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1.
The slope stability of levees during hurricane overtopping conditions involving storm surge and wind generated wave action is an important aspect to assess the safety of earthen levees. A comprehensive slope stability investigation was conducted in this study for an earthen levee subjected to full-scale overtopping scenarios, including storm surge only overflow, wave only overtopping, and combined wave and surge overtopping conditions. The crest and the landside of the levee were strengthened by high performance turf reinforcement mat (HPTRM) to protect against overtopping erosion. A conceptual model for HPTRM strengthened levee as well as a methodology for analysis and incorporation of various overtopping flow conditions in levee slope stability is presented. The findings of this study indicate that HPTRM strengthening of the levee improves the stability of the levee significantly during wave only as well as combined storm surge and wave overtopping conditions. However, during the storm surge conditions, the factor of safety is only improved slightly as a result of strengthening of the levee by HPTRM.  相似文献   

2.
Post-Katrina investigations revealed that most earthen levee damage occurred on the levee crest and land-side slope as a result of either wave overtopping, storm surge overflow, or a combination of both. This study addresses erosion resistance performance of a levee strengthening technique—high performance turf reinforcement mat under combined wave and surge overtopping conditions using full-scale flume tests as well as erosion function apparatus (EFA) tests. Based on the results of full-scale flume tests, an “upper limit” of soil loss is observed for certain flow conditions. Erosion rate was presented as a function of velocity and freeboard. The effect of duration of overtopping on the erosion depth is also determined. The results of EFA tests indicate that the presence of grass roots substantially improve the critical velocity and soil erodibility.  相似文献   

3.
为了研究三角洲河口风暴潮溃堤时的盐水运动规律,建立一、二维耦合的盐度数学模型对风暴潮溃堤时的盐水运动进行模拟。模型考虑洪泛区建筑物对盐水运动的影响以及溃口的渐变发展过程。用2008年多个测站的实测数据对河网模型的潮位和盐度计算结果进行了验证。将模型应用于珠江三角洲河网某近海溃口风暴潮溃堤的盐水运动模拟,并绘制了最大盐度等值面图。计算结果表明,该溃口大部分区域的溃堤积水盐度超过了4psu,因此,溃堤洪水的高盐度积水影响不容忽视。通过比较“溃堤”和“不溃堤”两种情况下的河网盐度计算结果,发现上游河道的溃堤分流增大了河道的纳潮量,促使涨潮量增大,增大了下游河网的咸潮上溯风险,减弱了上游来流对咸潮的压制效果。  相似文献   

4.
Stability of levees is critical to the safety of human and structures, especially at high water levels. Levees may fail due to the existence of soft soil foundations or seepage of water through the levees or rapid drawdown. Deep mixing technology has been considered one of the good alternatives to solve foundation and seepage problems while geosynthetics can be used to stabilize slopes during rapid drawdown. Studies have shown that deep mixed columns and geosynthetics can increase the stability of highway embankments over soft soils. In those studies, however, no ponding water exists on either side of the embankment, which is not the case for levees. Experimental studies have shown that deep mixed columns under a combination of vertical and horizontal force could fail due to shear or tension/bending or rotation. A finite difference method, incorporated in the FLAC (Fast Lagrangian Analysis of Continua) Slope software, and a limit equilibrium method (specifically Bishop's method), incorporated in the ReSSA software, were adopted in this study to investigate the stability of the levee with ponding water or under rapid drawdown. In this study, deep mixed columns were installed in continuous wall patterns, which were modeled as 2D deep mixed walls. Geosynthetic layers were modeled using cable elements with grout properties between geosynthetic and soil in the numerical analysis. Mohr-Coulomb failure criteria were used for the levee, the soft soil, and the deep mixed walls. The stability of a levee at different stages (end of construction, average service condition, high water surge, and rapid drawdown from the service condition and the highest water level condition) was examined. The study clearly demonstrated that the deep mixed walls can enhance the stability of the levee by providing shear/moment resistance and hindering seepage through the levee and geosynthetics can enhance the riverside slope stability of the levee by providing tensile resistance to the soil.  相似文献   

