Investagation of the sediment connectivity under freeze-thaw meltwater compound erosion condition on loessal slope

2021 ◽  
Author(s):  
Tian Wang ◽  
Peng Li ◽  
Jingming Hou ◽  
Zhanbin Li ◽  
Shengdong Cheng ◽  
...  
Keyword(s):  
Flow Rate ◽  
Laboratory Experiments ◽  
Overland Flow ◽  
Structural Connectivity ◽  
Surface Erosion ◽  
Rill Erosion ◽  
Erosion Process ◽  
Freeze Thaw ◽  
Concentrated Flow ◽  
Sediment Connectivity

<p>The connectivity of rill erosion and overland flow are significantly affected by freeze-thaw cycles. Meltwater concentrated flow laboratory experiments were carried out to assess the soil erosion connectivity of different frozen conditions based on simplified hydrological curve and relative surface connection function. The experiments were performed over frozen, shallow-thawed, and unfrozen soil-filled flumes under 1, 2, and 4 L/min flow rates with the temperature around 5 °C. The results imply that according to the spatial distribution of the high connected areas on the slope, the connectivity of the sediment structure on the slope is obviously enhanced with the increase of the flow rate. The order of the structural connectivity of the sediment on the slope with different freeze-thaw states under the same flow rate is: frozen slope > shallow-thawed slope > unfrozen slope. Under different flows and soil frozen conditions, the laws of the vertical and horizontal connectivity rates of the slope are relatively similar which increase first and then stabilize, while the horizontal connectivity rate first decreases and then stabilizes. From the perspective of horizontal connectivity, the erosion form at the beginning of the experiment was mainly surface erosion; as the experiment progressed, the erosion form gradually changed from surface erosion to rill erosion. The results of this research would provide specific implications about meltwater erosion connectivity for improving the erosion process understand.</p>

Structural, Hydrologic, and Sediment Connectivity in a Shrub-Encroached and Restored Semiarid Grassland

2021 ◽  
Author(s):  
Justin Johnson ◽  
Jason Williams ◽  
Phillip Guertin ◽  
Steven Archer ◽  
Philip Heilman ◽  
...  
Keyword(s):  
Sediment Yield ◽  
Soil Loss ◽  
Rainfall Intensity ◽  
Overland Flow ◽  
Spatial Scales ◽  
Structural Connectivity ◽  
Post Treatment ◽  
Semiarid Grassland ◽  
Concentrated Flow ◽  
Shrub Canopy

<p>Shrub encroachment of semiarid grasslands is influenced by connected runoff and erosion patterns that preferentially accumulate resources under vegetated patches (canopy microsites) and deplete interspaces. Soil loss from dryland hillslopes results when areas of bare ground become structurally and functionally connected through overland flow. Although these patterns have been well-described, uncertainty remains regarding how these feedbacks respond to restoration practices. This study compared the structure and hydrologic function of a shrub-encroached semiarid grassland treated five years prior with the herbicide, tebuthiuron, to that of an adjacent untreated grassland. Through a series of hydrologic experiments conducted at increasing spatial scales, vegetation and soil structural patterns were related to runoff and erosion responses. At a fine scale (0.5 m<sup>2</sup>), rainfall simulations (120 mm·h<sup>-1</sup> rainfall intensity; 45 min) showed herbicided shrub canopy microsites had greater infiltration capacities (105 and 71 mm·h<sup>-1</sup> terminal infiltration rates) and were less susceptible to splash-sheet erosion (3 and 26 g sediment yield) than untreated shrub canopy microsites, while interspaces were statistically comparable between study sites. Concentrated flow simulations at a coarse scale (~9 m<sup>2</sup>) revealed that gaps between the bases of vegetation (i.e. basal gaps) > 2 m<sup></sup>were positively related to both concentrated flow runoff (r = 0.72, p = 0.008) and sediment yield (r = 0.70, p = 0.012). Modeled hillslope-scale (50 m<sup>2</sup>) runoff and erosion (120 mm·h<sup>-1</sup> rainfall intensity; 45 min) indicated less soil loss in the tebuthiuron-treated site (1.78 Mg·ha<sup>-1</sup> tebuthiuron; 3.19 Mg·ha<sup>-1</sup> untreated), even though runoff was similar between sites. Our results suggest interspaces in shrub-encroached grasslands continue to be runoff sources following herbicide-induced shrub mortality and may be indicators of runoff responses at larger spatial scales. In contrast, sediment sources are limited post-treatment due to lesser sediment detachment from sheet-splash and concentrated flow processes. Reduced sediment supplies provide evidence that connectivity feedbacks that sustain a shrub-dominant ecological state may have been dampened post-treatment. Our study also highlights the utility of simple measures of structural connectivity, such as basal gaps, as an indicator of hillslope susceptibility to increased runoff and erosion.</p>

