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1.
Geomorphic considerations for erosion prediction   总被引：9，自引：0，他引：9  
 Current soil-erosion prediction technology addresses processes of rainsplash, overland-flow sediment transport, and rill erosion in small watersheds. The effects of factors determining sediment yield from larger-scale drainage basins, in which sediment movement is controlled by the combined small-scale processes and a complex set of channel and other basin-scale sediment-delivery processes, such as soil creep, bioturbation, and accelerated erosion due to denudation of vegetation, have been poorly evaluated. General suggestions are provided for the development of erosion-prediction technology at the geomorphic or drainage-basin scale based on the separation of sediment-yield data for channel and geomorphic processes from those of field-scale soil loss. An emerging technology must consider: (1) the effects on sediment yield of climate, geology and soils, topography, biotic interactions with other soil processes, and land-use practices; (2) all processes of sediment delivery to a channel system; and (3) the general tendency in most drainage basins for progressively greater sediment storage in the downstream direction. Received: 8 November 1995 · Accepted: 20 November 1995  相似文献   

2.
We measured 10Be and 26Al in 29 sediment samples to infer the history and millennial-scale rates of change down a low-gradient piedmont, a common but enigmatic landform that dominates the Mojave Desert. Nuclide data suggest that a large volume of sediment was deposited on the proximal East Range Road piedmont in Fort Irwin, California, ∼ 75,500 yr ago. Since then, this material has been stable or eroding slowly. In contrast, on the distal piedmont (3.5 km from the upland source basins) soil stratigraphy suggests that there have been alternating periods of surface stability, erosion, and deposition over the last 70,000 yr. Nuclide data from samples amalgamated along cross-piedmont transects suggest that long-term average down-gradient sediment speeds range from 9 cm yr− 1 near the uplands to 22 cm yr− 1 6 km down-piedmont. These speeds are similar to 10Be-estimated sediment speeds down three other piedmonts in the Mojave Desert, suggesting that piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates. The timing of surface process change down the East Range Road piedmont is determined by a combination of sediment available in the source basins, sediment transport rates, and the size of the piedmont.  相似文献   

3.
Deriving transport pathways in a sediment trend analysis (STA)   总被引：1，自引：0，他引：1  
Sediment trend analysis (STA) is a technique that enables patterns of net sediment transport to be determined by relative changes in grain-size distributions of all naturally occurring sediments. In addition, STA can determine the dynamic behaviour of bottom sediments with respect to erosion, accretion or dynamic equilibrium. The data requirements for STA are the full grain-size distributions taken from sediment grab samples collected at a regular spacing over a particular area of interest. Two types of methods are presently used in the derivation of the transport pathways: a line-by-line approach, in which transport pathways are determined by searching for sample sequences in which the distributions change, in a statistically acceptable manner; and various vector approaches, in which each sample is compared to neighbouring sites from which a vector sum is calculated.The basic assumption for STA is that the processes that cause sediment transport will affect the statistics of sediment distributions in a predictable way. In reality, this type of analysis is complicated through the inclusion of a number of uncertainties, or noise. The goal of STA is to extract the information (the transport pathways) from the noisy signal (the grain-size distributions), an approach that is made difficult because neither the nature of the information nor the noise is known. Because of this, obtaining results by simply applying its theory in a “black-box” approach may provide poor solutions.The line-by-line approach to STA draws from communications theory to achieve a solution. In some communications systems, the information from many sources is combined into one signal. The resulting signal is, from a statistical viewpoint, nothing but noise. The extraction of specific information assumes that information is indeed present, and determines if that assumption is consistent with the received signal. For STA, the procedure is to assume a transport direction over an area comprising many sample sites. From this assumption, the predicted sediment trends are compared with the pathways determined by the actual samples. The assumed transport direction is repeatedly modified until the best fit is achieved.Vector techniques may be very helpful to provide insights and guidance to the line-by-line approach. However, the approach is ultimately necessary to finalize a credible solution as well as providing important further information on the dynamic behaviour of the sediments, and to delineate specific sediment transport environments.  相似文献   

