Influence Of Slope Gradient Research Articles

The Influence of Slope Gradient on Termite Assemblages and Soil Physico-Chemical Properties in Koudi Secondary Forest Patches of the Central Region of Cameroon

Soil is the Cameroon’s primary economic driver and an indispensable natural resource for agriculture. Various factors including physical, chemical and biological directly affect agricultural production by enhancing soil fertility. The influence of relief on termites’ diversity was extensively studied. However, the effect of the slope gradient on termite diversity and functional groups remains less studied. This study evaluated termite assemblages in relation to some edaphic parameters, with emphasis on gradual changes in soil slope. The study was conducted in Koudi, in the semi-deciduous forest zone of Southern Cameroon. The study aimed to evaluate the effect of slope gradient on termite diversity and some soil physico-chemical factors; the influence of some physico-chemical soil properties on termites. To achieve these, three slope gradients: gentle slope: A [0 - 15°]; moderate slope: B [15.1°- 31°]; and steeper slope: C [x > 31°[were chosen. The experimental design was composed of 66 rectangular quadrants of 5m x 2m in order to determine the presence or absence of termites. Two soil samples were taken per slope gradient for the determination of physico-chemical parameters. Termite community was characterized using species richness, Shannon diversity, Pielou Evenness and Simpson dominance indexes. Data obtained were subjected to Spearman correlation test and ANOVA followed by the Tukey HSD test at a threshold p = 0.05. Our findings suggested thirty-five(35) termite species belonging to eighteen (18) genders, six (6)subfamilies that were sampled and identified. Termites’ diversity and species richness decreased as slope gradient increased; slope gradient displayed a significant detrimental correlation with sand (%) and total organic (g/kg) content, with a positive significant correlation with clay (%) content, according to Spearman's test. It appeared that variations of slope at soil surface have been identified as one of the factors controlling nutrients and termite diversity.

The influence of slope gradient and gully channel on the run-out behavior of rockslide-debris flow: an analysis on the Verghereto landslide in Italy

Rockslide-debris flow may cause catastrophic damages because of its high speed and long run-out distance. The influences of slope gradient and gully channel on the entrainment, deposition, and run-out behavior of this type of landslide were not sufficiently investigated by previous studies. To achieve a better understanding toward this type of landslide, a recent rockslide-debris flow that occurred in the Northern Apennines of Italy is studied through field investigation and numerical simulation. The run-out process of this landslide is simulated by an improved depth-averaged model, paying special attention to analyzing the influence of slope gradient and gully channel. The simulation results are compared with the detailed field data of entrainment and deposition distributions. It shows that the depth-averaged model can reasonably simulate the entrainment and deposition characteristic of this landslide by adopting different basal friction strengths for the rockslide region and debris flow region. Entrainment occurs in both high and low slope gradient zones. However, entrainment can only be observed in the high slope gradient zones, while in the low gradient zones, the post-failure topography shows accumulation and deposition. The simulation results also demonstrate that the presence of a gully channel is a key factor in determining landslide mobility and run-out distance. In comparison to a landslide with similar size and geological settings but without a gully channel, the run-out distance is much less, and the landslide does not develop into a flow.

Influence of Slope Gradient and Aspect on Soil Organic Carbon Content in the Region of Niš, Serbia

Topography-induced microclimate differences determine the local spatial variation of soil characteristics as topographic factors may play the most essential role in changing the climatic pattern. The aim of this study was to investigate the spatial distribution of soil organic carbon (SOC) with respect to the slope gradient and aspect, and to quantify their influence on SOC within different land use/cover classes. The study area is the Region of Niš in Serbia, which is characterized by complex topography with large variability in the spatial distribution of SOC. Soil samples at 0–30 cm and 30–60 cm were collected from different slope gradients and aspects in each of the three land use/cover classes. The results showed that the slope aspect significantly influenced the spatial distribution of SOC in the forest and vineyard soils, where N- and NW-facing soils had the highest level of organic carbon in the topsoil. There were no similar patterns in the uncultivated land. No significant differences were found in the subsoil. Organic carbon content was higher in the topsoil, regardless of the slope of the terrain. The mean SOC content in forest land decreased with increasing slope, but the difference was not statistically significant. In vineyards and uncultivated land, the SOC content was not predominantly determined by the slope gradient. No significant variations across slope gradients were found for all observed soil properties, except for available phosphorus and potassium. A positive correlation was observed between SOC and total nitrogen, clay, silt, and available phosphorus and potassium, while a negative correlation with coarse sand was detected. The slope aspect in relation to different land use/cover classes could provide an important reference for land management strategies in light of sustainable development.

