Geophysics and Tectonics Seminar spring-2024

River systems form the arteries of Earth’s water and rock cycles, and directly sustain more than half the global population with food, water, and energy. As a geophysicist, I tackle fundamental questions about the origins and evolution of river systems on Earth and other planets, as well as practical concerns about environmental hazards and sustainability. In this talk, I highlight my research to date on three topics: river deltas, channel patterns, and the connection between rivers and the shallow subsurface. (1) First, I concentrate on river deltas. Using field data, morphodynamic modeling, and laboratory experiments, I quantify the natural river-diversion processes that give deltas their fundamental size and shape. By coupling this river-diversion model with next-century projections for sea-level rise, I show that mitigating flood hazards will require more sediment resources than previously thought. (2) Second, I investigate the origin of fundamental river channel patterns (e.g., meandering, braided). I present a state-of-the-art remote-sensing tool for quantifying riverbank migration—the first of its kind that is equally applicable to all river patterns—and apply it to 36 years of global Landsat imagery. My results demonstrate that river patterns originate from channel width (in)stability. Where riverbank erosion and accretion are in balance, rivers maintain stable meandering patterns. In contrast, where erosion outpaces accretion, rivers repeatedly widen and split to form braided patterns. (3) Third, I present ongoing work on how rivers interact with Earth’s shallow subsurface. Using a suite of geophysical methods (e.g., GPS/GNSS, rod-surface-elevation tables, sediment cores), I am characterizing how rivers build, deform, and at times contaminate subsurface aquifers in lowland Bangladesh. Preliminary results highlight saltwater-contamination risks in coastal farmlands, where man-made embankments disrupt natural connectivity between rivers and the subsurface. In partnership with the leading Bangladesh-based nonprofit organization (BRAC), this ongoing work supports the development of climate-change-adaptation plans to secure drinking water and sustainable agriculture for the 35+ million people living in lowland Bangladesh.