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1 INTRODUTIONTaiwan is a hilly-mountainous island lying across the center of the tropic. The slopeland accounts fortwo thirds of the total area of Taiwan. Most mountains are consisted of geologically young rocks incategories of fissile slates and shales which are easily eroded by weather. TOrrents combined with fissileslates and shales form debris flows with a very strong destrUctive power. This kind of debris flow canpotentially occur for almost all torrents whose gradient is steeper th… 相似文献
2.
Y. CHEN: Department of Civil & Environmental Engineering University of Bradford Bradford West Yorkshire BD DP United Kingdom P. A. MACKINNON: School of Civil Engineering The Queen''''s University of Belfast Belfast BT AG United Kingdom G. THOMPS 《国际泥沙研究》2000,(3)
I INTRODUCTIONSediment dredging operations are effective means of maintaining the natural navigation channel ofshipping for transportation of passengers and cargoes (Goldbeck 1998, Wakeman 1998). Expansions ofexisting ports to facilitate the groWth in marine traffic often necessitate navigation channel dredgingactivities (Foxworthy et. al. 1995, Luger et. al. 1998). Dredging is also heavily used for marine mining ofthe scabed deposits for gold or minerals (Anon 1996, Gamett 1996), and … 相似文献
3.
为研究河流底泥疏浚工程对富营养化河流水生生态系统的影响,选取巢湖双桥河开展为期一年的河流生态监测与调查,对比分析了巢湖双桥河疏浚前和疏浚后的水质指标、浮游甲壳动物群落结构及生物多样性指数.研究发现：底泥疏浚后双桥河水质得到明显改善,其中氮、磷营养盐分别削减48.09%和19.09%;底泥疏浚对浮游甲壳动物群落结构影响显著,疏浚后浮游甲壳动物生物量从1.86 mg/L下降到0.25 mg/L,下降了86.40%;疏浚后生物多样性指数高于疏浚前,且受季节影响较大;浮游甲壳动物与水环境因子相关性研究发现：pH、温度、铵态氮、硝态氮、可溶性氮、总氮和氮磷比对浮游甲壳动物总生物量均有极显著影响.研究结果表明,河流底泥疏浚工程能显著削减水体中氮、磷营养盐,并从一定程度上改善河流浮游甲壳动物群落结构,促进河流水生生态系统向健康、安全的方向发展.因此,对于双桥河这种受城市外源污染影响较大的城市污染型河流,在削减外源营养盐特别是氮输入的条件下,实施底泥疏浚工程可以促进其水生生态系统的修复. 相似文献
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DESIGN OF SLIT DAMS FOR CONTROLLING STONY DEBRIS FLOWS 总被引：3，自引：0，他引：3
Hui-Pang LIEN 《国际泥沙研究》2003,18(1)
1 INTRODUCTION Stony debris flows are natural, highly concentrated water-sediment mixture, which forms wherever the simultaneous availability of water, debris material and an adequate slope, steeper than o10 are satisfied (Gregoretti, 2000). In mountainous regions of Taiwan, due to vast development and utilization of hills, stony debris flows are important from the point of disaster prevention, since they occur frequently and often bring about heavy loss of lives and properties. Therefo… 相似文献
5.