Measuring Soil Loss and Subsequent Nutrient and Organic Matter Loss on Farmland

2017 ◽  
Author(s):  
Vito Ferro ◽  
Vincenzo Bagarello
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Loss ◽  
Soil Structure ◽  
Overland Flow ◽  
Organic Matter Content ◽  
Matter Content ◽  
Water Infiltration ◽  
Surface Erosion ◽  
Rill Erosion

Field plots are often used to obtain experimental data (soil loss values corresponding to different climate, soil, topographic, crop, and management conditions) for predicting and evaluating soil erosion and sediment yield. Plots are used to study physical phenomena affecting soil detachment and transport, and their sizes are determined according to the experimental objectives and the type of data to be obtained. Studies on interrill erosion due to rainfall impact and overland flow need small plot width (2–3 m) and length (< 10 m), while studies on rill erosion require plot lengths greater than 6–13 m. Sites must be selected to represent the range of uniform slopes prevailing in the farming area under consideration. Plots equipped to study interrill and rill erosion, like those used for developing the Universal Soil Loss Equation (USLE), measure erosion from the top of a slope where runoff begins; they must be wide enough to minimize the edge or border effects and long enough to develop downslope rills. Experimental stations generally include bounded runoff plots of known rea, slope steepness, slope length, and soil type, from which both runoff and soil loss can be monitored. Once the boundaries defining the plot area are fixed, a collecting equipment must be used to catch the plot runoff. A conveyance system (H-flume or pipe) carries total runoff to a unit sampling the sediment and a storage system, such as a sequence of tanks, in which sediments are accumulated. Simple methods have been developed for estimating the mean sediment concentration of all runoff stored in a tank by using the vertical concentration profile measured on a side of the tank. When a large number of plots are equipped, the sampling of suspension and consequent oven-drying in the laboratory are highly time-consuming. For this purpose, a sampler that can extract a column of suspension, extending from the free surface to the bottom of the tank, can be used. For large plots, or where runoff volumes are high, a divisor that splits the flow into equal parts and passes one part in a storage tank as a sample can be used. Examples of these devices include the Geib multislot divisor and the Coshocton wheel. Specific equipment and procedures must be employed to detect the soil removed by rill and gully erosion. Because most of the soil organic matter is found close to the soil surface, erosion significantly decreases soil organic matter content. Several studies have demonstrated that the soil removed by erosion is 1.3–5 times richer in organic matter than the remaining soil. Soil organic matter facilitates the formation of soil aggregates, increases soil porosity, and improves soil structure, facilitating water infiltration. The removal of organic matter content can influence soil infiltration, soil structure, and soil erodibility.

