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1.
Relationship between suspended sediment load, channel geometry and land area increment in the Yellow River Delta 总被引：5，自引：0，他引：5
The annual river discharges and suspended sediment loads into the Yellow River Delta show a declining tendency with some distinct fluctuations over the last 50 years. The decrease of river discharge and suspended sediment load and the change in the river channel must influence the evolution of the Yellow River Delta. During this period several new river mouths formed via channel switch at the river delta, and the old watercourse was gradually abandoned. Recently, in years with very low annual suspended load, erosion of land area has been recorded for the delta. The aims of this work are (1) to determine what is the critical suspended sediment load needed in order to maintain the land balance of the Yellow River Delta for two periods before and after 1976 (the last time the channel shifted), and (2) to examine the variation in the channel geometry and gradient in response to changes in suspended sediment load and delta area at the river mouth. In order to estimate these critical values, we used statistical method to analyze the relationships between land area increment, and suspended sediment load and channel geometry. In order to examine the variation in the channel geometry, the channel cross-sections of the Q1 and Q6 were compared. The results show that to maintain the land area balance between 1953 and 1973, when the river mouth was the Diaokouhe, the critical annual suspended sediment load entering the delta was 4.21 108 tonnes/a. After the main channel switched to Qingshuigou in 1976, the critical value to maintain the Qingshuigou mouth between 1976 and 1997 was 1.51 108 tonnes/a. To maintain the land area balance for the entire Yellow River Delta between 1976 and 1997 the critical suspended sediment load was 3.18 108 tonnes/a. The annual mean channel thalweg elevation and channel gradient at the river delta increase with increasing land area increment at the Qingshuigou mouth. The critical channel gradient at the channel reach between cross sections Q1 and Q6 is 0.000095. The channel has narrowed during the time period from 1976 to 1997. Also, lateral channel migration has decreased remarkably, resulting in enhanced hydraulic efficiency of the deltaic channel and artificial levees. This channel geometry evolution was influenced by river adjustment and human activities. These results are of importance for the management of the lower Yellow River channel and the delta. Future water diversion or river damming should consider the balance between suspended sediment delivery and delta growth. 相似文献
2.
黄河中游多沙粗沙区水土保持减沙的近期趋势及其成因 总被引：8，自引：1，他引：8
本研究以1950～1997年的长系列水文资料和面雨量资料,分析了黄河中游河口镇至龙门区间年输沙量和年降水量的时间变化趋势,发现在1970年以来多沙粗沙区入黄泥沙量减少的总体背景之上,出现了1986～1997年间入黄泥沙量增加的近期趋势。这一增加趋势,与20世纪80年代以后淤地坝修建量大为减少,70年代修建的淤地坝与拦沙库容已大部分失效有密切关系。此外,90年代人为增沙量大幅度增加,已占水土保持减沙量的22%左右,部分抵消了水土保持措施的减沙效益,这也是90年代入黄泥沙增加的重要原因。针对存在的问题提出了若干对策建议。 相似文献
3.
定量研究延河流域淤地坝拦沙贡献率和未来可拦沙潜力,对流域淤地坝建设效益分析具有重要的参考价值。根据延河流域1952—2018年的径流输沙数据和2011年全国水利普查中的骨干坝建坝年限、控制面积、总库容和淤积库容等资料,构建了延河流域骨干坝拦沙量反推计算模型,计算了延河流域骨干坝逐年拦沙量与减沙贡献率,预测了骨干坝未来可拦沙年限。结果表明:不同年代延河流域骨干坝年均拦沙量持续增加,2000—2011年多年平均拦沙量为401万t/a,达到最大值;人类活动是延河流域年输沙量减少的主要因素,1997—2005年和2006—2011年人类活动对延河流域减沙量的贡献率分别为63.44%和84.98%;骨干坝拦沙量在人类活动减沙量中的占比呈减小趋势,1997—2005年占比24.67%,2006—2011年占比7.46%;截止2019年,延河流域62%的骨干坝未来拦沙年限为30年以内,并且北部骨干坝未来可拦沙能力大于南部骨干坝。研究结果可为延河流域水土流失防治与效益评价、水土保持措施规划与布局以及流域综合管理等提供参考依据。 相似文献
4.
