Amount Of Sediment Deposition Research Articles

How Does Human Activity Shape the Largest Estuarine Bay of the Pearl River Estuary, South China (1964–2019)

The morphological changes in an estuarine bay are affected by fluvial and oceanic dynamics, as well as human activities. Human activity has increased considerably in recent years, especially in Lingding Bay of the Pearl River Estuary. Based on mass measured bathymetric data and remote sensing images, morphological changes in Lingding Bay were examined and its long-term morphological evolution from 1964 to 2019 was studied using GIS method and EOF methods. The water area of Lingding Bay gradually decreased through this period due to shore reclamation and the evolutionary characteristics of the underwater topography were different before and after 2007 due to changes in the intensity of human activities. From 1964 to 2007, the water depth and volume of Lingding Bay decreased slightly and the bay experienced a slow silting process with the geomorphic pattern of “three shoals and two troughs” under low-intensity human activity. From 2007 to present, high-intensity sand-dredging activities in the bay have led to considerable deepening and a significant increase in water volume in the East Trough and Middle Shoal areas. The amount of sediment loss caused by the sand-dredging activities after 2007 far exceeded the amount of sediment deposition over the past four decades prior to 2007. Therefore, even if the sand-dredging activities had been banned, the eroded parts of Lingding Bay (i.e., East Trough and Middle Shoal) may not recover in a short time due to the small sediment load from the Pearl River. These recent morphological changes in Lingding Bay may bring about challenges for estuary regulation, disaster control, environmental protection, and the operational safety of the nearby ports and channels. Consequently, the subsequent evolution of the bay requires further research. This will enrich the scientific work for estuarine and coastal research and be conducive to revealing the interaction mechanisms between humans and nature, guiding sustainable development, estuarine disaster control, and promoting interdisciplinary innovation in estuarine research.

Community composition and abundance of complete ammonia oxidation (comammox) bacteria in the Lancang River cascade reservoir

The construction of the reservoir has changed the nitrogen migration and transformation processes in the river, and a large amount of sediment deposition in the reservoir may also lead to the spatial differentiation of complete ammonia oxidation (comammox) bacteria. The study investigated the abundance and diversity of comammox bacteria in the sediments of three cascade reservoirs, namely, Xiaowan, Manwan, and Nuozhadu on the Lancang River in China. In these reservoirs, the average amoA gene abundance of clade A and clade B of comammox bacteria, ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB) was 4.16 ± 0.85 × 105, 1.15 ± 0.33 × 105, 7.39 ± 2.31 × 104, and 3.28 ± 0.99 × 105 copies g−1, respectively. The abundance of clade A was higher than that of other ammonia oxidizing microorganisms. The spatial variation of comammox bacteria abundance differed among different reservoirs, but the spatial variation trends of the two clades of comammox bacteria in the same reservoir were similar. At each sampling point, clade A1, clade A2, and clade B coexisted, and clade A2 was usually the dominant species. The connection between comammox bacteria in the pre-dam sediments was looser than that in non-pre-dam sediments, and comammox bacteria in pre-dam sediments exhibited a simpler network structure. The main factor affecting comammox bacteria abundance was NH4+-N, while altitude, temperature, and conductivity of overlying water were the main factors affecting comammox bacteria diversity. Environmental changes caused by differences in the spatial distribution of these cascade reservoirs may be the main driver of the changes of community composition and abundance of comammox bacteria. This study confirms that the construction of cascade reservoirs results in niche spatial differentiation of comammox bacteria.

