Parameterizing a physically based shallow landslide model in a data poor region     

Sekhar L. Kuriakose  L. P. H. van Beek  C. J. van Westen 《地球表面变化过程与地形》2009,34(6):867-881

Shallow landslides and consequent debris flows are an increasing concern in the Western Ghats of Kerala, India. Their increased frequency has been associated with deforestation and unfavourable land‐use practices in cultivated areas. In order to evaluate the influence of vegetation on shallow slope failures a physically based, dynamic and distributed hydrological model (STARWARS) coupled with a probabilistic slope stability model (PROBSTAB) was applied to the upper Tikovil River basin (55·6 km²). It was tuned with the limited evidence of groundwater conditions during the monsoon season of 2005 and validated against observed landslide activity in the hydrological year 2001–2002. Given the data poor conditions in the region some modifications to the original model were in order, including the estimation of parameters on the basis of generalized information from secondary sources, pedo‐transfer functions, empirical equations and satellite remote sensing data. Despite the poor input, the model captured the general temporal and spatial pattern of instability in the area. Sensitivity analysis proved root cohesion, soil depth and angle of internal friction as the most dominant parameters influencing slope stability. The results indicate the importance of root cohesion in maintaining stability and the critical role of the management of rubber plantations in this. Interception and evapotranspiration showed little influence on the development of failure conditions. The study also highlights the importance of high resolution digital terrain models for the accurate mechanistic prediction of shallow landslide initiation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Wood distribution in neotropical forested headwater streams of La Selva,Costa Rica     

Daniel Cadol  Ellen Wohl  Jaime R. Goode  Kristin L. Jaeger 《地球表面变化过程与地形》2009,34(9):1198-1215

Surveys of wood along 30 forested headwater stream reaches in La Selva Biological Station in north‐eastern Costa Rica represent the first systematic data reported on wood loads in neotropical streams. For streams with drainage areas of 0·1–8·5 km² and gradients of 0·2–8%, wood load ranged from 3 to 34·7 m³ wood/100 m channel and 41–612 m³ wood/ha channel. These values are within the range reported for temperate streams. The variables wood diameter/flow depth, stream power, the presence of backflooding, and channel width/depth are consistently selected as significant predictors by statistical models for wood load. These variables explain half to two‐thirds of the variability in wood load. These results, along with the spatial distribution of wood with respect to the thalweg, suggest that transport processes exert a greater influence on wood loads than recruitment processes. Wood appears to be more geomorphically effective in altering bed elevations in gravel‐bed reaches than in reaches with coarser or finer substrate. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

桂林毛村岩溶地下河流域水土流失遥感动态监测研究   总被引：3，自引：1，他引：2  

杨成英  吴虹 《中国岩溶》2009,28(2):206-211

为了给西南岩溶地区石漠化发展演变的研究工作提供一定的科学依据和决策支持,选择桂林毛村岩溶地下河流域作为研究区,利用两期遥感影像对该区影响水土流失的三个主要自然要素,即地形坡度、植被覆盖度和土地利用方式进行信息提取,并以地理信息系统为分析平台,参考水土流失强度分级标准,对该区两个时期的水土流失状况进行对比分析。调查监测结果显示,研究区随着坡度的增大,水土越容易流失,而且水土流失强度级别增大;植被覆盖度对水土流失强度起着控制性作用,为抑制并缩减水土流失面积,应保护植被,退耕还林;研究区土地利用变化比较缓慢,导致水土流失面积变化幅度不大。上述结果表明,利用遥感技术手段,可为当地的经济发展和水土流失的监测、评价、预测及治理提供参考。   相似文献   

Characterizing turbulent wind flow around dryland vegetation          下载免费PDF全文

Jerome R. Mayaud  Giles F.S. Wiggs  Richard M. Bailey 《地球表面变化过程与地形》2016,41(10):1421-1436