Influence of Slope Gradient on Coffee Soil Fertility in Goma Woreda of Oromia Region

Influence of Slope Gradient on Coffee Soil Fertility in Goma Woreda of Oromia Region

Evolution of rock cover, surface roughness, and its effect on soil erosion under simulated rainfall

The dynamic interaction between erosion, surface morphology and flow hydraulics, causes steeper slopes to develop greater physical and hydraulic roughness, such that the slope can evolve toward a state of equilibrium wherein runoff velocity is independent of slope gradient. This study tests, under controlled condition, the hypothesis that erosion rate may also evolve toward a state wherein erosion rate is uniform across slope gradients after slope-velocity-equilibrium is established. A series of rainfall simulations (intensities of 59 and 178 mm hr−1) were conducted on 2 m by 6.1 m stony soil plot under three slope treatments (5%, 12% and 20%, replicated) with surface elevation, rock cover, flow velocity and sediment measurements. The results showed: 1) rock cover, and both surface physical (random roughness) and hydraulic roughness (Darcy–Weisbach friction) increased as rainfall progressed, leading to reductions in flow velocities and soil loss rates; 2) steeper slopes developed greater surface physical and hydraulic roughness; 3) the final soil loss rates ranged from 0.87 to 1.28 g min−1 m−2, and from 5.36 to 16.01 g min−1 m−2, which were approximately 6% to 15% of the initial maximum values, under low and high rainfall intensity, respectively; 4) soil loss rate was inversely correlated with rock cover while exhibiting no correlation with the random roughness index; 5) the linear coefficient of slope gradient relative to erosion rate measured on the most evolved surface were only 6.5% and 7.3% of those on initial surfaces under low and high rainfall intensity, respectively, implying that erosion rate evolved toward being less sensitive to slope gradient than it would otherwise be; 6) flow velocity and effective shear stress were found to be appropriate predictors for soil loss rate. This study supports the hypothesis of erosion equilibrium, implying that erosion rate decreases as a function of erosion pavement and that influence of slope gradient on soil erosion declines due to the dynamic interactions between soil erosion, surface morphology, and flow hydraulics.

Probability analysis of submarine landslides based on the Response Surface Method: A case study from the South China Sea

As deep-sea engineering develops, it becomes essential to analyze the stability of submarine slopes when considering the stability of submarine foundations or evaluating the safety of offshore structures. However, the traditional method for analyzing slope stability does not give adequate consideration to the uncertainty of soil properties, and so the reliability method has been proposed and used to settle the variation of soil parameters. Regarding the northern slope of the South China Sea, the present paper summarizes its geomorphic features, seismic characteristics, and the soil strength at certain boreholes. A typical slope section is chosen with which to conduct probability analysis using the polynomial-based Response Surface Method (RSM) and the Advanced First Order Second Moment method(AFOSM). A novel form of the RSM based on Gaussian Process Regression (GPR) is also proposed and applied in this case to approximate the limit state function, and its efficiency is confirmed. The simulation results of Latin-hypercube analysis are set as the benchmark for the other methods. The influences of slope gradient and seismic action on the stability of submarine slopes are also investigated.

