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1.
Side-scan, seismic and surficial sediment data accompanied by current meter records highlight across-shelf sediment transport in Hauraki Gulf, an island-studded embayment off northern New Zealand. Calm weather currents are locally dominated by the tides, with periodic incursions of oceanic water from detached meanders of the East Auckland Current. Under these conditions, bedload transport occurs mainly in three 15–20 km-wide channels, where bathymetric intensification of the flow brings about near-bottom speeds of up to 82 cm s−1 for Colville Channel and 33–44 cm s−1 in Jellicoe and Cradock Channels. Surficial sediments are gravelly to muddy sand, winnowed in places, leaving a lag deposit of mainly biogenic carbonate gravel. Modelling results suggest that in Colville Channel, dominant fine to medium sand modes are mobile for 20–60% of the time, with a net eastward movement for fine sand. In Jellicoe and Cradock Channels, the prevailing direction of transport is southwards across the shelf, with sand mobile for up to 33% of the time. Oceanic incursions have the potential to boost flow in the western Gulf, however such incursions are transitory, and there is no measurable expression of oceanic water in the sedimentary record. Because of their association with prolonged periods of calm weather, the incursions are unlikely to accompany storm events, where their cumulative effect might be important for sediment transport. Near-bottom currents resulting from oceanic incursion may reinforce peak tides inside the Gulf by up to 2–4 cm s−1. Enhancement of prevailing water motions occurs during periods of extreme weather. During cyclone Drena (January 1997), measured flow speeds in Jellicoe Channel reached 48 cm s−1. Furthermore, the disturbance generated large waves that stirred bottom sediments down to over 100 m water depth. Such events are probably the major agent of sediment redistribution in the Hauraki Gulf. The net effect of storm and calm weather currents is to move sediment across the outer to middle shelf where, in the western and central Gulf it accumulates, and in the eastern Gulf it escapes eastward via Colville Channel. 相似文献
2.
Longshore drift estimation using fluorescent tracers: New insights from an experiment at Comporta Beach, Portugal 总被引：1，自引：0，他引：1
Ana Silva Rui Taborda Aurora Rodrigues Joo Duarte Joo Cascalho 《Marine Geology》2007,240(1-4):137-150
A fluorescent sand-tracer experiment was performed at Comporta Beach (Portugal) with the aim of acquiring longshore sediment transport data on a reflective beach, the optimization of field and laboratory tracer procedures and the improvement of the conceptual model used to support tracer data interpretation.
The field experiment was performed on a mesotidal reflective beach face in low energetic conditions (significant wave height between 0.4 and 0.5 m). Two different colour tracers (orange and blue) were injected at low tide and sampled in the two subsequent low tides using a high resolution 3D grid extending 450 m alongshore and 30 m cross-shore. Marked sand was detected using an automatic digital image processing system developed in the scope of the present experiment.
Results for the two colour tracers show a remarkable coherence, with high recovery rates attesting data validity. Sand tracer displayed a high advection velocity, but with distinct vertical distribution patterns in the two tides: in the first tide there was a clear decrease in tracer advection velocity with depth while in the second tide, the tracer exhibited an almost uniform vertical velocity distribution. This differing behaviour suggests that, in the first tide, the tracer had not reached equilibrium within the transport system, pointing to a considerable time lag between injection and complete mixing. This issue has important implications for the interpretation of tracer data, indicating that short term tracer experiments tend to overestimate transport rates. In this work, therefore, longshore estimates were based on tracer results obtained during the second tide.
The estimated total longshore transport rate at Comporta Beach was 2 × 10− 3 m3/s, more than four times larger than predicted using standard empirical longshore formulas. This discrepancy, which results from the unusually large active moving layer observed during the experiment, confirms the idea that most common longshore transport equations under-estimate total sediment transport in plunging/surging waves. 相似文献
3.
中国近岸海区沿岸流和海岸流对沉积物的搬运 总被引：4，自引：0，他引：4
中国近岸海区存在两种海流:沿岸流和海岸流。前者是波浪产生的,主要搬运破波带以内的沉积物。后者是中国边缘海环流系统的一部分,位于破波带外,主要搬运粉砂和黏土细粒沉积物。在一些中文文献中两者都称作"沿岸流"。这容易形成概念上的混乱和分析问题上的错误。为了避免混淆,属于边缘海环流系统一部分的"沿岸流"应该称作海岸流,对于具体的"沿岸流"如"渤莱沿岸流"可以直接称呼为渤莱海流。两种海流的方向可以相同、相反或者呈一定角度。山东北部海岸沉积物的空间分布明显地受波浪、近岸环流系统(沿岸流、裂流)及海岸流控制。 相似文献
4.
