Earthen Levees Research Articles

The effect of long-term water table manipulations on dissolved organic carbon dynamics in a poor fen peatland

Dissolved organic carbon (DOC) production, consumption, and quality displayed differences after long-term (~55 years) hydrological alterations in a poor fen peatland in northern Michigan. The construction of an earthen levee resulted in areas of a raised and lowered water table (WT) relative to an unaltered intermediate WT site. The lowered WT site had greater peat aeration and larger seasonal vertical WT fluctuations that likely elevated peat decomposition and subsidence with subsequent increases in bulk density, vertical hydraulic gradient, decreased hydraulic conductivity (Ksat), and a greater pore water residence time relative to the unaltered site. The raised WT site displayed a decreased Ksat combined with seasonal upwelling events that contributed to a longer residence time in comparison to the unaltered site. These differences are potentially contributing to elevated DOC concentrations at the lowered and raised WT site relative to the unaltered site. Additionally, spectrophotometric indices and chemical constituent assays indicated that the lowered site DOC was more aromatic and contained elevated concentrations of phenolics compared to the intermediate site. The raised site DOC was less aromatic, less humified, and also had a greater phenolic content than the intermediate site. Furthermore, an incubation experiment showed that DOC in the raised site contained the greatest labile carbon source. Based on our results, long-term WT alterations will likely impose significant effects on DOC dynamics in these peatlands; however, WT position alone was not a good predictor of DOC concentrations, though impoundment appears to produce a more labile DOC whereas drainage increases DOC aromaticity.

Integrated seismic and cone penetration test observations at a distressed earthen levee: Marrero, Louisiana, U.S.A.

Seismic refraction velocity-versus depth models can complement our understanding of natural soils beneath flood protection levees at locations between geotechnical sites. Levee failures in New Orleans in 2005 are attributable in part to poor understanding of sediments between geotechnical sites. To a first order, subsurface fluvial–deltaic facies in the lower Mississippi delta plain correlate with general geotechnical properties of water content and cohesive strength, but are too laterally variable to be easily predicted from geotechnical sites spaced 100m apart.An artificial earthen levee, suitable for seismic investigation, lies ~15km S of the city of New Orleans, Louisiana. Values of shear-wave velocity (VSH) versus depth (0–20m) are derived by forward-ray-trace models of seismic refraction arrivals which match key boundaries identified at (geotechnical) cone-penetration testing sites, spaced at 300m apart. In particular, a 100-m section along the levee crest shows continuous cracks which are as much as 10cm wide, and 30cm deep at their northern end. Cracking may relate to high strain, induced by variable near-surface subsidence of organic-rich sediments. Topographic cross-sections across the levee show variable differential subsidence of 1–2m. Based on effective medium theory, VP- and VSH-versus-depth profiles indicate unexpectedly greater saturation and lower shear moduli on the unprotected levee side adjacent to the cracks.Integration of geophysical, sedimentary and topographic data, even if only at a few locations can help locate anomalous zones in sub-levee soil between geotechnical boring sites. Future preventive monitoring of flood-protection barriers stands to benefit greatly from integrated data sets “ground truthed” to geotechnical data.

MAPPING WEAKNESSES IN THE MISSISSIPPI RIVER LEVEE SYSTEM USING MULTI-TEMPORAL UAVSAR DATA

Levees are extended embankments naturally or artificially constructed that regulate water levels. The Mississippi Levee system in USA dates from early 1900's, and was designed to keep farmlands safe during the flooding. Today it is considered one of the most extensive engineering infrastructure projects in the world. The Mississippi Levee system comprises over 5,600 km of earthen wall structure designed to protect the agricultural areas of the Mississippi River Valley, thus monitoring the physical condition of the levees is vital for flood control. The dynamics of subsurface water events cause continuous damage on levee structures which are not easily spotted prior to the appearance of slough slides or through-seepage. The traditional method used for detecting these events involves physical surveys, always time consuming and expensive. Synthetic Aperture Radar (SAR) technologies are capable of identifying variations in soil properties that are related to the potential for such events. This paper presents a compendium of methods and results of applying the NASA Unmanned Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to the task of identifying problems on Mississippi's earthen levee system. UAVSAR is a multi-polarized SAR system, and the data exploration in this study included both single-look and multi-look records. The team investigated soil moisture, soil electrical conductivity, sand boils, landslide events, and vegetation backscatter. Different feature detection and classification algorithms were tested, including radiometric and textural methods. The levee structure and flood control system is managed by the United States Army Corps of Engineers (USACE), who would benefit from having a unified tool capable of mapping the weakness of the levee segments. The data and methods presented in this paper are incorporated into the Multi-Tabbed Levee Assessment Tool. The solution provides a user-friendly, open-source geospatial platform to perform visualization, manipulation and analysis of SAR data products.

