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The study of soil erosion is one of the necessities of watershed management, and erosion control requires understanding the behavior of runoff and sediment production in different conditions. This study aims to evaluate the effect of soil particle percentage, soil organic carbon (OC) content, slope, and initial moisture on runoff components and the amount of sediment at the plot scale. In this study, a rainfall simulator has been used to generate rainfall in the Shamsabad area, Ardabil province, Iran, and was performed at 58 points through synthetic rainfall with 20-min duration. Also, soil samples were taken and their properties were determined through laboratory analysis. The GIS was used to produce slope layers and Topographic Wetness Index. The average percentage of soil OC was 0.90, and the average of clay, sand, and silt was 24.39%, 50.26%, and 24.35%, respectively. Taylor diagram and triple diagram models were used to determine the dependence of runoff and sediment behavior on independent variables. The average percentage of soil OC was 0.90, and the average of clay, sand, and silt was 24.39%, 50.26%, and 24.35%, respectively. The results showed that runoff termination time is directly related to soil clay content and inversely related to soil sand content; in other words, with increasing sand to more than 35%, runoff production time became longer. The amount of sediment or soil clay has shown a positive relationship with the percentage of sand, and the amount of slope is negatively related. By increasing the amount of soil clay to above 40%, the amount of sediment has reached its highest level in gentle slope values (< 10 degrees). Considering the complexity of sediment production behavior and the role of various factors on runoff and sediment production in interaction with all influential factors should be considered. [ABSTRACT FROM AUTHOR]

In the Dolomitic region, abundant coarse hillslope sediment is commonly found at the toe of rocky cliffs. Ephemeral channels originate where lower permeability bedrock surfaces concentrate surface runoff. Debris flows initiate along such channels following intense rainfall and determine the progressive erosion and deepening of the channels. Sediment recharge mechanisms include rock fall, dry ravel processes and channel‐bank failures. Here we document debris flow activity that took place in an active debris flow basin during the year 2015. The Cancia basin is located on the southwestern slope of Mount Antelao (3264 m a.s.l.) in the dolomitic region of the eastern Italian Alps. The 2.5 km2 basin is incised in dolomitic limestone rocks. The data consist of repeated topographic surveys, distributed rainfall measurements, time‐lapse (2 s) videos of two events and pore pressure measurements in the channel bed. During July and August 2015, two debris flow events occurred, following similarly intense rainstorms. We compared rainfall data to existing rainfall triggering thresholds and simulated the hydrological response of the headwater catchment with a distributed model in order to estimate the total and peak water discharge. Our data clearly illustrate how debris entrainment along the channel is the main contributor to the overall mobilized volume and that erosion is dominant when the channel slope exceeds 16°. Further downstream, sediment accumulation and depletion occurred alternately for the two successive events, indicating that sediment availability along the channel also influences the flow behaviour along the prevailing‐transport reach. The comparison between monitoring data, topographical analysis and hydrological simulation allows the estimation of the average solid concentration of the two events and suggests that debris availability has a significant influence on the debris flow volume. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Post-wildfire runoff was investigated by combining field measurements and modelling of infiltration into fire-affected soils to predict time-to-start of runoff and peak runoff rate at the plot scale (1 m2). Time series of soil-water content, rainfall and runoff were measured on a hillslope burned by the 2010 Fourmile Canyon Fire west of Boulder, Colorado during cyclonic and convective rainstorms in the spring and summer of 2011. Some of the field measurements and measured soil physical properties were used to calibrate a one-dimensional post-wildfire numerical model, which was then used as a 'virtual instrument' to provide estimates of the saturated hydraulic conductivity and high-resolution (1 mm) estimates of the soil-water profile and water fluxes within the unsaturated zone. Field and model estimates of the wetting-front depth indicated that post-wildfire infiltration was on average confined to shallow depths less than 30 mm. Model estimates of the effective saturated hydraulic conductivity, Ks, near the soil surface ranged from 0.1 to 5.2 mm h−1. Because of the relatively small values of Ks, the time-to-start of runoff (measured from the start of rainfall), t p, was found to depend only on the initial soil-water saturation deficit (predicted by the model) and a measured characteristic of the rainfall profile (referred to as the average rainfall acceleration, equal to the initial rate of change in rainfall intensity). An analytical model was developed from the combined results and explained 92-97% of the variance of t p, and the numerical infiltration model explained 74-91% of the variance of the peak runoff rates. These results are from one burned site, but they strongly suggest that t p in fire-affected soils (which often have low values of Ks) is probably controlled more by the storm profile and the initial soil-water saturation deficit than by soil hydraulic properties. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Abstract: Runoff initiation from raindrops falling onto an inclined planar impervious surface is investigated in a laboratory rainulator experiment. Visual observations, Forward Looking Infrared imagery and direct cluster statistics measurements indicate that runoff initiation is associated with complex changes in connectivity of drop clusters on the surface. Depending on the surface inclination several different regimes of flow initiation have been observed. For very small inclinations flow initiation is governed by critical clusters merging, a phenomenon known from the mathematical percolation theory. For intermediate inclinations the rivulets regime takes place resulting from clusters non-critical coalescence and sliding. Finally, for high inclinations flow in the form of threads is generated as a result of almost immediate sliding of small clusters and individual drops. The role of several effects is emphasized, such as critical clusters merging, coalescence shrink, and the presence of wetted trails. In particular, critical merging of drop clusters on the surface leads to the abrupt emergence of surface runoff on impervious surfaces with low inclination, e.g. such as most paved surfaces in urban areas. To our knowledge, this is the first study considering the details of flow initiation from raindrops falling onto impervious surfaces. [Copyright &y& Elsevier]