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1.
Variable complexity of the US Continental Divide trace   总被引：1，自引：0，他引：1  
Abstract

Map-view complexity of 65 contiguous segments of the conterminous US Continental Divide trace was evaluated by the divider method, with each segment’s geometry approximated by a fractal dimension (D) value, or two D values applying to fine and coarse scales of inspection. Results support a generalization that D values in the range 1.05–1.12 are typical for drainage divides viewed at regional to national scales. However about 20% of cases reviewed in this study are smoother (D = 1.01–1.04) or more complex (D = 1.13–1.18) traces. Complexities of these watershed boundary segments show no significant correlation with physiographic province or local relief. The primary influence of bedrock lithology and surface process is seen in zones of Quaternary volcanism, where uncommonly smooth and highly complex divide trace segments are more the rule than exception. Uncommonly smooth divide traces are also found descending mountain pediments in areas of parallel drainage, and some of the most tortuous traces are associated with drainage patterns disrupted by non-fluvial processes. Divide trace segments crossing terrain with uniform lithology show decreased complexity, but traces with the broadest range of complexity, including highest D values, occur in areas with moderate, not extreme, degrees of bedrock diversity.  相似文献   

2.
Relief shading is the most common type of cartographic relief representation for print and digital maps. Manual relief shading results in informative and visually pleasing representations of terrain, but it is time consuming and expensive to produce. Current analytical relief shading can be created quickly, but the resulting maps are not as aesthetically appealing and do not show landscape features in an explicit manner. This article introduces an automated digital method that produces shaded relief with locally adjusted illumination directions to simulate the techniques and cartographic principles of manual relief shading. Ridgelines and valley lines are derived from a digital terrain model, vectorized, and used in a diffusion curve algorithm. A graph analysis generalizes the lines before using them for diffusion curve shading. The direction of illumination is adjusted based on the spatial orientation of ridgelines and valley lines. The diffusion curve shading is combined with standard analytical relief shading to create a final diffusion relief shading image. Similar to manual relief shading, major landforms and the structure of the terrain are more clearly shown in the diffusion relief shading. The presented method best highlights major landforms in terrain characterized by sharp, clearly defined ridges and valleys.  相似文献   

3.
流域地貌演化的不同阶段沟壑密度与切割深度关系研究   总被引：9，自引：3，他引：6  
张丽萍  马志正 《地理研究》1998,17(3):273-278
主要探讨了在流域地貌演化的不同阶段,沟壑密度与切割深度的复杂关系,建立了沟壑密度随切割深度变化的理论极值模型及相应阶段的函数,补充了各演化阶段地貌形态要素的定量、定性描述;反之,可用沟壑密度与切割深度的关系推断流域地貌的演化阶段。  相似文献   

4.
This paper examines the effect of scale (exhibited by spatial sampling) in modeling mean slope from lidar data using two representations of scale: lidar posting density (i.e. post‐spacing) and DEM resolution (i.e. cell size). The study areas selected include six small (i.e. approximately 3 km2) urban drainage basins in Richland County, SC, USA, which share similar hydrologic characteristics. This research spatially sampled an airborne lidar dataset collected in 2000 at a 2 m nominal posting density to simulate lidar posting density at various post‐spacings, from 2 m through 10 m. DEMs were created from the lidar observations at a corresponding cell size using spatial interpolation. Finally, using these DEMs, a sensitivity analysis between modeled terrain slope and lidar post‐spacing was conducted. Results of the sensitivity analyses showed that the deviation between mean slope and modeled mean slope decreases with finer posting density and DEM resolution. The relationship of mean slope with varying cell sizes and post‐spacing suggests a linear and a logarithmic function, respectively, for all study areas. More importantly, cell size has a greater effect on mean slope than lidar posting density. Implications of these results for lumped hydrologic modeling are then postulated.  相似文献   

