三江源地区近50年降水变化分析   总被引：27，自引：1，他引：26  

唐红玉  杨小丹  王希娟  史津梅  徐亮 《高原气象》2007,26(1):47-54

利用西北及三江源(黄河、金沙江及澜沧江)地区122个气象观测台站1956—2004年近50年的逐日降水量及月总降水量资料,分析了三江源地区降水变化特征。结果表明:近50年来三江源地区的年降水量呈减少趋势,减少幅度为6.73mm/10a;降水日数的趋势变化呈较为明显的减少趋势,递减率为2.7d/10a;平均降水强度总体呈弱的增强趋势,增强速率平均为0.20mm/d/10a,增强幅度比中国西北地区平均水平强;从4~9月最长无降水日数趋于增长反映出西北地区干旱化的趋势。  相似文献   

Study of substrate and physico-chemical base classification of the rivers of Nepal     

JHA Bibhuti Ranjan  WAIDBACHER Herwig  SHARMA Subodh  STRAIF Michael 《地球空间信息科学学报》2010,13(1):70-76

The rivers in Nepal are classified in terms of geographical regions but a more scientific classification such as on the ba-sis of morphology is clearly lacking. This study was done in 9 rivers namely Jhikhukhola of the Koshi system, Aandhikhola, Arungkhola, East Rapti, Karrakhola, Seti and main channel Narayani of the Gandaki system, and two independent systems within Nepal, Bagmati and Tinau. Among the morphologies, river bed or the substratum was taken as the main variable for the analysis which was categ...  相似文献   

Entrainment,displacement and transport of tracer gravels     

Peter R. Wilcock 《地球表面变化过程与地形》1997,22(12):1125-1138

The mass and size distribution of grain entrainment per unit bed area may be measured by replacing a volume of the bed with tracer gravels and observing the mass difference before and after a transport event. This measure of spatial entrainment is relevant to any process involving size-selective exchange of sediment between transport and bed and may be directly used in calculations of sediment transport rate using an elementary relation for fractional transport components presented here. This relation provides a basis for evaluating tracer data collected by different methods and may be used to provide physical insight regarding the expected behaviour of tracer grains. The variation with grain size of total displacement length L_ti depends on the degree of mobilization of the individual fractions on the bed surface: L_ti is independent of D_i for smaller, fully mobile sizes and decreases rapidly with D_i for larger fractions in a state of partial transport (in which a portion of the surface grains remain immobile through the flow event). The boundary between fully and partially mobile grain sizes increases with flow strength. These inferences are supported by values of L_ti calculated from flume experiments and provide a physical explanation for a summary relation between L_ti and D_i based on field data. © 1997 John Wiley & Sons, Ltd.  相似文献   

A general Lagrangian tracking methodology for riverine flow and transport     

Jonathan Nelson  Yasuyuki Shimizu  Tomoko Kyuka  Scott Charlton 《地球表面变化过程与地形》2023,48(1):87-103

This article presents a new public domain tool for generalized Lagrangian particle tracking in rivers. The approach can be applied with a variety of two- and three-dimensional flow solvers. Particle advection by the flow is incorporated using flow fields from the chosen solver assuming particles follow the Reynolds-averaged flow, although some other simple passive and active particle behaviors are also treated. Turbulence effects are treated using a random walk algorithm with spatial step lengths randomly chosen from Gaussian distributions characterized by the diffusivity from the flow solver. Our work extends this concept to a general framework that is solver and coordinate system independent to allow easy comparisons between differing flow treatments. To better treat problems where detailed information is required in specific regions, the approach includes novel cloning and colligation algorithms which enhance local resolution at modest computational expense. We also provide tools for computing local concentrations and total exposure over a user-specified time interval. Several examples of predictions are provided to illustrate applications of the technique, including examination of the role of curvature-driven secondary flows, storage in lateral separation eddies, treatment of larval drift, treatment of fuel spill dispersion, river-floodplain connections, and sedimentation in floodplain ponds by tie channel connections. We also demonstrate that the model can reproduce analytically derived concentration profiles for simple diffusivities. These examples show that the Lagrangian particle tracking approach and the extensions proposed here are broadly applicable and viable for treating difficult river problems with multiple temporal and spatial scales. The examples also illustrate the utility of the cloning/colligation extensions and show how these can decrease the computational effort required on problems where high local resolution is required. Enhancement of the tools and even broader applicability can be achieved through the inclusion of multiple particle populations and particle–particle interactions.  相似文献   

