Levee Safety Research Articles

A Study on Evaluation System of River Levee Safety Map to Improve Maintenance Efficiency and Disaster Responsiveness

A Study on Evaluation System of River Levee Safety Map to Improve Maintenance Efficiency and Disaster Responsiveness

A study to determine the location of perforated drainpipe in a levee for controlling the seepage line

Levees are facilities constructed along river to protect floodplains against flooding. However, levee failures are also possible if seepage reaches landside surface of the levee. The seepage on the surface of the landside slope can be prevented by efficient design of levee drainage systems. This study aims to show the seepage control potential on levees by installation of perforated drainpipes, which was verified through hydraulic experiments. Scenarios were performed with four different water stages at riverside. For each scenario, the piezometric heads located at the bottom of the experimental levee were measured. The results of the hydraulic experiments showed that the precise positioning of perforated drainpipes is vital since it greatly affects the amount of seepage in the levee. The SEEP/W model that was calibrated and verified with the experiment results was used to suggest appropriate installation location range of the perforated drainpipe. From the numerical simulation, as the central location of perforated drainpipe is closer to landside levee toe horizontally and to foundation surface vertically, the safety of levee was increased from the seepage failure.

Study on Levee Visual Inspection Information System Building Using Mobile Technology

In this paper, we propose the mobile visual inspection information system using DGPS and portable range finder for levee safety inspection. Instead of existing visual inspection management method that is stored hand-written data, this system is designed to manage directly the visual inspection information using mobile devices in the field of levee. And through extracting accurate DGPS coordinates information about damage location of levee, this system is developed to ensure efficiency for the main task arising from the levee site such as inspection, maintenance and reinforcement. Furthermore, when damage has occurred at the point that inspector is not able to approach, this system can record the damage site data correctly, by converting data such as position, orientation and height of the damage point into the World Geodetic System coordinates. The position, orientation and height data was extracted automatically through the DGPS and portable range finder. And by applying the augmented reality method, this system was implemented for inspector to revisit the point of damage easily in order to perform the management, maintenance and reinforcement of the levee later.

2차원 수리해석에 의한 하천 제방 위험도 평가분석

실무에서 사용되고 있는 제방의 안전도 평가는 여러 가지 붕괴원인 중 하나의 요인에 대해서만 평가를 하거나 주로 제방의 물리적인 특성을 이용한 1차원 수리분석을 통한 평가에 국한되어 왔다. 하지만 이러한 평가기법들은 제방의 다양한 붕괴원인을 동시에 고려할 수 없으며, 정확한 지형정보를 필요로 하는 곳에서 신뢰도가 떨어지는 문제점을 안고 있다. 따라서 본 논문에서는 정확한 지형정보를 반영한 2차원 수리해석을 결과를 이용하여 제방의 다양한 붕괴원인인 월류, 침투, 침식위험도를 동시에 고려한 제방 위험도 지수를 제안하였다. 낙동강 유역의 주요 합류부에 대해 하천준설사업 전 후의 지형 변화를 고려하여 2차원 수리모형을 이용한 수리해석을 실시하고 그 결과를 통해 제방 위험도를 평가하였다. 본 연구는 정확한 하천의 형상을 반영한 수리해석 결과를 이용한 객관적이고 신뢰도 높은 제방위험도 평가에 기여할 수 있을 것으로 기대된다. Levee safety is being evaluated using one of the several failure causes including overtopping, infiltration and erosion or 1D hydraulic analysis considering physical characteristics of levee in practical engineering works. However, mentioned evaluation methods are not able to consider various failure causes of levee at the same time and to get reliable results where requires the accurate topographic information. This study proposed the flood hazard index which is able to consider several hazard factors involving overtopping, infiltration and erosion risk simultaneously. The index was generated from results of 2D hydraulic analysis reflecting accurate topographic information. The study areas are the confluences of the Nakdong River and two streams(Gamcheon and Hoecheon). Levee safety was evaluated using results based on 2D hydraulic analysis considering riverbed changes of before and after dredging work in the study area. This study will contribute to estimate the reliable safety evaluation of levee where may have hazards during extreme flood events.

