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The hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer
Abstract
Rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface. For a given cover level, rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation. Compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface. For the same cover level, rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer. The effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage. Micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by Poesen (1986): i.e. runoff generated as rock flow or as Horton overland flow can (partly) infiltrate into the unsealed soil surface under the rock fragments, provided that they are not completely embedded in the top layer. Hence, rock fragment position, beside other rock fragment properties, should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers. A simple model, based on the proportions of bare soil surface, soil surface occupied by embedded rock fragments, and soil surface covered with rock fragments resting on the soil surface, describes the runoff coefficient data relatively well.
... The presence of rock fragments on the soil surface can either decrease or increase infiltration (Brakensiek and Rawls, 1994). For example, some studies have shown that increasing the proportion of RF on the surface or partially incorporating RF has caused a reduction in infiltration and increased surface runoff (Stuart and Dixon, 1973;Constantz et al., 1988;Poesen et al., 1990;Ingelmo et al., 1994;Simanton and Toy, 1994;Wu et al., 2021). Other studies have reported an increase in infiltration with an increase in the fraction of RF on the soil surface (Simanton et al., 1984;De Figueiredo and Poesen, 1998;Mandal et al., 2005;Pahlavan-Rad et al., 2020). ...
... The steady-state infiltration rate in the High RF profile was 16 times greater than in the Low RF profile (Figure 2). These results contrast with those of studies that observed a reduction in infiltration with an increase in RF on the surface or RF partially incorporated in the soil profile (Stuart and Dixon, 1973;Constantz et al., 1988;Poesen et al., 1990;Ingelmo et al., 1994;Simanton and Toy, 1994;Wu et al., 2021). Opposite results for relationships between infiltration rate and RF show that infiltration does not depend solely on the quantity of rock fragments. ...
... Preferential flow due to incomplete filling and protection of porosity by RF are plausible explanations for higher infiltration rates in the High RF and Medium RF sites (100 mm h -1 and 61 mm h -1 , respectively) compared to the location without RF (6 mm h -1 ), which does not create such conditions ( Figure 2). Therefore, in soil with RF only on the surface or partially incorporated in the top layers of the soil profile, a decrease in infiltration with increasing quantity of RF is plausible (Stuart and Dixon, 1973;Constantz et al., 1988;Poesen et al., 1990;Ingelmo et al., 1994;Simanton and Toy, 1994;Wu et al., 2021). In those cases, RF on the surface or the partially incorporated RF decreases the effective infiltration area and do not promote preferential flow inside the soil profile below the layer affected by RF. ...
A widespread assumption among researchers and technicians is that stony soils are more susceptible to degradation. However, the role of rock fragments in the hydrology of stony soils, especially in regard to infiltration, is still a research gap. The aim of this study was to test the hypothesis that an increase in rock fragments in the soil profile increases the water infiltration rate. Infiltration tests using a double-ring infiltrometer were conducted on February 11, 2021, and December 11, 2022, at three sites of Entisols with different fractions of rock fragments. The results supported the hypothesis of this study. The infiltration rate was up to sixteen times greater in profiles whose horizons had at least 60 % rock fragments in relation to profiles with a lower fraction of rock fragments. These findings provide evidence that some stony soils may not be as susceptible to degradation by water erosion as it was suposed.
Keywords
stony soils; soil water flow; double-ring infiltrometer
... This work will be helpful for further understanding of the effect mechanisms of splash erosion on the whole soil erosion. Many researchers have noticed the effect of the lack of laterally ejected splashed particles at the border area of an eroded slope on diffuse erosion (Borselli et al., 2001;Bradford & Foster, 1996;Poesen et al., 1990;Zartl & Klik, 2001). Nonetheless, few scholars are concerned about the specific changes in sediment transport between slope border areas and slope central erosion areas. ...
... Accordingly, a four-area soil pan, including the border erosion test area that lacks that part of the splashed particles (A and C), central erosion test area (B), splash collection area and splash compensate border area, could be used to monitor splash erosion and rain-induced overland flow diffuse erosion synchronously ( Figure 2; Hu et al., 2016;Wu, Wei, et al., 2018), and investigate the effect of the missing laterally ejected splashed particles on the rain-induced overland flow erosion at the slope border effect area. According to previous studies, the diffuse erosion test area should be balanced by the input of splash from the surrounding buffer areas (Borselli et al., 2001;Bradford & Foster, 1996;Poesen et al., 1990;Zartl & Klik, 2001). In the central erosion test area (B), the laterally ejected soil particles were replenished by using all boundary areas surrounding the central area. ...
... The border erosion test area (A and C) that lacks the part of the splashed particles was used to monitor the sediment erosion under a slope border effect. Splash and diffuse erosion can be simultaneously monitored by setting the splash collection area between the border areas and central diffuse erosion test areas Poesen et al., 1990;. The upper splash compensate border area was only used to balance the downward-ejected particles of all erosion test areas. ...
Splash erosion plays a vital role in the loss of eroded materials. Unlike those in slope central areas, laterally ejected splashed materials in slope border areas cannot be replenished easily because slope edges prevent splash erosion particles from entering the slope. Thus, splashed materials in slope border areas are less than those in slope central areas because of the lack of source areas for splash‐eroded materials. However, this phenomenon, called the slope border effect, has received minimal attention by researchers. The partially missing splash erosion induced by the slope border effect on sediment transport was investigated to understand the slope erosion mechanism further in this paper. A modified soil pan divided into four areas, namely, central erosion test area (length = 100 cm, width = 35 cm, depth = 45 cm), border erosion test area (length = 100 cm, width = 35 cm, depth = 45 cm), splash compensate border area (length = 110 cm, width = 30 cm, depth = 45 cm) and splash collection area (length = 100 cm, width = 2.5 cm, depth = 45 cm) was used to monitor diffusion and splash erosion under simulated rainfall. Results showed that the splash detachment rate increased with the increase in slope but initially decreased and then increased with the increase in rainfall intensity. The runoff rate and diffuse erosion rates for complete splash erosion ( SE ) treatments were higher than those without partial splash erosion ( SE L ). Under low rainfall erosive power and runoff transport capacity (e.g., 5° slope and 60 mm h ⁻¹ ), the transported clay in SE treatments was approximately 2% more than that in SE L treatments. This amount changed to more than 2% sand under high rainfall and runoff erosive power. However, the mass fraction accounted for by silt particles in the sediments of the SE L treatments was more than that in the SE treatments. Thus, the partially missing splash erosion can weaken the selective transport ability of runoff for sediments. The effect of missing partial splash erosion on diffuse erosion was enhanced with an increase in erosive power. The results of our paper will provide insights into the effect of the boundary effect zone of slope on soil erosion and its related mechanisms.
... En algunas investigaciones la relación entre los FR y la Kq no se ha podido establecer Khetdan et al. 2017;Li et al. 2008 (Hlaváčiková et al. 2015;Hung et al. 2007;Rudolph et al. 1996;Unger, 1971;Yuanjun y Ming'an, 2006). Se ha demostrado también que a nivel de la superficie del suelo, la CobFR, especialmente aquellos embebidos y parcialmente embebidos en la superficie, pueden disminuir el ingreso y posterior movimiento de agua en el suelo (Poesen 1986;Poesen et al. 1990). ...
... Por otra parte, el contacto de los FR con la matriz de suelo puede generar algunas macroporosidades que facilitan el movimiento de agua. Otros autores como Poesen et al. (1990) Fuente: El autor. ...
Los fragmentos de roca son elementos minerales con tamaño igual o superior a 2 mm,cuyas propiedades pueden ocasionar variaciones en el comportamiento hidrodinámico de los suelos. Si bien, generalmente la presencia de fragmentos de roca en los suelos se ha relacionado con disminuciones en la infiltración y propiedades hidráulicas de los mismos, diversas investigaciones han demostrado incrementos y comportamientos ambivalentes (aumentos y disminuciones) de estas variables hidrodinámicas en un mismo suelo afectado por la presencia de fragmentos de roca. Lo anterior, implica que el comportamiento de estas relaciones aún no está totalmente comprendido en los suelos, especialmente en aquellos localizados en zonas tropicales. Esta investigación tuvo por objetivo evaluar el comportamiento hidráulico de suelos con presencia de fragmentos de roca en el perfil, localizados en la microcuenca Zanja Honda, cuenca del río Combeima (Ibagué, Colombia). Se distribuyeron 50 sitios de muestreo en la microcuenca empleando un sistema de muestreo estratificado, en el cual se utilizaron las Unidades de Respuesta Hidrológica (URH) de la microcuenca como estratos del mismo.
Esta investigación es una de las primeras que se realizan en Colombia sobre este tema y es pionera en la inclusión de la espacialidad como parte del análisis que relaciona a los fragmentos de roca con las propiedades hidrodinámicas de los suelos. Se espera que los hallazgos reportados en este trabajo sirvan como un aporte a la modelación espacial de variables hidrodinámicas en suelos tropicales con presencia de fragmentos de roca, y subsecuentemente, contribuya a disminuir la incertidumbre de los modelos hidrológicos que dependen de dichas variables. También, se espera que los resultados contribuyan con la planificación y toma acertada de decisiones respecto al recurso edáfico en los suelos de la microcuenca Zanja Honda
... Infiltration into DPs is limited; thus, little water is stored in the subsoil or permeates to plant roots (Young et al., 2004). In contrast, under the high evapotranspiration conditions, soluble salts are likely to move upward from the subsoil into the topsoil beneath the pavement layer (Abrahams & Parsons, 1991;Poesen et al., 1990). Therefore, plants might experience both drought conditions (dry soil) and salt stress, thus leading to sparse vegetation on DP surfaces (Kaseke et al., 2012;Rostagno & Degorgue, 2011). ...
... As a result, the effect of gravel coverage on infiltration is related to the gravel within the pavement layer. Previous studies have explained how the relationship between gravel coverage and water infiltration depends on the amount of gravel embedded in the earth (Abrahams & Parsons, 1991;Poesen et al., 1990). Therefore, the pavement layer inhibits water infiltration, thus prolonging the infiltration time and allowing excess rainfall to be conveyed to other areas. ...
Desert pavements (DPs) are critical for maintaining ecological stability and promoting near-surface hydrological cycling in arid regions. However, few studies have focused on eco-hydrological processes of DPs in the ecological systems of fluvial fans. Although DP surfaces appear to be barren and flat, we found that the surfaces are characterized by surface mosaic patterns of desert pavement (mosaic DP) and bare ground (mosaic BG). We investigated the effects of mosaic DP on water infiltration and vegetation distribution at six sites in fluvial fans (one on a hillside and five within the sectors of fans) along a southwest belt transect in northern Linze County, in the central Hexi Corridor (China). We found significant differences in mosaic DP between the hillside and sector sites in terms of pavement thickness and vesicular horizon thickness (Av thickness), particle composition, and bulk density, although significant differences were absent for mass soil water content (SWC), gravel coverage, and surface gravel size. The mosaic DP inhibited water infiltration by the pavement layer, where the sorptivity (S), initial infiltration rate (iint), steady-state infiltration rate (isat), and infiltration time (T) averaged 1.19 cm/min-0.5, 0.64 cm/min, 0.13 cm/min, and 12.76 min, respectively. Where the pavement layer was scalped, the S, iint, and isat increased by 0.27 cm/min-0.5, 0.52 cm/min, and 0.40 cm/min, respectively, and the T reduced by 7.42 min. Water infiltration was mainly controlled by the pavement layer thickness (+), Av thickness (−), surface gravel coverage (−), fine earth (+), and fine gravel (−) in the pavement layer. The DP surfaces only had a sparse covering of shrubs, but an abundance of herbs. Few shrubs were present on the mosaic DP, but a greater number of shrubs and herbs grew on the mosaic BG. It can be concluded that DPs can maintain vegetation stability for different surface mosaic patterns. This study deepens our understanding of the eco-hydrological cycle of DP landscapes in arid regions.
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... The impact of rock fragments on the water dynamic depends on their relative position to the ground surface. Partially embedded rock fragments increase surface sealing, thereby decreasing the infiltration rate, while loosely resting rock fragments impedes the water's overland flow, thereby increasing the infiltration rate at that point (Poesen et al., 1990;Lavee et al., 1991). ...
... Of these rock fragments, over 80% are partially embedded in the ground (Stavi et al., 2018). Unlike resting rock fragments, which increase on-site infiltration of water (Poesen and Lavee, 1994), the partially embedded ones increase the sealing of the ground surface, decreasing water infiltrability and increasing runoff ratio (Poesen et al., 1990). Therefore, in the heterogeneous hillslopes, the dominant surface process in the inter-shrub spaces is water overland flow, which accumulates in the shrubby patches (Stavi et al., 2018). ...
Geodiversity effects on ecosystem productivity were investigated using remotely sensed data and a mathematical model, by introducing a spatially non-uniform surface-water infiltration. Two hillslope types, with different geodiversity levels, as determined by the soil depth and stoniness, were selected for this study. Low-geodiversity hillslopes ('homogenous hillslopes') were identified by their dense herbaceous vegetation cover, and lack of rock fragments cover. High-geodiversity hillslopes ('heterogeneous hillslopes') are characterized by a more sparse cover of herbaceous vegetation, and relatively high rock fragment cover (>20%). Calculating Soil Water Index (SWI) from Landsat-5 TM, Landsat-7 ETM+ (SLC-ON) and Landsat-8 satellite images for the years 1994-2017 shows that during most of these years, SWI was higher at the heterogeneous hillslopes. This was particularly prominent after 2009 when mass mortality of shrubs took place on the homogenous hillslopes but not in the heterogeneous ones. Numerical simulations show that after a prolonged drought, the vegetation in the homogenous system dried out, and the system did not recover even after the yearly rainfall amounts returned to normal. In the heterogeneous system, the vegetation patches survived the drought episode and then recovered. This demonstrates the crucial role played by hillslope geodiversity in determining the durability of vegetation under prolonged droughts in semiarid regions.
