Rainfall Simulators as a tool in Soil Science, Geomorphology and Hydrology research and teaching

A special issue of Hydrology (ISSN 2306-5338).

Deadline for manuscript submissions: closed (30 September 2016) | Viewed by 83921

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Physical Geography and Environmental Change, University of Basel, Basel, Switzerland
Interests: soil erosion; experimental methods; soil degradation and desertification; geomorphodynamics; peri-/glacial morphology

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Department of Physical Geography, Trier University, Trier, Germany
Interests: geomorphological, hydrological and soil-physical processes; process-based analysis of soil erosion and recent geomorphodynamics
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Wageningen Environmental Research, Team Soil, Water and Land Use, Wageningen University, 6708PB Wageningen, The Netherlands
Interests: water and sediment connectivity; catchment processes; nature-based solutions; forest fire; sustainable land management
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Special Issue Information

Dear Colleagues,

Rainfall simulation is a method used worldwide to assess the generation of overland flow, soil erosion, infiltration, and related processes, such as soil sealing, crusting, splash, and redistribution of solids and solutes by raindrop impact. Data obtained from these simulations are of great significance for both the analysis of simulated processes and input data for soil erosion modeling. The reliability of these data is of major importance and, consequently, the quality management of rainfall simulation procedures is a general responsibility of the rainfall simulation-community. Rainfall simulators are also an excellent education tool that allows students to visually observe the hydrological and erosion processes that occur within the landscape. This Special Issue will join contributions that use simulated rainfall experiments for research and teaching purposes. Research studies, state-of-the-art contributions and technical notes are very welcome. We especially welcome studies that highlight challenges of the present and near future use of rainfall simulations concerning the comparability of results and scales, the quality of the data, and further technical developments. Early stage researchers are strongly encouraged to present their research.

Dr. Thomas Iserloh
Prof. Dr. Artemi Cerdà
Dr. Wolfgang Fister
Dr. Saskia Keesstra
Guest Editors

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Keywords

  • rainfall simulation
  • soil erosion
  • soil hydrology
  • experimental geomorphology

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Published Papers (10 papers)