Characteristics of incoming runoff and sediment load in the Three Gorges Reservoir during high flood period after the operation of the cascade reservoirs in the lower Jinsha River

泥沙淤积问题直接影响着三峡水库的使用寿命及综合效益的发挥,研究其入库水沙特性对于解决水库泥沙淤积问题具有重要意义。根据水文站实测数据,分析了三峡水库入库水沙输移特性及来源组成变化,重点研究了金沙江下游梯级水库运行后的三峡水库高洪水期入库水沙特性。结果表明:2003-2021年,三峡水库入库泥沙集中于汛期的高洪水期,2013年以后该现象更为显著,泥沙来源也由金沙江为主转变为嘉陵江为主。寸滩站洪峰流量高于50000 m³/s的高洪水期三峡入库沙量显著大于30000~50000 m³/s区间的高洪水期,三峡水库泥沙调度关键在于上游发生编号洪水期间。三峡水库上游沱江或嘉陵江等支流发生流域性大洪水时,易引起高洪水期入库水沙出现“小水大沙”的特点。金沙江下游梯级水库运行后,三峡水库高洪水期入库泥沙大幅减少,中小洪水调度期间泥沙淤积量也大幅减小。研究结果可为三峡水库的泥沙精细化调度和长期高效使用提供基础数据支撑。;The problem of sediment deposition directly affects the lifespan and comprehensive benefits of the Three Gorges Reservoir (TGR). It is of great importance to explore the characteristics of incoming runoff and sediment load in the TGR, which is conducive to solving the problem of sediment deposition in the reservoir. Based on the measured hydrological data, this paper analyzes the flow and sediment transport characteristics and source composition in the TGR, with special emphasis on such characteristics during the high flood period after the operation of the cascade reservoirs in the Lower Jinsha River. The results show that: The incoming sediment load in the TGR was mainly concentrated in the high flood period from 2003 to 2021, and this phenomenon was more significant after 2013. The main source of the sediment load has also changed from the Jinsha River to the Jialing River after 2013. Besides, for the high flood period in which the peak discharge at Cuntan Station was higher than 50000 m³/s, the sediment load in the TGR was significantly greater than those in the peak discharge intervals of 30000-50000 m³/s. The key periods for the sediment regulation of the TGR was during the numbered flood periods in the Upper Yangtze River. Additionally, the basin floods occurred in the tributaries upstream of the TGR, such as the Tuo River or the Jialing River, may cause the phenomenon of “little water carries massive sediment” happened in the TGR during the high flood period. After the operation of the cascade reservoirs in the Lower Jinsha River, the sediment load in the TGR during the high flood period has been significantly decreased, which has greatly reduced the amount of sediment deposition during the middle and small flood operation. This study can provide technical support for the refined sediment regulation of the TGR, and provide a solid guarantee for the long-term use of the TGR.

Prediction of the Amount of Sediment Deposition in Tarbela Reservoir Using Machine Learning Approaches

Tarbela is the largest earth-filled dam in Pakistan, used for both irrigation and power production. Tarbela has already lost around 41.2% of its water storage capacity through 2019, and WAPDA predicts that it will continue to lose storage capacity. If this issue is ignored for an extended period of time, which is not far away, a huge disaster will occur. Sedimentation is one of the significant elements that impact the Tarbela reservoir’s storage capacity. Therefore, it is crucial to accurately predict the sedimentation inside the Tarbela reservoir. In this paper, an Artificial Neural Network (ANN) architecture and multivariate regression technique are proposed to validate and predict the amount of sediment deposition inside the Tarbela reservoir. Four input parameters on yearly basis including rainfall (Ra), water inflow (Iw), minimum water reservoir level (Lr), and storage capacity of the reservoir (Cr) are used to evaluate the proposed machine learning models. Multivariate regression analysis is performed to undertake a parametric study for various combinations of influencing parameters. It was concluded that the proposed neural network model estimated the amount of sediment deposited inside the Tarbela reservoir more accurately as compared to the multivariate regression model because the maximum error in the case of the proposed neural network model was observed to be 4.01% whereas in the case of the multivariate regression model was observed to be 60.7%. Then, the validated neural network model was used for the prediction of the amount of sediment deposition inside the Tarbela reservoir for the next 20 years based on the time series univariate forecasting model ETS forecasted values of Ra, Iw, Lr, and Cr. It was also observed that the storage capacity of the Tarbela reservoir is the most influencing parameter in predicting the amount of sediment.

