Maarten G. Kleinhans
The 2026 Ralph Alger Bagnold Medal is awarded to Maarten G. Kleinhans for impactful research in fluvial and coastal biogeomorphology through analog and numerical modeling.
Maarten Kleinhans is a pioneering scientist in fluvial and coastal geomorphology, recognised for integrating experiments, numerical modeling, and theory. He was the first to simulate and numerically model meandering rivers with riparian vegetation in both laboratory and digital models, resolving a long-standing challenge in the field. His research covers rivers, deltas, estuaries, valleys, and debris flow on Earth and Mars, with major innovations in sediment mixture studies, the use of live vegetation, and the identification of experimental conditions that mimic natural landscapes. A landmark achievement is his invention of 'Metronome'; a periodically tilting flume, which allowed for the first analog simulation of tidal environments. This opened an entirely novel repertoire of experiments in biogeomorphology, and is particularly relevant to coastal and deltaic environments facing sea-level rise. His work extends from small-scale sediment processes to river networks, floodplain patterns, and coastal ecosystems, often incorporating biological interactions such as mangroves and benthic fauna. He is also active in the philosophy and history of science, recognised as a pioneer in the philosophy of geosciences and promoting clear, reflective approaches in research and education.
Beyond research, Maarten Kleinhans contributes strongly to society and education. He collaborates with policymakers, including the Netherland Parliament on land-use issues. He founded a national lecture series connecting scientists, consultants, and decision-makers. He has always been devoted to science education, recently helping establish primary-level science hubs across the Netherlands, and leading curriculum renewal at Utrecht University to include 21st-century skills.
As a mentor, Maarten Kleinhans inspires students at all levels, with many co-authoring articles, and PhD candidates achieving high distinction. His former students now hold successful careers worldwide in academia, government, and consultancy. Overall, given his past and ongoing contributions to the biogeomorphology of fluvial and coastal systems, his experimental innovations, high-quality teaching, inspiring mentorship, and focus on society, Maarten Kleinhans is a worthy recipient of the Ralph Alger Bagnold Medal.