Three male researchers measuring natural radioactivity at a beach in South Africa, as part of the field testing of the newly developed in situ monitoring systems, 2023. (Photo: University of Stellenbosch)
Many coastal regions worldwide face significant environmental challenges related to sediment transport and coastal dynamics. Launched to help countries in effective coastal management, an IAEA project revealed that natural radioactivity present in sediments can trace sediment sources, transport processes, and deposition patterns without introducing additional materials into the environment.
Persistent erosion in littoral zones leads to long term shoreline retreat and the gradual loss of beaches, threatening coastal ecosystems, infrastructure and local economies. Also, during harbour maintenance operations, when dredged sediments are disposed of at poorly selected sites, the material can be transported back into navigation channels, reducing the effectiveness of dredging activities while increasing maintenance costs.
Understanding sediment movement is essential for addressing these challenges. Tracking sediment pathways and transport rates has so far been done using artificial radiotracers - an industrial application that is becoming increasingly restricted due to regulatory concerns in some countries.
In this context, naturally occurring radionuclides provide a valuable alternative. By analysing the natural radioactivity present in sediments, scientists can trace sediment sources, transport processes, and deposition patterns without artificial radiotracers. This approach offers an effective and more acceptable method for studying sediment dynamics and supporting informed coastal and harbour management decisions.
Labs, Algorithms Help Coastal Management
To better understand and tackle issues related to sediment transport dynamics, the IAEA launched a Coordinated Research Project (CRP) in 2021 Development of Radiometric Methods and Modelling for Measurement of Sediment Transport in Coastal Systems and Rivers (F22074) to investigate how non-destructive nuclear techniques, such as radiotracers, can advance coastal engineering and harbour management.
Under the CRP, institutions from 14 countries, namely Brazil, Canada, Egypt, Ghana, Greece, India, Kenya, Malaysia, Morocco, Netherlands, South Africa, Spain and Tunisia, contributed to developing and testing portable underwater and beach gamma ray sensors capable of real time in situ mapping of sediment radioactivity. These systems were successfully deployed in several countries in diverse field environments, confirming the feasibility of natural radionuclide tracing for sediment dynamics. Geostatistical tools enhanced data analysis and interpretation of spatial mapping of erosion and sedimentation.
Complementary computational fluid dynamics and numerical models of sediment transport dynamics were developed and validated with data from in situ mapping and laboratory radioanalytical techniques. A Monte Carlo simulation model - an algorithm that uses repeated random sampling to predict possible outcomes - was also developed to optimize the quantity of naturally radioactive black sand used in tracer applications, ensuring scientific precision and environmental responsibility.
Tool to Address Coastal Erosion
The project demonstrated the strong operational value of monitoring natural radioactivity in coastal sediments as a practical tool for addressing coastal erosion and dredging optimization. The research confirmed that naturally occurring radionuclides can be used as effective tracers of sediment movement, enabling countries to track transport pathways across coastal and aquatic environments with greater accuracy and efficiency.
"What our researchers demonstrated can be a game changer in some countries," said Celina Horak, Head of the IAEA Radiochemistry and Radiation Technology Section. "By simply monitoring naturally occurring radioactivity, without the need for additional sources or regulatory approvals, countries can gain actionable insights to better manage their coastlines, reduce costs, and support evidence-based coastal planning."
Another important outcome of the CRP is the recognition that the spatial distribution of natural radionuclides provides valuable information about sediment properties. The research demonstrated that maps of radionuclide concentrations can be translated into maps of key sediment characteristics, such as grain size distribution or heavy mineral content. However, further work is required to refine the models used to convert radionuclide measurements into robust and reliable sediment property maps. Furthermore, sediment property maps alone do not directly reveal sediment transport processes. Understanding sediment dynamics requires tracking how these spatial patterns evolve over time. To address this, future work should incorporate repeated monitoring campaigns that capture temporal variability, enabling radiometric observations to be more directly linked to sediment movement, erosion process, and deposition pathways.
While the current CRP focused primarily on demonstrating the feasibility of radiometric methods for evaluating sediment dynamics, the IAEA is planning a follow up project with stronger emphasis on more practical applications and operational use. In particular, active involvement of end users such as coastal modellers, environmental managers and government authorities will be essential to ensure that the scientific results are translated into decision support tools that directly inform evidence-based coastal management.
CRP results were published in 40 peer-reviewed articles and 50 conference proceedings, and were the focus of six PhD and Master's theses.