5.
Terrain maps displaying hill-shading with curvature   总被引：2，自引：0，他引：2  
Patrick J. Kennelly   《Geomorphology》2008,102(3-4):567-577
Many types of maps can be created by neighborhood operations on a continuous surface such as provided by a digital elevation model. These most commonly include first derivatives slope or aspect, and second derivatives planimetric or profile curvature. Such variables are often used in geomorphic analyses of terrain. First derivatives also provide subtle enhancements to hill-shaded maps. For example, some maps combine oblique and vertical illumination, with the latter reflecting variations in slope.This study illustrates how second derivative maps, in conjunction with hill-shading, can cartographically enhance topographic detail. A simple conic model indicates that image-tone edges where slope or aspect varies by less than 0.5° are visible on curvature maps. Hill-shaded images combined with curvature enhance the continuity of naturally occurring tonal edges, especially in strongly illuminated areas. Variations in planimetric and profile curvature seem to be especially effective at highlighting convergent and divergent drainages and variations in erosion rate between or within sedimentary units, respectively. Shading curvature with consideration given to illumination models can add detail to hill-shaded terrain maps in a manner similar to cognitive models employed by map viewers.  相似文献   

6.
Sediments from Lake Pepin on the Mississippi River, southeastern Minnesota, are used as provenance tracers to assess variations in hydrology and sediment-transport during the middle Holocene. Three rivers contribute sediment to Lake Pepin, and each catchment is characterized by a distinctly different geologic terrain. The geochemical fingerprint for each drainage basin was determined from the elemental composition of heavy minerals in the silt-sized fraction of modern sediment samples. Down-core elemental abundances were compared with these fingerprints by use of a chemical-mass-balance model that apportions sediment to the source areas. We observed a decreased contribution from the Minnesota River during the interval ~6700–5500 14C yr BP, which we attribute to decreased discharge of the Minnesota River, likely controlled by a combination of precipitation, snow melt, and groundwater input to the river. This hydrologic condition coincides with the mid-Holocene prairie period recorded by fossil pollen data. The occurrence of this feature in a proxy record for hydrologic variations supports the hypothesis that the mid-Holocene prairie period reflects drier conditions than before or after in midwestern North America.  相似文献   

7.
针对当前单一地貌划分单元造成的分类结果破碎或漏分问题,该文引入双尺度流域单元划分方法,即采用两种不同大小流域单元的组合作为地貌划分基本单元,以提高地貌划分的细分性和完整性。以30 m ASTER GDEM数据为数据源,基于最佳地形因子组合(高程、地势起伏度、坡度、坡度变率、光照模拟值)、双尺度流域单元、CART决策树算法,实现了北回归线(云南段)地区平原(2类)和山地(7类)共9类地貌的划分,双尺度流域单元划分的最佳流量阈值分别为500、2000。通过平均值、标准差、Moran′s I和人工判读结果对分类结果进行检验,发现基于CART决策树的双尺度流域单元地貌分类方法在北回归线(云南段)地区总体精度可达82.1%,Kappa系数为0.793,总体能够准确识别出研究区的地貌类型空间分布特征,是地貌类型划分的一种可行方法。  相似文献   

8.
In this paper we explore the development and assimilation of a high resolution topographic surface with a one-dimensional hydraulic model for investigation of avulsion hazard potential on a gravel-bed river. A detailed channel and floodplain digital terrain model (DTM) is created to define the geometry parameter required by the 1D hydraulic model HEC-RAS. The ability to extract dense and optimally located cross-sections is presented as a means to optimize HEC-RAS performance. A number of flood scenarios are then run in HEC-RAS to determine the inundation potential of modeled events, the post-processed output of which facilitates calculation of spatially explicit shear stress (τ) and level of geomorphic work (specific stream power per unit bed area, ω) for each of these. Further enhancing this scenario-based approach, the DTM is modified to simulate a large woody debris (LWD) jam and active-channel sediment aggradation to assess impact on innundation, τ, and ω, under previously modeled flow conditions. The high resolution DTM facilitates overlay and evaluation of modeled scenario results in a spatially explicit context containing considerable detail of hydrogeomorphic and other features influencing hydraulics (bars, secondary and scour channels, levees). This offers advantages for: (i) assessing the avulsion hazard potential and spatial distribution of other hydrologic and fluvial geomorphic processes; and (ii) exploration of the potential impacts of specific management strategies on the channel, including river restoration activities.  相似文献   