Intertidal intercepted sediment at jetties along the Gulf of Thailand

Sand bypassing is one of the promising solutions to rectify jetty-induced coastal erosion. Estimating alongshore sediment transport rate and understanding hydrodynamic conditions at a jetty are crucial for successful downdrift erosion management. This research investigated three major jetties in Thailand (Cha Am jetty, Krai jetty, and Na Saton jetty) that protrude across the surf zone and completely intercept alongshore sediment transport. Sub-aerial and inter-tidal field surveys by Real Time Kinematic (RTK) technique were undertaken in 2019 and 2020. The collected data was processed and overlaid to calculate the amount of sediment deposition at the updrift jetty. Numerical simulations using MIKE21 SW and MIKE21 HD were carried out in order to understand how waves and water currents interacted with the jetties. From the results, we found that the Cha Am jetty trapped approximately 38,187 cu.m/yr of the alongshore sediment. While the Krai jetty intercepted approximately 34,170 cu.m/yr of the alongshore drift, and approximately 65,951 cu.m/yr of longshore sediment transport was blocked by the Na Saton jetty. Such estimated amounts of deposited sediment are the quantities that should be bypassed at each jetty. Budgets and implementation plans for sand bypassing can be prepared. Decision makers can decide how to manage updrift deposition and downdrift erosion.

The Analysis of Song Putri Reservoir Storage Area on Sedimentation Rate Using Mathematical Model Approach

Song Putri Reservoir is an artificial reservoir with the aim of irrigation channels for rice fields and flood control. This reservoir is located in Eromoko District, Wonogiri Regency Sedimentation modeling in the Song Putri reservoir is needed to analyze the amount of sediment deposition against the Song Putri Reservoir. To analyze the flow patterns and sediment distribution that occurs in reservoirs, SMS (Surface-water Modeling System) 8.0 Softwarse is used. This study aims to determine the flow patterns and effects of sediment distribution on reservoir changes. The data used include Song Putri Reservoir technical data, daily rainfall data for 10 years (2009-2018), sediment data, reservoir inflow data, and bathymetry maps. To analyze the magnitude of inflow and outflow of Song Putri Reservoir, hydrological analysis using empirical methods is used, while sedimentation modeling simulation uses SMS 8.0. Software based on the simulation, result the highest flow velocity in the 50 year return period is 0.097 m / s and the smallest is 0.00 m / s. Based on the simulation results of changes in the reservoirs base for 720 hours (1 month), the values ​​that in the return period of 50 years, 100 years and the highest 1000 years the highest was 5.795 m and the smallest of 0.001 m. Based on the calculation of prediction of sediment growth rates, it obtained the results of sediment growth rates with a percentage for a 50 year return period of 35.68% with a range of percentages between 19% - 21% and a percentage of 29.103% for a 100 year return period with a range of percentages between 22% - 24%, while the percentage growth rate of 1000 year return period sediments is 98 , 20% with a percentage range between 55% - 57%.

Effects of environmental factors on the methane and carbon dioxide fluxes at the middle of Three Gorges Reservoir

Abstract In recent years, scientists have paid special attention to the greenhouse gas emissions of the Three Gorges Reservoir. This study took Fuling to Wanzhou, located at the middle section of the Three Gorges Reservoir, as the research locations. From August 2017 to August 2018, the partial pressure of carbon dioxide (CO2) and methane (CH4) and the flux of CO2 and CH4 at the water–gas interface were studied. Spearman's correlation between the partial pressure and discharge flux of CO2 and CH4 in water and environmental variables was analyzed. The research results showed that the variation of partial pressure and flux was consistent. At different sample locations, there was no statistical difference in CO2 and CH4 fluxes, but under different operating periods, the CO2 and CH4 fluxes were significantly different. The highest values happened during the drainage period as well as the low-water period, respectively. Total organic carbon and total nitrogen were significantly positively correlated, and dissolved oxygen was extremely negatively correlated. The high value of CH4 flux in the middle of the reservoir area was related to the spatial distribution of the sediment and the amount of sediment deposition.

