Eco-geotechnical engineering plays a pivotal role in enhancing global sustainability and upholding the perfor-mance of earthen structures.The utilization of vegetation to stabilise geotechnical infrastructures is wide...Eco-geotechnical engineering plays a pivotal role in enhancing global sustainability and upholding the perfor-mance of earthen structures.The utilization of vegetation to stabilise geotechnical infrastructures is widely recognized and embraced for its environmentally friendly attributes.The spectre of climate change further in-tensifies the focus on the effects of temperature and humidity on vegetated soil.Consequently,there is a pressing need for research exploring the influence of changing climates on vegetated infrastructures.Such research de-mands a holistic and interdisciplinary approach,bridging fields such as soil mechanics,botany,and atmospheric science.This review underscores key facets crucial to vegetated geotechnical infrastructures,encompassing climate projections,centrifuge modelling,field monitoring,and numerical methodologies.展开更多
The hydro-mechanical responses of vegetated deposited slopes are complex and far from clear.On one hand,the soils in deposited slopes are typically poorly consolidated and widely graded,making them vulnerable to inter...The hydro-mechanical responses of vegetated deposited slopes are complex and far from clear.On one hand,the soils in deposited slopes are typically poorly consolidated and widely graded,making them vulnerable to internal erosion during rainfall infiltration.On the other hand,vegetation plays a significant role in influencing the hydro-mechanical properties of the soil at the slope surface.This paper presents a coupled seepage-erosion model to investigate the rainfall-induced internal erosion process within vegetated deposited slopes and its impact on slope stability.The detailed seepage-erosion coupling processes were simulated for a series of 1D rooted soil columns with varying root distributions,as well as 2D vegetated layered slopes under both light and heavy rainfall conditions.The numerical results reveal that roots can significantly mitigate rainfall-induced internal erosion,even with shallow root lengths.However,their protective effect on the slope increases as the root density in the superficial soil layer increases.Transpiration can rapidly restore matric suction in the shallow soil during rain intervals,slowing the rainfall-induced seepage-erosion process and thereby increasing slope stability.However,in the absence of transpiration,roots may either accelerate or inhibit the seepage-erosion process,depending on the specific rainfall conditions.展开更多
The objective of this study is to explore how different layer thicknesses affect the desiccation cracking behaviour of vegetated soil.During the experiment,an electronic balance was employed to quantify water evaporat...The objective of this study is to explore how different layer thicknesses affect the desiccation cracking behaviour of vegetated soil.During the experiment,an electronic balance was employed to quantify water evaporation,while a digital camera was utilized to capture the initiation and progression of soil surface cracking.Results indicate that in the early drying process,the rate of evapotranspiration in vegetated soil correlates positively with leaf biomass.For soil samples with the same layer thickness,the constant rate stage duration is consistently shorter in vegetated soil samples than in their bare soil counterparts.As the layer thickness increases,both vegetated and bare soil samples crack at higher water content.However,vegetated soil samples crack at lower water content than their bare soil counterparts.Vegetation significantly reduces the soil surface crack ratio and improves the soil crack resistance.The crack reduction ratio is positively correlated with both root weight and length density.In thicker vegetated soil layers,the final surface crack length noticeably declines.展开更多
Vegetation in slopes can effectively improve slope stability.However,it is difficult to estimate the effects of vegetation on slope stability because of variations in plant species and environmental conditions.Moreove...Vegetation in slopes can effectively improve slope stability.However,it is difficult to estimate the effects of vegetation on slope stability because of variations in plant species and environmental conditions.Moreover,influences of plant growth on slope stability change with time,resulting in changes in the safety factor.This study was conducted to evaluate the stability of vegetated slopes with time and investigate the effects of different layouts of plant species on slope stability.Here,we used a plant growth model and slope stability analysis to build an evaluation model.To accomplish this,one species of tree,shrub and grass was chosen to set six layout patterns.A slope with no vegetation served as a control.The safety factors of the seven slopes were then calculated using the developed evaluation model and differences in the safety factors of slopes were compared and discussed.The slope vegetated with Platycladus orientalis reached the most stable state at the age of 60 years.Shrub slope(Vitex negundo)had the maximum safety factor after 20 years.Overall,the safety factor of vegetated slopes increased from 12.1%to 49.6% compared to the slope with no vegetation.When wind force was considered,the safety factor value of the slope changed from 3.5%to 43.5%.Vegetation mixtures of trees and grasses resulted in the best slope stability.Planting grasses on slopes can improve slope stability of trees to a greater degree than that of slopes with shrubs in the early stage of growth.展开更多
The existence of vegetation plays an important role to protect the ecosystem and water environment in natural rivers and wetlands, but it alters the velocity field of flow, consequently influencing the transport of po...The existence of vegetation plays an important role to protect the ecosystem and water environment in natural rivers and wetlands, but it alters the velocity field of flow, consequently influencing the transport of pollutant and biomass. As a pre-requisite for the analysis of environmental capacity in a channel, the vertical velocity distribution of flows has attracted much research attention;however, there is yet lack of a good prediction model available. For the channel with submerged vegetation, the vertical velocity distribution in the lower vegetation layer will be different from that in the upper flow layer of non-vegetation. In this paper, after review on the most recent two-layer model proposed by Baptist et al., the author has proposed an improved two-layer analytical model by introducing a different mixing length scale (λ). The proposed model is based on the momentum equation of flow with the turbulent eddy viscosity assumed as a linear relationship with the local velocity. The proposed model is compared with the Baptist model for different datasets published in the literature, which shows that the proposed analytical model can improve the vertical velocity distribution prediction well compared with the Baptist model for a range of data. This study reveals that the λ is well related with the submergence of vegetation (H/h), as suggested by . When the constant β is taken as 3/100, the proposed model shows good agreement with a wide range of datasets studied: flow depth (H)/vegetation height (h) in 1.25 to 3.33, different vegetation densities of a in 1.1 to 18.5 m−1 (a defined as the frontal area of the vegetation per unit volume), and bed slopes in (1.38 - 4.0) × 10−3.展开更多