本文设计彩沙示踪法于厦大滨海沙滩东段进行试验 ,取得了沙粒运动方向、最大运移速度、扩散范围、沿岸输沙率及粒度分异运移状态等定量数据 ,弥补了以往示踪法难以定量分析的缺陷。结果表明 :调查期间 ,厦大滨海沙滩东段沙粒运动是构成厦门岛南岸岸滩在偏东向波浪作用下形成的西南向沿岸漂沙之一个环节 :沙粒大体平行岸线向北运动 ;沙粒沿岸最大运移速度为 2 0 0m/d ;经一个潮周期 ,沙粒向两侧的最大横向扩散距离为 2 0m ,最大垂直扩散深度达 7cm ;岸滩横断面沿岸输沙率为 42 5t/d ;在该岸段沿岸漂沙中 ,粗粒沙偏向低潮带一侧 ,而细粒沙偏向高潮带。 相似文献
5.
A mathematical model of spit growth and barrier elongation adjacent to an inlet (of arbitrary width), supplied by sediment coming from longshore sediment transport, was developed based on the spit growth model proposed by Kraus (1999). The fundamental governing equation is the conservation equation for sand, where the width of the spit is assumed constant during growth. The portion of the longshore sediment transport feeding the spit has been estimated based on the ratio between the depth of the inlet channel and the depth of active longshore transport. Sediment transport from the channel due to the inlet flow, as well as other sinks of sand (e.g., dredging), are taken into account. Measured data on spit elongation at Fire Island Inlet, United States, and at Badreveln Spit, Sweden, were used to validate the model. The simulated results agree well with the measured data at both study sites, where spit growth at Fire Island was restricted by the inlet flow and the growth at Badreveln Spit was unrestricted. The model calculation for Fire Island Inlet indicates that the dredging to maintain channel navigation is the major reason for the stable period observed from 1954 to 1994 at the Fire Island barrier. The average annual net longshore transport rate at the eastern side of the Fire Island inlet obtained in this study was about 220,000 m3/yr, of which approximately 165,000 m3/yr (75% of the net longshore transport) is deposited in the inlet feeding the spit growth, whereas the remaining portion (25%) is bypassed downdrift through the ebb shoal complex. 相似文献
6.
The south-western shoreline along the entrance channel inside the Port of Richards Bay has experienced continued erosion. Four groynes were constructed to stabilise the shoreline. Monitoring of shoreline evolution provided valuable data on the accretion adjacent to two of the groynes and on the sediment transport rates at these groynes. Tides, beach slopes, winds, wave climate, current regime, and sand grain sizes were documented. The one site is “moderately protected” from wave action while the other is “protected” according to the Wiegel [Wiegel, R. L. (1964). Oceanographical engineering. Prentice Hall, Inc., Englewood Cliffs, NJ.] classification. The shoreline accreted progressively at the two groynes at 0.065 m/day and 0.021 m/day respectively. The shorelines accreted right up to the most seaward extremity of the groynes. Equilibrium shorelines were reached within about 3.5 years to 4 years, which compare well with other sites around the world. The mean wave incidence angle is large and was found to be about 22°. The median sand grain sizes were 0.33 mm and 0.37 mm. The groynes acted as total traps, the beach surveys were extended to an adequate depth, and cross-shore sediment transport did not cause appreciable net sand losses into the entrance channel. The net longshore transport rate along the study area, which is north-westbound, is only slightly lower than the gross longshore transport. The actual net longshore transport rates are 18 000 m3/year and 4 600 m3/year respectively at the two groynes. A rocky area limits the availability of sand at one groyne. There is fair agreement between the predicted and measured longshore transport rates at the other groyne. 相似文献
7.
Estimating the age of particles in marine environment constitutes an invaluable tool to understand the interactions between complex flows and sediment dynamics, particularly in highly energetic coastal areas such as the Belgian Coastal Zone (Southern Bight in the North Sea). To this end, the Constituent Age and Residence time Theory – CART – introduced by Delhez, E.J.M., Campin, J.-M., Hirst, A.C., Deleersnijder, E. [1999a. Toward a general theory of the age in ocean modelling. Ocean Modelling 1, 17–27] for passive water constituents is extended to describe the sediment dynamics. It is then used in combination with a three-dimensional coupled hydrodynamic-sediment transport model to investigate sediment processes in the Belgian Coastal Zone focusing on two complementary aspects of the sediment dynamics: the internal sediment motion and redistribution within the Belgian coast; and the horizontal transport. 相似文献
8.
