NH1.6

Vegetation as nature-based solution for mitigating hydro-meteorological geohazards on slopes and streambanks

Climate-induced geohazards are known to increase with climate change causing more intense rainfall and more frequent extreme weather events. Use of vegetation on potentially unstable slopes and along stream banks is an example of Nature-Based Solutions (NBS) that can mitigate climate induced geohazards due their role at the soil-atmosphere interface. Vegetating slopes or stream banks are also key for ecological restoration and rewilding, providing several additional co-benefits. However, researchers in different fields of science or practitioners do not easily communicate, even though they are addressing aspects of the same problem.
Interdisciplinary research and bilateral communication are needed to document the effects of vegetation in hazard-prone areas in a measurable and applicable manner. These NBS must have an ecological approach, where in the long-term perspective, a multiple approach for biodiversity and ecosystem services will give mutual synergies.

This session aims to stimulate interdisciplinary communication, knowledge exchange and dissemination on plant-soil-atmosphere interaction, with focus on vegetation mitigating climate-induced geohazards, particularly shallow landslides and erosion.
Contributions documenting how vegetation and roots can be beneficial also in land use planning, restoration ecology, climate change adaptation are welcome within the fields of geotechnical engineering, plant ecology, biodiversity, alpine timberline, hydrogeology and agronomy.
Interaction between research and industry, with involvement of NBS entrepreneurs, are particularly welcome.

Topics of interested are listed, including, but not limited to:
• Experimental, either laboratory or field, or numerical investigation of plant-soil-atmosphere interaction and its relation to slope or bank stability
• How to implement morpho-mechanical parameters of plants in engineering design?
• Measuring and quantifying the effects of vegetation as NBS to mitigate climate-induced geohazards
• Tools, approaches, and frameworks demonstrating how vegetation can be used to mitigate climate-induced geohazards, while providing additional co-benefits
• Investigation on upscaling potential from laboratory to slope and catchment scale
• Case studies of restoration or stabilisation works, especially on design principles and performance assessment
• Ensuring interdisciplinary interaction and mutual synergies for studies containing vegetation as NBS among different disciplines

Co-organized by GM3/HS13
Convener: Vittoria CapobiancoECSECS | Co-conveners: Sabatino Cuomo, Dominika Krzeminska, Anil YildizECSECS, Alessandro FraccicaECSECS
Presentations
| Tue, 24 May, 15:10–18:24 (CEST)
 
Room C

Presentations: Tue, 24 May | Room C

Chairpersons: Anil Yildiz, Alessandro Fraccica
15:10–15:15
15:15–15:22
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EGU22-8523
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Virtual presentation
Anthony Leung and Ali Akbar Karimzadeh

Plant roots increase soil shear strength. The increase primarily depends on the relative direction of the root orientation and the principal strains/stresses of the rooted soils. Most of the published work focused on the direct-shear behaviour of rooted soil, of which both the magnitude and direction of the principal stresses could not be controlled nor measured. Indeed, in the scenario of slopes, the stress path experienced by direct-shear soil samples and the associated shear strength parameters (e.g. cohesion and friction angle) derived are only relevant to the soil elements that are sheared in the direction parallel to the slope. The shearing behaviour of rooted soil following other stress paths, such as triaxial compression (near slope crest) and triaxial extension (near slope toe), have rarely been investigated. In this study, we conduct a comprehensive laboratory test campaign to study the effects of stress paths on the shearing behaviour including stress-strain (hardening and softening) on coarse-grained soils reinforced by the roots of vetiver grass (Chrysopogon zizanioides). Root-reinforced soil samples prepared to different root volume ratios (RVR; defined as the ratio of total root volume to total specimen volume) were subjected to undrained triaxial compression and extension stress paths at different confining stresses. We will present key experimental evidence to demonstrate how the different stress paths and RVRs affect the stress–strain behaviour of the soil. We will also present the effects of stress path on cohesion and friction angle and discuss the strength anisotropy of the rooted soils. The new test results will shed light on the selection of plants of desirable root architecture at different slope locations (i.e. crest, mid-slope, toe) to maximise the root reinforcement effects to shallow soils.

How to cite: Leung, A. and Karimzadeh, A. A.: Stress path effects on the shearing behaviour of root-reinforced soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8523, https://doi.org/10.5194/egusphere-egu22-8523, 2022.

15:22–15:29
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EGU22-12479
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ECS
Alessandro Fraccica, Enrique Romero, and Thierry Fourcaud

The focus of geotechnical researchers and practitioners has recently been on the impact of vegetation on the mechanical behaviour of the soil as nature-based techniques against erosion and landslides. Although numerous laboratory studies have already been produced on this subject, there seems to be a lack of discussion on the significance of the results in relation to the representative elementary volume (REV) used. An excessive or scarce root/soil ratio can result in over- or underestimation of the strength of the soil specimen tested, respectively. In addition, a root/soil ratio very different from that which the plants have in-situ would risk making the laboratory results difficult to upscale to the slope or catchment level. To this end, the aim of this study is to present triaxial compression tests of large vegetated soil specimens (h = 400 mm Φ = 200 mm).

Silty sand was used and statically compacted at a dry density ρd = 1.60 Mg/m3 and at a water content w = 15%. Samples were then thoroughly poured with water up to a high degree of saturation (Sr ≈ 0.95). Eight of them were seeded with Cynodon dactilon, maintaining fixed seeding spacing and density. Samples were irrigated for eight months to induce sprouting and root growth: during this period, matric suction was monitored. The same procedure was followed to prepare ten fallow specimens.

Prior to testing, samples were sealed and left in the darkness in a temperature/relative humidity-controlled room for 24 hours, to equalise the desired value of initial suction. An isotropic consolidation stress between 10 and 50 kPa was imposed prior to shearing at a vertical displacement rate of 0.016 mm/min. Matric suction was measured by a tensiometer and the water content was checked at the beginning and at the end of each test. Finally, soil samples were washed to retrieve the entire root architecture, to assess root volume and tensile strength. The resulting values of the root volume ratio of Cynodon dactilon were in good agreement with those observed in-situ in literature studies.

Generally, the higher the initial soil matric suction, the higher the strength observed in the tests, with vegetated soil systematically showing greater strength than the bare one at similar hydro-mechanical states. In fact, at low values of suction, additional resistance in vegetated soil was observed once reaching large shear deformations, whereas, in drier soils, root reinforcement was activated at smaller strains. Indeed, soil hydraulic state affected the root failure mechanism. In nearly saturated soil, the roots subjected to shearing/tension are free to stretch and slip whereas in slightly saturated soil they are firmly bonded within the matrix and so they experience a more immediate breakage.  

Despite the root reinforcement, the vegetated samples exhibited larger volume deformations upon shearing, due to the changes generated by root growth on soil fabric (fissures).

A shear strength criterion for partially saturated soils was used to interpret successfully the results, considering suction, degree of saturation, and soil microstructure. Roots predominantly increased the apparent cohesion of the soil, with minor changes on the friction angle.