Draining toward the South China Sea, the Pearl River is the third largest river in China. Based on datasets begun in the 1950s of water and sediment flux at the main gauging stations and measured deposition rates in some reservoirs, this paper examines the impact of dam construction on the sediment flux of the Pearl River. The results and conclusions are as follows: (1) The total storage capacity of reservoirs in the Pearl River basin had reached 65 km3 by 2005, which is 23% of the annual water discharge of the Pearl River. (2) The total deposition rate in the reservoirs has now probably reached 600 Mt/yr, one order of magnitude higher than the annual sediment flux into the sea (40 Mt/yr in 2000–2005). (3) The sediment flux of the Pearl River has shown a drastically decreasing trend since the mid-1980s, which is attributed mainly to deposition in the reservoirs. (4) A further decrease in sediment flux into the sea is expected to occur in the Pearl River in future decades because of the construction of new dams. This drastic decrease in sediment flux may be very import for the environments of the river channel, the estuary and the coastal areas, which need to paid considerable attention in scientific research and management. 相似文献
5.
Michael C. Slattery Lee M. Todd Jonathan D. Phillips John A. Breyer 《Journal of Soils and Sediments》2010,10(4):640-651
Purpose
This study uses sediment cores to quantify Holocene sedimentation rates in the Trinity River delta, Texas. An important question is whether modern fluvial sediment input from the Trinity River is adequate to sustain sedimentation in the delta, thereby combating subsidence and further wetland loss. Our objective was to quantify sedimentation rates within the delta in order to assess whether the delta is in- or out-of-phase with modern sediment delivery rates. 相似文献6.
7.
《Land Degradation \u0026amp; Development》2017,28(4):1482-1492
Since the 1960s, the implemented soil conservation measures on steep slopes and the densely planted shelterbelts as well as the constructed reservoirs and ponds in Baiquan County, northeastern China have dramatically altered the landscape and would greatly influence soil erosion and sediment yield (SY ). However, how these land use changes and the constructed dams affected soil erosion and SY still remained unclear. A physically distributed soil erosion model WaTEM/SEDEM that has been calibrated and validated using 25 reservoir SY s in the study area was applied using nine land use scenarios (land uses in 1954, 1975 and 2010, each with 8, 32 and without dams) to assess their impacts on sediment delivery at the Shuangyang catchment (915 km2). The results show that land use changes as well as the increased dam numbers progressively decreased catchment sediment delivery and the impact of dams on sediment delivery was more efficient under the intensified land use condition (1954 land use without reservoirs). With respect to 1954 land use without dams, current land use condition (2010 land use with 32 dams) was simulated to decrease SY by 61·8%. Soil conservation measures (terrace and contour tillage as well as shelterbelts) on the slopes greatly influenced SY and over 80% of the reduced SY were caused by land use changes. This study indicates that soil conservation measures are sustainable sediment control measures for the black soil region because the accumulation of sediment in dams causes shortening of the useful life in reservoirs and ponds and implies increasing financial costs. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
8.
