Soil Erosion in the Alps

118 Pages·2014·5.09 MB·English

2014 > Environmental studies > Soil
> Soil Erosion in the Alps
Experience gained from case studies (2006–2013)

> Environmental studies > Soil
> Soil Erosion in the Alps
Experience gained from case studies (2006–2013)
Published by the Federal Office for the Environment FOEN
Bern, 2014
Publisher
Federal Office for the Environment (FOEN)
The FOEN is an office of the Federal Department of Environment,
Transport, Energy and Communications (DETEC).
Authors
Dr. Katrin Meusburger, Prof. Dr. Christine Alewell
Environmental Geosciences, Department Environmental Sciences,
Bernoullistr. 30, 4055 Basel, Switzerland
E-Mail: [email protected]
In-house consultant
Jean-Pierre Clement, Dr. Roland von Arx
Soil and Biotechnology Division, Soil Section
Suggested form of citation
Meusburger K., Alewell C. 2014: Soil Erosion in the Alps. Experience
gained from case studies (2006–2013). Federal Office for the
Environment, Bern. Environmental studies no. 1408: 116 pp.
Design
Stefanie Studer, 5444 Künten
Cover picture
Dr. Katrin Meusburger
Link to PDF file
www.bafu.admin.ch/uw-1408-e
(no printed version available)
© FOEN 2014
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> Table of contents

> Table of contents

Abstracts 5 3.1.2 Fallout radionuclides: a tool for assessment
Acknowledgements 6 of soil erosion rate in alpine areas? 60
Foreword 7 3.1.3 Stable isotopes as indicators of soil
Summary 8 perturbation 62
Introduction 12 3.2 Mapping erosion features and erosion risk factors
on catchment scale 68
3.3 Evaluation of suitable models for soil erosion risk
1 Soil erosion in three Alpine valley areas: mapping 72
Evaluation of the current status 19
1.1 Observations of an increase in shallow landslide
incidence 21 4 Future development and likely scenarios for soil
1.2 Quantification of sheet erosion rates – a challenging stability in the Alps 75
task in (sub-)alpine areas 23 4.1 Possible effects of climate variability 75
1.2.1 Soil erosion estimates derived from field 4.2 Effects of land-use change 78
measurements 23
1.2.2 Soil erosion estimates resulting from erosion
risk models 25 5 Mitigation of soil erosion by careful land-use
1.3 Comparison of soil erosion rates for different management (by Jakob Troxler) 85
processes and scales 29

6 Reporting on two workshops on “Soil Erosion in
2 Causes and risk factors for alpine soil loss 31 the Alps” (Andermatt 2007, Basel 2012) 92
2.1 Shallow landslide susceptibility factors 31 6.1 Workshop in Andermatt, 2007 92
2.1.1 Factors affecting natural landslide 6.2 Workshop in Basel, 2012 95
susceptibility: topography, geology,
hydrology, and soil 31
2.1.2 Factors related to trends in landslide 7 Conclusion 102
susceptibility: climate and land use 38
2.2 Sheet erosion risk factors 48
2.2.1 Climatic factors: precipitation and snow 48 Bibliography 105
2.2.2 Sheet erosion risk factors related to Abbreviations, figures and tables 114
vegetation cover and land-use management 54
2.3 Consequences for soil erosion assessment in the
Alps 56

3 Methods to assess processes of soil erosion and
causal factors in alpine areas 58
3.1 Field measurements with classical methods and
isotopes as indicators for soil erosion 58
3.1.1 Determining spring and summer sediment
yield with sediment traps, sediment cups,
and rainfall simulation 58