A Framework for Assessing Spatial Distribution of Soil Properties in Levee Systems Based on Underlying Geology and River Morphology

Flood protection systems are complex, interconnected engineered systems, where failure at one location means the failure of the entire system. Earthen levees, the systems’ major component, are at risk from many causes of failure including seepage, overtopping, erosion and instability due to seismic loading. Levees stretch for long distances and are formed through various geologic processes and human activities over time, however information regarding soil properties is collected only at limited point locations and varies significantly both laterally and with depth. Prediction of levee performance in locations where no soil data is available becomes a limitation for system risk assessment studies. This study attempts to test the hypotheses that spatial variability of soil properties is correlated to regional variables such as distance from nearest river segment, river meandering sinuosity index and surface geology. A geostatistical ordinary kriging approach was used for developing these correlations. The specific areas used for data collection and analysis and model development in this study were sub-sections of the larger Sacramento River Flood Control Project (SRFCP) in northern California. Soil strength parameters of identified levee stratigraphy layers were statistically analyzed using a geostatistical ordinary kriging approach and correlated to preselected regional variables. Global observations that applied across the study area included the increasing trend of undrained shear strength for cohesive soils, Su, with increasing distance from the river, and decreasing trend of Su with increasing river Sinuosity Index levels. Only local trends were observed in the relation of friction angle of cohesionless soils, ?, with Sinuosity Index, as well as in the relation of Su and ? with geological formations.

Modeling earthen dikes using real-time sensor data

• Analysis of sensitivity of tide-induced pressure fluctuations in the dike to the variation of diffusivity. • Comparison of 1D analytical model with 2D numerical model. • Use of live sensor data for heterogeneous dike diffusivities calibration. • Generic procedure for automatic diffusivities calibration. The paper describes the concept and implementation details of integrating a finite element module for dike stability analysis “ Virtual Dike ” into an early warning system for flood protection. The module operates in real-time mode and includes fluid and structural sub-models for simulation of porous flow through the dike and for dike stability analysis. Real-time measurements obtained from pore pressure sensors are fed into the simulation module, to be compared with simulated pore pressure dynamics. Implementation of the module has been performed for a real-world test case, an earthen levee protecting a sea-port in Groningen, The Netherlands. Sensitivity analysis and calibration of diffusivities have been performed based on pore pressure sensor data during tidal fluctuations. An algorithm for automatic diffusivities calibration for a heterogeneous dike is proposed and studied. Analytical solutions describing tidal propagation in a one-dimensional saturated aquifer are employed in the algorithm to generate initial estimates of diffusivities.

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.

Simplified Methodology for Consideration of Two-Dimensional Dynamic Response of Levees in Liquefaction-Triggering Evaluation

AbstractLevees are very challenging engineering structures to study, in part because they are not typically well-engineered structures. Unfortunately, there is little to no guidance as to how to evaluate the seismic vulnerability of levees. This study focuses on systematically studying the dynamic response of levees using a wide range of input ground motions and developing a simplified procedure for the liquefaction triggering evaluation of earthen levees, accounting for the dynamic response of the levee. The study was based on three levee sites representative of three select California Central Valley regions; however, because floodplains tend to generally have similar depositional environments, the study can be extended to other regions as long as some of the principal characteristics are still applicable. A wide range of input ground motions was used to capture and assess the variability in response and performance because of multiple possible earthquake scenarios. Two aspects of the dynamic response an...

A GIS-Enabled Approach for Assessing Damage Potential of Levee Systems Based on Underlying Geology and River Morphology

Flood protection levee systems are complex, interconnected systems, where failure at one location means failure of the entire system. Levees are formed through various geologic processes and human activities over time and information regarding soil properties is collected only at limited point locations and varies significantly both laterally and with depth. Prediction of levee performance in locations where no soil data is available becomes a limitation for system risk assessment studies. Geographic Information Systems (GIS) are particularly suitable for the complex and efficient management of spatial information, georeferencing capabilities, and geostatistical analysis. A GIS enabled approach for assessing damage potential of levees systems is presented. Spatial variability of soil properties is correlated with regional variables such as distance from nearest river segment, river meandering sinuosity index, and surface geology. A geostatistical ordinary kriging approach is used for developing these correlations. Soil strength parameters of identified levee stratigraphy layers were statistically analyzed using a geostatistical ordinary kriging approach and correlated with preselected regional variables. A levee system in Northern California is used as a pilot study for the proposed approach. Excessive underseepage and loss of freeboard due to soil liquefaction are evaluated as the two damage indices for earthen levees.