How to cite: Fraccica, A., Romero, E., and Fourcaud, T.: Large-scale triaxial tests of vegetated soil at low confining stresses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12479, https://doi.org/10.5194/egusphere-egu22-12479, 2022.

15:29–15:36
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EGU22-12986
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ECS
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Virtual presentation
Ali Akbar Karimzadeh and Anthony Kwan Leung

Revealing the liquefaction mechanism and anisotropy behaviour of root-reinforced soils: an energy-based approach

 

Ali Akbar Karimzadeh, Anthony Kwan Leung

Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR

 

Abstract:

Recent physical modelling work has demonstrated that plant roots provide seismic resistance to geotechnical infrastructure such as slopes and pipelines against liquefaction. Indeed, there is evidence from published triaxial data that the presence of roots increased the liquefaction resistance of soil and changed the liquefaction failure mode from limited flow failure to cyclic mobility, depending on the amount of cyclic stress ratio applied and the available root volume. However, effects of root orientation on soil anisotropy and energy dissipation during the process of liquefaction, have not been adequately addressed in the literature. In this presentation, we will present a new energy-based framework and its application to reinterpret a set of published triaxial data concerning on the undrained strain-controlled cyclic behaviour of root-reinforced soils. Based on the framework, the changes in the amount of dissipated energy required to reach the liquefaction criteria (i.e. 5% double-amplitude axial strain) of the soil due to the presence of roots of different volume ratio will be determined. We will use this energy term and the strain values at the compressive and extensive sides of a cyclic loading at the liquefaction state to explore how root orientations would affect the soil anisotropy. A new correlation between normalised cumulative dissipated energy (∑ΔW/σc, where σc is the effective confining pressure) and the cyclic resistance ratio at the cycle number of 15 (CRR15) will be established. We will also present the correlation between the ∑ΔW/σc with the normalised cumulative strain energy (∑4W/σc) which is representative to the the demand energy of an earthquake event. Finally, we will discuss any effects of the recycling and recovering of strain energy upon cyclic loading, and their importance in the energy interpretation to root-reinforced soils.

Keywords: Energy-based approach, Root-reinforced soil, Anisotropy, Liquefaction, Triaxial cyclic tests

How to cite: Karimzadeh, A. A. and Leung, A. K.: Revealing the liquefaction mechanism and anisotropy behaviour of root-reinforced soils: an energy-based approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12986, https://doi.org/10.5194/egusphere-egu22-12986, 2022.

15:36–15:43
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EGU22-13252
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ECS
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Virtual presentation
Xu-Guang Gao, Ji-Peng Wang, Yi-Ran Tan, Jiong Zhang, and Bertrand François

Rainfall infiltration is the main inducing factor for the instability of unsaturated soil slopes, and root water uptake and reinforcement play an important role in preventing shallow landslide. In order to explore the influence of vegetation root on the soil hydraulic and mechanical properties under rainfall, a self-designed soil permeability coefficient measuring device considering the effects of vegetation was used to study the soil water characteristic curve (SWCC) and permeability coefficient of Festuca Arundinacea, Ophiopogon Japonicus, Ligustrum Vicaryi and bare soil under two different rainfall conditions (3.0mm/h and 5.0mm/h) were studied. Then, the direct shear tests of root-soil composite with different water contents and root contents were carried out. Finally, the slope stability under different rainfall and vegetation was simulated by GeoStudio. Results show that: root water uptake can effectively reduce soil water content and increase soil suction, and its influence range is about 2-3 times the length of the root system. Root water uptake can also significantly improve the soil water retention capacity. The air entry value of vegetation soil is larger than that of bare soil, and the permeability coefficient of vegetation soil is about one order of magnitude lower than that of bare soil. Among the three different types of vegetation, the effect of Festuca Arundinacea and Ophiopogon Japonicus on soil water content and suction is more significant than Ligustrum Vicaryi. Root reinforcement mainly increases the soil shear strength by improving the cohesion of the root-soil composite, but has little effect on the internal friction angle. The cohesion of the root-soil composite is affected by soil water content, root content and root distribution, which increases with the increase of root content, and decreases with the increase of water content. When the roots are vertically distributed, the cohesion of the root-soil composite is greater than when the roots are placed horizontally and inclined. Vegetation can effectively improve the stability of the shallow slope under various rainfall conditions, but has little effect on the stability of a deep slope. The safety factor of all three types of vegetated slopes is higher than that of bare soil slopes.

How to cite: Gao, X.-G., Wang, J.-P., Tan, Y.-R., Zhang, J., and François, B.: Effect of vegetation roots on soil hydraulic and mechanical characteristics under rainfall, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13252, https://doi.org/10.5194/egusphere-egu22-13252, 2022.

15:43–15:50
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EGU22-9004
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ECS
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Virtual presentation
Rozaqqa Noviandi, Takashi Gomi, Roy C. Sidle, Rasis P. Ritonga, and Yuko Hasunuma

Landslides are common natural hazards that greatly impact lives and property worldwide. The magnitude of landslide impacts depends strongly on how far landslide sediments travel, widely known as landslide mobility. Numerous studies showed that landslide mobility is complex, but largely affected by initial water content during landslide initiation. Here, water acts as a medium that carries the collapsed landslide mass downslope. Vegetation root systems may alter the initial water content by modifying the flow path within the soil. The mechanical reinforcement of root systems may also limit the spatial propagation of the landslide mass. Thus, vegetation root systems may exert significant effects on landslide mobility. Nevertheless, effects of root systems on landslide mobility have rarely been discussed in landslide studies. The objective of this study is to evaluate the effect of rooting systems on landslide mobility.

A flume constructed at a 1:70 scale was used to evaluate the effect of root systems on landslide mobility. The flume consisted of two segments representing landslide initiation (120 cm long, 35° inclination) and deposition (150 cm long, 35° inclination). All segments were 80 cm wide, 15 cm high, and constructed with 1-cm thick acrylic material. Sand (density=1.4 g/cm3, D50=0.23 mm) was placed in the initiation segment to a depth of 10 cm. For conditions with vegetation (V), we grew pea (Pisum sativum L.) bean sprouts in the sand to simulate the root system. Sprouts were grown at 3 cm intervals for two weeks to simulate the root system on 2200 stem/ha of Japanese cedar forest. To initiate landslides, 90 mm/h of rainfall was applied via nozzles installed at 2 m above the flume. Timing of landslide initiation was then measured. Water content was also measured by TDR sensors installed at 3 and 7 cm depths below the soil surface. The L/H ratio was estimated based on total travel distance and total descent height of the landslide mass.

Vegetated conditions (V; n=3) were more stable than non-vegetated conditions (NV; n=3). Indeed, landslides initiated at 889-959 s (SD=41 s) on V, while on NV was 510-519 s (SD=5 s). Mean volumetric water content during landslide initiation was 0.2-0.22 (SD=0.01) on V, while on NV was 0.16-0.2 (SD=0.02). Because V had higher water content than NV, V was 1.2-1.4 times more mobile than NV. The L/H was 2.2-2.4 (SD=0.09) on V, while on NV it was 1.7-1.8 (SD=0.06). In general, vegetation root systems maintain slope stability by adding more cohesion to soils. Due to this reinforcement, greater gravitational forces and pore water pressure are needed to destabilize the slope. This consequently elevates the threshold of water content for landslide initiation. Since water content greatly influences mobility, wetter conditions enhance the mobility of the collapsed landslide mass. Our findings concur with previous studies that root reinforcement can mitigate slope instability. However, we highlight that such reinforcement can also enhance the mobility, which may elevate the potential impacts of landslides. We further investigate the effect of various stem densities on landslide mobility.