Coastline sand waves have been observed at “El Puntal” spit, located on the north coast of Spain. The spit has been monitored by an Argus video system since 2003 and the formation and destruction of sand waves has been observed. Coastline data from the video images are analyzed by means of principal components analysis, obtaining a mean sand wave length of 125–150 m and a maximum amplitude of ≈ 15 m. It is also observed that sand waves reach their maximum amplitude at about 15 days. No propagation of these sand waves is noticed during the approximately two-month-long events analyzed. Sand wave formation and evolution are examined in relation with the prevailing local wave conditions during that period. Incident waves at the west end of the spit approach from the east–northeast, with a very high angle with respect to the shoreline. Field observations suggest that sand waves may result from an instability in alongshore sediment transport caused by moderate-energy waves with a high-angle incidence. 相似文献
9.
《Coastal Engineering》2005,52(2):159-175
The Frisian Inlet is one of the tidal basins of the Dutch Wadden Sea. In 1969, its basin area was reduced by 30%. As documented by bathymetric surveys, this has led to an import of sediment of 30×106 m3 over the first 18 years. The study presented in this paper seeks to establish the mechanisms responsible for the passage of the sediment through the throat cross-section of the inlet channel. Emphasis is on a 14-day period of relative calm when sediment transport can be attributed solely to tidal currents. Use is made of continuous measurements of velocity, sand and silt concentration. The measurement station was located on one side of the throat cross-section in a water depth of approximately 6 m. For both the sand and silt fraction of the sediment, suspended load transport is the dominant transport mode. It is shown that for sand, concentration variations and net transport are determined by the local (in the throat section) velocity. Especially the residual velocity and tidal velocity asymmetry play an important role in the net sand flux. For silt, except for transport associated with locally generated vertical mixing, the net transport is largely determined by sedimentation–erosion processes in the basin and the silt concentration in the North Sea. Comparison with measurements in a station located in the middle of the throat section shows considerable difference in residual velocity and tidal velocity asymmetry. As a result, the sediment fluxes also differ. Accurately determining the net sediment flux in the throat section would require a dense net of measurement stations. 相似文献
10.
Calculation of longshore sediment transport 总被引：1，自引：0，他引：1
I. O. Leont’yev 《Oceanology》2014,54(2):205-211
Calculation approaches to longshore transport of sandy sediments are discussed. The estimation of the total sediment transport rate is shown to be possibly based on the so-called CERC formula, where the proportionality factor K should be calculated from relationships of Bayram et al. [8] or Leont’yev [4]. In both cases, the results are very close to each other if the author’s determination of the wave breaking depth is used. Under the condition of contrasting variations in the sediment grain size over the coastal profile or in the case of fragmentary sand distribution on the surface of the bed, the local approach implying process-based modeling is more effective. A model is suggested to compute the local longshore sediment transport rates. 相似文献
11.
12.
Alan William Niedoroda Donald J.P. Swift Thomas Sawyer Hopkins Chen-Mean Ma 《Marine Geology》1984,60(1-4):331-354
An open ocean shoreface typical of long, wave-dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation. Sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents. Sand on the middle and lower shoreface, as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents.
Storm events have been studied and modeled for the shoreface off Tiana Beach, Long Island. The dominant effect of coastal frontal storms is to cause significant shore-parallel bedload transport with important shore-normal secondary components. These storms tend to result in net offshore transport of sand removed from the beach and surf zone systems. The bedload transport during a storm is convergent on the shoreface leading to accretion. Most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf. Longer-term equilibrium can be maintained by slow return of sand up the shoreface during non-storm conditions.
Annual and geologic time-scale budgets of shoreface sand transport and sedimentation yield equilibrium, net accretion or net deposition. The annual balance results from an integration of the event-scale bedload transport patterns and morphologic responses. These processes and responses have feedback mechanisms which stabilize the system over longer, but not geologic, time scales. Geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event-scale shoreface and transporting processes providing the mechanism to produce the changes in long-term morphology and sedimentation patterns. In the area of study, the long-term pattern is one of net shoreface erosion, and the permanent loss of sand to the shelf floor. 相似文献
13.