不同泥沙埋深对几种一年生草本枯落物分解及养分动态特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同泥沙埋深对几种一年生草本枯落物分解及养分动态特征的影响 DOI: 10.5846/stxb201912032625 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 重庆市建设科技项目（城科字2019第1-4-2）；重庆市科技兴林首席专家团队项目（TD2019-2）；中央林业改革发展资金科技推广示范项目（渝林科推2017-12）；国家国际科技合作专项（2015DFA90900） Effects of different simulative sediment depths on litter decomposition and nutrient dynamic change of several annual herbaceous plants Author: Affiliation: Fund Project: This research was financially supported by the Chongqing Municipality Housing and Urban Construction Committee (No. Chengkezi 2019 1-4-2), Chongqing Municipality Key Forestry Research Project (No. TD2019-2), Forestry Extension Project of China Central Finance (No. Yulinketui 2017-12) and International Sci-Tech Cooperation Project of Ministry of Science and Technology (No. 2015DFA90900). 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探究三峡消落带泥沙淤积条件下一年生草本枯落物的分解及养分变化特征，通过模拟实验，采用分解袋法，研究不同泥沙埋深对4种一年生草本分解及养分动态的影响。所选择的三峡消落带4种一年生优势草本植物包括马唐（Digitaria sanguinalis）、稗（Echinochloa crusgali）、狼杷草（Bidens tripartita）、苍耳（Xanthium sibiricum），设置了无掩埋（0 cm）、中度掩埋（5 cm）和深度掩埋（10 cm）3个泥沙掩埋深度，试验周期为180 d。结果表明：（1）在整个实验期间，4种一年生草本枯落物的分解速率均呈现先快后慢的特点，与0 cm泥沙埋深处理相比，5、10 cm埋深下4种一年生草本枯落物的分解速率均显著降低；（2）在分解结束时，4种一年生草本枯落物C含量变化不大，P元素处于释放状态，而在泥沙掩埋下N元素处于富集状态；（3）除马唐和稗枯落物的P含量变化外，4种一年生草本枯落物C、N、P含量均表现为0 cm掩埋处理显著低于5、10 cm处理组；相反，4种一年生草本枯落物K含量则表现为0 cm掩埋处理显著高于5、10 cm处理组。研究表明消落带大量泥沙淤积抑制枯落物的分解和C、N、P元素释放，有利于降低对三峡库区水体富营养化及营养物质悬浮的贡献率，一定程度上，对库区水质保护有正面效应。 Abstract:To explore traits related to litter decomposition and the nutrient change of annual herbaceous species under the condition of sediment deposition in the Three Gorges Reservoir. The effects of different sediment depths on ground litter decomposition and nutrient dynamic characteristics of four annual dominant herbaceous species (Digitaria sanguinalis, Echinochloa crusgali, Bidens tripartita, and Xanthium sibiricum) in the water-level fluctuation zone of the Three Gorges Reservoir were investigated using the litter-bag method. Three sediment depths included no burial (0 cm), moderate burial (5 cm) and deep burial (10 cm), were treated with an experimental period of 180 days. The results showed that:(1) During the experiment period, the decomposition rate of litters of four annual herbaceous species was fast at first and then slow. Compared with 0 cm sediment depth treatment, the decomposition rate significantly decreased in 5 cm and 10 cm. (2) When the decomposition ended, the carbon (C) content of four annual herbaceous species litters remained stable, the phosphorus (P) element was released, while the nitrogen (N) was enriched under sediment burial. (3) Except for changes in phosphorus content of D. sanguinalis and E. crusgali litter, the content of carbon, nitrogen and phosphorus of four annual herb litter in 0 cm was significantly lower than that in 5 cm and 10 cm treatment groups. On the contrary, the potassium (K) content of four annual herbs species litters in 0 cm was significantly higher than that in 5 cm and 10 cm treatment group. The results revealed that a large amount of sediment deposition in the water-level fluctuation zone inhibited the decomposition and C, N, and P release of the litter, which is beneficial to reduce the contribution of litter decomposition to water eutrophication and nutrient suspension in the Three Gorges Reservoir, and to a certain extent, has a positive effect on water quality protection. 参考文献 相似文献 引证文献

