July 01, 2023
Unfreezing Permafrost Influence on Rivers
Permafrost limits the rate of riverbank erosion.
Across the Arctic, floodplains frozen continuously for more than 2 years are considered to be part of the permafrost layer. Rivers flowing through permafrost areas can erode these floodplains, releasing gravel, sediment, sand, and carbon into rivers, thereby affecting river biogeochemistry and ultimately, the geomorphology of coastal floodplains. Before ice-bounded sediments can be eroded by flowing water, they must be thawed. Using aerial photographs, satellite imagery, and direct field observations, a recent study found that permafrost slows the rate rivers erode their banks relative to rivers without permafrost. The effect of permafrost, however, varies with the size of the river, and the erosion rates of large rivers are disproportionately slowed by permafrost. As a result, permafrost thaw due to climate change will likely increase erosion rates on large rivers. Although erosion rates on small rivers are likely to be much more limited, little data for small rivers in the Arctic are available.
On average, bank erosion rates for rivers with permafrost are 9 times lower than rivers without permafrost. The difference in erosion rates increases with the size of the river, with the largest permafrost rivers eroding riverbanks up to 40 times slower than similar non-permafrost rivers. These results answer a long-standing question regarding the influence of permafrost on riverbank erosion and indicate that bank erosion on large Arctic rivers may accelerate as permafrost areas melt.
A multi-institutional team of researchers analyzed thousands of kilometers of riverbank erosion rates across the Arctic using aerial photographs, satellite imagery, and direct field observations, and they also assembled a global database of published erosion rates. Bank erosion rates between permafrost and non-permafrost rivers were compared to assess the impact of permafrost on erosion rates. This research also explored how erosion rates varied with the discharge and steepness of rivers. Alternative hypotheses based on differences in total water yield and erosional efficiency were tested to explain different erosion rates of Arctic hydrology and river sediment loads. Neither of these factors, nor differences in river sediment loads, provided compelling alternative explanations for bank erosion rates. Results showed that permafrost lowers maximum bank erosion rates by about 9 times on average. But on larger rivers, the erosion rate difference increases up to 40 times. While the findings suggest that Arctic warming and hydrologic changes are likely to increase bank erosion rates on larger rivers, the erosion rates on small rivers and streams may be reduced.
Los Alamos National Laboratory
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
Primary funding for this research was provided by the U.S. Department of Energy, Office of Science, Biological and Environmental Research (BER) Program Early Career Award and the Regional and Global Model Analysis Program funded Interdisciplinary Research for Arctic Coastal Environments (InteRFACE) project. Additional funding was provided by Los Alamos National Laboratory–Directed Research and Development for the work on Selawik River. Other funding was provided by Caltech Terrestrial Hazards Observation and Reporting Center, Foster and Coco Stanback, the Linde Family, the Resnick Sustainability Institute, National Science Foundation Awards 2127442 and 2031532, the National Defense Science and Engineering Graduate Fellowship, and the Fannie and John Hertz Foundation Cohen/Jacobs and Stein Family Fellowship.
Rowland, J. C., et al. "Scale-Dependent Influence of Permafrost on Riverbank Erosion Rates." Journal of Geophysical Research: Earth Surface 128 (7), e2023JF007101 (2023). https://doi.org/10.1029/2023JF007101.