天狼星无人机航测技术在河湖划界中的应用     

李涛  高波  张允涛  高佳佳 《测绘通报》2019,(3):151-154

由于河湖覆盖面广、线路长、体量大,同时历史遗留问题较多,采用常规测量手段存在诸多难题。本文结合具体工程案例,通过天狼星无人机航测技术手段,论证了新技术方案的可行性与有效性;阐述了天狼星免像控无人机在河湖划界工作中的优势和高精度航测成果一图多用的重要意义。本文方案对类似工程的开展具有一定的参考借鉴意义。  相似文献   

Input of organic carbon as determinant of nutrient fluxes,light climate and productivity in the Ob and Yenisey estuaries     

Dag O. Hessen  JoLynn Carroll  Berit Kjeldstad  Anton A. Korosov  Lasse H. Pettersson  Dmitry Pozdnyakov  Kai Sørensen 《Estuarine, Coastal and Shelf Science》2010

Spectral light attenuation profiles and concentrations of total and dissolved carbon (C), nutrients and chlorophyll a (Chla) were studied along transects running from the river mouth to the Kara Sea during late summer 2003 for the Yenisey and fall 2005 for the Ob estuaries. Earth Observation data were used to generate composite images of water color and Chla distribution over the estuaries and the Kara Sea to reveal the spatial impact of the river efflux in terms of optical properties.  相似文献   

环太湖江苏段入湖河道污染物通量与湖区水质的响应关系   总被引：1，自引：1，他引：0  

吕文  杨惠  杨金艳  马倩  高晓平  蒋如东  王晓杰  徐勇  聂青 《湖泊科学》2020,32(5):1454-1462

基于2008-2018年环太湖江苏段入湖河道污染物通量及湖区水质数据,从时空变化及相关关系两个方面探讨了入湖污染物通量与湖区水质的响应关系,并分析了污染物进入湖体影响水质的主要因子.结果表明:太湖污染减排已见成效,氨氮、总氮、高锰酸盐指数和化学需氧量入湖污染物通量整体呈下降趋势,年均下降率分别为8.0%、2.0%、1.6%和2.2%,湖体氨氮和总氮时间格局响应较好,年均下降率分别为2.1%和2.3%.湖体氨氮、总氮、总磷、高锰酸盐指数和化学需氧量与入湖污染物通量整体由西北部、西部湖区向东南部、东部湖区递减,空间格局上响应基本一致.全湖区年尺度总氮、氨氮浓度与入湖河道污染物通量分别呈显著正相关、极显著正相关关系;影响湖区总氮、氨氮的主要因子为入湖河道的总氮、氨氮浓度,其次为入湖河道浓度与原湖区水质差值,因此亟需加强入湖河道水质浓度的控制.  相似文献   

Amphitheatre-headed canyons of Southern Utah: Stratigraphic control of canyon morphology     

Andrew J. Ryan  Kelin X. Whipple 《地球表面变化过程与地形》2020,45(14):3607-3622

Amphitheatre-headed canyons are common on Earth and Mars and researchers have long sought to draw inferences about canyon-forming processes from the morphology of canyon heads and associated knickpoints, often suggesting that amphitheatre heads indicate erosion by groundwater seepage erosion. However, the conditions and processes that lead to amphitheatre-headed canyon formation have been debated for many years. We consider two hypotheses that attribute the amphitheatre-headed canyon formation to fluvial erosion of strong-over-weak stratigraphy or, alternatively, groundwater spring discharge and seepage erosion. A spatial analysis of canyon-form distribution with respect to local stratigraphy along the Escalante River and on Tarantula Mesa, Utah indicates that canyon form is most closely related to variations in local sedimentary rock strata, rather than inferred groundwater spring intensity. Lateral facies variations that affect the continuity of strong layers can induce or disrupt the formation of amphitheatres. Furthermore, we find that amphitheatre retreat rate is dictated by the interaction of fluvial processes downstream of the amphitheatre headwalls and stratigraphy, rather than waterfall and groundwater processes that likely importantly influence headwall form. We conclude that fluvial erosion of strong-over-weak stratigraphic layering alone is sufficient to form amphitheatres at knickpoints and canyon heads. Thus, we re-affirm that formation process should not be inferred from canyon-head morphology, particularly where a strong-over-weak layering is known or plausible. © 2020 John Wiley & Sons, Ltd.  相似文献   

