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AO Hughes 《新西兰海洋与淡水研究杂志》2016,50(2):277-290
Improvements in riparian management, such as shrub/tree planting and livestock exclusion, are often assumed to result in reduced stream bank erosion and associated catchment sediment yield. Studies that quantify the effectiveness of riparian interventions aimed at reducing bank erosion and river sediment yields are, however, rare. This paper discusses how bank erosion processes can vary throughout catchments (with particular reference to their scale dependence) and hence how the effectiveness of different riparian interventions can be variable. The findings of known published accounts of the effectiveness of riparian management interventions for reducing stream bank erosion in New Zealand are also summarised. Only nine relevant studies were identified and most used qualitative or semi-quantitative analysis methods. Most studies compared stream banks in pasture catchments (with unlimited livestock access) with stream banks where livestock were excluded and riparian shrubs/trees were present. Many studies reported that managed stream banks were in better condition than unmanaged banks. The exclusion of livestock from riparian areas was generally reported as the principal factor in the measured improvements or differences. Only two studies specifically attributed reduced stream bank erosion to the presence of riparian vegetation. The dearth of research identified here highlights the need for further quantitative studies to determine the effectiveness of riparian management measures for reducing bank erosion. 相似文献
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State-of-the-art process-based models have shown to be applicable to the simulation and prediction of coastal morphodynamics. On annual to decadal temporal scales, these models may show limitations in reproducing complex natural morphological evolution patterns, such as the movement of bars and tidal channels, e.g. the observed decadal migration of the Medem Channel in the Elbe Estuary, German Bight. Here a morphodynamic model is shown to simulate the hydrodynamics and sediment budgets of the domain to some extent, but fails to adequately reproduce the pronounced channel migration, due to the insufficient implementation of bank erosion processes. In order to allow for long-term simulations of the domain, a nudging method has been introduced to update the model-predicted bathymetries with observations. The model-predicted bathymetry is nudged towards true states in annual time steps. Sensitivity analysis of a user-defined correlation length scale, for the definition of the background error covariance matrix during the nudging procedure, suggests that the optimal error correlation length is similar to the grid cell size, here 80–90 m. Additionally, spatially heterogeneous correlation lengths produce more realistic channel depths than do spatially homogeneous correlation lengths. Consecutive application of the nudging method compensates for the (stand-alone) model prediction errors and corrects the channel migration pattern, with a Brier skill score of 0.78. The proposed nudging method in this study serves as an analytical approach to update model predictions towards a predefined ‘true’ state for the spatiotemporal interpolation of incomplete morphological data in long-term simulations. 相似文献