... Thus, the rock outcrops had a positive impact on soil infiltrability in this karst area, which is a conclusion consistent with that of previous studies. For example, Wilcox et al. (1988) and Poesen, Ingelmo-Sanchez, and Mucher (1990) found that rocks protect soil against splash erosion and surface sealing, resulting in a remarkable correlation between rock cover and K. Gregory et al. (2009) reported an extremely low surface runoff coefficient (<5%) in a limestone karst landscape because of the extremely high infiltration rate of soil, which changed the runoff generation mechanism in the region. Runoff generation generally combines saturationexcess and infiltration-excess runoff (Ries, Lange, Schmidt, Puhlmann, & Sauter, 2015). ...
... In addition, gaps between the soil and rock were observed (Figure 5a), particularly when soil shrinking became more intense during dry conditions. In karst areas, soil cracks (Sohrt et al., 2014;Zhu et al., 2019), together with rock fragment (Poesen et al., 1990), can greatly promote water movement from surface to groundwater, because they provide preferential flow paths and greatly reduce the infiltration time; this may also explain the high K of few locations found in the NRP. Additionally, a relatively dense distribution of rock outcrops on the ground surface can prevent soil from being compacted by human activities, such as grazing, plowing, and trampling, which increase soil bulk density and negatively affect soil porosity and infiltration (Blevins, Holowaychuk, & Wilding, 1970;Boix et al., 1995;Chandler & Chappell, 2008;Dadkhah & Gifford, 1980;Mwendera & Saleem, 1997;Whalley, Leeds-Harrison, Leech, Risely, & Bird, 2004). ...
Rock outcrops are widespread across the surface of the earth, particularly in karst environments, and they play an important role in infiltration‐runoff processes by triggering preferential flow. However, the characteristics of the preferential flow network at the soil–rock interface and its influencing factors in karst areas remain poorly understood. To clarify how the emergence of outcrops on the land surface affects soil infiltrability and water flow behavior, soil hydraulic conductivity (K) measurements and dye tracing experiments were conducted in a karst area with two contrasting surface features (i.e., rock outcrop plot [RP] and non‐rock‐outcrop plot [NRP]) in Yunnan Province, Southwest China. Results showed that (i) in the immediate vicinity of rock outcrops in the RP, K values were significantly increased, and other soil properties and plants were also improved when compared with results 1 m away from outcrops and in the NRP; and (ii) in the RP, the soil–rock interface dominated the preferential flow network surrounding outcrops, and the connected conduits produced by plant roots and soil fauna were also involved in this infiltration process. Matrix flow was the dominant flow behavior in the NRP. We concluded that rock outcrops, by improving soil properties and building a well‐connected preferential flow network, can greatly change infiltrability and water flow behavior in karst soil. This implied that outcrops will facilitate quick infiltration after most rainfall events and thus reduce rain‐induced surface runoff and soil erosion, as well as increasing groundwater recharge and the water supply to nearby plants.
... Soil erosion is the natural process in which the topsoil of a field is carried away by one or more natural or factitious erosive forces (wind, rain, runoff, gravity, farming, etc.) [1]. In tropical, temperate and Mediterranean regions, soil erosion is increasing due to anthropogenic impacts [2][3][4][5]. ...
The hydrological characteristics of gravel-containing soils are different from those of gravel-free soils, so it is worth further understanding and enriching the theory of soil and water conservation. In this study, adjustable slope (10°, 20°, 30°) test soil boxes with different surface gravel contents (0%, 25%, 50%, 75%, 100%) were prepared to study the runoff erosion characteristics of gravel-covered land slopes under different rainfall conditions (10 mm/h, 20 mm/h, 30 mm/h). Compared with the bare soil, the runoff start time of the three slopes covered with 100% soil surface gravel content is delayed by 38.90, 32.83 and 73.39%, the runoff producing rate of gravel condition under different slopes decreased by 7.20–71.52% and the total amount of sediment yield decreased by 7.94~84.57%. Surface gravel cover can effectively reduce runoff and sediment yield, which is beneficial for better soil and water conservation. The results of this study have a certain reference value for the theory of soil and water conservation and can be used as a basis for guiding efficient agricultural production in gravel-mulched land and construction (like road slope improvement).
... The literature on rock cover effects on infiltration is contradictory (Kidwell et al., 1997), depending on whether the rock cover is under a plant canopy or in the interspace area between plant canopies. Rock cover has been shown to enhance infiltration when resting on the soil surface and to impede infiltration where embedded in the soil surface (Poesen et al., 1990). Regardless, an increase in vegetation ground cover closer to 100% would replace the cover impact of rock. ...
Highlights
Effective hydraulic conductivity ( K e ) predictive equations in all RHEM versions have satisfactory performance.
New K e predictive equations were developed for RHEM applications over broader rangeland conditions.
K e values on most rangelands can be estimated through readily measurable ground cover and soil texture data.
Abstract. Effective hydraulic conductivity (K e ) is an important parameter for the prediction of infiltration and runoff by the Rangeland Hydrology and Erosion Model (RHEM). Three sets of equations to predict K e have previously been used in RHEM. These equations are mainly based on rainfall simulation data representing undisturbed sites and have not undergone comprehensive evaluation for various rangeland conditions, particularly after disturbances. The goal of this research was to evaluate these equations using independent data obtained from rainfall simulations conducted at multiple rangeland sites. Additionally, we developed and evaluated a new set of K e predictive equations applying readily measurable cover and soils data spanning a wide range of vegetation, soil textures, and disturbance conditions. The results show that all previous K e equations in RHEM have a “satisfactory” performance with index of agreement (d) > 0.75 and R ² > 0.4. The new K e approach resulted in “very good” performance with d > 0.9 and R ² > 0.5. The new set of equations enhances RHEM for applications over broader rangeland conditions, including sparse vegetation cover following disturbances or community transitions. Keywords: Disturbed Rangelands, Hillslope Runoff, Infiltration.
... This mainly occurred in the slightly flatter areas, behind vegetation patches, and behind rocks (e.g., flow path no. 3 in Fig. 10). Quicker and more pronounced OF responses on hillslopes with large rock cover and stone cover have been reported by others (e.g., Lavee and Poesen, 1991;Poesen et al., 1990;Poesen and Lavee, 1994). The positive, rather than negative, correlation between K sat and sediment transport can be explained by the fact that K sat was measured for the sediment between the rocks and not on the impermeable areas of the large rocks. ...
Glacial retreat uncovers large bodies of unconsolidated sediment that are prone to erosion. However, our knowledge of overland flow (OF) generation and sediment transport on moraines that have recently become ice-free is still limited. To investigate how the surface characteristics of young moraines affect OF and sediment transport, we installed five bounded runoff plots on two moraines of different ages in a proglacial area of the Swiss Alps. On each plot we conducted three sprinkling experiments to determine OF characteristics (i.e., total OF and peak OF flow rate) and measured sediment transport (turbidity, sediment concentrations, and total sediment yield). To determine and visualize where sediment transport takes place, we used a fluorescent sand tracer with an afterglow as well as ultraviolet (UV) and light-emitting diode (LED) lamps and a high-resolution camera. The results highlight the ability of this field setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The higher rock cover on the younger moraine resulted in longer sediment transport distances and a higher sediment yield. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the sediment transport pathways. Thus, this study demonstrates the potential of the use of fluorescent sand with an afterglow to determine sediment transport pathways as well as the fact that these observations can help to improve our understanding of OF and sediment transport processes on complex natural hillslopes.
... This mainly occurred in slightly flatter areas, behind vegetation patches, and behind rocks. Previous studies have also reported quicker and more pronounced OF responses on hillslopes with large rockand stone cover (Lavee and Poesen, 1991;Poesen et al., 1990;Poesen and Lavee, 1994). The positive, rather than negative, 555 correlation between Ksat and sediment transport (chapter 4.4) can be explained by the fact that Ksat was measured for the sediment between the rocks and not on the impermeable areas of the large rocks. ...
Glacial retreat uncovers large bodies of unconsolidated sediment that are prone to erosion. However, our knowledge of over-land flow (OF) generation and sediment transport on moraines that have recently become ice-free is still limited. To investi-gate how surface characteristics affect OF and sediment transport on young moraines, we installed five bounded runoff plots on two moraines of different ages in a proglacial area of the Swiss Alps. On each plot we conducted three sprinkling experiments to determine OF characteristics (i.e., total OF, peak OF flow rate) and measured sediment transport (peak tur-bidity, sediment concentrations, and total sediment yield). To determine sediment transport distances and to visualize where sediment transport takes place, we used a fluorescent sand tracer with an afterglow, together with UV and LED lamps and a high-resolution camera. The results highlight the ability of this field setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The higher rock cover on the younger moraine with higher surface connec-tivity resulted in longer sediment transport distances and a higher sediment yield. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the sediment transport pathways. The study, thus, demonstrates the potential of the use of fluorescent sand with an afterglow to determine sediment transport pathways, and that these observations can help to improve our understanding of OF and sediment transport processes on complex natural hillslopes.
... L'approche par l'observation micromorphologique de la surface de sol a considérablement contribué à la compréhension des processus de formation des différentes structures observées (Evans et Buol 1968;Mücher et De Ploey 1977;Chen et al. 1980;Gal et al. 1984;Onofiok et Singer 1984;Bresson et Boiffin 1990;Bresson et Cadot 1992;Slattery et Bryan 1992;Valentin et Bresson 1992;West, Chiang, et Norton 1992;Bresson et Valentin 1994;Pagliai 1993;Chiang, West, et Radcliffe 1994;Pagliai et Stoops 2010). En parallèle, les mesures d'infiltration de l'eau, les tests impliquant différentes taille ou énergie des gouttes de pluie, l'analyse minéralogique du sol ou encore l'effet de la concentration en sel(s) (principalement le sodium) de la solution du sol (McIntyre 1958a;Bradford et al. 1986;Southard, Shainberg, et Singer 1988;Poesen, Ingelmo-Sanchez, et Mucher 1990;Mermut et al. 1995;Wakindiki et Ben-Hur 2002;Lado et Ben-Hur 2004) ont permis d'expliquer l'évolution de la structure de la surface et d'interpréter les processus qui ont conduit à la formation de croûte de battance. Face à la complexité des différents facteurs externes et paramètres intrinsèques du sol à considérer, les résultats tendent en général à décrire le comportement local d'un sol. ...
L’une des problématiques environnementales majeure et actuelle conduisant à la dégradation des sols et à la perte des terres est l'érosion hydrique. Dans ce contexte, la formation de croûte de battance à la surface du sol jour un rôle clé dans le processus d’érosion hydrique car elle limite l'infiltration de l’eau et favorise le ruissellement en surface. Suite aux événements pluvieux, la formation de croute de battance résulte de la réorganisation en surface des particules du sol, notamment les particules les plus fines comme les minéraux argileux. Les différents stades de formation des croûtes de battance sont généralement observés par l’étude micromorphologique de leur structure interne. Si l’effet des conditions physico-chimiques des sols joue un rôle essentiel sur la structuration des croûtes de battance à travers leur impact sur les minéraux argileux, l’interprétation des mécanismes à l’œuvre reste limitée car l’identification des particules argileuses impliquées restent délicates. L’objectif de cette thèse est ainsi de caractériser la minéralogie et l'organisation des argiles pour améliorer notre compréhension sur les mécanismes de formation des croûtes de battance en fonction des conditions physico-chimiques du sol.Le panel d’échantillons de surface de sol étudié est issu du site expérimental longue durée des 42 parcelles de l’INRAE de Versailles. L’atout majeur de ce site est d’offrir la possibilité de comparer l’effet des conditions physico-chimiques grâce à l’apport de différents traitements chimiques appliqués depuis plus de 90 ans sur le même sol. Dans un premier temps, les échantillons de croûte de battance à structure conservée ont été analysés au microscope électronique à balayage à partir de mosaïque d’images en électrons rétrodiffusés à l’échelle centimétrique afin de proposer une description micromorphologique des différentes structures observées. Sur la base de ces observations, des zones d’intérêt représentatives ayant des surfaces pluri-millimétriques ont été sélectionnées pour être cartographiées en microdiffraction 2D de rayons X (µDRX 2D) au synchrotron SOLEIL sur la ligne CRISTAL. Les données spatialisées (résolution de 75 x 75 µm) de µDRX 2D ont ensuite étaient traitées pour cartographier la distribution spatiale des différents minéraux argileux (chlorite, illite, kaolinite) et leur organisation propre à travers le degré d’orientation préférentielle des particules.L’interprétation des données micromorphologiques et minéralogiques spatialisées a permis de mettre en évidence des différenciations faibles entre les zones d’érosion de départ des particules qui montrent au global des organisations isotropes appauvries en particules argileuses sans différenciation minéralogiques. En comparaison, les zones de dépôt montrent des signatures très contrastées entre les traitements physico-chimiques étudiés. Les anisotropies les plus marquées ont été observées sur des dépôts très fins (épaisseur <150 µm) pour le traitement au sodium (NaNO3) et pour le sol modérément acide sans traitement avec une différenciation minéralogique des argiles probablement liée à une ségrégation en taille des particules lors de leur sédimentation dans une micro-dépression. Les traitements basiques (CaCO3) et très acide ((NH4)2HPO4) présentent des séquences de dépôts quasi-isotropes à faiblement orientées sans variation minéralogiques notables, très probablement en lien avec le transport de micro-agrégats. Au final, les différentes signatures minéralogiques et organisationnelles des minéraux argileux au sein des différentes séquences de dépôt sont discutées afin d’améliorer notre compréhension des mécanismes conduisant à la formation des croutes de battance pour un contexte physico-chimique donné.