The US Army Corps of Engineers Scalable Approach to Estimating Loss of Life from Flooding

Although flooding can lead to many types of severe consequences, the primary objective of the US Army Corps of Engineers (USACE) dam and levee safety programs are to manage risk to the public who rely on those structures to keep them reasonably safe from flooding. Thus, reducing the risk associated with loss of life is paramount. USACE employs a scalable approach to estimating loss of life, where the goal is to invest an appropriate amount of resources to answer the question at hand. Given the large number of dams and levees within the USACE portfolio (over 700 dams and 15,000 miles of levees), a “one size fits all” approach does not work. Screening level risk assessments are carried out to initially characterize risk. That initial risk characterization informs prioritization of additional efforts such as interim risk management activities and more detailed risk assessments. More detailed risk assessments inform investment in long-term risk reduction measures, which include analysis and selection of major modification activities and implementation of non-structural measures including emergency management and evacuation planning. This paper describes the USACE scalable approach for estimating loss of life from flood events.

Comparison of evacuation methods used in the Netherlands and the USACE Dam and Levee Safety Programs for the Natomas Basin (CA)

Both in the USA and in the Netherlands, extensive studies on approaches for identifying flood risks (the combination of levee failure probabilities and consequences) are ongoing. A related topic concerns evacuation and emergency management (EEM). The magnitude of life loss is directly influenced by the effectiveness of EEM. Different models can be used to define the effectiveness of evacuation. The main objective of this study is to compare Dutch and American methods for evacuation as part of flood risk management strategies for a number of case studies in the US. A second, additional objective is to explore how approaches for EEM that have been recently developed in the Netherlands, can be applied in the United States. This research shows the benefits and limitations for the application of different types of models. This research contributes to the improvement of methods for emergency management, in the Netherlands, the US and other countries.

Flood risk management with HEC-WAT and the FRA compute option

United States Army Corps of Engineers (USACE) policy states that USACE will analyze water resources projects, including flood risk management projects, using a risk framework that incorporates watershed, systems and life-cycle approaches. However, software to directly support these requirements has not been available. The current software sed within USACE to perform these types of analyses, HEC-FDA (Flood Damage Reduction Analysis), has a number of limitations. For this reason and others, USACE’s Hydrologic Engineering Center (CEIWR-HEC) developed the Watershed Analysis Tool (HEC-WAT). HECWAT was initially developed to assist USACE personnel conduct water resources studies of complex riverine systems with an integrated, comprehensive and systems based approach. However, since USACE also requires a life-cycle analysis, CEIWR-HEC added capability through the Flood Risk Analysis (FRA) compute option that allows risk analysis computations while incorporating a life-cycle approach. HEC-WAT/FRA includes systems and life-cycle approaches, event-based sampling, parameter sampling, and the ability to do scenario and alternative analyses. Applications of the FRA compute include levee certification studies, dam and levee safety studies, and planning and design studies. This paper will introduce HEC-WAT/FRA, describe scientific advancements included within it and provide applications to demonstrate how it will advance USACE modeling approaches.

흐름상태와 제내지 및 제외지의 표고변화에 따른 제방의 파이핑안정성 평가

Nowadays, the world has suffered by natural disaster of climate change due to global warming. Korea has also faced with similar situation. To prevent these natural disaster, Four Major River Management has conducted. One of conducted content in Four Major River Management is the levee maintenance which classified into fill-up the inland, levee of reinforcement and so on. These maintenances may make the characteristics of groundwater flow change and affect to the levee safety (piping phenomenon). Therefore, analysis on groundwater fluctuation according to level of riverside and inland should be required. This study focus on levee of Hoe stream, which is connected to Nakdong river, and piping safety factor in the levee analyzed by using pore water pressure. Besides, groundwater fluctuation, which is depended on level of riverside and inland, is simulated by using the SEEP/W (2D ground water model). This simulation considered steady flow and unsteady flow. As a result, piping safety factor increased due to rising the inland level. Piping safety factor of riverside was effected by only river water level. Therefore, external levee factor considering inland level raising and suitable control of river water level is need to increase piping safety factor.