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Detailed morphological analyses of a Pleistocene-Holocene submarine channel system in terms of its hierarchical framework, were carried out using a 3D seismic volume from offshore Espírito Santo, SE Brazil. The channel morphology shows marked variations, with five segments (Segments a to e) being identified along its full length. For example, the cross-sectional area of the channel decreases by a factor of 70 from Segment a to Segment c, and is then followed by a nearly four-fold increase from Segment c to Segment d. The significant changes in channel morphology relate to temporal and spatial variations in flow volume within the channel. In the same channel system, the valley reveals three distinct segments (Segments A to C), with similar aspect ratios but marked variations in morphology along the valley distance. Valley morphological changes are chiefly affected by erosional processes. Segment B is characterised by the largest valley-base width, valley width, and cross-sectional area compared to the other two segments. Valley enlargement in Segment B results from relatively high degrees of lateral channel migration and associated cut bank erosion, leading to the widening of the valley, especially the valley base. In Segment C, the valley is characterised by inner bank erosion in the form of shallow-seated mass failures, which only enlarged the upper part of the valley wall. The spatial variations in both channel and valley morphology documented here suggest an important role of local factors (e.g. salt diapirs, tributaries, overbank collapse) in the development of channel systems. Hence, the morphological analyses developed in this work provide an effective tool for studying channels and valleys on continental slopes around the world. 相似文献
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Anomalous morphological features within large estuaries may be: (1) recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes, and (2) possible predictors of cycles of future coastal change. At the entrance to Willapa Bay, Washington, chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of Cape Shoalwater. Northward channel migration since the late 1800s conforms to the long-term net sediment transport direction. What requires explanation is periodic southward relocation of the trunk channel by as much as 5 km, and attendant construction of moderately large sand spits on the north side of the bay such as Kindred Island, Tokeland Peninsula, and Cape Shoalwater.Both autocyclic and allocyclic processes may have been responsible for trunk channel realignment and associated spit deposition. Channel recycling may occur when the main channel becomes overextended to the north and the tidal flow is inefficient because of its decreased gradient and increased susceptibility to shoaling by the growth and migration of tidal sand ridges. Under those conditions trunk channel relocation would be facilitated by increased wave heights and water levels of El Niño winter storms. However, co-seismic subsidence is the most likely mechanism for abruptly increasing sand supply and longshore transport that would favor discrete periods of channel relocation and spit deposition. Unless external forcing changes sand supply and predominant sediment transport directions in the future, the relative rise in sea level, frequent winter storms, and local deficit in the sand budget assure that beach erosion will continue at the mouth of this large estuary. 相似文献