岔巴沟流域淤地坝对泥沙存贮-释放的影响（英） 总被引：4，自引：1，他引：3
为分析黄河中游流域产输沙对人类干预增强的响应机制,该文选取岔巴沟为坝系小流域研究区,探讨淤地坝的建设和发展对流域内泥沙存贮-释放时空变化的影响。研究表明,20世纪80年代岔巴沟处于泥沙存贮状态,10 a平均泥沙输移比为0.325,经分析,始于20世纪50年代,并于60、70年代得到发展,80、90年代趋于稳定的岔巴沟淤地坝拦截了大量泥沙是造成泥沙存贮的主要原因。和拦沙作用相比,其减少高含沙水流发生频率,降低高含沙水流发育程度的作用更大。值得注意的是,淤地坝在几十年的发展过程中可淤库容显著下降,多数原有坝地淤满,加上20世纪80年代以后坝体建设速度减缓,以及设计标准低,后期管理和维护不利,垮坝和毁坝造成泥沙再释放的潜在性在增加。 因此,今后在对淤地坝作为一项重要的水保措施引起足够重视的同时,维护和巩固现有淤地坝的拦泥库容也非常必要。 相似文献
9.
Urszula Aleksander-Kwaterczak Edeltrauda Helios-Rybicka 《Journal of Soils and Sediments》2009,9(1):13-22
Background, aim, and scope Elevated levels of heavy metals in the aquatic and soil systems can be caused by the weathering of mineralized rocks. This
enrichment is often considerably enlarged by historical and current mining and smelting activities. In Poland, the most contaminated
river systems are those in the Silesia region. The metalliferous ore mining and smelting industries have been the main sources
of heavy metal pollutions over the last 100–170 years. The previous and present studies have shown very high concentrations
of heavy metals in the bottom sediments of the Mala Panew River, the most polluted tributary of the Oder River. The main objective
of this work was to study temporary changes of selected metal (Zn, Pb, and Cd) concentrations in upper layer of bottom sediments
at the measuring point near the outlet of the Mala Panew River into the Oder River, and to determine the vertical distribution
of the metals in the sediment cores from the most polluted middle part of this river. The mobility of the metals and their
potential bioavailability were assessed based on metal partitioning in the sediments and metal concentrations in pore waters.
The presented data were compared with metal concentrations in aquatic sediments from similar historical mining and smelting
sites in Poland and other countries.
Methods The upper layer of bottom sediment samples from the same Mala Panew River measuring point were collected six times in the
period 1997–2005, while five sediment cores were collected once from the middle course of Mala Panew River in 2006. Abiotic
parameters such as pH and Eh have been determined in situ. Metal contents were determined in the <20 and <63 μm size fractions
of sediments after digestion in a microwave oven with aqua regia or concentrated nitric acid. Metal mobility was assessed
in the selected sediment cores by the chemical forms of metals (sequential extraction method) and their concentrations in
pore waters were investigated.
Results The concentrations of Cd, Pb, and Zn in the upper layer of sediments varied, depending on both the season and the year of
sampling. Their mean concentrations (from six samplings) are [mg/kg]: Zn 1,846, Pb 229 and Cd 73. The metal concentrations
in the sediment cores varied with the depth in the range of [mg/kg]: 0.18–559 for Cd, 26.2–3,309 for Pb and 126–11,153 for
Zn, although the highest accumulations generally could be observed in the deeper layers. The most mobile metal fractions,
i.e., exchangeable, carbonate and easily reducible fractions, are typical of Zn and Cd. Cadmium was found to be the most mobile
metal and its relative contribution ranges from 84 to 96%, while in the case of Zn it ranged from 45 to 94%. Lead is mainly
associated with the moderately reducible fraction (30–60%). Relative contributions of metal chemical forms slightly vary with
the depth in the sediment profile. The results obtained for the pore water samples show very high concentrations of the metals
studied, especially in the case of Cd (31–960 μg/dm3) and Zn (300–4,400 μg/dm3).
Discussion Accumulation of Cd, Pb, and Zn in the upper layer of the bottom sediments and in the sediment core samples from the Mala Panew
River is very high, considerably exceeding the local geochemical background. High contributions of mobile Cd and Zn and the
toxicity of cadmium can cause environmental risk. Our measurements also suggest that mobile metals can migrate into groundwater,
whereas the groundwater itself can leach some chemicals from river sediments, because of a relatively high water table in
the study area, especially during rainfall periods. Comparison of the results obtained with the literature data from the last
decade shows that the concentrations of Cd and Zn in the sediments from the Mala Panew River are the highest among other submersed
sediments in Poland and other regions (e.g., the Mulde River, Germany).