4.
Characterizing stream erosion in any steep mountain landscape is arduous, but the challenge level increases when the stream flows through a glaciated catchment frequently modified by hillslope debris.Glacial landforms and stochastic mass wasting in alpine systems may interfere with sediment delivery to downstream sites where detrital sediments are often collected to represent upstream bedrock sources.To use detrital sediments as indicators of erosion, we need to understand potential sediment accumulation in flat glaciated reaches or behind rockfall barriers. This study investigates the stream channel in Garnet Canyon, a glaciated catchment located in the central Teton Range, to describe hillslope coupled channel morphology and the subsequent effects on sediment transport throughout the catchment.Stream cross-section surveys and sediment size measurements of the surface bedload were collected in the field within a glacially flattened segment of Garnet Canyon. Calculations of shear stress conditions allowed evaluation of the importance of mineral densities on potential grain entrainment. The length of the Garnet Canyon stream observed in this study was coupled with hillslope deposits. Critical shear stresses were sufficient to move gravel-sized sediments through all sections when calculated with quartz mineral density and through most sections when applying apatite mineral density. These results verify the application of detrital sediments to evaluate erosion rates or spatial bedrock sources because snowmelt stream flow efficiently moves entrained sediment past glacially reduced slopes and potential talus barriers.  相似文献   

5.
In recent years, research on spatial scale and scale transformation of eroded sediment transport has become a forefront field in current soil erosion research, but there are very few studies on the scale effect problem in Karst regions of China. Here we quantitatively extracted five main factors influencing soil erosion, namely rainfall erosivity, soil erodibility, vegetative cover and management, soil and water conservation, and slope length and steepness. Regression relations were built between these factors and also the sediment transport modulus and drainage area, so as to initially analyze and discuss scale effects on sediment transport in the Wujiang River Basin (WRB). The size and extent of soil erosion influencing factors in the WRB were gauged from: Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM), precipitation data, land use, soil type and Normalized Difference Vegetation Index (NDVI) data from Global Inventory Modeling and Mapping Studies (GIMMS) or Advanced Very High Resolution Radiometer (AVHRR), and observed data from hydrometric stations. We find that scaling effects exist between the sediment transport modulus and the drainage area. Scaling effects are expressed after logarithmic transformation by a quadratic function regression relationship where the sediment transport modulus increases before decreasing, alongside changes in the drainage area. Among the five factors influencing soil erosion, slope length and steepness increases first and then decreases, alongside changes in the drainage area, and are the main factors determining the relationship between sediment transport modulus and drainage area. To eliminate the influence of scale effects on our results, we mapped the sediment yield modulus of the entire WRB, adopting a 1 000 km2 standard area with a smaller fitting error for all sub-basins, and using the common Kriging interpolation method.  相似文献   

6.
Wind waves in the innershelf of the south-central Kerala coast, south-west India were measured at four locations during different seasons. Simultaneously, numerical models were developed to simulate the wave and sediment transport regime of the innershelf. Strong monsoonal influence is seen in the wave characteristics with greater amplitudes, lower periods and switch-over from SW to SWW–W direction. The net annual longshore sediment transport is southerly in the innershelf and northerly in the surf zone. These counter-directional transports are linked by seasonally reversing the cross-shore transports. In the locations where the transports in the longshore and cross-shore directions are balanced, stable beaches prevail. Erosion/accretion tendency prevails in locations where these transports are not balanced. The southern and northern parts of the coast where onshore transports are predominant could be accreting zones. The erosion/accretion pattern deduced from the sediment transport model corresponds well with the long-term erosion/accretion trend for this coast.  相似文献   

