SSS11.4

After pyroclastic materials are deposited in a watershed following a volcanic eruption, the risk of debris flow initiation may increase during subsequent rainfall events. Clarifying the rainfall-runoff process on tephra-covered slopes is essential to understand the mechanism of debris flow initiation after an eruption. Because the quality and quantity of pyroclastic materials vary from volcano to volcano, and from eruption to eruption of the same volcano, each rainfall-runoff process is expected to differ accordingly. Laboratory rainfall simulation is useful to highlight parameters (rainfall and sample conditions) that may affect the surface runoff process on slopes during and after a volcanic eruption. In this study, a laboratory experiment was conducted using a calibrated rainfall simulator to investigate how the occurrence of surface runoff during the first rainfall after an eruption depends on the fine particle content. Pyroclastic material was volcanic ash collected on Mount Sakurajima, Japan and the fine particle content F_c was adjusted using artificial silt: Sample A (F_c = 20%, control) and Sample B (F_c = 30%, adjusted). The experimental plots (1723.4 cm² of the projection area) were prepared by filling each sample with a 5 cm thickness at a constant pressure on highly permeable silica sand, and placed at an inclination of 10°. The initial moisture condition of both samples was assumed to be dry (≈ 5% of water content ratio). The rainfall simulation was performed for 3 hours on each sample at an intensity of 30 mm h^-1. Runoff water including sediment from the experimental plot during the simulation was captured at the lower end of the plot and the weight was recorded. Two soil moisture sensors were buried 2.5 cm below the surface of each sample to measure the change in volumetric water content (VWC) over time. Runoff water including sediment occurred and increased with time on Sample B though hardly occurred on Sample A. In both samples, the VWC increased with time and eventually approached a constant value. However, the maximum value of the VWC, and the time to reach the maximum value, were different; lower and slower in Sample B. The saturated hydraulic conductivity of Sample B was one order of magnitude lower than that of Sample A. These comparative results suggested that surface runoff may be greater during the first rainfall after an eruption because the infiltration is lower when the fine particle content, that is particle size distribution, in pyroclastic materials is high.

How to cite: Hiraoka, M., Imamori, N., Shimizu, T., and Ishida, K.: Laboratory rainfall simulation for surface runoff generation on tephra-covered slopes with different fine particle content, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6737, https://doi.org/10.5194/egusphere-egu22-6737, 2022.

Sedimentation has been a crucial problem in the management of storage in farm ponds, which cuts down the capability of ponds in aspects of irrigation, flood detention, and water retention. The Hydrosuction sediment removal system features low energy consumption and reduction of structural modifications to the existing shaft, which is an economically feasible method to remove siltation in storage areas. However, the effect of desilting might be limited due to the position of inflow orifice of siphon-type pipe which controls the scope of desilting affected area. This study aims to enhance the desilting effect of a fixed siphon system through connected a designed drainage tube.

The experiments were conducted in a cubic tank with a volume of 1.0 m³. Inside the tank, a vertical square shaft with the height of 80cm connected to an outlet channel was placed, and the siphon-type pipe was arranged from the inner of the tank to the outlet channel along with the shaft with a 3.0 cm inner diameter. The tests were performed in two kinds of inflow conditions in three water heights (60, 70, 80 cm), one is constant head inflow condition for continuous inflow provided, the other is falling head inflow condition with limited inflow supply. The initially deposited depths of sediment varied from 30 or 40cm. The designed 24cm long tube which has three added upward orifices with two types of diameters (1.0, 2.0 cm) could be connected to the inflow orifice of the siphon pipe to compare the desilting effect with the original arrangement in the above flow conditions.

The experimental results revealed that the effect of desilting was promoted by the connection of the designed tube to the siphon system. Besides, the efficiency of desilting was affected by the sizes of discharge orifices on the designed tube in different inflow conditions. In the constant head inflow condition, the arrangement of the connected 2cm discharge orifice tube performed better results due to the larger amount of outflow induced by the larger orifice. On the contrary, the arrangement of the connected 1cm discharge orifice tube had better desilting effect in falling head inflow condition induced by the longer time of disturbance between flow and sediment in smaller discharge. The results indicate that the capability and efficiency of sediment removal in the siphon system might be promoted by connecting an extended drainage tube with an appropriate size of upward discharge orifices.

How to cite: Lai, T.-Y., Hsu, Y.-C., Wang, J.-S., Su, Y.-W., Fu, G.-L., and Hung, C.-Y.: Experimental Study on the Efficiency of a Hydrosuction System for Desilting Sediment from a Farm Pond, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1148, https://doi.org/10.5194/egusphere-egu22-1148, 2022.