Conclusions The Mala Panew River is one of the most polluted rivers when compared with similar historical mining and smelting areas in
Poland and elsewhere. The sediments studied are strongly polluted with the metals analyzed. In the upper layer of the bottom
sediments there has been no reduction of Zn and Cd amounts over the last decade, which could suggests a long-term migration
and a secondary contamination. Considerably higher accumulations of metals in overbank sediment cores and in the deeper core
section could result from strong contamination in previous decades and translocation of Cd and Zn (secondary pollutants).
The relatively high concentrations of the two metals in pore waters support these findings. Cadmium is crucial in the environmental
risk assessment because of its high mobility and toxicity. These data are important for water/sediment management in the transboundary
Oder River catchment, situated in Poland, Germany and the Czech Republic.
Recommendations and perspectives It is important to assess mobility phase and pore water in the contaminated historical aquatic sediments. Such studies may
help explain the changes, which take place in the sediment layers as well as at the water–sediment interface. Obtained results
should be used for the risk assessment of the historical contaminated sediments at the local river-basin scale. The treatment
of contaminated sediments, e.g., dragging activity, should be considered as very important in management strategies in order
to avoid remobilization of metals. 相似文献
10.
11.
D. E. Walling A. L. Collins H. M. Sichingabula G. J. L. Leeks 《Land Degradation \u0026amp; Development》2001,12(5):387-415
In many developing countries, the management of sediment‐related environmental problems is severely hampered by a lack of information on sediment mobilization and delivery in river basins. The sediment budget concept represents a valuable framework for assembling such information, which can, in turn, be used to assist with the design and implementation of soil erosion and sediment control policies. However, the information necessary to construct a catchment sediment budget is difficult to assemble. Against this background, an integrated approach to establishing a catchment suspended sediment budget, involving a river monitoring station, the use of 137Cs measurements to estimate soil erosion and deposition and floodplain accumulation rates within the catchment, and sediment source fingerprinting, has been developed and tested in the 63 km2 catchment of the upper Kaleya River in southern Zambia. The approach developed not only provides detailed information on individual components of the suspended sediment delivery system, but also permits the establishment of the overall catchment sediment budget. A sediment budget for the upper Kaleya catchment is presented and both its key features and its wider implications for catchment management are discussed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
12.
Background, Aims, and Scope Sediment management in coastal zones is taking place in high complex environments. Present management options do not have
a sophisticated way of dealing with the actual complexity of the physical and the social systems and with the unpredictability
that is inherent with these systems. Therefore, a new approach in both policy making and sediment management is needed that
takes this complexity into account. The aim of this article is to explore the dynamics in social and natural systems and to
draw the contours of this new approach for policy processes and sediment management that fits to the dynamics of the systems.
Methods Three case studies concerning sediment management in Germany and the Netherlands are analysed in this article, in which unpredictability,
or whimsicality, appeared through the occurrence of unexpected events. The case studies are analysed from the perspective
of complexity theory. Complexity theory is a systemic theory, which means that it explains empirical phenomena from complex
system behaviour. To understand the capricious character of sediment management in coastal zones, we need to frame the issue
as the interdependency between the physical system and the social system, causing the two systems to develop in mutual adjustment
through feedback. The process of mutual adjustment is one that is characterised by a non-linear nature. This is caused by
the multiple relationships and the feedback within and between the systems, and the occurrence of chance events. Chance events
(surprises) happen suddenly without an apparent cause and are important triggers for change in the systems. In three empirical
cases, the occurrence, nature and response to these chance events are analysed as these factors influence the course of sediment
management.