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> Abstracts

> Abstracts
This publication of the FOEN “Environmental studies” series gives an overview of the Keywords:
knowledge gained on soil erosion in the Alps during several case studies between 2006 Alps, soil erosion, landslide,
to 2013. Many Alpine areas experience an increase in soil erosion, which is demon- climate change, land use change
strated for three sites in the cantons Uri, Valais and Ticino. Potential causes for the
increased erosion susceptibility as well as controlling factors in general are analysed
and suitable methods for soil erosion assessment in Alpine areas evaluated.
Die vorliegende Publikation in der BAFU-Reihe «Umwelt-Wissen» präsentiert die Er- Stichwörter:
kenntnisse zur Bodenerosion in den Alpen, die in zahlreichen Einzelstudien von 2006 Alpen, Bodenerosion, Rutschung,
bis 2013 gewonnen wurden. In vielen Alpinen Gebieten ist eine Zunahme der Bodene- Klimawandel,
rosion zu beobachten. Diese wird exemplarisch an drei Gebieten im Kanton Uri, Wallis Landnutzungswandel
und Tessin aufgezeigt. Mögliche Ursachen der Zunahme der Schäden, sowie generelle
Steuergrössen der Bodenerosion werden analysiert und Methoden zur Boden-
erosionserfassung auf Ihre Eignung in Alpinen Gebieten beurteilt.
La présente publication qui paraît dans la série OFEV «Connaissance de l’environne- Mots-clés:
ment» établit l’état des connaissances sur l’érosion des sols dans les Alpes résultant de Alpes, érosion des sols,
nombreuses études réalisées de 2006 à 2013. Une augmentation de l’érosion est consta- glissements de terrain,
tée dans de nombreuses régions alpines. Cette augmentation est illustré par l’étude de changement climatique, évolution
trois régions dans les cantons d’Uri, du Valais et du Tessin. Les diverses facteurs qui des utilisations des sols
pourraient expliquer le constat de l’augmentation de la fréquence des atteintes, ainsi
que les facteurs qui contribuent généralement à l’érosion des sols sont analysés. Des
méthodes destinées à l’évaluation et la quantification de l’érosion dans les régions al-
pines sont présentées et commentées.
La seguente pubblicazione della serie «Studi sull’Ambiente» dell’UFAM offre una Parole chiave:
panoramica dei risultati di diversi casi studio, svolti tra il 2006 e il 2013, dedicati alla Alpi, erosione del suolo,
ricerca dell’erosione del suolo nelle Alpi. La ricerca, condotta in tre diversi siti nei frana, cambiamento climatico,
cantoni Uri, Vallese e Ticino, evidenzia un aumento dell’erosione del suolo nelle aree cambiamento dell'uso del suolo
alpine. Nel presente studio, le cause potenziali di questo aumento nonchè i principali
parametri di controllo del fenomeno vengono presi in considerazione e analizzati. Sono
infine descritti e valutati i diversi metodi di stima dell’erosione del suolo nelle Alpi.
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Soil Erosion in the Alps. Experience gained from case studies (2006–2013) FOEN 2014

> Acknowledgements
The presented compilation of case studies on “Soil erosion in the Alps” was only
possible through the support and collaboration of many. First of all, we would like to
thank the Swiss National Science Foundation and the State Secretariat for Education
and Research, in the framework of the European COST action 634: “On- and Off-site
Environmental Impacts of Runoff and Erosion” for co-funding.
The important study on soil erodibility and rainfall erosivity was only possible within
the collaboration agreement (No. 31576) between the European Union (Institute for
Environment and Sustainability) and the Swiss Federal Council (Federal Office for the
Environment). Thanks go to the Soil Action for their hospitality and in particular to
Panos Panagos for the excellent co-operation.
Especially the assessment of the former land use situation was a challenge. For the
Obergomer Valley we were supported by Bruno Anthenien, Norbert Agten and Florian
Hallenbarter. In the Urseren Valley we were supported by Martin Schaffner from the
History Department and Erika Hiltbrunner from the Plant Ecology group of the Uni-
versity of Basel. Moreover, Meinrad Müller from the Korporation Urseren was very
helpful throughout the project. Thanks go also to the farmers of the valleys who agreed
to the investigation of the sites and were open for interviews.
Further, we would like to thank the PhD students Monika Schaub and Nadine Konz
for their large contribution to the qualitative and quantitative soil erosion assessment
in the Alps. Interesting results on the role of vegetation could be established by the
Master students Yael Schindler-Wildhaber, Cyrill Martin and Andreas Merz. Support
regarding the use of fallout radionuclides came from the Master students Bastian
Brun, Gregor Juretzko and the Bachelor students Clara Brutsche, Martina Polek,
Annette Ramp and Andrea Walter.
Last but not least, we would like to thank Alexander Imhof from the Environmental
Protection Agency, Canton Uri for his constant support and for the organisation of the
Soil erosion Workshop in Andermatt.
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> Foreword