5.
Characterizing soil erosion and predicting levee erosion rates for various levee soils and storm conditions during floodwall overtopping events is necessary in designing levee-floodwall systems. In this study, a series of laboratory scaled levee-floodwall erosion tests were conducted to determine erosion characteristics of fine grained soils subject to overtopping from different floodwall heights with variable flow-rates. A decreasing rate of erosion was observed as a pool of water was generated in the created scour hole at the crest of the levee model. The erosion rates were also assessed using jet erosion test (JET) and erosion function apparatus (EFA) tests. The results of levee-floodwall overtopping along with soil geotechnical characteristics such as plasticity index, compaction level, and saturation level of the levee soils as well as hydraulic parameters such as water overtopping velocity were used to develop a levee-floodwall erosion rate prediction model. Then, the results of JET and EFA were integrated to develop another prediction model for levee-floodwall erosion rate estimation. Consequently, the prediction models were evaluated by conducting additional tests and comparing the prediction results with the actual measured erosion rates.  相似文献   

6.
Submarine channel levees aggrade through repeated overspill events from the channel axis. The shape of the levees may therefore reflect some characteristic(s) of the overspilling flow. It has been noted that basin floor levees typically have a relatively low-relief and taper exponentially to their termination; in contrast slope channel levees may be much steeper close to the channel. A simple physical experiment was performed where a surge-like sediment-laden current flowed through a curved channel. Significant overspill occurred and generated a deposit flanking the channel on either side. The experiment was repeated 25 times to build up low-relief channel-levees. It was found that in proximal areas, levees were steep and characterised by power-law decays, a transitional zone of logarithmically thinning levee was found a little further down-channel, followed by exponential decays in medial to distal areas. The style of levee decay is a function of spatial variation in overbank sedimentation rates. Where flows rapidly lose momentum and deposit across the grain-size spectrum, i.e., in proximal areas, levees tend to be steep; farther down the channel, the steep levee slope gives way to a more gradually tapering deposit. In more distal parts of the channel, deposition is directly related to sediment settling velocity (rather than the suspended load exceeding flow transport capacity as is the case in proximal areas), the deposit reflects this with relatively simple exponential thickness decays. Additionally, small-scale sediment waves developed under lee wave conditions on the inner-bend overbank. The waves initially migrated slightly towards the channel, but as the style of overspill evolved due to intra-channel deposition, flows moved out of the lee wave window and sedimentation became out of phase with the wavelength of the features and the topography was healed.  相似文献   

7.
Consideration of the average pore water pressure and average unit weight of soil in the slope of a levee, ignoring the position of phreatic line for stability analysis is not correct. In addition, the influence of a rock-filled portion on the upstream slope, ignored in Kozeny analysis, plays a significant role in the stability of the downstream slope. In this study, levees resting on an impervious base, without a filter and with a filter, taking into consideration a realistic pore water pressure and corresponding seepage force, with unsaturated and saturated unit weights of soil above and below the phreatic line, respectively, by taking into account the capillary effect, location of the inverted filter and rock-filled portion of the upstream slope have been analysed. A numerical technique has been applied to compute the elevation of the phreatic line and a computer program was developed. The appropriate unit weight of soil above and below the phreatic line, taking into consideration the capillary effect, and actual pore water pressure ensure greater safety of the downstream slope. The factor of safety has been found to be 16.5% more for a levee with a filter than a levee without a filter for an upstream pondage depth of 18 m, this is increased by 22.0% in cases where there is an upstream rock-filled portion.  相似文献   

8.
The main focus of this research is to detect vulnerabilities on the Mississippi river levees using remotely sensed Synthetic Aperture Radar (SAR) imagery. Unstable slope conditions can lead to slump slides, which weaken the levees and increase the likelihood of failure during floods. On-site inspection of levees is expensive and time-consuming, so there is a need to develop efficient automated techniques based on remote sensing technologies to identify levees that are more vulnerable to failure under flood loading. Synthetic Aperture Radar technology, due to its high spatial resolution and potential soil penetration capability, is a good choice to identify problem areas along the levee so that they can be treated to avoid possible catastrophic failure. This research analyzes the ability of detecting the slump slides on the levee with NASA JPL’s Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data. The main contribution of this research is the development of a machine learning framework to (1) provide improved knowledge on the status of the levees, (2) detect anomalies on the levee sections, (3) provide early warning of impending levee failures, and (4) develop efficient tools for levee health assessment. Textural features have been computed and utilized in the classification tasks to achieve efficient levee characterization. The RX anomaly detector, a training-free unsupervised classification algorithm, detected the active slides on the levee at the time of image acquisition and also flagged some areas as “anomalous,” where new slides appeared at a later date.  相似文献   