Use of terrestrial photosieving and airborne topographic LiDAR to assess bed grain size in large rivers: a study on the Rhine River     

Valentin Chardon  Laurent Schmitt  Hervé Piégay  Dimitri Lague 《地球表面变化过程与地形》2020,45(10):2314-2330

Most grain size monitoring is still being conducted by manual sampling in the field, which is time consuming and has low spatial representation. Due to new remote sensing methods, some limitations have been partly overcome, but methodological progress is still needed for large rivers as well as in underwater conditions. In this article, we tested the reliability of two methods along the Old Rhine River (France/Germany) to estimate the grain size distribution (GSD) in above-water conditions: (i) a low-cost terrestrial photosieving method based on an automatic procedure using Digital Grain Size (DGS) software and (ii) an airborne LiDAR topo-bathymetric survey. We also tested the ability of terrestrial photosieving to estimate the GSD in underwater conditions. Field pebble counts were performed to compare and calibrate both methods. The results showed that the automatic procedure of terrestrial photosieving is a reliable method to estimate the GSD of sediment patches in both above-water and underwater conditions with clean substrates. Sensitivity analyses showed that environmental conditions, including solar lighting conditions and petrographic variability, significantly influence the GSD from the automatic procedure in above-water conditions. The presence of biofilm in underwater conditions significantly altered the GSD estimation using the automatic procedure, but the proposed manual procedure overcame this problem. The airborne LiDAR topographic survey is an accurate method to estimate the GSD of above-water bedforms and is able to generate grain size maps. The combination of terrestrial photosieving and airborne topographic LiDAR methods is adapted to assess the GSD over several kilometers long reaches of large rivers. © 2020 John Wiley & Sons, Ltd.  相似文献   

Event-scale floodplain accretion revealed through tree-ring analysis of buried plains cottonwoods,Powder River,MT, USA     

Tara L. Metzger  James E. Pizzuto  Shelia M. Trampush  Jonathan M. Friedman  Derek M. Schook 《地球表面变化过程与地形》2020,45(2):345-360

Six plains cottonwoods along the axis of a meander were excavated to determine if dendrochronology could identify the year and location of germination and date past overbank sedimentation events. Samples from all excavated trees showed clear anatomical changes associated with burial, including increased vessel size, decreased definition of annual ring boundaries, and decreased ring widths. Some of these burial signatures were created by deposition of only a few centimeters of sediment, and most burial events were detected by multiple samples from the same tree. Four of the trees germinated at or near the upper surfaces of bar deposits, while two germinated within thin overbank deposits draped over bar deposits, indicating that germination is closely associated with bars. Dates and inferred thicknesses of overbank sedimentation events are consistent with repeated topographic surveys and data obtained from cesium-137 (¹³⁷Cs) analyses. However, the record of overbank sedimentation extracted from the trees does not entirely reflect the history of past peak discharges documented by stream gaging, largely because individual trees are progressively less likely to be flooded through time as the river migrates farther away. Germination dates and locations closely track past positions of the river channel. Germination elevations and the elevations of the tops of point bars appear to be decreasing with time as the bend migrates, implying vertical incision by Powder River at a rate of 7.1 ± 4.3 mm/yr. The rate of floodplain growth determined by elevation changes decreases progressively through time, ultimately reaching an apparent plateau after 0.8–1.3 m of vertical accretion. While similar patterns of vertical accretion have previously been interpreted as resulting from decreasing flood probability with increasing floodplain elevation, distance from the channel is also a first-order control on vertical floodplain growth. © 2019 John Wiley & Sons, Ltd.  相似文献