Measuring bluff erosion part 2: pairing aerial photographs and terrestrial laser scanning to create a watershed scale sediment budget

Abstract

Effectively managing and reducing high suspended sediment loads in rivers requires an understanding of the magnitude of major sediment sources as well as erosion and transport processes that deliver excess fine sediments to the channel network. The focus of this research is to determine the magnitude of erosion from tall bluffs, a primary sediment source in the 2880 km2 Le Sueur watershed, Minnesota, USA. We coupled analyses of seven decades of aerial photographs with four years of repeat terrestrial laser scanning (TLS) to determine erosion rates on bluffs. Together, these datasets provide decadal‐scale retreat rates throughout the entire watershed and high‐resolution geomorphic change detection on a subset of bluffs to both constrain erosion rates and document how environmental conditions affect bluff retreat. Erosion rates from aerial photographs and TLS were extrapolated from 243 and 15 measured bluffs, respectively, to all 480 bluffs in the Le Sueur watershed using multiple techniques to obtain estimates of sediment loading from these features at the watershed‐scale. Despite different spatial and temporal measurement scales, the aerial photograph and TLS estimates yielded similar results for bluff retreat rate and total mass of sediment derived from bluffs, with bluffs in the Le Sueur watershed yielding 135 000 ± 39 000 Mg/yr of fine sediment. Comparing this value to the average annual total suspended solids (TSS) load determined from gauging from 2000 to 2010, we determined that bluffs comprise 57 ± 16% of the total TSS load, making bluffs the single most abundant fine sediment source in the basin. Copyright © 2012 John Wiley & Sons, Ltd.

Landscape-scale geomorphic change detection: Quantifying spatially variable uncertainty and circumventing legacy data issues

“…Slope and elevation error values were modified based on checkpoint data. Net change results for bluffs were compared to each other and also to the reported erosion rate measured by Terrestrial Laser Scanning (TLS) for one bluff from another study in the same area, 132 m 3 y −1 (TrB1 in Day et al, 2013b), which is not a perfect comparison because the time periods do not coincide exactly, but is a useful comparison nevertheless. Net change on the bluff using the chosen FIS was 223 m 3 y −1 which is higher than the TLS estimate (FIS 3 in Table 2).…”

Human amplified changes in precipitation–runoff patterns in large river basins of the Midwestern United States

“…We selected these basins for the following reasons: all are agricultural, to various degrees, primarily producing corn and soybeans; all are located mainly within the Central Lowland physiographic province and were affected by continental glaciation resulting in mostly flat, poorly drained uplands and incised river valleys (Arnold et al, 1999;Barnes, 1997;Belmont et al, 2011;Day et al, 2013;Gran et al, 2009;Groschen et al, 2000;Rosenberg et al, 2005;Stark et al, 1996); and all are characterized by a humid, temperate climate (Kottek et al, 2006 (Fig. 1).…”

Monitoring Riverbank Erosion in Mountain Catchments Using Terrestrial Laser Scanning

“…Secondly, trees' canopies may prevent the visibility of some riverbanks in the aerial photos. These problems might result in potential errors in the delineations of bank crests as well as the geo-rectification of aerial photographs [56].…”