Applications of Close-range Imagery in River Research - Fluvial Remote Sensing for Science and Management - page 344

figure reveals features that only the deployment of such
a camera could provide. Among other things, it can be
seen that falling rocks and boulders are the most fre-
quently observed events, accounting for more than 50%
of the total observed movements. Also, the vast majority
of events (80%) occur in the upper and middle bank
section causing some impact on the lower bank section.
Finally, when compared with local meteorological data
(Figure 15.9e), the results indicate the observed subaerial
processes occur mainly when the air temperature oscil-
lated around zero. The movements are also more frequent
during fall and spring time.
The deployment of a ground based camera in this case,
provided information that would be difficult to obtain in
another way. Erosion pins, for example, allow the erosion
or accumulation of sediment on a river bank to be mea-
sured, but it remains difficult to establish which process
causes the morphological change (Lawler, 1993). In this
context, the use of time lapse cameras become highly valu-
able when combined with other means of measurements,
such as erosion pins. In her study, Hamel (2011) used
monthly LIDAR surveys to extract volumetric changes
on the bank. The camera complemented the study by
giving key information about the physical processes that
accounted for the volumetric changes and their timing.

characterised by a braided pattern with a highly variable
cover of vegetated islands, and is fringed by continuous
riparian woodland.
We selected two different study reaches: i) a bar-
braided reach named the 'Cornino reach', located near
Cornino just upstream of the bridge of the same name;
and ii) an island-braided reach, 2 km upstream of the
Pinzano bridge, near Flagogna. These two reaches have
been subject to an intense multidisciplinary investigation
carried out by various European research groups (Bertoldi
et al., 2009). The first reach is about 1000 m long and
850 m wide and lies at an elevation of about 210 m above
sea level. The mean bed slope is 0.4%, and the sediment
size calibre ranges from fine sand to cobbles, with a D 50
of about 40 mm. and D 90 ranging from 50 to 150 mm.
The study area is dominated by Monte Prat on the right
side of the valley. The morphology is bar braided, with
a large area of exposed gravel and very few vegetated
stable areas. The reach is laterally unconstrained and does
not show evident human impacts apart from the small
embankment on the left side and a groin on the right side
to protect the bridge.
The 'Flagogna' reach is narrower, with an average
braidplain width of 700 m. The longitudinal bed slope is
about 0.3%. Sediment size is quite similar to the 'Cornino'
reach, with a larger fraction of sand that reduces D 50
to about 30 mm. The reach is dominated by Monte
Ragongna, on the left side of the valley. This reach is
characterised by the presence of large, well-established
vegetated islands, formed mainly by Poplar and Willow
species. Occurrence of difference size vegetated patches
leads to complex interactions between vegetation growth,
sediment movement, and river morphology (Bertoldi
et al., 2011).
Inundation dynamics were studied through the
ground-based camera system described in section 2.1 (see
also Figure 15.1). Approximately 70 images have been
orthorectified and classified, to highlight the planform
differences between exposed gravel and inundated areas
for various hydraulic conditions. To establish the interior
and exterior orientation parameters of the images the
digital

15.4.4 Inundationdynamicsofbraidedrivers

Monitoring braided river systems is a challenging task,
which requires high spatial resolution and rapid execution
to describe changes occurring on scales ranging from a
single branch and node up to the whole braidplain (West-
away et al., 2003). Frequent temporal surveys are resource
intensive, particularly if topographical and geomorphic
information are required during (or after each) flood.
However, the ground-based automated image acquisition
system developed for the Tagliamento River (Italy) and
introduced above, shows that it is possible to document
the morphological evolution of a large braided channel at
an hourly temporal scale and to use that information to
understand, for example, inundation dynamics.
The Tagliamento River is a large, gravel-bed braided
river located in the Friuli Venezia Giulia region, northeast
Italy, flowing from the southern limit of the Alps to the
Adriatic Sea. It still maintains a high degree of naturalness,
where morphological and ecological processes can be
observed (Tockner et al., 2003; Bertoldi et al., 2009). The
main stem of the Tagliamento River flows through an
immenseactivezoneofabout150km 2 and the floodplain
width is up to 1.5 km. Most of the active floodplain is

photogrammetric system ERDAS IMAGINE

OrthoBASE Pro ™ was used. The geometric distortion

inherent in imagery was removed using the Ortho

Resampling process of OrthoBASE Pro .Inorderto

fix the camera orientation 20 ground control points
were identified and surveyed with a standard DGPS
technique (Chandler et al., 2002). The precision of the
orthorectified images have ranges between 2 m and 6 m,
depending on distance from the camera. Figure 15.10

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