潮流界以下河段航道整治水位确定方法研究——以长江江阴以下河段为例     

徐元  贾雨少 《海洋工程》2018,36(2):64-72

在总结分析现有整治水位确定方法的基础上,根据潮流界以下河段的水沙运动特性,本文提出一种基于输沙能力的航道整治水位确定方法。考虑上游来水、下游潮汐为独立事件,统计潮流界以下河段上游来水、下游潮汐不同等级组合出现的频率,采用数学模型计算相应组合下河段沿程的潮位、流速过程,以流速四次方代表水流的输沙能力,统计不同潮位等级对应的综合净输沙能力,确定最大综合净输沙能力对应的水位为(最优)航道整治水位。以长江下游白茆沙水道和福姜沙水道为例,计算了所在河段的航道整治水位,并探讨了起动流速对整治水位计算的影响和最高整治水位概念对工程的意义。  相似文献   

Prograded coastal barriers provide paleoenvironmental records of storms and sea level during late Quaternary highstands          下载免费PDF全文

Amy J. Dougherty 《第四纪科学杂志》2018,33(5):501-517

  相似文献   

A regime shift in sediment export from a coastal watershed during a record wet winter,California: Implications for landscape response to hydroclimatic extremes          下载免费PDF全文

Amy E. East  Andrew W. Stevens  Andrew C. Ritchie  Patrick L. Barnard  Pamela Campbell‐Swarzenski  Brian D. Collins  Christopher H. Conaway 《地球表面变化过程与地形》2018,43(12):2562-2577

Small, steep watersheds are prolific sediment sources from which sediment flux is highly sensitive to climatic changes. Storm intensity and frequency are widely expected to increase during the 21st century, and so assessing the response of small, steep watersheds to extreme rainfall is essential to understanding landscape response to climate change. During record winter rainfall in 2016–2017, the San Lorenzo River, coastal California, had nine flow peaks representing 2–10‐year flood magnitudes. By the third flood, fluvial suspended sediment showed a regime shift to greater and coarser sediment supply, coincident with numerous landslides in the watershed. Even with no singular catastrophic flood, these flows exported more than half as much sediment as had a 100‐year flood 35 years earlier, substantially enlarging the nearshore delta. Annual sediment load in 2017 was an order of magnitude greater than during an average‐rainfall year, and 500‐fold greater than in a recent drought. These anomalous sediment inputs are critical to the coastal littoral system, delivering enough sediment, sometimes over only a few days, to maintain beaches for several years. Future projections of megadroughts punctuated by major atmospheric‐river storm activity suggest that interannual sediment‐yield variations will become more extreme than today in the western USA, with potential consequences for coastal management, ecosystems, and water‐storage capacity. The occurrence of two years with major sediment export over the past 35 years that were not associated with extremes of the El Niño Southern Oscillation or Pacific Decadal Oscillation suggests caution in interpreting climatic signals from marine sedimentary deposits derived from small, steep, coastal watersheds, to avoid misinterpreting the frequencies of those cycles. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

Offshore aeolian sediment transport across a human‐modified foredune          下载免费PDF全文

Karl F. Nordstrom  Nancy L. Jackson 《地球表面变化过程与地形》2018,43(1):195-201

Concepts derived from previous studies of offshore winds on natural dunes are evaluated on a dune maintained for shore protection during three offshore wind events. The potential for offshore winds to form a lee‐side eddy on the backshore or transfer sediment from the dune and berm crest to the water are evaluated, as are differences in wind speed and sediment transport on the dune crest, berm crest and a pedestrian access gap. The dune is 18–20 m wide near the base and has a crest 4.5 m above backshore elevation. Two sand‐trapping fences facilitate accretion. Data were obtained from wind vanes on the crest and lee of the dune and anemometers and sand traps placed across the dune, on the beach berm crest and in the access gap. Mean wind direction above the dune crest varied from 11 to 3 deg from shore normal. No persistent recirculation eddy occurred on the 12 deg seaward slope. Wind speed on the berm crest was 85–89% of speed at the dune crest, but rates of sediment transport were 2.27 times greater during the strongest winds, indicating that a wide beach overcomes the transport limitation of a dune barrier. Limited transport on the seaward dune ramp indicates that losses to the water are mostly from the backshore, not the dune. The seaward slope gains sand from the landward slope and dune crest. Sand fences causing accretion on the dune ramp during onshore winds lower the seaward slope and reduce the likelihood of detached flows during offshore winds. Transport rates are higher in access gaps than on the dune crest despite lower wind speeds because of flatter slopes and absence of vegetation. Transport rates across dunes and through gaps can be reduced using vegetation and raised walkover structures. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Comparing grain size distribution of sediment and original soil under raindrop detachment and raindrop-induced and flow transport mechanism   总被引：3，自引：0，他引：3  

