Water Resources Engineering and Science Seminars

Abstract
Sediment and water delivered by rivers build and sustain coastal landforms such as deltas and wetlands, which are densely populated and ecologically vital areas threatened by rising sea levels. In this talk, I highlight theory-driven and field-based research to understand how coastal land building operates across broad river delta plains and how human activity affects these processes. On the theoretical front, inspired by Hack’s law (the scaling between watershed drainage area and channel length in tributary networks), we analyzed a global dataset of distributary delta networks. We discovered a nearly identical scaling relationship between distributary channel length and nourishment area, the land-building counterpart to drainage area. Despite this apparent global scaling, we identified two distinct local land-building patterns: Uniform Delta Networks consistently follow Hack’s law, while Composite Delta Networks exhibit a scale break, transitioning from space-filling growth around the delta apex to quasi-linear growth near the coast. These surprising growth patterns suggest that global simplicity and local variability coexist in how river deltas grow and organize. To assess regional variability and human impacts, we combined remote sensing with field observations in the Lower Rio Grande, finding that the river currently carries about one-third of its median discharge in the 1900s and that only about 0.3% of its natural flow reaches the Gulf due to human consumption. This reduction leads to channel contraction, resulting in higher water levels for the same discharge and thus increasing local flood risks. I conclude by highlighting a few ongoing/future research directions on deltaic land building, including sedimentation influenced by human engineering and wind-driven sediment redistribution.

Bio
Tian Y. Dong is an Assistant Professor in the School of Earth, Environmental, and Marine Sciences at the University of Texas Rio Grande Valley (UTRGV). He earned his Ph.D. and M.Sc. in Earth Science from Rice University and previously held an NSF Earth Sciences Postdoctoral Fellowship at the University of Texas at Austin. His research focuses on how rivers and deltas build and reorganize landscapes, integrating field observations, remote sensing, and theory to understand sediment transport, channel-network dynamics, and stratigraphic signatures across Earth and planetary settings. His work has been supported by federal agencies including NASA, the U.S. Department of Energy, the U.S. Geological Survey, and NSF. He has published in outlets such as Science Advances, Nature Geoscience, Journal of Geophysical Research: Earth Surface, and Geology, and he teaches courses spanning geomorphology, sediment transport, and coastal/deltaic processes while mentoring graduate and undergraduate researchers.