How to cite: Noviandi, R., Gomi, T., Sidle, R. C., Ritonga, R. P., and Hasunuma, Y.: Do Vegetation Root Systems Affect Landslide Mobility? A Flume Experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9004, https://doi.org/10.5194/egusphere-egu22-9004, 2022.

15:50–15:57
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EGU22-4236
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Highlight
Josif Josifovski and Aleksandra Nikolovska Atanasovska

Climate change has a significant impact on slope stability through atmospheric perturbations, water infiltration and soil erosion, which is often accompanied by local or shallow sliding of the slopes. Usually, the erosion is not seen as a stability-treating occurrence, but with time it can develop to a reduction of the shear soil strength and raise in the pore water pressure that can disturb the slope stability.

In order to overcome these problems, it is necessary to introduce techniques for surface stabilization of soil slopes that increase erosion resistance and reduce surface water infiltration. Moreover, they have to be environmentally friendly, thus recommendations refer to the application of natural polymer compounds that do not pollute the environment, and at the same time represent an effective and economical measure for slope stabilization. Very often, as an additional measure in the application of these biopolymer solutions on the surfaces of the slopes, at the same time, the application of seeds from low and medium vegetation is performed. In the first months, the biopolymers form a bond between the solid soil particles, which increases the erosion resistance and reduces the ability to infiltrate and absorb surface water. In parallel, the biopolymer helps and accelerates the growth of vegetation to ensure long-term erosion and slope stability.

The aim of the presented study was to investigate the effects of the xanthan gum as a compound and to develop an original biopolymer solution which will be later tested. The testing methodology was organized in two phases: laboratory tests on natural and biopolymer treated soil in the first phase, and experimental testing of biopolymer treated slope in the second phase.

In the first phase, the classification and strength parameters of treated and untreated soil were determined through standard laboratory tests. The tests were performed on specimens with various percentages of the xanthan gum additive, moreover, specimens were tested on days 1, 7, and 14 to examine the curing effects. From the results, it was observed that Xanthan gum has significantly increased the strength of the soil, up to 50% after the 14 days of curing time.

In the second phase, the erosion of treated and untreated soil was experimentally tested on the 1:1.5 slope during a rainfall of 10 liters per hour which was simulated for 180 minutes. The obtained results were better than expected showing a significant erosion resistance on the treated slope. During the 180 minutes of rainfall on the treated slope, there was no eroded soil registered. The Xanthan gum binder with a content of 1.0% filling the pores was able to limit the water infiltration into the soil, which improves interparticle cohesion and shows increased erosion resistance. In contrast, the amount of eroded soil on the untreated slope with an area of 1.0m2 was about 1900gr or soil erosion of 9.5%.

Finally, from the study can be concluded that the proposed biopolymer is a natural-based solution for erosion control which has major potential because they represent efficient, economic and environmentally sustainable engineering solutions.

How to cite: Josifovski, J. and Nikolovska Atanasovska, A.: Biopolymer soil stabilization as protection from slope erosion and shallow sliding, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4236, https://doi.org/10.5194/egusphere-egu22-4236, 2022.

15:57–16:04
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EGU22-12425
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ECS
Sadegh Nadimi, Nina Kemp, Vasileios Angelidakis, and Saimir Luli

Enhancing the overall resilience of vegetated slopes against shallow mass movement can be achieved by better understanding soil-root interaction.  To predict the behaviour of vegetated slopes during design, parameters representing the root system structure, such as root distribution, length, orientation and diameter, should be considered in slope stability models. Microscale quantifications of how root growth influences soil characteristics, able to inform computational models, are scarce in the literature, especially for stratified soils. This study quantifies the relationship between soil physical characteristics and root growth, emphasising particularly on (1) how roots influence the physical architecture of the surrounding soil structure and (2) how soil structure influences root growth. A systematic experimental study is carried out using high-resolution X-ray micro-computed tomography (µCT) to observe the root behaviour in layered soil. In total, 2 samples are scanned over 15 days of growth, enabling the acquisition of 10 sets of images. A machine learning algorithm for image segmentation is trained to act at 3 different training percentages, resulting in the processing of 30 sets of images, with the outcomes prompting a discussion on the size of the training data set. An automated in-house image processing algorithm is developed to provide values of void ratio and root volume ratio for Regions of Interest at varying distance from the root. This work investigates the effect of stratigraphy on root growth, along with the effect of image-segmentation parameters on soil constitutive properties.

How to cite: Nadimi, S., Kemp, N., Angelidakis, V., and Luli, S.: Observations of root growth in stratified soils at the microscopic scale: Insights from micro-computed tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12425, https://doi.org/10.5194/egusphere-egu22-12425, 2022.

16:04–16:11
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EGU22-13331
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ECS
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On-site presentation
Floriana Anselmucci, Hongyang Cheng, Yijian Zeng, Xinyan Fan, and Vanessa Magnanimo

Climate change strongly affects the hydro-mechanical properties of soil. Due to drought and heavy rains
the soil is subjected to severe hydro-mechanical loads, that, in turn, alter the microstructure of the soil.
The most affected area is the so-called vadose zone, the layer of soil situated between the ground surface and
the water table. Here the presence of vegetation has a strong impact, related to the elongation/expansion
of the root architecture and the hydro-mechanical interactions with soil. Additionally, the presence of plant
roots facilitate the evapotranspiration process from deeper soil layers.
The research presents an experimental investigation, aimed to reproduce the typical hydro-mechanical
conditions as found in the vadose zone in controlled laboratory conditions. Drying-wetting cycles are induced
in soils samples, where maize plants are free to sprout and develop as well as in reference non-vegetated
samples. The water content and distribution within the soil matrix are studied through 4D (3D+time)
in-vivo x-ray computed tomography and effects on the soil-root microstructure are quantified with 3D
image analysis. Those are correlated with above ground measurements such as fluorescence (through a
spectroradiometer) that, in turn, provides leaf water potential, and the stomatal conductance that controls
the evapotranspiration.

How to cite: Anselmucci, F., Cheng, H., Zeng, Y., Fan, X., and Magnanimo, V.: Impact of wetting-drying cycles on the hydro-mechanical behaviour of vegetated soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13331, https://doi.org/10.5194/egusphere-egu22-13331, 2022.