7.
The study of the hydrologic characters of a water course permits the correct management of the corresponding basin and a greater control over the water resources of the whole basin; therefore, a suitable planning and maintenance of the necessary interventions along the water course, especially in proximity of the outlet to sea, becomes necessary. An evaluation of the solid transport allows an estimation of the erosion to which the basin is subjected as a result of the river flow, and further helps to prevent hydrologic disasters in the possible risk zones. Among the various experimental techniques in use for measuring the suspended-solid transport, nuclear methods have been preferably used in this research, which are based on monitoring the concentration of the suspended sediments. The suspended-solid concentration is detected by the attenuation of radioactivity emitted by a source of 241Am dipped in the water. This attenuation, due to the presence of the sediments transported in great amounts during events of flood is measured using a scintillation detector made up of a crystal of NaI(Tl). With appropriate calibration curves built both in the laboratory and in the field, it is possible to trace the amount of suspended-solid transport in a certain river section that is located in the proximity of the river outlet. This methodology, applied to different equipped basins in Italy and Africa, is particularly useful for small and medium water courses (similar to those of the Apennine ranges in Italy), allowing an assessment of the erosion in the whole watershed. In this note, the techniques used are introduced in detail, with particular attention to the instrument calibration, and the numerical results obtained for some basins in the Marche region (Italy) are compared with some empirical formulae used in previous reports for the calculation of erosion.  相似文献   

8.
中大流域水沙耦合模拟物理概念模型   总被引：24，自引：1，他引：24       下载免费PDF全文
根据黄河中游、北方干旱地区流域的超渗产流水文特征和冬季积雪的累积及融化机制,提出了中大流域水流模拟模型,结合黄土地区小流域坡面产沙、汇沙和沟蚀产沙、汇沙计算公式,构成了中大流域水沙耦合模拟物理概念模型。该模型较好地处理了北方干旱地区中大流域用下渗曲线计算地面径流中存在的观测资料缺乏、数据处理量太大两大难题;考虑了大流域气候、下垫面因素空间的不均匀性和雨洪径流产沙与融雪径流产沙间的差异。经流域实测资料的模拟检验表明,模型结构较合理,模拟结果较好。  相似文献   

9.
Modelling of Late Quaternary paleoceanography and sedimentation in the northern North Atlantic (NNA) is achieved by coupling the ocean general circulation model SCINNA (Sensitivity and Circulation In the NNA) to the sedimentation models SENNA (Sedimentation In the NNA) and PATRINNA (PArticle Tracing In the NNA).SCINNA is based on the primitive equations with conservation of mass, momentum, energy, heat and salt. SENNA and PATRINNA are driven by temperature, salinity and velocity fields derived from SCINNA. The modelling includes three-dimensional circulation of the ocean, sediment transport in the water column and two-dimensional sedimentary processes in a thin bottom layer. SENNA calculates the erosion, transport and deposition of sediments, resulting in sedimentation patterns for specific time intervals. PATRINNA models the transport paths of single sediment grains corresponding to the ocean circulation.The NNA reacts in a highly sensitive manner to small forcing changes, as shown by our sensitivity experiments. From these experiments it is possible to model specific circulation regimes for glacial and interglacial periods, for melt water events and for the onset of glaciation. The different climatic stages in the circulation model produce different sediment patterns in the sedimentation models, which correspond closely to the sedimentary record.  相似文献   

10.
Natural runoff observation fields with different vegetation coverage were established in the Zuomaoxikongqu River basin in the headwater area of the Yangtze River, and in the Natong River basin and the Kuarewaerma River basin in the headwater area of the Yellow River, China. The experiments were conducted using natural precipitation and artificially simulated precipitation between July and August to study the runoff and sediment-producing effects of precipitation under the conditions of the same slope and different alpine meadow land with coverage in the headwater areas. The results show that, in the three small river basins in the headwater areas of the Yangtze and the Yellow Rivers, the surface runoff yield on the 30° slope surface of the alpine meadow land with a vegetation cover of 30% is markedly larger than that of the fields with a vegetation cover of 95, 92, and 68%. Furthermore, the sediment yield is also obviously larger than the latter three; on an average, the sediment yield caused by a single precipitation event is 2–4 times as large as the latter three. Several typical precipitation forms affecting the runoff yield on the slope surface also influence the process. No matter how the surface conditions are; the rainfall is still the main precipitation form causing soil erosion. In some forms of precipitation, such as the greatest snow melting as water runoff, the sediment yield is minimal. Under the condition of the same precipitation amount, snowfall can obviously increase the runoff yield, roughly 2.1–3.5 times as compared to the combined runoff yield of the Sleet or that of rainfall alone; but meanwhile, the sediment yield and soil erosion rate decrease, roughly decreasing by 45.4–80.3%. High vegetation cover can effectively decrease the runoff-induced erosion. This experimental result is consistent in the three river basins in the headwater areas of the Yangtze and Yellow Rivers.  相似文献   