Wind flow has been studied in situations where it encounters porous and solid windbreaks, but there has been a lack of research exploring turbulent wind dynamics around and in the lee of real vegetation elements. In dryland contexts, sparse vegetation plays an important role in modulating both the erosivity of the wind and the erodibility of surfaces. Therefore, understanding the interactions between wind and vegetation is key for improving wind erosion modelling in desert landscapes. In this study, turbulent wind flow around three typical dryland vegetation elements (a grass clump, a shrub, and a tree) was examined in Namibia using high‐frequency (10 Hz) sonic anemometry. Spatial variations in mean wind velocity, as well as Reynolds stresses and coherent turbulent structures in the flow, were compared and related to the porosities and configurations of the study elements. A shelter parameter, originally proposed by Gandemer ( 1979 , Journal of Wind Engineering and Industrial Aerodynamic 4 : 371–389), was derived to describe the combined impact of the different elements on the energy and variability of horizontal wind flow. Wind velocity was reduced by 70% in the immediate lee of the grass and 40% in the lee of the shrub, but velocity recovered exponentially to equilibrium over the same relative distance in both cases (~9 element heights downwind). Quadrant analysis of the high‐frequency wind flow data revealed that the grass clump induced a small recirculation zone in its lee, whereas the shrub did not. Also, higher Reynolds shear stress and higher ‘flow positivity magnitude’ [ratio of Q1 (outward interaction) and Q4 (sweep) quadrants to Q2 (ejection) and Q3 (inward interaction) quadrants] was generally observed in the wake of the grass. These differences arose because the porosity of the grass clump (53%) was lower than the porosity of the shrub (69%), and thus bleed flow through the shrub was more significant. The bluff‐body behaviour of the grass resulted in a more intense and more extensive sheltering effect than the shrub, which implies that overall sediment transport potential is lower in the wake of the grass. The tree displayed a different wake structure to the grass and shrub, owing to the elevation of its crown. A ‘bottom gap’ effect was observed, whereby wind velocities increased possibly due to streamline compression in the gap between the ground and the underside of the tree crown. Differences in flow momentum between the bottom gap and the low‐pressure leeward region of the crown are a probable explanation for the formation of a large recirculation vortex. The bottom gap effect led to decreased sheltering up to three tree heights downwind, but the surface became increasingly protected by the frontal impact of the crown over a further eight tree heights downwind (~30 m). The extraction of momentum from the air by the tree therefore resulted in a far more extensive sheltering effect compared to the grass and shrub. This study represents an important investigation of the impact of different vegetation types on turbulent wind flow, and results can be integrated as parameterizations into spatial sediment transport models that explore landscape‐scale change on semi‐vegetated desert surfaces. Copyright © 2016 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.  相似文献   

Wetland buffers: numerical modeling of wave dissipation by vegetation          下载免费PDF全文

Jane McKee Smith  Mary Anderson Bryant  Ty V. Wamsley 《地球表面变化过程与地形》2016,41(6):847-854

The resiliency of coastal communities is imperative because these areas experience risk of damage from coastal storms as well as increasing population pressures and development. The severity of this hazard is compounded by sea level rise and a potential increase in storm intensities due to climate change. The ability of coastal communities to plan for, resist, and quickly and completely recover from severe coastal storm events and flooding is of critical importance. There is a growing interest in applying complementary and redundant approaches to reduce the flood risk of these vulnerable communities, such as incorporating natural and nature‐based features into the project planning process. However, accounting for the benefits of these nature‐based features in coastal design is still challenging. One of the natural features generally acknowledged to offer coastal protection benefits is wetlands. Using laboratory experiments of artificial vegetation as a foundation, the bounds of wave dissipation by vegetation are explored analytically and the effectiveness of wave dissipation by vegetation over large scales is investigated using the spectral wave model STWAVE. Wave heights modeled using a vegetation dissipation formulation are compared to those modeled with the current practice of representing vegetation using bottom friction, particularly the Manning formulation. The vegetation dissipation formulation reduced more wave energy than the Manning bottom friction formulation for submerged wetlands. Because the Manning formulation does not integrate vegetation properties, to achieve consistent results would require varying the Manning n coefficient to account for the spatial and temporal variation in form drag induced by the plants due to changes in plant density, diameter, and degree of plant submergence. Thus, a re‐evaluation of existing methods for assessing wave dissipation by vegetation is recommended for wider application of vegetation dissipation formulations in numerical models. Such models are critical for evaluating coastal resiliency of communities protected by wetland features. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