16:11–16:18
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EGU22-7386
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ECS
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Virtual presentation
Narryn Thaman, Ross Stirling, and Jonathan E. Chambers

Vegetation is an important tool for managing urban surface water and shallow geotechnical assets. However, root water uptake driven changes in slope hydrology (soil water content, matric suction, and hydraulic conductivity) are poorly understood in heterogeneous soils and under extreme climatic conditions. Slope stability is affected by intrinsic factors, including geometry, soil properties, groundwater and vegetation driven matric suction. Field evidence indicates that engineered slopes are susceptible to hydrometeorological slope instability mechanisms and that these pose a potential failure hazard to asset operation and public safety. The UK hosts 15,800 km of railway network and 7100 km of strategic road network, accounting for 49,000 slopes. This is a significant portfolio of slopes that must be managed and maintained at considerable expense.

To better understand the influence of vegetation on soil water dynamics in geotechnical infrastructure, Electrical Resistivity Tomography (ERT) is being used. ERT is a non-invasive tool for measuring and imaging subsurface soil moisture dynamics volumetrically. ERT can be used to quantitatively establish how the presence of roots influences transient soil moisture content and suction to assess the effectiveness of vegetation in managing slope hydrology and excess surface water issues in the built environment. This research aims to use 4-D ERT to determine the impact of vegetation on the hydrological behaviour of a high plasticity clay derived sub-soil used in the construction of infrastructure slopes in the southern half of the UK. Laboratory-scale experiments are underway at the UK National Green Infrastructure Facility, Newcastle, using a controlled environment chamber. A suite of soil columns is planted with vegetation, False Oat Grass (Arrhenatherum elatius) and Common Bent (Agrostis capillaris) and feature a 3D ERT electrode array and point sensors for measurement of volumetric water content, matric suction, and electrical conductivity throughout the profile. Through frequent imaging of soil-water-plant interactions and correlation with destructive root architecture imaging, this research aims to highlight how these relationships change over time and respond to extreme weather conditions (drought/inundation) to better predict, manage, and mitigate the occurrence of slope failure. Furthermore, the work aims to improve understanding of vegetation-driven soil moisture movement in the near-surface to better assess seasonal and longer-term slope stability to inform asset management strategies.

How to cite: Thaman, N., Stirling, R., and Chambers, J. E.: Developing Novel Geophysical Tools to Investigate Urban Vegetated Soil Moisture Dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7386, https://doi.org/10.5194/egusphere-egu22-7386, 2022.

16:18–16:25
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EGU22-12708
Sabatino Cuomo, Mariagiovanna Moscariello, and Vito Foresta

The effect of a long-root grass on the shear strength response of a partially saturated pyroclastic soil was investigated through a field and laboratory experimental program. Field measurements of soil water content, suction, temperature, and laboratory tests aimed to estimate the shear strength of differently rooted soils were performed. The experimental investigation was carried out on a test site located in Nocera Inferiore, (Campania region, Italy), a few kilometers far from sites of past catastrophic flow-like landslides. The experimental program was carried out on three species of Perennial graminae grass species, characterized by fine and fasciculate long roots.  

In the field, soil temperature, pH, humidity, and suction were monitored from seeding. The trends were compared with those of air temperature and humidity. Moreover, soil suction and water content trends were related to daily rainfall.

Undisturbed pyroclastic soil specimens containing roots of perennial graminae grass species were collected after 5 months from seeding and tested at natural water content in standard and suction controlled direct shear equipment. The specimens exhibited different Root Volume ratio (RV) and suction. The shear envelopes were extrapolated using Bishop formulation of effective stress, which allows to consistently consider the partially saturated condition of the soils. The experimental results outlined that the shear strength envelope of vegetated specimens moves upwards in the τ-σ’ space, but also rotates counterclockwise. In general, the cohesion intercept increases, while the effective frictional angle reduces. Moreover, the RV influence on the magnitude of friction angle and cohesion has been assessed. Densely vegetated soils undergo larger modifications of the shear strength envelop than poorly vegetate specimens.   

The authors would like to acknowledge Prati Armati S.r.l. that provided the grass species used for the tests.

How to cite: Cuomo, S., Moscariello, M., and Foresta, V.: Shear strength of unsaturated soils artificially vegetated in a field test site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12708, https://doi.org/10.5194/egusphere-egu22-12708, 2022.

16:25–16:32
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EGU22-9829
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Virtual presentation
Mikael Ånäs

The Swedish Civil Contingencies Agency, the Swedish Geotechnical Institute, the Swedish Road Administration and the Swedish University of Agriculture have together been involved a project named “Vegetation as a mean for slope stabilisation”. The aim of the project was to introduce soil-bioengineering methods in Sweden through demonstration projects and to obtain experiences regarding the function and effect of plants on slope stability within Swedish conditions.

In three selected areas, the plant- and soil conditions were studied, with tests commencing in the spring of 2004 and in the beginning of 2005, respectively. The project ended in 2007 in a report containing recommendations, based on the experiences from the project, for the continued use of soil bioengineering methods.

In the test site Bispgården, a new road was built in 2004 through a gully area. The soil consists of highly erodible silt and sand material. Hedge- and brushlayers with grass seeding were selected to protect the soil from erosion in one slope. Equipment for measurements of pore pressure and precipitation were installed in the summer of 2004. Studies of the plant conditions were conducted several times during the first two years of the project.

In the test site Bydalen, a reconstruction of a country road was conducted in 2005, as the road was plagued with annually recurring erosion along it’s existing silty-till slopes. These slopes were to be restabilised during reconstruction. All together nine existing slopes were stabilised in early 2005 by different soil bioengineering methods proposed by the project group. The group analysed the function of the plants together with automated recordings of precipitation.

In the test site Näsåker, steep slopes of a country road were repaired in 2005-2008, due to continuing erosion and landslides in the silty soil slopes along the existing road. The slopes were stabilised with soil bioengineering and soil nailing.

Different soil bioengineering methods have been used in some new production sites, following this demonstration project. The methods may also be implemented in future projects.

The results from the demonstration in project sites, will be described in this presentation.

How to cite: Ånäs, M.: Vegetation as a remedial measure against erosion and shallow landslides in steep soil slopes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9829, https://doi.org/10.5194/egusphere-egu22-9829, 2022.

Coffee break
Chairpersons: Alessandro Fraccica, Anil Yildiz
17:00–17:02
17:02–17:09
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EGU22-2641
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ECS
Lorenzo Marzini, Enrico D'Addario, Michele Pio Papasidero, Michele Amaddii, Leonardo Disperati, and Francesco Chianucci

