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1.
Spatial analysis of stream power using GIS: SLk anomaly maps   总被引：2，自引：0，他引：2  
The stream length‐gradient index (SL) shows the variation in stream power along river reaches. This index is very sensitive to changes in channel slope, thus allowing the evaluation of recent tectonic activity and/or rock resistance. Nevertheless, the comparison of SL values from rivers of different length is biased due to the manner in which the index is formulated, thus making correlations of SL anomalies along different rivers difficult. Therefore, when undertaking a comparison of SL values of rivers of different lengths, a normalization factor must be used. The graded river gradient (K) has already been used in some studies to normalize the SL index. In this work, we explore the relationships between the graded river gradient (K), the SL index and the stream power, proposing the use of a re‐named SLk index, which enables the comparison of variable‐length rivers, as well as the drawing of SLk anomaly maps. We present here a GIS‐based procedure to generate SLk maps and to identify SLk anomalies. In order to verify the advantages of this methodology, we compared an SLk map of the NE border of the Granada basin with both simple river profile–knickpoint identification and with an SL map. The results show that the SLk map supplies good results with defined anomalies and suitably reflects the main tectonic and lithological features of the study area. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

2.
Relationships between slope form and stream magnitude, drainage area and stream gradient are investigated in a small upland catchment experiencing active stream incision. Profiles selected on a stratified random basis provide data on five slope form variables. The observed relationships suggest a spatial sequence of slope form, associated with a downstream increase in discharge, characterized by decreasing overall slope convexity and increasing mean slope angle and attributed to a reduction in the relative length of the upslope convexity with respect to the essentially stream-controlled main slope.  相似文献   

3.
Knickpoint behaviour is a key to understanding both the landscape responses to a base‐level fall and the corresponding sediment fluxes from rejuvenated catchments, and must be accommodated in numerical models of large‐scale landscape evolution. Knickpoint recession in streams draining to glacio‐isostatically uplifted shorelines in eastern Scotland is used to assess whether knickpoint recession is a function of discharge (here represented by its surrogate, catchment area). Knickpoints are identified using DS plots (log slope versus log downstream distance). A statistically significant power relationship is found between distance of headward recession and catchment area. Such knickpoint recession data may be used to determine the values of m and n in the stream power law, E = KAmSn. The data have too many uncertainties, however, to judge definitively whether they are consistent with m = n = 1 (bedrock erosion is proportional to stream power and KPs should be maintained and propagate headwards) or m = 0·3, n = 0·7 (bedrock incision is proportional to shear stress and KPs do not propagate but degrade in place by rotation or replacement). Nonetheless, the E Scotland m and n values point to the dominance of catchment area (discharge) in determining knickpoint retreat rates and are therefore more consistent with the stream power law formulation in which bedrock erosion is proportional to stream power. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

4.
The upper New River basin of the southern Appalachian Mountains, a major tributary of the modern Ohio River, represents the unglaciated headwaters of the Tertiary Teays River system of eastern North America. Dating of relict fluvial gravels have suggested that New River incision may be outpacing lowering of the surrounding uplands, but physical evidence of transient topographic disequilibrium has yet to be identified. We use focused topographic analysis of the upper New River basin to delineate a perched, low‐relief paleo‐landscape that is experiencing transgressive dissection due to incision by the New River and its tributaries. Accelerated incision has decoupled hillslopes from the drainage network, generating knickpoints which represent the boundary between remnants of the paleo‐landscape and actively adjusting topography downstream. Steepening of hillslopes downstream of knickpoints suggests dynamic headward migration which, along with knickpoint occurrence throughout the drainage network, is inconsistent with the development of fixed stream profile convexities atop strike‐extensive geologic contacts. In the absence of tectonic forcing, we favor a climatically‐forced drop in external base level as driver of the incision pattern we observe. Plio‐Pleistocene glacial damming and diversion of the Teays River to form the modern Ohio River lowered regional base level for the study area, potentially forcing the paleo‐landscape developed during the Teays era to adjust to the modern drainage pattern. The upper New River may therefore represent the potential for glacially‐driven drainage rearrangement to drive transient topographic evolution hundreds of kilometers away from the ice margin, long after the disappearance of ice sheets. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