11.
Suspended sediment concentration is a major variable influencing soil erosion and loss, study on which at different spatial scales is of great meaning to understand soil erosion mechanism and sediment transport process. Based on data from 4 sloping surfaces and 7 basins ranging from 0.0003 to 187 km2 in area, the suspended sediment concentration in flood season (SSC) with drainage area is studied. With increasing drainage area on the slope surfaces, the mean suspended sediment concentration in flood season (MSSC) enhances continuously until a peak value of 685 kg m−3 occurs at the whole slope surface No. 7 runoff plot resulting from harder and harder erosion forms downslope. Entering basin systems, the diluted action of subsurface water on the toeslope on MSSC and small water flow power Ω make a minimum MSSC value of 568 kg m−3 occur in the first-order basin system Tuanshangou basin at an area of 0.18 km2, and then from Tuanshangou basin to larger basins, the positive feedback function among drainage density, water flow energy, and hyperconcentrated flow as well as its reduction of settling velocity of coarser particles generates continuously increasing MSSC with drainage area.  相似文献   

12.
 A shallow landslide erosion and sediment yield component, applicable at the basin scale, has been incorporated into the physically based, spatially distributed, hydrological and sediment transport modelling system, SHETRAN. The component determines when and where landslides occur in a basin in response to time-varying rainfall and snowmelt, the volume of material eroded and released for onward transport, and the impact on basin sediment yield. Derived relationships are used to link the SHETRAN grid resolution (up to 1 km), at which the basin hydrology and final sediment yield is modelled, to a subgrid resolution (typically around 10–100 m) at which landslide occurrence and erosion is modelled. The subgrid discretization, landslide susceptibility and potential landslide impact are determined in advance using a geographic information system (GIS), with SHETRAN then providing information on temporal variation in the factors controlling landsliding. The ability to simulate landslide sediment yield is demonstrated by a hypothetical application based on a catchment in Scotland. Received: 30 October 1996 · Accepted: 25 June 1997  相似文献   

13.
The largest plain in the North Vietnam has formed by the redundant sediment of the Red River system. Sediment supply is not equally distributed, causing erosion in some places. The paper analyzes the evolvement and physical mechanism of the erosion. The overlay of five recent topographical maps (1930, 1965, 1985, 1995, and 2001) shows that sediment redundantly deposits at some big river mouths (Ba Lat, Lach, and Day), leading to rapid accretion (up to 100 m/y). Typical mechanism of delta propagation is forming and connecting sand bars in front of the mouths. Erosion coasts are distributed either between the river mouths (Hai Hau) or nearby them (Giao Long, Giao Phong, and Nghia Phuc). The evolvement of erosion is caused by wave-induced longshore southwestward sediment transport. Meanwhile sediment from the river mouths is not directed to deposit nearshore. The development of sand bars can intensively reduce the erosion rate nearby river mouths. Erosion in Hai Hau is accelerated by sea level rise and upstream dams. Sea dike stability is seriously threatened by erosion-induced lowering of beach profiles, sea level rise, typhoon, and storm surge.  相似文献   