Shallow landslides susceptibility assessment by physically based methods relies on the parametrization of both hydraulic and geotechnical properties of soils, which in turn depend on the conditions of root structures and vegetation cover. Vegetation roots contribute to the shear strength of soils, but their quantitative contribution is currently uncertain. Saturated hydraulic conductivity (Ks) is also relevant for slope stability as it influences infiltration rates and runoff. While the literature clearly shows the dependence of Ks on soil texture, there is a general understatement of the role of root structures on this parameter. Moreover, the distribution patterns of vegetation follow relations with surface morphologies which are not fully understood and therefore, are worthy of further investigations. For these reasons, this work focuses on the quantitative assessment of the influence of vegetation on shear strength for shallow landsliding and the investigation of the relationships between vegetation characters, saturated hydraulic conductivity and topographic parameters. Study areas affected by shallow landslides are chosen in the Garfagnana and Alpi Apuane regions (Northern Apennines, Italy), as well as in the Mt. Amiata volcano area (Southern Tuscany, Italy), where field measurements of below-ground vegetation (Root Area Ratio - RAR), above-ground vegetation (Leaf Area Index - LAI and vegetation load) and Ks are acquired inside, in the neighbour and far from shallow landslide sites. To this aim, a multi-temporal landslide inventory is already available for the study area. Below-ground data are collected in trench profiles, while above-ground data are acquired by using a digital relascope as well as implementing vegetation cover photography methods. Measurements of Ks are carried out by means of both constant and falling head approaches. The morphometric analysis is performed by using some morphometric variables (eg. slope and hillslope curvatures) derived from a digital elevation model with cell size of 10 m. Morphometric clustering of these variables allows us to extract a set of land units where the distribution of vegetation characters and Ks are assessed. First results show that: a) root reinforcement to soil in terms of root-related cohesion plays a relevant role within the soil depths involved in shallow landslides; b) the weight of above-ground vegetation plays a “mild” negative role on slope stability; c) Ks is correlated with both RAR and soil depth, suggesting possible criteria for the straightforward parametrization of input parameters.

How to cite: Marzini, L., D'Addario, E., Papasidero, M. P., Amaddii, M., Disperati, L., and Chianucci, F.: Investigating the relationships among vegetation characters, saturated hydraulic conductivity and surface morphology at catchment scale by integrating new field data and morphometric analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2641, https://doi.org/10.5194/egusphere-egu22-2641, 2022.

17:09–17:16
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EGU22-2953
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Highlight
Daniele Bocchiola, Francesca Casale, and Leonardo Stucchi

The Mera River watershed in the Rhaetian Alps, between Italy and Switzerland, is subject to distributed erosion, and soil degradation, affecting slope stability, and sediment transport in the river. In the future under climate change, erosion is projected to increase especially in winter, as due to larger rainfall share, and smaller snow accumulation. It is therefore necessary to develop best practices for the maintenance of slopes, such as terracing, to reduce erosion and soil loss in the area. We present the results of the recent GE.RI.KO Mera Interreg, and IPCC MOUPA projects.

We first calibrate a hydrological model Poli-Hydro in the study area during 2010-2019, against discharge data, and snow cover area from satellite. Then a Dynamic-RUSLE (D-RUSLE) model is used to simulate spatially distributed soil erosion. The model considers snow melt/accumulation, and the year round dynamics of vegetation. Potential soil erosion is validated against sediment transport data taken in a sample station in the Mera River.

The dynamics of snow cover is simulated using Poli-Hydro, while the C-factor of land cover is corrected using NDVI (Normalized Difference Vegetation Index) from satellite images, accounting for variable vegetation stages, and larger leaf cover (LAI) in summer. The C-factor is further corrected for pasture areas, using productivity data as calculated using the Poli-Pasture model, mimicking pasture growth and biomass productivity. We considered two index species for high/low altitudes, and inter-specific competition.

We then project future scenarios of climate change, and impacts thereby. Six GCMs and four SSPs of the IPCC AR6 are used, to develop 24 climate change scenarios for precipitation and temperature. We also consider changes in CO2 concentration, and temperature increase, upon land cover, through variation of timberline and growing season. Based upon our results, conservative practices may be devised, to help improvement of pasture productivity, and reduce soil erosion.

How to cite: Bocchiola, D., Casale, F., and Stucchi, L.: Changes in pasture productivity may affect potential soil erosion under climate change. The case study of Mera watershed., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2953, https://doi.org/10.5194/egusphere-egu22-2953, 2022.

17:16–17:23
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EGU22-9254
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ECS
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On-site presentation
Marceline Vuaridel, Massimiliano Schwarz, Virginia Ruiz-Villanueva, Paolo Perona, and Denis Cohen

Bern University of Applied Sciences, School of Agricultural, Forest and Food Sciences, COSCI, Hydraulic Platform LCH, Institute of Civil Engineering, EPFL-ENAC, Lausanne, CH and University of Lausanne, Institute of Earth Surface Dynamics (marceline.vuaridel@unil.ch)

Floods and intense surface runoff are recurring hazards known for triggering erosion processes at the channel and the catchment slope scales, respectively. Whilst the firsts determine the removal of streambank material, also referred to as hydraulic streambank erosion (e.g., Ruiz-Villanueva et al., 2014), the seconds are typically responsible for destabilizing shallow landslides. Both processes are exacerbated by extreme precipitation events, and can cause important damages to forests, agriculture, civil structures, and settlements through the loss of land masses. Moreover, streambank erosion and shallow landslides can be responsible for the recruitment of large wood (LW), whose transport during floods may strongly impacts on downstream infrastructures of urbanized areas (e.g Ruiz-Villanueva et al., 2014).

Via augmented mechanical stabilization, plant roots may significantly decrease the susceptibility of riverbanks to hydraulic erosion as well as shallow landslides. Under certain conditions, plant roots can be considered an alternative protection against such processes with respect to other civil engineering measures (Stokes et al., 2014). However, root reinforcement effectiveness depends on many factors such as roots density, soil properties, and soil thickness (Cohen and Schwarz, 2017), which implies that some vegetated areas have a more significant effect than others. Most available models ignore the contribution of plant roots with acceptable spatial resolution.

In this work, we present BankforNET and SlideforNET, two physically-based modelling tools, which have been developed to take the different stabilizing effects of soil reinforcement mechanism by plant roots into account. This is important for proper modeling of bank erosion and landslides processes during extreme events, and to optimize forest protection strategies. BankforNET is a one-dimensional, probabilistic model which simulates expected hydraulic streambank erosion by considering channel morphology, bank sediment material, vegetation roots, and a certain discharge scenario. The SlideforNET is a probabilistic model based on the 3D analysis of slope stability and takes the lateral and basal root reinforcement into account. Ultimately, it gives an estimation of the degree of protection of a forest against landslides.

These tools are currently being tested in a catchment of 29 km2 in NW Switzerland for the priorisation of protective forests against risks related to LW transport during floods. Based on the model results, the possible silvicultural measures are defined considering quantitative criteria such as the risk mitigation effect of the forest stands, or their risk increment due to LW recruitment and transport. This study is an example of how quantitative tools can be use by decision makers to priories the role of protection forest in a catchment and to support the definition of silvicultural measure to mitigate the risks due to LW transport.

How to cite: Vuaridel, M., Schwarz, M., Ruiz-Villanueva, V., Perona, P., and Cohen, D.: Roots mechanical effects on hydraulic riverbanks erosion and on shallow landslides: tools for the protection forest management along channels, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9254, https://doi.org/10.5194/egusphere-egu22-9254, 2022.