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Research

5846 KiB  
Article
Hydrological Modelling Using a Rainfall Simulator over an Experimental Hillslope Plot
by Arpit Chouksey, Vinit Lambey, Bhaskar R. Nikam, Shiv Prasad Aggarwal and Subashisa Dutta
Hydrology 2017, 4(1), 17; https://doi.org/10.3390/hydrology4010017 - 2 Mar 2017
Cited by 19 | Viewed by 11087
Abstract
Hydrological processes are complex to compute in hilly areas when compared to plain areas. The governing processes behind runoff generation on hillslopes are subsurface storm flow, saturation excess flow, overland flow, return flow and pipe storage. The simulations of the above processes in [...] Read more.
Hydrological processes are complex to compute in hilly areas when compared to plain areas. The governing processes behind runoff generation on hillslopes are subsurface storm flow, saturation excess flow, overland flow, return flow and pipe storage. The simulations of the above processes in the soil matrix require detailed hillslope hydrological modelling. In the present study, a hillslope experimental plot has been designed to study the runoff generation processes on the plot scale. The setup is designed keeping in view the natural hillslope conditions prevailing in the Northwestern Himalayas, India where high intensity rainfall events occur frequently. A rainfall simulator was installed over the experimental hillslope plot to generate rainfall with an intensity of 100 mm/h, which represents the dominating rainfall intensity range in the region. Soil moisture sensors were also installed at variable depths from 100 to 1000 mm at different locations of the plot to observe the soil moisture regime. From the experimental observations it was found that once the soil is saturated, it remains at field capacity for the next 24–36 h. Such antecedent moisture conditions are most favorable for the generation of rapid stormflow from hillslopes. A dye infiltration test was performed on the undisturbed soil column to observe the macropore fraction variability over the vegetated hillslopes. The estimated macropore fractions are used as essential input for the hillslope hydrological model. The main objective of the present study was to develop and test a method for estimating runoff responses from natural rainfall over hillslopes of the Northwestern Himalayas using a portable rainfall simulator. Using the experimental data and the developed conceptual model, the overland flow and the subsurface flow through a macropore-dominated area have been estimated/analyzed. The surface and subsurface runoff estimated using the developed hillslope hydrological model compared well with the observed surface runoff for a rainfall intensity of 100 mm/h. The surface runoff hydrograph was very well predicted by the model, with correlation coefficient (R2) and Nash–Sutcliffe efficiency coefficient (E) as 0.95 and 0.91, respectively. The observed soil/macropore storage component was estimated with the help of water balance equation and compared with the model predicted macropore storage. The error in computing the soil/macropore storage was estimated as 0.38 mm i.e., 13%. Full article
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2090 KiB  
Article
Influence of Crust Formation on Soil Porosity under Tillage Systems and Simulated Rainfall
by Jaqueline Dalla Rosa, Miguel Cooper, Frédéric Darboux, João Carlos Medeiros, Carla Campanaro and Luiz Roberto Martins Pinto
Hydrology 2017, 4(1), 3; https://doi.org/10.3390/hydrology4010003 - 5 Jan 2017
Cited by 5 | Viewed by 5858
Abstract
Surface crusts, formed by raindrop impact, degrade the soil surface structure causing changes in porosity. An experiment was conducted with the objective of evaluating the influence of the formation of a crusting layer on the porosity (percentage of area, shape and size) of [...] Read more.
Surface crusts, formed by raindrop impact, degrade the soil surface structure causing changes in porosity. An experiment was conducted with the objective of evaluating the influence of the formation of a crusting layer on the porosity (percentage of area, shape and size) of a Haplic Acrisol under three tillage systems, and simulated rainfall. The tillage systems were: conventional tillage (CT), reduced tillage (RT) and no-tillage (NT). Each tillage system was submitted to different levels of simulated rainfall (0, 27, 54 and 80 mm) at an intensity of 80 mm·h−1. Undisturbed soil samples were collected and resin impregnated for image analysis in two layers: layer 1 (0–1 cm) and layer 2 (1–2 cm). Image analysis was used to obtain the pore area percentage, pore shape and size. The degradation of the soil surface and change in porosity, caused by rainfall, occurred differently in the tillage systems. In the CT and RT systems, the most pronounced pore changes caused by rainfall occurred in layer 1, but in the NT system, this change occurred in layer 2. The rainfall caused change of pore area percentage in the CT and RT systems, with reduction of complex and an increase of rounded pores. The NT system showed greater occurrence of the rounded pores (vesicles), originated by processes of wetting below the residue cover, and by alternating periods of wetting and drying. In this study, the changes in porosity were attributed to two main factors: (1) to the effect of the raindrop directly on the soil surface (for CT and RT tillage systems) and (2) water transfer processes in the soil surface (for NT systems). Full article