... Previous studies have not consistently examined the effects of gravel coverage on hydrological processes (soil erosion, runoff, infiltration, subsurface flow, evaporation) [71]. Moreover, both positive and negative relationships have been found between gravel coverage and soil hydrological processes [72][73][74][75][76]. The effects of gravel coverage also depend on soil type and climatic conditions [71,77]. ...
High-speed railway embankments are the supporting body of a train and track and are directly exposed to complex climate conditions, such as rainfall, evaporation, and other environmental events. These conditions change the water content, suction, and shear strength of embankment-filling soil, thereby affecting the stability of an embankment. This paper devises a coupled moisture–heat flow model for unsaturated soil embankments that considers soil–atmosphere interactions. The model is verified by comparison of data it generates with the data measured at a highway embankment in Rouen, France. Moreover, based on the actual meteorological data of two cities in China (Beijing and Shanghai), the moisture response of a high-speed railway embankment is calculated to investigate the effects of climate conditions and soil types. This reveals that the degree of saturation at shallow depths is affected significantly by rainfall precipitation and increases by approximately 10–40% after rainfall events. The average degree of saturation in clayey embankment soil is the highest, as it is nearly twice that of silty embankment soil and triple that of sandy embankment soil. The depth of influence is greater when the fill material is finer and under dry subhumid climate conditions. The hydraulic responses are mainly influenced by evaporation under the weather conditions of Beijing, whereas they are more affected by precipitation under the weather conditions of Shanghai. The average degree of saturation in the sandy embankment soil under Shanghai weather conditions is greater than that in this soil under Beijing weather conditions.
... Rock outcrops play an important role in hydrology and ecology in drought areas. Certini et al. and Poesen et al. discovered that the rock fragments not only altered soil erosion processes and runoff generation, but also affected soil hydrological processes by modifying soil physical and chemical properties [5,6]. Furthermore, Li et al. discovered that the more advanced the karstification process was, the greater its water catchment capacity [7]. ...
Understanding the temporal variability of soil water and carbon is an important prerequisite for restoring the vegetation in fragile karst ecosystems. A systematic study of soil moisture and carbon storage capacity under drought conditions in different karst habitats is critical for cultivating suitable crops in karst regions. The hydrological characteristics of soil and changes in soil HCO3−, pH, and EC values under drought conditions were measured on simulated rock outcrops and non-outcrops in an indoor pot experiment. The results showed that the rock outcrops had less evaporation and significantly greater water retention capacity than the non-outcrops, which gave the retained water in the rock outcrops sufficient reaction time to dissolve atmospheric CO2, as well as to promote dissolution at the rock–soil interface. Therefore, the carbon sequestration capacity of the rock outcrops was higher than that of the non-outcrops. Due to the rock–soil–water interaction in the early stage of drought, the soil HCO3− concentration in the rock outcrops fluctuated with soil water content, but the soil HCO3− concentration tended to be stable in the whole drought period, showing a phenomenon of zero-carbon sink. No obvious change was observed in the soil HCO3− concentration in non-outcrops during the drought period, which indicated that the carbon sequestration of rock outcrops was mainly attributed to the dissolution of rocks. Therefore, rock outcrops were more effective for water and carbon storage, compared with non-outcrops, under drought, and could provide more available water and carbon resources for supporting the photosynthesis of plants in karst regions.
... This can be explained by the assumption that over a uniform lower layer big blocks allow a higher concentration of water above limited patches of the lower layer than does small gravel, (Figure 2.8). This conclusion was supported later by Poesen et al. (1990), who argued that this positive correlation between infiltration and stone cover depends on whether the rocks are partially buried or resting on the surface. They clearly indicated that rock fragment position in topsoil, susceptible to surface sealing, has a significant effect on water intake rate and on runoff generation. ...
p>This study presents an integrated approach to estimating the risk of flash floods in arid wadis. Flash floods impact seriously on the infrastructure and development of Egyptian desert towns, such as Marsa Alam, and their surrounding areas. The study developed a method using the example of the wadi El-Alam, which has an area of approximately 407 km<sup>2</sup>. The method has three stages. First, the construction of a Digital Elevation Model from which morphometric properties of the brain were calculated. In particular, representing the flat areas and the sharp junctions between badland slopes and the adjacent wadi system (which generally characterised arid landscapes), were among the major issues facing this study. Second, the derivation of land cover from satellite remote sensing data which were rigorously pre-processed with the aid of aerial photographs and fieldwork measurements. Third, the application of a hydrological model, incorporating the basin morphometry and land cover data, to transform rainfall into runoff and route the floodwater through the sub-catchments of the wadi.
The hydrological model system (HMS) was run to simulate discharge at the main wadi outlet (where the town of Marsa Alam is located) and at each sub-basin intersecting the Idfu-Alam highway that runs through the wadi. From these results, sites vulnerable to flash flood and their risk classes were identified. The sites judged to have the highest flood hazard along the highway were exactly the sites damaged in the 1991 flash flood. Thus, as an outcome of this study, the first digital database that includes information on land cover, geomorphology and hydrology of wadi El-Alam was developed. This database can be used to highlight regions vulnerable to flood damage.</p
... The rate of initial infiltration and the steady infiltration rate of MS2 were the lowest in the 40-60 cm layer. There are many factors that affect the soil infiltration characteristics, such as soil texture, particularly the content of sand; the gravel fraction and rock fragments in the soil; the soil use pattern; and the vegetation type [10,51,52]. The highest initial infiltration rate and steady infiltration rate were observed at the top of the slope ( Figure 5). ...
The soil water behavior of sandy soils was studied under semiarid conditions in the Shendong mining area (China). The soil water content (θ) was measured under different depths and to-pographies using an HH2 moisture meter. The infiltration process was studied using a Guelph soil permeameter. A set of hydrodynamic variables was calculated in the laboratory. The θ of the first 20 cm was the lowest and increased with depth. The content of soil water increased from the top slope to the bottom slope. The infiltration experiments showed that the steady state in-filtration rate was >40 mm h−1 in most cases. Owing to the higher contents of sand and soil macropores at the top of the slope and the top 0–20 cm of surface soil, the initial infiltration rate and steady infiltration rate were higher. The average available water capacity was 18.28%, which was consistent with the predominance of a sandy textural fraction. The results of a soil water re-tention curve and a rainfall simulation experiment showed that there was a low soil water re-tention capacity throughout the whole profile. This study contributes to the understanding of several aspects of the soil water behavior of sandy soils and provides key information for envi-ronmental management and land reclamation under semiarid conditions in the Shendong min-ing area.
... The substantially higher OF on the 1990 moraine and the results of the multiple linear model suggest that the high rock-and stone cover led to considerable OF generation, even-though the Ksat values for the topsoil were high (and higher than for the 1860 moraine). This is in agreement with several studies that have reported quicker and more pronounced OF responses on hillslopes with large rock-and stone cover (Lavee and Poesen, 1991;Poesen et al., 1990;Poesen and Lavee, 1994). The rocks and stones on the 1990 moraine are also responsible for the larger microtopography. ...
The surface of the earth is constantly changing, especially in mountain areas, where glacial retreat uncovers large bodies of unconsolidated sediment. However, our knowledge on overland flow (OF) generation and related sediment transport is still limited, partly due to a lack of methods to trace the pathways of water and sediment on the surface. To investigate how different surface characteristics affect hydrological- and sediment connectivity on natural hillslopes, we studied five plots on two moraines of different ages in a proglacial area of the Swiss Alps. On all plots, we performed sprinkling experiments to determine OF characteristics, i.e., total OF, peak OF flow rate, peak turbidity and sediment concentrations, and total sediment yield. Here we test if a fluorescent sand tracer, together with UV lamps and a high-resolution camera, can be used to visualize the pathways of OF and to determine the typical sediment transport distances. The results highlight the ability of the setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The experiments also revealed that the higher rock cover on the younger moraine enhanced surface hydrological connectivity and resulted in larger sediment transport distances. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the surface flow pathways and erosion. The study, thus, demonstrates the potential of the new method to improve the observation of surface hydrological connectivity and sediment transport. These observations can help to improve our understanding of OF and sediment transport in complex natural settings.
... Though former studies were performed at the catchment scale , we do not know how soil properties, including soil surface features at the very fine scale, can modify seed displacement by runoff in tropical agricultural areas. All factors that influence runoff/water infiltration could affect seed displacement on the soil surface: (1) rainfall characteristics (Wang et al., 2014), (2) soil properties linked to soil surface features such as soil roughness, crust formation, texture, structure, bulk density, organic matter content or hydraulic conductivity and sorptivity (Janeau et al., 1999;Le Bissonnais, 1996;Poesen et al., 1990) and (3) agricultural practices such as ploughing (Ndiaye et al., 2007;Podwojewski et al., 2008;Scheffler et al., 2011). Seed characteristics can themselves influence seed displacement Wang, Jiao, et al., 2013). ...
Soil erosion due to land use change is a major concern in agricultural areas. There is an urgent need to develop appropriate agricultural practices that promote higher biodiversity and improve soil properties. Little is known about the processes of natural vegetation recovery after disturbance by human activities in tropical humid climates. This is particularly the case for dispersion by water (hydrochory) that affects seeds. The displacement of native plant seeds on the soil surface by runoff may be influenced by soil properties and by the use of biochar in agriculture. As these effects have not been documented in tropical agroecosystems and on steep slopes, we present here an in‐field experiment on a steeply sloping maize field affected by rainfall and tillage erosion in Northern Thailand. Our objectives were to test the effect of catena position and biochar use on seed displacement, soil loss and nutrient losses. We used 24 plots of 1 m ² located at four positions in the catena. Two treatments were tested: (1) conventional system with tillage and (2) biochar incorporated into the soil. We measured the displacement of plastic beads (to imitate round seeds), runoff volume, soil and nutrient losses and soil surface features during in‐situ rainfall simulations. After two simulated rainfall events and four natural rainfall events, total bead exportation was 7.2%. We found that catena position and biochar had an impact on runoff, soil and nutrient losses. In this study, previously incorporated biochar reappeared at the soil surface after 8 months under natural conditions and acted like a crust at the soil surface. This biochar crust increased runoff, increased potassium concentration and decreased phosphorus concentration in runoff, decreased bead displacement and had no effect on soil loss. This study, under tropical climate and steep slope conditions, highlights differences in soil surface features and runoff along the catena. We should consider catena position for improving soil management and using appropriate agroecological practices.
Highlights
The effect of catena position and biochar use on seed displacement, soil loss and nutrient losses were tested.
These effects have not been documented in tropical agroecosystems and steep slopes.
Catena position and biochar use had an impact on runoff, soil and nutrient losses.
Catena position for improving soil management and using agroecological practices should be considered.
... The high stone-and rock cover of the young moraines ( Figure S14) are likely important for OF generation (cf. Descroix et al., 2001;Mayor et al., 2009;Poesen et al., 1990;Valentin, 1994; #8 in Figure 1). Especially large, closely spaced stones and rocks (Lavee & Poesen, 1991) near the bottom of the plots may act as an impermeable layer, from which water can flow to the collection gutters (Figures 3 and S14). ...
In many areas of the world, the surface of the earth is changing rapidly. This can affect the partitioning of precipitation into overland flow (OF) and infiltration. OF can reach the stream quickly and thus strongly influences the streamflow response to precipitation. It can also cause surface erosion. However, our knowledge of the changes in OF responses during landscape evolution is still limited. To investigate how hillslope aging effects OF, we studied three plots on four different aged moraines (several decades to ∼13.5 thousand years old) at a silicate and carbonate proglacial area in the Swiss Alps. We used sprinkling experiments to determine OF characteristics (such as the runoff ratio and timing) and used tracers (δ²H and NaCl) to identify the mixing of rainfall and soil water. Sediment concentrations and turbidity measurements provided an estimate of OF‐driven soil erosion rates. The OF ratios were largest (42%) for the oldest moraines because the clay‐rich layer at 20–40 cm below the surface caused saturated OF. However, OF occurred more frequently on the youngest moraines due to the high stone cover. Soil and vegetation development increase the soil water retention capacity and the pre‐event water fractions in OF for the old moraines, but decreased the suspended sediment yield. The results show that OF characteristics and sediment transport change markedly during landscape evolution. This needs to be taken into account when simulating runoff and erosion responses for rapidly changing Alpine areas, and can—together with the outcomes for subsurface flow (see companion paper Maier et al., 2021, https://doi.org/10.1029/2021WR030223)—be used to improve landscape evolution models.
... Infiltration is a complex physical process that refers to water penetrating the soil, and can be regulated by soil surface conditions 27 . Previous studies reported that mulching gravel on the soil surface was beneficial to promote water penetration 49,50 . Our findings revealed that the initial infiltration rate and the average infiltration rate increased with the increase in the mulch thickness, whereas the stable infiltration rate decreased (Table 2). ...