17:23–17:30
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EGU22-11679
Massimiliano Schwarz, Denis Cohen, Filippo Giadrossich, Dominik May, Christine Moos, and Luuk Dorren

Root reinforcement is a variable factor that influences the disposition of shallow landslides over different time scales. Natural or anthropogenic forest disturbances, such as forest fires or clear cuts, may modify considerably the vegetation cover on a short time scale, with major consequences on several ecosystem services, including the mitigation of risks due to shallow landslides. After catastrophic forest disturbances, it is of primary importance for decision makers to assess how risks will change in order to evaluate the most appropriate protection measures. Therefore, the quantification of the effect of the temporal dynamic of root reinforcement is of fundamental importance to estimate the occurrence probability of shallow landslides.

Data on root distribution and pullout tests for spruce (Picea abies) and beech (Fagus silvatyca) trees are used to upscale the basal and lateral root reinforcement at the stand scale (Schwarz et al., 2012). The decay of root reinforcement is calculated based on data collected in a burnt (Vergani et al., 2017) and a clear-cut area (Vergani et al., 2016). The recovery of root reinforcement after disturbances is estimated considering the growing conditions of the stands (Flepp et al., 2021). The quantification of the dynamic of the forest stands and the derived root reinforcement at stand scale is based on the analysis of four Swiss National Forest Inventory (NFI 1-4). The estimated time-dependent variation of root reinforcement is implemented in the SlideforNET model (ecorisq.org) to calculate the occurrence probability of shallow landslide after disturbances.

The results show that the recovery of root reinforcement after disturbance is effective to reduce the hazards of shallow landslide only for a narrow range of disposition factors. Given a defined rainfall statistic, slope inclination is the factor that most influence the effectiveness of root reinforcement recovery, within a range of inclination variations of 4-8°. Further relevant factors are soil thickness and runoff contributing area.

The extended version of SlideforNET quantifies how effective is the recovery of root reinforcement in stabilizing shallow landslides after stand replacing forest disturbances. This information is fundamental to evaluate if additional temporal or permanent technical measures are needed to keep an acceptable level of risk after forest disturbances.

How to cite: Schwarz, M., Cohen, D., Giadrossich, F., May, D., Moos, C., and Dorren, L.: Influence of the temporal dynamic of root reinforcement on the disposition of shallow landslides, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11679, https://doi.org/10.5194/egusphere-egu22-11679, 2022.

17:30–17:37
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EGU22-13261
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ECS
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On-site presentation
Feiko van Zadelhoff, Massimiliano Schwarz, Denis Cohen, and Chris Philips

In New Zealand shallow landslides are a prominent contributor to soil erosion in unvegetated slopes (hill country) and to water quality degradation. Selective well-planned re-vegetation of steep slopes can reduce shallow landslide hazard with comparatively low economic consequences.

The main non-native planted tree species that contribute to slope stability are Poplar species (Populus sp.) and Pine (Pinus radiata). We will present field data quantifying the root distribution and root strength of poplar and pine trees from New Zealand. 4 poplar trees with a medium Diameter at Breast Height (DBH) of 0.48 m are included. Circular trenches have been dug at fixed distances from stem and the roots counted and their diameter measured systematically. 64 root pull-out tests over varying soil depth and root diameter provide calibration for lateral root reinforcement (Gehring et al., 2019; equation 3). The combination of root counts and root reinforcement calibration enables the parametrization of root reinforcement on a single tree scale. The Pinus radiata calibration is the adopted from Giandrossich et al., 2020 which applied a similar methodology.

Using the slope stability model SlideforMap, we assess and compare (re)vegetation scenarios and their effect on slope stability. In addition to a detailed inclusion of vegetation, SlideforMap takes local soil and hydrology into account in the parametrization. Scenarios without poplar/radiata stands, dispersed trees and plantations are run and compared under varying precipitation conditions.

We believe this approach enables regional decision makers to optimize tree planting to significantly reduce slope instability at minimal economic costs.

Literature:

Gehring, E., Conedera, M., Maringer, J., Giadrossich, F., Guastini, E., & Schwarz, M. (2019). Shallow landslide disposition in burnt European beech (Fagus sylvatica L.) forests. Scientific Reports, 9(1), 1–11. https://doi.org/10.1038/s41598-019-45073-7

Giadrossich, F., Schwarz, M., Marden, M., Marrosu, R., & Phillips, C. (2020). Minimum representative root distribution sampling for calculating slope stability in pinus radiata d.Don plantations in New Zealand. New Zealand Journal of Forestry Science, 50, 1–12. https://doi.org/10.33494/nzjfs502020x68x

How to cite: van Zadelhoff, F., Schwarz, M., Cohen, D., and Philips, C.: Quantifying the effect on shallow landslide activity of actual and potential poplar and pine stands in New Zealand hill country., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13261, https://doi.org/10.5194/egusphere-egu22-13261, 2022.

17:37–17:44
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EGU22-13300
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Virtual presentation
Gerrit Meijer, Jonathan Knappett, Glyn Bengough, David Muir Wood, and Teng Liang

Plant roots can help to stabilise riverbanks and slopes by providing additional mechanical reinforcement through tensioning of root material. This problem has typically been studied at the ultimate limit state, focussing on quantifying the peak root-reinforced soil strength. Existing models however rarely account for the gradual mobilisation of root-reinforcement associated with increasing soil displacements. Understanding these deformations is important when deformation tolerances are low, for example when constructing infrastructure embankments, or when deformations may serve as an early warning signal for slope failure.

Several new models to quantify mechanical reinforcement were developed, with varying levels of complexity. At the most basic level, fibre bundle model theory was combined with early pioneering work by Wu and Waldron to form a new fibre bundle approach that remains simple to use yet respects the physics of soil and root deformation. A second and more comprehensive analytical model was developed that can calculate reinforcements as a function of increasing soil shear displacement. This model includes key parameters such as the elasto-plastic biomechanical root behaviour, three-dimensional root orientations, root slippage and changes in the geometry of the localised shear zone in the soil. A third model comprises a full set of constitutive stress-strain relationships for rooted soil that can be used in numerical finite-element simulations. In this framework, the rooted soil is treated as a single, composite material in which the soil and root phase can each be assigned their own unique material behaviour. The composite approach simplifies model parameterisation by using independently measurable root and soil parameters, and is also powerful enough to investigate the complicated interaction between stresses and deformations in the soil skeleton and in the roots.

These models all provided good predictions of experimentally measured root reinforcements in direct shear tests. They will be useful tools both for the engineering industry, in terms of rapid quantification of root reinforcement, as well as for directing future research into the drivers of mechanical root-reinforcement.

How to cite: Meijer, G., Knappett, J., Bengough, G., Muir Wood, D., and Liang, T.: New modelling tools for quantification of mechanical reinforcement of soil by plant roots, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13300, https://doi.org/10.5194/egusphere-egu22-13300, 2022.

