The meandering course of Shoshone Creek in Dixie Valley, Nevada, is one of the key watercourses considered in the study, as it displays well-developed meanders in the absence of vegetation. Photo Credit: Dr. Alessandro Ielpi
Scientists have long believed that rivers form bends with the help of plants that stabilize and anchor their banks.
This theory is rooted in the evidence that rivers became more winding or “sinuous” around 425 million years ago—about the same time that land plants first evolved.
But research recently published in Science is putting a new twist on that theory. UBC Okanagan’s Dr. Alessandro Ielpi co-authored the paper with Michael Hasson, a Stanford University doctoral student. Dr. Ielpi, Associate Professor of Geomorphology and the newly-appointed Forest Renewal BC Watershed Enhancement Research Chair in UBCO’s Irving K. Barber Faculty of Science, is a long-term collaborator with the Stanford Earth and Planetary Research Group.
Here, Dr. Ielpi explains why this new study is making researchers rethink their long-held beliefs.
What makes this research significant?
Most of the world’s population lives in river lowlands, many of which are occupied by meandering rivers. The more we understand how plants influence these rivers, the better we can plan for life in regions facing deforestation, wildfires and climate change—factors that affect vegetation along river banks and riparian corridors. These kinds of adaptations can save us from costly damages or even loss of life in response to floods.
What are the key discoveries in this new research?
Many geoscientists believe that the evolution of plants caused major changes in how rivers behave. In particular, ancient river rocks suggest that rivers became more winding around the time land plants first appeared.
This led scientists to believe that the rise of vegetation caused rivers to start meandering, owing to stabilization of their banks by roots. But recent studies of modern, active meandering rivers in desert areas challenge this notion, showing that well-cemented banks alone can sustain meandering. In this study, we suggest that while vegetation isn’t needed for meanders to form, it does affect how their shape and direction change over time.
What rivers did you study for this work?
We studied more than 4,400 river bends from 49 rivers around the world to get clear results across different climates and ecological regions. This includes rivers in desert environments almost entirely barren of any type of vegetation year-round, such as the Great Basin in the western USA and the Altiplano-Puna Plateau of South America. For comparison, we also looked at rivers in vegetated regions, including Alaska, the eastern USA and Oceania.
How was this determined?
By analyzing satellite images of active rivers, we found that vegetation along the banks changes the direction in which meanders grow, favouring outward growth instead of downstream-ward growth of meanders. This also helps explain why it has been difficult to identify meandering river deposits that are physically older than the rise of vegetation on Earth.
To learn more about this research, visit: sustainability.stanford.edu/news/rise-plant-life-changed-how-rivers-move-study-shows