Populus nigra L. establishment and fluvial landform construction: biogeomorphic dynamics within a channelized river          下载免费PDF全文

Dov Corenblit  Johannes Steiger  Gaspard Charrier  José Darrozes  Virginia Garófano‐Gómez  Alexandre Garreau  Eduardo González  Angela M. Gurnell  Borbála Hortobágyi  Frédéric Julien  Luc Lambs  Sébastien Larrue  Thierry Otto  Erwan Roussel  Franck Vautier  Olivier Voldoire 《地球表面变化过程与地形》2016,41(9):1276-1292

Populations of the riparian pioneer species Populus nigra L. which establish on alluvial bars within river channels modulate sediment dynamics and fluvial landforms. Dense cohorts of P. nigra have colonized gravel point bars along the channelized River Garonne, France, during the last 20 years and have enhanced the vertical, lateral and longitudinal development of the bars. For this period, the geomorphic characteristics of two wooded point bars on this laterally stable river are closely linked to the spatial distribution and intensity of establishment and resistance of different cohorts of P. nigra. Furthermore, P. nigra colonization dynamics were controlled by engineer effects of this same species. This relationship is illustrated by a significant correlation between key geomorphic and biological variables measured in situ and characterized with a set of four aerial photographs taken between 2000 and 2010. The development of wooded point bars, which are discrete biogeomorphic units, over the studied period, appear to result from a specific biogeomorphic positive feedback of matter aggregation and vegetation establishment related to sediment trapping and stabilization by pioneer engineer plants. We propose a conceptual model of biogeomorphic unit construction for channelized, lateral stable rivers. We consider the resultant biogeomorphic units as functional from an ecological point of view because P. nigra enhances at the cohort scale (i) its own inherent capacity to resist hydrogeomorphic disturbances, and (ii) its resilience capacity as a result of successful colonization, especially downstream of mature poplar stands. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Comparative analysis of the response of various land covers to an exceptional rainfall event in the central Spanish Pyrenees,October 2012          下载免费PDF全文

N. Lana‐Renault  E. Nadal‐Romero  M. P. Serrano‐Muela  B. Alvera  P. Sánchez‐Navarrete  Y. Sanjuan  J. M. García‐Ruiz 《地球表面变化过程与地形》2014,39(5):581-592

The hydrological and geomorphological effects of an exceptional rainstorm event that occurred in the central Spanish Pyrenees during 19–21 October 2012 were studied in five experimental catchments under various land covers: (i) subhumid badlands; (ii) dense forest; (iii) an abandoned farmland area recolonized by shrubs and forest patches; and (iv) subalpine grasslands. Hydrographs and sedigraphs demonstrated that vegetation cover is a major factor affecting the control of floods even during exceptional rainstorms, at least at the spatial scale at which the phenomenon was studied (catchment sizes: 0.3–2.8 km2) and under dry catchment conditions. The combined precipitation over the two days (c. 250 mm) was the greatest for any two‐day event recorded since 1950 in the central‐western Pyrenees for all but one of the stations in the study. Five pulses of most intense rainfall were recorded. The forested catchment did not react to the two most intense rainfall pulses, because of the very low antecedent level of the water table. The main peak flow occurred only when at least a part of the catchment was saturated. The abandoned farmland catchment had two small peak discharges at the beginning of the event, which were produced by infiltration excess overland flow from eroded areas close to the main stream. During the third most intense rainfall period a large part of this catchment contributed to runoff and a relatively high peak discharge was produced. The badland catchment reacted immediately from the beginning of the rainstorm, yielding very high discharges accompanied by high suspended sediment concentrations. The subalpine catchment showed a hydrograph mirroring the hyetograph, with brief but intense hydrological responses to increased precipitation, because of the marked gradients and the presence of bare rock in the headwaters. A high volume of bedload was carried during the peak discharge. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Effects of slope angle and aspect on plant cover and species richness in a humid Mediterranean badland   总被引：1，自引：0，他引：1       下载免费PDF全文