Influence of slope gradient on the behavior of saltating sand particles in a wind tunnel

Current theoretical and experimental studies of windblown sand movement are mostly conducted on flat sand surfaces. However, sand dunes, basic forms of desert landscapes, have slope gradients that greatly influence the transportation of sand particles. In this study, sand velocity on the windward and leeward slopes of barchans dunes was measured using a laser Phase Doppler Particle Analyzer in a wind tunnel. Our results measured from slope are quite different from existing data of flat surface. The average velocity of sand particles increased from bottom to top of the windward slope. And the particle velocity on leeward slope is not greatly impact by position and wind speed. Unlike exponential decay on flat bed, the lift-off angle on windward slope shows left-skewed distribution with a single peak, and the distribution of impact and lift-off angle on leeward slope are entirely different from those obtained on flat bed. On the leeward slope, impact and lift-off angle were affected remarkably by the position on the slope. On the leeward slope, the number of particles with wind direction horizontal velocity is basically the same as those of particles with headwind direction horizontal velocity. The vertical and horizontal turbulence intensity reached the maximum when the particles were located 20mm from the bed surface near the bottom of leeward slope; and the minimum at 60mm from the bed surface. Both vertical and horizontal turbulence intensity of particles increased with increasing wind velocity. The increase in the horizontal turbulence intensity was greater than the increase in the vertical turbulence intensity. The findings from this study would provide a better understanding of movement of blown sands over sand dunes and mechanism underlying the formation of sand dunes.

Analysis of Impact of Terrain Factors on Landscape-scale Solar Radiation

Incident solar radiation is one of the major sources of energy for driving biological and physical processes on earth. In this paper, simple conversion factors are designed to determine how the four landforms (i.e. plain, plateau, hill and mountain) will affect incident solar radiation at one month intervals using the ArcGIS tool appropriate for regional solar radiation analysis. A comparison is made between simulation results and those measurements taken in actual radiation stations, providing a correlation R 2 of 0.9063. Results indicate first, that if the ratio of the monthly mean of the DEM-based regional solar radiation to the monthly mean of the hypothesis DEM-based regional solar radiation is defined as the conversion factor (R) of the solar radiation and the ArcGIS tool for regional solar radiation analysis is employed, then the computation can be simplified and the impact of terrain factors on incident solar radiation can be correctly represented. Secondly, with each of the four landforms, R varies according to the season, slope gradient and aspect; the season induces more impacts than the terrain factors; R increases first and then decreases when the aspect changes clockwise, but decreases continuously with an increase in slope grade; R varies in a complex way in the case of mountains, especially for grade-five slopes. Thirdly, R increases initially and then decreases in a sinusoidal manner with an increase in aspect under the influence of slope gradient during the winter; R varies in a linear and somewhat symmetric manner (monotone increasing, monotone decreasing and stable) with the increase in slope gradient and under the influence of the aspect. These results are helpful in studying the impact of terrain factors of different landforms on incident solar radiation on the landscape scale using the simple conversion factors.

Rainfall intensity and slope gradient effects on sediment losses and splash from a saline–sodic soil under coastal reclamation

Rainfall intensity and slope gradient play important roles in soil erosion processes. This study was conducted to investigate the effects of rainfall intensity and slope gradient, as well as of their interactions, on splash and overland flow transport on saline–sodic soil slopes. Rainfall intensities of 85, 95, 110 and 125mmh−1 were applied to slope gradients of 6°, 11°, 22° and 35°. Splash was partitioned into four directional components. Runoff, sediment and splash samples were collected throughout the rainstorms and infiltration was calculated. The final infiltrations under the lower rainfall intensities of 85mmh−1 were the largest for every slope gradient, but they decreased by 39.3% as the slope gradient increased from 6° to 35°. However, the final infiltration rates exhibited an increasing–decreasing trend for rainfall intensities higher than 85mmh−1 as the slope gradient increased. The critical slope gradient was about 11°. The influence of rainfall intensity on runoff was considerably reduced at the higher slope gradients due to increased infiltration. The influence of slope gradient on sediment loss was reduced as rainfall intensity increased, while the effect of rainfall intensity on sediment losses was greater on the gentler slopes than on the steeper slopes. The upslope splash (mean value) initially increased from 4.8 to 7.2gm−1h−1 before it decreased to 3gm−1h−1 as the slope gradient increased. The maximum measured value occurred when the slope gradient was 22°. Total splash increased to maximum levels as the slope gradient increased to 11°, but decreased with further increases in gradient. These results indicated that the effects of slope gradient and rainfall intensity on sediment losses, runoff and splash were interconnected.