Changes in climate may significantly affect how sediment moves through watersheds into harbours and channels that are dredged for navigation or flood control. Here, we applied a hydrologic model driven by a large suite of climate change scenarios to simulate both historical and future sediment yield and transport in two large, adjacent watersheds in the Great Lakes region. Using historical dredging expenditure data from the U.S. Army Corps of Engineers, we then developed a pair of statistical models that link sediment discharge from each river to dredging costs at the watershed outlet. Although both watersheds show similar slight decreases in streamflow and sediment yield in the near‐term, by Mid‐Century, they diverge substantially. Dredging costs are projected to change in opposite directions for the two watersheds; we estimate that future dredging costs will decline in the St. Joseph River by 8–16% by Mid‐Century but increase by 1–6% in the Maumee River. Our results show that the impacts of climate change on sediment yield and dredging may vary significantly by watershed even within a region and that agricultural practices will play a large role in determining future streamflow and sediment loads. We also show that there are large variations in responses across climate projections that cause significant uncertainty in sediment and dredging projections. 相似文献
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The process of dam removal establishes the channel morphology that is later adjusted by high-flow events. Generalities about process responses have been hypothesized, but broad applicability and details remain a research need. We completed laboratory experiments focused on understanding how processes occurring immediately after a sediment release upon dam removal or failure affect the downstream channel bed. Flume experiments tested three sediment mixtures at high and low flow rates. We measured changes in impounded sediment volume, downstream bed surface, and rates of deposition and erosion as the downstream bed adjusted. Results quantified the process responses and connected changes in downstream channel morphology to sediment composition, temporal variability in impounded sediment erosion, and spatial and temporal rates of bedload transport. Within gravel and sand sediments, the process response depended on sediment mobility. Dam removals at low flows created partial mobility with sands transporting as ripples over the gravel bed. In total, 37% of the reservoir eroded, and half the eroded sediment remained in the downstream reach. High flows generated full bed mobility, eroding sands and gravels into and through the downstream reach as 38% of the reservoir eroded. Although some sediment deposited, there was net erosion from the reach as a new, narrower channel eroded through the deposit. When silt was part of the sediment, the process response depended on how the flow rate influenced reservoir erosion rates. At low flows, reservoir erosion rates were initially low and the sediment partially exposed. The reduced sediment supply led to downstream bed erosion. Once reservoir erosion rates increased, sediment deposited downstream and a new channel eroded into the deposits. At high flows, eroded sediment temporarily deposited evenly over the downstream channel before eroding both the deposits and channel bed. At low flows, reservoir erosion was 17–18%, while at the high flow it was 31–41%. 相似文献
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1 INTRODUCTION 1. 1 Dam Removal The aging of the more than 75,000 dams in the U.S., coupled with the increasing awareness of their environmental costs, has made dam decommissioning and removal a topic of current interest to the scientific community, management agencies, and the general public. It is estimated that 85% of the dams in the U.S. will be near the end of their operational lives by the year 2020 (FEMA, 1999), necessitating thorough consideration of dam removal or repair for… 相似文献
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Matthew J. Cashman Allen C. Gellis Eric Boyd Mathias J. Collins Scott W. Anderson Brett D. McFarland Ashley M. Ryan 《地球表面变化过程与地形》2021,46(6):1145-1159
In this study, we captured how a river channel responds to a sediment pulse originating from a dam removal using multiple lines of evidence derived from streamflow gages along the Patapsco River, Maryland, USA. Gages captured characteristics of the sediment pulse, including travel times of its leading edge (~7.8 km yr−1) and peak (~2.6 km yr−1) and suggest both translation and increasing dispersion. The pulse also changed local hydraulics and energy conditions, increasing flow velocities and Froude number, due to bed fining, homogenization and/or slope adjustment. Immediately downstream of the dam, recovery to pre-pulse conditions occurred within the year, but farther downstream recovery was slower, with the tail of the sediment pulse working through the lower river by the end of the study 7 years later. The patterns and timing of channel change associated with the sediment pulse were not driven by large flow or suspended sediment-transporting events, with change mostly occurring during lower flows. This suggests pulse mobility was controlled by process-factors largely independent of high flow. In contrast, persistent changes occurred to out-of-channel flooding dynamics. Stage associated with flooding increased during the arrival of the sediment pulse, 1 to 2 years after dam removal, suggesting persistent sediment deposition at the channel margins and nearby floodplain. This resulted in National Weather Service-indicated flood stages being attained by 3–43% smaller discharges compared to earlier in the study period. This study captured a two-signal response from the sediment pulse: (1) short- to medium-term (weeks to months) translation and dispersion within the channel, resulting in aggradation and recovery of bed elevations and changing local hydraulics; and (2) dispersion and persistent longer-term (years) effects of sediment deposition on overbank surfaces. This study further demonstrated the utility of US Geological Survey gage data to quantify geomorphic change, increase temporal resolution, and provide insights into trajectories of change over varying spatial and temporal scales. 相似文献
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《国际泥沙研究》2022,37(6):766-779
Sediment forecasting at a dam site is important for the operation and management of water and sediment in a reservoir. However, the forecast results generally have some uncertainties, which may hinder the operation of the dam. In this study, a real-time sediment concentration probabilistic forecasting model is proposed based on a dynamic network model. Under this framework, the Elman neural network (ENN) and nonlinear auto-regressive with exogenous inputs (NARX) neural network models were established for sediment concentration forecasting with different lead times. A hybrid algorithm, which combined the Levenberg–Marquardt algorithm and real-time recurrent learning, was used to train the model. Using the aforementioned method, the sediment concentration was forecast for at the Sanmenxia Dam, China, and, subsequently, the forecast results were evaluated. Among the selected lead time, the results at 5 h exhibited the highest accuracy and practical significance. Compared with the ENN model, the sediment concentration peak error using the NARX neural network was reduced by 4.5%, and the sediment yield error was reduced by 0.043%. Therefore, the NARX neural network was selected as the deterministic sediment forecasting model. Additionally, the probability density function of the sediment concentration was derived based on the heterogeneity of the error distribution, and the sediment concentration interval, with different confidence levels, expected values, and median values, was forecast. The Nash–Sutcliffe coefficient of efficiency for the sediment concentration, as forecasted based on the median value, was the highest (0.04 higher than that using a deterministic model), whereas the error of the sediment concentration peak and sediment yield remained unaltered. These results indicated the accuracy and superiority of the proposed real-time sediment probabilistic forecasting hybrid model. 相似文献
10.
