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1.
The pattern of relative denudation at the soil-bedrock interface over a wooded Magnesian Limestone hillslope was investigated using micro-weight loss bedrock tablets. The resulting pattern of weight loss after emplacement for one year indicated a consistent upslope increase in solutional denudation. Results from tablets emplaced for two years confirmed this. Dye tracing and gypsum sphere weight loss results showed that water movement over the slope was by vertical percolation and not by throughflow. The pattern of solutional denudation was related to changes in soil type and associated changes in soil pH. Continued slope development by solutional denudation will ultimately lead to slope decline. Comparison with a similar study suggests that a general soil chemistry based model of hillslope solutional denudation can be proposed.  相似文献   

2.
A hydrochemical budget is used to quantify the rate of chemical weathering and solutional denudation on Old Red Sandstone in East Twin drainage basin (0.2 km2) on the Mendip Hills for the 1972–73 Water Year. Net nutrient uptake by the biomass and precipitation inputs are subtracted from stream solute outputs to give an estimate of the solutes released to the system by weathering. The mineralogies of the sandstone and the soil are compared to predict possible weathering reactions for the primary and secondary minerals. Tentative estimates of primary mineral alteration and secondary mineral formation are then made by substituting the hydrochemical balances into the formulated weathering reactions. Finally the rate of solutional denudation (0.8 tonnes/a or 1.6 mm/100 a) is compared with other estimates of solutional and mechanical denudation at East Twin and with similarly derived results for other lithologies.  相似文献   

3.
Previous studies of the downslope movement of soil moisture have been largely confined to two-dimensional slope profiles—the influence of contour curvature (three-dimensional) on moisture movement has received little attention. An automatic tensiometer system has been used to monitor soil moisture status continuously in a single hollow and adjacent spurs. Maximum saturated hillslope flow is shown to coincide with the stream discharge ‘throughflow peak’. Relative to the hollow, little saturation is evident at the base of the spurs. This subcatchment model is applied to a major portion of the catchment, showing the general importance of topography in the control of stream discharge.  相似文献   

4.
Variation in solute concentrations of soil and stream water during throughflow events was studied at Bicknoller Combe, Somerset, England. The main hydrological process acting in the catchment involves a delayed throughflow discharge pulse a day or two after the rainfall event. During the period of storm runoff, coincident with the rainfall, the solutes in the stream are diluted, but their concentration in the throughflow remains unchanged. During the delayed throughflow pulse, concentrations of both soil and stream water increase. This is due to additional leaching from the soil in hollows where saturated moisture conditions prevail. The results suggest that two distinct erosional environments may exist: on the spurs, leaching seems to be related solely to infiltration processes, whilst in the hollows, saturated throughflow also contributes to the solute removal. This contrast in erosional processes may perhaps account for the difference in slope form and development between the hollow and spur zones.  相似文献   

5.
Upper Sinking Cove, dissecting the eastern escarpment of the Cumberland Plateau, is characterized by a multiple aquifer, predominantly vadose hydrologic system with minor surface components. There is a central trunk channel along the axis of the cove and a network of independent tributaries. Aquitards within the limestones, particularly Hartselle Formation shales, have influenced both cave and surface landform development by perching ground waters and slowing the vertical growth of closed depressions. Long-term solutional denudation in the portion of the cove underlain by limestones (40 per cent) is an estimated 56 mm per 1000 years, suggesting that karst development began 15–16 million years ago. Despite lower soil CO2 and spring water hardness, 61 per cent of annual denudation occurs in the six winter months when 76 per cent of yearly runoff occurs. Landform development in Upper Sinking Cove appears to have begun as stream erosion carved a valley first in the sandstone caprock of the escarpment and later in the underlying Pennington Formation limestones containing numerous shale layers which promoted surface stream flow. Eventually stream erosion exposed the massive Bangor limestones which allowed deep ground water flow. Surface streams were pirated underground with the eventual formation of the chain of three closed depressions which constitute Upper Sinking Cove.  相似文献   

6.
Much of the short-term solute process research in the last 20 years has focused on hydrochemical behaviour. This can help with the identification of solute source area type, but not the actual location of the solutional loss. The location and the spatial distribution of erosion are crucial to the identification of long-term landscale evolution. The way ahead lies in the fact that catchment budgeting and geochemical studies have been able to provide solute uptake rates. If these can be related to soil type, through a knowledge of soil mineralogy, reactive surface area and water flow rate, it may be possible to characterize the location and spatial distribution of solutional erosion through terrain analysis and soil maps in a geographical information system. © 1997 by John Wiley & Sons, Ltd.  相似文献   