Meandering rivers are one of the most complex earth-surface systems and have a significant impact on riverine ecosystem mechanics. Because of the fascinating intricacy of meander morphodynamics, scholars from various disciplines, from fluid mechanics, fluvial hydraulics, and geomorphology, have been fascinated by meandering rivers. In spite of many years of research still, many processes regarding meandering rivers are not answered. Recent decades of research are reviewed herein in this paper. Scholars and experts have studied about flow features and processes such as a distorted profile of longitudinal velocity, secondary flow, inner and outer banks flow separation, etc., and sedimentological processes such as point bars, bend scour, lateral bed slope, etc. Many of them studied time-mean flow, Reynolds stresses, turbulence intensities (TI), turbulent kinetic energy, quadrant analysis, and turbulence scales, etc. under the effect of meandering bends. Many laboratory experiments are carried out to understand the individual processes under different conditions. Due to the rapid enhancement of soft computational techniques, these experimental data sets can be validated. Some future recommendations are also suggested in the field, laboratory, and numerical modelling.

Keywords: Meandering rivers, secondary flow, Reynolds stresses, turbulent kinetic energy, turbulence scales

How to cite: Gurugubelli, Y., Timbadiya, P. V., and Barman, B.: Review on Morphology and Turbulence Characteristics in Meandering Rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7001, https://doi.org/10.5194/egusphere-egu22-7001, 2022.

Rainfall simulators are devices commonly used to study soil erosion in field and laboratory conditions. There is still an effort to develop equipment that will: not require a large number of workers, be easy to manipulate, have simple control systems, and automatically record data and parameters.

This paper shows a new variable rainfall simulator with many possibilities, it consists of four independent sections that can be joined into larger simulator. Each section can simulate rain on a 2x4m area. The rain is generated by swinging and pulse mechanisms. Soil sensors and rain gauges are integrated into the control unit.

The whole device is placed on a trailer that is moveable by car. On the trailer, there is also a 1m³ water reservoir, control unit based on WAGO control unit with electric switchboard, water pump, hydraulic system and valves. The device could be controlled by any laptop or smartphone with a wifi connection.

Each section (4 total) consists of a boom with 3 nozzles connected to a stepper motor for swinging. Each nozzle has a valve to interrupt the water supply to the nozzle. These sections can be connected linearly to increase the length of the rainfall area (to maximum 16 meters), or they can be used parallelly, thereby performing multiple replications at one time on multiple areas side by side. All these sections are computer-controlled and are independent of each other. Each section contains sensors for measuring soil moisture and tipping bucket rain gauges for continuous monitoring of actual soil properties and control of the rainfall. Remote control also allows for variable rainfall scenarios. The device allows the use of both pulsed and swinging rainfall formation or their combination and thus a large variability in the choice of nozzles according to the purpose of the experiment. Water is pumped by the gas water pump throughout the redistributions and pressure reducing valve, which can manage the required stable pressure. It also contains a datalogger so all measurements and parameters are collected in one device.

This study has been supported by the Grant Agency of the Czech Technical University in Prague, grant No. SGS20/156/OHK1/3T/11 and the Project QK1910029.

How to cite: Kavka, P., Neumann, M., Laburda, T., Devátý, J., and Dostal, T.: New opportunity of RS - variable rainfall simulator for plots variable plots area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6585, https://doi.org/10.5194/egusphere-egu22-6585, 2022.

Rainfall simulators (RS) are commonly used tools for soil erosion research under natural conditions. This research was focused on the plot scale effect in the formation of surface runoff and soil loss. Two surface conditions were tested - grass and bare soil. All experiments were performed in field conditions on undisturbed soil samples located on the experimental site Řisuty, where CTU has been performing experiments with rainfall simulators for many years. Three experiments were performed to investigate the formation of surface runoff depending on area size, surface type and precipitation intensity. These experiments were performed on a surface with grass cover and also on a plot of ​​cultivated bare soil. For the bare soil experiment, the area was prepared just prior to the experiment itself. The grass plots were left to develop naturally for 2 years after sowing. A large rainfall simulator with a maximal experimental area of 16 m² (8 m length 2 m wide) was used for this experiment. Four plots with lengths of 1, 2, 4 and 8 m (with widths of 1 m) were placed under the RS. Soil moisture sensors were placed on the plot at various depths to monitor the evolution of soil moisture over time. For the plot with the grass cover, a rainfall with variable intensity over 75 minutes was used (rainfall intensities 40, 60, 90 mm/h). Two follow-up experiments were conducted on the plot with bare soil. Rainfall intensities were a constant 60 mm/h for 30 minutes after surface runoff starts. The second experiment started 15 minutes after the conclusion of the first one. This same methodology has been used in other, past, experiments with RS so our results are directly comparable to those previously conducted experiments. All results were recalculated to 1m² and 1 minute intervals for comparison in addition to the cumulative values for each experiment.