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14800 KiB  
Article
Feasibility of High-Resolution Soil Erosion Measurements by Means of Rainfall Simulations and SfM Photogrammetry
by Phoebe Hänsel, Marcus Schindewolf, Anette Eltner, Andreas Kaiser and Jürgen Schmidt
Hydrology 2016, 3(4), 38; https://doi.org/10.3390/hydrology3040038 - 17 Nov 2016
Cited by 45 | Viewed by 8109
Abstract
The silty soils of the intensively used agricultural landscape of the Saxon loess province, eastern Germany, are very prone to soil erosion, mainly caused by water erosion. Rainfall simulations, and also increasingly structure-from-motion (SfM) photogrammetry, are used as methods in soil erosion research [...] Read more.
The silty soils of the intensively used agricultural landscape of the Saxon loess province, eastern Germany, are very prone to soil erosion, mainly caused by water erosion. Rainfall simulations, and also increasingly structure-from-motion (SfM) photogrammetry, are used as methods in soil erosion research not only to assess soil erosion by water, but also to quantify soil loss. This study aims to validate SfM photogrammetry determined soil loss estimations with rainfall simulations measurements. Rainfall simulations were performed at three agricultural sites in central Saxony. Besides the measured data runoff and soil loss by sampling (in mm), terrestrial images were taken from the plots with digital cameras before and after the rainfall simulation. Subsequently, SfM photogrammetry was used to reconstruct soil surface changes due to soil erosion in terms of high resolution digital elevation models (DEMs) for the pre- and post-event (resolution 1 × 1 mm). By multi-temporal change detection, the digital elevation model of difference (DoD) and an averaged soil loss (in mm) is received, which was compared to the soil loss by sampling. Soil loss by DoD was higher than soil loss by sampling. The method of SfM photogrammetry-determined soil loss estimations also include a comparison of three different ground control point (GCP) approaches, revealing that the most complex one delivers the most reliable soil loss by DoD. Additionally, soil bulk density changes and splash erosion beyond the plot were measured during the rainfall simulation experiments in order to separate these processes and associated surface changes from the soil loss by DoD. Furthermore, splash was negligibly small, whereas higher soil densities after the rainfall simulations indicated soil compaction. By means of calculated soil surface changes due to soil compaction, the soil loss by DoD achieved approximately the same value as the soil loss by rainfall simulation. Full article
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6513 KiB  
Article
Rainfall Simulator Experiments to Investigate Macropore Impacts on Hillslope Hydrological Response
by Yvonne Smit, Martine J. Van der Ploeg and Adriaan J. Teuling
Hydrology 2016, 3(4), 39; https://doi.org/10.3390/hydrology3040039 - 15 Nov 2016
Cited by 4 | Viewed by 7504
Abstract
Understanding hillslope runoff response to intense rainfall is an important topic in hydrology, and is key to correct prediction of extreme stream flow, erosion and landslides. Although it is known that preferential flow processes activated by macropores are an important phenomena in understanding [...] Read more.
Understanding hillslope runoff response to intense rainfall is an important topic in hydrology, and is key to correct prediction of extreme stream flow, erosion and landslides. Although it is known that preferential flow processes activated by macropores are an important phenomena in understanding runoff processes inside a hillslope, hydrological models have generally not embraced the concept of an extra parameter that represents ‘macropores’ because of the complexity of the phenomenon. Therefore, it is relevant to investigate the influence of macropores on runoff processes in an experimental small artificial hillslope. Here, we report on a controlled experiment where we could isolate the influence of macropores without the need for assumptions regarding their characteristics. Two identical hillslopes were designed, of which one was filled with artificial macropores. Twelve artificial rainfall events were applied to the two hillslopes and results of drainage and soil moisture were investigated. After the experiments, it could be concluded that the influence of macropores on runoff processes was minimal. The S90 sand used for this research caused runoff to respond fast to rainfall, leading to little or no development of saturation near the macropores. In addition, soil moisture data showed a large amount of pendular water in the hillslopes, which implies that the soil has a low air entry value, and, in combination with the lack of vertical flow, could have caused the pressure difference between the matrix and the macropores to vanish sooner and result in equilibrium being reached in a relatively short time. Nevertheless, a better outline is given to determine a correct sand type for these types of experiments and, by using drainage recession analysis to investigate the influences of macropores on runoff, heterogeneity in rainfall intensity can be overcome. This study is a good point of reference to start future experiments from concerning macropores and hillslope hydrology. Full article