Characteristics of Flood Flow with Active Sediment Transport in the Sozu River Flood Hazards at the Severe Rainfall Event in July 2018

This study reveals the characteristics of flood flow with active sediment transport that caused the Sozu River flood disaster in July 2018. The results of field surveys revealed that the basin contains steep mountains and flat areas, facilitating the rapid transport of sediment produced in the mountains to downstream areas during the disaster. Two-dimensional numerical simulations of flood flow with sediment transport are conducted to realize the flood flow characteristics. As a result of the simulation, a huge amount of sediment deposition in the channel near the top of the alluvial fan increases the inundation damage at downstream areas. The results indicate that within two flood peaks during the disaster, the inundation in the second flood peak is more severe than that in the first peak, whereas the discharge of the second peak is much less than that in the first peak, caused by the reduction in the capacity of the original channel owing to the sand deposition during the first and second flood peaks.

Groundwater Quality Assessment Using Fuzzy-AHP in An Giang Province of Vietnam

Along with rapid population growth in Vietnam, there is an increasing dependence on groundwater for various activities. An Giang province is known to be one of the agricultural intensification areas of The Vietnamese Mekong Delta (VMD). This study aimed to evaluate the spatiotemporal variation of groundwater quality for a period of ten years from 2009 to 2018 in An Giang. The weighted groundwater quality index (GWQI) was developed based on the fuzzy analytic hierarchy process (Fuzzy-AHP) for assigning weighted parameters. The results show that that shallow wells in the Northeast and Southeast regions of An Giang were mostly categorized under “bad water” quality with high arsenic (As) concentration over the years partly due to huge amounts of sediment deposition in monsoon season. Overall, the reason for the poor groundwater quality in An Giang was the combined effect of both natural and human activities. On the other hand, we detected high values of GWQI links with high As concentration in areas where people extract more groundwater for irrigation. Temporal variation of GWQI suggested that groundwater quality at eight wells has improved from 2009 to 2018 in the wet season as compared to the dry season. The reason behind the improvement of groundwater quality during wet season was the decrease in river discharge, which causes less deposition of suspended solids near the flood plains. Moreover, the filling of unused wells can reduce the movement of pollutants from unused wells to groundwater aquifers. Although there was not sufficient evidence to show the relationship between As and sediment concentration, the temporal reduction trend in river discharge and suspended solids was detected in An Giang. The understanding of groundwater quality can help policymakers protect and manage limited water resources in the long-term.

EXPLORING THE INFLUENCE OF LAND RECLAMATION ON SEDIMENT GRAIN SIZE DISTRIBUTION ON TIDAL FLATS: A NUMERICAL STUDY

We explore the effects of land reclamation on the morphological evolution and sediment sorting on a tidal flat using a state-of-the-art numerical model (Delft3D). Consistent with existing field observations and analytical theories, model results indicate that the longitudinal profile adjusts itself converging to new equilibrium states (narrower and steeper) after a series of reclamations. Relatively fine sediments deposit adjacent to the sea dike, due to the flood-dominated tidal hydrodynamics. The amount of sediment deposition in front of the dike peaks when the dike is designed at mean sea level. After sequential reclamations, sediment grain size appears to be coarser offshore and on the tidal flat. Overall, this study suggests that land reclamation can lead to the readjustment of tidal flat profile shapes and coarsening of sediment grain size, which should be taken into account when reclamation projects are planned.