Results from the plots with grassland showed significant differences between plots of different lengths. Experimental plots with bare soil provided higher variability in results on the plots in their natural moisture (dry condition), than those of the fully saturated samples. Results showed that the length of the plot is more important for soil loss than for surface runoff processes. The heterogeneity of the infiltration soil properties would play significant role on the experiment results.

This study has been supported by Grant Agency of the Czech Technical University in Prague, grant No. SGS20/156/OHK1/3T/11 and the Project QK1910029.

How to cite: Neumann, M., Kavka, P., Kubínová, R., Tejkl, A., Vrána, M., Kubát, J.-F., and Laburda, T.: Rainfall Simulators – how plot scale affects results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4947, https://doi.org/10.5194/egusphere-egu22-4947, 2022.

The Dynamic Image Analysis (DIA), standardised in ISO 13322-2:2006 and ISO 9276-6:2008 standards, introduces a simple and fast analysis of diverse particle shape and size parameters, compared to a manual method or static image analysis, respectively. While the DIA method is time conserving, as it is a quasi-3D method, it is susceptible to greater variations in results compared to a real-3D, time consuming static image analysis. A variation analysis of the DIA results as a function of the analysed particles’ shape was the focus of our study. The particle shape plays a role in various processes, including wearing off (mechanical abrasion) during sediment transport or due to in-situ abrasion of larger sediment particles in fluvial environments.

More than 40 particles were randomly selected for the DIA analysis. Analysed particles included quarried, angular rock particles and rounded fluvial sediment particles. The selected particles had a geometric mean diameter in the range between 15 mm and 70 mm (coarse gravel to cobble size). The mass of particles was between 10 and 400 g. All particles were divided into four shape groups (bladed, prolate, equant, and oblate) according to Zingg’s shape classification. Axes' lengths used for shape classification were manually measured using a caliper. All particles were also individually analysed in a dynamic image analyser (quasi-3D image analyser) Microtrac Camsizer XL, using the accompanying software, PartAn 3D. The software evaluates 33 size and shape parameters of analysed particles, including dimensional (e.g. length, width, thickness, surface area, etc.) and dimensionless (e.g. ellipticity, sphericity, convexity, etc.) parameters. Three DIA repetitions of each particle were applied to estimate the mean values and variation (coefficients of variation, CV) in its results.

Furthermore, the effect of particles’ size, mass, and Zingg’s shape on the variability of the DIA results was investigated. Particles’ size, as well as particles’ angularity, showed no obvious effect on the variation in the DIA results. Quarried, angular particles had CV of 3.54% on average for all parameter results, while rounded, fluvial particles had CV of 3.68% for all parameter results. On the other hand, Zingg’s shape class showed an effect on the variation of both, dimensional and dimensionless DIA resulting parameters. Bladed particles displayed the greatest variations of all the resulting parameter values, with an average CV of 6.85%, and the greatest scatter of parameters’ CVs. When analysing such particles, it would be beneficial to conduct more than three repetitions for more accurate results. Since the DIA analysis is a fast method, this is not a problem in order to get a robust estimation of coarse particle shape. Additionally, observing the parameters themselves, “concavity” and “angularity” had the highest CVs, namely 13.35% and 10.24%, as well as the greatest scatter of the CVs. Parameters “convexity”, “solidity”, and “sphericity” had the lowest CVs, namely 0.12%, 0.26%, and 0.96%, respectively, as well as the lowest scatter of the CVs.

How to cite: Kuzmanić, T. and Mikoš, M.: Effect of coarse gravel and cobble size particles’ shape on their dynamic image analysis results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4865, https://doi.org/10.5194/egusphere-egu22-4865, 2022.

The level and type of saturation of the petroleum reservoirs is an essential parameter in reserve estimation because it determines the effective volume of the hydrocarbon that is being stored. At the same time, rock wettability influences the displacement of oil by water from oil-producing reservoirs, especially during water-flooding processes. Low-field Nuclear Magnetic Resonance (NMR) spectrometry evaluates the pore size distribution and has proved a powerful tool in determining the type of saturation and assessing the solid-fluid affinity (Katika et al., 2017).