Results and Discussion The case studies show that chance events can occur in the biophysical and in the social system. In the three cases, players
or actors in the decision process are left with the choice to adapt themselves to the occurring chance events or to refrain
from any adaptive behaviour. Chance events can open up new possibilities by activating (new) actors and by coupling to new
issues. If the situation is too locked-in (i.e. a stalemate) and is intentional on behalf of the actors, than the chance event
will have no effect. There are, however, situations of lock-in that are unintentional, and in such situations a chance event
can remove this lock-in. The effects depend largely on the adaptive capacity of the actors to respond adequately and timely
to such situations. The adaptive capacity can be increased (and uncertainty reduced) by a better understanding of both the
physical and the social system. The case studies show that adaptation is an adequate way of dealing with the occurrence of
chance events.
Conclusions We conclude that the way to deal with non-linear developments is through an adaptive policy approach with short feedback loops
in order to allow for timely adjustments and learning loops that will progress the understanding of the systems — both social
and physical. Besides the instruments that are already available, like modelling and forecasting, instruments like observation
and monitoring, stakeholder involvement processes, and learning and adaptation should be developed in this new adaptive approach.
Monitoring of the physical system is a key element in this approach as all involved parties and stakeholders can learn how
the physical system behaves. In this adaptive approach, whimsicality — that occurs through unexpected events — is an interesting
challenge for all concerned with sediment management.
Recommendations and Perspectives The proposed adaptive policy approach should be developed further and should be experimented with in real life situations
that are well monitored. 相似文献
13.
黄河中上游地区水利水保措施蓄水拦沙作用分析评价 总被引：2，自引：0，他引：2
对黄河中上游地区水利水保措施的蓄水拦沙作用分析的结果表明,现阶段水保措施年均蓄水量为10亿m~3,年均拦沙量3亿t,支流水库和淤地坝的拦沙量占水保措施拦沙量的77.8％。这种蓄水拦沙作用是在80、90年代降雨量减少的情况下得出的,由于前期积累、隐蔽、潜伏着许多泥沙问题,某些支流遇到较大暴雨产沙量激增,这对黄河下游可能会造成一定影响。当前应当把更多的精力和投资放在沟道的整治和利用上,大力修建控制性的大型骨干水库或淤地坝。 相似文献
14.
Purpose
The aim of this work was to develop a comprehensive fluvial suspended sediment budget for a large regulated river, the lower River Ebro (NE Spain).Materials and methods
The sediment loads of the Ebro mainstem and its main tributaries were estimated from continuous records of water discharge and turbidity (appropriately transformed to suspended sediment concentrations). Records were obtained at ten monitoring sections during the relatively dry 2008–2011 period.Results and discussion
The sediment load estimated for the River Ebro upstream of the Mequinenza Reservoir is remarkable (i.e. mean suspended load of 0.6?×?106?t?year?1), despite the fact that the site is already affected by a sediment deficit due to upstream reservoirs. Further downstream, and owing to their humid characteristics, the contribution of the Pyrenean tributaries (Segre and Cinca Rivers) is much larger compared with their Iberian Massif counterparts (Matarranya and Algars Rivers), with sediment loads of 0.49?×?106 and 2,260 t, respectively. The suspended sediment load trapped in the Mequinenza-Ribarroja-Flix Dam Complex for the study period was estimated at 2.3?×?106?t. Below the dams, the sediment load was reduced by 95 % but increased gradually in a downstream direction due to the erosion processes that clear water (i.e. very low sediment concentrations) flood flows exert on the river bed and banks and the episodic contribution from ephemeral tributaries.Conclusions
Reservoirs have reduced the overall sediment load and the natural variability of flow and sediment transport in the River Ebro. In addition, the sediment budget revealed that floods were not the only drivers of the sediment dynamics in the lower Ebro. For instance, the particular location of the monitoring sections showed that episodic contributions from small tributaries alter the general sediment load of the river during certain torrential events. 相似文献15.
