Download linkages between hydraulics, morphodynamics and ecological

ECOHYDROLOGY
Ecohydrol. 6, 507–510 (2013)
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/eco.1414
Preface
Ecohydraulics: linkages between hydraulics, morphodynamics
and ecological processes in rivers
Koen Blanckaert,1,2,3 Xavier-François Garcia,2* Johannes Steiger4 and Wim Uijttewaal5
1
2
State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences (RCEES), Chinese Academy of Sciences
(CAS), Beijing, China
Department of Limnology of Shallow Lakes and Lowland Rivers, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany
3
Laboratory of Hydraulic Constructions (LCH), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
4
UMR GEOLAB CNRS, Université Blaise Pascal, Clermond-Ferrand, France
5
Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands
ABSTRACT
The articles in this issue are a selection of the 15 main presentations made at the EUROMECH Colloquium 523 ‘Ecohydraulics:
linkages between hydraulics, morphodynamics and ecological processes in rivers’ that was organized in Clermont-Ferrand,
France, from 15 to 17 June 2011. The Colloquium was attended by 51 participants from 15 countries. Copyright © 2013 John
Wiley & Sons, Ltd.
KEY WORDS
renaturation; ecohydraulics; riparian vegetation; ecological models; field surveys; laboratory experiments
INTRODUCTION
Many river systems have been heavily regulated and
channelized in the past, with the aim to reclaim fertile land
in the floodplain, to protect cities and constructions against
natural hazards, to improve navigation, or to use water for
hydropower and irrigation. River regularization and
channelization often lead to modified hydrological cycles
with reduced flooding frequencies, high linearity, high
spatial homogeneity in flow conditions and bed morphology and reduced longitudinal (main channels and
tributaries) and lateral (main channel and riparian corridor)
ecological connectivity. The renaturation projects aim at reestablishing the major ecological functions of the river
system and enhancing the connectivity, without jeopardizing the economical functions of the river (e.g. navigation
and hydropower production) or the protection against
natural hazards (stabilization of structures such as bridge
piers and abutments or channel banks). River renaturation,
therefore, essentially aims at recreating some natural river
dynamics in a controlled way.
The effective design and implementation of river
renaturation projects requires good knowledge of hydrodynamic, morphodynamic and ecological processes, as well as
their mutual interactions. At present, knowledge and expertise
are still largely divided along monothematic lines. To bring
together scientists, practitioners and engineers with different
background and expertise, the EUROMECH Colloquium
523 ‘Ecohydraulics: linkages between hydraulics,
morphodynamics and ecological processes in rivers’ was
organized in Clermont-Ferrand, France, from 15 to 17 June
2011. The Colloquium was attended by 51 participants from
15 countries. This Special Issue of the Journal Ecohydrology
reports a selection of 15 main contributions to the
EUROMECH Colloquium 523.
Obviously, linkages between hydrodynamic, morphodynamic
and ecological processes cover an extremely wide field of
topics and research methodologies. Tables 1 and 2
classifies the contributions in the present special issue
according to their topic and methodology, respectively.
This preface aims to briefly introduce the contents of the
current special issue and to distill some lessons learned
from the Colloquium that can guide future research.
CONTENT OF THIS SPECIAL ISSUE
*Correspondence to: Xavier-François Garcia, Department of Limnology
of Shallow Lakes and Lowland Rivers, Leibniz-Institute of Freshwater
Ecology and Inland Fisheries (IGB), Berlin, Germany.
E-mail: [email protected]
Copyright © 2013 John Wiley & Sons, Ltd.
It is obvious that river regularization and channelization
impairs the ecological functions of a river. A good
understanding of the eco-hydro-morphological response
508
K. BLANCKAERT ET AL.
Table I. Topics covered in the present special issue.
Water quality,
temperature and
ecosystem
metabolism
Flow and morphology
Benthic
invertebrates
Casado et al.
Hondzo et al.
Henning and Hentschel
Jamieson et al.
Gostner et al.
Blanckaert et al.
Bruno et al.
of a river system to anthropogenic modifications is a first
requirement for the successful design of mitigation
measures and river renaturation schemes.