5.
The impact of afforestation on stream bank erosion and channel form   总被引：1，自引：0，他引：1  
Modification of the land use of a small catchment through coniferous afforestation is shown to have influenced stream bank erosion and channel form. Field mapping and erosion pin measurements over a 19-month period provides evidence of more active bank erosion along forested channel reaches than along non-forested. Extrapolation of downstream increases in bankfull width, bankfull depth, and channel capacity with increasing basin area for the non-forested catchment has demonstrated that afforestation of the lower part of the catchment has had a marked effect on channel form. Channel widths within the forest are up to three times greater than that predicted from the regression. These changes in bankfull width have led to stream bed aggradation and the development of wide shallow channels within the forest, and channel capacities within the forest are over two times that predicted from the basin area. The relationship between channel sinuosity and valley gradient for non-forested reaches of the river also indicated decreased sinuosity resulting from afforestation. These changes in channel form result from active bank erosion within the forest with coarse material being deposited within the channel as point-bars and mid-channel bars. Active bank erosion is largely attributed to the suppression by the forest of a thick grass turf and its associated dense network of fine roots, and secondly to the river attempting to bypass log jams and debris dams in the stream channel.  相似文献   

6.
Abstract Extensive subduction-related and intraplate volcanism characterize Cenozoic magmatism in the North Is., New Zealand. Volcanics in the central North Is., predominantly intermediate to felsic, form above the dipping seismic zone and show tectonic/geochemical features common to magmatism in most subduction zones. Basaltic volcanism in Northland, the northern part of the North Is., has chemical characteristics typical of intraplate magmatism and may be caused by the upwelling of asthenospheric materials from deeper parts of the mantle. The rifting just behind the present volcanic front (the Taupo-Rotorua Depression), which follows the trench ward migration of the volcanic front and the gradual steepening of the subducted slab, is also a feature of the North Is. A possible mechanism for the back-arc rifting in the area is injection of asthenospheric materials into the mantle wedge; this asthenospheric flow results from the mantle upwelling beneath Northland and pushes both the rigid fore-arc mantle wedge and the subducted slab trenchwards. This mechanism is also consistent with the stress fields in the North Is.: dilatation in Northland, northwest-southeast tension in the Taupo-Rotorua Depression, and the northeast-southwest compression in the fore-arc region.  相似文献   

7.
慢激波的演化受其上游介质性质的制约，在等离子体热压与磁压之比β值和离子、电子温度比Ｔｉ／Ｔｅ大于１的介质中不利于慢波变陡形成慢激波。由飞船ＨｅｌｉｏｓＡ，Ｂ探测资料看出，在日心距０．３-１．０ＡＵ区间只有慢速太阳风流中存在有利于慢激波形成的条件。但理论计算和飞船观测指出，在快激波下游流场中β值和Ｔｉ／Ｔｅ都增大，因而在上述区间不论何种流速的太阳风中当有快激波经过后其下游流场内很难形成慢激波。  相似文献   

8.
A morphometric comparison of valleys has been made for the Ben Ohau Range in the central Southern Alps of New Zealand. The range is undergoing rapid tectonic transport and uplift. The humid north of the range is a glacial trough-and-arête landscape, with a temperate glacial climate. The dry south has rounded divides and plateau remnants dissected by fluvial valleys. Assuming that space–time substitution allows today's spatial valley-form transition to represent evolutionary stages in valley development, the tectonic history allows time constraints to be placed on the rate of transition to an alpine glacial landscape. Morphometric change has been quantified using hypsometric curves, and distance–elevation plots of cirque and valley-floor altitudes. Ancestral fluvial valleys have less concave long profiles but are stepped at altitude owing to the presence of high-level cirques and remnant plateau surfaces, and possess a low proportion of land area at low elevation. Increasing glacial influence is manifest as smoother, more deeply concave long profiles and U-shaped cross-profiles associated with a higher proportion of the land area at lower elevation. The full morphological transition has involved up to 2.4 km of vertical denudation over the 4 Ma lifetime of the mountain range, of which 80 per cent would have occurred by preglacial fluvial erosion. Combining the trajectory of tectonic transport with reconstructed glaciation limits and climatic history, it is indicated that about 200 ka of temperate glacial erosion produces recognizable trough-and areête topography. Mean and modal relief increase where glacial activity is confined to cirques, but decrease when trough incision by ice becomes established as a dominant process in the landscape. © 1997 by John Wiley & Sons, Ltd.  相似文献   