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1871 KiB  
Article
Conditions for the Occurrence of Slaking and Other Disaggregation Processes under Rainfall
by Frédéric Darboux, Jaqueline Dalla Rosa and Miguel Cooper
Hydrology 2016, 3(3), 27; https://doi.org/10.3390/hydrology3030027 - 5 Jul 2016
Cited by 10 | Viewed by 5015
Abstract
Under rainfall conditions, aggregates may suffer breakdown by different mechanisms. Slaking is a very efficient breakdown mechanism. However, its occurrence under rainfall conditions has not been demonstrated. Therefore, the aim of this study was to evaluate the occurrence of slaking under rain. Two [...] Read more.
Under rainfall conditions, aggregates may suffer breakdown by different mechanisms. Slaking is a very efficient breakdown mechanism. However, its occurrence under rainfall conditions has not been demonstrated. Therefore, the aim of this study was to evaluate the occurrence of slaking under rain. Two soils with silt loam (SL) and clay loam (CL) textures were analyzed. Two classes of aggregates were utilized: 1–3 mm and 3–5 mm. The aggregates were submitted to stability tests and to high intensity (90 mm·h−1) and low intensity (28 mm·h−1) rainfalls, and different kinetic energy impacts (large and small raindrops) using a rainfall simulator. The fragment size distributions were determined both after the stability tests and rainfall simulations, with the calculation of the mean weighted diameter (MWD). After the stability tests the SL presented smaller MWDs for all stability tests when compared to the CL. In both soils the lowest MWD was obtained using the fast wetting test, showing they were sensitive to slaking. For both soils and the two aggregate classes evaluated, the MWDs were recorded from the early beginning of the rainfall event under the four rainfall conditions. The occurrence of slaking in the evaluated soils was not verified under the simulated rainfall conditions studied. The early disaggregation was strongly related to the cumulative kinetic energy, advocating for the occurrence of mechanical breakdown. Because slaking requires a very high wetting rate on initially dry aggregates, it seems unlikely to occur under field conditions, except perhaps for furrow irrigation. Full article
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3769 KiB  
Article
Runoff and Soil Erosion Assessment on Forest Roads Using a Small Scale Rainfall Simulator
by Julian J. Zemke
Hydrology 2016, 3(3), 25; https://doi.org/10.3390/hydrology3030025 - 1 Jul 2016
Cited by 56 | Viewed by 10354
Abstract
Forestry operations can significantly alter hydrological and erosional processes in a catchment. In the course of developing timberland, a network of persistent roads and skid trails causing soil compaction is usually established. Hereby, the infiltration rate of the soil is distinctly reduced, which [...] Read more.
Forestry operations can significantly alter hydrological and erosional processes in a catchment. In the course of developing timberland, a network of persistent roads and skid trails causing soil compaction is usually established. Hereby, the infiltration rate of the soil is distinctly reduced, which leads to the generation of overland flow—this may also cause soil erosion. In this study, a small-scale rainfall simulator is used to investigate hydrological and erosional processes on forest roads and skid trails. The results show increased runoff rates on forest roads, up to 25 times higher than on undisturbed forest topsoil. On skid trails, the runoff rates were altered especially in rutted areas (16 times higher) while unrutted parts showed a lesser change (four times higher). With sufficient overland flow, soil erosion rates also rose, particularly when the vegetation cover of the surface was removed: bare road surfaces featured higher mean erosion rates (195 g·m−2) than partly or completely vegetated skid trails (13 g·m−2) and undisturbed sites (5 g·m−2). The findings presented in this study indicate the need for the use of compaction reducing technology during forestry operations and a revegetation of road surfaces in order to minimize the detrimental factor of roads and skid trails on water retention and soil conservation. Full article
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4836 KiB  
Article
Determination of Watershed Infiltration and Erosion Parameters from Field Rainfall Simulation Analyses
by Mark E. Grismer
Hydrology 2016, 3(3), 23; https://doi.org/10.3390/hydrology3030023 - 28 Jun 2016
Cited by 14 | Viewed by 7037
Abstract
Realistic modeling of infiltration, runoff and erosion processes from watersheds requires estimation of the effective hydraulic conductivity (Km) of the hillslope soils and how it varies with soil tilth, depth and cover conditions. Field rainfall simulation (RS) plot studies provide an [...] Read more.