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Stream channels are narrower in pasture than in forest 总被引：1，自引：0，他引：1
Robert J. Davies‐Colley 《新西兰海洋与淡水研究杂志》2013,47(5):599-608
In the Hakarimata Range, west of Hamilton, New Zealand, second‐order streams appear to be wider in native than in pasture catchments, whereas streams in pine plantations (18 years old) appear to be suffering active stream‐bank erosion. A working hypothesis to explain these observations was that pasture vegetation replacing original forest encroaches on the stream channel, causing it to become narrower. To test the hypothesis, channel widths were measured up stream and down stream of “transitions” from native forest to pasture in 20 streams of different size in marginal ranges of the Waikato Basin. Small streams (catchment area <1 km2, width in forest <2 m) were found to be half the width in pasture reaches as in forest. The degree of channel narrowing decreased as stream size increased and was minimal in large streams (catchment area >30 km2, width in forest >10 m). This narrowing of stream channels implies that native forest clearance in New Zealand has reduced stream channel habitat. A concern regarding riparian planting for stream restoration is that sediment stored in pasture stream banks could be mobilised if grasses are extinguished by shading, resulting in turbid streamwater and sedimentation of fines in the channel. 相似文献
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防护丁坝抗冲刷失效安全可靠性分析 总被引：1，自引：1，他引：0
分析了防护丁坝冲刷的机理,用概率分析方法研究了在随机因素影响下防护丁坝抗冲刷的可靠性问题.应用Rosen-blatt变换确定防护丁坝抗冲刷破坏的功能函数在随机因素影响下的可靠性指标.提出了用丁坝端部冲刷坑的当量坡度小于冲刷坑坡度的临界值JD作为丁坝抗冲刷破坏的安全（稳定性）准则.分别考虑了水道流速、土颗粒等效直径、冲刷坑半径、冲刷坑后坡度临界值和水流方向角为相关或独立的非高斯随机参数时的可靠性问题.该分析能为防护丁坝系统的抗冲刷可靠性评估和设计提供有实用价值的方法. 相似文献
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To assess the flood protection capacity of dunes in The Netherlands, a semi-probabilistic dune-erosion prediction method is currently in use in which uncertainties in input parameters of an empirical dune erosion model were taken into account, with the exception of the uncertainty in the extreme surge distribution. Previous research has shown that the surge is by far the most influential parameter affecting erosion in the currently used erosion model, which is due both to the influence of the surge level itself and to the conditional dependence of the wave height and period on the surge level in the probabilistic model used for the assessment. Furthermore, the distribution of extreme surge levels has been shown to contain large statistical uncertainty. The inclusion of uncertainty in input variables into probabilistic models results in more extreme events (in this case erosion) for the same exceedance probability, largely due to the incorporation of higher values of the input variables. The goal of the research described in this paper was to determine the impact of the inclusion of uncertainty in the extreme surge distribution on the estimate of critical erosion (erosion associated with an exceedance frequency of 10− 5 per year). The uncertainty in the surge distributions was estimated and parameterized, and was incorporated into the probabilistic model. A reduction in uncertainty was subsequently imposed to estimate what value a reduction in uncertainty can offer, in terms of the impact on critical erosion. The probabilistic