7.
Data are presented on daily fluctuations of soil pH in organic soils overlying Carboniferous Limestone in Co. Clare, Eire. High rainfall leads to a drop in pH, as acid waters percolate through the soil, but after rainfall the solution of carbonates in the soil or the solution of the bedrock leads to a return of soil pH to alkalinity. Carbonates tend to remain in the soil on poorly drained sites but solutional removal of calcium occurs on freely drained sites and in the latter case the return to alkalinity is not so rapid. The presence of Calluna vulgaris is thought to be important as it appears to increase the acidity of percolating soil waters. On freely draining sites bedrock erosion may progress to such an extent that deep runnels form, down which soil may be lost.  相似文献   

8.
Soil pipes are common and important features of many catchments, particularly in semi‐arid and humid areas, and can contribute a large proportion of runoff to river systems. They may also signi?cantly in?uence catchment sediment and solute yield. However, there are often problems in ?nding and de?ning soil pipe networks which are located deep below the surface. Ground‐penetrating radar (GPR) has been used for non‐destructive identi?cation and mapping of soil pipes in blanket peat catchments. While GPR can identify subsurface cavities, it cannot alone determine hydrological connectivity between one cavity and another. This paper presents results from an experiment to test the ability of GPR to establish hydrological connectivity between pipes through use of a tracer solution. Sodium chloride was injected into pipe cavities previously detected by the radar. The GPR was placed downslope of the injection points and positioned on the ground directly above detected soil pipes. The resultant radargrams showed signi?cant changes in re?ectance from some cavities and no change from others. Pipe waters were sampled in order to check the radar results. Changes in electrical conductivity of the pipe water could be detected by the GPR, without data post‐processing, when background levels were increased by more than approximately twofold. It was thus possible to rapidly determine hydrological connectivity of soil pipes within dense pipe networks across hillslopes without ground disturbance. It was also possible to remotely measure travel times through pipe systems; the passing of the salt wave below the GPR produced an easily detectable signal on the radargram which required no post‐processing. The technique should allow remote sensing of water sources and sinks for soil pipes below the surface. The improved understanding of ?owpath connectivity will be important for understanding water delivery, solutional and particulate denudation, and hydrological and geomorphological model development. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

9.
Relief generation in non‐glaciated regions is largely controlled by river incision into bedrock but datable fluvial terraces that allow quantifying incision rates are not always present. Here we suggest a new method to determine river incision rates in regions where low‐relief surfaces are dissected by streams. The approach consists of three steps and requires the 10Be concentrations of a stream sediment sample and a regolith sample from the low‐relief surface. In the first step, the spatial distribution of 10Be surface concentrations in the given catchment is modelled by assuming that denudation rates are controlled by the local hillslope angles. The slope–denudation rate relation for this catchment is then quantified by adjusting the relation between slope angle and denudation rate until the average 10Be concentration in the model is equal to the one measured in the stream sediment sample. In the second step, curved swath profiles are used to measure hillslope angles adjacent to the main river channel. Third, the mean slope angle derived from these swath profiles and the slope–denudation relation are used to quantify the river incision rate (assuming that the incision rate equals the denudation rate on adjacent hillslopes). We apply our approach to two study areas in southern Tibet and central Europe (Black Forest). In both regions, local 10Be denudation rates on flat parts of the incised low‐relief surface are lower than catchment‐wide denudation rates. As the latter integrate across the entire landscape, river incision rates must exceed these spatially averaged denudation rates. Our approach yields river incision rates between ~15 and ~30 m/Ma for the Tibetan study area and incision rates of ~70 to ~100 m/Ma in the Black Forest. Taking the lowering of the low‐relief surfaces into account suggests that relief in the two study areas increases at rates of 10–20 and 40–70 m/Ma, respectively. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