However, assessing the pore-fluid distribution of rocks with complex mineral composition at laboratory conditions, such as chalk and argillaceous sandstones, that are commonly found in the North Sea oil reservoirs, often requires further investigation. NMR data are combined with a visual inspection or with traditional techniques, such as MICP, to evaluate the microtexture of rocks (Katika et al., 2018, Faÿ-Gomord et al., 2016). Considering that laboratory low-field NMR can be used as a guide to interpreting logging data, improving the evaluation of lab measurements has a profound influence on the field.

Deep Learning (DL), as an artificial intelligence technique utilizing neural networks, has the potential to transform low-field NMR into a more efficient and powerful tool in reservoir characterization.

The various peaks in NMR T₂ relaxation spectra differ in rocks with multiple types and levels of saturation, rock-fluid affinity, or pore size distribution. In the present study, we aim to improve the interpretation of the T₂ spectra and automate peak picking. Using laboratory data for reservoir rocks from the literature (Katika et al., 2017), a Deep Neural Network (DNN) was trained to optimize the internal network parameters and successfully evaluate the type of peaks existing in T₂ spectra. The successful evaluation is confirmed with visual inspection and correlated with geophysical data derived from the same literature.

References

Katika, K., Saidian, M., Prasad, M. and Fabricius, I.L., 2017. Low-Field NMR Spectrometry of Chalk and Argillaceous Sandstones: Rock-Fluid Affinity Assessed from T1/T2 Ratio. Petrophysics-The SPWLA Journal of Formation Evaluation and Reservoir Description, 58(02), pp.126-140. SPWLA-2017-v58n2a4

Faÿ-Gomord, O., Soete, J., Katika, K., Galaup, S., Caline, B., Descamps, F., Lasseur, E., Fabricius, I.L., Saïag, J., Swennen, R. and Vandycke, S., 2016. New insight into the microtexture of chalks from NMR analysis. Marine and Petroleum Geology, 75, pp.252-271. https://doi.org/10.1016/j.marpetgeo.2016.04.019

Katika, K., Alam, M.M., Alexeev, A., Chakravarty, K.H., Fosbøl, P.L., Revil, A., Stenby, E., Xiarchos, I., Yousefi, A. and Fabricius, I.L., 2018. Elasticity and electrical resistivity of chalk and greensand during water flooding with selective ions. Journal of Petroleum Science and Engineering, 161, pp.204-218. https://doi.org/10.1016/j.petrol.2017.11.045

How to cite: Katika, T. and Michalis, P.: Machine Learning for low-field NMR to improve pore fluid characterization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2558, https://doi.org/10.5194/egusphere-egu22-2558, 2022.

Soil erosion has environmental and socioeconomic significances. Most of the loess soils throughout the world are subjected to increased land uses such, which increased soil destruction and dust emission to the atmosphere. There is a distinguish interest in applications for dust control and soil stabilization. This study examines empirically the use of a metakaolin-based geopolymer for dust control and soil stabilization in a semi-arid loess soil that is subjected to land uses and erosional processes. The application of the geopolymer for dust control in comparison with common products (brine, bitumen, PVA) resulted with no soil erosion and dust emission by wind tunnel simulations. As a soil stabilizer, the geopolymer tested in this study provides remarkably good results in the tensile test. The most successful composition of the geopolymer, which is activation solution of sodium silicate and sodium hydroxide (NaOH) together with an addition of 30% metakaolin, obtained soil strength of 23900N after 28 days. The attempt to replace NaOH with lime (CaO) in the activation solution was far inferior to the original composition.

How to cite: Katra, I.: A clay-based geopolymer in loess stabilization to water and wind soil erosion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8329, https://doi.org/10.5194/egusphere-egu22-8329, 2022.

Aeolian megaripples are a landscape formation widespread on Earth and Mars that develop in sand surfaces with a bimodal grain size distribution of coarse and fine grains. Megaripples are relatively high with a greater wavelength compared with normal sand ripples. Previous works provided quantitative information on the morphological characteristics, development, flattening mechanisms, longevity, and transverse instability of megaripples. It has been hypothesized that the sorting process of the initial bimodal size distribution is a key factor in megaripple formation. In this study, we experimentally explored the impact of the grain size distribution on the crest characteristics under different wind velocities in a boundary-layer wind tunnel. The controlled experiments allowed measurements of sand fluxes, particle size distributions, and ripple morphology by a laser module. The results reveal links between the rate of growth of the incipient megaripples, ripple height, and the armoring layer thickness and composition to wind velocity. The ripples grow higher as the wind velocity increases, and the armoring layer is thicker up to a certain wind velocity when erosion of the crest starts. In addition, the correlation between the armoring layer's nonlinear thickening rate and the ripples growth rate seems to indicate a fundamental connection between ripples height and the formation of the armoring layer, which is crucial for megaripples formation.