The construction of an integrated numerical model is presented in this paper to deal with the interactions between vegetated surface and saturated subsurface flows. A numerical model is built by integrating the previo...The construction of an integrated numerical model is presented in this paper to deal with the interactions between vegetated surface and saturated subsurface flows. A numerical model is built by integrating the previously developed quasi-three-dimensional （Q3D） vegetated surface flow model with a two-dimensional （2D） saturated groundwater flow model. The vegetated surface flow model is constructed by coupling the explicit finite volume solution of 2D shallow water equations （SWEs） with the implicit finite difference solution of Navier-Stokes equations （NSEs） for vertical velocity distribution. The subsurface model is based on the explicit finite volume solution of 2D saturated groundwater flow equations （SGFEs）. The ground and vegetated surface water interaction is achieved by introducing source-sink terms into the continuity equations. Two solutions are tightly coupled in a single code. The integrated model is applied to four test cases, and the results are satisfactory.展开更多
The transport and deposition of particulate organic matter (POM) in river streams has recently received much attention as one of important ecological processes in rivers. We focused on interacted behaviors of sand par...The transport and deposition of particulate organic matter (POM) in river streams has recently received much attention as one of important ecological processes in rivers. We focused on interacted behaviors of sand particles in bed load and POM in vegetated area on sand bars. The purpose of this study is to clarify the characteristics of deposition of POM with bed load on sandbars with the riparian vegetation. A basic experiment on POM transport and deposition with vegetation is conducted in a laboratory flume. It demonstrates that several issues still remain to be future investigated. In particular, the shear due to the bed roughness in the vegetated area and the transport and deposition process of sand particles and POM are required to be described by the proper modeling which will be introduced into a simulation model of various fluvial processes. The main results of this study are that ripples are formed by bed load in riparian vegetation and POM deposition is promoted by ripple behavior. Based on these results, the POM deposition with ripples in vegetated area is described by a conceptual model which will affect various aspects in ecosystem management based on fluvial processes.展开更多
This paper analyzed the temporal and spatial evolution of vegetation dynamics in various land covers in the basin of the Laguna Bustillos, Region of Cuauhtémoc, Chihuahua, Mexico. We used an NDVI time series for ...This paper analyzed the temporal and spatial evolution of vegetation dynamics in various land covers in the basin of the Laguna Bustillos, Region of Cuauhtémoc, Chihuahua, Mexico. We used an NDVI time series for the months of March to April (early spring). The series was constructed from Landsat TM images for the period 1986-2011. The results show an increase of NDVI for vegetated areas, especially in conifer cover, while shrub and grassland showed a positive trend but with lower statistical significance. The increase in minimum temperatures in early spring, during the study period, was the most important factor in explaining the increase of NDVI in vegetated areas. A spatially distributed analysis shows large areas without an NDVI trend, corresponding to areas with sparse vegetation cover (degraded areas). Moreover, there are also areas with a negative trend (loss of vegetation), explained by the exploitation of trees to produce firewood which is mainly carried out by the ejidos in the region. These results help to focus human and financial resources in places where the benefit will be greatest.展开更多
The lateral distributions of depth-averaged velocity in open compound channels with emerged and submerged vegetated floodplains were analyzed based on the analytical solution of the depth-integrated Reynolds-Averaged ...The lateral distributions of depth-averaged velocity in open compound channels with emerged and submerged vegetated floodplains were analyzed based on the analytical solution of the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term to account for the effects of vegetation.The three cases considered for open channels were two-stage rectangular channel with emerged vegetated floodplain,rectangular channel with submerged vegetated corner,and two-stage rectangular channel with submerged vegetated floodplain,respectively.To predict the depth-averaged velocity with submerged vegetated floodplains,we proposed a new method based on a two-layer approach where flow above and through the vegetation layer was described separately.Moreover,further experiments in the two-stage rectangular channel with submerged vegetated floodplain were carried out to verify the results.The analytical solutions of the cases indicated that the corresponding analytical depth-averaged velocity distributions agree well with the simulated and experimental prediction.The analytical solutions of the cases with theoretical foundation and without programming calculation were reasonable and applicable,which were more convenient than numerical simulations.The analytical solutions provided a way for future researches to solve the problems of submerged vegetation and discontinuous phenomenon of depth-averaged velocity at the stage point for compound channels.Understanding the hydraulics of flow in compound channels with vegetated floodplains is very important for supporting the management of fluvial processes.展开更多
The objective of this study was to evaluate the potentials of beds vegetated with medicinal species (Brillantaisia bauchiensis and Polygonum salicifolium) in a constructed wetland for domestic wastewater treatment in ...The objective of this study was to evaluate the potentials of beds vegetated with medicinal species (Brillantaisia bauchiensis and Polygonum salicifolium) in a constructed wetland for domestic wastewater treatment in the Western Highlands of Cameroon. The study was carried out between March and September 2017 on plants collected from a natural wetland in Penka-Michel. The two plants species selected based on their ethnobotanical importance were transplanted and allowed to grow to maturity in a prepared natural wetland at Penka-Michel and a constructed wetland for domestic wastewater treatment on the campus of the University of Dschang. Growth parameters were followed for the two plants species in both wetlands. The physicochemical parameters and faecal bacteria concentrations were measured only for the vegetated and non-vegetated/control beds in the constructed wetland. Overall, the two plants species showed increased growth in height, diameter, leaf number and plants density. The change in diameter and density were very significantly influenced by species type in the constructed wetland than in the natural wetland. Generally, plant growth in height, diameter and density were higher with B. bauchiensis in the constructed wetland than with P. salicifolium in both wetlands. The mean faecal bacteria removal was higher in the vegetated beds for some bacteria than in the non-vegetated/control bed. There was a significant difference in the reduction efficiency of TSS, turbidity, BOD, Faecal streptococci and Total coliforms bacteria between the inflow and the outflow of some treatment beds especially the bed vegetated with Brillantaisia bauchiensis. There were correlations between the two plants species as concerns increased plants height, diameter, leave number, shoot number and nutrients uptake in the constructed wetland beds compared with the natural wetland.展开更多
This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vege...This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vegetation are considered as the drag force item. The secondary currents are also taken into account in the governing equations, and the preliminary estimation of the secondary current intensity coefficient K is discussed. The predicted results for the straight channels and the apex cross-section of meandering channels agree well with experimental data, which shows that the analytical model presented here can be applied to predict the flow in compound channels with vegetated floodplains.展开更多
