Rural roads play an important role in daily life across Cambodia, connecting communities to schools, healthcare, markets, and other essential services. They also support the movement of goods and help sustain local economies. However, many rural roads are exposed to seasonal flooding, disrupting travel and trade, affecting livelihoods, and increasing maintenance and repair costs.
Working with the World Bank, we developed and tested a flood risk assessment methodology for two rural road sections in Kampong Speu Province. The study was designed as a proof of concept to demonstrate how flood risk modelling can inform road planning before designs are finalised and construction begins. By testing proposed upgrades in advance, it helped identify potential flood impacts, quantify resilience benefits and assess wider catchment effects early in the decision-making process.
The project also explored how resilience outcome indicators could be used to measure and compare the benefits of infrastructure investments consistently across future investment programmes.
To assess the proposed road improvements, the project compared flood risk under two scenarios: existing conditions and a future design scenario in which the upgraded roads, bridges and drainage infrastructure were assumed to be in place. This helped quantify the resilience benefits of the proposed improvements.
The assessment combined hydrological, hydraulic and probabilistic risk modelling to evaluate flood behaviour and its consequences for road performance under both existing and upgraded conditions.
The analysis showed how the improvements could influence:
By quantifying the difference between the baseline and upgraded scenarios, the modelling provided decision-relevant evidence to compare design options, support investment prioritisation and demonstrate where proposed improvements would make the biggest difference during flood events.
The study also showed why road improvements need to be assessed within their wider catchment context.
Measures such as raised embankments, new culverts and bridge upgrades can reduce flooding and disruption on the road itself. However, they can also alter how water moves through the surrounding landscape.
In one location, the proposed upgrades reduced flood impacts on the road but increased flood depths in some nearby upstream areas. In another, the effects on surrounding flood behaviour were more localised.
These findings highlighted the value of assessing wider flood behaviour early in the design process. This helps planners and engineers understand where proposed upgrades are likely to improve resilience, where further design refinement may be needed, and where surrounding communities or assets could be affected.
Although the modelling focused on road infrastructure, the findings have wider relevance for communities, livelihoods and local economies.
Maintaining access during and after floods helps communities reach schools, healthcare, markets and essential services. It also supports more reliable local transport networks and reduces disruption to livelihoods.
By identifying vulnerable road sections and comparing intervention scenarios, the methodology helps decision-makers understand where investment is likely to deliver the greatest benefit for communities while supporting more resilient transport networks.
A key outcome of the project was a tested flood risk assessment methodology that can be applied to future rural transport investments. The approach provides a practical, repeatable framework to support investment prioritisation, design optimisation, monitoring and reporting, while enabling the development of consistent resilience outcome indicators across infrastructure programmes.
By helping planners and engineers compare design options, understand wider catchment impacts and quantify resilience benefits before construction begins, the methodology supports more resilient, better-targeted infrastructure investment.
Contact our team to learn more about this project.