Realistic modeling of infiltration, runoff and erosion processes from watersheds requires estimation of the effective hydraulic conductivity (Km) of the hillslope soils and how it varies with soil tilth, depth and cover conditions. Field rainfall simulation (RS) plot studies provide an opportunity to assess the surface soil hydraulic and erodibility conditions, but a standardized interpretation and comparison of results of this kind from a wide variety of test conditions has been difficult. Here, we develop solutions to the combined set of time-to-ponding/runoff and Green– Ampt infiltration equations to determine Km values from RS test plot results and compare them to the simpler calculation of steady rain minus runoff rates. Relating soil detachment rates to stream power, we also examine the determination of “erodibility” as the ratio thereof. Using data from over 400 RS plot studies across the Lake Tahoe Basin area that employ a wide range of rain rates across a range of soil slopes and conditions, we find that the Km values can be determined from the combined infiltration equation for ~80% of the plot data and that the laminar flow form of stream power best described a constant “erodibility” across a range of volcanic skirun soil conditions. Moreover, definition of stream power based on laminar flows obviates the need for assumption of an arbitrary Mannings “n” value and the restriction to mild slopes (<10%). The infiltration equation based Km values, though more variable, were on average equivalent to that determined from the simpler calculation of steady rain minus steady runoff rates from the RS plots. However, these Km values were much smaller than those determined from other field test methods. Finally, we compare RS plot results from use of different rainfall simulators in the basin and demonstrate that despite the varying configurations and rain intensities, similar erodibilities were determined across a range of infiltration and runoff rates using the laminar form of the stream power equation. Full article
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5288 KiB  
Article
Surface Runoff in Watershed Modeling—Turbulent or Laminar Flows?
by Mark E. Grismer
Hydrology 2016, 3(2), 18; https://doi.org/10.3390/hydrology3020018 - 4 May 2016
Cited by 8 | Viewed by 7789
Abstract
Determination of overland sheet flow depths, velocities and celerities across the hillslope in watershed modeling is important towards estimation of surface storage, travel times to streams and soil detachment rates. It requires careful characterization of the flow processes. Similarly, determination of the temporal [...] Read more.
Determination of overland sheet flow depths, velocities and celerities across the hillslope in watershed modeling is important towards estimation of surface storage, travel times to streams and soil detachment rates. It requires careful characterization of the flow processes. Similarly, determination of the temporal variation of hillslope-riparian-stream hydrologic connectivity requires estimation of the shallow subsurface soil hydraulic conductivity and soil-water retention (i.e., drainable porosities) parameters. Field rainfall and runoff simulation studies provide considerable information and insight into these processes; in particular, that sheet flows are likely laminar and that shallow hydraulic conductivities and storage can be determined from the plot studies. Here, using a 1 m by 2 m long runoff simulation flume, we found that for overland flow rates per unit width of roughly 30–60 mm2/s and bedslopes of 10%–66% with varying sand roughness depths that all flow depths were predicted by laminar flow equations alone and that equivalent Manning’s n values were depth dependent and quite small relative to those used in watershed modeling studies. Even for overland flow rates greater than those typically measured or modeled and using Manning’s n values of 0.30–0.35, often assumed in physical watershed model applications for relatively smooth surface conditions, the laminar flow velocities were 4–5 times greater, while the laminar flow depths were 4–5 times smaller. This observation suggests that travel times, surface storage volumes and surface shear stresses associated with erosion across the landscape would be poorly predicted using turbulent flow assumptions. Filling the flume with fine sand and conducting runoff studies, we were unable to produce sheet flow, but found that subsurface flows were onflow rate, soil depth and slope dependent and drainable porosities were only soil depth and slope dependent. Moreover, both the sand hydraulic conductivity and drainable porosities could be readily determined from measured capillary pressure displacement pressure head and assumption of pore-size distributions (i.e., Brooks-Corey lambda values of 2–3). Full article
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3335 KiB  
Article
Soil Erosion Processes in European Vineyards: A Qualitative Comparison of Rainfall Simulation Measurements in Germany, Spain and France
by Jesús Rodrigo Comino, Thomas Iserloh, Xavier Morvan, Oumarou Malam Issa, Christophe Naisse, Saskia D. Keesstra, Artemio Cerdà, Massimo Prosdocimi, José Arnáez, Teodoro Lasanta, María Concepción Ramos, María José Marqués, Marta Ruiz Colmenero, Ramón Bienes, José Damián Ruiz Sinoga, Manuel Seeger and Johannes B. Ries
Hydrology 2016, 3(1), 6; https://doi.org/10.3390/hydrology3010006 - 18 Feb 2016
Cited by 72 | Viewed by 9971
Abstract