The governing equation of the discharge per unit width, derived from the flow continuity equation and the momentum equation in the vegetated compound chan- nel, is established. The analytical solution to the discharge...The governing equation of the discharge per unit width, derived from the flow continuity equation and the momentum equation in the vegetated compound chan- nel, is established. The analytical solution to the discharge per unit width is presented, including the effects of bed friction, lateral momentum transfer, drag force, and secondary flows. A simple＇ but available numerical integral method, i.e., the compound trapezoidM formula, is used to calculate the approximate solutions of the sub-area discharge and the total discharge. A comparison with the published experimental data from the U. K. Flood Channel Facility （UK-FCF） demonstrates that this model is capable of predicting not only the stage-discharge curve but also the sub-area discharge in the vegetated com- pound channel. The effects of the two crucial parameters, i.e., the divided number of the integral interval and the secondary flow coefficient, on the total discharge are discussed and analyzed.展开更多
The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the un...The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the unit volume where the effect of the vegetation on the flow is considered as a drag force item, The compound channel is divided into 3 sub-regions in the transverse direction, and the coefficients in every region＇s differential equations were solved simultaneously. Thus, the analytical solution of the transverse distribution of the depth-averaged velocity for uniform flow in a partially vegetated compound channel was obtained. The results can be used to predict the transverse distribution of bed shear stress, which has an important effect on the transportation of sediment. By comparing the analytical results with the measured data, the analytical solution in this paper is shown to be sufficiently accurate to predict most hydraulic features for engineering design purposes.展开更多
Alpine revegetated dunes have been barely researched in terms of morphological change and migration within its regional aeolian environments. To reveal the sand-fixing and land-reforming mechanisms of artificial veget...Alpine revegetated dunes have been barely researched in terms of morphological change and migration within its regional aeolian environments. To reveal the sand-fixing and land-reforming mechanisms of artificial vegetation, we observed the morphology and migration of four dunes with four revegetated types(Hippophae rhamnoides Linn., Salix cheilophila Schneid., Populus simonii Carr., and Artemisia desertorum Spreng.) using unpiloted aerial vehicle images and GPS(global positioning system) mapping in 2009 and 2018. Spatial analysis of GIS(geographic information system) revealed that the revegetated dunes exhibited a steady progression from barchan dune shapes to dome or ribbons shapes mainly through knap planation, wing amplification, and slope symmetrization. Generally, conditions of northern aspects, smaller slope degree, and larger altitude of unvegetated dunes would suffer more serious wind erosion. The southward movement of dune wings with a migration speed of 2.0–5.0 m/a and the alternating motion of sand ridges in eastwestern directions led greater stability in revegetated dunes. The moving distances of revegetated dunes remarkably changed in patterns of quadratic or linear function with depositional depth. Compared with unvegetated dunes, the near-surface wind velocity of revegetated dunes decreased by 20%–30%, which led to heavy accumulation in low-flat dunes and erosion in high-steep dunes, but all vegetation species produced obvious sand-fixing benefits(100%–450% and 3%–140% in the lower and higher dune scales of revegetated dunes, respectively) with decreasing sand transport rates and increasing coverages. In practice, the four vegetation species effectively anchored mobile dunes by adapting to regional aeolian environment. However, future revegetation efforts should consider optimizing dune morphology by utilizing H. rhamnoides as a pioneer plant, S. cheilophila and P.microphylla in windward and northward dune positions, and A. desertorum in a sand accumulative southward position. Also, we should adjust afforestation structure and replant some shrub or herbs in the higher revegetated dunes to prevent fixed dune activation and southward expansion.展开更多
Land desertification and aeolian activity are currently the greatest threats to alpine ecological environments and are also the primary challenges of desertification control and ecological restoration projects.Affores...Land desertification and aeolian activity are currently the greatest threats to alpine ecological environments and are also the primary challenges of desertification control and ecological restoration projects.Afforestation of sandy lands around the Qinghai Lake in China has effectively controlled the desertification of this watershed.However,certain issues remain which challenge its overall success,including lack of diverse biological species and poor theoretical understanding of aeolian processes,such as controlling wind-sand flow in relation to complex alpine ecological factors.Therefore,to help improving afforestation techniques,this research focused on Hippophae rhamnoides,Salix cheilophila,Pinus sylvestris,Populus simonii and Artemisia desertorum vegetation implanted in the mobile dunes on the eastern shore of Qinghai Lake.Aeolian transport characteristics and annual changes to community ecological factors from 2010–2016 were monitored in comparison with uncontrolled sand dunes.Based on simultaneous observations using gradient anemometers and sand samplers,it was found that the aeolian activities exhibited the following features:1)In re-vegetated lands,the logarithmic growth of wind speed was disrupted by the wind speed amplification in the middle and high layers and wind speed reduction in the low layers,while vegetation had significant wind-breaking(>37%)and sand-fixing(>85%)effects in 2016.2)Wind speeds in re-vegetated lands and mobile dunes showed a linear correlation,especially in lower layers of H.rhamnoides and S.cheilophila,while sand transport in re-vegetated land increased linearly or exponentially with increasing wind speed.3)The four artificial shrubs and forests had greater sand deposition with intensities of 280–860 t/(ha·yr),largely concentrated during winter and spring which accounted for 60%–85%of the annual cycle,while A.desertorum experienced significant root undercutting;and 4)Intensity of aeolian activity in re-vegetated lands,except for A.desertorum,was significantly negative with respect to plant growth structure,community cover,topsoil moisture,and regional precipitation.Overall,these five sand-binding species produced optimistic wind-sand protection effects for the alpine sandy lands,which relied on the plants’physical disturbance of wind-sand flow during the early stages of community development.In comparison,H.rhamnoides and S.cheilophila individually maintained stable wind-sand protection effects,while P.sylvestris and P.simonii were better in mixing with other shrubs and herbs to achieve a comprehensive ecological system for future control of aeolian activity.展开更多