9.
The purpose of this investigation was to examine storm surge and wave reduction benefits of different environmental restoration features (marsh restoration and barrier island changes), as well as the impact of future wetland degradation on local surge and wave conditions. Storm surge simulations of two representative hurricanes were performed using the ADCIRC storm surge model with the inclusion of radiation stress gradients from the STWAVE nearshore wave model. Coupled model simulations were made for a number of landscape configurations that involved both restored and degraded wetland features. The impact of barrier island condition on hurricane surge and waves was also evaluated. Effects of landscape features were represented by changes in elevation and frictional resistance. Restoration and degradation of marsh resulted in decreases (for restoration cases) and increases (for degradation cases) in both surge and waves. The magnitude of change was correlated with the magnitude of the horizontal extent and elevation changes in the marsh. In general, the wave change patterns are consistent with the water level changes. Deflation of the Chandeleur Islands (barrier island chain) resulted in slightly increased surge. Results suggest that coastal marsh does have surge and wave reduction potential. Results also indicate that the impact of the landscape features is amplified in areas where there are levee “pockets.” Barrier islands and coastal ridges reduce wave heights, even if in a degraded condition and thus can reduce wave energy in wetland areas, protecting them from erosion.  相似文献   

10.
This study presents a risk analysis model to evaluate the failure risk for the flood-control structures in the Keelung River due to the uncertainties in the hydrological and hydraulic analysis, including hydrologic, hydraulic, and geomorphologic uncertainty factors. This study defines failure risk as the overtopping probability of the maximum water level exceeding the levee crown, and the proposed risk analysis model integrates with the advanced first-order and second-moment (AFOSM) method to calculate the overtopping probability of levee system. The proposed model is used to evaluate the effects of the freeboard and flood-diversion channel on the flood-control ability of the levees in the Keelung River, which were designed based on the 3-day, 200-year design rainfall event. The numerical experiments indicate that the hydrologic uncertainty factors have more effect on the estimated maximum water level than hydraulic and geomorphologic uncertainty factors. In addition, the freeboard and the flood-diversion channel can effectively reduce the overtopping probability so as to significantly enhance the flood-control capacity of the levee system in the Keelung River. Eventually, the proposed risk analysis successfully quantifies the overtopping risk of the levee system under a scenario, the increase in the average 200-year rainfall amount due to climate change, and the results could be useful when planning to upgrade the existing levee system.  相似文献   

11.
Shanghai is physically and socio-economically vulnerable to accelerated sea level rise because of its low elevation, flat topography, highly developed economy and highly-dense population. In this paper, two scenarios of sea level rise and storm surge flooding along the Shanghai coast are presented by forecasting 24 (year 2030) and 44 (year 2050) years into the future and are applied to a digital elevation model to illustrate the extent to which coastal areas are susceptible to levee breach and overtopping using previously developed inflow calculating and flood routing models. Further, the socio-economic impacts are examined by combining the inundation areas with land use and land cover change simulated using GeoCA-Urban software package. This analysis shows that levee breach inundation mainly occurs in the coastal zones and minimally intrudes inland with the conservative protection of dike systems designed. However, storm surge flooding at the possible maximum tide level could cause nearly total inundation of the landscape, and put approximately 24 million people in Shanghai under direct risk resulting from consequences of flooding (e.g. contamination of potable water supplies, failure of septic systems, etc.).  相似文献   

12.
Coastal wetlands are receiving increased consideration as natural defenses for coastal communities from storm surge. However, there are gaps in storm surge measurements collected in marsh areas during extreme events as well as understanding of storm surge processes. The present study evaluates the importance and variation of different processes (i.e., wave, current, and water level dynamics with respect of the marsh topography and vegetation characteristics) involved in a storm surge over a marsh, assesses how these processes contribute to storm surge attenuation, and quantifies the storm surge attenuation in field conditions. During the Fall of 2015, morphology and vegetation surveys were conducted along a marsh transect in a coastal marsh located at the mouth of the Chesapeake Bay, mainly composed of Spartina alterniflora and Spartina patens. Hydrodynamic surveys were conducted during two storm events. Collected data included wave characteristics, current velocity and direction, and water levels. Data analysis focused on the understanding of the cross-shore evolution of waves, currents and water level, and their influence on the overall storm surge attenuation. Results indicate that the marsh area, despite its short length, attenuates waves and reduces current velocity and water level. Tides have a dominant influence on current direction and velocity, but the presence of vegetation and the marsh morphology contribute to a strong reduction of current velocity over the marsh platform relative to the currents at the marsh front. Wave attenuation varies across the tide cycle which implies a link between wave attenuation and water level and, consequently, storm surge height. Storm surge reduction, here assessed through high water level (HWL) attenuation, is linked to wave attenuation across the front edge of the marsh; this positive trend highlights the reduction of water level height induced by wave setup reduction during wave propagation across the marsh front edge. Water level attenuation rates observed here have a greater range than the rates observed or modeled by other authors, and our results suggest that this is linked to the strong influence of waves in storm surge attenuation over coastal areas.  相似文献   

