Geography Reference
In-Depth Information
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0.8
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Distance (m)
Distance (m)
Distance (m)
Distance (m)
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(a)
(b)
~ 1 m
~ 0.9 m
(c)
(d)
Figure 14.4
Laser scans compared with photographs to show the nature of gravel surfaces across exposed gravel bar areas on the
River Feshie, Scotland (a and c) and Bury Green Brook, UK (b and d). Reproduced from Hodge, R., Brasington, J. and Richards, K.
(2009b) In situ characterization of grain-scale fluvial morphology using terrestrial laser scanning.
Earth Surface Processes and
Landforms
34: 954-968, with permission from John Wiley & Sons, Ltd.
(although this varies with surface reflectivity). The field
laser scanner, connected to a Panasonic Toughbook
Figure 14.5 demonstrates the detail captured during
the scanning campaign. The survey data revealed a mor-
phology where sub-bar units could easily be identified
(Figure 14.5a), and allowed a useful comparison of sedi-
ment lobe sedimentology and dynamics with previously
published studies. Slumped blocks were generated follow-
ing small scale fluvial undercutting of the fine gravel bar
edges can be seen in the enlarged box view (Figure 14.5b).
Subtraction of repeat surface scans also documents the
development of subtle chute channel features acting as
a precursor to bar dissection through headward erosion
of these surfaces (Figure 14.5c). A similar study using
the same instrument covering a longer reach of the River
Coquet, Northumberland, UK is reported by Entwistle
and Fuller (2009). Despite use of fewer scans and reduced
multiple scan overlap, the average point spacing across
the 10 600m
2
point bar surface was 0.04m. Again the
definition across the bar surface enables sub-bar features
to be identified and grain scale maps were derived from
local surface roughness measures (Figure 14.6).
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computer, was used to conduct high-resolution scans of
the study area on a daily basis for ten days (although no
data could be gathered on day 8 because of fog). The
study area was scanned in four component sections and
subsequentlymergedusingRiScan-Pro™ post-processing
software. All four survey stations were slightly elevated
from the river, one being on a roche moutonnee and the
others on lateral and terminal moraines (Figure 14.5).
Survey control was facilitated by RiScan Pro
survey
software, capable of visualising point cloud data in the
field. Scans were generally restricted to 240
◦
in front of
the scanner, and were collected with substantial overlap,
ensuring that the surface of the study reach was recorded
from several directions. The effect of this approach was
to increase the point density across the surface and to
reduce the occurrence of occluded areas due to the shad-
owing effect of roughness elements along the line of
each scan.
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