In the northern glaciated plain of North America, the duration of surface water in seasonal wetlands is strongly influenced by the rate of infiltration and evaporation. Infiltration also plays important roles in nutrient exchange at the sediment–water interface and groundwater recharge under wetlands. A whole‐wetland bromide tracer experiment was conducted in Saskatchewan, Canada to evaluate infiltration and solute transport processes. Bromide concentrations of surface water, groundwater, sediment pore water and plant tissues were monitored as the pond water‐level gradually dropped until there was no surface water. Hydraulic head gradients showed strong lateral flow from under the wetland to the treed riparian zone during the growing season. The bromide mass balance analysis showed that in early spring, almost 50% of water loss from the wetland was by infiltration, and it increased to about 70% in summer as plants in and around the wetland started to transpire more actively. The infiltration contributed to recharging the shallow, local groundwater under the wetland, but much of it was taken up by trees without recharging the deeper groundwater system. Emergent plants growing in the wetlands incorporated some bromide, but overall uptake of bromide by vegetation was less than 10% of the amount initially released. After one summer, most of the subsurface bromide was found within 40–80 cm of the soil surface. However, some bromide penetrated as deep as 2–3 m, presumably owing to preferential flow pathways provided by root holes or fractures. Copyright © 2004 Crown in the Right of Canada. Published by John Wiley & Sons, Ltd. 相似文献
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Physical barriers are widely used to control seawater intrusion (SWI). Amongst different kinds of physical barriers, mixed physical barriers (MPBs) are shown to be an effective approach to prevent SWI. However, the system may hinder the discharge of fresh groundwater and the removal of residual saltwater trapped in the inland aquifers of MPBs. Herein, using the validated numerical model, for the first time, we investigated the dynamics of residual saltwater and groundwater discharge after the installation of MPBs. For examining the applicability of MPB and its response to structural variations and hydraulic gradient, the comparison with traditional physical barriers and sensitivity analysis was also carried out. The MPB increased the mixing area of freshwater and saltwater at the beginning of the removal process, resulting in the reduction of the saltwater wedge length (RL) by 74.6% and the removal of total salt mass (RM) by 62.6% within the 4% of the total removal time. Meanwhile, the groundwater discharge (Q') rose rapidly after a sharp decline from 100% to 40% in the first stage. As the residual saltwater wedge was retreated, the mixing intensity and removal efficiency decreased substantially in the second stage. Similarly, Q' raised with a declining rate at this stage. The removal efficiency was positively correlated with wall depth and hydraulic gradient and there were optimal distance of the middle spacing and height of lower dam to reach the highest efficiency. The groundwater discharge reduced monotonously with the increase of dam height and wall depth as well as the decrease of barrier spacing and hydraulic gradient. Under certain conditions, the efficiency of MPB in removing residual saltwater could be 40%–100% and 0%–56% higher than that of traditional subsurface dam and cutoff wall, respectively. The laboratory scale conclusions provide valuable physical insight for the real field applications regarding dynamic mechanism and regularity. These findings will always help decision makers choose proper engineering measures and protect groundwater resources in coastal areas. 相似文献
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A borehole permeameter is well suited for testing saturated hydraulic conductivity (K(sat)) at specific depths in the vadose zone. Most applications of the method involve fine-grained soils that allow hand auguring of test holes and require a small water reservoir to maintain a constant head. In non-cohesive gravels, hand-dug test holes are difficult to excavate, holes are prone to collapse, and large volumes of water are necessary to maintain a constant head for the duration of the test. For coarse alluvial gravels, a direct-push steel permeameter was designed to place a slotted pipe at a specific sampling depth. Measurements can be made at successive depths at the same location. A 3790 L (1000 gallons) trailer-mounted water tank maintained a constant head in the permeameter. Head in the portable tank was measured with a pressure transducer and flow was calculated based on a volumetric rating curve. A U.S. Bureau of Reclamation analytical method was utilized to calculate K(sat). Measurements with the permeameter at a field site were similar to those reported from falling-head tests. 相似文献