The influence of vegetation and sediment on flow characteristics in open channels cannot be neglected. To study the flow variability under the effects of the instream natural vegetation and sediment supply, experiment...The influence of vegetation and sediment on flow characteristics in open channels cannot be neglected. To study the flow variability under the effects of the instream natural vegetation and sediment supply, experiments were conducted with varied water and sediment supply in a movable bed of a river prototype. The instantaneous threedimensional velocities near two types of vegetation patches(the shrub and the weed) and along the centerline of the main channel with vegetation belts were measured using a 3-D side-looking acoustic Doppler velocimetry. The experimental results show that both the instream vegetation and sediment supply strongly affect the flow and turbulence characteristics. In the case of vegetation patches, both the shrub and weed have a considerable influence on the distribution of the streamwise velocity and turbulence intensity of their surrounding water. The streamwise velocity distribution followed as J-shape and linear shape around the weed and shrub under different experimental conditions. The turbulence intensity was large at the top of the weed and shrub;the shrub had its greatest influence on the downstream water flow. In the case of vegetation belts,the streamwise velocity along the centerline of the main channel exhibited an S-shape, J-shape and linear shape at different locations under varied water,vegetation structures and riverbed configurations.The turbulence intensity along the centerline of the main channel ranged from 0.0 to 0.1. The upstream turbulence intensity was affected considerably by a sediment supply, while the downstream turbulence intensity changed with the varied vegetation characteristics and riverbed topography. The second flow coefficient M-value increased longitudinally and was almost positive along the centerline of the main channel, implying that the rotational direction of the secondary current cell was clockwise.展开更多
The present paper discusses the effects of small plants on the dump mass reinforcement and slope stability.The roots of smaller plants(such as grasses and shrubs)do not go deep.However,they stabilize the slope by bind...The present paper discusses the effects of small plants on the dump mass reinforcement and slope stability.The roots of smaller plants(such as grasses and shrubs)do not go deep.However,they stabilize the slope by binding the upper layer of dump slope.Shear strength of the dump mass with and without root reinforcement is determined by laboratory shear box instrument.The increased cohesion(apparent cohesion)of upper layer of the dump mass due to plants is determined by fabricated shear box.The kinetic behavior of the dump has been investigated using the FLAC software.The factor of safety has been calculated in order to determine the possible effect of small plants on the stability of the dump slope.It is observed that the small plants do not significantly improve the factor of safety(FOS)of slope.However,it could be useful for early stabilization.The grasses quickly bind the upper surface,whereas shrubs too immensely strengthen the stability of the dump in the initial stage.展开更多
A simple idealized model to describe the hydraulic resistance caused by vegetation is compared to results from flow experiments conducted in natural waterways. Two field case studies are considered: fixed-point flow m...A simple idealized model to describe the hydraulic resistance caused by vegetation is compared to results from flow experiments conducted in natural waterways. Two field case studies are considered: fixed-point flow measurements in a Green River (case 1) and vessel-borne flow measurements along a cross-section with floodplains in the river Rhine (case 2). Analysis of the two cases shows that the simple flow model is consistent with measured flow velocities and the present vegetation characteristics, and may be used to predict a realistic Manning resistance coefficient. From flow measurements in the river floodplain (case 2) an estimate was made of the equivalent height of the drag dominated vegetation layer, as based on measured flow characteristics. The resulting height corresponds well with the observed height of vegetation in the floodplain. The expected depth-dependency of the associated Manning resistance coefficient for could not be detected due to lack of data for relatively shallow flows. Furthermore, it was shown that topographical variations in the floodplain may have an important impact on the flow field, which should not be mistaken as roughness effects.展开更多
We examine the genesis of coherent vortices in submerged vegetated flows by means of a linear stability analysis.The mathematical framework is comprised of the conservation equations of fluid mass and momentum.The pro...We examine the genesis of coherent vortices in submerged vegetated flows by means of a linear stability analysis.The mathematical framework is comprised of the conservation equations of fluid mass and momentum.The problem is tackled by imposing normal mode perturbations over an underlying undisturbed flow.We find that the growth rate of perturbations takes maximum magnitude for a specific wavenumber,termed as the critical wavenumber.The critical wavenumber indicates the most favorable wavenumber of coherent vortices emerging in submerged vegetated flows.The critical wavenumber amplifies as the flow Reynolds number,and vegetation height and density augment.The migration velocity of incipient coherent vortices characterizes minimum magnitude for a selected value of the vegetation height.The unstable zone in the stability diagram embarks beyond a critical Reynolds number.The critical Reynolds number designates the onset of coherent vortex appearance in submerged vegetated flows.The predictions of the present study are congruent with the existing theoretical and experimental works.展开更多
Aquatic vegetation is a vital component of natural river ecosystems,playing a crucial role in maintaining ecological balance,providing habitat and improving water quality.However,the presence of vegetation results in ...Aquatic vegetation is a vital component of natural river ecosystems,playing a crucial role in maintaining ecological balance,providing habitat and improving water quality.However,the presence of vegetation results in increased resistance in vegetated channels compared with non-vegetated channels,rendering traditional sediment movement predictions inadequate for the latter.Consequently,the concept of a vegetation influence factor,denoted by CDah,has been proposed by previous researchers to represent the effect of vegetation on sediment movement in watercourses.In this study,we focus on exploring the vegetation resistance coefficient(CD)among the vegetation influence factors,evaluating two different calculation methods for vegetation resistance coefficient,and presenting two expressions through genetic algorithm analysis to predict the incipient flow velocity of sediment in vegetated watercourses.The predicted values from the new formulae show excellent agreement with measured data,highlighting the high accuracy of the proposed methods in predicting the incipient flow velocity of sediment.Our results provide a solid theoretical basis for understanding the influence of aquatic vegetation on sediment particle movement.展开更多
文摘Eco-geotechnical engineering plays a pivotal role in enhancing global sustainability and upholding the perfor-mance of earthen structures.The utilization of vegetation to stabilise geotechnical infrastructures is widely recognized and embraced for its environmentally friendly attributes.The spectre of climate change further in-tensifies the focus on the effects of temperature and humidity on vegetated soil.Consequently,there is a pressing need for research exploring the influence of changing climates on vegetated infrastructures.Such research de-mands a holistic and interdisciplinary approach,bridging fields such as soil mechanics,botany,and atmospheric science.This review underscores key facets crucial to vegetated geotechnical infrastructures,encompassing climate projections,centrifuge modelling,field monitoring,and numerical methodologies.
