Experimental Setup for Splash Erosion Monitoring—Study of Silty Loam Splash Characteristics

An experimental laboratory setup was developed and evaluated in order to investigate detachment of soil particles by raindrop splash impact. The soil under investigation was a silty loam Cambisol, which is typical for agricultural fields in Central Europe. The setup consisted of a rainfall simulator and soil samples packed into splash cups (a plastic cylinder with a surface area of 78.5 cm2) positioned in the center of sediment collectors with an outer diameter of 45 cm. A laboratory rainfall simulator was used to simulate rainfall with a prescribed intensity and kinetic energy. Photographs of the soil’s surface before and after the experiments were taken to create digital models of relief and to calculate changes in surface roughness and the rate of soil compaction. The corresponding amount of splashed soil ranged between 10 and 1500 g m−2 h−1. We observed a linear relationship between the rainfall kinetic energy and the amount of the detached soil particles. The threshold kinetic energy necessary to initiate the detachment process was 354 J m−2 h−1. No significant relationship between rainfall kinetic energy and splashed sediment particle-size distribution was observed. The splash erosion process exhibited high variability within each repetition, suggesting a sensitivity of the process to the actual soil surface microtopography

Using 3D observations with high spatio-temporal resolution to calibrate and evaluate a process-focused cellular automaton model of soil erosion by water

Future global change is likely to give rise to novel combinations of the factors which enhance or inhibit soil erosion by water. Thus, there is a need for erosion models, necessarily process-focused ones, which are able to reliably represent the rates and extents of soil erosion under unprecedented circumstances. The process-focused cellular automaton erosion model RillGrow is, given initial soil surface microtopography for a plot-sized area, able to predict the emergent patterns produced by runoff and erosion. This study explores the use of structure-from-motion photogrammetry as a means to calibrate and evaluate this model by capturing detailed, time-lapsed data for soil surface height changes during erosion events. Temporally high-resolution monitoring capabilities (i.e. 3D models of elevation change at 0.1 Hz frequency) permit the evaluation of erosion models in terms of the sequence of the formation of erosional features. Here, multiple objective functions using three different spatio-temporal averaging approaches are assessed for their suitability in calibrating and evaluating the model's output. We used two sets of data from field- and laboratory-based rainfall simulation experiments lasting 90 and 30 min, respectively. By integrating 10 different calibration metrics, the outputs of 2000 and 2400 RillGrow runs for, respectively, the field and laboratory experiments were analysed. No single model run was able to adequately replicate all aspects of either the field or the laboratory experiments. The multiple objective function approaches highlight different aspects of model performance, indicating that no single objective function can capture the full complexity of erosion processes. They also highlight different strengths and weaknesses of the model. Depending on the focus of the evaluation, an ensemble of objective functions may not always be necessary. These results underscore the need for more nuanced evaluation of erosion models, e.g. by incorporating spatial-pattern comparison techniques to provide a deeper understanding of the model's capabilities. Such calibrations are an essential complement to the development of erosion models which are able to forecast the impacts of future global change. For the first time, we use data with a very high spatio-temporal resolution to calibrate a soil erosion model.</p

Characterization of an artificially generated rainfall used for a soil erosion research

Vodní eroze půdy se běžně studuje v laboratořích, experimenty bývají založeny na uměle generovaných srážkách s využitím dešťových simulátorů. Typicky je vyhodnocován vliv různých faktorů, jako jsou intenzita nebo úhrn srážky, nebo sklon a délka erozní plochy na erozi. Vzhledem k tomu, že eroze je iniciována dešťovou srážkou, je pro přenositelnost výsledků z laboratoře do krajiny zásadní, aby se simulovaná srážka co nejvíce blížila charakteristikám přírodních srážek. Intenzita deště se kontroluje poměrně snadno, ale klíčový dopad na erozní procesy má kinetická energie deště. Cílem tohoto příspěvku je komplexní vyhodnocení charakteristik simulovaného deště a porovnání jeho kinetické energie s energií přírodních srážek. Součástí výsledků je i porovnání několika běžně využívaných disdrometrů a diskuze využitelnosti disdrometrů pro charakterizaci simulovaných srážek. Experiment byl proveden na laboratorním dešťovém simulátoru Fakulty stavební, ČVUT v Praze. Kinetická energie deště o různých intenzitách byla monitorována pomocí disdrometrů LPM (Thies Clima), Parsivel (OTT) a PWS 100 (Campbell Sci.), za referenční údaj intenzity srážky byla povážována data z překlopného srážkoměru MR3 (Meteoservis). Intenzitu deště měří všechny testované disdrometry uspokojivě. Přístroje naměřily 106 % (LPM), 79 % (Parsivel) a 116 % (PWS100) hodnoty naměřené pomocí překlopného srážkoměru. V případě měření kinetické energie nebyla nastavena žádná referenční hodnota, ale přístroje byly porovnávány mezi sebou. LPM oproti ostatním dvěma přístrojům měří výrazně nižší kinetickou energii, jím naměřené hodnoty odpovídají v průměru 83% hodnot naměřených Parsivelem, respektive 59% hodnot naměřených PWS100. Nejvyšší hodnoty kinetické energie měřil PWS100. Klíčovým závěrem je, že přívalová srážka simulovaná laboratorním dešťovým simulatorem má znatelně nižší kinetickou energii než přírodní srážky o shodných intenzitách.A rainfall simulator is a common laboratory tool for soil erosion research. Typical objective of the rainfall experiments is the evaluation of various factors on soil erosion processes, such as the effect of rainfall intensity, rainfall duration, soil characteristics, plot’s slope and length. Due to the fact that the soil erosion is initiated by the rainfall, it is crucial to keep the simulated rainfall characteristics as close as possible to the natural rainfall. Rainfall intensity is usually easy to control, but the rainfall kinetic energy is the driving force of the initial stage of the erosion. The aim of this study is to evaluate the simulated rainfall characteristics, incl. its drop size distribution and kinetic energy, and compare the simulated rainfall to the natural rainfall. Within a study we also compared three common disdrometers and we show limitation of the disdrometers to monitor the artificially generated rainfall. The experiments were done with a use of nozzle type rainfall simulator. The rainfall characteristics were monitored by disdrometers LPM (Thies Clima), Parsivel (OTT) and PWS 100 (Campbell Sci.), standard raingauge was used as a reference measurement for the intensity monitoring. The intensity, recorded with the disdrometers, was very similar to the rain gauge. In the average it measured 106 % (LPM), 79 % (Parsivel) and 116 % (PWS100) of rain gauge value. There was a large difference between the disdrometers in the measured kinetic energy values. LPM significantly underestimated the kinetic energy compared to the other disdrometers it measured 83 % of Parsival value and 59 % of PWS100 value. The highest values were measured with the PWS 100. The key conclusion is, that a simulated rainfall with the intensity above 20 mm h-1, has significantly lower kinetic energy, compared to a natural rainfall with same intensity