제방형상과 홍수파형에 의한 제방의 파이핑 안정성 평가

최근 지구온난화 및 기후변화에 의한 재난이 빈발하고 있어 미국이나 네덜란드 같은 제방 선진국에서는 특수한 경우 적게는 500년, 크게는 10,000년 빈도의 홍수위까지도 고려하는 극단적인 수준의 제방설계기준을 적용하고 있다. 우리나라도 지난 몇 년간 국가하천을 중심으로 대하천 정비사업이 추진되었다. 주로 하천준설과 제방증축 및 신축 등으로 진행된 사업에 의해 하천환경이 광범위하게 변화되었으나 제방의 안전과 관련된 하천환경 변화에 대응하는 구체적인 대응방안을 제시하지는 못하고 있는 실정이다. 따라서 본 연구에서는 제방침투감지시스템 Testbed가 구축되어 있는 낙동강 회천의 율지제를 대상으로 제방 안전성을 평가하였다. 평가방법은 간극수압 계측자료를 이용하여 2차원 지하수 침투모형인 SEEP/W를 이용하여 제방의 파이핑 현상을 분석하였으며, 제방의 형상과 홍수파형에 따른 침투현상을 모의하여 제방안정성을 평가하였다. Because of the rapid rising of water related disasters due to the global warming, the extreme design criteria of levee construction for severe flood has been applied in several developed countries such as USA and Netheland. In Korea, the national river restoration projects were carried out on 4 major rivers in recent several years. The projects consisted of riverbed dredge and levee reinforcement, and new construction have caused wide change of river environment. However, concrete countermeasures for levee safety and river management have not been suggested until now. Therefore, this study assesses the levee safety of Yulji levee located in Hoechon, Nakdong Basin, where the Levee Seepage Monitoring System installed. The stability of levee is assessed based on the simulation performed by SEEP/W(2D unsaturated seepage model) and the simulated results are compared with the observed data. The effects of the flood wave and levee shape on the levee safety are investigated through several simulations.

Experimental Studies on Regressive Erosion of Piping in Double-Layer Levee Foundation

Seepage piping seriously threatens the safety of levee, but study on mechanism of regressive erosion is not in-depth. According to the characteristics of piping channel upstream movement, we designed a set of experiment equipment. In given experiment condition, we did the experiments with 2 kinds of overburden and 2 different position of piping channel, and measured the value of each piezometric tube. As the experiment results shows, the tip hydraulic gradient can better reflect the problems of regressive erosion, comparing with average hydraulic gradient between piping exit and outer river. The development of the regressive erosion is determined by the tip hydraulic gradient. It will stop expanding when the tip hydraulic gradient decreases after large-scale upstream movement. This paper lays a foundation for further theoretical study.

Design of System for Monitoring Seepage of Levee Engineering Based on Distributed Optical Fiber Sensing Technology

Seepage is the major factor and monitoring index of levee safety. Leakage may be undetected by conventional monitoring methods and techniques, but optical fiber distributed temperature sensor (DTS) temperature measuring system can achieve real-time temperature monitoring in internal soil of levees. According to the temperature field obtained by DTS system, monitoring and inversion methods of seepage velocity based on double-line heat source and single-line heat source are introduced, respectively. An experiment is designed and composed of DTS temperature measuring system, the heating system, the water supply system, and the computer-aided analysis system to test and verify the effectiveness and feasibility of the monitoring method. On this basis, the system of monitoring seepage based on distributed optical fibers is put forward and designed. Optical fiber intelligent monitoring system will improve the current situation of safety monitoring of levee engineering on the basis of its unique superiority.