Water availability seriously affects vegetation restoration in arid mining areas, and mulching is an effective way to improve soil water conditions. Coal gangue occupies large swathes of land resources, resulting in ecological fragility and various environmental problems. Despite coal gangue having mineral elements similar to those in soil, its potential function as a mulch for soil water conservation has been unclear. Herein, mulching on the surfaces of soil columns with 30 cm height and 15 cm inner diameter was conducted using coal gangue with four particle size ranges (0–0.5, 0.5–1, 1–2, and 2–4 cm) and four thicknesses (4, 8, 12, and 16 cm) under laboratory conditions to investigate water infiltration and evaporation under different conditions. The cumulative infiltration of the treatments with mulching thicknesses of 4 cm (T1), 8 cm (T2), 12 cm (T3), and 16 cm (T4) was 16.1%, 22.9%, 28.6%, and 41.6% greater than that of the control, respectively. The cumulative evaporation of the treatments with particle size ranges of 0–0.5 cm (P1), 0.5–1 cm (P2), 1–2 cm (P3), and 2–4 cm (P4) was 6.5%, 28.6%, 22.9%, and 18.6% lower than the control, respectively. Overall, to enhance the soil water storage capacity in mining areas, the results suggest that coal gangue mulching with a thickness of 8–16 cm and particle size range of 0.5–2 cm is suitable.
... In ltration refers to the water penetrating the soil, and soil surface conditions (such as soil surface roughness, soil structure, and stone cover) can regulate soil water in ltration and runoff generation [30]. Previous studies have shown that the water in ltration for gravel mulching at the soil surface was more pronounced than when the gravel was buried in the surface layer or embedded in the top layer [49][50], and water in ltration on these rough surfaces was approximately 1.5-2 times greater than that on smooth surfaces [51]. In addition, coal gangue located in the top soil position was more bene cial for water in ltration than that at the intermediate layer [31]. ...
Water availability seriously affects vegetation restoration in arid mining areas, and mulching is an effective way to improve soil water conditions. Coal gangue occupies large swathes of land resources, resulting in ecological fragility and various environmental problems. Despite coal gangue having mineral elements similar to those in soil, its potential function as a mulch for soil water conservation has been unclear. Herein, mulching on the surfaces of soil columns was conducted using four particle size ranges and four thicknesses under laboratory conditions to investigate water infiltration and evaporation under different conditions. Apart from the treatments with particle size of 0–0.5 cm, the remaining mulch treatments with 16 cm thickness involved greater infiltration and lower evaporation. Therefore, we recommend a 16 cm-thick mulch treatment as the preferred mulching style. Treatments with a particle size of 0–0.5 cm and those with 4-cm thickness are not suggested due to their lower infiltration and higher evaporation characteristics. Overall, to enhance the soil water storage capacity in mining areas, the results suggest that mulching coal gangue with particle size exceeding 0.5 cm and a thickness exceeding 8 cm is suitable.
... Overall, while establishing singletracks, the most important issues are minimizing ground surface disturbance, and maintaining the protective cover of stones [40] and of physical, biological, or biophysical crusts [41]. As a by-product, sustaining ground surface geodiversity negates hydrological connectivity of hillslopes and reduces the erosive power of alluvial processes [42]. ...
Mountain biking, also known as singletracking, is an emerging sector in outdoor recreation activities. Experience shows that although bicycling is considered a low-impact activity, singletracking may have adverse environmental footprints. Here, we review and conceptually analyze the forces applied on singletracks, and implement mathematical modeling of these forces, for a range of climatic conditions and geographic settings. Specifically, we focus on the hydrological and geomorphic impacts of singletracking, and highlight the importance of applying geomorphic principles in their design. Also, we demonstrate specific measures for establishing singletracks on hillslopes and in ephemeral stream channels. We discuss how climate, topography, surface roughness, hydrological connectivity, and pedology determine the processes of water runoff and soil erosion on singletrack trails. Further, we demonstrate how riders' behavior determines the rate of shearing, wearing, compaction, deformation, and rutting of the singletrack, as well as the expansion of physical damages to the track's surroundings. These conditions and effects determine the durability of singletracks, with implications for maintenance requirements over time. The specific implications of the emerging sector of electric mountain bikes on singletrack durability are discussed. Insights of this paper will benefit landscape designers and land managers aiming to foster ecotourism and sustainable recreation opportunities.
... La retención de agua en el suelo es la PHS que más ha sido evaluada por las diferentes investigaciones, así como el proceso de infiltración. (Poesen et al. 1990) Al igual que en i, teóricamente se ha asumido una disminución en K cuando hay FR. ...
Los fragmentos de roca (FR) son aquellas partículas del suelo con diámetro equivalente igual o mayor a 2 mm, su presencia en el suelo está estrechamente ligada a la génesis del mismo. Debido a que los FR pueden tener diversas posiciones en el suelo, su presencia puede ejercer una compleja influencia sobre diversos procesos hidrológicos (infiltración, evaporación, escorrentía, entre otros), ya que pueden afectar la arquitectura edáfica y tener gran relevancia en el comportamiento de las propiedades hidráulicas del suelo (PHS). Esta revisión hizo especial énfasis en buscar información científica que permitiera identificar la influencia de los FR en la infiltración y PHS, fue realizada mediante el análisis minucioso de trabajos científicos publicados, los cuales fueron accedidos por medio de las principales bases de datos reconocidas académicamente y documentación relacionada al tema. Se construyó una base de datos con 163 documentos científicos relacionados directamente con el tema investigativo y se abordaron 57 años de investigación (1943-2020); geográficamente se reportaron estudios en todos los continentes, a excepción de la Antártida. Los resultados permiten afirmar que los efectos de la presencia de FR en el suelo sobre la infiltración y PHS puede ser positivo, negativo o en ocasiones tener un comportamiento ambivalente. La influencia de los FR en el comportamiento de estas propiedades edáficas está estrechamente ligado a las propiedades de los FR, tales como son: contenido, tamaño, posición, distribución, material parental, porcentaje de cobertura, entre otras; lo cual explica la gran dificultad para obtener un conceso en la temática. Así mismo, se encontró que los suelos ecuatoriales o pertenecientes al área tropical es donde menos se han realizado investigaciones sobre la influencia de los FR en la infiltración y PHS, siendo estas investigaciones mucho más frecuentes en países como E.E.U.U, China y España. Con esta revisión se espera contribuir con el conocimiento sobre la caracterización y comportamiento de los suelos con fragmentos de roca.
... It was reported that the high-geodiversity hillslopes help shrubs in coping with water deficits during prolonged droughts [15,17,19,20]. The positive impact of stoniness on the soil-water content could be simultaneously affected by several mechanisms, including (1) the formation of a water film, which wraps the rock fragments in the soil profile [21]; (2) water storage in the pores of rock fragments across the soil profile [21]; and (3) rock fragments on the ground, which affect the formation of water overland flow [22]. Regardless, the soil moisture regime is also affected by the thickness of the soil down to the underlying bedrock, as well as by the bedrock's weathering and cracking [17]. ...
Soil moisture content (SMC) is a limiting factor to ecosystem productivity in semiarid shrublands. Long-term droughts due to climatic changes may increase the water stress imposed on these lands. Recent observations demonstrate positive relations between geodiversity-expressed by the degree of soil stoniness-and SMC in the upper soil layers. This suggests that areas of high geodiversity can potentially provide a haven for plant survival under water scarcity conditions. The objective of this study was to assess the effect of geodiversity on the dynamics of SMC in semiarid environments, which so far has not been fully investigated. The optical trapezoid model (OPTRAM) applied to six-year time series data (November 2013-July 2018), obtained from LANDSAT 8 and highly correlated with field measurements (R 2 = 0.96), shows here that the SMC in hillslopes with high geodiversity is consistently greater than that in hillslopes with low geodiversity. During winter periods (December-March), the difference between the two hillslope types was ~7%, while during summer periods (June-September) it reduced to ~4%. By using the high-resolution spectral-spatiotemporal VENμS data, we further studied the geodiversity mechanism during summertime, and at a smaller spatial scale. The VENμS-based Crop Water Content Index (CWCI) was compared with the OPTRAM measurements (R 2 = 0.71). The Augmented Dickey-Fuller test showed that water loss in the high-geodiversity areas during summers was very small (p-value > 0.1). Furthermore, the biocrust index based on the VENμS data showed that biological crust activity in the high-geodiversity hillslopes during summers is high and almost stationary (ADF p-value > 0.1). We suggest that the mechanism responsible for the high SMC in the high-geodiversity areas may be related to lower evaporation rates in the dry season and high runoff rates in the wet season, both of which are the combined result of the greater presence of developed biocrusts and stoniness in the areas of higher geodiversity.
... The rock fragments affect soil properties, vegetation cover and soil erosion (Simanton et al., 1984;Poesen et al., 1990;Poesen and Lavee, 1994) and they reduce soil losses Moustakas et al., 1995;Cerdà, 2001). Topsoils rich in rock fragments dry out quickly and stones act as a barrier against evaporation (van Wesemael et al., 1996), and therefore the infiltration and evaporation noted in hydrology models should be corrected for the surface rock fragments and recharge for sub-surface rock fragment content (van Wesemael et al., 2006). ...
Rock fragments are key components of soil systems. However, the role of rock fragments is only sporadically researched and therefore it is essential to establish how they control soil physical, biological and chemical properties and to assess the impacts of land-use on soil functions. Further, rock fragments affect soil water retention and infiltration capacity, and this is relevant for the fate of soils because water determines soil biota and weathering and decomposition processes in the soil system. Herein, we investigated abandoned arable, meadow and forest soils to determine the effect of land-use on soil water retention properties in soils containing rock fragments. Results showed that forest soil had the highest content of rock fragments and that previous ploughing on shallow abandoned arable soil on dolomite bedrock ensured that this had higher rock fragment content than meadows. We then compared coarse rock fragment effects on water retention in three research plots. Measured points in the water retention curves depict the total porosity and water retention determined at 3–1000 hPa suction in the undisturbed soil samples and 1.5 MPa in disturbed samples. Two models with different macro-porosity expressions were applied to the experimental data, and their derivatives provided pore size distribution curves with maxima for textural, structural and macro-pores. However, a new combined model with six independent fitting parameters has proven more suitable to approximate tri-modal soil water retention curves. The textural porosity was highest in the meadows due to the direct effect of organic carbon content and the indirect influence of coarse fragments which reduced the volume of small pores in the soil. Organic carbon content positively affected water retention properties in these soils. This included the permanent wilting point, field capacity and plant available water capacity, but the coarse fragment content negatively correlated with these properties. In addition, the results highlighted the stones’ positive effect on structural pores in forest soils and on macro-pore formation in all soils, while structural pores in all soils were mainly influenced by organic carbon content. The combined structural and macro-pores determine the soil air capacity and this is positively influenced by the increased content of coarse rock fragments. The soil air capacity was therefore highest in the forest soil. Finally, although the irreversible increase in rock fragment content in the abandoned soil has negative impact on agricultural use, the coarse fragment influence on macro-pore volume is positive and this increases soil infiltration capacity and reduces surface runoff and soil erosion, as confirmed in the literature review.
... Les feuilles mortes recouvrent le sol de façon importante seulement pendant une courte période, mais localement elles peuvent persister durant toute l'année. Le terme "feuille morte" concerne les feuilles en décomposition juste après la chute jusqu'à celles manifestant une fragmentation avancée (mais non humifiées). 2 étroitement lié à l'OSS dans la mesure où de forts taux de cailloux (70%, (Poesen et al., 1990) représentent un groupe d'OSS (Gaddas, 1997 ;Hatier, 2000) ; 3 le seul lien avec les pratiques culturales est une faible présence apparente après labour ; 4 des taux de recouvrement de 0 à 100% sont rencontrés. Humidité 1 peut favoriser l'infiltration en neutralisant une éventuelle hydrophobie de la surface, mais si elle représente une forte humidité à travers toute la couche superficielle du sol, occupant une partie importante de la porosité, cela peut freiner l'infiltration ; 2 pas liée à l'OSS ; 3 pas liée aux pratiques culturales (absence d'irrigation) ; 4 varie de sec à saturé. ...
*Unité Sol et Environnement, INRA Montpellier (FRA) Diffusion du document : Unité Sol et Environnement, INRA Montpellier (FRA) Diplôme : Dr. Ing.
... The effect of soil tillage or the amount of grass cover, for instance, can be very important in reducing runoff, but these factors are not constant in time and thus not easy enough to map to be considered here. However, the presence of stones on the surface was also recognized as a key parameter that can increase the soil infiltration capacity (Poesen et al., 1990;Wassenaar et al., 2005). In our study, the soils with numerous and not embedded stones on the surface were thus classified as type 1 soils. ...