Modelling of Solute Transfer to Surface Runoff

1992 ◽  
Vol 26 (7-8) ◽  
pp. 1851-1856 ◽  
Author(s):  
J. L. Lai ◽  
K. S. L. Lo
Keyword(s):  
Potassium Chloride ◽  
Surface Runoff ◽  
Laboratory Experiments ◽  
Overland Flow ◽  
Chloride Concentration ◽  
Runoff Water ◽  
Mixing Depth ◽  
Change Rate ◽  
Solute Transfer ◽  
The Media

A mixing-based model for describing solute transfer to overland flow was developed. This model included a time-dependent mixing depth of the top layer and a complete-mixed surface runoff zone. In a series of laboratory experiments, runoff was passed at various velocities and depths over a medium bed. The media were saturated with uniform concentration of potassium chloride solution. Runoff water was sampled at the beginning and end of the flume and the potassium chloride concentration analyzed. Using this model, dimensionless ultimate mixing depth and dimensionless change rate of mixing depth from experimental data were investigated and implemented. The results showed that the Reynolds number and relative roughness are two important factors.

Ravinas: processo de formação e desenvolvimento

1997 ◽  
Vol 20 ◽  
pp. 9-26
Author(s):  
Antonio José Teixeira Guerra
Keyword(s):  
Soil Erosion ◽  
Laboratory Experiments ◽  
Agricultural Soils ◽  
Erosion Process ◽  
Erosion Processes

The present paper concerns rill initiation and evolution, taking into account its role on the erosion process. Therefore, several aspects of the process are developed, such as: the process itself, evidences of the process, through field and laboratory experiments, the importance of the models, the consequences to agricultural soils and the conectivity with other soil erosion processes.

Impact of a volcanic eruption on the sediment connectivity of a Chilean river basin: the Calbuco study case

2021 ◽  
Author(s):  
Marco Andreoli ◽  
Lorenzo Martini ◽  
Marco Cavalli ◽  
Andrés Iroumé ◽  
Lorenzo Picco
Keyword(s):  
Land Cover ◽  
River Basin ◽  
Volcanic Eruption ◽  
Overland Flow ◽  
Volcanic Eruptions ◽  
Landsat 8 ◽  
Strong Impact ◽  
Low Resolution ◽  
Multi Temporal ◽  
Sediment Connectivity

&lt;p&gt;Volcanic eruptions are natural disturbances capable of introducing large quantities of sediment into river systems as to upset the transport regime for several years. Such a disturbance can have a strong impact on the water and sediment flows and consequently on the transport capacity. Moreover, changes in morphological settings and land cover lead to an alteration of the sediment connectivity within the catchment. This study aims to investigate the changes of sediment connectivity in a catchment affected by an explosive volcanic eruption using the Index of Connectivity (IC) with a multi-temporal approach. Potential variations were analyzed at the catchment scale over a period of 6 years, before and after the eruption. The study area, located in southern Chile, is the Blanco Este River basin (39,6 km&amp;#178;), affected by the eruption of the Calbuco volcano (April 2015, total volume of sediment expelled of about 0,28 km&amp;#179;) which profoundly changed its vegetation cover, geomorphology and hydrology. IC analyses were based on low-resolution and freely available data (i.e., GDEM, Landsat 8 satellite images). Through supervised image classification and field data survey, a Manning's n coefficient for overland flow is derived as weighting factor (W) due to its suitability to represent the impedance to sediment flows in catchments characterized by land cover variations. Following the eruption, bare soil cover on the basin doubled (from 5% to 10% of total basin area). Consequently, the multi-temporal analysis results in an overall increase of IC with the median value ranges from -3,58 to -3,26 in pre-eruptive (2015) and first post-eruptive scenario (2016), respectively. The connectivity maps show that the higher IC values (i.e. range from -1,23 to 1,66) are persistently located in three areas: at the base of the volcanic dome, on the steepest slopes near the main channel and in a sub-basin on the right side of the catchment. Moreover, the Difference of IC (DoIC) among different scenarios highlighted the major variations. Such changes are found along the volcano slopes, in a flat area located in the upper part of the basin and along the lower valley of the Rio Blanco Este. The study proposes a useful methodology to evaluate the sediment connectivity, and its evolutionary trends, in environments affected volcanic eruptions starting from low-resolution data and field survey. These results may help to better define types, location and typologies of interventions to improve the river management approaches, considering the ongoing cascading processes. This research is funded by the Fondecyt 1200079 project.&lt;/p&gt;

scholarly journals The Influence of Grain Size Distribution on the Hydraulic Gradient for Initiating Backward Erosion

