Evolution of the Bonneville shoreline scarp in west-central Utah: Comparison of scarp-analysis methods and implications for the diffusion model of hillslope evolution     

J.D. Pelletier  S.B. DeLong  A.H. Al-Suwaidi  M. Cline  Y. Lewis  J.L. Psillas  B. Yanites 《Geomorphology》2006,74(1-4):257-270

Wave-cut pluvial shoreline scarps are ideal natural experiments in hillslope evolution because the ages of these scarps are often precisely known and because they form with a range of heights, alluvial textures, and microclimates (i.e., orientation). Previous work using midpoint-slope methods on pluvial scarps in the Basin and Range concluded that scarp evolution is nonlinear and microclimatically controlled. The purpose of this study was to further examine the influence of scarp height, texture and microclimate in an attempt to calibrate a nonlinear model of scarp evolution. To do this, over 150 profiles of the Bonneville shoreline in the adjacent Snake and Tule Valleys, west-central Utah were collected and analyzed by fitting the entire scarp profile to diffusion-equation solutions, taking into account uncertainty in the initial scarp angle. In contrast to previous studies, this analysis revealed no evidence for nonlinearity or microclimatic control. To understand the reason for this discrepancy, we undertook a systematic study of the accuracy of each scarp-analysis method. The midpoint-slope-inverse method was found to yield biased results, with systematically higher diffusion ages for young, tall scarps. The slope-offset method is unbiased but has limited resolution because it requires many scarp profiles to yield a single diffusion age. A method that incorporates the full scarp profile and uncertainty in the initial scarp angle was found to be the most accurate technique. The application of the full-scarp method to the Bonneville shoreline supports the use of a linear diffusion model for scarps up to 20 m in height. Scarp orientation had no discernable effect on diffusivity values. Soil texture was found to have a weak but significant inverse relationship with diffusivity values.  相似文献   

The effects of soil piping on contributing areas and erosion patterns     

J. A. A. Jones 《地球表面变化过程与地形》1987,12(3):229-248

Natural piping doubles the dynamic contributing area on the upper Maesnant stream in mid-Wales, mainly through linking points well beyond the riparian zones of seepage to the stream. Both discharge and sediment transport rates in the major pipes are closely related to the size of shallow surface microtopographic hollows in which they lie, and which themselves are largely created by piping erosion. However, pipe dischrges are frequently generated by contributing areas larger than these surface depressions and some pipes run counter to the surface topography. The redistribution and acceleration of hillslope drainage processes by piping has implications for theories of hillslope development, especially through plan-form modifications, and also for channel discharge and erosion.  相似文献   

The continuity equation slope model and basal boundary conditions: A further comment     

M. J. Kirkby 《地球表面变化过程与地形》1983,8(3):287-288

Intermediates between a fixed basal elevation and a constant rate of downcutting throughout the slope profile are perhaps more realistic than either extreme case.  相似文献   

Hillslope gullying in the Solway Firth — Morecambe Bay region, Great Britain: Responses to human impact and/or climatic deterioration?     

R.C. Chiverrell  A.M. Harvey  G.C. Foster 《Geomorphology》2007,84(3-4):317

In the Solway Firth — Morecambe Bay region of Great Britain there is evidence for heightened hillslope instability during the late Holocene (after 3000 cal. BP). Little or no hillslope geomorphic activity has been identified occurring during the early Holocene, but there is abundant evidence for late Holocene hillslope erosion (gullying) and associated alluvial fan and valley floor deposition. Interpretation of the regional radiocarbon chronology available from organic matter buried beneath alluvial fan units suggests much of this geomorphic activity can be attributed to four phases of more extensive gullying identified after 2500–2200, 1300–1000, 1000–800 and 500 cal. BP. Both climate and human impact models can be evoked to explain the crossing of geomorphic thresholds: and palaeoecological data on climatic change (bog surface wetness) and human impact (pollen), together with archaeological and documentary evidence of landscape history, provide a context for addressing the causes of late Holocene geomorphic instability. High magnitude storm events are the primary agent responsible for gully incision, but neither such events nor cooler/wetter climatic episodes appear to have produced gully systems in the region before 3000 cal. BP. Increased gullying after 2500–2200 cal. BP coincides with population expansion during Iron Age and Romano-British times. The widespread and extensive gullying after 1300–1000 cal. BP and after 1000–800 cal. BP coincides with periods of population expansion and a growing rural economy identified during Norse times, 9–10th centuries AD, and during the Medieval Period, 12–13th centuries AD. These periods were separated by a downturn associated with the ‘harrying of the north’ AD 1069 to 1070. The gullying episode after 500 cal. BP also coincides with increased anthropogenic pressure on the uplands, with population growth and agricultural expansion after AD 1500 following 150 years of malaise caused by livestock and human (the Black Death) plagues, poor harvests and conflicts on the Scottish/English border. The increased susceptibility to erosion of gullies is a response to increased anthropogenic pressure on upland hillslopes during the late Holocene, and the role of this pressure appears crucial in priming hillslopes before subsequent major storm events. In particular, the cycles of expansion and contraction in both population and agriculture appear to have affected the susceptibility of the upland landscape to erosion, and the hillslope gullying record in the region, therefore, contributes to understanding of the timing and spatial pattern of human exploitation of the upland landscape.  相似文献   