Background, Aims and Scope Sediment management in rivers basins has tended to deal with local issues associated with either excessive amounts of sediment
(clean and contaminated) or sediment deficit. With sediment management increasingly needing to address both sediment quantity
and sediment quality issues, it is becoming increasingly apparent that for sediment management to be effective the river basin
represents the most appropriate scale for consideration. Although local and site-specific sediment issues are still likely
to be the main scales at which interventions are made they need to be placed within a broader context and with full appreciation
and consideration of their impacts within the river basin. This paper describes some of the reasons why the river basin scale
represents the most appropriate scale for sediment management, while recognizing the needs for site-specific interventions.
It also describes the development of conceptual river basin models (CRBM) for sediment.
Main Features A CRBM should identify, in a conceptual framework, the relevant key environments (subsystems) within a river basin and the
interrelationships between the environments. From a sediment perspective, key information includes the identification of sources
of sediment (and associated contaminants and nutrients), the pathways of sediment and contaminants within and between the
various environments, and the role of storage elements. Additional information that informs the CRBM includes, the assessment
of sediment fluxes (including storage), the residence time of sediment storage, and information on exchanges between sediment
and contaminants, although such information is often not available at the scale of the river basin. An example of a CRBM for
sediment for a hypothetical river basin and examples of several sediment budgets (for basins in USA and Zambia, and for Europe)
are presented which are based on data and information on sediment sources, sediment fluxes and storage. These are discussed
and some of the advantages and disadvantages for decision-making for sediment management are described.
Conclusion and Recommendation Conceptual frameworks and models for sediment offer considerable potential for certain stages of the management process.
They are, however, only part of a much larger decision-making process, which involves, amongst other things, stakeholder participation,
evaluation of the appropriate legislation and guidelines, and the use of risk assessment and societal cost-benefit analysis. 相似文献
16.
The assessment of sediment screening risk in Venice Lagoon and other coastal areas using international sediment quality guidelines 总被引：3，自引：0，他引：3
Sabine E. Apitz Andrea Barbanti Alberto Giulio Bernstein Martina Bocci Eugenia Delaney Laura Montobbio 《Journal of Soils and Sediments》2007,7(5):326-341
Background, Aims and Scope A number of studies carried out in recent years have shown the presence of a wide range of contaminants in the Venice Lagoon.
It is important to have a good understanding of the ecological quality of Venice Lagoon sediments, in order to: i) define
and locate areas where a threat to the environment is present and therefore an intervention is needed (i.e. in situ assessment and management); and ii) define sustainable and environmentally correct ways of managing sediments which are to
be dredged for navigational purposes or in relation to other interventions (i.e., ex situ management).
Methods To examine how various regional and international SQGs ‘classed’ screening risk in Venice Lagoon sediments, data on median
contaminant levels in surface sediments in Venice Lagoon resulting from a literature review were compared to a range of local
and international sediment quality guidelines (SQGs). Then data on sediment contaminant levels in various areas and sub-basins
of Venice Lagoon (main Lagoon, Porto Marghera and Venice City Canals) and in other regional and international transitional
and coastal ecosystems with various levels of human impact (urbanization and industrialization) were evaluated based upon
a selected consensus-based SQG. Finally, screening sediment quality for all of Venice Lagoon was mapped and contoured, relative
to this consensus-based SQG and briefly compared with direct toxicity measurement through a battery of bioassays.
Results SQGs allow the sediment areas to be put in terms of potential, or screening, risk. Although there were some differences depending
upon which specific SQGs were applied, the Venice SQGs and other international SQGs provided the same general picture of screening
risk in Venice Lagoon despite geographic differences. Venice Lagoon South has the lowest screening risk levels, Venice Lagoon
Central/North has the highest (and is nearest to the Porto Marghera and Venice City Canals sites).