Influence of Slope Gradient on Distribution Rule of Geostress Field in River Valleys

During the construction of hydropower station, the change of slope gradient in river valleys often takes place. In order to study influence of slope gradient change on distribution rule of geostress field, the three dimensional unloading models under different slope gradients were established by finite difference software (FLAC3D). After numerical simulation, the results were as follows: (1) The phenomenon of stress concentration at the bottom of river valleys was obvious, which appeared the typical stress fold. Both the depth of stress concentration zone and the principal stress values significantly increased with the increment of slope gradient. (2) Maximum principal stress values increased less in shallow part of upper bank slope (low stress zone) but increased more in the nearby slope foot with the increment of slope gradient, causing great difference in geostress field of bank slope. (3) There was some difference in released energy of bank slope due to slope gradient change in river valleys. In order to distinguish the difference, stress relief zone was further divided into stress stably released zone and stress instability released zone. Finally, take Ada dam area of the western route project of South-to-North Water Transfer as an example, the results by numerical simulation were reliable through comparing the distribution rule of geostress field for the dam, which could provide important reference for stability of the design and construction of steep and narrow river valleys.

Influence of rocky slope gradient on root anchorage of Vitex negundo L.

Root anchorage adds stability to rocky slopes because the roots penetrate the shallow soil and extend into fractures in the bedrock. The influence of slope gradient on root anchorage has, however, rarely been investigated. Direct observation and pull-out tests in the field were used to investigate several root anchorage characteristics in 11-year-old Vitex negundo L. growing in three rocky slope conditions with varying gradients: low (29°), moderate (41°), and high gradient (53°). The results show that high- and moderate-gradient slopes in particular affect root anchorage resistance by increasing the tensile strength as well as the number and diameter of secondary upslope lateral roots that grow into the fractures. The upslope lateral roots contributed to anchorage to a greater extent than the downslope lateral roots. The contribution of upslope lateral roots to anchorage was 83% on high-gradient slopes, approximately 78% on moderate-gradient slopes, and 72% on low-gradient slopes. The conclusion of the study is that slope gradient is positively related to the distribution and anchorage of V. negundo L. on rocky slopes.

SOIL DETACHMENT BY SHALLOW FLOW

A precise understanding of soil detachment rates is necessary to establish a basic understanding of soil erosionand to develop a fundamentally based erosion model. This study was conducted to investigate the relationships between soildetachment rates and flow discharge, slope gradient, flow depth, mean flow velocity, shear stress, unit stream power, andstream power. A 5m long
0.4m wide hydraulic flume with constant artificial roughness upstream of and surrounding thesample area was used. Flow discharge ranged from 0.25 to 2.0 L s 1 and slope gradient varied from 3.5% to 46.6%. Theexperimental results indicated that detachment rates increased with both greater flow discharge and slope gradient.Detachment rate was affected more by discharge than by slope gradient. The influence of slope gradient on detachment ratewas greater at high slopes. The effect of flow depth on soil detachment rate was also dependent on slope gradient. Stepwisevariable selection analyses indicated that detachment rate could be predicted by a power function of discharge and slopegradient (R 2 = 0.97). Substituting flow depth for discharge gave a poorer prediction (R 2 = 0.92). Mean flow velocity was moreclosely correlated to detachment than was any other hydraulic parameter (r 2 = 0.90). Flow detachment rates were bettercorrelated to a power function of stream power (r 2 = 0.89) than to functions of either shear stress or unit stream power. Theresults of this study suggest that soil detachment by shallow flow is more closely related to flow energy than to shear stress.

