Geography Reference
In-Depth Information
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Figure 7.7a
a) Topographic survey points collected in the study reach. b) The location of waveforms identified by the ALPS
shallow-water bathymetry algorithm in 2002 along the Rowe Sanctuary study reach. c) Georeferenced aerial natural-colour imagery
taken on March 26, 2002. For reference and clarity the black lines in Figures a, b, and d (representing the edges of the banks and
islands) are shown in yellow on Figure c. d) Location of emergent sandbars defined using aerial thermal infrared imaging. Flow is
from lower left to upper right.
sand-bedded channel in central Nebraska, USA. The river
channel and riparian corridor have been transformed
by diminution of flows from upstream water-resource
development.
On March 26, 2002 ten passes were made with the
EAARL over a 1-km reach of the Platte River within the
Rowe Sanctuary. Simultaneously, measurements of chan-
nel topography and water-surface elevations were made
by wading in the channel using a survey-grade global
positioning system (Figure 7.7a-A). The waveforms col-
lected from the EAARL in the reach, both from emergent
and submerged topography, were first processed with the
USGS Airborne LiDAR Processing Software (ALPS) using
a first-return algorithm (Bonisteel et al., 2009). This algo-
rithm operated on all the waveforms regardless of their
shape and associated target type. The waveforms were
then processed using a shallow-water bathymetric algo-
rithm. Fewer points resulted from bathymetric processing
because of the processing criteria used for discrimination.
Figure 7.7a-B shows the location of the waveforms identi-
fied by the ALPS bathymetry algorithm. The points follow
the braided channels. An aerial natural colour photograph
taken at the same time as the EAARL survey is shown for
comparison (Figure 7.7a-C). The locations of the bathy-
metric waveforms correspond well to the darker portions
of the aerial photograph indicating locations where water
influences the transmission of sunlight to the camera.
The following procedure was used to examine the
influence of using EAARL-collected channel topography
over conventional measurements in a multidimensional
computational hydraulic model. The topographic points
collected with the conventional survey were used with
EAARL points collected along the emergent floodplain
and islands to map the topography of the river reach.
These points were used as input to MD_SWMS, a software
interface created by the United States Geological Sur-
vey for multidimensional hydraulic models (McDonald
et al., 2006). The depth-averaged 2-dimensional hydraulic
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