17:44–17:51
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EGU22-13423
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ECS
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Virtual presentation
Vittoria Capobianco, Bjørn Kalsnes, James Strout, and Anders Solheim

LaRiMiT (Landslide Risk Mitigation Toolbox) is a web-based database and user portal for identifying and selecting mitigation measures for a specific landslide case, assisted by an embedded expert scoring system. The webtool, developed within KLIMA2050, contains more than 80 structural landslide mitigation measures, including active (aimed at reducing the likelihood of a landslide) and passive (aimed at reducing the consequences) measures. For each mitigation measure a description, examples of application and design methods are provided, as well as references from literature. An Analytic Hierarchy Process resident in the toolbox provides a ranked list of suitable mitigation measures for a specific case. The quantitative scores reflect the input relevance weights and option scores. Recently, the database has been expanded to include also Nature-based solutions (NBS). NBS applied to landslide hazard mitigation are mostly known as soil and water bio-engineering (SWB) and the main SWB techniques have been categorized and added to the database. For these measures, the period of installation, the materials involved, advantages, and disadvantages are also provided. The database containing all the mitigation measures has open access to all users at https://www.larimit.com/. 

A survey was sent to a group of experts in landslide management and SWB selected worldwide, with a focus on Europe, asking them to assign scores to each mitigation measure in the toolbox. The survey was made using Microsoft Forms. Each measure was linked to a dedicated response page through a hyperlink, and the experts could submit a response for the mitigation measures they felt more comfortable with giving scores. For each mitigation measure selected, the experts were asked to assess the measure by scoring 33 parameters, based on existing landslide classifications with regards to the type of movement, material type, rate of movement of the landslide (among others), as well as feasibility, economic suitability, and environmental suitability. A total of 153 experts, among landlide mitigation managers and experts of SWB practices, were asked to fill the survey. An innovative methodology for utilising experts' scoring directly within the decision support tool, was proposed and used to calculate the final scores for each parameter of the landslide mitigation measures. It consisted in 5 phases, namely Data analysis, Data filtering, data weighing, Data comparison, and Score selection.

A total of 38 out of the 153 invited experts (corresponding to just over 25%) contributed scores for at least one mitigation measure. In total, 296 responses were received of which 172 were for traditional mitigation measures, 111 for NBS, and 13 for hybrid solutions (combination of NBS and traditional engineering solutions). The results from this first pooling are discussed and analyzed, and the scores of 56 measures were updated on the basis of the pooling answers. All the NBS measures received between 3 and 9 responses, confirming that the NBS listed in the database were well known to most of the SWB experts who participated to the survey. 

The survey is still open and we encourage landslide mitigation experts that are willing to provide their contribution, to reach out the survey managers at vittoria.capobianco@ngi.no.

How to cite: Capobianco, V., Kalsnes, B., Strout, J., and Solheim, A.: Nature-based solutions for mitigating erosion and shallow landslides in LaRiMiT toolbox: use of expert scoring for evaluation of NBS measures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13423, https://doi.org/10.5194/egusphere-egu22-13423, 2022.

17:51–17:58
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EGU22-4768
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Highlight
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On-site presentation
Alexia Stokes, Maarten De Boever, Jonas Bodyn, Saskia Buysens, Liesbet Rosseel, Sarah Deprez, Charles Bielders, Aurore Degré, and Amaury Frankl

Abstract:

Vegetative barriers are narrow strips of plants or plant residues that are increasingly being used as measures to reduce the connectivity of catchments in terms of water and sediment fluxes (Frankl et al., 2021a). They can mostly be found at plot edges where they do not hinder farming activities too much. Their principal function is to reduce sediment export from cropland and thus mitigate negative off-site effects of erosion (e.g. muddy floods, pollution of rivers). Being implemented in concentrated flow zones where ephemeral gullying is recurrent, they also prevent their development (Frankl et al., 2018). Although vegetative barriers are increasingly being implemented in open agricultural areas, little information is available on the effectiveness of vegetation barriers at buffering the flows of water and sediment. Here, we focus on vegetative barriers that are widely implemented in Flanders (Belgium) and which are made of straw bales, wood chips or bales of coconut fibre. Based on three simulated runoff experiments performed in the field, we calculated the hydraulic roughness and sediment deposition ratio. Our experiments show that the barriers made of coconut-fibre bales performed markedly better than those of straw bales or wood chips (Frankl et al., 2021b). However, as vegetative barriers have to be renewed every few years because of the decomposition of organic material, barriers made of locally available materials are more sustainable as a nature-based solution to erosion. We conclude that the vegetative barriers are an effective way of mitigating the negative effects of soil erosion. While barriers made of coconut-fibre bales are superior in their regulation of flows of runoff and sediment, barriers made of locally sourced materials are more sustainable.

 

Keywords: agriculture, erosion control, hydrological connectivity, runoff, sediment

 

References:

Frankl, et al. (2021a) Gully prevention and control: Techniques, failures and effectiveness. Earth Surf. Process. Landforms: 46: 220– 238. https://doi.org/10.1002/esp.5033.

Frankl, A., et al. (2021b). Report on the effectiveness of vegetative barriers to regulate simulated fluxes of runoff and sediment in open agricultural landscapes (Flanders, Belgium). Land Degrad. Dev. 32: 4445– 4449. https://doi.org/10.1002/ldr.4048

Frankl, A. et al. (2018). The success of recent land management efforts to reduce soil erosion in northern France. Geomorphology 303: 84–93. doi:10.1016/j.geomorph.2017.11.018

 

How to cite: Stokes, A., De Boever, M., Bodyn, J., Buysens, S., Rosseel, L., Deprez, S., Bielders, C., Degré, A., and Frankl, A.: The implementation and effectiveness of vegetative barriers to regulate fluxes of runoff and sediment in open agricultural landscapes (Flanders, Belgium), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4768, https://doi.org/10.5194/egusphere-egu22-4768, 2022.

17:58–18:05
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EGU22-7965
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Virtual presentation
Antonio Pignalosa, Nicola Silvestri, Francesco Pugliese, Carlo Gerundo, Alfonso Corniello, Nicola Del Seppia, Massimo Lucchesi, Nicola Coscini, and Francesco De Paola

Many types of Nature-Based Solutions (NBSs) have been applied worldwide to mitigate impacts of hydro-meteorological hazards produced by anthropic activities such as grazing and agriculture. Among them, vegetated buffer strips (VBSs) and winter cover crops (WCCs) are suitable solutions for reducing runoff and soil erosion rates from cultivated fields. However, their mitigating effects depends largely on local conditions such as morphology and soil nature.

This study investigated these aspects by modelling the NBS effects on soil and water dynamics in two test sites located within the Massaciuccoli agricultural plain (Vecchiano, Pisa, Central Italy) and characterised by different soil types (peaty and silty soils). The SWAT+ model has been chosen to simulate hydraulic and hydrological phenomena using high-resolution data such as digital terrain models (DTMs) from close-range photogrammetry, detailed land cover mapping, actual crop rotations, and detailed calendars of agronomic operations. We considered two types of NBSs: i) 3 m wide VBSs planted along both sides of field ditches, covering about 10% of the agricultural land, and ii) WCCs sowed after harvesting summer cash crops. Both NBSs exert their action on 30% of the experimental area. The mitigating effect was tested by comparing simulation results from NBS and control (conventional agriculture) scenarios under ongoing climatic conditions and future climate changes.