Small portable rainfall simulators are considered a useful tool to analyze soil erosion processes in cultivated lands. European research groups in Spain (Valencia, Málaga, Lleida, Madrid and La Rioja), France (Reims) and Germany (Trier) have used different rainfall simulators (varying in drop size [...] Read more.
Small portable rainfall simulators are considered a useful tool to analyze soil erosion processes in cultivated lands. European research groups in Spain (Valencia, Málaga, Lleida, Madrid and La Rioja), France (Reims) and Germany (Trier) have used different rainfall simulators (varying in drop size distribution and fall velocities, kinetic energy, plot forms and sizes, and field of application) to study soil loss, surface flow, runoff and infiltration coefficients in different experimental plots (Valencia, Montes de Málaga, Penedès, Campo Real and La Rioja in Spain, Champagne in France and Mosel-Ruwer valley in Germany). The measurements and experiments developed by these research teams give an overview of the variety of methodologies used in rainfall simulations to study the problem of soil erosion and describe the erosion features in different climatic environments, management practices and soil types. The aims of this study are: (i) to investigate where, how and why researchers from different wine-growing regions applied rainfall simulations with successful results as a tool to measure soil erosion processes; (ii) to make a qualitative comparison about the general soil erosion processes in European terroirs; (iii) to demonstrate the importance of the development of standard method for measurement of soil erosion processes in vineyards, using rainfall simulators; and (iv) and to analyze the key factors that should be taken into account to carry out rainfall simulations. The rainfall simulations in all cases allowed infiltration capacity, susceptibility of the soil to detachment and generation of sediment loads to runoff to be determined. Despite using small plots, the experiments were useful to analyze the influence of soil cover to reduce soil erosion, to make comparisons between different locations, and to evaluate the influence of different soil characteristics. The comparative analysis of the studies performed in different study areas points out the need to define an operational methodology to carry out rainfall simulations, which allows us to obtain representative and comparable results and to avoid errors in the interpretation in order to achieve comparable information about runoff and soil loss. Full article
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1538 KiB  
Article
A Combined Raindrop Aggregate Destruction Test-Settling Tube (RADT-ST) Approach to Identify the Settling Velocity of Sediment
by Liangang Xiao, Yaxian Hu, Philip Greenwood and Nikolaus J. Kuhn
Hydrology 2015, 2(4), 176-192; https://doi.org/10.3390/hydrology2040176 - 16 Oct 2015
Cited by 13 | Viewed by 5981
Abstract
The use of sediment settling velocity based on mineral grain size distribution in erosion models ignores the effects of aggregation on settling velocity. The alternative approach, wet-sieved aggregate size distribution, on the other hand, cannot represent all destructive processes that eroded soils may [...] Read more.
The use of sediment settling velocity based on mineral grain size distribution in erosion models ignores the effects of aggregation on settling velocity. The alternative approach, wet-sieved aggregate size distribution, on the other hand, cannot represent all destructive processes that eroded soils may experience under impacting raindrops. Therefore, without considering raindrop impact, both methods may lead to biased predictions of the redistribution of sediment and associated substances across landscapes. Rainfall simulation is an effective way to simulate natural raindrop impact under controlled laboratory conditions. However, very few methods have been developed to integrate rainfall simulation with the settling velocity of eroded sediment. This study aims to develop a new proxy, based on rainfall simulation, in order to identify the actual settling velocity distribution of aggregated sediment. A combined Raindrop Aggregate Destruction Test-Settling Tube (RADT-ST) approach was developed to (1) simulate aggregate destruction under a series of simulated rainfalls; and (2) measure the actual settling velocity distribution of destroyed aggregates. Mean Weight Settling Velocity (MWSV) of aggregates was used to investigate settling behaviors of different soils as rainfall kinetic energy increased. The results show the settling velocity of silt-rich raindrop impacted aggregates is likely to be underestimated by at least six times if based on mineral grain size distribution. The RADT-ST designed in this study effectively captures the effects of aggregation on settling behavior. The settling velocity distribution should be regarded as an evolving, rather than steady state parameter during erosion events. The combined RADT-ST approach is able to generate the quasi-natural sediment under controlled simulated rainfall conditions and is adequately sensitive to measure actual settling velocities of differently aggregated soils. This combined approach provides an effective tool to improve the parameterization of settling velocity input for erosion models. Full article
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