technique first-order reliability method (FORM) was applied to determine the relative contribution of the uncertainty in the surge distribution (as well as the remaining stochastic variables) to the critical erosion. The impact of the inclusion of uncertainty in the surge distribution on the critical retreat distance was found to be substantial with increases ranging from 34% to 93% of the original estimate at five locations along the Dutch coast. The reduced uncertainty showed a more subtle impact, with increases in critical retreat distance ranging from 10% to 26% of the original estimate. The relative importance analysis showed that the uncertainty in the surge distribution has a strong influence, with the relative importance ranging from 10% to 23% for an exceedance frequency of 10− 5 per year. 相似文献
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三峡截流以来长江洪季潮区界变动河段冲刷地貌 总被引：4，自引：0，他引：4
潮区界河段河势演变对三峡工程的响应是长江经济带建设中的重要问题。然而受观测手段所限,对三峡截流以来潮区界变动范围及其地貌演变的客观认识亟待探讨。对大通站洪季水位资料进行频谱分析,初步判断了近期长江洪季潮区界位置;对比1998年和2013年水下地形资料,分析了三峡大坝截流以来该河段河槽的冲淤演变特征;利用多波束测深系统对冲刷明显河段的微地貌进行了高分辨率观测。结果显示:（1）1998-2013年潮区界变动河段河槽整体冲刷5 649.7万m3。其中,上段全面冲刷,太白、太阳两洲并岸,铜陵沙被冲开,主槽刷深达5.6 m;中段主泓摆动,天然洲南冲北淤,黑沙洲中水道淤死,南水道左岸最大冲深达8.9 m;下段近岸冲刷强烈,北岸最大冲深达15.4 m;（2）该河段近期处于剧烈的冲刷环境,左岸冲刷尤为显著;（3）冲刷深槽分布在顺直河段,深达5.4~12.6 m;冲刷坑分布在分汊河段平面形态突变处,最大冲深达28.1~30.5 m;水下侵蚀陡坡分布在近岸侵蚀严重的顺直河段,坡度为0.59~0.62。 相似文献
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渔场资源与位置的变动由空间与环境因子共同驱动,远洋渔场时空演变信息的精准预测是远洋捕捞的关键支撑。该研究考虑渔业生产统计数据,并兼顾同期海洋环境数据包括海表面温度（Sea surface temperature, SST）、海表面盐度（Sea surface salinity, SSS）、初级生产力（primary productivity, PP）和溶解氧浓度（dissolved oxygen concentration, O2）,提出了一种融合卷积长短期记忆网络（ConvLSTM）和卷积神经网络（CNN）的渔场时空分布预测模型。首先对时空因子进行编码,提取高层时空特征;其次采用CNN提取海洋环境变量的抽象特征,并基于ConvLSTM提取渔业数据的时空特征,最后融合高层时空关联信息对渔场时空演变趋势进行预测。以1995－2018年太平洋海域的延绳钓生产数据对模型进行验证,模型的根均方误差为0.1036,实验对比发现较传统渔场预报模型的预测误差降低15%~40%,预测的高产渔区与实际作业的高渔获量区匹配度高。该研究构建的渔场时空预测模型能够准确地预测出太平洋长鳍金枪鱼的时空分布,为太平洋长鳍金枪鱼的延绳钓渔业提供科学参考依据。 相似文献
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琼东南盆地北礁凹陷梅山组单向迁移水道特征及成因探讨 总被引：2，自引：1，他引：1
深水区重力流与底流交互作用的过程、响应及动力学机制是海洋沉积学研究的前沿和薄弱环节。本文通过三维地震资料，在深水区北礁凹陷南西部梅山组发现多条相间分布的长条形顺直强振幅水道，垂直于西沙隆起（南部隆起）北斜坡走向，向南西方向单向迁移，水道具有南西陡（凹岸或陡岸）北东缓（凸岸或缓岸）的特征，该类水道分为侵蚀界面和水道砂-堤岸泥过渡复合体系两个单元，侵蚀界面在凹岸的削截反射明显多于凸岸，水道砂-堤岸泥过渡复合体振幅强度由凹岸强振幅逐渐过渡为凸岸弱振幅。分析认为，该类水道发育于中中新世半深海环境，不同于向底流下游方向单向迁移的峡谷，它们向底流上游方向发生单向迁移，并提出其成因模式:前期来自南部的浊流下切形成负向地貌单元（水道），底流对这一地貌单元进行改造，形成迎流面缓（凸岸）背流面陡（凹岸）的地貌，同时驱使浊流上部顺底流方向偏移，形成溢岸浊流沉积，致凹岸沉积速率低，凸岸沉积速率高，这样就迫使水道逆底流方向偏移。沉积物源、中层水相关底流、古气候和海平面的变化、北礁凸起古地形控制是该区单向迁移强振幅水道发育的因素。本研究在南海首次发现这种向底流上游方向单向迁移的水道，是底流与重力流交互作用的新型类型，对古海洋、古气候研究，深水油气勘探有着重要的意义，希望引起地质学家的重视。 相似文献
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Submarine channel-levee systems commonly develop in structurally active deepwater settings. Despite their widespread development in such settings, only recently have researchers begun to address the response of channel-levee system evolution to deformation. Key factors which govern channel evolution and morphological development are relative rates of deformation and channel deposition and erosion, and also the number and scale of deformational structures, relative to the scale of the submarine channel. Submarine channel-structure interactions can be split into four end-members: deflection, blocking, diversion and confinement. Where deformation is coeval with channel development, an increase in the relative rate of uplift versus deposition and erosion causes a transition from channel