Abstract
Whether the presence of permafrost systematically alters the rate of
riverbank erosion is a fundamental geomorphic question with significant
importance to infrastructure, water quality, and biogeochemistry of high
latitude watersheds. For over four decades this question has remained
unanswered due to a lack of data. Using remotely sensed imagery, we
addressed this knowledge gap by quantifying riverbank erosion rates
across the Arctic and subarctic. To compare these rates to
non-permafrost rivers we assembled a global dataset of published
riverbank erosion rates. We found that erosion rates in rivers
influenced by permafrost are on average six times lower than
non-permafrost systems; erosion rate differences increase up to 40 times
for the largest rivers. To test alternative hypotheses for the observed
erosion rate difference, we examined differences in total water yield
and erosional efficiency between these rivers and non-permafrost rivers.
Neither of these factors nor differences in river sediment loads
provided compelling alternative explanations, leading us to conclude
that permafrost limits riverbank erosion rates. This conclusion was
supported by field investigations of rates and patterns of erosion along
three rivers flowing through discontinuous permafrost in Alaska. Our
results show that permafrost limits maximum bank erosion rates on rivers
with stream powers greater than 900 W/m-1. On smaller rivers, however,
hydrology rather thaw rate may be dominant control on bank erosion. Our
findings suggest that Arctic warming and hydrological changes should
increase bank erosion rates on large rivers but may reduce rates on
rivers with drainage areas less than a few thousand km2.