Two-dimensional slope stability analysis of earthen levee strengthened by articulated concrete block system under hurricane overtopping flow conditions

A critical component of the evaluation of safety of earthen levees is the consideration of their global stability during hurricanes. Very little information is available regarding the slope stability of levees during hurricane overtopping conditions involving storm surge and wind generated wave action. In this research, a comprehensive slope stability investigation was undertaken where an earthen levee, representing full scale overtopping conditions, was subjected to 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 the articulated concrete block (ACB) system to protect against overtopping. This paper presents a conceptual model for ACB strengthened levee as well as a methodology for analysis and incorporation of various hurricane overtopping flow conditions in levee slope stability evaluation. The results of this study indicate that ACB strengthening systems increase the stability of the levee significantly during all the overflow conditions, especially wave only overtopping as well as combined storm surge and wave overtopping conditions. The findings of this study show that the slope stability of both the natural and the ACB strengthened levees decreases with larger equivalent random wave pressures. However, during the storm surge conditions, the factor of safety decreases as a result of higher surge regardless of the magnitude of equivalent random wave pressure. In addition, it has been shown that the effect of duration of random wave pressure on the stability of the ACB strengthened levee is limited.

Mitigation of flooding by improved dams and dykes

Following past flood disasters in Europe, safe and modern levee cross-sections have been implemented using geosynthetics. The use of filter nonwovens between the levee core and drainage and up-lift ballast berms at the inner levee embankment, or the arrangement of geosynthetic clay liners (bentonite mats, GCLs) at the outer levee embankment are included along with well-established alternatives in current guidelines. The efficiency of stabilisation measures with geosynthetics integrated into the levee has been investigated and the high stability of these construction methods in the case of overtopping has been documented. Erosion at the inner levee embankment and unexpected levee failures can be prevented or delayed. The likelihood that such levees will break is minimal because the earthen levee cannot be eroded. This approach to dramatically improving the safety of levees by integrating geosynthetics into the levee cross-section could significantly reduce danger and potential flood damage in many parts of the world.

The Influence of Current on the Height of Wind Wave Run-Up: A comparison of experimental results with the Czech National Standard

The Influence of Current on the Height of Wind Wave Run-Up: A comparison of experimental results with the Czech National StandardOne of the basic questions related to the safety of dikes and river levees is the size of the freeboard. One of the important parameters for freeboard design is the height of waves and wave run-up on levee slopes. Routine and standardised calculations of wave run-up deal with the freeboards of dams where wind waves originate on the still water of the reservoir. In the case of running water in streams (thereinafter only "currents") the effect of wave and current interaction on wave run-up is usually not taken into account due to the lack of reliable knowledge regarding the phenomenon. In the Czech Republic this question is topical in the case of large rivers such as the Elbe, the Vltava and the Morava. Within the framework of the projects Hydralab III and NAZV QI 92A139, hydraulic research and further analysis focused on wave run-up as a result of the combination of current and wind wave parameters were performed. The laboratory research was carried out in a hydraulic flume with a wavemaker on the right bank and a levee with a slope of 1:3 installed on the left bank opposite the wavemaker. Waves were generated both perpendicular and oblique to the levee axis; the angle of oblique wave attack varied within the range of ± 30°. The aim of this paper is to compare the results of the mentioned research with recommendations mentioned in the Czech National Standard CSN 75 0255Calculation of wave effects on water structuresand to quantify the effect of current on the wave run-up height.

Slope stability of earthen levee strengthened by roller-compacted concrete under hurricane overtopping flow conditions

Although an important aspect of the assessment of safety of earthen levees is the consideration for its global stability, little is known regarding the slope stability of levees during hurricane overtopping conditions involving storm surge and wind generated wave action. In this study, a comprehensive slope stability investigation was undertaken where an earthen levee, representing full-scale overtopping conditions, was subjected to 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 roller-compacted concrete (RCC) to protect against overtopping. This paper presents a conceptual model for an RCC strengthened levee as well as a methodology for analysis and incorporation of various overtopping flow conditions in levee slope stability. The findings of this study indicate that RCC 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, strengthening of the levee by RCC does not increase the factor of safety during the storm surge conditions.