Estela Nadal‐Romero  Kristien Petrlic  Els Verachtert  Esther Bochet  Jean Poesen 《地球表面变化过程与地形》2014,39(13):1705-1716

Soil erosion is one of the most severe land degradation processes in the Mediterranean region. Although badlands occupy a relatively small fraction of the Mediterranean area, their erosion rates are very high. Many studies have investigated to what extent vegetation controls soil erosion rates. This study, however, deals with the impact of erosion on vegetation establishment. In semi‐arid badlands of the Mediterranean, soil water availability constitutes the main limiting factor for vegetation development. As a consequence, south‐facing slopes are typically less vegetated due to a very large water stress. However, these findings do not necessarily apply to humid badlands. The main objective of this paper is to determine the topographic thresholds for plant colonization in relation to slope aspect and to assess the spatial patterns of vegetation cover and species richness. We surveyed 179 plots on highly eroded badland slopes in the Central Pyrenees. We defined four aspect classes subdivided into slope angle classes. Colonization success was expressed in terms of vegetation cover and species richness. Slope angle thresholds for plant colonization were identified for each slope aspect class by means of binary logistic regressions. The results show that a critical slope angle exists below which plants colonize the badland slopes. Below this critical slope angle, plant cover and species richness increase with a decreasing slope angle. The largest critical slope angles in humid badlands are observed on south‐facing slopes, which contrasts with the results obtained in semi‐arid badlands. North‐facing slopes however are characterized by a reduced overall vegetation cover and species richness, and lower topographic threshold values. The possible underlying processes responsible for this slope‐aspect discrepancy in vegetation characteristics are discussed in terms of environmental variables that control regolith development, weathering and erosion processes. Moreover, possible restoration strategies through the use of vegetation in highly degraded environments are highlighted. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Ecomorphodynamics of rivers with converging boundaries          下载免费PDF全文

Paolo Perona  Benoît Crouzy  Stuart McLelland  Peter Molnar  Carlo Camporeale 《地球表面变化过程与地形》2014,39(12):1651-1662

Many rivers worldwide show converging sections where a characteristic limiting front for vegetation establishment on gravel bars is observed. An important conceptual model was advanced in 2006 by Gurnell and Petts, who demonstrated that for the convergent section of the Tagliamento River the downstream front of vegetation establishment can be explained by unit stream power. We introduce a theoretical framework based on 1D ecomorphodynamic equations modified to account for the biological dynamics of vegetation. We obtain the first analytical result explaining the position and river width where vegetation density is expected to vanish in relation to a characteristic streamflow magnitude and both hydraulic and biological parameters. We apply our model to a controlled experiment within a convergent flume channel with growing seedlings perturbed by periodic floods. For a range of timescales where hydrological and biological processes interact, we observe the formation of a front in the convergent section beyond which vegetation cannot survive, the location of which is explained by flow magnitude. This experiment confirms that the timescales of the involved processes and the unit stream power determine the existence and the position of the front within convergent river reaches, respectively. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Determining drag coefficients and their application in modelling of turbulent flow with submerged vegetation     

《Advances in water resources》2014

Vegetation is a key aspect of water resources and ecology in natural rivers, floodplains and irrigation channels. The hydraulic resistance of the water flow is greatly changed when submerged vegetation is present. Three kinds of drag coefficients, i.e., the drag coefficient for an isolated cylinder, the bulk drag coefficient of an array of cylinders and the vertically distributed or local drag coefficient, have been commonly used as parameters to represent the vegetation drag force. In this paper, a comprehensive experimental study of submerged stems in an open channel flow is presented. Empirical formulae for the three drag coefficients were obtained based on our experimental results and on data from previous studies. A two-layer model was developed to solve the mean momentum equation, which was used to evaluate the vertical mean velocity profile with each of the drag coefficients. By comparing the velocity distribution model predictions and the measurement results, we found that the model with the drag coefficient for an isolated cylinder and the local drag coefficient was good fit. In addition, the model with the bulk drag coefficient gave much larger velocity values than measurements, but it could be improved by adding the bed friction effect and making choice of the depth-averaged velocity within the canopy layer.  相似文献