> Foreword
In Switzerland, the erosion of arable land has been the subject of numerous studies
aimed at understanding its causes and mechanisms. These have led to the introduction
of monitoring and prevention measures and the development of tools for estimating the
risks. The Guide to Combating the Erosion of Arable Soil (1991) Ordinance Relating
to Impacts on the Soil (OIS)(1998), the online map of the potential risk to agricultural
soil in Switzerland (2012) and the module on the protection of agricultural soil (2013)
all contribute to forming the legislative and technical framework for protecting arable
land against water erosion.
Whereas the erosion of arable land and erosion due to natural dangers (such as ava-
lanches, flooding or rockfalls) have been extensively studied, this is not the case as
far as Alpine pastures are concerned. Around ten years ago, aware of this lack of
knowledge in Switzerland and in the other Alpine countries, the FOEN decided to
support research being conducted by the Institute for Environmental Geosciences at
the University of Basel that aims to address these deficiencies.
This scientific publication summarises and presents the results of this research, carried
out over the past ten years, together with the conclusions reached at two workshops on
the same subject. This overview sets out the state of knowledge and paves the way for
future developments with a view to improving understanding, and takes account of the
risks that erosion poses to Alpine pastures.
Gérard Poffet
Vice Director
Federal Office for the Environment (FOEN)
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Soil Erosion in the Alps. Experience gained from case studies (2006–2013) FOEN 2014

> Summary
Mountain soils are characterized by an intrinsic fragility and low resilience (i.e. the
capability to recover after severe stress), making the process of soil erosion almost
irreversible.
Until recently, soil erosion research almost exclusively concentrated on arable land. As
a consequence, suitable methods to describe and predict soil erosion in mountain areas
with low accessibility, steep topography, and extreme climate are missing. Shallow
landslides are an evident soil erosion feature in the Alps, but they are traditionally seen
as a natural hazard and their relevance for soil loss and the connected on-site damage is
rarely considered.
The second major process responsible for soil loss is soil erosion by water, which is the
transport of single soil particles. It is influenced by many factors, which can be summa-
rized as rainfall erosivity, soil erodibility, slope steepness, the protection due to soil
cover and vegetation, and – in alpine areas – the erosivity of the snow movement and
snowmelt.
In the presented work, we aim at a holistic evaluation of methods of assessing soil loss
in alpine areas as well as the possible processes and causes responsible for it.
Switzerland is one of the countries where strong climate change impacts are expected.
The temperature increase in the Swiss Alps is clearly above the global average and
future projections suggest decreasing return periods of extreme rainfall events. In
addition, all over the European Alps, major land use changes are observed. Such land-
use and climate changes are expected to affect the susceptibility of mountain soils. In
order to react to these changes or even to allow their timely prevention, a better under-
standing and assessment of alpine soil erosion is needed.
Since 2005, the University of Basel (Environmental Geosciences) has been engaged in
filling this knowledge gap. New methods of assessing and mapping soil erosion and
soil erosion risk factors in the Alps have been developed. They range from remote
sensing, modelling, and isotope analysis (13C, 15N, 18O, 137Cs, 239+240Pu) to field meas-
urements and soil mapping.
Three Alpine valley sites that differ in land-use history, climatic conditions, and geolo-
gy have been chosen: the Obergoms (65 km²), Urseren, (30 km²) and Bedretto/Piora
valleys (90 km²). All three sites show increasing trends of the maximum of cumulative
three-day rain events (relevant for landslide triggering). Regarding land use in the
Obergoms and Urseren valleys, productive areas are in continuous use, and land use
has often been intensified while less productive areas have been abandoned, leading to
natural shrub encroachment and reforestation. In the Bedretto/Piora valleys, land use
management has remained almost unchanged for decades.