Quantifying the effects of freeze-thaw processes on riverbank erosion in the White Clay Creek Watershed, PA
Date
2019
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Publisher
University of Delaware
Abstract
Subaerial erosion of riverbank sediments in the Mid-Atlantic region of the eastern United States is of particular concern with regard to sediment supply and water quality. One process heretofore understudied in this region that may play a role in erosion is the freezing and thawing of riverbank sediments, a process that occurs repeatedly as a consequence of the region’s temperate winters. Over the last two years, observations of needle, segregated, and pore-space ice on riverbanks of the White Clay Creek suggest that the region’s silty and sandy soils are prone to riverbank erosion and sediment entrainment related to soil freeze-thaw processes. Prior studies have acknowledged that soil freeze-thaw likely contributes to riverbank erosion but without direct quantification. To better understand the climatic conditions driving these processes and to attempt to quantify their effect on sediment erosion, an array of techniques were employed, including measurement of near-surface temperature and soil water content, erosion pins, and close-range digital photogrammetry surveying to monitor change over days to weeks for two vertical riverbanks. Through the winters of 2017 to 2019, periods of rapid freezing followed by significant thawing of water-saturated banks were repeatedly observed. The applied photogrammetry surveying techniques allowed for topographic models with sufficient resolution to quantify centimeter-scale retreat and expansion over the course of freeze-thaw events, fluxes which were validated by traditional erosion pin surveying measurements. These observations help to quantify the heretofore underestimated importance of soil freeze-thaw processes to an overall sediment budget. Additionally, the techniques presented herein lay the groundwork for further study to examine the contribution of freeze-thaw cycling to overall bank erosion rates for the White Clay Creek.