基金supported by National Natural Science Foundation of China(Grant No.42372330)Science and Technology Research Program of Institute of Mountain Hazards and Environment,Chinese Academy of Sciences(Grant No.IMHE-CXTD-01-IMHE-ZYTS-12)Sichuan Science and Technology Program(Grant No.2024NSFSC0102).
文摘The hydro-mechanical responses of vegetated deposited slopes are complex and far from clear.On one hand,the soils in deposited slopes are typically poorly consolidated and widely graded,making them vulnerable to internal erosion during rainfall infiltration.On the other hand,vegetation plays a significant role in influencing the hydro-mechanical properties of the soil at the slope surface.This paper presents a coupled seepage-erosion model to investigate the rainfall-induced internal erosion process within vegetated deposited slopes and its impact on slope stability.The detailed seepage-erosion coupling processes were simulated for a series of 1D rooted soil columns with varying root distributions,as well as 2D vegetated layered slopes under both light and heavy rainfall conditions.The numerical results reveal that roots can significantly mitigate rainfall-induced internal erosion,even with shallow root lengths.However,their protective effect on the slope increases as the root density in the superficial soil layer increases.Transpiration can rapidly restore matric suction in the shallow soil during rain intervals,slowing the rainfall-induced seepage-erosion process and thereby increasing slope stability.However,in the absence of transpiration,roots may either accelerate or inhibit the seepage-erosion process,depending on the specific rainfall conditions.
基金support from the National Natural Science Foundation of China(Grant No.42172290,42230710,41925012)the Natural Science Foundation of Jiangsu Province(Grant No.BK20221250).
文摘The objective of this study is to explore how different layer thicknesses affect the desiccation cracking behaviour of vegetated soil.During the experiment,an electronic balance was employed to quantify water evaporation,while a digital camera was utilized to capture the initiation and progression of soil surface cracking.Results indicate that in the early drying process,the rate of evapotranspiration in vegetated soil correlates positively with leaf biomass.For soil samples with the same layer thickness,the constant rate stage duration is consistently shorter in vegetated soil samples than in their bare soil counterparts.As the layer thickness increases,both vegetated and bare soil samples crack at higher water content.However,vegetated soil samples crack at lower water content than their bare soil counterparts.Vegetation significantly reduces the soil surface crack ratio and improves the soil crack resistance.The crack reduction ratio is positively correlated with both root weight and length density.In thicker vegetated soil layers,the final surface crack length noticeably declines.
基金supported by the Traffic Science and Technology Projects in Shandong Province(NO.2017JHKY2)the Operating Expenses for Basic Research Project of the Central Public Welfare Institute(NO.20160630Y)。
文摘Vegetation in slopes can effectively improve slope stability.However,it is difficult to estimate the effects of vegetation on slope stability because of variations in plant species and environmental conditions.Moreover,influences of plant growth on slope stability change with time,resulting in changes in the safety factor.This study was conducted to evaluate the stability of vegetated slopes with time and investigate the effects of different layouts of plant species on slope stability.Here,we used a plant growth model and slope stability analysis to build an evaluation model.To accomplish this,one species of tree,shrub and grass was chosen to set six layout patterns.A slope with no vegetation served as a control.The safety factors of the seven slopes were then calculated using the developed evaluation model and differences in the safety factors of slopes were compared and discussed.The slope vegetated with Platycladus orientalis reached the most stable state at the age of 60 years.Shrub slope(Vitex negundo)had the maximum safety factor after 20 years.Overall,the safety factor of vegetated slopes increased from 12.1%to 49.6% compared to the slope with no vegetation.When wind force was considered,the safety factor value of the slope changed from 3.5%to 43.5%.Vegetation mixtures of trees and grasses resulted in the best slope stability.Planting grasses on slopes can improve slope stability of trees to a greater degree than that of slopes with shrubs in the early stage of growth.
文摘The existence of vegetation plays an important role to protect the ecosystem and water environment in natural rivers and wetlands, but it alters the velocity field of flow, consequently influencing the transport of pollutant and biomass. As a pre-requisite for the analysis of environmental capacity in a channel, the vertical velocity distribution of flows has attracted much research attention;however, there is yet lack of a good prediction model available. For the channel with submerged vegetation, the vertical velocity distribution in the lower vegetation layer will be different from that in the upper flow layer of non-vegetation. In this paper, after review on the most recent two-layer model proposed by Baptist et al., the author has proposed an improved two-layer analytical model by introducing a different mixing length scale (λ). The proposed model is based on the momentum equation of flow with the turbulent eddy viscosity assumed as a linear relationship with the local velocity. The proposed model is compared with the Baptist model for different datasets published in the literature, which shows that the proposed analytical model can improve the vertical velocity distribution prediction well compared with the Baptist model for a range of data. This study reveals that the λ is well related with the submergence of vegetation (H/h), as suggested by . When the constant β is taken as 3/100, the proposed model shows good agreement with a wide range of datasets studied: flow depth (H)/vegetation height (h) in 1.25 to 3.33, different vegetation densities of a in 1.1 to 18.5 m−1 (a defined as the frontal area of the vegetation per unit volume), and bed slopes in (1.38 - 4.0) × 10−3.