9.
Predicting sediment flux from fold and thrust belts   总被引：8，自引：1，他引：8  
The rate of sediment influx to a basin exerts a first-order control on stratal architecture. Despite its importance, however, little is known about how sediment flux varies as a function of morphotectonic processes in the source terrain, such as fold and thrust growth, variations in bedrock lithology, drainage pattern changes and temporary sediment storage in intermontane basins. In this study, these factors are explored with a mathematical model of topographic evolution which couples fluvial erosion with fold and thrust kinematics. The model is calibrated by comparing predicted topographic relief with relief measured from a DEM of the Central Zagros Mountains fold belt. The sediment-flux curve produced by the Zagros fold belt simulation shows a delay between the onset of uplift and the ensuing sediment flux response. This delay is a combination of the natural response time of the geomorphic system and a time lag associated with filling, and then subsequently uplifting and re-eroding, the proximal part of the basin. Because deformation typically propagates toward the foreland, the latter time lag may be common to many ancient foreland basins. Model results further suggest that the response time of the bedrock fluvial system is a function of rock resistance, of the width of the region subject to uplift and erosion, and, assuming a nonlinear dependence of fluvial erosion upon channel gradient, of uplift rate. The geomorphic response time for the calibrated Zagros model is on the order of a few million years, which is commensurate with, or somewhat larger than, typical recurrence intervals for episodes of thrusting. However, model experiments also highlight the potential for significant variations in both geomorphic response time and in sediment flux as a function of varying rock resistance. Given a reasonable erodibility contrast between resistant and erodible lithologies, model sediment flux curves show significant sediment flux variations that are related solely to changes in rock resistance as the outcrop pattern changes. An additional control on sediment flux to a basin is drainage diversion in response to folding or thrusting, which can produce major shifts in the location and magnitude of sediment source points. Finally, these models illustrate the potential for a significant mismatch between tectonic events and sediment influx to a basin in cases where sediment is temporarily ponded in an intermontane basin and later remobilized.  相似文献   

10.
Hydrologic data derived from digital elevation models (DEM) has been regarded as an effective method in the spatial analysis of geographical information systems (GIS). However, both DEM resolution and terrain complexity has impacts on the accuracy of hydrologic derivatives. In this study, a multi-resolution and multi-relief comparative approach was used as a major methodology to investigate the accuracy of hydrologic data derived from DEMs. The experiment reveals that DEM terrain representation error affects the accuracy of DEM hydrological derivatives (drainage networks and watershed etc.). Coarser DEM resolutions can usually cause worse results. However, uncertain result commonly exists in this calculation. The derivative errors can be found closely related with DEM vertical resolution and terrain roughness. DEM vertical resolution can be found closely related with the accuracy of DEM hydrological derivatives, especially in the smooth plain area. If the mean slope is less than 4 degrees, the derived hydrologic data are usually unreliable. This result may be helpful in estimating the accuracy of the hydrologic derivatives and determining the DEM resolution that is appropriate to the accuracy requirement of a particular user. By applying a threshold value to subset the cells of a higher accumulation flow, a stream network of a specific network density can be extracted. Some very important geomorphologic characteristics, e.g., shallow and deep gullies, can be separately extracted by means of adjusting the threshold value. However, such a flow accumulationbased processing method can not correctly derive those streams that pass through the working area because it is hard to accumulate enough flow direction values to express the stream channels at the stream's entrance area. Consequently, errors will definitely occur at the stream’s entrance area. In addition, erroneous derivatives can also be found in deriving some particular rivers, e.g., perched (hanging up) rivers, anastomosing rivers and braided rivers. Therefore, more work should be done to develop and perfect the algorithms.  相似文献   