10.
In order to identify the distribution of aluminium (Al) within an acid hillslope and its release to a stream, the spatial distribution of acid ammonium oxalate extractable Al (Alo) and exchangeable Al3+ have been investigated on a podzolized hillslope in Bicknoller Combe, Somerset, UK. The eluviated Al from topsoils is mainly deposited in the lower soil horizons forming podzolic B horizons, but some Al flows downslope carried by lateral throughflow. Al oxides may provide the main source of exchangeable Al3+ on the study slope due to high soil acidity. Examination of the spatial distribution of exchangeable Al3+ suggests that the slope hollow, where active convergent throughflow occurs, and the saturation wedge at the base of the slope are the main delivery routes of dissolved Al3+ to the stream. Divalent base cations (Ca2+ and Mg2+), supplied from atmospheric input and organic decomposition and carried by throughflow, exchange Al3+ via cation exchange reactions under high water content. Laterally illuviated Al oxides in the lower hollow adjacent to the saturation wedge probably provide a pool for continuous delivery of Al either as soluble or complexed forms to the stream via the saturated wedge. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

11.
How soil erosion rates evolved over the last about 100 ka and how they relate to environmental and climate variability is largely unknown. This is due to a lack of suitable archives that help to trace this evolution. We determined in situ cosmogenic beryllium-10 (10Be) along vertical landforms (tors, boulders and scarps) on the Sila Massif to unravel their local exhumation patterns to develop a surface denudation model over millennia. Due to the physical resistance of tors, their rate of exhumation may be used to derive surface and, thus, soil denudation rates over time. We derived soil denudation rates that varied in the range 0–0.40 mm yr-1. The investigated boulders, however, appear to have experienced repositioning processes about ~20–25 ka bp and were therefore a less reliable archive. The scarps of the Sila upland showed a rapid bedrock exposure within the last 8–15 ka. Overall, the denudation rates increased steadily after 75 ka bp but remained low until about 17 ka bp . The exhumation rates indicate a denudation pulse that occurred about 17–5 ka bp . Since then the rates have continuously decreased. We identify three key factors for these developments – climate, topography and vegetation. Between 75 and 17 ka bp , climate was colder and drier than today. The rapid changes towards warmer and humid conditions at the Pleistocene–Holocene transition apparently increased denudation rates. A denser vegetation cover with time counteracted denudation. Topography also determined the extent of denudation rates in the upland regime. On slopes, denudation rates were generally higher than on planar surfaces. By determining the exhumation rates of tors and scarps, soil erosion rates could be determined over long timescales and be related to topography and particularly to climate. This is key for understanding geomorphic dynamics under current environmental settings and future climate change. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.  相似文献   

12.
An area of shallow karst depressions in St. Ann parish, Jamaica is examined. Shallow, ‘temperate’ forms such as these are common in tropical karst areas. Depressions are analyzed morphometrically and a considerable degree of structural control appears to be exhibited. Some morphometric parameters, in particular the depth/diameter ratio, which have been used to postulate depression origin, are examined. Depression hydrology is investigated. Depressions appear to exhibit characteristics of small drainage basins. The occurrence of sporadic flood events is suggested as an important element in the development of surface channel networks. The integration of the depressions into the regional drainage system is investigated by water tracing of ‘underground flow sections’. Chemical analysis of waters in various parts of the drainage system reveals variations which point to the importance of solutional activity at the soil-bedrock interface. The influence of a soil cover in promoting solutional activity is indicated.  相似文献   

13.
Time patterns of karst denudation in northwest Georgia (U.S.A.) were investigated at three spring sites for 12 months and at five stream sites for 10 years. Rainfall was evenly distributed and showed no significant seasonality. At the springs, as well as the streams, water hardness was largely controlled by discharge. At the springs, soil pCO2 and water pH were strongly correlated (r + -0·69 to -0·83). Solute transport in spring waters was highly seasonal, with two conduit flow springs removing more limestone in the winter, and the diffuse flow spring removing more during the growing season. At the stream sites, most denudation occurred during the winter and spring seasons, and least during the summer. Fourier analysis showed that variations in denudation occur on deterministic (long-wave) as well as stochastic (shortwave) time scales. As contributing variables, discharge varied in short-wave and long-wave cycles, whereas soil pCO2 showed only a long-wave cycle. The 12 month deterministic cycles were the most important, with changes in discharge taking precedence over soil pCO2. Time series regression explains up to 69 per cent of changes in denudation through rain and soil pCO2. Time cycles in available water are the key controlling factor of denudation, and amounts of available soil CO2 may not be as important in the temporal patterns of karst downwearing as has been believed previously.  相似文献   

