Flood Protection Levees Research Articles

Dredged Canals, Wetland Loss, and Legacy

AbstractThe direct effects of converting coastal wetlands to open water by dredging them can be magnified by indirect effects. For example, dredged canals allow for recovery of mineral fluids 1000 s of m belowground which may induce geological subsidence or faulting; the dredged material deposited at the surface creates levees that redirect overland water flows. These indirect factors may stress wetland plants enough so that additional wetland habitat is converted to open water as a result of longer intervals of wetland soil waterlogging and drying, sulfide toxicity, less organic matter and sediment accumulation, and greater erosion. We quantified the indirect effects by demonstrating a robust dose–response relationship between coastal land loss and canal density in the Mississippi and Niger river deltas over 5 decades. Importantly, the ratio of land loss to canal area increases with time—a legacy effect. Surface impediments to water movements rather than belowground subsidence are the dominant causal factor. We also found that flood protection levees on the main river channel did not significantly magnify the effect of dredging on wetland loss. The cumulative effect of these direct and indirect consequences in coastal Louisiana is enormous and continuing, equaling many tens of billions dollars annually. Understanding these effects supports the rejection of a hypothesis that regional river channel flood protection levees or fluid withdrawal is of greater importance than the local changes in wetland hydrology. Wetland restoration/mitigation of dredging impacts on these two coasts can be implemented at a relatively low cost and quickly if this paradigm of the causes of coastal wetland losses is adopted.

Impact of water loss on sustainability of the Mississippi River channel in its deltaic reach

AbstractThe Mississippi River channel from New Orleans to the Gulf of Mexico (GOM) is a key deep draft navigation channel and an active deltaic lobe. Natural and engineered lateral exits from this reach into adjacent receiving basins historically has provided mineral sediment for wetland accretion in the face of rising relative sea level and supported estuarine‐coastal food webs. However, our analysis indicates water losses from the channel have increased by 25% since 2004 due to (1) bank failures during large floods since 2012 that have created several large exit channels downriver of the flood protection levee, and (2) the opening of an engineered diversion at West Bay in 2004. This has resulted in a 60%–80% loss in stream power in the lowermost navigation channel that is accompanied by net shoaling between 2012 and 2022 and an increased dredging need. Our 2022 survey in the GOM exit passes indicates that only 20% of the freshwater, 5% of the total suspended sediment (2% of the sand) at New Orleans now reaches the GOM: this supports previous research indicating the delta front is retreating after centuries of progradation. Together these results indicate that (1) river containment and the sustainability of the navigation channel is threatened, (2) sediment load reaching the seaward end of the delta may be insufficient to avoid major degradation, and (3) the increased freshwater flux into adjacent shallow coastal water bodies has unknown implications for coastal hypoxia and food webs, including commercial species (e.g., oysters) and marine mammals. Future acceleration in sea level rise rates and tropical storm frequency/intensity would likely worsen these trends.

A global open-source database of flood-protection levees on river deltas (openDELvE)

Abstract. Flood-protection levees have been built along rivers and coastlines globally. Current datasets, however, are generally confined to territorial boundaries (national datasets) and are not always easily accessible, posing limitations for hydrologic models and assessments of flood hazard. Here, we bridge this knowledge gap by collecting and standardizing global flood-protection levee data for river deltas into the open-source global river delta levee data environment, openDELvE. In openDELvE, we aggregate levee data from national databases, reports, maps, and satellite imagery. The database identifies the river delta land areas that the levees have been designed to protect. Where data are available, we record the extent and design specifications of the levees themselves (e.g., levee height, crest width, construction material) in a harmonized format. The 1657 polygons of openDELvE contain 19 248 km of levees and 44 733.505 km2 of leveed area. For the 153 deltas included in openDELvE, 17 % of the land area is confined by flood-protection levees. Around 26 % of delta population lives within the 17 % of delta area that is protected, making leveed areas densely populated. openDELvE data can help improve flood exposure assessments, many of which currently do not account for flood-protection levees. We find that current flood hazard assessments that do not include levees may exaggerate the delta flood exposure by 33 % on average, but up to 100 % for some deltas. The openDELvE is made public on an interactive platform (https://www.opendelve.eu/, 1 October 2022), which includes a community-driven revision tool to encourage inclusion of new levee data and continuous improvement and refinement of open-source levee data.