PLAN FORM AND PROFILE FORM OF HILLSLOPES     

A. J. Parsons 《地球表面变化过程与地形》1979,4(4):395-402

For 27 hillslope profiles located within four first-order drainage basins on the dip slope of the South Downs in East Sussex, contour curvature (P), measured in degrees per 100 m, is highly variable within any one hillslope. Hillslopes may be described as wholly concave in plan where P is less than ?40, wholly convex in plan where P is greater than +40 and convexo-concave in plan where P lies between ?40 and +40. One measure of P taken at the profile sampling line is found to give a better estimate of P than measuring P at the steepest point on the hillslope. P is found to be significantly negatively correlated with slope in 38 per cent of cases, correlated with distance from the divide in 55 per cent of cases (positively where P <0 and negatively where P <0) and positively correlated with profile curvature in 70 per cent of cases. Implications of these correlations for hillslope process-response models are discussed.  相似文献   

THE STABILITY OF ROCK-VENEERED HILLSLOPES     

Terrence J.TOY  +  W.R.OSTERKAMP  + 《国际泥沙研究》1999,(3)

1　ＩＮＴＲＯＤＵＣＴＩＯＮ　Ｕｎｄｅｒｓｔａｎｄｉｎｇｈｉｌｌｓｌｏｐｅｄｅｖｅｌｏｐｍｅｎｔｒｅｍａｉｎｓａｎｅｌｕｓｉｖｅｇｏａｌｆｏｒｅａｒｔｈｓｃｉｅｎｔｉｓｔｓ.Ｔｈｅｏｒｉｅｓｂａｓｅｄｕｐｏｎｏｂｓｅｒｖａｔｉｏｎ,ｌｏｇｉｃ,ａｎｄｓｐ...  相似文献   

Flow time estimation with spatially variable hillslope velocity in ungauged basins   总被引：2，自引：0，他引：2  

Salvatore Grimaldi  Andrea Petroselli  Gustavo Alonso  Fernando Nardi 《Advances in water resources》2010

The automated spatial estimation of the hillslope runoff dynamics is used as a valuable tool for the estimation of the travel time distribution (flow time), a major factor for the hydrologic prediction in ungauged basins. In fact, while the flow time function is usually obtained by rescaling the flow paths with constant channel and hillslope velocities, in this work a spatially distributed kinematic component, as a function of terrain features and in particular slope and land use, is implemented and its influence on the hydrologic response is tested by means of the Width Function Instantaneous Unit Hydrograph (WFIUH) framework. Hillslope surface flow velocities are evaluated by applying different uniform flow formulas within an automated DEM-based (terrain analysis) algorithm. A comparison test of the performances of the Manning, Darcy, Maidment and Soil Conservation Service uniform flow equations is performed for several case studies in Italy pertaining to different climatic and geomorphic conditions. Results provide new insights for a better understanding of the flow time function also introducing a more parsimonious and physically-based calibration scheme of the WFIUH.  相似文献   

Evolution of undercut slopes on abandoned incised meanders in the Eastern Highland Rim of Tennessee, USA     

Hugh H. Mills  Richard T. Mills   《Geomorphology》2001,38(3-4)