文摘The construction of an integrated numerical model is presented in this paper to deal with the interactions between vegetated surface and saturated subsurface flows. A numerical model is built by integrating the previously developed quasi-three-dimensional （Q3D） vegetated surface flow model with a two-dimensional （2D） saturated groundwater flow model. The vegetated surface flow model is constructed by coupling the explicit finite volume solution of 2D shallow water equations （SWEs） with the implicit finite difference solution of Navier-Stokes equations （NSEs） for vertical velocity distribution. The subsurface model is based on the explicit finite volume solution of 2D saturated groundwater flow equations （SGFEs）. The ground and vegetated surface water interaction is achieved by introducing source-sink terms into the continuity equations. Two solutions are tightly coupled in a single code. The integrated model is applied to four test cases, and the results are satisfactory.
文摘The transport and deposition of particulate organic matter (POM) in river streams has recently received much attention as one of important ecological processes in rivers. We focused on interacted behaviors of sand particles in bed load and POM in vegetated area on sand bars. The purpose of this study is to clarify the characteristics of deposition of POM with bed load on sandbars with the riparian vegetation. A basic experiment on POM transport and deposition with vegetation is conducted in a laboratory flume. It demonstrates that several issues still remain to be future investigated. In particular, the shear due to the bed roughness in the vegetated area and the transport and deposition process of sand particles and POM are required to be described by the proper modeling which will be introduced into a simulation model of various fluvial processes. The main results of this study are that ripples are formed by bed load in riparian vegetation and POM deposition is promoted by ripple behavior. Based on these results, the POM deposition with ripples in vegetated area is described by a conceptual model which will affect various aspects in ecosystem management based on fluvial processes.
文摘This paper analyzed the temporal and spatial evolution of vegetation dynamics in various land covers in the basin of the Laguna Bustillos, Region of Cuauhtémoc, Chihuahua, Mexico. We used an NDVI time series for the months of March to April (early spring). The series was constructed from Landsat TM images for the period 1986-2011. The results show an increase of NDVI for vegetated areas, especially in conifer cover, while shrub and grassland showed a positive trend but with lower statistical significance. The increase in minimum temperatures in early spring, during the study period, was the most important factor in explaining the increase of NDVI in vegetated areas. A spatially distributed analysis shows large areas without an NDVI trend, corresponding to areas with sparse vegetation cover (degraded areas). Moreover, there are also areas with a negative trend (loss of vegetation), explained by the exploitation of trees to produce firewood which is mainly carried out by the ejidos in the region. These results help to focus human and financial resources in places where the benefit will be greatest.
基金Under the auspices of National Basic Research Program of China(No.2011CB403303)National Key Research and Development Program of China(No.2016YFC0402408-5)National Natural Science Foundation of China(No.51179181,40788001)
文摘The lateral distributions of depth-averaged velocity in open compound channels with emerged and submerged vegetated floodplains were analyzed based on the analytical solution of the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term to account for the effects of vegetation.The three cases considered for open channels were two-stage rectangular channel with emerged vegetated floodplain,rectangular channel with submerged vegetated corner,and two-stage rectangular channel with submerged vegetated floodplain,respectively.To predict the depth-averaged velocity with submerged vegetated floodplains,we proposed a new method based on a two-layer approach where flow above and through the vegetation layer was described separately.Moreover,further experiments in the two-stage rectangular channel with submerged vegetated floodplain were carried out to verify the results.The analytical solutions of the cases indicated that the corresponding analytical depth-averaged velocity distributions agree well with the simulated and experimental prediction.The analytical solutions of the cases with theoretical foundation and without programming calculation were reasonable and applicable,which were more convenient than numerical simulations.The analytical solutions provided a way for future researches to solve the problems of submerged vegetation and discontinuous phenomenon of depth-averaged velocity at the stage point for compound channels.Understanding the hydraulics of flow in compound channels with vegetated floodplains is very important for supporting the management of fluvial processes.
文摘The objective of this study was to evaluate the potentials of beds vegetated with medicinal species (Brillantaisia bauchiensis and Polygonum salicifolium) in a constructed wetland for domestic wastewater treatment in the Western Highlands of Cameroon. The study was carried out between March and September 2017 on plants collected from a natural wetland in Penka-Michel. The two plants species selected based on their ethnobotanical importance were transplanted and allowed to grow to maturity in a prepared natural wetland at Penka-Michel and a constructed wetland for domestic wastewater treatment on the campus of the University of Dschang. Growth parameters were followed for the two plants species in both wetlands. The physicochemical parameters and faecal bacteria concentrations were measured only for the vegetated and non-vegetated/control beds in the constructed wetland. Overall, the two plants species showed increased growth in height, diameter, leaf number and plants density. The change in diameter and density were very significantly influenced by species type in the constructed wetland than in the natural wetland. Generally, plant growth in height, diameter and density were higher with B. bauchiensis in the constructed wetland than with P. salicifolium in both wetlands. The mean faecal bacteria removal was higher in the vegetated beds for some bacteria than in the non-vegetated/control bed. There was a significant difference in the reduction efficiency of TSS, turbidity, BOD, Faecal streptococci and Total coliforms bacteria between the inflow and the outflow of some treatment beds especially the bed vegetated with Brillantaisia bauchiensis. There were correlations between the two plants species as concerns increased plants height, diameter, leave number, shoot number and nutrients uptake in the constructed wetland beds compared with the natural wetland.