Factor of Safety Reduction Factors for Accounting for Progressive Failure for Earthen Levees with Underlying Thin Layers of Sensitive Soils

The effects of progressive failure on flood embankments with underlying thin layers of soft, sensitive soils are investigated. Finite element analysis allows for investigation of strain-softening effects and progressive failure in soft and sensitive soils. However, limit equilibrium methods for slope stability analysis, widely used in industry, cannot capture these effects and may result in unconservative factors of safety. A parametric analysis was conducted to investigate the effect of thin layers of soft sensitive soils on the stability of flood embankments. A flood embankment was modeled using both the limit equilibrium method and the finite element method. The foundation profile was altered to determine the extent to which varying soft and sensitive soils affected the stability of the embankment, with respect to progressive failure. The results from the two methods were compared to determine reduction factors that can be applied towards factors of safety computed using limit equilibrium methods, in order to capture progressive failure.

SPH Modeling of Surge Overflow over RCC Strengthened Levee

Surge overflow may cause damage on earthen levees. Levee strengthened on the levee crest and landward-side slope can provide protection against the erosion damage induced by surge overflow. In this paper, surge overflow of a roller compacted concrete RCC strengthened levee was studied in a purely Lagrangian and meshless approach, the smoothed particle hydrodynamics (SPH) method. After verifying the developed model with analytical solution and comparing the results with full-scale experimental data, the roughness and erosion parameters were calibrated. The water thickness, flow velocity, and erosion depth at crest, landward-side slope and toe were calculated. The characteristics of flow hydraulics and erosion on the RCC strengthened levee are given. The results indicate that the RCC strengthened levee can resist erosion damage for a long period.

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.

Ground Motion Selection for Liquefaction Evaluation Analysis of Earthen Levees

Guidelines for selecting ground motions for liquefaction evaluation analysis of earthen levees are proposed. These guidelines were developed based on results from dynamic analyses of characteristic earthen levee cross sections using a wide range of ground motions (~1,500). The effect of a number of ground motion parameters on the dynamic response of the levees in terms of liquefaction susceptibility was studied, and the parameters that correlated best to the response were identified. For the liquefaction triggering evaluation, the mean period of the ground motion ( Tm) is best correlated to the cyclic stress ratio (CSR). Regression relationships between CSR and Tm are proposed for a series of levee types and shaking intensities.

Smoothed Particle Hydrodynamics Modeling of Combined Wave and Surge Overtopping and Hydraulic Erosion of an Articulated Concrete Block-Strengthened Levee System

Abstract Rao, X.; Li, L.; Amini, F., and Tang, H., 2012. Smoothed particle hydrodynamics modeling of combined wave and surge overtopping and hydraulic erosion of an articulated concrete block-strengthened levee system. Combined wave and surge overtopping may cause damage on earthen levees. Levee strengthened on the levee crest and landward-side slope can provide protection against the erosion damage induced by the combined wave and surge overtopping. In this paper combined wave overtopping and storm surge overflow of a levee with a trapezoidal cross section strengthened by an articulated concrete block (ACB) system was studied in a purely Lagrangian and meshless approach, two-dimensional smoothed particle hydrodynamics (SPH) model. By comparing with the results of full-scale experiment data, the model was verified, and the erosion parameters were calibrated. Time series of overtopping discharge and flow thickness at six locations on the levee crest and landward-side slope were calculated. New equations we...

Full-Scale HPTRM-Strengthened Levee Testing under Combined Wave and Surge Overtopping Conditions: Overtopping Hydraulics, Shear Stress, and Erosion Analysis

ABSTRACT Pan, Y.; Li, L.; Amini, F., and Kuang, C., 2013. Full-scale HPTRM-strengthened levee testing under combined wave and surge overtopping conditions: overtopping hydraulics, shear stress, and erosion analysis. Post–Hurricane Katrina investigations revealed that most earthen levee damage occurred on the levee crest and landward side slope as a result of wave overtopping, storm surge overflow, or a combination of both. This study was conducted to investigate the hydraulic parameters and erosion characteristic of one levee strengthening technique, a high-performance turf reinforcement mat (HPTRM), under combined wave and surge overtopping conditions, about which little is known. Because the HPTRM system can only be tested using a full-scale model, a full-scale laboratory study on combined wave and surge overtopping of a levee crest and landside slope strengthened by the HPTRM was conducted in a two-dimensional laboratory wave/flow flume. The overtopping hydraulic features were summarized during the tes...

