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| Titel |
Identification and prediction of channel heads from gridded elevation data |
| VerfasserIn |
Stefano Orlandini, Giovanni Moretti, Paolo Tarolli, Giancarlo Dalla Fontana |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037847
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| Zusammenfassung |
| The representation and prediction of stream channels in drainage basins has been a perennial
concern in geomorphology, with implications for understanding of drainage basin origin,
scale and morphology, basin hydrology, and effects of natural and man-induced process
changes. The channel (or stream) network is defined by channels with well-defined banks and
sources. In theory, the channel network includes all the minor rills which are definite
watercourses, even including all the ephemeral channels in the furthermost headwaters. In
practice, the direct survey of all channels is normally a prohibitive task, and the
detail with which the channel network is represented is dependent on the scale
of the map used to trace the channels. In actual fact, the headward limits of the
blue lines do not reflect any statistical characteristic of streamflow occurrence, but
they are drawn to fit a rather personalized aesthetic. On the other hand, the explicit
description of the mechanisms determining the channel heads is a nontrivial task since it
requires complex fluvial and/or landsliding processes to be considered singly or in
combination. However, the increasing availability of highly accurate digital elevation data
derived from LiDAR surveys, reliable terrain analysis methods, and observations
collected in the field or remotely, offers new potential for developing and/or evaluating
prediction models for channel initiation. In addition to detailed models, simpler
generalizations from field facts can be sought by incorporating the broad features of climate,
topography, and geology. In the present study, three threshold conditions for channel
initiation are evaluated by using gridded elevation data derived from high-precision
LiDAR surveys, a reliable algorithm for the determination of surface flow paths,
and accurate field observations of channel heads for sites located in the eastern
Italian Alps. These three threshold conditions are determined by considering part of
the observed channel heads and computing for them the related values of (1) the
drainage area A, (2) the monomial function AS2 of the drainage area A and the local
slope S, and (3) the Strahler order Ï* of surface flow paths extracted from gridded
elevation data. Attention is focused on the dependence of the obtained threshold
values on the size of grid cells involved, and on the ability of threshold conditions to
reproduce the observed channel heads. The results indicate that (i) the uncertainty in the
threshold values of the Strahler order Ï* is significantly smaller than that affecting the
threshold values of the drainage area A and the area-slope function AS2, (ii) threshold
values of A, AS2, and Ï* are all significantly dependent on grid cell size, and (iii)
the threshold values of the Strahler order Ï* follow quite well a power function
relationship of grid cell size. The comparison between reproduced and observed
channel networks for several drainage basins indicates that Strahler classification
of surface flow paths and pruning of exterior links provides a sound rationale for
the determination of channel heads formed essentially by surface erosion, but it
reveals that more comprehensive methods are needed to reproduce channel heads
in areas affected by strong geologic controls and groundwater seeping upwards. |
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