13.
Polders in the Netherlands are protected from flooding by flood defence systems along main water bodies such as rivers, lakes or the sea. Inside polders, canal levees provide protection from smaller water bodies. Canal levees are mainly earthen levees along drainage canals that drain excess water from polders to the main water bodies. The water levels in these canals are regulated. During the last decades, probabilistic approaches have been developed to quantify the probability of failure of flood defences along the main water bodies. This paper proposes several extensions to this method to quantify the probability of failure of canal levees. These extensions include a method to account for (i) water-level regulation in canals, (ii) the effect of maintenance dredging on the geohydrological response of the canal levee and (iii) survival of loads in the past. The results of a case study demonstrate that the proposed approach is capable of quantifying the probability of failure of canal levees and is useful for exploring the relative benefit of risk mitigating measures for canal levees.  相似文献   

14.
A novel particle based Bluff Morphology Model (BMM) developed by the authors is extended in this paper to investigate the effect of two dimensional seepage on the stability and collapse of soil slopes and levees. To incorporate the seepage in the model, Darcy’s law is applied to the interactions among neighbouring soil particles and ghost particles are introduced along the enclosed soil boundary so that no fluid crosses the boundary. The contribution of partially saturated soils and matric suction, as well as the change in hydraulic conductivity due to seepage, are predicted well by the present model. The predicted time evolution of slope stability and seepage induced collapse are in reasonable agreement with the experimental results for homogeneous non-cohesive sand and multiple layered cohesive soils. Rapid drawdown over a sand soil is also investigated, and the location and time of the levee collapse occurrence are well captured. A toe erosion model is incorporated in the BMM model, and the location and quantity of erosion from lateral seepage flow is well predicted. The interplay of erosion, seepage and slope instability is examined.  相似文献   

15.
《Sedimentology》2018,65(3):931-951
Submarine leveed channels are sculpted by turbidity currents that are commonly highly stratified. Both the concentration and the grain size decrease upward in the flow, and this is a fundamental factor that affects the location and grain size of deposits around a channel. This study presents laboratory experiments that link the morphological evolution of a progressively developing leveed channel to the suspended sediment structure of the turbidity currents. Previously, it was difficult to link turbidity current structure to channel–levee development because observations from natural systems were limited to the depositional products while experiments did not show realistic morphodynamics due to scaling issues related to the sediment transport. This study uses a novel experimental approach to overcome scaling issues, which results in channel inception and evolution on an initially featureless slope. Depth of the channel increased continuously as a result of levee aggradation combined with varying rates of channel floor aggradation and degradation. The resulting levees are fining upward and the grain‐size trend in the levee matches the upward decrease in grain size in the flow. It is shown that such deposit trends can result from internal channel dynamics and do not have to reflect upstream forcing. The suspended sediment structure can also be linked to the lateral transition from sediment bypass in the channel thalweg to sediment deposition on the levees. The transition occurs because the sediment concentration is below the flow capacity in the channel thalweg, while higher up on the channel walls the concentration exceeds capacity resulting in deposition of the inner levee. Thus, a framework is provided to predict the growth pattern and facies of a levee from the suspended sediment structure in a turbidity current.  相似文献   

16.
刘璐  沈扬  刘汉龙  楚剑 《岩土力学》2016,37(12):3410-3416
为防治漫顶引起侵蚀造成堤坝破坏,将微生物诱导碳酸钙沉淀即MICP技术应用于加固堤坝表层。通过向堤坝表层喷洒微生物细胞以及营养盐,最终在砂土孔隙中快速析出碳酸钙胶凝结晶,以改善堤坝表层砂的力学性能。首先,采用喷洒法处理堤坝表层;其次,对处理好的堤坝模型进行水槽试验,研究其抗侵蚀性;最后,对堤坝表层的试样进行强度与渗透试验。试验结果表明,采用MICP技术加固堤坝模型表层可有效提高其抗侵蚀力,防治由漫顶引起的堤坝破坏。对加固后的表层取样进行测试,结果表明：无侧限抗压强度可高达9 MPa,渗透系数从4×10?4 m/s 降低至7.2×10?7 m/s。试验说明,微生物胶结技术在加固堤坝表层方面具有潜在的工程实用价值和广阔的应用前景。  相似文献   