ON LAND SLIDE DETECTION USING TERRASAR-X OVER EARTHEN LEVEES

Abstract. Earthen levees have an important role to protect large areas of inhabited and cultivated land in the US from flooding. Failure of the levees can threaten the loss of life and property. One of the problems which can lead to a complete failure during a high water event is a slough slide. In this research, we are trying to detect such slides using X-band SAR data. Our methodology consists of the following four steps: 1) segmentation of the levee area from background; 2) extracting features including backscatter features and texture features; 3) training a back propagation neural network classifier using ground-truth data; and 4) testing the area of interest and validation of the results using ground truth data. A dual-polarimetric X-band image is acquired from the German TerraSAR-X satellite. Ground-truth data include the slides and healthy area. The study area is an approximately 1 km stretch of levee along the lower Mississippi River in the United States. The output classification shows the two classes of healthy and slide areas. The results show classification accuracies of approximately 67% for detecting the slide pixels.

Numerical study of combined wave and surge overtopping over RCC strengthened levee systems using the smoothed particle hydrodynamics method

Most earthen levee damages occurred on the levee crest and landward-side slope after Hurricane Katrina as a result of either wave overtopping, storm surge overflow, or a combination of both. It is important to understand the overtopping hydraulics in the combined wave and surge overtopping condition for levees strengthened by roller compacted concrete (RCC). In this paper, combined wave overtopping and storm surge overflow of a levee with a trapezoidal cross section, strengthened by RCC, were studied in a purely Lagrangian and meshless approach, two-dimensional smoothed particle hydrodynamics (SPH) model. After verifying the developed SPH model in this study with full-scale overtopping experimental data and previous equations, time series of discharge, and water depths at two locations on the levee crest and flow thickness at five locations on the landward-side slope, 27 combinations of wave/surge overtopping cases were simulated. New equations are presented for average overtopping discharge, mean flow thickness, RMS wave height, mean velocity, and velocity of the wave front down the landward-side slope. The range of the application of these equations is discussed.

Full scale study of combined wave and surge overtopping of a levee with RCC strengthening system

Most earthen levee damages have occurred on the levee crest and landward-side slope after Hurricane Katrina as a result of either wave overtopping, storm surge overflow, or a combination of both. The goal of this study was to investigate the performance and develop design guidelines for crest and landward-side strengthening system—Roller compaction concrete (RCC). A full-scale experimental study on combined wave and surge overtopping of a levee armored with RCC was conducted in a two-dimensional laboratory wave/flow flume. Erosion of RCC surface was checked after each test. It was found most of the erosion occurred after the first test and, the erosion was related to initial quality of RCC surface. Flow parameters including time series of flow thickness and velocity at 5 locations on the levee crest and landward-side slope were measured. New equations were developed to estimate distribution of instantaneous discharge, distribution of individual wave volumes as well as flow parameters on landward-side slope, including mean flow thickness, RMS wave height, mean velocity, and wave front velocity for the RCC strengthened levee.

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.

Decision Fusion of Textural Features Derived From Polarimetric Data for Levee Assessment

Texture features derived from Synthetic Aperture Radar (SAR) imagery using grey level co-occurrence matrix (GLCM) can result in very high dimensional feature spaces. Although this high dimensional texture feature space can potentially provide relevant class-specific information for classification, it often also results in over-dimensionality and ill-conditioned statistical formulations. In this work, we propose a polarization channel based feature grouping followed by a multi-classifier decision fusion (MCDF) framework for a levee health monitoring system that seeks to detect landslides in earthen levees. In this system, texture features derived from the SAR imagery are partitioned into small groups according to different polarization channels. A multi-classifier system is then applied to each group to perform classification at the subspace level (i.e., a dedicated classifier for every subspace). Finally, a decision fusion system is employed to fuse decisions generated by each classifier to make a final classification decision (healthy levee versus landslide in this work). The resulting system can handle the high dimensionality of the problem very effectively, and only needs a few training samples for training and optimization.

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.