How to cite: saban, L., Katra, I., and Yizhaq, H.: Impact of grain size distribution and wind velocity on the armoring layer of aeolian megaripples, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3891, https://doi.org/10.5194/egusphere-egu22-3891, 2022.

The Souss-Massa basin features unique and centuries old human–environment interactions in a vulnerable arid ecosystem. A high pressure caused by intense agriculture combined with increasing water scarcity causes degradation of soils and vegetation cover. The test sites are located on alluvial fans from the flanking High Atlas Mountains in the north and the northern talus of the Anti Atlas in the south. Wind-tunnel tests were applied to investigate susceptibility to wind erosion from sparse argan forest, badland and wadi surfaces. The results show diverse potential for emission of coarser and finer mineral dust with highest values found on freshly tilled surfaces in the extensively managed argan forest and sandy wadi surfaces. For one tested wadi section, very erodible areas were found in close vicinity to areas with much lower sediment yield. The wind-erosion dynamics are thus closely related to fluvial processes previously influencing surface characteristics as well as previous sorting processes by wind impact. The strongly crusted surfaces attributed to badland environments are least susceptible to wind erosion, with the exception of higher emissions measured on the wadi rim.

The data give insight into possible wind-erosion patterns under non-extreme wind regime and are a valuable basis for investigation of interactions between fluvial and aeolian processes in wadi structures.

How to cite: Marzen, M., Kirchhoff, M., Marzolff, I., Aït Hssaine, A., and Ries, J. B.: Experimental wind erosion study in argan woodlands, badlands and wadis in the Souss-Massa Basin, Morocco, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9688, https://doi.org/10.5194/egusphere-egu22-9688, 2022.

Have you ever applied the Schmidt hammer method and wondered what the R‑value represents? What SI unit it would have and which material properties it actually assesses? The Schmidt rebound hammer is a device initially intended to test the curing state and strength of concrete. Since then, the concept has been transferred to determine the strength, weathering, and sometime even surface exposure age of rocks in geomorphology. The advantage of the Schmidt hammer that it is non-destructive, easy to handle, light, and readily applicable in the field. However, the method is only based on correlation, without physical explanation of the measured value being provided, and using a seemingly arbitrary resolution of the scale without reference. Here we present our approach to put the Schmidt hammer and especially the physics behind the R‑value on solid ground. Using a dataset of material properties and R‑Values, we find that the Schmidt hammer best represents the elasticity of the material. The elasticity and, along with it, the elastic modulus, can be independently and complementarily assessed with other geophysical methods. Both metrics are known to vary with i) moisture level, ii) stress state, and iii) temperature. Consequently, we conducted controlled experiments to constrain the influence of these conditions on R‑values. A major disadvantage of the Schmidt hammer, the resolution of the scale, remains and needs further calibration.

How to cite: Huxol, B., Pruß, G., Voigtländer, A., Dietze, M., and Turowski, J. M.: Making the Schmidt Hammer Great Again!, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1841, https://doi.org/10.5194/egusphere-egu22-1841, 2022.

There is a knowledge gap concerning the identification and quantification of transported soil particles in subsurface flows. If these soil particles reach relevant amounts, protective measures against soil erosion applied on the surface may be partially ineffective, and the soil may degrade further and unnoticed. In consequence, there is a need to develop a method to determine this subsurface particle transport in situ. A laboratory flume experiment was developed to examine the processes of fine soil material transport as well as the development of sediment traps for in situ measurements. Since, steep-slope vineyard soils are especially prone to subsurface flows they were subject of first investigations: The shallow steep-slope vineyard soils of the Mosel wine region are mainly developed from Devonian argillaceous schists and Pleistocene terrace sediments. Among the main physical characteristics are a very high rock fragment content and a loose surface layer over a strongly compacted layer caused by the combined action of tillage and weathering. This structure is presumably prone to subsurface flows within the upper horizon, especially in periods of very high soil moisture. The results of this laboratory experiment clearly confirm the presence of subsurface particle transport and the applicability of a sediment trap prototype consisting of a relatively simple and low-cost drain structure. 

How to cite: Kögler, L., Iserloh, T., Helmer, A., Ruby, A., Marzen, M., Seeger, M., and Ries, J. B.: Experimental laboratory setup for identification and quantification of transported soil particles in subsurface flows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5032, https://doi.org/10.5194/egusphere-egu22-5032, 2022.