Field surveys, location-for-time reasoning, and computer modeling were used to study the evolution of slopes on valley walls of abandoned bedrock meanders on the Eastern Highland Rim, Tennessee. Hillslopes on the undercut slopes of cutoff incised meanders were ordered as to relative age by the height of their meander floors above the modern stream level. The assumption is that the undercut slope is actively eroded by the stream until abandonment of the meander, at which time the slope begins to evolve to a different form. More-advanced stages of evolution occur on walls of higher meanders that were abandoned earlier. The most rapid change in this initial form is the elimination of a free face, which occurs soon after the meander is abandoned. In addition, the hillslopes associated with even the lowest (youngest) cutoff meanders show somewhat gentler overall gradients than the actively undercut slopes. Hillslopes associated with meanders 3 to about 20 m above modern stream level maintain straight segments with angles showing only a slight decrease from the 36–38° associated with the lowest cutoffs; overall angles decrease, however, as the straight segment becomes shorter. The oldest slopes, those on cutoffs 30 m or greater above modern stream level, have developed into convex–concave slopes with maximum slopes of 15°.A hillslope evolution model based on previously published algorithms was used to simulate the transition of actively undercut hillslopes into hillslopes on abandoned meanders. Hillslope modeling is particularly useful in this setting. If the valley incision rate is known, an age can be estimated for the cutoff and hence for the hillslope. Alternatively, if hillslope process rates are known, a model age obtained for the hillslope can be used to estimate an incision rate. Even where both incision rates and hillslope process rates are poorly constrained, as in the present setting, modeling allows assumptions about specific rates to be evaluated by determining their implications for other rates. For example, for three cutoff meanders along one stream, best-fit criteria were used to select process rates for the model. Model ages of hillslopes were then obtained and compared with those calculated from a valley-incision rate measured elsewhere in the same physiographic province. For two of the hillslopes, model ages were found to be much younger than those calculated from the incision rate. In order to make the two ages agree, unreasonably low process rates had to be used in the model, thus implying that the incision rate probably underestimates the actual incision rate in this valley.Experimentation with heights of initial profiles, again using best-fit criteria, suggests that since abandonment of the highest cutoff, the plateau has been downwasting at a rate about one-fourth that of the valley incision rate, a finding in agreement with published rates of chemical denudation in the area.  相似文献   

The role of topography in controlling throughflow generation: A discussion     

J. Garry Speight 《地球表面变化过程与地形》1980,5(2):187-191

The distributions of specific catchment area and specific dispersal area values over the hillside studied by Anderson and Burt (1978) relate much more closely to the observed distributions of soil water matric potential than do the occurrences of contour concavity on which the authors rely. Highest potential always occurred in the zone of large specific catchment area except immediately after rainfall, when it occurred in the zone of small dispersal area. Isolines of low potential persistently conformed to those of specific dispersal area.  相似文献   

Combining field and modelling techniques to assess rockfall dynamics on a protection forest hillslope in the European Alps   总被引：4，自引：0，他引：4  

Luuk K. A. Dorren  Bernhard Maier  Uif S. Putters  Arie C. Seijmonsbergen 《Geomorphology》2004,57(3-4):151-167

Adequate management of a mountain forest that protects downslope areas against impacts of rockfall requires insight into the dynamics of the hillslope environment. Therefore, we applied a combined approach, using field and modelling techniques, to assess the determining factors for rockfall source areas, rockfall tracks and rockfall runout zones on a forested slope in mountainous terrain. The first objective of this study was to understand why rockfall occurs in the study area. The second objective was to translate the knowledge obtained in the field into a model that simulates rockfall dynamics on a forested slope realistically. The third objective was to assess which hillslope characteristics primarily determine the distribution of active rockfall tracks. To achieve these objectives, we made a geomorphological map of the whole study area, and we measured the major discontinuity planes in the bedrock that are exposed in the rockfall source areas. Furthermore, a test site for simulation modelling within the larger study area was defined in which both a forest and a hillslope inventory were carried out. The available data and our developed rockfall simulation model allowed us to assess the slope characteristics that mainly determine the distribution of areas affected by rockfall. We found that in decreasing order of importance, both standing and felled trees, the surface roughness and rockfall resistant shrubs primarily determine the distribution of rockfall-affected areas. Simulation tests without a forest cover produced similar rockfall runout zones as fossil rockfall events identified in the field. We believe that the combined field and modelling approach is a prerequisite for understanding how forests can protect against rockfall.  相似文献