A Geo-processing Modeling of Deltaic Suspended Sediment Variability

An automated geo-processing modeling of sediment variability has been designed with a variety of geo-processing tools and used for the assessment of sediment load volumetric change. The Azhikode estuary on the western coast of Kerala state, India, confluences with west flowing river of the Western Ghats and is one of the dynamic zones due to the discharge of river Periyar to the Arabian Sea. The volumetric change in seabed sediment load has been estimated in the Azhikode estuary by analyzing the vertical difference of bathymetry-surveyed data published by Hydrographic Survey Wing, Government of Kerala, India, for the year 2000 during the seasons of pre- and post-monsoons. The bathymetry values collected from surveyed points were interpolated into a continuous surface using ordinary kriging technique of ArcGIS 10.2 software. The geo-processing modeling of volumetric change detection of sediment load reveals a deposition of 12, 21,727.06 m3 and erosion of 3, 39,197.86 m3 in an area of 5.77 km2. Spatial variability of sediment load indicates shallow bed in various parts of the estuary experiences larger amounts of sediment deposition due to the suspension of discharged sediments from rivers and channels compared to deep depth of the offshore. The model-derived volumetric changes has been validated using field measurement that shows strong correlation almost in all locations with the variability of measurement estimated less than 1%. This is an automated system that provides insight for understanding deltaic environment and helpful for periodic dredging activities for fishing port and coastal management in the future.

Influencing factors of sediment deposition and their spatial variability in riparian zone of the Three Gorges Reservoir, China

Many factors can affect the sediment deposition and soil erosion process in riparian zone, including terrain, sediment transport and water level fluctuations. Clarifying the factors influencing sediment deposition process in the riparian zone of the Three Gorges Reservoirs is an important problem to determine the key area of sediment deposition and its trend of development in the study area. In order to reveal the influence of these environmental factors on the sediment deposition in riparian zone of the Three Gorges Reservoir, this study investigated 1) the amount of deposited sediment in different environmental conditions, 2) the potential factors affecting sediment deposition in riparian zone of the Three Gorges Reservoir, 3) the relationship between the deposited sediment amount and these factors previously mentioned using correlation analysis, and 4) the influence of human activities considered as an additional factor. This study found that 1) slope gradient, elevation, inundating duration and human activities were the main factors influencing sedimentation in riparian zone of the Three Gorges Reservoir, and 2) the impact of each factor varied with spaces. Specifically, in the upper reach from Jiangjin to Fuling, human activities such as gravel dredging, bank revetment and ports and wharfs constructing disturbed considerable amounts of deposited sediment, as a result, there was no natural law to dictate the distribution. In the middle reach from Fuling to Fengjie, slope gradient and inundating duration were the controlling factors, and the sediment deposition amount was greater in the areas with a gentler slope or lower elevation. Water flow on gentler slopes generally had lower velocity, resulting in more sediment to deposit. Sites with lower elevations would be drowned by sediment-laden flow with a longer duration resulting from hydrologic regime controlled by the operating strategy of the Three Gorges Reservoir, leading to a larger amount of sediment deposition. In the lower reach from Fengjie to Zigui, slope gradient was similar to the middle reach, performing a primary factor, while other factors showed little relationship with sediment amount.