11.
Topographic change in regions of active deformation is a function of rates of uplift and denudation. The rate of topographic development and change of an actively uplifting mountain range, the Santa Monica Mountains, southern California, was assessed using landscape attributes of the present topography, uplift rates and denudation rates. Landscape features were characterized through analysis of a digital elevation model (DEM). Uplift rates at time scales ranging from 104 to 106 years were constrained with geological cross-sections and published estimates. Denudation rate was determined from sediment yield data from debris basins in southern California and from the relief of rivers set into geomorphic surfaces of known age. First-order morphology of the Santa Monica Mountains is set by large-scale along-strike variations in structural geometry. Drainage spacing, drainage geometry and to a lesser extent relief are controlled by bedrock strength. Dissection of the range flanks and position of the principal drainage divide are modulated by structural asymmetry and differences in structural relief across the range. Topographic and catchment-scale relief are ≈300–900 m. Mean denudation rate derived from the sediment yield data and river incision is 0.5±0.3 mm yr?1. Uplift rate across the south flank of the range is ≈0.5±0.4 mm yr?1 and across the north flank is 0.24±0.12 mm yr?1. At least 1.6–2.7 Myr is required to create either the present topographic or the catchment-scale relief based on either the mean rates of denudation or uplift. Although the landscape has had sufficient time to achieve a steady-state form, comparison of the time-scale of uplift and denudation rate variation with probable landscape response times implies the present topography does not represent the steady-state form.  相似文献   

12.
Degrading river network due to urbanization in Yangtze River Delta   总被引：1，自引：0，他引：1  
Evolution of river systems under the background of human activities has been a heated topic among geographers and hydrologists. Spatial and temporal variations of river systems during the 1960s–2010s in the Yangtze River Delta (YRD) were investigated based on streams derived from the topographic maps in the 1960s, 1980s and 2010s. A list of indices, drainage density (Dd), water surface ratio (WSR), ratio of area to length of main streams (R), evolution coefficient of tributaries (K) and box dimension (D), were classified into three types (quantitative, structural, and complex indices) and used to quantify the variations of stream structure. Results showed that: (1) quantitative indices (Dd, WSR) presented decreasing trend in the past 50 years, and Dd in Wuchengxiyu, Hangjiahu and Yindongnan have decreased most, about 20%. Structurally, the Qinhuai River basin was characterized by significant upward R, and K value in Hangjiahu went down dramatically by 46.8% during the 1960s–2010s. Decreasing tendency in D was found dominating across the YRD, and decreasing magnitude in Wuchengxiyu and Hangjiahu peaks for 7.8% and 6.5%, respectively in the YRD. (2) Urbanization affected the spatial pattern of river system, and areas with high level of urbanization exhibited least Dd (2.18 km/km2), WSR (6.52%), K (2.64) and D (1.42), compared to moderate and low levels of urbanization. (3) Urbanization also affected the evolution of stream system. In the past 50 years, areas with high level of urbanization showed compelling decreasing tendency in quantitative (27.2% and 19.3%) and complex indices (4.9%) and trend of enlarging of main rivers (4.5% and 7.9% in periods of the 1960s–1980s and the 1980s–2010s). In the recent 30 years, areas with low level of urbanization were detected with significant downward trend in Dd and K. (4) Expanding of urban land, construction of hydraulic engineering and irrigation and water conservancy activities were the main means which degraded the river system in the YRD.  相似文献   