Results indicated that VBSs and WCCs showed different capabilities to reduce runoff and sediment losses, and the adoption of both can enhance the mitigation effect significantly. NBSs resulted effective also in completely flat areas since slight topographic irregularities can cause local preferential flows resulting in high runoff rate and sediment losses. Furthermore, it is demonstrated how the soil variability in texture and organic matter content can affect the amount of runoff and sediment loss on a local scale. Consequently, the mitigating effects of NBS can be closely driven by the soil nature and heterogeneity. This influence is even more significant under extreme climatic conditions such as higher temperatures and more aggressive rainfall events. In these cases, NBSs can play an essential role in mitigating runoff and soil erosion phenomena on fine-textured mineral soils. In contrast, they lose much of their effectiveness on peat soils.

How to cite: Pignalosa, A., Silvestri, N., Pugliese, F., Gerundo, C., Corniello, A., Del Seppia, N., Lucchesi, M., Coscini, N., and De Paola, F.: Modelling the effects of NBS adoption in mitigating soil losses of a land reclamation area in the Massaciuccoli lake catchment (Central Italy) , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7965, https://doi.org/10.5194/egusphere-egu22-7965, 2022.

18:05–18:12
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EGU22-13319
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On-site presentation
Sisay Debele, Paul Bowyer, Jeetendra Sahani, Silvia Maria Alfieri, Massimo Menenti, Thomas Zieher, and Prashant Kumar

Climate change is increasing the probability of extreme precipitation in many regions, which will lead to an increased risk of major flooding events. Recent years have seen an interest in the use of so-called nature-based solutions (NbS) to help respond and reduce the risk posed by such extreme events. This paper provides an analysis of the use of NbS to help reduce flood risk at the open-air laboratory Germany (OAL-Germany), which is part of the EU Horizon 2020 project OPERANDUM. OAL-Germany is located in the Biosphere Reserve Lower Saxony Elbe Valley. Following major flooding events which occurred in OAL-Germany in 2002 and 2013, a cooperative flood management NbS was implemented over the period 2014-2015 and has been in place since then. The NbS consisted of cutting back woody vegetation in certain locations along the riverbank which impeded overbanking during flood events, and the use of various grazing animals to try and prevent the regrowth of such woody vegetation. The objective of this study is to evaluate the efficiency of NBS against flood risk under present-day climate change scenarios and assess future flood inundations and velocities in OAL-Germany. The daily precipitation data obtained from the EURO-CORDEX project dataset for 1971–2000 and 2051–2080 represented historical and future simulations, respectively. The hydrologic model HEC-HMS was integrated with the hydraulic model HEC-RAS to simulate discharge, flood velocity, and water depth/inundations of past and future events. For HEC-RAS model boundary conditions, daily flow data with long-term quality-controlled data, obtained from the Global Runoff Data Centre were used. The model was simulated for two scenarios: (1) pre-NBS implementation, considering the landcover of mixed forest; and (2) post-NBS implementation using pastureland, which is the current NBS/landcover in place. The results of the simulation show that the pastureland released the floodwater from the main river system faster than the previous landcover. Overall, the floodwater velocity of pastureland increased by 21%, while flood depth showed a decrease of 2% compared with mixed forest. Therefore, if the modelled NBS had actually been in place in 2012, then it is reasonable to expect that they would have contributed to a reduction in flood risk further downstream from the modelled NBS areas, in the June 2013 flood event. This study can help to improve NBS uptake and upscaling, which is critical to improve NBS planning, implementation, and effectiveness assessment.

 

Keywords: Nature-based solutions; HEC-RAS Model; Flood depth; Flood Velocity; Roughness coefficients; Climate Change

 

Acknowledgments

This work has been carried out under the framework of OPERANDUM (OPEn-air laboRAtories for Nature baseD solUtions to Manage hydro-meteo risks) project, which is funded by the European Union's Horizon 2020 research and innovation programme under the Grant Agreement No: 776848.

How to cite: Debele, S., Bowyer, P., Sahani, J., Alfieri, S. M., Menenti, M., Zieher, T., and Kumar, P.: Evaluating the Efficiency of a Nature-Based Solution on Flood Risk Reduction under climate change scenarios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13319, https://doi.org/10.5194/egusphere-egu22-13319, 2022.

18:12–18:19
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EGU22-4499
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Highlight
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Virtual presentation
Federico Preti, Vittoria Capobianco, and Paola Sangalli

Soil and Water Bioengineering (SWB) is a discipline established in the second half of XX century, finding its roots in ancient practices, which implies the use of vegetation and natural materials for natural hazards mitigation and ecosystem restoration. Nature-based solutions (NBS) is a recent collective term for solutions supported and/or inspired by nature to address climate-related challenges.

Although NBS cover a wide range of approaches based or inspired by natural processes and have many objectives in common with SWB, almost no attempts have been done so far to find overlaps and differences, which is needed especially when definitions are linked to legislations and funding mechanisms.

We present the results of a systematic comparison of NBS definitions, and other terminologies that fall under the NBS concept, with the definition of SWB. First, we identified applications that are related to the NBS umbrella concept, with their relative definitions, with a special focus on flood risk mitigation, ecosystem restoration, landslide and erosion mitigation. The applications analysed include: Watershed Management or hydraulic-forestry arrangements (WM), Nature-based Solutions (NBS), Green/blue Infrastructure (GI), Urban Forestry (UF), Ecological Engineering (EE), as well as Ecosystem-based Disaster Risk Reduction (Eco-DRR).

Secondly, a comparison matrix was proposed and developed. The matrix was developed by comparing the main aspects of SWB practice with the aims of the other NBS-related applications.

The structure of the matrix was the following:

  • each row represents each of the 3 main aspects of SWB practices: namely "main aims", "fields of application" and "other objectives";
  • the matrix columns designate all the other NBS-related terminologies, named above.

The three main aspects of the SWB discipline cover the following:

  • main aims: the four main objectives of SWB; namely: technical, ecological, landscape and socio-economic objectives.
  • fields of application: main domains of applications and fields of interventions;
  • other objectives: the multi-purpose functions exerted by SWB.

Excerpts from relevant peer-review and grey literature on NBS were included in the matrix to cross-check the 3 main aspects of the SWB practice. We observed that SWB approaches have at least 2 "aims" in common with all the terms, particularly that all 3 main aspects are covered by the NBS definitions. In terms of "fields of application", the highest number of similarities are found between SWB and EE, and, to a smaller extent, WM, GBI and Eco-DRR.

In this work we conclude that SWB discipline can be recognized as a concept falling under the NBS unifying concept to prioritise nature to integrate climate change adaptation, mitigation and disaster reduction efforts. SWB overlaps and, in some cases, compliments many NBS-related terminologies. Thus, SWB can and should be recognized as having always been an NBS.

How to cite: Preti, F., Capobianco, V., and Sangalli, P.: Systematic comparison of definitions and aims between Soil and Water Bioengineering (SWB) and Nature-Based Solutions (NBS), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4499, https://doi.org/10.5194/egusphere-egu22-4499, 2022.

18:19–18:24