14.
Denudation rates of small tributary valleys in the upper Rhone valley of the Swiss Central Alps vary by more than an order of magnitude within a very small distance (tens of kilometers). Morphometric data indicate two distinct erosion processes operate in these steep mountain valleys. We determined the rates of these processes using cosmogenic beryllium‐10 (10Be) in pooled soil and stream sediment samples. Denudation in deep, glacially scoured valleys is characterized by rapid, non‐uniform processes, such as debris flows and rock falls. In these steep valleys denudation rates are 760–2100 mm kyr?1. In those basins which show minimal previous glacial modification denudation rates are low with 60–560 mm kyr?1. The denudation rate in each basin represents a binary mixture between the rapid, non‐uniform processes, and soil creep. The soil production rate measured with cosmogenic 10Be in soil samples averages at 60 mm kyr?1. Mixing calculations suggest that the debris flows and rock falls are occurring at rates up to 3000–7000 mm kyr?1. These very high rates occur in the absence of baselevel lowering, since the tributaries drain into the Rhone trunk stream up‐stream of a knickzone. The flux‐weighted spatial average of denudation rates for the upper Rhone valley is 1400 mm kyr?1, which is similar to rock uplift rates determined in this area from leveling. The pace and location of erosion processes are determined by the oscillation between a glacial and a non‐glacial state, preventing the landscape from reaching equilibrium. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

15.
When designing buried structures using a performance-based framework, it is important to estimate their uplift displacement. A simplified method is proposed for predicting the uplift displacement of a hollow cylinder structure buried in shallow backfill based on the equilibrium of vertical forces acting on the structure during earthquakes. However, this method only provides the maximum value, which frequently is overestimated in practical applications. To offset this limitation, first, the uplift behavior of buried hollow cylinder structures subjected to strong earthquake motions was simulated. Then, two-dimensional effective stress analyses based on the multiple shear mechanism for soil were conducted, and the results were compared with the centrifuge test data. The soil parameters were evaluated based on laboratory test results. The seismic response data from 20 g centrifuge tests were analyzed, and the results were generally consistent with the results of centrifuge model tests. In particular, the effective stress model showed a reasonable ability to reproduce the varying degrees of uplift displacement depending on the geotechnical conditions of trench soils adjacent to the hollow cylinder structures buried in shallow ground.  相似文献   

16.
Rates of surface processes on slopes,slope retreat and denudation   总被引：1，自引：0，他引：1  
Results taken from 270 publications on rates are summarized, and collated with those from 149 publications reviewed previously (Young, 1969, 1974). The data are classified by major climatic zone, normal or steep relief, and consolidated or unconsolidated rocks. Representative rates and their ranges are given for soil creep, solifluction, surface wash, solution (chemical denudation), rock weathering, slope retreat, cliff (free face) retreat, marine cliff retreat, and denudation, the last being compared with representative rates of uplift. Solifluction is of the order of 10 times faster than soil creep, but both cause only very slow ground loss. Solution is an important cause of ground loss for siliceous rocks, on which it may be half as rapid as on limestones. Total denudation, brought about mainly by surface wash, reaches a maximum in the semi-arid and probably also the tropical savanna zones. Acceleration of natural erosion rates by human activities ranges from 2–3 times with moderately intense land use to about 10 times with intensive land use (and considerably higher still where there is recognized accelerated soil erosion). Where there is active uplift, typical rates are of the order of 10 times faster than denudation, although in some high, steep mountain ranges these may approach equality.  相似文献   

17.
水闸闸基隐患探测雷达图像特征分析   总被引：6，自引：5，他引：6  
水闸闸基隐患严重威胁水闸安全，闸基淘空是水闸较常见的隐患之一。闸底地基垫层在水闸上下游水位差的作用下，经一段时间的运行后，往往会形成强渗流层和淘空区，洪水到来时便产生管涌，危及水闸的安全运行和人民的生命财产安全。利用探地雷达技术可探测出闸基冲刷剥蚀程度、淘空区的位置、范围、发育程度及规模，便于及早采取防范措施，进行加固处理。探地雷达技术是水闸闸基隐患探测的有效手段，雷达图像的特征分析是雷达资料解释的关键，通过雷达图像的特征分析，可判译出闸基隐患的具体部位和类型。  相似文献   

