Geography Reference
In-Depth Information
11
Biophysical Characterisation
of Fluvial Corridors at Reach
to Network Scales
Herv ´ePiegay
1
, Adrien Alber
1
, J. Wesley Lauer
2
, Anne-Julia
Rollet
3
and Elise Wiederkehr
1
1
University of Lyon, CNRS, France
2
Department of Civil and Environmental Engineering, Seattle University, Seattle,
WA, USA
3
University of Caen Basse-Normandie, Geophen, CNRS, France
Europe where the European Water Framework Directive
implementation requires managers to plan restoration
efforts at large hydrographic network scales even when
only local scale processes are well characterised.
From a management perspective, there is a need for
expanding the extent of spatial analysis from that of local
sites of a few metres to a few hundred metres to that of river
reaches of several km (e.g. the main stem of a large river)
or of an entire stream network of a watershed. Network-
scale analysis requires an extension of the reach-scale
perspective, opening new methodological issues in terms
of data availability, statistical analysis, and scale effects. It
is now common to characterise fluvial corridor features,
i.e. the channel and its natural margins, at the network
scale. For example, the concept of a cascading sedi-
mentary system is becoming a central tool in watershed
management and explicitly considers sources, transfers
and depositions of sediment in an integrated framework
(Sear et al., 1995; Brierley et al., 2006). In addition to
characterising natural processes, such approaches inform
decisions that balance the interests of a range of stake-
holders who may focus on natural resources management,
ecosystem value, risk assessment and/or mitigation, and
11.1 Introduction
Previous chapters have discussed the extraction and
classification of features representing in-stream habitat,
vegetation patches, or other biophysical characteristics
(bar grain-size, vegetation structure, water depth, tem-
perature, relative elevation, etc.). The question we address
here is how to expand local extractions to larger scales,
and in particular how to evaluate the temporal trajectory
of rivers at reach to network scale. Because of the ever
increasing amount of spatial data and new technologies
to analyse them, reach scale analysis offers a strategic
perspective in terms of knowledge production (Fergu-
son, 2007). For example, classification of reach-scale
patterns potentially allows rapid identification of eco-
logically interesting fluvial corridors or reaches adversely
altered by human activities (Thorp et al., 2006). It can also
provide basic physical data for better estimating the time
necessary for a river reach to adjust to human pressure.
This is a key issue of a geomorphic audit (Kondolf et al.,
2003). Such analyses, often referred to as regionalisation
studies (Bryce and Clark, 1996; Higgins et al., 2005), have
gained increasing importance recently, particularly in
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