Dams have been built on numerous rivers in the past, to
increase flood retention capacity and to exploit water for
hydropower and irrigation. Dams affect all components of
the river ecosystem on a large spatial scale. In the present
special issue, Bruno et al. (this issue) and Casado et al.
(this issue) investigated the effect of dams on the thermal
regime of the river, Garófano-Gómez et al. (this issue),
Ncube et al. (this issue) and Ye et al. (this issue)
investigated the impact on vegetation and Han et al. (this
issue) investigated their effect on the fish dynamics.
Other human interventions, such as groynes that protect
riverbanks and improve navigation, only have an effect in
the immediate vicinity of the structure. In the present
special issue, Henning and Hentschel (this issue) and
Jamieson et al. (this issue) optimized the design of groynes
to improve their ecological value and hydraulic function.
River channelization often causes bottlenecks in the
ecological connectivity of the river system. Branco et al.
(this issue) optimized the design of boulders as a local
mitigation measure that improves the migration of fish.
Monitoring is essential to assess the evolution of the
ecological status of a river in response to anthropogenic
modifications. The monitoring typically has to be performed
over long temporal scales. Dam construction, for example,
modifies the hydrological characteristics and typically reduces
Fish
Vegetation
Branco et al.
Han et al.
Parasiewicz et al.
García-Arias et al.
Garófano-Gómez et al.
Luce et al.
Ncube et al.
Ye et al.
the inundation frequency of riparian zones and floodplains.
Riparian vegetation will only slowly adapt to new hydrological
conditions on a timescale that may range from years to
decennia. In a similar way, the river ecosystem also responds to
renaturation measures. Garófano-Gómez et al. (this issue) and
Ncube et al. (this issue) reported long-term monitoring of
changes in riparian vegetation and floodplains following dam
construction, whereas García-Arias et al. (this issue) monitored
changes in plant assemblages and distribution following river
renaturation.
Changes in the river ecosystem are relatively easy to
observe and monitor, but it is extremely difficult to assess
quantitatively the eco-hydro-morphological status of a river
and its evolution over time. Water managers, policymakers
and decision makers do, however, need a quantitative
assessment by means of simple metrics in order to evaluate
the cost–benefit ratio, the feasibility and the success of
renaturation projects. Gostner et al. (this issue) and
Parasiewicz et al. (this issue) proposed metrics for
quantitative assessment. These metrics are essentially
based on the hypothesis that physical heterogeneity, mainly
in flow depth and velocity, is an indicator of ecological
integrity. These metrics quantify the status of a river on the
temporal scale of a river reach. These metrics are not
process based but merely represent a descriptive statistical
quantification of the global ecological state of a river.
The most important but also the most difficult
component in the optimal design of a human intervention
Table II. Research methodologies covered in the present special issue.
Experiments on
ecological processes
in laboratory flumes
and mesocosms
Blanckaert et al.
Branco et al.
Bruno et al.
Han et al.
Field experiments on
flow and morphology
Field experiments on
ecological processes
Henning and Hentschel
Jamieson et al.
Branco et al.
Garófano-Gómez et al.
Hondzo et al.
Luce et al.
Ncube et al.
Ye et al.
Copyright © 2013 John Wiley & Sons, Ltd.
Process-based
ecological models
Han et al.
Ye et al.
Statistical
ecological models
García-Arias et al.
Ye et al.
Ecohydrol. 6, 507–510 (2013)
509
PREFACE
on a river is the prediction of the ecological response of the
river system. Ecological models can be divided into two
categories: statistical models and process-based models.
Statistical models relate in a statistical way the main
characteristics of a biological variable (such as biomass
of vegetation) to the main hydro-morphological drivers
(such as characteristics of the velocity and the flow
depth). García-Arias et al. (this issue) and Ye et al. (this
issue) used statistical models to investigate the evolution
of riparian vegetation. A limitation of statistical models
is that the statistical relation between biological and
hydro-morphological parameters is case dependent.
Therefore, these models cannot easily be commuted
between different rivers and require a reference state for
calibration.