18.
内蒙古大青山的新生代剥蚀和隆起   总被引：6，自引：1，他引：5       下载免费PDF全文
内蒙古大青山及其毗邻的呼和浩特断陷盆地是研究剥蚀和地壳均衡隆起的理想地区。本文提供了大青山新生代等高峰顶面和晚第四纪河流阶地拱曲变形的证据 ;依据呼和浩特盆地的地震探测获得的沉积厚度 ,计算出大青山的剥蚀和地壳均衡隆起量 ;提出地壳均衡隆起是大青山晚第三纪以来主要的区域变形机制 ;指出由於地壳均衡隆起 ,剥蚀作用最终只是使大青山高度略微降低 ;同时复原了大青山新生代景观演化历史。本文还讨论了剥蚀和地壳均衡隆起之间的耦合关系以及断裂作用在其中的地位 ,认为大青山新生代景观演化是在剥蚀去荷失去重力平衡和均衡隆起恢复重力平衡的长期自身耦合作用中进行的 ,在此过程中断层的下降盘由主动盘变成被动盘  相似文献   

19.
Landform evolution models are powerful tools for determining long-term erosional stability and denudation rates spanning geological timescales. SIBERIA, CAESAR and CHILD are examples of these model. The newly developed State Space Soil Production and Assessment Model (SSSPAM) coupled soilscape-landform evolution model has the ability to assess overall erosion rates of catchment scale landforms either using short-term precipitation events, variable precipitation or time-averaged precipitation (annual average). In addition, SSSPAM has the capability of developing the subsurface soil profile through weathering and armouring. In SSSPAM, physical processes of pedogenesis such as erosion and armouring, diffusion, sediment deposition and weathering are modelled using a state space matrix approach. In this article we simulate the short-term evolution (100 years) of a proposed post-mining landform using both SIBERIA and SSSPAM and compare the erosion and sediment output results. For the short-term simulations SSSPAM's armouring capability was disabled. The models were then used to simulate the evolution of the catchment for 10,000 years. Results demonstrate that the short-term SSSPAM simulation results compare well with the results from the established landform evolution model SIBERIA. The long-term armouring disabled SSSPAM simulations produces simulated erosion rates comparable with SIBERIA simulations both of which are similar to upper limit of field measured denudation rates. The SSSPAM simulation using armouring demonstrated that armouring reduced the erosion rate of the catchment by a factor of 4 which is comparable with the lower limit of field measured denudation rates. This observation emphasizes the importance of armouring in long-term evolution of landforms. Soil profile cross-sections developed from the same results show that SSSPAM can also reproduce subsurface soil evolution and stratification and spatial variability of soil profile characteristics typically observed in the field.  相似文献   

20.
Cosmogenic nuclides in rock, soil, and sediment are routinely used to measure denudation rates of catchments and hillslopes. Although it has been shown that these measurements are prone to biases due to chemical erosion in regolith, most studies of cosmogenic nuclides have ignored this potential source of error. Here we quantify the extent to which overlooking effects of chemical erosion introduces bias in interpreting denudation rates from cosmogenic nuclides. We consider two end‐member effects: one due to weathering near the surface and the other due to weathering at depth. Near the surface, chemical erosion influences nuclide concentrations in host minerals by enriching (or depleting) them relative to other more (or less) soluble minerals. This increases (or decreases) their residence times relative to the regolith as a whole. At depth, where minerals are shielded from cosmic radiation, chemical erosion causes denudation without influencing cosmogenic nuclide buildup. If this effect is ignored, denudation rates inferred from cosmogenic nuclides will be too low. We derive a general expression, termed the ‘chemical erosion factor’, or CEF, which corrects for biases introduced by both deep and near‐surface chemical erosion in regolith. The CEF differs from the ‘quartz enrichment factor’ of previous work in that it can also be applied to relatively soluble minerals, such as olivine. Using data from diverse climatic settings, we calculate CEFs ranging from 1.03 to 1.87 for cosmogenic nuclides in quartz. This implies that ignoring chemical erosion can lead to errors of close to 100% in intensely weathered regolith. CEF is strongly correlated with mean annual precipitation across our sites, reflecting climatic influence on chemical weathering. Our results indicate that quantifying CEFs is crucial in cosmogenic nuclide studies of landscapes where chemical erosion accounts for a significant fraction of the overall denudation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

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