Slope Stability Analysis of Earthen Levee Strengthened by High Performance Turf Reinforcement Mat under Hurricane Overtopping Flow Conditions

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.

The ups and downs of levees: GPS–based change detection, Middle Mississippi River, USA

Changes in levee-crest elevations were measured along 328 km of Mississippi River levees between St. Louis, Missouri, and Cairo, Illinois, in 1998 and 2007. We also compared 1998 and 2007 survey data with 50 yr fl ood elevation profi les to assess levels of levee protection. Levee heights, stability, and safety are nationwide concerns, especially since Hurricane Katrina and fl oodwall failures in New Orleans, Louisiana, in 2005. The majority of surveyed levees were stable at the centimeter to decimeter level during the 9 yr measurement interval. Change was measured in other areas, including increases of as much as 1.49 m and decreases of as much as 1.26 m between 1998 and 2007. The increases corresponded to local crevasse repairs, smallscale road maintenance, and larger levee-raising projects. Decreases in levee elevations are interpreted as small-scale surface erosion and larger compaction or subsidence of levee and/or foundation materials. Levee crests in 2007 were locally as much as 2.0 m below the 50 yr fl oodgrade elevations. Levee degradation reduces protection levels for fl oodplain residents, often without easily visible symptoms. Intentional levee raising without necessary studies, engineering, or permitting has a range of potential negative impacts including both a false sense of security and the potential for exporting fl ood risk to neighboring levee communities. Regional surveying of levee elevations and change over time can provide a preliminary tool for assessing levee conditions, stability, and compliance with levee regulations.

Inventory of U.S. levees planned

New legislation to create an inventory of U.S. levees was supported by witnesses at a 6 April hearing of the U.S. House of Representatives Transportation Subcommittee on Water Resources and Environment.The Levee Safety Program Act of 2005, H.R. 4650, would authorize the U.S. Army Corps of Engineers to inspect levees constructed or maintained by the Corps or other levees upon a governor's request. The Corps would create and maintain an inventory of levees and issue safety guidelines.

Raising the Bar for Levees

Engineers have worked for millennia to control natural flooding through dams and levees. While the fundamental principles and challenges of holding back water have not changed, the tools brought to the task continue to evolve. Among other tools being tested and implemented today are elaborate sensors to detect stresses and strains within structures, and impermeable lining materials known as geomembranes, which are laid underneath the structure before it is built to prevent water seepage.

하천 홍수범람모의를 위한 불확실도 해석기법의 적용

본 연구는 홍수위 계산에 있어서 도입되는 불확식성의 원인을 분석하고 정량화하여 확률론적 홍수위 계산을 실시함으로서 제방원류에 대한 제내지의 범람특성을 해석할 수 있는 모형을 개발하였다. 이를 위해서 홍수위에 영향을 미치는 각종 영향인자를 통계학적으로 분석하였고, 이들 인자를 부등류와 부정류 해석과정에 Monte Carlo 모의를 도입함으로써 홍수위에 미치는 영향을 정량화하였다. 개발된 모형의 검증을 위해 낙동강 유역의 현풍∼적포교구간에 적용하였다. 제내지로의 범람양상과 역류양상을 합리적으로 모의하였고 질량보존도 잘 모의하고 있는 것으로 나타났다. 또한 제내지 침수양상 모의시 붕괴폭, 붕괴시간 등의 불확실도를 고려하여 침수수심 및 침수면적을 산정하였다. The reliability model is developed for analyzing parameter uncertainty and estimating of flood inundation characteristics in a protected lowland. The approach is based on the concept of levee safety factor and the statistical analysis of model parameters affecting the variability of flood levels. Monte Carlo simulation is incorporated into the varied flow and unsteady flow analysis to quantify the impact of parameter uncertainty on the variability of flood levels. The model is applied to a main stem of the Nakdong River from Hyunpoong to Juckpogyo station. Simulation results show that the characteristics of channel overflow and return now are well simulated and the mass conservation was satisfied. The inundation depth and area are estimated by taking into consideration of the uncertainty of width and duration time of levee failure.