Evolution of TARPs in infrastructure risk management

In this challenging context, Trigger Action Response Plans (TARPs) provide a structured, consistent framework for responding to natural hazard events and maintaining the safety and functionality of critical infrastructure. WSP Technical Principal for Road Network Resilience Willis Macbeth, and Service Line Leader for Bridge Asset Management Ben Baty explain.

The concept of TARPs has evolved over time, drawing on traditional practices and modern innovations. A well‑known historical parallel is the 'canary in the coalmine' method once used by miners to detect dangerous gas levels. Canaries, being highly sensitive to toxins such as carbon monoxide, served as an early warning system - alerting miners to evacuate before conditions became life‑threatening.

In a similar way, TARPs act as early warning tools for infrastructure risk management. By monitoring defined indicators and triggers, they help identify emerging threats before they escalate and support timely mitigation. Over the years, TARPs have been adapted for different sectors and hazards, increasingly incorporating real‑time monitoring, technology, and data analytics to improve accuracy, visibility, and responsiveness.

In New Zealand’s roading network, TARPs are a relatively recent management technique. They were widely used in the Kaikōura Earthquake response by the North Canterbury Transport Infrastructure Rebuild (NCTIR) team to manage geological risk from unstable slopes above State Highway 1, where rockfall hazards increased significantly during rain events.

They have also been applied on vulnerable bridges, such as the SH6 Waiho River Bridge and the SH1 Ashburton River Bridge. These traditional TARPs typically relied on manual interpretation of weather forecasts or basic weather‑station thresholds to activate predetermined controls.

A more advanced evolution of this approach is WSP’s Canary Infrastructure Risk Management System. This system integrates real‑time data and predictive analytics to enhance and modernise the TARP process. It represents a step‑change, enabling proactive risk management and giving asset managers the ability to anticipate, communicate, and mitigate risks more effectively.

Well-developed TARPs define specific actions to be taken when certain trigger levels are reached. These triggers are based on observed or forecasted data related to natural hazards such as rainfall, river flow, ground-movement, wind, earthquakes, or extreme temperatures. But TARPs are not just a technical tool - they offer practical benefits that make managing natural hazard risks easier and more effective; letting asset managers respond proactively and effectively to emerging risks, protecting life safety, minimising damage and ensuring continuity of service:

Proactive Risk Management
The TARP framework supports improved risk visibility and definition, and allow for the anticipation of potential issues, and the implementation of preventive measures before a hazard event occurs.

Improved Decision-Making
By providing clear guidelines and engineering led actions, TARPs support consistent and informed decision-making – simplifying complex interpretation and decision-making in often chaotic and dynamic emergency events.

Resource Optimisation
TARPs help clarify required actions and allocate resources efficiently, which is crucial in a fiscally constrained environment. For example, in during a significant rainfall, systems can identify which parts of the networks are likely to have had the most rain and where is most likely to have been damaged. This is critical information for network wide events when resources are limited, and triaging recovery efforts can mean the difference between life and death for assets left compromised.

Optimising Investment in Hazard Resilience
Investment to fully mitigate vulnerability to natural hazard risk is potentially unaffordable (and hard to justify) for many assets, particularly across a diverse portfolio. Implementation of TARPs is a relatively low-cost method of providing technically robust and defendable life safety mitigation to the public during and after natural hazard events.

TARPs can also be a good risk management strategy for assets nearing their end-of-life while funding is sought or renewal implemented. In addition, TARPs can play an important role in supporting investment decisions by highlighting asset vulnerability and automatically capturing outcomes and frequency of exposure through events. This evidence base can help justify and prioritise future physical works.

The Canary system, developed by WSP, is an advanced risk management tool designed to support the implementation of TARPs. It integrates real-time data from various sources and advanced analytics to provide comprehensive insights into asset performance and risk exposure through events. It features:

Real-Time Monitoring: 
Canary continuously monitors environmental conditions and asset performance, providing up-to-date information on potential risks.

Automated Alerts and Notifications: 
The system generates alerts when trigger levels are reached, ensuring timely responses to emerging threats.

Data Integration and Visualisation: 
Canary integrates various data sources and presents information through intuitive dashboards, facilitating easy interpretation and decision-making.

Canary's core modules are bridge flood risk,' road slip risk,' and 'bridge seismic'.

The Canary system is compatible with any forecastable or monitored data, such as wind, temperature, or waves, where an API is available. This flexibility supports using the most relevant data to the risk, and allows evolution of the system as understanding improves or further data sources are added.

Bridge Flood Risk Module

This module monitors rainfall data and forecasts, triggering TARPs for bridges and low-level fords when predefined thresholds are met. Thresholds are developed using Earth Science New Zealand’s High Intensity Rainfall Data (HIRDS) model combined with auto-calculated Time of Concentration for each bridge catchment.

Forecast and observed rainfall are distributed across the catchment to determine whether triggers (based on Average Recurrence Interval, ARI) have been exceeded. A further benefit of this approach is that it identifies when events have met NZTA’s Emergency Works thresholds – which include the requirement to have exceeded a 1 in 10 year event.

Road Slip Risk Module

Similar to the Bridge Flood Risk Module, this module uses rainfall forecast and observed data to monitor when the roading network is at higher risk of slips. Triggers are set using historical slip records and rainfall correlation to identify ARIs that have previously caused issues, helping predict future risk for specific network sections.

Bridge Seismic Module

The seismic module integrates directly with GeoNet to pull live earthquake data and overlay it against the bridge network. It identifies structures that may have exceeded a predetermined seismic peak ground acceleration (PGA) threshold, enabling targeted inspections and rapid response. The system provides alerts within 20 minutes of any seismic activity supporting this rapid response.