Multi-Hazard Assessment of a Flood Protection Levee

Earthquake-induced liquefaction is one of the main causes of levee breaches that can threaten human life and property. Conventionally, liquefaction hazard has been assessed in terms of the factor of safety FoS against liquefaction which ignores the potential variability of groundwater table (GWT) due to precipitation events. A probabilistic methodology, taking into account these GWT variations over time, is therefore presented in this study to assess the liquefaction hazard of an earthen flood protection levee. A frequency analysis based on the Annual Maxima/Generalised Extreme Value (AM/GEV) approach is first used to characterize the distribution of GWT extreme values. The CPT-based method is then applied with the provided GWT scenarios to predict liquefaction and display the hazard curves. Assuming a single constant GWT estimate during an earthquake revealed a certain liquefaction hazard within a sandy layer. Considering GWT variations during earthquakes showed, however, that liquefaction is unlikely to occur with an FoS threshold set at 1.0. These findings highlight: (1) the conservatism of the conventional approach that overestimates the liquefaction hazard, (2) the importance of the proposed probabilistic approach as a complementary tool for more reliable decision-making, and (3) the dependency of liquefaction hazard predictions on the degree of uncertainty in GWT estimates and FoS threshold.

Sediment transport in a restored, river-influenced Pacific Northwest estuary

Predicting the success of future investments in coastal and estuarine ecosystem restorations is limited by scarce data quantifying sediment budgets and transport processes of prior restorations. This study provides detailed analyses of the hydrodynamics and sediment fluxes of a recently restored U.S. Pacific Northwest estuary, a 61 ha former agricultural area near the mouth of the Stillaguamish River in Washington, USA. Water level, flow velocity, and suspended-sediment concentration (SSC) were measured between 21 March 2014 and 1 June 2015 at breaches excavated in the former flood-protection levee to determine transport patterns and the net sediment budget of the restoration area. SSC within the restoration area was primarily controlled by SSC variability of the nearby main stem Stillaguamish, but coastal processes also played a major role in sediment delivery. Fluvial sediment loading was dominated by runoff events associated with rainfall that lasted hours to a few days. Additionally, the 22 March 2014 SR 530 (Oso) landslide elevated sediment supply to the restoration area and coastal region for several weeks, indicating the importance of distal geomorphic events to coastal sediment budgets in small mountainous river systems. Sediment fluxes were controlled by river SSC and tidal dynamics, which set the quantity of water transported into the restoration area. Peak water discharge at the restoration area was about 12% of the river discharge, and peak sediment flux at the restoration area was about 5% of the river sediment discharge, although net sediment import was <1% of the total river load. Although sediment was imported to the restoration area, and inferred rates of accretion appear sufficient to keep pace with present rates of local sea-level rise, full recovery is challenged by significant lost grade from historical subsidence and will likely take decades to centuries. These results have implications for estuary restoration planning globally and indicate the importance of understanding coupled fluvial–coastal processes.

Hydrogeological Analysis Supported by Remote Sensing Methods as A Tool for Assessing the Safety of Embankments (Case Study from Vistula River Valley, Poland)

We aim to answer a question: how does the evolution of fluvial environment affect to risk of embankments failure in lowland rivers and how can we identify and describe places at risk of levees failure using the remote sensing data? The study was carried out in the Vistula River valley near Magnuszew (middle Vistula course, central Poland). 24 geological boreholes were drilled to a depth of 2.0–8.5 m and groundwater table observations were conducted in a monitoring network consisting of 22 wells, 5 piezometers (screened within the Holocene alluvial aquifer) and 2 temporary water gauges. Identification of the diversity of the geological structure of the floodplain was supported by airborne laser scanning imaging, as well as high resolution satellite images and aerial photos. This remote sensing study allowed the creation of a conceptual model of hydrogeological conditions. Study takes into account the effects of the land forming activity of flood waters resulting from the evolution of the fluvial environment in the Holocene. Created conceptual model subsequently fed into the construction and calibration of a mathematical groundwater flow model using MODFLOW software. The study allowed the identification and characterisation of intensified groundwater flow zones. Concentrated flow in the substrate of flood protection levees constitutes a threat to their stability. Documented in many publications climate change will induce in future climate scenarios an increase in rainfall and prolongation of dry periods. The implementation of the methodology of identifying the geological forms with the use of presented techniques allows the identification of sections of flood embankments potentially at risk of failure.