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《国际泥沙研究》2019,34(6):537-549
Dam removal can generate geomorphic disturbances, including channel bed and bank erosion and associated abrupt/pulsed release and downstream transfer of reservoir sediment, but the type and rate of geomorphic response often are hard to predict. The situation gets even more complex in systems which have been impacted by multiple dams and a long and complex engineering history. In previous studies one-dimensional (1-D) models were used to predict aspects of post-removal channel change. However, these models do not consider two-dimensional (2-D) effects of dam removal such as bank erosion processes and lateral migration. In the current study the impacts of multiple dams and their removal on channel evolution and sediment delivery were modeled by using a 2-D landscape evolution model (CAESAR-Lisflood) focusing on the following aspects: patterns, rates, and processes of geomorphic change and associated sediment delivery on annual to decadal timescales. The current modeling study revealed that geomorphic response to dam removal (i.e., channel evolution and associated rates of sediment delivery) in multiple dam settings is variable and complex in space and time. Complexity in geomorphic system response is related to differences in dam size, the proximity of upstream dams, related buffering effects and associated rates of upstream sediment supply, and emerging feedback processes as well as to the presence of channel stabilization measures. Modeled types and rates of geomorphic adjustment, using the 2-D landscape evolution model CAESAR-Lisflood, are similar to those reported in previous studies. Moreover, the use of a 2-D method showed some advantages compared to 1-D models, generating spatially varying patterns of erosion and deposition before and after dam removal that provide morphologies that are more readily comparable to field data as well as features like the lateral re-working of past reservoir deposits which further enables the maintenance of sediment delivery downstream. 相似文献
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Hydraulic model tests for evaluating sediment control function with a grid-type Sabo dam in mountainous torrents 总被引：2，自引：0，他引：2
There are two kinds of Sabo dams in order to control sediment transport by debris flow and flash floods in mountainous area, which are closed and open-type＇s dams. In Japan, open-type＇s Sabo dams are constructed taking into account the continuity of sediment routing from upstream to downstream reach in a basin. A plan to construct a 20 m high grid-type Sabo dam which can capture a sediment volume of 400,000 m3 is proposed in the Amahata river basin in Japan. Hydraulic model tests are conducted to decide on the section for a dam （Section A, B） and the grid size such as clearance of vertical/horizontal bars for evaluating the plan. Several runs of flume tests are conducted and the sediment control function of the Sabo darn is discussed using several experimental data such as dimensionless sediment runoff rate from Sabo dam, temporal changes of bed profile and mean diameter and so on. It was found that sediment deposition in sediment storage area of Sabo dam was affected by curved channel, and that next the grid size of steel bars and thirdly the section of a dam was able to capture sediment in storage area of Sabo dam. Sediment was controlled well in the section B and in the grid size of 1.0×d95, and the problems related to sediment runoffafter sediment capturing in Sabo dam are pointed out. 相似文献
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Abstract Reservoir silting is one of the principal problems affecting the performance of dams in Algeria from the standpoint of reservoir capacity for storage. Foum El Kherza Reservoir (also known as Foum El Gherza), near Biskra Town, Algeria, is subject to dredging operations with the intent of recovering 70% of its initial storage capacity of 47 hm3 (million cubic metres). The forecasting of sediment volume trapped in the reservoir is essential to plan the future use of this resource and to sustain irrigation for the palm groves characteristic of the region. However, there are currently no sediment data, nor a sediment rating curve, for predicting sediment inflow based on hydrological data. This paper describes the optimization of a cumulative trapped sediment curve for Foum El Kherza Reservoir based on 44 years of daily inflows, by using a spreadsheet optimization tool, Microsoft Excel® Solver to calibrate the cumulative sediment load against the cumulative sediment inflow as documented by eight bathymetric surveys since the dam construction. Editor D. Koutsoyiannis; Associate editor A. Montanari Citation Tebbi, F.Z., Dridi, H., and Morris, G.L., 2012. Optimization of cumulative trapped sediment curve for an arid zone reservoir: Foum El Kherza (Biskra, Algeria). Hydrological Sciences Journal, 57 (7), 1368–1377. 相似文献
16.