L’influence des fossés dans les phénomènes de crue, d’érosion hydrique des sols ou de transferts de polluants agricoles est bien connue à l’échelle locale. Cependant, on ne dispose que de peu de connaissances sur la variabilité spatio-temporelle des réseaux de fossés et de l’effet de cette variabilité sur les processus hydrologiques. L’objectif de ce travail de thèse vise donc à quantifier la relation entre l’organisation spatiale et temporelle des réseaux de fossés, éléments de la structure du paysage, et le fonctionnement hydrologique des paysages viticoles méditerranéens. Dans un premier temps, on propose d’analyser comment la densité des réseaux de fossés varie dans les paysages et à quel point elle est conditionnée par le milieu physique. Ensuite, un algorithme de simulation de réseaux est chaîné à un modèle hydrologique afin de quantifier le rôle de la densité des réseaux dans la régulation des écoulements de surface.En lien avec son rôle d’interception du ruissellement, l’effet anti-érosif des réseaux de fossés est alors analysé grâce à l’utilisation d’indicateurs géomorphologiques. Dans un second temps, on s’intéresse à la dynamique spatio-temporelle de la végétation des fossés et à son impact sur les transferts de pesticides. Pour cela, on caractérise puis simule les pratiques d’entretien des fossés et leurs impacts sur la végétation.On montre alors en mobilisant différents indicateurs que les pratiques actuelles ne sont pas optimales d’un point de vue de la rétention des pesticides. Cette thèse, qui s’appuie sur des méthodes de simulation du paysage, montre l’intérêt du chaînage entre modèles de structure et de fonctionnement du paysage. Ce chaînage a permis de quantifier le rôle des réseaux de fossés dans la modulation des processus hydrologiques.
... Soil erosion is one of the most important environmental issues in natural and anthropized territories [1,2]. Understanding the key parameters and factors of soil erosion will enable the conservation of soil system goods, services and resources, and will avoid the damage outside of fields caused by transported and accumulated sediments and water [3,4]. The dynamics of erosive processes are changing along with new trends of pluviometric patterns due to well-identified climate change, which is becoming an extra factor in soil degradation [5,6]. ...
In this Special Issue, we have tried to include manuscripts about soil erosion and degradation processes and the accelerated rates due to hydrological processes and climate change. We considered that the main goal was successfully reached. The new research focused on measurements, modelling, and experiments under field or laboratory conditions developed at different scales (pedon, hillslope, and catchment) were submitted and published. This Special Issue received investigations from different parts of the world such as Ethiopia, Morocco, China, Iran, Italy, Portugal, Greece and Spain, among others. We are happy to see that all papers presented findings characterized as unconventional, provocative, innovative and methodologically new. We hope that the readers of the journal Water can enjoy and learn about hydrology and soil erosion using the published material, and share the results with the scientific community, policymakers and stakeholders new research to continue this amazing adventure, featuring plenty of issues and challenges.
... Rock fragments can also change some features of plants, such as transpiration and water use efficiency (Mi et al., 2016). However, the apparent effects of rock fragments on soil water behaviour are inconsistent, either showing reduced infiltration and increased runoff (Ingelmo et al., 1994;Constantz et al., 1988), or the opposite effect (Poesen et al., 1990;Dadkhah and Gifford, 1980), stressing the influence of specific soil conditions (compaction, rock coverage, etc.) and the need of additional research efforts (Zhang et al., 2016) on how to implement better soil management practices. Soils with substantial amounts of rock fragments are widespread in Mediterranean areas (>60% of the land) (Poesen and Lavee, 1994;Poesen et al., 1999) and the scientific community is more and more interested on this issue because of its implications on agriculture, forestry and, in general, on soil services to human well-being that should necessarily contribute to achieving the United Nations sustainable development goals (Keesstra et al., 2016). ...
Water is the main component in the conservation and functioning of Mediterranean ecosystems. There is a trade-off between plant water use during establishment and soil water conservation. Rock fragments and cultural management are two key factors affecting soil water dynamics on forest establishment. In this work, we studied the interactions of different cultural management techniques (tillage, herbicide and mulching) with soil rock fragment content (soil gravel) and their effects on the spatio-temporal water dynamics and efficiency of water use in Mediterranean forest plantations. Soil water content (SWC, l/m³), soil water depletion rate (k) and water use efficiency (WUE, μmol CO2/mol H2O) were monitored along a two-year period in a holm oak reforestation. The results show that SWC and its spatio-temporal dynamics were defined by a significant interaction between the cultural management techniques and the rock fragment content. Cultural management techniques had weak effects on SWC when compared to the control treatment, although significant differences were found. The soil rock fragment content accounted for most of the variability in SWC; and soils with a content below 5% had higher water contents. The cultural treatments showed some influence on water behaviour under SWC more limited conditions, that is, when rock fragment contents was higher than 15% and/or in summer periods. Finally, SWC was also a limiting factor for the WUE of holm oak seedlings, being the WUE values higher when the soil water supply was more restricted. The maximum WUE was reached at a rock fragment content in the soil profile of 17%, combined with mulch treatment, during dry summer conditions. Thus, the interaction between the rock fragment content and cultural management is a key element in trade-offs between water conservation and plant water-use objectives in Mediterranean forest restoration strategies.
... Foster et al. (1989) reported that rock fragment cover increases the roughness coefficient and friction factor of the soil surface. Also, the field and laboratory studies conducted by Poesen et al. (1990) and Guo et al. (2010) respectively report that rock fragment cover increases the soil surface roughness by decreasing the flow velocity and increasing the flow depth. ...
Soil loss is a major global challenge threatening the future of soil and water resources. The significant implications of soil loss necessitate the adoption of appropriate soil conservation practices and soil management solutions according to the regional climate. Investigation of the effects of soil cover on soil erosion process can provide the information necessary for the success of soil and water conservation practices. In this study, the effect of rock fragment and wheat straw covers on the hydraulic properties, runoff, and sediment yield were investigated in plot scale laboratory experiments using artificial rainfall. Experiments were carried out on the plots prepared based on two types of soil cover (rock fragment, wheat straw) and three coverage ratios (35%, 65%, and 90%) in addition to a control (bare soil) plot, each with three replications. In these experiments, 2 m long, 0.55 m wide, and 0.30 m deep plots with a 15% slope were subjected to artificial rainfall with a duration of 70 min and an intensity of 90 mm h−1. The results showed a significant difference at the 5% level between the mean runoff rate of rock fragment cover (0.38 mm min−1) and that of wheat straw cover (0.42 mm min−1), but no such difference was found in terms of sediment production (Sig. = 0.73). The Wheat straw cover was more effective than rock fragment cover in increasing the Manning roughness (n) and Darcy-Weisbach friction (F) coefficients, and flow depth (h) and reducing the velocity (V), Reynolds (Re) and Froude (Fr) numbers. It was also found that, for both covers, increasing the coverage ratio increased the h, F, and n and decreased the runoff and sediment production, V, Re, and Fr. After investigating the relationship between hydraulic properties and sediment concentration in different plots, a direct linear regression relationship with a relatively high coefficient of determination (R2 > 0.614) and a significant relationship at the 1% level (P < 0.01) were found between sediment concentration and discharge per unit width (q), V, h, and Re. In general, it can be concluded that rock fragment cover and wheat straw cover both have a satisfactory effect on the hydraulic properties and runoff and sediment production.
... -Existe una correlación evidente entre los valores de conductividad hidráulica (KMR y KMP en particular) y el contenido en elementos gruesos (EGP y EGV) , esto de acuerdo a lo constado en escurrimiento y erosión; -La pendiente (PEN) la densidad aparente total (DAT, matriz del suelo más elementos gruesos) y el diámetro del bulbo de humectación (D8B) no tienen relación notoria con la conductividad hidráulica Esos parámetros físicos explican las fuertes variaciones de conductividad hidráulica entre los diferentes estados de superficie (Descroix el al., 2001) . El punto más importante parece ser el papel de la pedregosidad (Poesen, 1990) y en particular el papel de las piedras grandes libres en los terrenos con pendiente . ...
... In the Dead Sea region, the area of convective cells has been observed to increase with latitude, following orography, while their rain intensity remained unaffected (Belachsen et al., 2017). At the hillslope scale, soil crusting and aggregation (Singer and Le Bissonnais, 1998;Yair, 1990), stone disposition (Abrahams and Parsons, 1991;Dunkerley, 1995;Poesen et al., 1990), vegetation (Faulkner, 1990;Francis and Thornes, 1990;Tongway and Ludwig, 1994;Ludwig and Tongway, 1995;Puigdefábregas, 2005;Thornes, 1985) and microtopography (Bergkamp, 1998;Dunne et al., 1991) have been observed to influence runoff generation in drylands. The combination of high rain intensity, low vegetation interception and low soil infiltration capacity increases the importance of infiltration excess (Hortonian) overland flow (Wheater et al., 2007). ...
Catchment-scale hydrological studies on drylands are lacking because of the scarcity of consistent data: observations are often available at the plot scale, but their relevance for the catchment scale remains unclear. A database of 24 years of stream gauge discharge and homogeneous high-resolution radar data over the eastern Mediterranean allows us to describe the properties of floods over catchments spanning from desert to Mediterranean climates, and we note that the data set is mostly of moderate intensity floods. Comparing two climatic regions, desert and Mediterranean, we can better identify specific rainfall-runoff properties. Despite the large differences in rainfall forcing between the two regions, the resulting unit peak discharges and runoff coefficients are comparable. Rain depth and antecedent conditions are the most important properties to shape flood response in Mediterranean areas. In deserts, instead, storm core properties display a strong correlation with unit peak discharge and, to a lesser extent, with runoff coefficient. In this region, an inverse correlation with mean catchment annual precipitation suggests also a strong influence of local surface properties. Preliminary analyses suggest that floods in catchments with wet headwater and dry lower section are more similar to desert catchments, with a strong influence of storm core properties on runoff generation.
Rock fragments play a pivotal role in influencing slope erosion processes, attracting increasing scientific interest and growing concerns regarding their potential impacts on erosion. This paper reviews the studies published in recent decades concerning the various impacts of rock fragments on soil erosion processes by water, highlighting the research gaps and outstanding challenges in exploring the erosion evolution process involving rock fragments. Systematic studies and illustrative examples have shown that the impacts of rock fragments characteristics (such as coverage, content, size, position, shape, and spatial heterogeneity) on erosion processes are complex and inconsistent (positive/negative). This uncertainty can be attributed to the intricate erosion process and the diverse rock fragment characteristics, complicating the development of accurate erosion prediction models. Current models predominantly focus on rock cover and often ignore the essential factors including rock size, position, and shape, thus impeding the precise understanding of how rock fragment characteristics specifically affect soil erosion within existing erosion models. Furthermore, this review discusses the perspectives for enhancing the research on rock fragment impacts on soil erosion processes and provides insights into potential research requirements and solutions.
The erodibility and erosion resistance of Quaternary sediments play a pivotal role in both the hydrologic and erosion processes of soil cut slopes. To investigate the runoff and sediment yield of soil cut slopes along the Pai-Mo road, we performed indoor simulated rainfall experiments under a 50° steep slope and high rainfall intensity (120 mm/h), based on the area’s climatic characteristics and Quaternary sediment properties. The experiments included various rock fragment contents (30%, 40%, and 50%), different levels of rock fragment roundness (i.e., rounded gravel, angular gravel), and varying soil cohesion. The results indicated that the average infiltration rate of the uncemented rounded gravel soil slope (URGSS) was higher than that of the uncemented angular gravel soil slope (UAGSS), resulting in less runoff and a delayed initial runoff time. The runoff shear stress, runoff power, drag coefficient, and Reynolds number of the URGSS were smaller than those of the UAGSS. In contrast, the Froude number and flow velocity of the URGSS were larger, resulting in a stronger runoff erosion capacity. The sediment yield of the URGSS was approximately two times that of the UAGSS, and the cumulative sediment yield was about 20% higher. The cemented angular gravel soil slope (CAGSS) had a larger runoff rate, runoff shear stress, runoff power, and flow velocity than those of the UAGSS, leading to less sediment yield. Overall, a more rounded shape and a larger radius of curvature of the spherical particles resulted in stronger erosion, due to local turbulence. Therefore, the rill density and cumulative sediment yield of the steep alluvial cut slope were greater than that of the steep colluvial cut slope under heavy rainfall. Moreover, due to its strong cohesion, only raindrop splash erosion and inter-rill erosion occurred on the steep moraine cut slopes under heavy rainfall.
Soil erosion poses a challenge to the environment and the sustainable use of natural resources, particularly in relation to agricultural production. The study aimed to assess the influence of different soil organic carbon (SOC) levels on runoff and soil erosion under varying levels of rainfall intensity. The study was conducted in pre-selected farmers' fields representing low, moderate and adequate SOC levels in Nitisols and Ferralsols. Two parallel experiments were set up in each type of soil using a split-plot layout arranged in Randomized Complete Block Design. The main plots were the different soil organic carbon levels while the sub-plots were the different simulated rainfall intensities. Rainfall simulation was then conducted to determine runoff and sediment losses on each soil type. The simulation was done using a land type sprinkler nozzle rainfall simulator (460 788 type) in an experimental plot of 1 m2, fenced with corrugated iron sheets with a small opening left for runoff collection. Runoff and sediment losses were determined from the volume collected in the jar. The data was subjected to analysis of variance and significant mean differences were determined using Tukey’s Honest Test at a 95% confidence level. Pearson correlation was applied to assess the relationship between runoff volume and sediment loss. The results showed that Ferralsols recorded significantly higher runoff and sediment losses compared to Nitisols, by 60.27% and 53.14% respectively. However, adequate SOC level portrayed a significant effect in reducing erosion in both soil types, where it reduced runoff and sediment loss by 45.30% and 48.38% in Ferralsols and by 65.31% and 48.22% in Nitisols, respectively. In both soil types, runoff yield was positively correlated to rainfall intensity while sediment yield was inversely correlated with SOC levels. Therefore, the study recommends incorporation of organic matter to adequate levels in both soils, for reduced soil erosion.