9.
严珍珍  张怀  范湘涛  杜小平  石耀霖 《地震》2013,33(4):105-114
在活动构造区, 河流地貌对构造活动具有明显的响应, 地貌形态和水系形态能够很好地记录构造活动信息。 基于地貌演化理论, 考虑断层的左旋错动作用及降雨等因素, 利用数值模拟方法, 定量研究河流形态在断层水平错动及流水侵蚀内外力作用下的动力学演变过程。 初步的计算结果显示了河流形态与断层走滑运动的耦合效应。 断层发生水平左旋滑动促使该处河道两侧的陡坎发生相对错动, 形成弯转水系, 伴随河流的侧向侵蚀作用, 河道上下游连续被拓宽, 河道下游右侧堆积了较厚的沉积物, 而河道上游左侧由于受到较强流水侵蚀作用很难堆积沉积物。 分别对河道上游和河道下游的横剖面形态进行对比分析, 表明由于断层水平错动效应, 使得河道下游两侧呈现不对称特征, 而河道上游依然保持着明显对称性。 同时, 河道剖面形态对断层水平错动作用有积极的响应, 由于断层持续左旋走滑运动, 断层处剖面的高程突然增加, 坡度也随之突然变陡。 数值模拟结果与实际地质考察结果有着很好的一致性, 证明了理论和数值模型的可靠性。  相似文献   

10.
A topological representation of a rural catchment is proposed here in addition to the generally used topographic drainage network. This is an object‐oriented representation based on the identification of the inlets and outlets for surface water flow on each farmer's field (or plot) and their respective contributing areas and relationships. It represents the catchment as a set of independent plot outlet trees reaching the stream, while a given plot outlet tree represents the pattern of surface flow relationships between individual plots. In the present study, we propose to implement functions related to linear and surface elements of the landscape, such as hedges or road networks, or land use, to obtain what we call a landscape drainage network which delineates the effective contributing area to the stream, thus characterizing its topological structure. Landscape elements modify flow pathways and/or favour water infiltration, thus reducing the area contributing to the surface yield and modifying the structure of the plot outlet trees. This method is applied to a 4·4‐km2 catchment area comprising 43 955 pixels and 312 plots. While the full set of 164 plot outlet trees, with an average of 7 plots per tree, covers 100% of the total surface area of the catchment, the landscape drainage network comprises no more than 37 plot outlet trees with an average of 2 plots per tree, accounting for 52 and 7% of the catchment surface area, when taking account of linear elements and land use, respectively. This topological representation can be easily adapted to changes in land use and land infrastructure, and provides a simple and functional display for intercomparison of catchments and decision support regarding landscape and water management. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
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12.
The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post‐orogenic landscape remain enigmatic. The non‐glaciated Cullasaja River basin of south‐western North Carolina, with uniform lithology, frequent debris flows, and the availability of high‐resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post‐orogenic landscape through the lens of hillslope–channel coupling. This investigation is limited to channels with upslope contributing areas >2.7 km2, a conservative estimate of the transition from fluvial to debris‐flow dominated channel processes. Values of normalized hypsometry, hypsometric integral, and mean slope vs elevation are used for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. The transient effect of knickpoint‐driven channel incision on basin hillslopes is captured by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the Cullasaja River. A conceptual model of area–elevation and slope distributions is presented that may be representative of post‐orogenic landscape evolution in analogous geologic settings. Importantly, the model explains how knickpoint migration and channel–hillslope coupling is an important factor in tectonically‐inactive (i.e. post‐orogenic) orogens for the maintenance of significant relief, steep slopes, and weathering‐limited hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