Process-based models represent the main processes in
the life cycle of the investigated species. Ye et al. (this
issue) developed a process-based model for riparian
vegetation and compared its capabilities to a statistical
model. For the same reach on the River Lijaing in China,
Han et al. (this issue) developed a process-based model
for fish dynamics. Process-based models are less case
dependent and have a more general validity range than
statistical models. But the modelling of all main processes
involves a multitude of empirical parameters that
inherently leads to a relatively large uncertainty in the
model predictions.
Enhanced understanding of the main ecological processes is a requisite to improve ecological models. This special
issue reports experimental research on real rivers, in
mesocosms and in laboratory flumes.
Experimental research on real rivers often aims at
monitoring and documenting processes as well as
gathering data for the validation of ecological models.
Garófano-Gómez et al. (this issue), Ncube et al. (this
issue) and Ye et al. (this issue) reported field
experiments on riparian vegetation, and Branco et al.
(this issue) reported on the use of boulders to improve
fish migration. Hondzo et al. (this issue) analysed and
modelled the dynamics of dissolved oxygen, and Luce
et al. (this issue) investigated the biomass loss of
periphyton due to abrasion by sediment transport.
To prevent the complexity of the real river environment,
experiments are often performed in dedicated mesocosms
and laboratory flumes. Branco et al. (this issue)
complemented their field research on the use of boulders
to improve fish migration with experiments in a full-scale
experimental fishway. Bruno et al. (this issue) investigated
the response of benthic invertebrates to interacting
hydropeaking and thermopeaking in a set of open air
flumes directly fed by an Alpine stream. Han et al. (this
issue) investigated the movement rules of a fish under
volitional swimming conditions in dedicated laboratory
experiments. Blanckaert et al. (this issue) focussed on the
Copyright © 2013 John Wiley & Sons, Ltd.
role of turbulence on the drift of benthic invertebrates in
laboratory experiments.
CONCLUSIONS
The large spectrum of topics and research methodologies
covered in this special issue demonstrate the relevance and
importance of the relatively recent field of ecohydraulics.
The discussions during the EUROMECH 523 colloquium
and the selected papers in this special issue provide some
tentative conclusions and guidelines for future research:
1. Most contributions investigate and model separately water
quality, thermal regime, river morphology, benthic
invertebrates, fish and vegetation. It is logical to focus in
a first step separately on each of these topics, but future
development should strive to a more integrated approach
that includes the multiple linkages between the different
components and processes.
2. Some contributions investigate and quantify the river
ecosystem on a large spatial scale, and some contributions
investigate ecological processes on a small spatial scale.
River systems are characterized by a broad range of
relevant spatial and temporal scales that interact. We
believe that the interaction between the different spatial
and temporal scales is a topic that merits further attention in
the form of a multi-scale approach. As an example, patterns
of flow, turbulence and morphology that are ecologically
important do exist on small spatial scales, such as behind
obstacles in the flow field, or in the vicinity of irregular
banks. These small spatial scales cannot be resolved by the
hydro–morphological models that are typically used for the
modelling of river reaches. Hence, research could focus on
a parameterization of these small-scale processes that can
be incorporated in large-scale models. Moreover, efforts
have to be made to understand how hydraulic processes
occurring at large spatial scale affect and drive processes at
smaller spatial scales.
3. This special issue includes contributions that adopt a
statistical approach and contributions that adopt a processbased approach. Obviously, both approaches have advantages and limitations regarding generalization, prediction
skills, complexity and costs. The best predictions of the
response of river ecosystems to human interventions can
probably be obtained by a combination of both approaches
and by combining the expertise of mathematicians,
statisticians, hydrologists, hydraulicians, geomorphologists
and ecologists. Incorporating uncertainty in deterministic
models provide much more information and allows to value
the results. In all cases, well-documented field surveys that
include ecology and hydromorphology as well as laboratory
studies of the physical and biological processes remain of
key importance.
Ecohydrol. 6, 507–510 (2013)
510
K. BLANCKAERT ET AL.
We hope that the present special issues will provide
inspiration and ideas and contribute to the further progress
in the field of Ecohydraulics.
The guest editors of this Special Issue:
Koen Blanckaert
Xavier-François Garcia
Johannes Steiger
Wim Uijttewaal
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Ecohydrol. 6, 507–510 (2013)