Winter annual plants play an important role in arid and semiarid ecosystems because of their rapid response to resource pulses, which drive primary production that provides resources for herbivores and pollinators. Understanding the factors that control annual plant growth is key to predicting how arid and semiarid ecosystems will respond to changes in climate and resource availability from anthropogenic activities. We used a long-term nutrient enrichment experiment that spanned precipitation and urbanization gradients in central Arizona, USA, to examine the effects of climate, surface soil properties, soil nutrient availability and shrub cover on winter annual plant growth. At a landscape scale, aboveground net primary production (ANPP) of winter annual plants had a positive, nonlinear relationship to the amount of precipitation received from October through March of the current growing season. We found evidence for sequential resource limitation of ANPP initially from water then nitrogen and phosphorus. The resource limitation cascade was modified by surface soil properties and location relative to shrubs (under or between shrubs), highlighting the effect of small-scale factors on large-scale processes. Specifically, gravel cover had a negative effect on ANPP, and the effect of shrub cover on ANPP depended on nitrogen and current season rainfall. Our study emphasizes how small-scale factors, such as gravel cover, nutrient availability and presence of shrubs, can interact with large-scale drivers, such as seasonal precipitation, to affect interannual variation in winter annual plant production in the northern Sonoran Desert.
Graphical Abstract
Sonoran Desert landscape showing production of winter annuals 363 x 241mm (300 x 300 DPI)
In the Northern Rio Grande region of New Mexico, USA, Ancestral Pueblo villages experienced rapid demographic and economic growth in the late 14th and 15th centuries A.D. Recent research has proposed that this growth was underwritten by cotton production for exchange. Gravel mulch was an important component of cotton agriculture, but its function and soil legacies are not well understood. Since water management was likely a critical feature of gravel mulch, this study examines soil variables affected by changes to water supply. Gravel mulch analyzed in this study was found to have a substantial impact on the surface soil particle size distribution, but other aspects of soil quality were unaffected. The depth profiles of base cation ratios in mulched and unmodified locations suggest that gravel mulch continues to enhance water infiltration. Based on the timing of cotton development and inferred infiltration depths associated with gravel mulch soils, gravel mulch technology is well suited to the monsoonal precipitation regime of the region and the phenology of cotton.
Infiltration depends on the surface conditions of the soils, such as the surface covering of rock fragments and some of the properties of the matrix such as total porosity. Research reports inconclusive results regarding the influence of rock fragment cover on soil water infiltration that usually does not involve the spatial component in the analyses. The objective of this research was to spatially model the base infiltration rate and its relationship to rock fragment cover and the total porosity in soils of an Andean micro-basin. Hydrological response units were used to carry out stratified sampling in the basin. Infiltration was measured in the field using double ring infiltrometers. Surface rock fragment cover was estimated visually, and total porosity was determined using a tension table. Results showed that higher values in the rate of soil infiltration predominated on the slopes of the upper parts of the basin, while in the lower parts the values were lower. Infiltration had a logarithmic-exponential type distribution. The spatial autocorrelation model showed the best performance (r = 0.863) to model the relationship between the variables. This was the first research involving spatial modeling in the relationship between rock fragment coverage and soil infiltration, showing that infiltration was a spatially correlated variable related to changes in total porosity and soil coverage of rock fragments on the ground surface. This provided new information on the behavior of soils with rock fragments in tropical areas that have been little studied.
Significant developments in soil erosion research for the period 1950-2000 are reviewed. The main emphasis is on work in Western Europe and North America. We highlight work on process studies in splash, rill and gully erosion. Important developments also occurred in monitoring, measuring, and modelling erosion as well as recording and understanding rates of erosion. We concentrate on cultivated and bare soils and have included badlands and peatland erosion in our review.
The study of hillslopes has been dominated by the expansion of studies into process rates and mechanisms. Perhaps the greatest volume of work has been on the ‘wash’ processes of soil erosion, but there has also been significant work on the diffusive mass movements of linear and non-linear ‘creep’ that shape the convexity of hilltops, on more rapid mass movements and on solution processes. There has also been fresh work on distinctive processes in coastal, arid and cold-climate environments.
Accompanying and integrated with process understanding, and made possible by ubiquitous computational power, modelling has developed from soluble mathematical simplifications to complex simulations that incorporate much of our understanding of process and climate.
Particular topics that have seen significant advance include a more complete understanding of drainage density and texture, and a broadening of interest to encompass the ‘critical zone’ that constructively unifies the land surface with the lower atmosphere, the biosphere and the regolith. There has also been a change of focus towards steeplands, dominated by mass movements, supply limited removal and tectonic activity.
Most recently, and now incorporated into the concept of the ‘Anthropocene’, human impact is now receiving increasing attention as we acknowledge its accelerating role in changing landscapes and their relationships.
Abstract Estimation of runoff and sediment yield are primarily required for watershed development planning involving soil and water conservation measures. Runoff is primarily responsible for sediment detachment and their transport during the erosion processes. In the study, GeoWEPP model was used to estimate the daily runoff and sediment yield from a small watershed located in the Lesser Himalaya, Uttarakhand state, India. GeoWEPP model requires input files of the land use/land cover, slope, climate, soil and land use management which were generated within the GeoWEPP interface. CLIGEN (CLImate GENerator) was used to generate the daily weather parameters for the model. The model was calibrated with measured data of the year 2015 and performance was evaluated with the data collected in the year of 2016 and 2017 for runoff and sediment yield of the watershed. The sensitivity analysis showed the effective hydraulic conductivity, critical shear, inter-rill and rill erodibility as the most sensitive model parameters. Calibration of model revealed high correlation coefficient (0.92 and 0.94) and NSE (0.67 and 0.85) value for daily runoff and sediment yield from the watershed. Performance of the model showed high coefficient of determination for runoff (R2 = 0.85) and sediment yield (R2 = 0.95) with low RMSE value of 4.35 mm and 2.53 t ha −1 , respectively. Lower scatter index (SI) value indicates acceptable RMSE for the model. The study showed a reliable estimation of daily runoff and sediment yield with GeoWEPP model in the lesser Himalayan landscape. "The final publication is available at link.springer.com". Vol.:(0123456789) 1 3 Modeling Earth Systems and Environment https://doi
Soil is a highly complex system which is influenced by several factors in its existence. Soil health refers to the capacity of a soil in sustaining biological productivity by promoting plant growth while maintaining or improving environmental quality. Soil health is a prerequisite for agricultural production and thus it becomes highly essential to support crop production and in delivering ecosystem services. With increasing concerns on food security, maintenance of soil health is the foremost challenge we are posed with. It becomes difficult to understand and manage the processes occurring in soil independently as all these are interrelated and are in a unique balance. The physical, chemical and biological properties together with their interactions need to strike that perfect balance in a healthy soil, which is actually determined by several abiotic and biotic factors. When the balance between these is lost, the equilibrium is disturbed indicating the deterioration in soil quality which is defined using soil degradation. The different threats to soil by means of nutrient depletion, decline in organic matter, soil contamination, addition of toxic materials to soil and lack of proper management of soil and land use would lead to a degraded soil. In this chapter, a discussion is made on the aspects of soil health and abiotic and biotic factors that influence soil health and soil degradation.
Four research sites were established along a climatic gradient in Israel representing Mediterranean, xeric Mediterranean, w Ž arid and extreme arid climate conditions. The cover percentage of eight soil surface components vegetation annual and. Ž. x perennial forms , biogenic crust mosses, lichens, cyanobacteria, and dwarf grass , stones and bare soil patches were Ž. measured. Transects along hillslopes on each of two opposite aspects south and north facing slopes were established at Ž. each site altogether eight transects. Dominance and soil surface cover diversity indices, and similarity coefficients between the transects were calculated. High similarity values in soil surface cover were found between the south facing slopes located in the xeric Mediterranean, arid, and extreme arid areas. These hillslopes are dominated by stones and bare soil patches. In Ž contrast, lower similarity values were found between the northern slope aspects dominated by biotic components vegetation. and biogenic crusts. The study along a climatic gradient together with the comparison between northern and southern aspects provide useful information that can be utilized for evaluation of changes in soil surface cover characteristics given various scenarios of future climate regimes in that region. q
Water-induced erosion of iron tailings is a serious problem affecting ecological restoration, but, little is known about how the occurrence of erosion on tailings slopes and types of reclaimed substrates that are beneficial to reducing slope erosion. This study measured the slope erosion characteristics of six reclaimed substrates including loose tailings (LT), crusty tailings (CT), tailings incorporating mushroom residues (TM), tailings incorporating soil (TS), tailings incorporating soil and mushroom residues (TSM) and soil (S) in experimental soil flumes under three simulated intermittent rainfall events, with intensity of 60, 90 and 120 mm h⁻¹ for the first, second and third event, respectively. Significant differences (p < 0.05) were found in erosion characteristics among the six reclaimed substrates. TM had the lowest sediment yield but the highest runoff volume without obvious rills. LT, CT and TS had the highest sediment yield rates and severe slope erosion morphology. With the increased number of rainfall events, the runoff rates of the six substrates all increased, but only the sediment yield rates of LT, CT and TS increased, the sediment yield rates of other substrates increased first and then decreased. Therefore, adding agricultural organic wastes such as mushroom residues to tailings and reducing soil addition may be an effective way to reduce erosion and promote ecological restoration in soilless tailings areas.
Surface soil properties can change as a result of soil disturbances, erosion, or deposition. When soils contain rock, surface soil properties can also change over time as a result of the process of soil armouring, which is the selective removal of finer particles by erosion, leaving an armoured layer of coarser particles that may reduce further soil loss. Rapid armouring is typically reported in steep and bare slopes on mine sites, construction sites, road embankments, and also rangelands. Changes in surface soil properties over time induced by armouring are not accounted for in current erosion models such as WEPP or RUSLE2 because little is known about rates of armouring over time as a function of rainfall intensity, rock content, slopes, and other factors. In this paper we simulate soil armouring induced by interrill erosion in two sets of experiments and propose ways to account for the process in WEPP and RUSLE2 without modifying the science behind the models. The first set of experiments was conducted to demonstrate and quantify the effect of armouring on sediment yields under varying rainfall intensities. Rainfall with intensities ranging from 22 to 80 mm h⁻¹ was simulated on 0.56 m² plots at slopes of 18 degrees (32.5%) using topsoil with high rock content from a mine restoration site. Results showed a clear relationship between rainfall intensity and armouring. There was an over 75% reduction in total soil loss under 22 mm h⁻¹ rainfall between freshly applied soils and highly armoured soils at the same slope. A second set of experiments was conducted to understand the relationships between soil rock content, rate of surface rock cover change, slope change and sediment yields. Sediment yields and surface rock cover were quantified for non-cohesive soils consisting of glass beads with a diameter range of 45 to 90 μm and 0, 20 and 40% rock content in 0.22 m² plots at a 15° (26.8%) slope under 80 mm h⁻¹ simulated rainfall. Linear relationships were observed between cumulative sediment yields and rock cover, and exponential relationships between total runoff and rock cover. The armouring process was modeled at the experimental scale with WEPP and RUSLE2 by iteratively altering the rock cover and the slope over time. WEPP event based simulations at this scale resulted in reasonable predictions of sediment yields throughout the armouring process, and RUSLE2 required modification of soil erodibility values to account for high rock content and changes in runoff over time. Automation of this process, however, would require modifications of the models to expose rock cover and change slope over time. A method for doing this is discussed for interrill processes, but interactions between rill erosion and armouring need further study. The effect of long-slope high-energy rill flows on armouring also needs further investigation through field scale experiments, as this study did not examine the extent to which rock is uncovered and/or moved on long slopes differently from the residues already modeled in WEPP and RUSLE2.
In agricultural lands, the way in which slope position affects the detachment of material and the runoff generation is not clear. There are complex interactions between slope position, slope gradient and a series of soil characteristics, and their impact on runoff generation and soil erosion may vary from site to site. We designed an experiment to investigate the initial hydrological responces of soils located on different slope positions (footslope, backslope and shoulder) in runoff and soil detachment generation. To achieve these goals, 25 high-intensity low frequency rainfall events were simulated in experiments with a return period of 5 years, on 0.25 m2 circular plots to measure the detachment along a hillslope in the Celler del Roure vineyards in Eastern Spain. The results of this investigation showed that soil erosion rates (3 Mg ha−1 h−1) were high and there were no significant differences between sites in relation to slope position; all the plots generated runoff (runoff coefficient of 24.8%). These results allow us to conclude that soil detachment and runoff generation in Mediterranean vineyards, where tillage is millennia-old management practice, could be also evenly distributed. Therefore, the used management practices in these vineyards contribute to creating net source areas of runoff and erosion with no areas that could act as a sink under intensive rainfall events. Based on our research and a literature review, we propose to implement nature-based solutions that would contribute to reducing soil erosion in agricultural land by creating sink areas in the form of hedgerows, ponds, or vegetation strips where the surface wash deposits and water can sediment and infiltrate. We also discussed other management practices contributing to reduction of erosion, such as mulching and inter-row crops. We state that there is an urgent need to apply strategies to reduce soil loss in vineyards.