13.
Abstract

Explicit and quantitative models for the spatial prediction of soil and landscape attributes are required for environmental modelling and management. In this study, advances in the spatial representation of hydrological and geomorphological processes using terrain analysis techniques are integrated with the development of a field sampling and soil-landscape model building strategy. Statistical models are developed using relationships between terrain attributes (plan curvature, compound topographic index, upslope mean plan curvature) and soil attributes (A horizon depth, Solum depth, E horizon presence/absence) in an area with uniform geology and geomorphic history. These techniques seem to provide appropriate methodologies for spatial prediction and understanding soil landscape processes.  相似文献   

14.
陕北黄土高原沟道小流域形态特征分析   总被引：4，自引：1，他引：3  
陈浩 《地理研究》1986,5(1):82-92
本文就黄土高原不同地貌类型区的小流域进行了形态量计分析。并以河网密度为地表切割程度指标,建立了河网密度与流域形态要素的复相关方程式。  相似文献   

15.
The scarcity of grain-size data from gravel-bed rivers has traditionally hindered hydraulic, sediment transport and river habitat studies. A new remote sensing methodology to estimate grain-size distribution is presented. It combines textural digital images of the riverbed at 1 : 1000 and 1 : 40 scales with grain-size sampling. It was applied to a 12-km reach of the Isábena River (Central Pyrenees NE Spain). First, textural patterns for each grain-size range were obtained, selecting the most closely related texture variables, including the use of semivariograms. Second, multiple linear regression equations were derived from the textural variables to estimate each value of the grain-size distribution. The highest correlation values (r2) were obtained from the central part of the distribution (D50 with a RMS error of 12.7%). Finally, new multiple linear regression equations to estimate the D50 and D84 were obtained from 1 : 1000 images and four textural variables. These were used to derive D50 and D84 maps of the riverbed, re-sampled at a resolution of 1.5 m pixels, with RMS estimation errors of 26% and 32%, respectively. Downstream change in grain-size is also well reproduced by the method. The mean D50 of 72 and 32 mm were estimated in the upper and the lower reaches of the river, respectively. The methodology shows great potential for application, the relation between the spatial resolution of the images and the mean grain-size of the riverbed sediment being the main issue for future development.  相似文献   

16.
Abstract

The effects and influence of tectonic processes on the Anjarakandy, Thalassery, Mahe, and Kuttiyadi watersheds and rivers of the South Indian Granulite Terrain in Kerala were examined to determine their spatial heterogeneity. Drainage basin asymmetry (Af), transverse topographic symmetry factor (T), hypsometric integral and curve (HI), longitudinal profile, stream length gradient index (SL), and stream concavity index (SCI) suggest heterogeneity in tectonic influence. Clusters of geomorphic anomalies in similar lithology rule out lithologic control on drainage development. However, the orientations of the drainage networks and predominant fractures/lineaments compare closely and reveal strong tectonic influence. Though the watersheds are considered to be in an advanced stage of erosion by the low HI (<30) and high values of SCI, variations in the shape of the hypsometric curves and differences in the SCI values indicate the different influence of tectonic process from watersheds in the north to the south. Among the watersheds, the Mahe and Kuttiyadi are more sensitive to tectonic processes than the Anjarakandy and Thalassery and indicate spatial heterogeneity in the influence of tectonic activity, confirming the grouping of watersheds based on structural and drainage patterns.  相似文献   

17.
The delta evolution and erosion process of the abandoned Yellow River Delta (AYRD) have been extensively studied. However, the variation of sediment at a large littoral scale along the north coast of Jiangsu is less understood. In this study, the data of surface sediment samples obtained in the littoral area of the Yellow River Delta in 2006 and 2012 is used to study the sediment variability and sediment transport trends by using the geostatistics analysis tool and the grain size trend analysis model. In order to ensure the applicability of the model, the geostatistics method is used to determine the characteristic distance (D c) with the average range value (Ao) of grain size parameter. Filtering method (removing data that not at a sampling station) is used to improve accuracy of data selection. The results show that sedimentary spatial correlation in Lianyun Port area and southern part of the abandoned Yellow River Delta (AS) is better than that in the northern part of the abandoned Yellow River Delta (AN). Sediment in the area is found to be anisotropy at the northeast-southeast direction. The grain size trend analysis reveals that the sediment trend is towards bayhead and southerly in the Haizhou Bay, southeasterly along the shoreline in the south Lianyun Port, northwesterly in AN and easterly-southeasterly in AS respectively. The investigation of possible relationships between D c, Ao, sediment transport and delta evolution shows a close link between D c and Ao of one sediment combination. It is also found that sediment transport trends could reasonably represent the delta evolution to a certain degree.  相似文献   