13.
The long‐term water level variations of the Dead Sea (DS) were assessed using a previously developed simulation model. The model establishes the condition of the DS by evaluating a series of ordinary differential equations describing mass balances on the water and major chemical species. The DS was modelled as a two‐layer system. The model was modified using up‐to‐date inflow data and recent hypsometric graphs to derive the volume–area–level relationships. Three scenarios were studied: continuation of current conditions; a cessation in industrial activity when the DS water level drops to a certain level; and a simplified weather change scenario. The model predicted that the DS will not dry up, but its level will continue to drop with a decelerating rate with no equilibrium level in 500 years. Changing climate would accelerate the level drop. In the 500 year period, after an initial increase, the DS salinity drops. The opposite behaviour is noted in the evaporation rate, which increases after an initial decrease. Ceasing industrial pumping would eventually restore the DS to its normal level, but with changed conditions. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

14.
Roads in rural, upland landscapes are important sources of runoff and sediment to waterways. The downstream effects of these sources should be related to the connectivity of roads to receiving waters. Recent studies have explored this idea, but only simple metrics have been used to characterize connectivity and few studies have quantified the downstream effects of road–stream connectivity on sediment or solute budgets and channel morphology. In this study, we evaluated traditional and newly developed connectivity metrics that utilized features of landscape position and delivery pathway to characterize road–stream connectivity in upland settings. Using data on stream geomorphic conditions developed by the Vermont Agency of Natural Resources (Montpelier, VT), we related road connectivity metrics to channel condition on a set of 101 forested, upland streams with minimal development other than predominantly gravel road networks. Logistic regression indicated that measures of road density, proximity and orientation successfully distinguished among categories of stream geomorphic condition at multiple geographic scales. Discriminant function analysis using a set of inherent channel characteristics combined with road connectivity metrics derived at the reach corridor scale successfully distinguished channel condition for over 70% of the channels evaluated. This research contributes to efforts to evaluate the cumulative downstream effects of roads on stream channels and aquatic resources and provides a new means of watershed assessment to derive metrics that can be used to predict channel condition. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

15.
One-dimensional Fickian dispersion models such as the advection diffusion equation (ADE) are commonly used to analyse and predict concentration distributions downstream of contamination events in watercourses. Such models are only valid once the tracer had entered the equilibrium zone. This paper compares previous theoretical, experimental and numerical estimates of the distance to reach the equilibrium zone with new experimental values, obtained by examining the change of skewness in a tracer profile, downstream of a cross-sectionally well mixed source. Closer agreement was found with Fischers’ theoretical estimate than prior experimental and numerical studies.  相似文献   

16.
对马尼拉俯冲带中段高精度地形数据编辑后绘制成图,联合之前所获取的地震剖面数据,对俯冲带增生楔的精细构造地貌特征及发育模式进行了深入探讨.在增生楔下构造区发现了大量狭长的微型圈闭盆地,经过对其平面断裂特点与深部应力状态的分析,发现增生楔从俯冲前缘到脊顶区其构造特点的转变对应着微型圈闭盆地4个完整的发育阶段,即初期的加积断裂阶段、中期的圈闭成盆阶段、后期的挤压消亡阶段乃至最终的隆升推覆阶段,揭示出一种新型的俯冲带增生楔发育模式,并推断其本质是深部板片俯冲活动所产生的压应力在海底面的表现.  相似文献   

17.
Pakistan has a long history of seismological activity. The devastation caused by Kashmir earthquake has been administered all over the world. In Pakistan first seismological network, consisting of analog accelerograms and seismographs, was setup in early 1969 at Tarbela, where the largest water reservoir of the country is located. An approach to convert analog ground motion records into digital form is explained using a simple technique. The digitized data was compared with the original analog record and found in good agreement. The data has been used to plot response spectra. The digitized data will be available for seismic response analysis of structures and seismic risk analysis of the region.  相似文献   