Flocculation and sediment deposition in a hypertidal creek

In the hypertidal Bay of Fundy, environmental impacts in response to commercial-scale tidal power development remain to be fully understood. The extraction of tidal energy may impact sediment dynamics in far-field environments, such as the intertidal zone, through potential alterations to tidal amplitude in the Minas Basin. Tidal conditions (e.g. current velocity, turbulence, suspended sediment concentration) were monitored in a sheltered salt marsh creek over 18 tidal cycles in various stages of the spring-neap cycle. Samples of deposited and suspended sediments were collected and analyzed for grain size using a Beckman Coulter Multisizer III. Results suggest that the flocculated component of both deposited and suspended sediment is consistently high over a wide range of tidal conditions. A routinely high incoming concentration of highly-flocculated material results in large amounts of sediment deposition in tidal creeks in response to individual tidal cycles. Resuspension and removal of newly deposited material is shown to vary with over-marsh, bankfull and channel-restricted tides. Disruption of the tidal regime due to a reduction in Minas Basin tidal amplitude may lessen the cumulative export capacity of tidal channels over time, potentially leading to gradual infilling of tidal creeks.

Characteristics of rainfall-induced landslides in Miocene formations: A case study of the Shenmu watershed, Central Taiwan

Fractured and high-permeability Miocene formations, exhibiting shallow soil layers and dense faults, and an increasing number of heavy rainfall events have caused severe and frequent landslides in the Shenmu watershed of Central Taiwan. The Shenmu watershed exhibited a landslide ratio that was typically greater than 1.0% during heavy rainfall events between 1996 and 2009, and can be considered one of the most landslide-prone areas in Taiwan. The landslide ratio in the lower hillslopes is approximately 2.8 to 43.3 times greater compared with that in the upper hillslopes. Analyzing based on a self-organized criticality (SOC) perspective indicated that the β value of the Shenmu watershed (1.24–1.26) was the lowest among landslide-prone areas, implying that small landslides dominated the distribution of landslides documented in available records. The six large landslides that occurred include four shallow landsides and two deep-seated landslides (with a landslide depth greater than 10m). Approximately 82.3% of the small landslides constituted bank-erosion landslides in the downstream watershed, whereas 96.2% of the large landslides occurred in upstream areas with dense faults. Large landslides occurred during only heavy rainfall events in which the accumulated rainfall was greater than 1000mm in fractured and high-permeability strata with dense faults. The large landslides deposited considerable amounts of sediment into streams, inducing significant bank-erosion landslides in the downstream watershed. Bank erosion in the downstream watershed caused additional small landslides along the river. Large landslides were typically caused by a fault density of 693.6m/km2, fractured strata with a permeability of 10−3 to 10−4m/s, and high levels of accumulated rainfall exceeding 1000mm. The apparent increase in bank erosion, which increased from 103% to 136% between 1996 and 2009, resulted from an increasing number of heavy rainfall events and the amount of sediment deposition caused by major landslides. Frequent landslides result from the increasing number of heavy rainfall events, fractured rock exhibiting dense faults, and steep and shallow-soil morphology in the Shenmu watershed.

Estimating sediment deposition volume in a reservoir using the physiographic soil erosion-deposition model

A traditional way to estimate the amount of sediment deposition in a reservoir is simply based on the variation in the elevation measurements made at different times. In the present study, a physiographic soil erosion-deposition (PSED) model is applied to Tseng-Wen reservoir watershed to compute the discharge and sediment concentration into the reservoir, and the deposition volume. The PSED model is verified using three storm events and then compared to the historic data recorded at the hydrological stations in the reservoir watershed, which shows close agreement between the simulated and recorded values of the flow discharge into the reservoir and the corresponding sediment yield. The numerical simulation was also conducted for all rainfall events from 1996 to 2001 to estimate the annual sediment deposition volume in the reservoir. Similarly, the simulated result was compared to that obtained from the cross-section elevation measurement. It is found that some measured data points had large uncertainty or were questionable. On the contrary, the model results and the measured data that renders the model credible. Therefore, regardless of the estimation for the flow discharge into the reservoir induced by a single rainfall event, the sediment yield, or the sediment deposition, the PSED model has successfully demonstrated its ability.