Fragility of flood protection levees for surge only overtopping erosion failure

El presente articulo describe un enfoque original para determinar curvas de fragilidad de bordos perimetrales, ante la falla por erosion debida al desbordamiento basado en la simulacion de variables aleatorias. El analisis de fragilidad toma en cuenta la incertidumbre asociada con la estimacion de los parametros de un modelo que describe la erosion superficial del material del bordo, y despues, las curvas de fragilidad se expresan en funcion del tirante de agua, por encima de la cresta del bordo. En los analisis de fragilidad, tradicionalmente se supone a priori una distribucion lognormal para las curvas de fragilidad y sus parametros se obtienen posteriormente, utilizando alguna tecnica de estimacion estadistica. Los resultados del presente articulo muestran que, al considerar una densidad de probabilidad no gaussiana para el coeficiente de erodibilidad, las curvas de fragilidad difieren de manera significativa de la distribucion lognormal.

Assessment and Prioritization of Flood Protection Levees along the Lower Tapi River, India

AbstractSurat city, located on the banks of the Tapi River near the Arabian Sea in India, has faced the wrath of severe flooding in the recent past. There has been an alarming reduction in the safe...

Morphology of fluvial levee series along a river under human influence, Maros River, Hungary

The development and morphometry of fluvial levees reflect the connection between channel and overbank processes, which can be altered by various human activities. The aims of this study are to investigate the morphology and spatial characteristics of fluvial levees and evaluate the role of some local- and catchment-scale human activities on their medium-term (150years) development. This study applies LiDAR data along a 53-km-long reach of the Maros River in Hungary.Six fluvial levee types are identified based on the beginning and end of their evolution. These levee types were generated by local nineteenth century channel regulation works (cutoffs) and mid-twentieth century channel narrowing, which was caused by gravel mining and water impoundment in the upstream sections. However, other human activities also influenced the development of active fluvial levees because their horizontal evolution could have been limited by embanked flood-protection levees or the widening of low-lying floodplain benches that were generated by channel narrowing. Additionally, revetment constructions influenced their vertical parameters as higher fluvial levees developed along the fixed banks. Generally, the older active fluvial levees are wider, while the younger active levees are narrower with steeper slopes but not always lower. On the low-lying floodplain levels (benches), the youngest fluvial levees evolved quite rapidly and consist of coarser material. Currently, only 9.8- to 38-year return-period floods could cover the fluvial levees, contributing to their evolution. This fact and the development of fluvial levee series with two-three members reflect a gradual decoupling of the channel from the floodplain.

A Stochastic Water Balance Framework for Lowland Watersheds

AbstractThe water balance dynamics in lowland watersheds are influenced not only by local hydroclimatic controls on energy and water availability, but also by imports of water from the upstream watershed. These imports result in a stochastic extent of inundation in lowland watersheds that is determined by the local flood regime, watershed topography, and the rate of loss processes such as drainage and evaporation. Thus, lowland watershed water balances depend on two stochastic processes—rainfall and local inundation dynamics. Lowlands are high productivity environments that are disproportionately associated with urbanization, high productivity agriculture, biodiversity, and flood risk. Consequently, they are being rapidly altered by human development—generally with clear economic and social motivation—but also with significant trade‐offs in ecosystem services provision, directly related to changes in the components and variability of the lowland water balance. We present a stochastic framework to assess the lowland water balance and its sensitivity to two common human interventions—replacement of native vegetation with alternative land uses, and construction of local flood protection levees. By providing analytical solutions for the mean and PDF of the water balance components, the proposed framework provides a mechanism to connect human interventions to hydrologic outcomes, and, in conjunction with ecosystem service production estimates, to evaluate trade‐offs associated with lowland watershed development.

Stability assessment of homogeneous slopes loaded with mobile tracked cranes—An artificial neural network approach