deflection to blocking. Diversion and confinement are linked by the number, scale and orientation of structures relative to the channel flow path. Increasing the number of structures and their scale typically results in channel confinement. Underlying all of these individual controls is the distribution of local accommodation, which is determined by specific structural style. This distribution of accommodation over relatively small (<10 km) length scales strongly affects local channel development in order to attain the equilibrium profile. Knowledge of these controls on submarine channel development can increase our understanding of how these deepwater sedimentary systems evolve and distribute sediment across deforming submarine slopes. Understanding the factors governing spatial variations in channel morphology may also be applied when exploring for hydrocarbon reservoirs in structurally active deepwater settings. 相似文献
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长江口南汇边滩冲淤变化规律与机制 总被引：2，自引：2，他引：0
根据1842—2004年海图资料分析发现,南汇边滩存在近百年尺度的强烈冲刷—淤积旋回。长江主泓走南港或北港是造成冲刷期"北滩、东滩淤积,南滩、过渡带冲刷"或淤积期冲淤态势反相的主要原因;冲刷期内风暴强度和频数明显多于淤积期,造成冲刷期滩面叠置记忆的是暴风浪成因的"高滩冲刷、低滩淤积"的冲淤态势,而淤积期保存的是弱风浪成因的"高滩淤积、低滩冲刷"叠置增强的剖面特征。尽管三角洲整体冲淤态势的转变主要受流域来沙量的控制,但不同岸段受河口河势分水分沙作用、潮流和波浪等共同作用,明显存在此冲彼淤、冲淤动态调整等特征。已有的入海泥沙含量阈值研究以点代面或以局部代整体,这是造成阈值估算偏高的主要原因。2003年三峡水库开始蓄水后平均年输沙量154 Mt/a已低于低阈值184 Mt/a,但三角洲尚未如预测那样发生由净淤积向净侵蚀的转变。已有的河口水文观察资料显示,水体含沙量也未发生明显下降,这可能是潮控型三角洲潮流对泥沙在河口的再分配起主导作用,并可能由此延长三角洲冲淤转变对入海泥沙量减少的滞后。今后需进一步加强潮控型河口复杂过程的综合研究,提高对泥沙含量阈值估算和应对可能面临的海岸侵蚀及其相关的环境地质灾害的能力。 相似文献
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开敞大河口滩槽冲淤对台风的响应及其动力泥沙机制探讨——以长江口南汇边滩—南槽—九段沙系统为例 总被引：7，自引：0，他引：7
台风期间 ,潮间带和潮下带岸坡总体上遭受侵蚀 ,而向岸一侧的沼泽和向海一侧的深槽则趋于淤积。台风期间的冲淤强度比正常天气的高 1- 2个数量级。台风期间裸滩的侵蚀机制是风将高能传递给水体使水体挟沙能力剧增 ,沼泽迅速淤积的机制与植被的消能捕沙功能、涨潮水体的高含沙量和明显的增水有关 ,而深槽的骤淤则是由于深水区底层相对较弱的动力条件与浅滩侵蚀所致的高含沙量不相适应。受径流和潮流对泥沙扩散作用的影响 ,台风所致的滩槽冲淤不一定达成平衡 相似文献
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海底冲淤变化预测的聚类指数增长模型研究 总被引：1，自引：0，他引：1
提出了一种新的聚类指数增长模型，并用该模型预测了江苏洋口港海区西太阳沙附近海底的冲淤变化。首先采用聚类分析法对空间连续的水深冲淤变化数据序列进行分类，然后针对各类具有不同的冲淤变化趋势的区域分别建立指数增长预测模型。经比较分析预测结果，发现在分类数较大及预测时间不太长的情况下，能够取得满意的预测结果；但随预测时间的增加，要不断的修正参数值，才能得到切合实际的预测结果，所以该模型还具有一定的时间局限性，还有待于改进。该模型的建立不但可以为江苏省东部沿海海港建设提供科学的决策依据，也可以成为近岸海底冲淤变化预测的发展方向之一，有较高的理论意义和广远的应用前景。 相似文献
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舟山群岛峡道底部高程及其冲刷对浙闽沿海泥沙供给的影响 总被引：6，自引：0，他引：6
根据舟山群岛峡道地区的钻孔资料，在有孔虫、花粉和沉积特性分析结果的基础上，分析了晚更新世海面变化，探讨了晚更新世末期峡道内的地面高程，进而根据海图量算结果，讨论了舟山群岛峡道底部的泥沙冲淤及其对浙闽沿海泥沙供给的影响。本文认为，晚更新世以来舟山群岛地区发生了三次海进海退，其中晚更新世末期低海面时，舟山群岛峡道高程约位于吴淞基面以下３８ｍ左右，全新世海侵以来，受峡道水动力的作用，除部分峡道内海湾发生淤积外，舟山群岛峡道底部发生了明显的冲刷，其最大冲刷厚度可达８０ｍ左右，为杭州湾乃至整个浙闽沿海提供了大量的泥沙 相似文献
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淤泥质潮流深槽最大冲刷深度的一个概念模型 总被引：3，自引：1，他引：2
以概念模式方法计算了淤泥质潮流深槽的最大深度,探讨了涨落潮流速、涨落潮历时、深槽淤泥质物质粒径、深槽顶底部原始深度、水道长度等因素对潮流深槽最大深度的影响。概念模式的假设条件是:(1)深槽形态为长方体,底部纵向坡度为0;(2)沉积物粒径无垂向变化;(3)只考虑潮流作用的影响,涨、落潮流速在时间序列上呈正弦分布;(4)不考虑细颗粒物质的粘性和絮凝作用。模拟结果显示:(1)涨、落潮历时对深槽最大深度的影响很小。(2)优势潮流流速与最大深槽深度之间存在着幂函数关系。(3)深槽的底质粒径、深槽的长度均与最大冲刷深度呈正相关关系。(4)深槽顶部水深与最大深度呈负相关关系。(5)由于潮汐水道深度与潮流流速和沉积物侵蚀强度之间具有负反馈关系,因此水道冲刷存在着一个极限,即最终可以达到均衡状态。潮流深槽的均衡态特征和达到均衡态所需的时间可运用沉积动力学方法来确定;同时,若应用深槽的真实参数,进一步减少模型的假设条件,可望使该模型具有实际的应用价值。 相似文献
20.
黄河三角洲清水沟河口区近期冲淤演变特征 总被引：1，自引：0，他引：1
黄河三角洲清水沟流路1996年汛前实施清8改汊工程后,河口区的冲淤发生了变化。据1996年10月至2005年9月清水沟滨海区固定断面测深资料的分析表明:新河口区总体上出现淤积,老河口区在总体上发生侵蚀。通过区域泥沙净冲淤量与入海沙量相关分析计算表明:新河口区的淤积速率与入海沙量呈正相关,老河口区的侵蚀速率与入海沙量互不相关。其原因在于:前者位于河流入海口,被海洋动力蚀失的泥沙能得到河流输沙的充足补给,属河流动力为主的河控型海岸;后者远离河流入海口,被海洋动力蚀失的泥沙得不到河流输沙的补给,属海洋动力为主的海控型海岸。 相似文献