17.
This study investigated the importance of rainfall and various geomorphological and geometrical factors to the vulnerability of earthen levees to slump slides. The study was performed using a database including 34 slump slides that occurred in the lower Mississippi River levee system from 2008 to 2009. The impact of rainfall within the six months prior to slide occurrence was studied for 23 slides for which an accurate occurrence date was available. Several variables were used to develop a logistic regression model to predict the probability of slump slide occurrence. The proposed model was verified for both slide and non-slide cases. The regression analysis depicts the impact of channel width, river sinuosity index, riverbank erosion, channel shape condition and distance to river. Excluding the sinuosity index, the impact of the other independent variables examined was found to be significant. Occurrence of riverbank erosion around the slide locations was the most significant predictor factor. A channel width of less than 1000?m was ranked as the second most significant variable. The proposed model can aid in locating high-risk areas on levees in order to take prompt protective measures, increase monitoring efforts and enable early response under emergency conditions.  相似文献   

18.
21世纪中叶天津沿海地区极端高水位趋势预测   总被引：6，自引：3，他引：3  
宋美钰  王福  王宏 《地质通报》2008,27(6):829-836
据统计,天津沿海地区50年一遇的风暴潮极端增水水位为 4.092m,开展控沉工作后的地面下沉速率约为15mm/a,目前沿岸海挡顶面高程一般为 4.332m.参考孟加拉湾、伦敦、汉堡等沿海地区在2050年海平面上升(取较今高约0.2m的推测值)背景下的极端增水趋势预测(增加0.5m),推测天津沿海地区2050年的极端高水位将增加到 4.792m(4.092m 0.2m 0.5m),现有海挡顶面高程将下沉至 3.687m(以2007年为起算年份).2050年极端高水位将比届时的海挡顶面高1.105m,由此将加重风暴潮水漫溢致灾的危险.如果再考虑波浪叠加、河口效应、极端海面上升等不确定因素的影响,危险将更加严重.  相似文献   

19.
Levees on the lower Tuross River in south-eastern Australia reflect a complex interplay between depositional and erosional processes. Stream power, conditioned primarily by valley width, is the key determinant of levee morphology and sedimentology in this confined valley setting. Three styles of levee are described. The Rewlee levee is functionally linked to a flood channel in narrow valley settings (< 250 m). These levees contain a diverse facies assemblage characterized by various scales of erosion surfaces. Vertical accretion on levees has produced conditions under which stream power values exceed the threshold for catastrophic floodplain stripping. The levee at the Mortfield site is associated with less confined settings (valley width 500–600 m), which present lower flood stage and stream power conditions. This levee hosts a wide range of facies, but erosion surfaces are seldom observed. In the more open valley setting at the Central site (valley width 700–1000 m), levees comprise uniform, fine-grained deposits, which grade to pronounced distal floodplains with backswamps. As levees reflect a combination of within-channel and overbank processes, both depositional and erosional, these geomorphic features influence the character and sedimentology of adjacent landforms and the associated alluvial architecture of the basin.  相似文献   

20.
ABSTRACT

This study investigates the storm surge caused by Typhoon Hato, which severely affected Macau, Hong Kong, and other coastal cities in China on 23 August 2017. A typhoon and storm surge coupling model demonstrated that the maximum storm surge height reached nearly 2.5?m along the coast of Macau, while that in Hong Kong was slightly below 2?m. Furthermore, a field survey of urban flooding revealed evidence of a 2.25-m inundation in downtown Macau and a 0.55-m inundation on Lantau Island, Hong Kong, which were likely exacerbated by a combination of storm surge, heavy rainfall, and surface water runoff over a complex hilly terrain. Significant wave overtopping and runup also occurred in beach and port areas. A typhoon track analysis confirmed that several comparably strong typhoons have followed similar ESE to WNW trajectories and made landfall in the Pearl River Delta in the last few decades. Although Hato was not the strongest of these storms, its forward speed of about 32.5?km/h was remarkably faster than those of other comparable typhoons. Higher levels of storm signal warnings were issued earlier in Hong Kong than in Macau, raising questions about the appropriate timing of warnings in these two nearby areas. Our analysis of the storm’s pattern suggests that both regions’ decisions regarding signal issuance could be considered reasonable or at least cannot be simply blamed, given the rapid motion and intensification of Hato and the associated economic risks at stake.  相似文献   

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