Mound development as an interaction of individual plants with soil, water erosion and sedimentation processes on slopes

In the Mediterranean region, semi-natural shrubland communities (named ‘matorral’) often present a discontinuous cover, where isolated perennial plants alternate with bare inter-plant areas. In such ecosystems, the patchy distribution of the vegetation is usually associated with microtopographic sequences of mounds that develop under isolated plants and break the overall slope continuity. In this study, the influence of three representative species of the Mediterranean matorral (Rosmarinus officinalis, Stipa tenacissima and Anthyllis cytisoides) on slope microtopography is determined and the processes that take part in the development of microtopographic structures beneath the plant canopy are identified. The influence of slope gradient, plant species and plant parameters on the shape and height of microtopographic structures is also studied. The shape of the microtopographic structures is described by using a two-dimensional microprofilemeter and mound height is determined by measuring in the field a ‘mound height index’ defined as the distance from the top to the bottom of the mound. The results obtained show that plant species play a major role in the shape and height of the microtopographic structures. Whereas terrace-type structures generally develop under Anthyllis shrubs, microtopographic forms associated with Rosmarinus and Stipa plants vary with slope gradient. The almost symmetric mound-type structures that develop under these two species on gentle slopes change into terrace-type structures as slope gradient increases. Moreover, statistically significant differences exist between the three species with regard to mound height. Mean values of mound height are 19·4, 14·6 and 4·3 cm under the canopy of Stipa, Rosmarinus and Anthyllis respectively. Plant parameters, essentially roughness, and slope gradient have a significant influence on mound height index. Four main processes were identified as affecting mound development in the studied field site: sedimentation, differential interrill erosion, differential splash erosion and bioturbation. Plant species interact in different ways with these processes according to their morphologies. Since Stipa and Rosmarinus plants are more efficient than Anthyllis shrubs in controlling water erosion, in retaining sediments and in modifying soil properties under their respective canopies, they give rise to higher microtopographic structures that facilitate water and nutrient storage by plants on slopes. Copyright © 2000 John Wiley & Sons, Ltd

The relationship of soil loss by interrill erosion to slope gradient

The influence of slope gradient on erosion rate differs for rill and interrill conditions. Rill erosion increases substantially more with increasing slope gradient than interrill erosion. Combining the two erosion processes into single data sets led to the development of regression equations (e.g., USLE) that overestimated the effect of slope gradient on erosion rate for low slope gradients and short slopes. This study investigated the change in interrill erosion rate with slope gradient and examined its relationship to runoff velocity. A sandy loam (grey brown luvisol) was packed in 100×40×10 cm 3 soil trays and subjected to simulated rainfall for a period of 75 min. Rain-impacted flow erosion and downslope splash were monitored, and runoff velocity measurements were made at three positions within the flume. Downslope splash erosion never accounted for more than 20% of the total erosion. Rain-impacted flow erosion peaked early in the simulation then decreased to a constant rate; erosion rate was therefore probably detachment-limited. For a constant runoff rate, rain-impacted flow erosion increased roughly with the square root of slope gradient, as did the runoff velocity. Soil loss was correlated (0.81) with runoff velocity under the experimental conditions.

STABILITY EVALUATION OF REINFORCED EMBANKMENTS BY CENTRIFUGE EXPERIMENT

As to an embankment reinforced with extensible materials like geogrids, reinforcement effect appears with deformation occurring in the embankment. In order to evaluate the actual stability of reinforced embankments, it is necessary to take account of the embankment deformation, In this paper, the influence of slope gradient and reinforcement length on the failure mode and the failure height of embankments on hard ground was investigated by centrifuge model tests. As a result, in case that the slope gradient is steep, slip surface approximately becomes plane. Also, it was found that the embankment deformation increasing with the gravitational acceleration could be expressed by a method with consideration for deformation.