The assessment of stability of homogeneous slopes found as part of embankments, approach ramps, in bridge construction or flood protection levees could be a complex task. Either during construction or at a point in the operating life of the earth structure it can be subjected to loads from the equipment operating on it. Mobile tracked cranes used in heavy lifting or dredging operations can apply loads due to their substantial self-weight combined with the load carried by them. It is important to be able to determine the minimum factor of safety for such slopes. However due to the combination of soil parameters, slope geometry and the variable nature of loading imposed, a substantial number (measured perhaps in hundreds of combinations) slope stability analyses would be required to find the minimum factor of safety. One approach to reduce the number of analyses needed is to develop an Artificial Neural Network, train it using a representative dataset of stability analyses, and rely on its predicting capabilities to determine the minimum factor of safety for the slope for any combination of model parameters. Artificial Neural Networks can simulate the central nervous system of a human brain, by training them using the input data and target data one can build a neural network and use them for the factor of safety prediction. Since this thesis considers the case of homogeneous constructed slopes, thus the slope stability analysis was performed using Bishop Simplified Method, and the load distribution due to mobile tracked cranes was represented by an equivalent triangular distribution acting on the slope surface. The slope stability analysis was performed using Slide (from rocscience Inc.) to obtain the training dataset and MATLAB was used to develop and train the artificial neural network. A detailed investigation to assess and improve the network accuracy was carried out, and it was established that by increasing the neuron numbers and hidden layers, the ultimate average error in predicting the factor of safety for an independent test data set was 0.677%. This error, considering the inherent uncertainty of soil properties, instils confidence in using the Artificial Neural Network for predicting the factor of safety of homogeneous slopes loaded by mobile cranes.

Evaluation of Sediment Diversion Design Attributes and Their Impact on the Capture Efficiency

AbstractMany riverine systems have been disconnected from their receiving basins by flood-protection levees and other engineered systems. Reconnecting these alluvial rivers with their receiving basins is a viable option to nourish and sustain existing coastal wetland systems as well as to build new land. This sediment nourishment can be accomplished through direct dredging and placement or through sediment diversions. Efficient design of sediment diversions is important to maximize the land building potential. This study’s objective is to quantitatively identify key design attributes of sediment diversions, influencing their ability to capture sediment. The outfall channel alignment angle (ϕ), intake invert elevation, and diversion size are hypothesized as key parameters. The analysis is limited to sediment grain sizes larger than 63 μm and has been performed using a validated three-dimensional numerical model. A time integrated sediment-water ratio was used as an indicator to reflect efficiency of sedime...

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.

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.

Evaluation of the effects by implementing and improving the ‘Flood Hazard Mapping Training Course’

AbstractIn addition to structural measures such as flood protection levees, dams and retarding basins, flood hazard maps (hereafter referred to as ‘FHMaps’), as a part of nonstructural measures, has recently been recognized as more important in Japan, which has suffered from recurrent flood disasters until today. By utilizing the experience of training on flood management, Japan International Cooperation Agency and the International Centre for Water Hazard and Risk Management implemented the ‘Flood Hazard Mapping Training Course’ (hereafter referred to as ‘FHM‐TC’) for 5 years from FY2004. The FHM‐TC was implemented successfully by improving the framework and curriculum of the training course and by reflecting comments and requests from trainees of the past training courses who participated in the follow‐up activities. This paper introduces the outline of FHM‐TC, which includes the recently developed field exercise method ‘Town‐watching’, and it describes the year‐by‐year improvement of the FHM‐TC from its implementation of the previous years (e.g. the enhancement of the management and support systems), and the development of supporting tools based on the feedbacks of the follow‐up seminars. It also evaluates the effect of the training course on the trainees' understanding level on flood hazard mapping, which was investigated by conducting questionnaire survey and giving simple test to the trainees. Furthermore, it presents the development of a new training course by utilizing the experiences of the FHM‐TC.

Simulated Wave-Induced Erosion of the Mississippi River–Gulf Outlet Levees during Hurricane Katrina

This case study on the Mississippi River Gulf Outlet earthen berm/spoil bank (EBSB) illustrates a method to quantitatively analyze wave-induced lateral erosion and breaching through the flood side of coastal flood protection levees with grass armor prior to overtopping. Lateral wave-induced erosion was evaluated based on a three-step process: (1) velocity profiles were generated using a general purpose transient dynamic finite element program; (2) resistance to wave-induced erosion as a result of grass cover (turf) on the flood face of the EBSB was estimated and no wave-induced erosion was applied until the grass cover protection failed; and (3) estimated soil erodibility characteristics were used, in combination with the estimated wave-induced flood face velocities, to estimate the magnitude of lateral erosion. This case study identified that soil erodibility characteristics directly impact coastal flood protection levee performance, grass/turf armoring provides erosion protection for a limited duration,...