Possible ways to improve sediment deposition in the Nemunas delta

The deposition of sediment in the inundated floodplains of rivers, particularly in their deltas, improves the water quality of the rivers themselves and of their receivers. It would be very useful if ways to increase the amount of sediment deposition could be identified. An investigation into a number of possibilities was carried out in the delta of the River Nemunas. Various factors can influence the increase or decrease of sediment deposition, e.g. the increase of water discharge flowing through the river valley, the growth of bushes on the floodplain, the building of road banks across the valley and changes in growth stages of grass (which affect its ability to entrap sediments). The effects of these factors are discussed, and the most successful ways for improvement in the Nemunas delta are proposed. Similar methods may also be applicable in other river deltas.

Channel Degradation Downstream from the Three Gorges Project and Its Impacts on Flood Level

The effects of the sediment regime on the flood level in the middle reach of the Yangtze River before and after the construction of the Three Gorges Dam (TGD) are investigated. Before the dam construction, the sediment regime has driven the flood level higher and higher over recent decades in the middle reach of the Yangtze River, which has reflected changes in the location and amount of sediment deposition. After dam completion, the magnitude and rate of channel degradation determines the process of flood stage lowering but they are difficult to estimate owing to insufficient understanding of the sediment discharge recovery process. To make a rational prediction of channel degradation of the Yangtze River downstream from the TGD, the sediment transport rate during channel degradation downstream from other dams is examined. It is found that, for any grain size, postdam sediment transport rates cannot exceed the predam level at any location along the downstream channel. Erosion amounts predicted for the re...

SEDIMENT DEPOSITION IN A SOUTH SULAWESI SEAGRASS BED

Deposition of suspended sediment was measured with sediment traps in shallow coastal waters colonized by Thallasia dominated seagrass in Pannikiang Island, South Sulawesi (Indonesia). The primary objective of this study was to compare the amounts of sediment deposition inside seagrass beds and in adjacent unvegetated area. The traps were placed in a seagrass bed (Station I, II, and III) and in an adjacent unvegetated area (Station IV) measuring the sediment flux on the seabed. The sediment fluxes due to deposition were significantly higher at stations I and II (P < 0.05) and station III (P < 0.01) than at station IV (unvegetated area). Results of this study suggest that sediment deposition was promoted by dense shoots of seagrass. The study provides quantitative evidence for the importance of seagrass bed as sites of sedimentation of fine particles. 

Influence of alpine plants growing on steep slopes on sediment trapping and transport by runoff

Understanding the interactions between soil and the organisms that are conducive to decreasing sediment runoff is a great concern on high-elevation ski trails. Intense rainfalls on steep slopes combined with soil formed on gypsum result in recurrent erosion. This study was conducted in the northern French Alps to determine the abilities of species: (1) to make mounds and (2) to trap sediment and thereby to control erosion at the slope scale. We also investigated relevant above-ground plant characteristics related to those abilities. Sediment runoff or deposition was investigated at small and large spatial scales. We assessed whether hoof prints in soil reflect sediment runoff at the slope scale by trapping sediment. Populations of plants growing on two slope angles (25° and 35°) and three vegetation cover densities (15%, 35%, 60%) were surveyed. An experiment was also conducted to measure the sediment deposit upslope of target species and over three months during the autumn. Small mounds were found upslope of the plant and sediment deposit measurements showed that they resulted from a sedimentation process. Nevertheless the species differed in their capacity to make mounds. Sesleria caerulea and Festuca alpina had the highest amount of sediment deposition over the experimental period. Among the plant characteristics, plant length was positively correlated with mound area, while the roundness index of the canopy was negatively correlated with mound height. Mound formation was also positively related to the number of tillers or shoots. Sediment accumulation in cow hoof prints was linked to runoff that occurred at the slope scale. Low deposition in hoof prints means low sediment runoff or a large deposition on mounds, due to the increase in vegetation cover. All the findings stressed that understanding the processes in action at larger scales requires studying processes at smaller scales.