18.
We present a simple method to derive spatial precipitation (P) and evapotranspiration (ET) for the typical steppe of the Xilin river catchment at 1 km and 8-day resolution during the main vegetation period (23 April to 28 August) of 2006. The hydrological model BROOK90 was parameterised from eddy covariance measurements. The daily model input data, precipitation, minimum (Tamin) and maximum air temperature (Tamax), were derived by manipulating MODIS leaf area index (LAI) and surface temperature data. P was estimated based on a linear regression of P measured at several sites against the mean gain of the MODIS LAI of surrounding 3 × 3 pixels areas (R2 = 0.76). Tamin and Tamax were derived using a relationship between measured Tamin and Tamax and MODIS surface temperatures (R2 = 0.92 and R2 = 0.88, respectively). The mean precipitation was 145 mm; it varied between 52 mm in the north-western region and 239 mm in the eastern region. In spring, the modelled ET was low (<0.8 mm d−1); evaporation dominated over transpiration and spatial differences were small. At the end of June, the mean ET reached its maximum (2 mm d−1) and spatial differences were pronounced. From July on, transpiration dominated over declining evaporation, and spatial differences decreased in August.  相似文献   

19.
Landslide inventory maps are necessary for assessing landslide hazards and addressing the role slope stability plays in landscape evolution over geologic timescales. However, landslide inventory maps produced with traditional methods — aerial photograph interpretation, topographic map analysis, and field inspection — are often subjective and incomplete. The increasing availability of high-resolution topographic data acquired via airborne Light Detection and Ranging (LiDAR) over broad swaths of terrain invites new, automated landslide mapping procedures. We present two methods of spectral analysis that utilize LiDAR-derived digital elevation models of the Puget Sound lowlands, Washington, and the Tualatin Mountains, Oregon, to quantify and automatically map the topographic signatures of deep-seated landslides. Power spectra produced using the two-dimensional discrete Fourier transform and the two-dimensional continuous wavelet transform identify the characteristic spatial frequencies of deep-seated landslide morphologic features such as hummocky topography, scarps, and displaced blocks of material. Spatial patterns in the amount of spectral power concentrated in these characteristic frequency bands highlight past slope instabilities and allow the delineation of landslide terrain. When calibrated by comparison with detailed, independently compiled landslide inventory maps, our algorithms correctly classify an average of 82% of the terrain in our five study areas. Spectral analysis also allows the creation of dominant wavelength maps, which prove useful in analyzing meter-scale topographic expressions of landslide mechanics, past landslide activity, and landslide-modifying geomorphic processes. These results suggest that our automated landslide mapping methods can create accurate landslide maps and serve as effective, objective, and efficient tools for digital terrain analysis.  相似文献   

20.
Abstract

Field work in geography often involves an exercise in which the student is required to make some type of map. Although most areas of the United States are well mapped, seldom are extremely large-scale (larger than 1:24,000) relief maps available. A method of contour-line mapping using small contour intervals and a large scale is appropriate in teaching several mapping principles and requires only a few simple tools and the use of elementary mathematics. Percent slope is established at uniform intervals along closely spaced traverses of the area to be mapped. Spot elevations are thus established from which contour lines can be determined. Accuracy in field-data collection and care in cartography will yield a very satisfactory map of terrain characteristics of small areas. Several concepts of maps and mapping are taught through direct student involvement.  相似文献   

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