In situ 《Estuarine, Coastal and Shelf Science》1999,49(6):813
Laboratory and in situ experiments were performed to assess the use of bromide as a tracer forin situ studies of benthic solute exchange. Bromide was used in the benthic chamber lander ‘ Elinor ’ for flux measurements in coastal sediments of the German Bight, Kiel Bight and Skagerrak (28–700 m water depth). Tracer and total oxygen uptake were monitored simultaneously in the same chamber incubation. Concurrently, in situ oxygen micro-profiles were recorded at the same locations by the profiling lander ‘ Profilur ’. Deployment in an anoxic silt (Kiel Bight) confirmed that in the absence of bioturbation and advection, tracer transport into the sediment was driven solely by molecular diffusion. This flux could be well described by a simple box model accounting for molecular diffusion only. In oxic sediments (German Bight and Skagerrak) enhanced exchange of bromide tracer due to bioirrigation parallelled enhanced oxygen uptake equivalent to a 4-fold molecular diffusive flux. Our experiments showed that incubations can be short. Depending on irrigation activity of the fauna, however, incubation length should exceed 3 h in order to provide a useful data base for flux calculations. The method demonstrating caveats is discussed and indicate possible improvements. The results show how the bromide tracer addition can be used as a tool for determining solute fluxes exceeding diffusive flux in benthic chamber incubations. 相似文献
14.
沙质海岸强浪作用下沿岸输沙问题研究 总被引：1，自引：0，他引：1
在沙质海岸上修建导流堤、丁坝等会引起局部海域水沙动力条件的改变和海床冲淤调整,因此准确预测沿岸输沙率是海岸工程建设前进行优化设计的基础条件之一.首先构建了刻画高强度推移质输沙过程中固-液混合体运动的理论模型,通过寻求模型的特解并推导成1D沿岸输沙率公式.该公式适宜计算强浪作用下的推移质输沙率,已得到了大型波浪水槽、往复流水道和海滩现场实测输沙率资料的良好验证.通过与物理模型试验实测输沙量结果的比较,进一步表明该公式能够较好地预测沙质海岸在寒潮大风浪(或台风浪)作用下的高强度输沙量(骤淤量). 相似文献
15.
a 《Estuarine, Coastal and Shelf Science》2001,52(6):783
In May and September 1999 11 stations were sampled in the southern and central North Sea, located in the German Bight, eastern Oyster Ground and Dogger Bank. The study focused on the influence of particle mixing on transport of chlorophyll a to deeper sediment layers and vertical bacterial distribution (max. DEPTH=10 cm). The sampling stations were chosen to reflect a gradient in environmental conditions in the North Sea. The sampling stations differed in respect to redox potential (eH up to −243 mV in the German Bight and up to 274 mV in the offshore regions), silt content (up to 54% in the German Bight and 0·34% at the northern Dogger Bank) and different proportion of fresh organic material on total organic matter content (C/N ratios ranging from 9·27 in the German Bight up to 1·72 in the offshore sediments). Although bacterial densities (8·55×109 g−1in the German Bight up to 0·35×109 g−1in offshore sediments) were significantly correlated to chlorophyll a content in the sediment (P<0·01), inconsistencies in the temporal pattern of both variables in the surficial sediment layer suggested, that the dynamics of bacterial densities is generally controlled by food supply but also by other variables. The chlorophyll a content in the surficial sediments of the German Bight (up to 1·84 μg g−1) was significantly higher than in the Oyster Ground (up to 0·58 μg g−1) and the Dogger Bank area (up to 0·68 μg g−1). With increasing chlorophyll a input to the benthic realm a subsequent enhanced burial of this compound into deeper sediment layers was expected either by biological (bioturbation) or by physical sediment mixing. However, the vertical profile of chlorophyll a decreased steeply in the sediments of the German Bight. Contrary, subsurface peaks were measured in the offshore areas. It was concluded from these results, that the vertical distribution of organic matter in sediments is less limited by the quantitative input from the water column but concomitant with particle mixing itself. The extent and possible mechanisms of particle mixing in the different study areas in relation to specific environmental factors is discussed. 相似文献
16.