Discussion The Venice Lagoon sediments have hazard quotients on the low end of the range of moderately urbanized and industrialized sites
and higher than background case studies reviewed. Hg levels in the Venice Lagoon were generally higher than equivalent sites,
while other contaminants were either equivalent or lower. In Porto Marghera (PM) and Venice City Canals (VC), for many contaminants
of interest, PM, and for some, VC sediments have the highest levels of any case study reviewed. Ranges are high, so in all
cases, remedial or disposal decisions should be based upon site-specific (and preferably tiered) data.
Conclusions The use of hazard quotients makes it possible to compare screening risks due to different mixes of contaminants within and
between sites, but results should be interpreted with caution. How these sites rank when compared to some of the other highly
industrialized sites depends upon how data are synthesized and communicated. Actual risk must be evaluated using a weight
of evidence (WOE) approach, as site-specific bioavailability and background levels will differ both regionally and internationally.
Recommendations and Perspectives Whilst there are subtle differences, the current Venice sediment classifications (A, B and C) ‘performed’ in a similar manner
to SQGs in similar classes, suggesting that regions of Venice Lagoon would not be classified much differently if other SQGs
such as TEL, ERL, PEL, ERM or AET were adopted. The Italian sediment quality objectives, on the other hand, are significantly
more conservative than any other SQGs examined, with the exception of the Flemish Reference values. A number of European nations
are considering criteria based upon contaminant levels in relatively pristine modern sites, or based upon derivations of historical
(pre-anthropogenic) contaminant levels. When used as a standard, such an approach lacks discriminating power, designating
almost all sediments within an urbanized or industrialized region as of concern, or even, in many cases, mandating action
or prohibiting various management approaches in a large percentage of sediments. While generally based upon the laudable desire
to return sites to unimpacted levels, there is a risk that overprotective criteria have the opposite effect: by designating
too large a percentage of sediments as requiring management or control, limited resources may be improperly allocated. Which
set of SQGs is most ‘appropriate’ for the Venice Lagoon sediments depends upon the questions being asked. However, the Venice
classifications are currently being used as pass-fail criteria, without consideration of site-specific conditions. The fact
that they performed similarly to SQGs in similar classes suggests that any work to develop more site-specific SQGs (with the
same general decision classes) would probably not make much difference in how sediments were ultimately classified and managed
unless the fundamental approach was changed from a pass-fail to a tiered and WOE approach integrated in a comprehensive decision
framework. For Venice Lagoon, and for other regions, although SQGs should be developed with care, in a scientifically defensible
and risk-based manner, an equally or more important issue to be addressed is their role in overall decision frameworks.
ESS-Submission Editor: Dr. Marc Babut (marc.babut@cemagref.fr) 相似文献
17.
Background, Aim and Scope The distribution of sediments in estuarine beaches is controlled by the interactions between sediment supply, hydrodynamic
processes and human intervention. The main purpose of this study is to characterize the sediments of Tagus estuarine beaches
in order to understand their origin and to contribute to a better knowledge of the Tagus estuary sediment budget.
Methods Surface sediment samples were collected across beach profiles and sand grain size analysis was performed by dry sieving. Grain
size statistics for the median (d50) and standard deviation (SDM) were obtained using the Moment method. This study was complemented by a qualitative evaluation
of the sediment composition. Cross-shore topographic surveys were conducted for selected sampling sites.
Results Tagus estuarine beach sediments are mainly composed of quartz sand particles which are fine-grained and well sorted near the
mouth of the estuary and medium to coarse-grained and moderately sorted in the inner domain. Compositional results show evidence
of active anthropogenic sediment sources, especially in the coarser fractions.
Discussion The analysis of the textural and compositional characteristics of beach sediments in the inner estuarine domain is compatible
with local sedimentary sources, while a marine signature is present at the mouth and inlet channel sediments. In the inner
domain, differences in the sedimentary processes are represented by the textural characteristics of the sediments, such as
the sorting degree and the gravel content. Sediment characteristics also reflect human intervention in the system, with the
introduction of anthropogenic and allochthonous particles and the mixture of sediments from different sources.