If You Build It, They Will Come - Management Planning for a Suburban Beaver Population in Arizona

Management for beaver now ranges from lethal removal of nuisance individuals to reintroduction of individuals for wetland restoration and to increase wildlife and habitat diversity. Management, or lack thereof, is driven largely by stakeholder concerns at the local and regional level. In many cases with management of beaver and other species, there are unclear visions of how wildlife populations may exploit resources after successful restoration or with changing landscape conditions (e.g., habitat quality and competition). With increasing conversion of the modern-day landscape, natural resource managers must make pragmatic decisions on the potential effects habitat alteration has on system stability. In 2000, the United States Army Corps of Engineers received approval from Congress to construct the Tres Rios Ecosystem Restoration and Flood Control Project in Phoenix, Arizona. Upon completion, this multi-phased, 7-mile (11.3-km), 1,500-acre (607-ha) project is designed to include a 4.25-mile (6.8-km) flood protection levee, an effluent pump station, and development/maintenance of emergent wetlands, riparian corridors, and open water marshes to replace existing non-native saltcedar. In 2000, Tres Rios constructed a demonstration area onsite that used reclaimed wastewater from the 91st Avenue Treatment Plant to establish wetland habitat. Simultaneously, we began the Tres Rios Beaver Research Project to determine the possible effects beaver have on riparian and wetland habitats. Studies within this project found that existing non-lethal management techniques were generally ineffective; however, topical application of fructose and polyethylene glycol showed promise as a technique to increase palatability of invasive Tamarisk spp., while palatability of native tree species could be reduced by application of an herbivore repellent. Other studies developed new techniques for anesthetizing beaver and increasing radio transmitter retention time on beaver. Through monitoring movement of beaver and using landscape genetic techniques to explore population diversity, researchers found deviations from published literature on beaver, suggesting that density-dependent factors may be driving beaver behavior and movement in this environment. We describe the planning process involved in developing these research studies to address stakeholder concerns.

Geomorphology, geography, and New Orleans after Iberville and Bienville

The geophysical and geographic legacy of New Orleans was partially exposed shortly after it was founded in 1718, and completely exposed in the tragic and chaotic events of the fall 2005 hurricane season. Frequent and strong hurricanes that make landfall on broad, low-lying coastal lands, along with seasonal river flooding, combined to make a risky environmental setting for the future metropolitan area that became New Orleans. This precarious setting was further supported by a geopolitical and cultural mélange that expanded into the organic soils between delta levees. Higher and more expansive flood protection levees were developed, which compensated—albeit intermittently—for the loss of the protective fringe of coastal wetlands. Repetitive disasters resulting from levee failure around and within New Orleans tragically demonstrate the inadequacy of scientific and engineering prowess operating in a restricted social–political framework. These problems beg for the clearly articulated and meaningful participation of all to appreciate the inevitability of change and the co-dependent interrelationships between people and place.

Wetland Sedimentation from Hurricanes Katrina and Rita

More than 131 x 10(6) metric tons (MT) of inorganic sediments accumulated in coastal wetlands when Hurricanes Katrina and Rita crossed the Louisiana coast in 2005, plus another 281 x 10(6) MT when accumulation was prorated for open water area. The annualized combined amount of inorganic sediments per hurricane equals (i) 12% of the Mississippi River's suspended load, (ii) 5.5 times the inorganic load delivered by overbank flooding before flood protection levees were constructed, and (iii) 227 times the amount introduced by a river diversion built for wetland restoration. The accumulation from hurricanes is sufficient to account for all the inorganic sediments in healthy saltmarsh wetlands.

The River Aire slope failure at the St. Aidans Extension Opencast Coal Site, West Yorkshire, United Kingdom

The St. Aidans Extension Opencast Coal Site is located in the flood plain of the River Aire 10 km southeast of Leeds, United Kingdom. In March 1988, a massive (600 000 m3) slope failure caused a breach of the riverbanks and flood-protection levee, and so connected the river to the opencast void, resulting in flooding of the site. A lake of about 100 ha and up to 70 m depth was created, and coal winning operations had to be suspended for 10 years. The causes of this slope failure included the effects of previous underground coal mining beneath those seams which were being surface mined, resulting in large tensile strains (up to 10 mm/m) in a heavily faulted zone that lay beneath the river bed and an adjacent navigation canal. The fracturing and opening of existing faults and joints greatly increased the permeability beneath the river, which then acted as a source of continuous recharge as the failed mass moved towards the opencast void. Subsequent remedial and recovery works (costing £20 million) have included the rerouting of the River Aire together with the canal, and pumping the flood water from the void and restarting opencast mining operations (tender sum £36 million) with a new box cut. This paper details the ground conditions and the history of events and discusses the probable mode of failure.Key words: opencast mining, slope failure, flooding, mining subsidence, ground strains, faulting.