Mahboobeh Kiani-Harchegani  Hossein Asadi 《水文科学杂志》2018,63(2):312-323

The grain size distribution (GSD) of sediment in comparison with the original soil GSD is discussed under different slopes (5, 15 and 25%) and rainfall intensities (30, 60 and 90 mm h^–1 with respective duration of 30, 15 and 10 min) but identical runoff (15 mm). The sediment quantification was carried out by raindrop-induced flow transport (RIFT) or/and transport by flow (FT) using a rainfall simulator and a 6 × 1 m² erosion plot and a silt loam. The results show a high degree of enrichment for size classes of 2–4 and 4–8 μm and a high degree of depletion for size classes of >63 μm under different slopes and rainfall intensities. In addition, the results show that the experimental enrichment ratio (ER) for particle size <16 μm under different slopes and rainfall intensities was greater than 1, while the ER for particle size >32 μm was less than 1.  相似文献   

生物土壤结皮铁代谢微生物组成及其功能基因对演替的响应     

王岩松  刘玉冰  王增如  赵丽娜  漆婧华  张雯莉 《中国沙漠》2020,40(3):193-200

采用微生物宏基因组学微阵列GeoChip 5.0技术，选择腾格里沙漠东南缘沙坡头地区不同年代人工固沙植被区的生物土壤结皮（BSC）为对象，分析BSC演替过程中参与铁代谢的功能微生物组成及其功能基因变化特征，研究微生物铁代谢对BSC演替的响应及调控。结果表明：真菌参与铁吸收和转运过程，古菌参与铁转运和贮存过程，细菌则在铁代谢吸收、转运和贮存过程中均起主要调控作用。门水平上，BSC铁代谢功能微生物组成变化对演替的响应不敏感，BSC铁代谢微生物主要为变形菌门（Proteobacteria）。BSC铁代谢功能基因多样性的显著提高和三类铁代谢过程基因信号强度达到最高水平需要经过61 a的演替。调控BSC铁吸收过程的主要功能基因为亚铁氧化酶编码基因iro；调控原核生物铁转运过程的主要功能基因，为羟基苯甲酰丝氨酸铁外膜转运体编码基因cirA和Fe（Ⅱ）转运蛋白编码基因feoB，真菌铁转运过程主要依靠含铁细胞转运体和铁氧化酶高亲和力的作用；调控铁贮存过程的主要功能基因为固定相类核蛋白编码基因dps。在BSC演替阶段末期，上述铁代谢功能基因强度的显著增加促进了微生物的铁代谢潜能。干旱、半干旱荒漠生态系统植被恢复过程中微生物铁代谢潜能的恢复需要较长时间。  相似文献   

湿地土壤和沉积物异化铁还原过程研究进展     

朱晓艳  袁宇翔  宋长春  姜明 《湿地科学》2020,18(1):122-128

异化铁还原是湿地土壤和沉积物中重要的生物地球化学过程,也是有机质矿化的主要途径之一。湿地干湿交替等过程会使土壤的氧化还原状态发生改变,影响铁元素及与其相关的元素的迁移和转化。总结了湿地土壤和沉积物中异化铁还原过程及其与碳、磷、硫等元素在生物地球化学循环关键过程中的相互作用,阐述了湿地土壤和沉积物中异化铁还原过程对微量金属元素迁移和转化的影响,分析了影响湿地土壤和沉积物异化铁还原过程的主要环境因子。未来相关研究应集中于湿地土壤和沉积物中异化铁还原微生物分析和纯化、不同有机质形式对异化铁还原过程的影响以及异化铁还原对土壤有机质矿化的贡献。  相似文献   