14.
流域侵蚀速率的时空变化对于理解活动造山带的地貌演化具有重要意义。以阿尔泰山8个山地流域为研究对象,利用1964—2011年的水文数据,采用河流输沙量法估算了年代际山地流域侵蚀速率。首先确定悬移质、推移质和溶解质对河流输沙量的贡献,然后计算各流域的年代际侵蚀速率,并结合已有研究结果,探讨了阿尔泰山流域侵蚀速率的时空特征及其控制因素。结果表明：阿尔泰山8个山地流域的平均侵蚀速率为0.03 mm·a-1,其中乌伦古河山地流域侵蚀速率最小（0.01 mm·a-1）,额尔齐斯河支流克兰河山地流域侵蚀速率最大（0.05 mm·a-1）。进一步对侵蚀速率与气候、地形、岩性、构造和植被等因素进行相关分析,发现流域侵蚀速率与地形因子（流域面积、地形起伏度）和气候因子（径流深度、平均温度）的相关性较强,表明这些因素可能对阿尔泰山山地流域侵蚀起主要影响。与阿尔泰山百万年尺度的剥蚀速率（0.07~0.3 mm·a-1）相比,研究时段内的流域侵蚀速率偏低,这表明中亚地区晚新生代持续的干旱气候可能制约了阿尔泰山地表侵蚀。  相似文献   

15.
陈界仁  曹淼 《水科学进展》2003,14(6):696-699
在坡面土壤侵蚀输沙计算中,可选用的输沙能力模式较多,但这些模式多运用于恒定输沙,在非恒定输沙中运用不多。建立了坡面土壤侵蚀非恒定输沙数学模型,模型中的输沙能力运用水流切应力、水流功率、单位水流功率3种模式,对模型过程采用有限差分格式离散求解。根据实测水沙资料进行模型参数率定,运用3种输沙能力模式于不同降雨强度、不同坡度的非恒定坡面输沙过程中。结果表明:在坡面非恒定输沙计算中,不同输沙能力模式对计算结果有明显影响,在降雨强度较小时,单位水流功率模式结果较其他两个模式为好,而在雨强较大时,切应力模式计算结果较好。  相似文献   

16.
 Suspended sediment transport effectiveness was examined near the mouths of three large impounded rivers (Rio Grande, Brazos, and Pearl Rivers) in differing precipitation regimes in the U.S. Gulf Coastal Plain. Magnitude and frequency analysis of suspended sediment transport was performed by examining the effectiveness of both discharge and time in transporting suspended sediment. Bivariate plots of discharge with infrequent values of silt/clay and sand provide an insight into the relative proportion of coarse-versus fine-grained sediment transport for the three rivers. Despite the aridity of the Rio Grande and Brazos drainage basins, which is often associated with infrequent or episodic transport of sediment, the duration of the effective discharge is similar to humid basins described in the literature. The majority of sediment transport occurs during the moderate discharge events, having a duration of 2.4%, 1.5%, and 4.4% for the Rio Grande, Brazos, and Pearl Rivers, respectively. This may be due to the influence of scale or the influence of upstream dams and reservoirs on discharge and sediment transport. Findings from this research suggest that magnitude and frequency analysis of discharge and suspended sediment near the mouths of large rivers may provide a useful framework for understanding the timing and delivery of riverine sediments to the nearshore coastal environment from rivers draining a range of geologic and climatic settings. Received: 6 September 1996 · Accepted: 4 February 1997  相似文献   

17.
黄河内蒙古河段输沙量与淤积量计算方法   总被引：2，自引：0，他引：2       下载免费PDF全文
基于多沙河流"多来多排"输沙基本公式,建立了考虑上站来沙量、前期累计淤积量、临界输沙水量及干支流泥沙粒径影响的输沙量一般表达式。进而根据黄河内蒙古河段1953—2010年实测水沙资料,得到了内蒙古巴彦高勒—头道拐全河段及巴彦高勒—三湖河口和三湖河口—头道拐分河段的年输沙量公式,并根据输沙率法采用建立的输沙量公式计算了各河段1953—2010年的逐年冲淤量。选取三湖河口—头道拐河段的计算结果分析表明,在输沙基本公式基础上增加前期累计淤积量、临界输沙水量及干支流泥沙粒径参数,所得公式计算的年冲淤量与实测值之间的相关系数R2由基本公式的0.41依次提高到0.50、0.75和0.80,说明在基本公式基础上进一步考虑这些参数的必要性。此外,全河及分河段输沙公式计算所得输沙量及各河段冲淤量和累计淤积量与实测值的符合程度均较好,表明建立的输沙公式能够用于不同水沙条件下的输沙量和冲淤量计算,可为分析内蒙古河段的输沙特性和长期淤积趋势提供参考。  相似文献   