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2644 ◽  
Author(s):  
Willem-Jan Dirkx ◽  
Rens Beek ◽  
Marc Bierkens
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Laboratory Experiments ◽  
Hydraulic Gradient ◽  
Concentrated Flow ◽  
Pipe Formation ◽  
Novel Method ◽  
Flow Through ◽  
The Stability

Backward erosion by piping is one of the processes that threaten the stability of river embankments in the Netherlands. During high river stages, groundwater flow velocities underneath the embankment increase as a result of the steepened hydraulic gradient. If a single outflow point exists or forms, the concentrated flow can entrain soil particles, leading to the formation of a subsurface pipe. The processes controlling this phenomenon are still relatively unknown due to their limited occurrence and because piping is a subsurface phenomenon. To study the initiation of piping, we performed laboratory experiments in which we induced water flow through a porous medium with a vertically orientated outflow point. In these experiments, we explicitly considered grain size variations, thus adding to the existing database of experiments. Our experiments showed that the vertical velocity needed for the initiation of particle transport can be described well by Stokes’ law using the median grain size. We combine this with a novel method to relate bulk hydraulic conductivity to the grain size distribution. This shows that knowledge of the grain size distribution and the location of the outflow point are sufficient to estimate the hydraulic gradient needed to initiate pipe formation in the experiment box.

scholarly journals Experimental study on gravitational erosion process of vegetation slope under freeze–thaw

2018 ◽  
Vol 151 ◽  
pp. 168-178 ◽  
Author(s):  
Dahu Rui ◽  
Mingchang Ji ◽  
Dai Nakamur ◽  
Teruyuki Suzuki
Keyword(s):  
Experimental Study ◽  
Erosion Process ◽  
Freeze Thaw

scholarly journals Granulometric characterization of sediments transported by surface runoff generated by moving storms

2008 ◽  
Vol 15 (6) ◽  
pp. 999-1011 ◽  
Author(s):  
J. L. M. P. de Lima ◽  
C. S. Souza ◽  
V. P. Singh
Keyword(s):  
Grain Size ◽  
Surface Runoff ◽  
Laboratory Experiments ◽  
Overland Flow ◽  
Temporal Distribution ◽  
Surface Flow ◽  
Constant Speed ◽  
Stream Power ◽  
Sediment Grain Size ◽  
Rain Simulator

Abstract. Due to the combined effect of wind and rain, the importance of storm movement to surface flow has long been recognized, at scales ranging from headwater scales to large basins. This study presents the results of laboratory experiments designed to investigate the influence of moving rainfall storms on the dynamics of sediment transport by surface runoff. Experiments were carried out, using a rain simulator and a soil flume. The movement of rainfall was generated by moving the rain simulator at a constant speed in the upstream and downstream directions along the flume. The main objective of the study was to characterize, in laboratory conditions, the distribution of sediment grain-size transported by rainfall-induced overland flow and its temporal evolution. Grain-size distribution of the eroded material is governed by the capacity of flow that transports sediments. Granulometric curves were constructed using conventional hand sieving and a laser diffraction particle size analyser (material below 0.250 mm) for overland flow and sediment deliveries collected at the flume outlet. Surface slope was set at 2%, 7% and 14%. Rainstorms were moved with a constant speed, upslope and downslope, along the flume or were kept static. The results of laboratory experiments show that storm movement, affecting the spatial and temporal distribution of rainfall, has a marked influence on the grain-size characteristics of sediments transported by overland flow. The downstream-moving rainfall storms have higher stream power than do other storm types.

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