基金supported by the National Natural Science Foundation of China (Nos. 50679061, 50709025,and 50749031)
文摘This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vegetation are considered as the drag force item. The secondary currents are also taken into account in the governing equations, and the preliminary estimation of the secondary current intensity coefficient K is discussed. The predicted results for the straight channels and the apex cross-section of meandering channels agree well with experimental data, which shows that the analytical model presented here can be applied to predict the flow in compound channels with vegetated floodplains.
基金Project supported by the National Natural Science Foundation of China(Nos.51279117 and 11072161)the Program for New Century Excellent Talents in University of China(No.NCET-130393)the National Science and Technology Ministry of China(No.2012BAB05B02)
文摘The governing equation of the discharge per unit width, derived from the flow continuity equation and the momentum equation in the vegetated compound chan- nel, is established. The analytical solution to the discharge per unit width is presented, including the effects of bed friction, lateral momentum transfer, drag force, and secondary flows. A simple＇ but available numerical integral method, i.e., the compound trapezoidM formula, is used to calculate the approximate solutions of the sub-area discharge and the total discharge. A comparison with the published experimental data from the U. K. Flood Channel Facility （UK-FCF） demonstrates that this model is capable of predicting not only the stage-discharge curve but also the sub-area discharge in the vegetated com- pound channel. The effects of the two crucial parameters, i.e., the divided number of the integral interval and the secondary flow coefficient, on the total discharge are discussed and analyzed.
基金the National Natural Science Foundation of China(Nos.50679061,50709025and50749031)
文摘The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the unit volume where the effect of the vegetation on the flow is considered as a drag force item, The compound channel is divided into 3 sub-regions in the transverse direction, and the coefficients in every region＇s differential equations were solved simultaneously. Thus, the analytical solution of the transverse distribution of the depth-averaged velocity for uniform flow in a partially vegetated compound channel was obtained. The results can be used to predict the transverse distribution of bed shear stress, which has an important effect on the transportation of sediment. By comparing the analytical results with the measured data, the analytical solution in this paper is shown to be sufficiently accurate to predict most hydraulic features for engineering design purposes.
基金funded by the Jiangxi Provincial Natural Science Foundation (20202BABL213028)the Open Project of the State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, China (2022-KF-07)the Doctoral Scientific Research Foundation of East China University of Technology (2019052, 2019045)。
文摘Alpine revegetated dunes have been barely researched in terms of morphological change and migration within its regional aeolian environments. To reveal the sand-fixing and land-reforming mechanisms of artificial vegetation, we observed the morphology and migration of four dunes with four revegetated types(Hippophae rhamnoides Linn., Salix cheilophila Schneid., Populus simonii Carr., and Artemisia desertorum Spreng.) using unpiloted aerial vehicle images and GPS(global positioning system) mapping in 2009 and 2018. Spatial analysis of GIS(geographic information system) revealed that the revegetated dunes exhibited a steady progression from barchan dune shapes to dome or ribbons shapes mainly through knap planation, wing amplification, and slope symmetrization. Generally, conditions of northern aspects, smaller slope degree, and larger altitude of unvegetated dunes would suffer more serious wind erosion. The southward movement of dune wings with a migration speed of 2.0–5.0 m/a and the alternating motion of sand ridges in eastwestern directions led greater stability in revegetated dunes. The moving distances of revegetated dunes remarkably changed in patterns of quadratic or linear function with depositional depth. Compared with unvegetated dunes, the near-surface wind velocity of revegetated dunes decreased by 20%–30%, which led to heavy accumulation in low-flat dunes and erosion in high-steep dunes, but all vegetation species produced obvious sand-fixing benefits(100%–450% and 3%–140% in the lower and higher dune scales of revegetated dunes, respectively) with decreasing sand transport rates and increasing coverages. In practice, the four vegetation species effectively anchored mobile dunes by adapting to regional aeolian environment. However, future revegetation efforts should consider optimizing dune morphology by utilizing H. rhamnoides as a pioneer plant, S. cheilophila and P.microphylla in windward and northward dune positions, and A. desertorum in a sand accumulative southward position. Also, we should adjust afforestation structure and replant some shrub or herbs in the higher revegetated dunes to prevent fixed dune activation and southward expansion.
基金Under the auspices of the Doctoral Scientific Research Foundation of East China University of Technology(DHBK No.2019052)National Natural Science Foundation of China(No.41961017,41661001)+1 种基金Key Research&Development and Transformation Plan of Qinghai Province(No.2019-HZ-814)State Key Laboratory of Earth Surface Processes and Resources Ecology(No.2020-KF-06)。
文摘Land desertification and aeolian activity are currently the greatest threats to alpine ecological environments and are also the primary challenges of desertification control and ecological restoration projects.Afforestation of sandy lands around the Qinghai Lake in China has effectively controlled the desertification of this watershed.However,certain issues remain which challenge its overall success,including lack of diverse biological species and poor theoretical understanding of aeolian processes,such as controlling wind-sand flow in relation to complex alpine ecological factors.Therefore,to help improving afforestation techniques,this research focused on Hippophae rhamnoides,Salix cheilophila,Pinus sylvestris,Populus simonii and Artemisia desertorum vegetation implanted in the mobile dunes on the eastern shore of Qinghai Lake.Aeolian transport characteristics and annual changes to community ecological factors from 2010–2016 were monitored in comparison with uncontrolled sand dunes.Based on simultaneous observations using gradient anemometers and sand samplers,it was found that the aeolian activities exhibited the following features:1)In re-vegetated lands,the logarithmic growth of wind speed was disrupted by the wind speed amplification in the middle and high layers and wind speed reduction in the low layers,while vegetation had significant wind-breaking(>37%)and sand-fixing(>85%)effects in 2016.2)Wind speeds in re-vegetated lands and mobile dunes showed a linear correlation,especially in lower layers of H.rhamnoides and S.cheilophila,while sand transport in re-vegetated land increased linearly or exponentially with increasing wind speed.3)The four artificial shrubs and forests had greater sand deposition with intensities of 280–860 t/(ha·yr),largely concentrated during winter and spring which accounted for 60%–85%of the annual cycle,while A.desertorum experienced significant root undercutting;and 4)Intensity of aeolian activity in re-vegetated lands,except for A.desertorum,was significantly negative with respect to plant growth structure,community cover,topsoil moisture,and regional precipitation.Overall,these five sand-binding species produced optimistic wind-sand protection effects for the alpine sandy lands,which relied on the plants’physical disturbance of wind-sand flow during the early stages of community development.In comparison,H.rhamnoides and S.cheilophila individually maintained stable wind-sand protection effects,while P.sylvestris and P.simonii were better in mixing with other shrubs and herbs to achieve a comprehensive ecological system for future control of aeolian activity.