Blocking is one of the important features when a beam dam intercepts debris flow, while self-cleaning is another when managing suspended debris flow. Both features determine the debris flow control benefits of beam dam but the latter often is not considered in practical engineering design. In this paper, a series of specially designed flume experiments were done to simulate blocking and self-cleaning processes. The blocking ratio and deposition features were measured to contrast the blocking and self-cleaning performance before and after artificial self-cleaning. The experimental results reveal that the beam dam net opening, particle diameter of sediment, sediment concentration, and gradient of the channel are the main factors affecting blocking performance. A new criterion of blocking performance of beam dams that considers the interaction of multiple factors and can provide guidance to practical project design is proposed. For all three types of blocking, sediment deposited upstream of a beam dam can be effectively transported downstream by erosion from post-debris-flow floods, Self-cleaning performance is most efficient for temporary blocking, followed by partial-blocking, and total-blocking. The efficiency of self-cleaning largely depends on the change of the sediment deposit due to erosion. Finally, a discussion is given for the optimal design of an open-type check dam and the feasibility of synergistic effects of self-cleaning in combination with artificial cleaning. Some supporting artificial silt-cleaning should be implemented in practice. A beam dam will, thus, have more storage capacity with which to control the next debris flow event. 相似文献
17.
Impacts of climate variability on water quality with best management practices in sub‐tropical climate of USA 
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下载免费PDF全文 Efficiency of non‐point source pollution control methods may be altered in future climate. This study investigated climate change impacts on sediment and nutrient transport, and efficiency of best management practices (BMPs), in the Upper Pearl River Watershed (UPRW) in Mississippi. The Soil and Water Assessment Tool was applied to the UPRW using observed flow, sediment and nutrient data. Water quality samples were collected at three US geological survey gauging stations. The model was successfully calibrated and validated for daily time steps (Nash Sutcliffe efficiency and coefficient of determination – R2 up to 0.7) using manual and automatic (sequential uncertainty fitting version 2) methods from February 2010 to May 2011. Future weather scenarios were simulated using the LARS‐WG model, a stochastic weather generator, with Community Climate System Model, global climate model, which was developed by the National Center for Atmospheric Research in the USA. On the basis of the Special Report on Emissions Scenarios A1B, A2 and B1 of the Intergovernmental Panel on Climate Change, climate change scenarios were simulated for the mid (2046–2065) and late (2080–2099) century. Effectiveness of four BMPs (Riparian buffer, stream fencing, sub‐surface manure applications and vegetative filter strips) on reducing sediment and nutrient were evaluated in current and future climate conditions. Results show that sediment, nitrogen and phosphorus loadings will be increased up to a maximum of 26.3%, 7.3% and 14.3%, respectively, in future climate conditions. Furthermore, the effectiveness of BMPs on sediment removal will be reduced in future climate conditions, and the efficiency of nitrogen removal will be increased, whereas phosphorus removal efficiency will remain unchanged. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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淀山湖底泥生态疏浚适宜深度判定分析 总被引：3，自引：3，他引：0
通过室内模拟实验,对淀山湖东部湖区的沉积物进行研究,测定沉积物在不同疏浚深度和疏浚温度下的铵态氮(NH4+-N)、正磷酸盐(NH43--P)和溶解性有机碳(DOC)的释放速率,并对该区域沉积物的理化指标进行检测.结果表明:淀山湖表层沉积物近年来总磷和有机质含量有较大增加.淀山湖东部湖区NH4+-N和DOC存在着释放趋势,NH43--P在夏季会从沉积物中向上覆水中释放,在年内会形成"源"和"汇"的转化.整个淀山湖东部湖区按不同研究区域划分,疏浚深度以10~20 cm最佳,疏浚季节以秋季为佳.通过对淀山湖东部湖区的沉积物在不同疏浚深度和疏浚时间下的污染物释放速率的研究,可以为淀山湖和其它类似湖泊的疏浚工作提供相应的科学依据. 相似文献
20.
《Marine pollution bulletin》2013,72(1-2):29-40
Plans are being made to construct Dalian Offshore Airport in Jinzhou Bay with a reclamation area of 21 km2. The large-scale reclamation can be expected to have negative effects on the marine environment, and these effects vary depending on the reclamation techniques used. Water quality mathematical models were developed and biology resource investigations were conducted to compare effects of an underwater explosion sediment removal and rock dumping technique and a silt dredging and rock dumping technique on water pollution and fishery loss. The findings show that creation of the artificial island with the underwater explosion sediment removal technique would greatly impact the marine environment. However, the impact for the silt dredging technique would be less. The conclusions from this study provide an important foundation for the planning of Dalian Offshore Airport and can be used as a reference for similar coastal reclamation and marine environment protection. 相似文献