Conclusions The sediments of the inner Tagus estuarine beaches are derived from local Plio-Pleistocene outcrops while inlet and outer
estuary beaches reveal a dominant marine source. Beach textural variability observed in the inner domain is not related to
wave forcing gradients, but mainly to variations in the sedimentary processes along the estuarine margins and to human intervention.
Results show that the Tagus estuarine beaches depended, almost exclusively, on sediment input from local sources until the
last century. With increasing human occupation, sediment transfers became dominated by anthropogenically related activities
mainly connected with the occupation of estuarine margins and dredging.
Recommendations and Perspectives Further studies should extend the present level of knowledge in what concerns sand transport patterns through additional compositional
and geochemical analysis, and the development of new techniques in order to allow the quantitative evaluation of the impact
of human activities on the sediment budget. 相似文献
18.
《Land Degradation \u0026amp; Development》2017,28(8):2446-2456
Knowing how much sediment check dams have trapped during their lifespan is essential to estimate their effectiveness or the sediment yields of their basins. Methods to calculate the volume of sediment trapped by check dams play an important role in the understanding of these issues. Several authors have proposed different methods to measure the volume of retained sediment, but their accuracy has, as yet, not been precisely determined and is currently a subject of debate. We compare the most frequently used methods (geometric: prism, pyramid and geometric; topographic: Digital Terrain Models (DTMs), trapezoids and sections methods) to evaluate their accuracy and precision in determining the volume of sediment retained by check dams. Our calculations are based on ten virtual check dams simulated in several gullies of Saldaña (Spain), where we determine their volumetric capacity for trapping sediment (real volume). This was made by means of an intensive topographic survey of these gullies, employing a terrestrial laser scanning system to obtain a high‐resolution digital elevation model (5 × 5 cm, ±2 mm). The results showed that topographic methods provided a very good fit to real volume with a difference of around 8%, being the sections method the most accurate. Geometric methods were less accurate, showing differences of up to 28%. Thus, the results obtained until now by geometric methods should be considered with caution. Although topographic methods were more accurate, they require many field data and much time than the others. So geometric methods can still be useful by correcting their results using our obtained percentage of variation. Knowing the accuracy of the methods before measuring is essential to obtain the most reliable results to analyse the role of check dams in controlling sediment, erosion processes and land degradation. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
19.
许炯心 《中国水土保持科学》2009,7(4):7-13
流域系统可以分为坡面系统和沟道-河道系统2大单元,可以分别建立泥沙收支平衡关系。结果表明：1）实施水土保持措施以后,无定河流域系统泥沙收支平衡中各变量均随时间而变化。沟道-河道系统泥沙输移比发生了极显著的减小趋势,泥沙存储量发生了显著的增大趋势,流域产沙量的变化发生了较显著的减小趋势,坡面净侵蚀量有所减少,但变化趋势不显著。2）对于不同的泥沙收支平衡变量的变化而言,水土保持措施变化和降雨变化的贡献率是不同的;对坡面净侵蚀量的变化而言,汛期降雨的变化起着决定性的作用,贡献率高达90.82%,坡面水土保持措施的贡献率仅为9.18%;对沟道河道系统泥沙存储量的变化而言,淤地坝拦沙的变化起着决定性的作用,贡献率高达76.16%,汛期降雨变化的贡献率仅为23.81%;对流域产沙量的变化而言,汛期降雨和水土保持措施的变化都起着重要作用,前者贡献率为57.84%,后者贡献率为42.16%。3）对沟道-河道系统泥沙输移比RSDRc的变化而言,淤地坝拦沙的变化起着决定性的作用,贡献率高达87.27%,汛期降雨变化的贡献率仅为12.73%。 相似文献