基金supported by the National Key Research and Development Program of China (2016YFC0402304 and 2017YFC1502504)the National Natural Science Foundation of China (51639007 and 51579163)
文摘The influence of vegetation and sediment on flow characteristics in open channels cannot be neglected. To study the flow variability under the effects of the instream natural vegetation and sediment supply, experiments were conducted with varied water and sediment supply in a movable bed of a river prototype. The instantaneous threedimensional velocities near two types of vegetation patches(the shrub and the weed) and along the centerline of the main channel with vegetation belts were measured using a 3-D side-looking acoustic Doppler velocimetry. The experimental results show that both the instream vegetation and sediment supply strongly affect the flow and turbulence characteristics. In the case of vegetation patches, both the shrub and weed have a considerable influence on the distribution of the streamwise velocity and turbulence intensity of their surrounding water. The streamwise velocity distribution followed as J-shape and linear shape around the weed and shrub under different experimental conditions. The turbulence intensity was large at the top of the weed and shrub;the shrub had its greatest influence on the downstream water flow. In the case of vegetation belts,the streamwise velocity along the centerline of the main channel exhibited an S-shape, J-shape and linear shape at different locations under varied water,vegetation structures and riverbed configurations.The turbulence intensity along the centerline of the main channel ranged from 0.0 to 0.1. The upstream turbulence intensity was affected considerably by a sediment supply, while the downstream turbulence intensity changed with the varied vegetation characteristics and riverbed topography. The second flow coefficient M-value increased longitudinally and was almost positive along the centerline of the main channel, implying that the rotational direction of the secondary current cell was clockwise.
文摘The present paper discusses the effects of small plants on the dump mass reinforcement and slope stability.The roots of smaller plants(such as grasses and shrubs)do not go deep.However,they stabilize the slope by binding the upper layer of dump slope.Shear strength of the dump mass with and without root reinforcement is determined by laboratory shear box instrument.The increased cohesion(apparent cohesion)of upper layer of the dump mass due to plants is determined by fabricated shear box.The kinetic behavior of the dump has been investigated using the FLAC software.The factor of safety has been calculated in order to determine the possible effect of small plants on the stability of the dump slope.It is observed that the small plants do not significantly improve the factor of safety(FOS)of slope.However,it could be useful for early stabilization.The grasses quickly bind the upper surface,whereas shrubs too immensely strengthen the stability of the dump in the initial stage.
文摘A simple idealized model to describe the hydraulic resistance caused by vegetation is compared to results from flow experiments conducted in natural waterways. Two field case studies are considered: fixed-point flow measurements in a Green River (case 1) and vessel-borne flow measurements along a cross-section with floodplains in the river Rhine (case 2). Analysis of the two cases shows that the simple flow model is consistent with measured flow velocities and the present vegetation characteristics, and may be used to predict a realistic Manning resistance coefficient. From flow measurements in the river floodplain (case 2) an estimate was made of the equivalent height of the drag dominated vegetation layer, as based on measured flow characteristics. The resulting height corresponds well with the observed height of vegetation in the floodplain. The expected depth-dependency of the associated Manning resistance coefficient for could not be detected due to lack of data for relatively shallow flows. Furthermore, it was shown that topographical variations in the floodplain may have an important impact on the flow field, which should not be mistaken as roughness effects.
文摘We examine the genesis of coherent vortices in submerged vegetated flows by means of a linear stability analysis.The mathematical framework is comprised of the conservation equations of fluid mass and momentum.The problem is tackled by imposing normal mode perturbations over an underlying undisturbed flow.We find that the growth rate of perturbations takes maximum magnitude for a specific wavenumber,termed as the critical wavenumber.The critical wavenumber indicates the most favorable wavenumber of coherent vortices emerging in submerged vegetated flows.The critical wavenumber amplifies as the flow Reynolds number,and vegetation height and density augment.The migration velocity of incipient coherent vortices characterizes minimum magnitude for a selected value of the vegetation height.The unstable zone in the stability diagram embarks beyond a critical Reynolds number.The critical Reynolds number designates the onset of coherent vortex appearance in submerged vegetated flows.The predictions of the present study are congruent with the existing theoretical and experimental works.
基金Project supported by the Natural Science Foundation of Beijing (Grant No.8232052)the National Natural Science Foundation of China (Grant No.51809286).
文摘Aquatic vegetation is a vital component of natural river ecosystems,playing a crucial role in maintaining ecological balance,providing habitat and improving water quality.However,the presence of vegetation results in increased resistance in vegetated channels compared with non-vegetated channels,rendering traditional sediment movement predictions inadequate for the latter.Consequently,the concept of a vegetation influence factor,denoted by CDah,has been proposed by previous researchers to represent the effect of vegetation on sediment movement in watercourses.In this study,we focus on exploring the vegetation resistance coefficient(CD)among the vegetation influence factors,evaluating two different calculation methods for vegetation resistance coefficient,and presenting two expressions through genetic algorithm analysis to predict the incipient flow velocity of sediment in vegetated watercourses.The predicted values from the new formulae show excellent agreement with measured data,highlighting the high accuracy of the proposed methods in predicting the incipient flow velocity of sediment.Our results provide a solid theoretical basis for understanding the influence of aquatic vegetation on sediment particle movement.