Overburdened stockpiles during construction projects are typically loose mixtures with different proportions of fines and gravel. They are common sources of anthropogenic accelerated erosion that threatens environmental quality and the quality of life for people in many parts of the world. Overburdened stockpiles have unique three-dimensional shapes. However, studies with these materials are usually performed in traditional planar soil bins. Therefore, in this study, a specially designed mobile experimental device was used to accurately evaluate the runoff erosion process on overburdened stockpiles in a three-dimensional conical shape. A series of indoor rainfall simulation experiments at 60 mm/h rainfall intensity was conducted using material with different gravel contents (0%, 10%, 20%, 30%, and 40%). The results showed that the runoff rate and flow velocity exhibited the same trend, i.e., a rapid increase, followed by a slow increase and then stabilization. The runoff regime in all experiments manifested as laminar and subcritical flow during the runoff process. Re and Fr values were much smaller than those on two-dimensional plane simulation of overburdened stockpiles. The presence of gravel caused the runoff to be slow and stable. Runoff rate, flow velocity, Re and Fr values all decreased with increasing gravel content. The sediment yield decreased logarithmically in response to the increasing gravel content. The study findings are not only helpful for understanding the hydraulic characteristics and erosion features that characterize overburdened stockpiles, but also have implications for prediction models of soil and water loss from this material during production and use in construction projects.
A new portable rainfall simulator has been developed for both field and laboratory soil erosion research at the University of Guelph. Employing several low- to medium-flow-rate, full-jet nozzles in a continuous-spray design, the simulator is capable of reproducing storm intensities ranging from 17. 5 mm/h to in excess of 200 mm/h. Simulated rainfall intensity varies with nozzle size, water pressure at the nozzle, and height of the nozzle above the plot surface. Uniformity of rainfall intensity over a 1-m by 1-m plot averages 88. 33% over all nozzles and settings, with many nozzles producing averages over 90%. The simulator and support equipment are portable to the extent that they can be loaded onto a half-ton truck for transport to the field.
Rainfall kinetic energy values measured with a Joss-Waldvogel rainfall distrometer near Canberra are reported and compared with other data obtained in Australia using the same measurement technique. Intensity-energy relationships for Canberra are similar to those previously obtained at Gunnedah, N.S.W. and should apply over a wide area of south-eastern Australia.
Des expériences en laboratoire sur la détachabilité et sur la transportabilité de neuf sédiments meubles étaient faites sur un bac d'essai mesurant 100 sur 20 cm. L'écran récepteur mesurait un mètre carré.
Le calcul de la détachabilité nécessite une connaissance exacte de la quantité de sédiment déplacé par unité d'énergie cinétique de la pluie. Egalement, la détermination de la transportabilité ne peut se faire que si la distance moyenne projetée de tous les grains déplacés est connue.
Il est certain, vu les dimensions limitées de l'appareillage, que seulement une partie des grains ou aggrégats déplacés ont été recueillis sur l'écran récepteur.
Il y a de fortes chances que le sédiment éjecté autour d'un point quelconque soit distribué selon une courbe exponentielle. Si en plus, la surface dans le bac d'essai est homogène, ainsi que la pluie tombant sur elle, il devient possible d'exprimer le rapport entre matériau recueilli et tout matériau déplacé, et le rapport entre la distance mesurée et la distance vraie, en fonction de l'exposant de l'équation susdite.
La distance apparente ou mesurée, étant également une fonction de cet exposant, est par conséquent le seul paramètre nécessaire pour la détermination des deux rapports. Dès lors, une abaque pouvait être construite.
Toutes les valeurs empiriques ont donc pu être transformés en valeurs exactes, relatives à la totalité des grains déplacés, même à l'intérieur du bac d'essai.
Des travaux de terrain ont été menés dans trois pays (Côte d'Ivoire, Haute Volta, Niger) afin de fournir davantage de donnéees concernant les différents facteurs qui inter viennent sur l'érosion hydrique en Afrique de l'Ouest. Deux types de simulateurs de pluies ont été utilisés. Une grande attention a été portée aux courbes intensité-durée, à l'énergie cinétique des pluies, et à la gamme d'humidités avant les averses. Les traitements ont été choisis en fonction des systèmes culturaux qui prédominent dans les diverses régions d'études. Les résultats sont conformes à ceux obtenus sous pluies naturelles. Ils expriment l'importance des éléments grossiers superficiels quant à la conserrvation des sols. En milieu tropical humide une protection naturelle est assurée par le couvert végétal qui compense ainsi les effets néfastes des pluies très violentes. L'influence des teechniques traditionnelles de lutte antiérosive est liée aux quantités d'eau infiltrée:à partir d'un cer tain seuil, les billons s'écroulent et l'érosion subit alors une vive augmentation. De même l'effet de l'utilisation de résidus de culture comme paillage dépend de la texture du matériel pédologique superficiel. Ainsi, l'utilisation, sans discernement, de l'équation universelle des pertes en terres dont les facteurs sont supposés indépendants peut être très hasardeuse. (RESUME D'AUTEUR)
Soil erosion in the vineyards relies on the determination of a hierarchical scale of erosion features and of natural land units on behalf of slope and soil maps. This type of mapping allows us to determine sensitivity of soil types and a scale of erosion hazard relying on intensity and possible rate of fluctuation of erosion. -from English summary
Laboratory and field results clearly indicate that sealing intensity is not only a function of soil (texture) and rainfall properties, but also of surface slope angle, provided that the soil is susceptible to sealing. Surface seal formation becomes less intense as slope steepens essentially because seal development is obstructed by intense rainwash. -from Author
Soil losses were monitored for 4 years on 11 sections of forest road in the central Appalachians. Average annual soil losses ranged from 47 tons/acre on the ungraveled road sections to 6 tons/acre on the sections surfaced with 3 inches of clean limestone gravel. - from AuthorsNortheastern Forest Experiment Station, Forest Service, U.S.Department of Agric, Parsons, WV 26287, USA.
Field measurements on a field plot in the Belgian loam region have been performed. Implications of the results with respect to a soil conservation technique, the soil erodibility factor (K) of the USLE, rill channel armoring, taphonomy, the genesis of stony colluvium and stream channel response to rock fragment transport on uplands by rill and gully flow are further discussed. -from Author
The theory and experimentation reported are for the purpose of determining the effect
of particle size proportions in soils on their maximum bulk densities and other properties
affected by compaction. If the different size classes in a bidisperse or tridisperse
mixture have very large effective diameter ratios and if certain other simplifying
requirements are followed, it is shown theoretically that the minimum bulk volume
of the mixtures can be predicted from the volume proportions of the different-sized
particles present. The minimum bulk volumes and hence maximum bulk densities of two
prepared textural sequences, Stockton silty clay and Monterey sand mixtures, were
obtained after kneading compaction at different water contents and were examined with
respect to the above theory. The relationships between water content and compacted
bulk density, between water content and suction of compacted soils, and the formally
calculated mean effective pore diameter distribution at minimum and maximum bulk density
are presented and discussed.
It is usually assumed that a forest canopy breaks the force with which rainfall strikes the soil, thus protecting it from erosion. To show that this is frequently untrue and that the protective value of the forest to the soil must, therefore, be due to lesser vegetation or to the layers of unincorporated organic material lying on the soil surface is the purpose of this paper.
Measurements were made of raindrop size beneath a red pine canopy and in an adjacent open field near New Haven, Connecticut during several storms in 1946 and 1947. By reference to published tables of velocities of falling water drops, the kinetic energy at the soil surface of the rain under the pine canopy and in an open field was determined. It was found that at rates of precipitation less than two inches per hour the kinetic energy of rainfall beneath the red pine canopy exceeded that of rainfall in the open.
This paper presents measurements of the velocities of water‐drops of sizes ranging from one to six mm in diameter, falling in still air from heights of 0.5 meter to 20 meters. A few measurements of raindrop velocities are also reported.
The measurements were undertaken to assist in an understanding of the action of rain, both real and artificial, in eroding soil. The drop‐sizes of rains have also been measured and will be reported separately. All of these studies were carried out at the Hydraulic Laboratory of the National Bureau of Standards as a part of the work of the Soil Conservation Service.
The objective of this study was to develop a quantitative relationship between rangeland rock fragment cover and erosion. Rainfall simulation on field plots of two soil surface treatments and a naturally-occurring soil surface was used to produce data necessary to develop this relationship. The study was conducted on the 150 km**2 Walnut Gulch experimental watershed in southeastern Arizona. This watershed, operated by the Agricultural Research Service, USDA, is representative of millions of hectares of brush and grass rangeland found throughout the semiarid Southwest.
A rotating disk rainfall simulator was used to examine infiltration-runoff relations from selected rangeland sites as influenced by a soil-vegetation complex. The simulator assisted in quantifying infiltration rates for different management practices on different soil types. Infiltration was greater for brush dominated plots than for either grazed plots or grass plots without grazing. Antecedent soil moisture decreased infiltration rates. Crown cover was approximately twice as much on brush plots as on grass plots and significantly influenced infiltration.
The effectiveness of various mulch materials and their rates of application on reducing soil erosion was examined. Eleven mulch treatments were applied to a Hagerstown silty clay loam soil on a two percent slope located under a rotating disc rainfall simulator applying rain at 135 mm/h. The treatments included straw at two rates, two sizes of bark chips, three commercially available materials and two sizes of rocks, all of which were compared to a fallow or no mulch treatment. The presence of the mulch treatments influenced the depths of runoff, the sediment concentrations and the erosion rates observed during the 10-min rainstorm events. (Edited author abstracts)
Highlight: Effects of pitting and rootplowing on surface runoff were determined on a desert shrub range in southeastern Arizona, and the time-dependent changes in the soil surface characteristics resulting from these practices were studied. Additional detention storage was provided by increased roughness in microtopography, thereby decreasing surface runoff when compared to the control. Rock and gravel were negatively correlated with surface runoff. Combining the two parameters showed a significant reduction in surface runoff. Increases in runoff were associated with exposed soil. Crown cover significantly reduced runoff. Litter was not significant in the reduction of runoff. Regulation of surface runoff is important for on-site rangeland improvements as well as reducing sediment yields. In arid and semiarid regions, rainfall is insufficient and distribution uncertain for maintaining vegetation that adequately protects the soil. Ranchers often try to convert the sparse vegetation, often not suited for grazing, to a more desirable plant species. To manage these critical rangelands for maximum productivity, it is important to know which factors control water yield. Many factors affect soil water yield, like storm intensity, watershed size, and soil surface characteristics. Rowe and Reimann (1961) also listed as important factors soil depth and water storage capacity, rainfall amount and distribution, and the type of vegetation, before and after site conversion.
In the no n-irrigated material the compaction affects t he iJ1ternal aggregate struc-ture at a well defined moisture level. In ti,e irrigated material it is shown that the successive irrig:aiol1s alld (Icssications have comple te l Y lIlodi (i ed tlte struc ture of the elelllentary aggregates by compactin g them up to an 011 III os t complete saturation (rolll approx im ately 20 % moisture conte nts . The behaviou r towards t he compaction o f the clayey material s irri gated for about 15 years indicates d,at this material has physical properties which are differ-ent from the non -irng;:lled soils. This phenomenon is due to the important compac-tion (o f the el emental Y aggregates) before the test was made . The in itial reason for this compaction remains however to be detennined. tOll PEDOLOGIE , XXX I/I , 1, p. 77-89,3 tab., 7 fig. Ghent 1983 A vesicul ar layer from North Patagon ia (Argentina) is described. After destruc-tion of the structure by sieving, the same material is subjec t to seve ral cy cles of wettin g and drying and to simulated rai nfall experiments. After 5,10,20 and 30 cycles thin sections are prepared of the undisturbed sam ples and evaluated micro-morph ological ly. For the micromorphometric analyses a Summagraphks digitizer , I in inte rface with a table computer Hewlett Packard 85 is used . The image of the thin section is projec ted o n the magnetic table by a mi croscope. This method proved to be preci se and relatively fast, compared to whole manual methods. The vesic ul ar st ru cture is recomposed after 5 cycles o f wettin g and drying and il takes 20 to 30 cycles to obtain gradually the ge neral appearan ce of the natural Av horiz on . This process is characteri zed by an increase o f the number, total area, size and sphericity o f th e vesicles. The platy structure is determined by fissures interconnecwlg large vesicles.
Simulated rainfall was used to study infiltration rates and sediment production of 28 plant communities and soils of five watershed areas in central and eastern Nevada. Two antecedent moisture conditions were used: soil initially air dry and initially at field capacity. Infiltration rates and sediment production of the various soils are largely controlled by extent and surface morphology of dune interspace soils. Vesicular horizons are unstable in dune interspace surface soils. These horizons seldom occur in coppice dunes or in well-aggregated dune interspace soils. Infiltration rate is negatively related, and sediment production positively related to the occurrence and morphology of vesicular horizons. More sediment is produced from soils with antecedent moisture initially at field capacity than from initially dry soil because of the instability of vesicular horizons when the soils were saturated.
AbStIWt The objective of tbis research was to determine the effects of selected vegetation, soil, rock, and slope variables on lnflltration of semiarid rangelands with slope gradients ranghtg from g-70%. Analyses were made on 2 sets of data collected a year apart in the Guadalupe Mountains of New Mexico and consisted of Pearson and partial correlation analysis of the dependent infiltration vari- ables and independent site variables. In addition, htfiltratioa was regressed against uncorreiated factors produced by factor analysis. Vegetal cover and biomass strongly ifiuenced infiltration. The relative importance of grasses, shrubs or litter was dependent on their respective abundance, especially grass. Soil depth also limited infiltration especially as soil water storage became satisfied. Infil- trability was negatively correlated with rock cover and the smallest rock size fragments were the most negatively related. When the effects of vegetal cover and slope were removed (using partial correiation analysis) however, the median sized rock fragments (26-150 mm) were positively related to infiltrabiiity, and the smai- lest rock fragements (2-12 mm) were negatively related. Partial correl8tion analysis also suggested 8 positive correlation between htfiltrabigty and slope gradient.
