Abstract
High-resolution terrestrial laser scanning (TLS) provides a unique opportunity to monitor short-term erosion and deposition processes in gully systems. This study quantified the pattern of erosion and deposition within an active gully in the sub-tropical environment of west Tennessee. Two TLS surveys were conducted on December 2014 and February 2015 to generate digital elevation models (DEMs) of different resolutions. The volumes of erosion and deposition were estimated by differencing the DEMs of these two dates with consideration of the spatially propagated errors associated with TLS-measured gully topography. The detected erosional and depositional volumes were 11.0 m^3 and 8.2 m^3, respectively, with a net loss of 2.8 m^3 of sediment at the DEM resolution of 2-cm. We found that both estimated volumes of erosion and deposition decrease as the DEM resolution becomes coarser. The estimated erosional volume decreases at a relatively high rate because erosion mainly occurs on steeper slopes where the propagated errors in TLS-measured topography are relatively higher, leading to rapid smoothing at coarser resolutions. In contrast, the depositional areas on gentler slopes have less propagated errors. This bias in the smoothing behavior of erosional and depositional areas appears to make coarser resolution DEMs dominated by deposition, a misleading interpretation of the sediment dynamics within the gully. We therefore suggest caution when using DEM difference to interpret the erosion-deposition processes within a gully system.
Highlights
Gullies are linear channels on hillslopes with steep sided and low width-depth ratio that expand through repeated flash flooding (Bocco, 1991; Morgan, 1996; Knighton, 1998)
We investigated the pattern of short term erosion and deposition within an active gully in the Meeman-Shelby Forest State Park, west Tennessee, based on two terrestrial laser scanning (TLS) scans over a 46-day period in 2014–2015
The estimated volumes of erosion and deposition were 11.0 and 8.2 m3, respectively, with a net loss of 2.8 m3 of sediment based on the 2-cm digital elevation models (DEMs) generated from the TLS surveys
Summary
Gullies are linear channels on hillslopes with steep sided and low width-depth ratio that expand through repeated flash flooding (Bocco, 1991; Morgan, 1996; Knighton, 1998). Gullies can be classified as ephemeral and permanent (Bull and Kirkby, 1997; Poesen et al, 1998; Poesen et al, 2003; Poesen et al, 2006). Ephemeral gullies are routinely infilled, leaving behind depressions that may promote the development of new gullies, while permanent gullies experience more pronounced erosion than deposition and are identifiable in the field (Bull and Kirkby, 1997). A common criterion to define gullies is based on a minimum width of 0.3-m and depths from 0.5 to 30-m with a threshold minimum cross-sectional area of 929 cm (1 ft2), named as the “square foot criterion” (Hudson, 1981; Poeson, 1993)
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