18.
We present new data about the morphological and stratigraphic evolution and the rates of fluvial denudation of the Tavoliere di Puglia plain, a low‐relief landscape representing the northernmost sector of the Pliocene‐Pleistocene foredeep of the southern Apennines. The study area is located between the easternmost part of the southern Apennine chain and the Gargano promontory and it is characterized by several orders of terraced fluvial deposits, disconformably overlying lower Pleistocene marine clay and organized in a staircase geometry, which recorded the emersion and the long‐term incision history of this sector since mid‐Pleistocene times. We used the spatial and altimetric distribution of several orders of middle to late Pleistocene fluvial terraces in order to perform paleotopographic reconstruction and GIS‐aided eroded volumes estimates. Then, we estimated denudation rates on the basis of the terraces chronostratigraphy, supported by published OSL and AAR dating. Middle to upper Pleistocene denudation rates estimated by means of such an approach are slightly lower than 0.1 mm yr‐1, in good agreement with short‐term data from direct and indirect evaluation of suspended sediment yield. The analysis of longitudinal river profiles using the stream power erosion model provided additional information on the incision rates of the studied area. Middle to late Quaternary uplift rates (about 0.15 mm yr‐1), calculated on the basis of the elevation above sea level of marine deposits outcropping in the easternmost sector of the study area, are quite similar to the erosion rates average value, thus suggesting a steady‐state fluvial incision. The approach adopted in this work has demonstrated that erosion rates traditionally obtained by quantitative geomorphic analysis and ksn estimations can be successfully integrated to quantify rates of tectonic or geomorphological processes of a landscape approaching steady‐state equilibrium. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

19.
Mesozoic and Cenozoic volcanic rocks are widely distributed in the circum-Pacific area of eastern China. These rocks have long been genetically linked to westward subduction of the paleo-Pacific oceanic plate to the eastern Asia continent[1,2]. Research in re-cent years[3―6] has attained conclusions that a simple paleo-Pacific subduction model does not work well in interpreting all the volcanic rocks in eastern China, although some of them could be attributed to circum-Pacific interaction …  相似文献   

20.
The on- and off-site effects of soil erosion in many environments are well known, but there is still limited understanding of the soil loss fluxes in downstream direction due, among other factors, to scarce and poor quality. A four year study to (i) evaluate water and sediment fluxes at different spatio-temporal scales and (ii) interpret the results in terms of processes involved and the controlling factors, was conducted in Thukela basin, South Africa. Five hierarchically nested catchments; namely microcatchment (0.23 km2), subcatchment (1.20 km2), catchment (9.75 km2), sub-basin (253 km2) and basin (29,038 km2), were used in addition to fifteen (1 m2) microplots and ten (10 m2) plots on five locations within the microcatchment. The results showed 19% decrease of unit-area runoff (q) from 3.1 L m−2 day−1 at microplot to 2.5 L m−2 day−1 at plot scale followed by steeper (56%) decrease at microcatchment scale. The q decreased in downstream direction to very low level (q ≤ 0.26 L m−2 day−1). The changes in q were accompanied by initial 1% increase of soil loss (SL) from 18.8 g m−2 day−1 at microplot to 19.1 g m−2 day−1 at plot scale. The SL also decreased sharply (by 39 fold) to 0.50 g m−2 day−1 at microcatchment scale, followed by further decrease in downstream direction. The decrease of q with spatial scale was attributed to infiltration losses, while initial increase of SL signified greater competence of sheet than splash erosion. The decrease of SL beyond the plot scale was attributed to redistribution of the soil on the hillslope and deposition on the stream channel upstream of the microcatchment outlet. Therefore, erosion control strategies focussing on the recovery of vegetation on the slope and stabilisation of gullies are recommended.  相似文献   

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