A one‐dimensional process‐based approach to study reservoir sediment dynamics during management operations          下载免费PDF全文

Lucie Guertault  Benoit Camenen  André Paquier  Christophe Peteuil 《地球表面变化过程与地形》2018,43(2):373-386

A comprehensive understanding of the dynamics of erosion and sedimentation in reservoirs under different management conditions is required to anticipate sedimentation issues and implement effective sediment management strategies. This paper describes a unique approach combining fluvial geomorphology tools and morphodynamic modeling for analyzing the sediment dynamics of an elongated hydropower reservoir subjected to management operations: the Génissiat Reservoir on the Rhône River. Functional sub‐reaches representative of the reservoir morphodynamics were delineated by adapting natural river segmentation methods to elongated reservoirs. The segmentation revealed the link between the spatial and temporal reservoir changes and the variability of longitudinal flow conditions during reservoir management operations. An innovative modeling strategy, incorporating the reservoir segmentation into two sediment transport codes, was implemented to simulate the dynamics of erosion and sedimentation at the reach scale during historic events. One code used a bedload approach, based on the Exner equation with a transport capacity formula, and the other used a suspended load approach based on the advection–dispersion equation. This strategy provided a fair quantification of the dynamics of erosion and sedimentation at the reach scale during different management operations. This study showed that the reservoir morphodynamics is controlled by bedload transport in upper reaches, graded suspended load transport of sand in middle reaches and suspended load transport of fine sediments in lower reaches. Eventually, it allowed a better understanding of the impact of dam management on sediment dynamics. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Connectivity assessment in Mediterranean vineyards using improved stock unearthing method,LiDAR and soil erosion field surveys   总被引：1，自引：0，他引：1       下载免费PDF全文

Jesús Rodrigo Comino  Saskia D. Keesstra  Artemi Cerdà 《地球表面变化过程与地形》2018,43(10):2193-2206

  相似文献   

Sediment and nutrient storage in a beaver engineered wetland          下载免费PDF全文

Alan Puttock  Hugh A. Graham  Donna Carless  Richard E. Brazier 《地球表面变化过程与地形》2018,43(11):2358-2370

Beavers, primarily through the building of dams, can deliver significant geomorphic modifications and result in changes to nutrient and sediment fluxes. Research is required to understand the implications and possible benefits of widespread beaver reintroduction across Europe. This study surveyed sediment depth, extent and carbon/nitrogen content in a sequence of beaver pond and dam structures in South West England, where a pair of Eurasian beavers (Castor fiber) were introduced to a controlled 1.8 ha site in 2011. Results showed that the 13 beaver ponds subsequently created hold a total of 101.53 ± 16.24 t of sediment, equating to a normalised average of 71.40 ± 39.65 kg m². The ponds also hold 15.90 ± 2.50 t of carbon and 0.91 ± 0.15 t of nitrogen within the accumulated pond sediment. The size of beaver pond appeared to be the main control over sediment storage, with larger ponds holding a greater mass of sediment per unit area. Furthermore, position within the site appeared to play a role with the upper‐middle ponds, nearest to the intensively‐farmed headwaters of the catchment, holding a greater amount of sediment. Carbon and nitrogen concentrations in ponds showed no clear trends, but were significantly higher than in stream bed sediment upstream of the site. We estimate that >70% of sediment in the ponds is sourced from the intensively managed grassland catchment upstream, with the remainder from in situ redistribution by beaver activity. While further research is required into the long‐term storage and nutrient cycling within beaver ponds, results indicate that beaver ponds may help to mitigate the negative off‐site impacts of accelerated soil erosion and diffuse pollution from agriculturally dominated landscapes such as the intensively managed grassland in this study. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献