18.
Erosion models have not often been applied to very steep terrain such as the gully catchments of the Chinese Loess Plateau. The purpose of this research was to evaluate the suitability of a number of transport equations for use in erosion modelling under Loess Plateau conditions. To do this the equations were programmed into the LISEM model, which was applied to the 3.5 km2 Danangou catchment in the rolling hills region of the Loess Plateau. Previous evaluations of transport equations used either flume tests or river sections, and did no spatial modelling. The results show that some equations predicted physically impossible concentrations (defined as above 1060 g/l). The results were evaluated by using two methods: 1) by comparing predicted and measured sedigraphs and sediment yield at the catchment outlet, and 2) by comparing the fraction of the catchment in which physically impossible transport capacities occurred. The results indicated that for the small grain sizes, high density flows and steep slopes of the gully catchments on the Loess Plateau the Shields parameter attained very high values. Furthermore, the transport threshold can usually be neglected in the equations. Most of the resulting equations were too sensitive to slope angle (Abrahams, Schoklitsch, Yalin, Bagnold, Low and Rickenmann), so that transport rates were overpredicted for steep slopes and underpredicted for gentle slopes. The Yang equation appeared to be too sensitive to grainsize. The Govers equation performed best, mainly because of its low slope dependency, and is therefore recommended for erosion models that simulate sediment transport by flowing water in conditions with small grain sizes and steep slopes.  相似文献   

19.
This study was taken up to investigate the effects of landscape patterns on the soil erosion processes in a mountain–basin watershed. The revised universal soil loss equation and sediment delivery distribution models were used to estimate the soil erosion processes. The landscape patterns include the landscape metrics at the landscape level, landscape composition and configuration indicators on the basis of source–sink landscape theory. In the study area, the grassland, bare land, farmland and construction land were the sediment-source landscape; the forest and shrub were the sediment-sink landscape. The correlation analysis results showed that the soil erosion processes were significantly associated with the landscape patterns of the study area. At the landscape level, fragmentation metric was positively correlated with soil erosion; diversity metric was negatively related to soil erosion and sediment yield at the sub-basin scale. Among the source–sink landscape composition and configuration indicators, the composition indicator was positively correlated with soil erosion rate and sediment yield. In the configuration landscape indices, the shape index was negatively correlated with soil erosion rate and sediment yield; the fragmentation index was positively correlated with soil erosion rate and negatively correlated with sediment delivery rate. These results indicated that the optimization measures, such as increase in the area, connectivity and regularity of sediment-sink landscape, or decrease in the proportion, connectivity and regularity of sediment-source landscape, were favorable for soil conservation. Furthermore, the landscape indicators based on the source–sink theory could provide more information for landscape pattern optimization to reduce soil erosion.  相似文献   

20.
前陆盆地挠曲沉降和沉积过程3D模型研究   总被引：1，自引：0，他引：1  
胡明卿  刘少峰 《地质学报》2012,86(1):181-187
前陆盆地是在造山带负荷作用下岩石圈发生挠曲沉降而形成的,并且被主要从造山带搬运的沉积物所充填。为了更好地理解和认识前陆盆地的形成演化机制,特别是受控于周缘多个造山带活动所形成的前陆盆地的演化机制,本文通过建立前陆盆地挠曲沉降与沉积过程的3-D模型,模拟展示了造山带逆冲推覆作用、岩石圈挠曲沉降响应及在山盆体系中由于动力地形变化而导致的河流体系的发育变化及其产生的剥蚀和沉积过程。模型的建立和实验完整体现了逆冲推覆、弹性挠曲沉降和沉积物搬运这三者之间的耦合机制,为全面深入研究前陆盆地动力学提供了理论依据和方法。  相似文献   

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