site.

Depending on the risk level and the site’s risk threshold, our response will be one of the following:

• No risk reduction required.
• Reduce to as low as reasonably practicable.
• Continue only after high level review.
• Close the site.

DOC Natural Hazard Risk Threshold Chart (PDF, 193K)

Example of a natural hazard risk assessment using the methodology

Problem: land instability near a popular foot bridge

The Rob Roy Suspension Bridge is located on a popular walking track in the Matukituki area that is used to view the Rob Roy Glacier. Local staff noticed land instability upstream from the bridge, and did not know whether they needed to do more to manage the risk of rockfalls or landslides at this site.

Solution: an expert geotechnical assessment

They engaged a geotechnical consultant who completed a preliminary assessment using the natural hazard risk analysis methodology. This initial screening rated the rockfall risk as ‘class 2’. The suggested action for a class 2 risk is to do further geotechnical analysis (termed a ‘basic assessment’) using the methodology. This provides a better understanding of the risk. Therefore, a second, more detailed assessment was commissioned – the basic assessment.

The consultant completed the basic assessment, producing a quantitative risk figure which was compared to the visitor risk threshold for the site.

Result: no changes needed

The basic assessment indicated that the risk of rockfall to visitors was low and no risk reduction was required.

The assessment provided confidence that the bridge did not need to be moved and no other rockfall mitigation was needed.