利用单波束测深仪和蚌式取样器进行了日照石臼港扩建码头西侧约50km~2海域1:2 000~1:10 000的水深地形测绘和底质分析工作。调查结果表明,日照港西部海域可分4个水深区,其地形和沉积特征如下:1)航道区,浅水航道区等深线平行于码头岸线,水深11m,经过疏浚已形成向南倾斜的四级阶梯地形,疏浚中心处水深24m。航道区底质以分选中等的砾砂为主;2)港池区,水深6 m,等深线与港池岸线平行,水深向南渐增,海底地形平坦,坡降比3‰。底质以分选较好的粉砂和砂质粉砂为主,近岸有少量分选较差的泥质砂质砾;3)涛雒-付疃河口区,水下三角洲地形明显,5m以浅等深线呈弧形向东南方向凸出,坡降比最大可达14.2‰,底质类型为分选极好的砂和粉砂质砂;4)浅海区,海底地形平坦,平均坡降比1.9‰,6~10m等深线呈NE-SW向平行向外海增大,近南扩码头端向东偏转,底质类型为分选好的砂质粉砂和粉砂,并呈平行于海岸线向深水区呈粗-细-粗的带状分布。底质类型分布与水深条件基本吻合,但深水区出现的底质粗化现象,分析认为可能与南扩码头的挑流作用有关,海底沉积物呈向南运移趋势。 相似文献
17.
水下沙丘形态演化的数值模拟实验 总被引：1，自引：0，他引：1
水下沙丘在海洋、湖泊、河流等浅水砂质沉积区广泛分布。基于过程的数值实验方法探讨了沙丘形态演化问题,试图解释在沙丘形成过程中各因素的作用及它们之间的关系。模拟中考虑了以下的变量:水深、沉积物粒度、沉积层厚度以及台风作用。模拟结果显示,沙丘的空间分布控制了空间流场的参数k2,沙丘波高受水深、沉积物粒度以及沉积层厚度等因素的影响,沉积层厚度决定了沙丘的形态是否饱满。在台风作用中,沙丘波峰的沉积物被侵蚀,高程降低,波高渐小;台风作用后,沉积物被重新输运至波峰,沙丘高度逐渐恢复。因此,沙丘的高度取决于台风作用的时间以及2次台风作用之间的间隔。沙丘形态和尺度在台风作用前后变化较小,但沙丘演化的速度却有所提高。根据台湾浅滩和北海南部地貌系统数据的验证,模拟具有较好的效果。 相似文献
18.
水下沙丘形态演化的数值模拟实验 总被引：1，自引：0，他引：1
水下沙丘在海洋、湖泊、河流等浅水砂质沉积区广泛分布。基于过程的数值实验方法探讨了沙丘形态演化问题,试图解释在沙丘形成过程中各因素的作用及它们之间的关系。模拟中考虑了以下的变量:水深、沉积物粒度、沉积层厚度以及台风作用。模拟结果显示,沙丘的空间分布控制了空间流场的参数k2,沙丘波高受水深、沉积物粒度以及沉积层厚度等因素的影响,沉积层厚度决定了沙丘的形态是否饱满。在台风作用中,沙丘波峰的沉积物被侵蚀,高程降低,波高渐小;台风作用后,沉积物被重新输运至波峰,沙丘高度逐渐恢复。因此,沙丘的高度取决于台风作用的时间以及2次台风作用之间的间隔。沙丘形态和尺度在台风作用前后变化较小,但沙丘演化的速度却有所提高。根据台湾浅滩和北海南部地貌系统数据的验证,模拟具有较好的效果。 相似文献
19.
The results of seismic studies in the shallow waters of the southwestern Kara Sea show the presence of a seismic unit that can be interpreted as relict submarine permafrost. The permafrost table has a strongly dissected upper surface and is located at a water depth of 5–10 m. A 3D modeling of the permafrost table suggests the presence of relict buried thermodenudational depressions (up to 2 km across) at a water depth of 5–10 m. The depressions may be considered to be paragenetic to thermocirques found at the Shpindler site. Relict thermocirques are completely filled with sediment and not exposed at the sediment surface. 相似文献
20.
东海不同底质类型海域春季悬浮体通量及影响因素 总被引：7，自引：2，他引：7
利用1994年4月在东海陆架不同底质类型海域即泥质和砂质区的水文和泥沙观测资料，分析和计算了两个站的悬浮体含量的分布、余流分布和悬浮体通量，以代表两个局部海域悬浮体含量分布和输送的特征。结果表明，在底质类型、生物活动、水动力环境和悬浮体物源各因素的影响下，两个海域的悬浮体通量和悬浮体含量垂直分布各有其特征，是东海悬浮体输送和垂直分布的两种典型类型。111站周围海域的悬浮体通量较大，上、中层水体（0－40m)中的悬浮体向东南方向输送，下层和底层的悬浮体向东北方向输送，且下层和底层的通量大于中上层；砂质区的悬浮体通量相对较小，且从表层到底层均向东北方向运移。 相似文献