Infiltration into the soil is regulated in part by sealing of the soil
surface by raindrop impact. Soil surfaces protected from such impact
maintained higher rates of infiltration than exposed soil surfaces. It
was hypothesized that the cover particles protected the covered portion
of the soil and prevented the reaction of raindrop impact on the soil
state. The soil under the cover particles remained in the original state
in which infiltration could occur. However, since the cover particles in
this study were impervious, infiltration could not occur on the covered
area but would occur along the available perimeter of the cover
particles. Water would then move in both vertical and lateral
directions. The effective lateral distance that the water moved after
entry was defined as the effective width. To evaluate the effects of
soil surface cover on the infiltration rate of soils exposed to raindrop
impact, simulated rainfall was applied at a constant rate to one soil
type in small plots with free drainage, and square and rectangular cover
particles of varying sizes and percentages were used as surface cover.
The study described was made to evaluate the effect of various amounts of slaty fragments on the surface on soil erosion by water and relate these results to the universal soil loss equation.
Runoff was measured on soils during rains applied with a rainfall simulator in the laboratory. These soils were dried and rained on again and this sequence was repeated several times with runoff measured during each rain. The texture providing maximum runoff consisted of high sand contents (50 to 80%). Higher percentages of clay and silt resulted in surface cracking and considerable infiltration through those cracks.
Marked increases occurred in runoff due to NaCl treatments and decreases occurred due to CaSO 4 treatments. Since the amounts of the salts required was small (244 to 896 kg/ha) and the cost of these salts is low (approximately $1.00/50 kg in bulk), emergency water control of bare surfaces using salt treatments appears to be economically feasible.
The influence of the coarse material in Caribou and Thorndike soils on infiltration, runoff and erosion was studied with the use of a laboratory infiltrometer which applied water at 2.5 inches per hour but with energy of impact appreciably less than that in natural rain of the same intensity. Various sized coarse particles were removed from both soils to determine the function of the coarse fraction. There was a significant decrease in the rate of infiltration and likewise an increase in runoff as the particles > 12.7 mm. were removed from both soils. A further decrease in infiltration resulted when all material > 4.76 mm. was removed; however, the fraction between 4.76 mm. and 2.38 mm. did not have a significant effect on infiltration and runoff.
The amount of soil in the runoff from the Caribou sample was found to be nearly proportional to the runoff. It also increased with runoff as the coarse fractions were removed from the Thorndike soil, but there was not a significant increase for the second and third trials on the same sample even though the runoff increased. Some of the practical implications of the coarse fraction are discussed in relation to land use and the possible removal of coarse material for increased mechanization of farming operations.
A knowledge of the spatial distribution of infiltration rates is essential to the application of realistic, distributed rainfall-runoff models in semiarid areas. One method of determining this distribution is to develop a predictive equation based on a readily observable surface property, such as stone cover. Previous studies of the relation between infiltration and stone cover on shrub-covered semiarid hillslopes have yielded both positive and negative correlations. It is suggested that positive correlations result where infiltration measurements are confined to areas between large shrubs. Negative correlations, on the other hand, reflect pronounced shrub-intershrub differences in infiltration and stone cover and are found where both shrub and intershrub areas are sampled.
Soil and water losses from plots representing field areas between rills were studied for four rates of straw mulch at four slope steepnesses. Three simulated rainstorms totaling 2 hours at 6.4 cm/hour were applied to a 61‐ by 61‐cm test area of Russell silt loam soil.
Interrill erosion was reduced about 40% by mulch applied at a rate of only 0.5 metric tons/ha and about 80% by 2 tons/ha, as compared with no mulch. Erosion was negligible at the 8 tons/ha rate. Soil losses from the interrill areas at 20% slope were only about double those measured at 2% slope, whereas widely used erosion equations show that total field erosion would increase about 20‐fold over this range of steepnesses.
Water loss by runoff was independent of slope steepness, but it was slightly reduced by mulch at a rate of 2 tons/ha and was greatly reduced by the 8 tons/ha rate. After 40 minutes of rainfall, sealing of the soil surface by raindrop impact had reduced infiltration rates for treatments with 0 to 2 tons/ha of mulch to only 20% of those with 8 tons/ha.
The purpose of the ordinance is to control erosion and production of sediment, and related environmental damage by establishing minimum standards and providing regulations for the construction and maintenance of land fills, excavations, cut and clearing of vegetation, revegetation of cleared areas, drainage control, as well as for the protection of exposed soil surfaces in order to promote the safety, public health, convenience, and general welfare of the community.
A digital computer model of basin regime was developed for the Negev Desert Highlands, a region which experiences a mean annual rainfall of about 100 mm. The model was based on 13 years of rainfall and runoff records. Relationships obtained from experiments were used to determine areal distribution of rainfall, infiltration rates of soils, effects of slope angle on runoff, stone cover, rainfall intensity, antecedent rainfall, basin size, soil crust, overland flow and channel losses. These relationships also explain how ancient civilizations were able to collect ample water from small basins in order to establish stable agricultural settlements. Résumé On a développé pour cette région un modèle à calculatrice numérique pour le régime du bassin versant. C'est une région qui subit à une précipitation moyenne annuelle de vers 100 mm. On a basé le modèle sur les rapports de précipitation et d'écoulement faits pendant 13 ans. On a utilisé les rapports obtenus des expériences pour déterminer la répartition sur aire, les taux d'infiltration des sols, les effets de pente sur l'écoulement, couverture de pierre, intensité de la pluie, pluie antécedente, grandeur du bassin versant, croÛte de sol, ruisellement de surface et les pertes des cours d'eau. Ces rapports expliquent comment les civilisations anciennes pouvaient capter assez d'eau des petits bassins versants pour établir des colonies agricoles stables.
Terra-Rossa soils cover large areas in the mountainous regions of Israel. A representative area in the Carmel mountains was chosen to test the effect of slope, type of cultivation and stone cover on the quantities of surface runoff and erosion.Twelve terraces, each 3.5 m by 50 m, were constructed to test all combinations of 1%, 3% and 5% down slopes, and 5%, 9%, 12% and 17% cross slopes.A simulated rain storm was applied, which approximated the most hazardous 10-year storm in this region. The applied storm consisted of 86 mm of rain including 30 minutes of 76 mm/hr intensity. Average annual precipitation in the Carmel mountains is 500–700 mm.The range of runoff quantities obtained was 5 to 20 mm per storm, and the quantities of soil eroded ranged between 100 and 1,000 kg per hectare per storm (extreme values excluded).From the analysis of the results obtained during three seasons, it was found that for conditions similar to those prevailing in the study area:1. The maximum allowable down slope for areas with 15% or more stone cover may exceed 5%.2. The maximum allowable cross slope for such areas may exceed 15%.3. Shallow cultivation with an “Ard” (Arab) plough, is superior to cultivation methods leaving deep, fast draining furrows.4. Stone cover is a very effective means to reduce runoff and soil erosion.
Laboratory experiments using simulated rainfall, splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time‐dependent phenomenon. In all, ten different sediments ranging from silt (D 50 = 24μm) to coarse sand (D 50 = 593 μm) were studied. The effect of three different initial states of the sediments, namely the air dry state T1, the field capacity state T2, and the desiccated state T3, on the erodibility was also assessed.
Variations in detachability during a rain erosion experiment can be explained by change in water content (including liquefaction and the development of a water layer on the surface), cohesion, and granulometric composition of the top layer. The coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state, T2. For the finer sediments, the highest detachability was found for the homogeneous and not yet compacted initial air dry state, T1. The effect of the initial desiccated state T3 on the detachability of the finer sediments was also a function of the rainfall duration.
The relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators. The highest detachability was found for a fine very well sorted sand with a median grain size of 96 μm.
Previous works dealing with the influence of a stone cover on runoff yield showed that runoff, attributed to the sealing effect of the topsoil by raindrops impact, was negatively related to the per cent of stone cover and stone size. These works were conducted on gentle slopes (3–11·5 degree) with a per cent of stone cover generally lower than 50 per cent, and composed of gravels. The present study deals with the runoff yield of steep talus slopes (26–36 degree) whose per cent of stone cover is very high (90–100 per cent), composed of cobbles and boulders. Three stimulated rainstorms were performed at various rainfall. intensities and durations on each one of six plots representative of the North eastern sector of Sinai. Although the contiguous stony cover prevented surface sealing by raindrops impact, runoff developed quite quickly on most slopes, and reached at peak discharge, after approximately ten minutes, up to 56 per cent of the rainfall. Differences between plots, in time lag, peak discharge and other hydrological variables, could be attributed mainly to the properties of the upper stony layer, with stone size as the most influential factor. Contrary to previous works, a positive relationship, was obtained between stone size to runoff yield. The result is explained by the process of water concentration. Each cobble and boulder behaves, on a smaller scale, like a bare rocky surface and yields per unit area water amounts beyond the infiltration rate of the limited uncovered areas. For a given stony cover the effect of water concentration is quicker with the big blocks than with gravels. A series of graphs trying to relate theoretically the relative importance of sealing and water concentration processes in runoff generation, at various conditions of stone cover and stone size, is proposed. The graphs enable to reconcile the results of the present study with those of previous works.
The effect of repeated freezing and thawing cycles on an experimentally-produced laminated silt loam was studied with the purpose of obtaining more insight into the genesis of macro- and microstructures observed in the loessic formations of Northwestern Europe.
The laminated silt loam was subsequently subjected to 18 cycles of alternate freezing and thawing. The minimum temperature recorded after 11 days of frost was − 7°C at a depth of 5 cm and − 4°C at 29 cm. The underlying sediments, compact loam (except its upper part) and sand, always remained unfrozen. The experiment reproduced a seasonal superficially frozen ground.
New structures and microfabrics in the form of vesicles, platy structures, shear planes, and micro-undulations were created by ice segregation and thawing, mechanical stress and subsequent frost-creep. The impact of the freezing and thawing cycles is very strong, all the laminae being deformed or broken. Judging by the abundance and the diversity of the structures created, freezing is a more important process than simple drying without frost.
As is evidenced by the range in temperature chosen for the experiment and the low number of cycles, these structures do not necessarily require severe climatic conditions to develop, unlike frost cracks or ice wedge casts. They could develop in winter conditions similar to those present today in the French Southern Alps.
The influence of five different slope angles and two different positions of simulated stones in the top layer of a sandy and a silty sediment on surface sealing intensity is examined in the laboratory. Sealing intensity is assessed by studying changes of percolation rate through a sediment layer with simulated rainfall duration and by measuring cohesion of the 5 mm thick upper sediment layer, a measure of seal strength, by means of a torvane. Slope has a negative influence on sealing intensity. For a constant per cent of simulated stone cover, sealing intensity is lowest in the case of stones placed on the sediment surface compared to the case of stones pushed into the surface layer. Explanations for these findings are given and some implications are further discussed.
Accelerated pluvial erosion on hillslopes modified by off-road vehicles (ORVs) is analysed using results from 50 rainfall simulation experiments conducted in the Mojave Desert, California. Sediment yield from 1 m2 hillslope plots subjected to intense, 20-minute rainfalls is typically increased 10 to 20-fold following ORV use. Salient effects of vehicle traffic, which reduce infiltration, increase runoff sediment transport efficiency, and enhance gully formation, are further studied by combining simple theoretical relations with experimental data. This analysis helps identify factors controlling erosion on natural desert hillslopes, as well as those used by ORVs.
Erosion of natural or vehicle-used desert surfaces is heavily influenced by runoff hydraulics. Calculated Darcy-Weisbach friction factors decrease by an average of 13-fold following vehicular slope modification, whereas runoff Reynolds numbers increase by an average of 5 1/2-fold. The capacity of overland flow to transport sediment is related to runoff power and its degree of localization, which usually increase considerably following ORV activity; however, the ability of overland flow to move large grains (competency) is related to a combination of factors not always systematically influenced by ORV use. Kinematic runoff routing, which is used to extrapolate experimental results to longer slope lengths, leads to the suggestion that the hydraulic roughness of desert hillslopes strongly influences their erosional behaviour.
Des expériences de laboratoire ont été menées pour savoir si la relation entre la longueur de la pente et le volume de ruissellement hortonien par unité de surface de sol pourrait être expliquée par les phénomènes d'érosion et de sédimentation observés dans les parcelles correspondantes. La relation entre le volume de ruissellement par unité de surface de sol et la longueur de pente est complexe et fortement influencée par la formation d'une pellicule de battance, par le développement de rigoles et de têtes de rigoles ainsi que la formation de dépôts de pente. Les modèles hydrologiques, ayant comme but de prédire le débit de ruissellement le long d'un versant, doivent être orientés en partie par un modèle d'érosion et de sédimentation.
Infiltration rate as affected by soil surface crusting caused by rainfall', in CallebautThe effects of surface slaty fragments on soil erosion by water
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Estudio de costras de deposito. Desarrollo de un protocolo experimental para su formacion, y primeros resultados de la medida de la infiltrabilidad del agua
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