Speaker: Dr. Douglas Edmonds
Rivers are among Earth's most dynamic features, constantly reshaping our planet's surface through powerful processes that operate across vastly different timescales. This movement creates and destroys land, poses significant hazards to communities worldwide, and over geological time, forms the subsurface reservoirs that store much of our oil and natural gas resources.
In this presentation, Dr. Edmonds will explore the fascinating mechanisms behind river movement, from the gradual meandering of channels to the dramatic sudden diversions called avulsions that can permanently alter entire landscapes. We'll examine how sediment transport, fluid dynamics, and topography interact to drive these processes. From the Mississippi River Delta to meandering streams in Indiana, this presentation will illuminate the complex forces that govern how rivers move—and why their movement matters more than ever in our changing world.
Dr. Douglas Edmonds is a Professor of Earth and Atmospheric Sciences and the Malcolm and Sylvia Boyce Chair in Geological Sciences at Indiana University. He earned his Ph.D. (2009) from Pennsylvania State University and his B.S. (2003) from St. Louis University. His research focuses on sedimentology, stratigraphy, and geomorphology of depositional systems, studying how sediment movement, fluid flow, and bed topography create rivers, deltas, and coastlines. His research has been published in high-impact journals including Nature and Science. Edmonds work has bee
Sponsored by Karen Bumb
Program: How Rivers Move
Speaker: Douglas Edmonds, PhD, Malcolm and Sylvia Boyce Chair of Geological Sciences, Indiana University – Bloomington and a 2025 Guggenheim Fellow
Introduced By: Karen Bumb
Attendance: NESC: 81, Zoom: 37
Guest(s): Ann Blunk, Nancy Kant, David and Magdalin Zauner
Scribe: John Peer
Editor: Carl Warner
Talk’s Zoom recording found at: https://www.scientechclubvideos.org/zoom/02232026.mp4
Our presenter today was Dr. Douglas Edmonds who is a Professor of Earth and Atmospheric Sciences and the Sylvia Boyce Chair in Geological Sciences at Indiana University. He earned his PhD from Pennsylvania State University and his BS from St. Louis University.
Dr. Edmonds described his love for his work as constantly interesting and joyful. He and his team scientifically monitor sediment movement in the White River by scanning the same points several times a year, recording movement in the sediment and the banks. He described the basic types of rivers commonly observed, but also another phenomenon call avulsion.
Meandering rivers, with one pathway, are common. Through natural erosion of the river banks, the meandering continues over time. The White River in Indiana is meandering, especially south of Indianapolis. The Ohio and Wabash Rivers are other examples.
Braided rivers have multiple pathways that are frequently changing. The multiple pathways look like braids weaving back and forth across the river bed. This is caused by the water flow moving sediment downstream creating new sediment (“sand”) bars redirecting the flow. The Yarling Zangbo River in Tibet is an example. Dr. Edmonds shared a time lapsed video covering over 60 yrs of the Padma River in Bangladesh that clearly demonstrated the movement of flows. Adding vegetation to the sediment stabilizes the sediment bars reducing the number of threads. Adding mud further stabilizes the sediment converting the river eventually into a meandering style.
Meandering rivers, through centrifugal force, erode the outer banks and deposit that sediment on the inner banks, ever increasing the width of the meander. Eventually the river erodes back to the main flow creating a shortcut and leaving an isolated oxbow segment.
The process of avulsion is a medical term for separation. In the river context, it is the creation of a new water pathway not returning to the original river. This process develops over hundreds to thousands of years. The Mississippi River, from the start of the Atchafalaya Basin, has had avulsions 4600 years ago as well as 3000, 2000, 1000, and 500 years ago. The process starts with sediment being deposited on river banks creating a levee which allows the river water level to rise. The river continues to fill with sediment which is deposited on the banks increasing the height of the levee. When the bottom of the river is higher than the surrounding land, the situation is ripe for an avulsion. If the river bank ruptures, a flood of water disgorges on the adjacent (now) lower land forming a new path separate from the original river. This can lead to catastrophic flooding. Some speculate that this process was involved in the floods reported in the Bible.
In Mississippi in 1830 an avulsion was aided when a log jam at the start of the Atchafalaya Basin was intentionally broken, which led to 30% of the Mississippi water being diverted to the Atchafalaya Basin Floodway. Congress invoked the Army Corps of Engineers to stabilize the diversion at 30% allowing the main flow of the Mississippi to be maintained.
Our thanks to Dr. Edmonds for a very educational presentation.
Douglas Edmonds
