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To quantify the effect of a current on the height of a wave’s run-up and overtopping combined with an oblique wave approach, the “FlowDike” hydraulic research project was carried out. Tests were performed on two dike slopes of 1:3 and 1:6. Waves were generated across (perpendicular to) the physical model and also inclined in-plane to the stream axis. Oblique waves were generated both towards and along the flow’s direction. The effect of the current and of the wave direction on the height of the wave run-up and amount of the wave overtopping was expressed by means of a combined correction factor for the wave’s inclination and flow velocity. The results of the research confirmed that the flow velocity had only a small effect.

Abstract Effective coastal management requires a fundamental understanding of the impacts of anthropogenic activities on sediment dynamics, yet it is challenging to isolate individual impacts in heavily altered regions. The Ayeyarwady Delta, Myanmar has been extensively deforested for agriculture but has few levees/polders. In this study, the relative resilience to subsidence was compared between a 45‐year‐old agricultural field and a nearby mangrove‐forest preserve. At both sites, water velocity and turbidity were measured in tidal channels, topography was mapped, and sediment cores were collected during 2018–2019. There was net sediment import at both sites due to sediment trapping by vegetation. Relative elevations were equivalent, suggesting that the field has aggraded at rates similar to the forest (0.7 cm/year). Unleveed fields may be less vulnerable to subsidence than leveed fields. However, uncertainties remain and the decision to replace mangroves with agricultural fields should weigh all the benefits provided by each environment.

There is serious concern that the hazard, or probability, of river floods is increasing over time. Starting from narratives that are sometimes discussed in public, the article addresses three hypotheses. The first suggests that land-use changes, such as deforestation, urbanisation and soil compaction by agriculture, increase flood hazards. This review finds that land-use effects on floods are particularly pronounced in small catchments since soil permeability plays an important role in infiltration at this scale. For regional floods, and the most extreme events, land use is usually not the most important control, since areas of soil saturation play a greater role in runoff generation, which are less dependent on soil permeability. The second hypothesis suggests that hydraulic interventions and structures, such as river training, levees and dams, increase flood hazards. This review finds that hydraulic structures have the greatest impact on events of medium magnitude, associated with return periods of tens to hundreds of years, and that their effects are usually local. Long-term interactions between humans and floods must be taken into account when predicting future flood hazards. The third hypothesis suggests that climate change increases flood hazard. This review finds that, in small catchments of a few hectares, flood hazards may increase due to convective storms. In large catchments, where regional floods occur, changes are not necessarily directly related to precipitation, nor are they directly related to rising air temperatures, but are determined by the seasonal interplay of soil moisture, snow and extreme precipitation via runoff generation. Increases and decreases in flood hazards have been observed worldwide. It is concluded that significant progress has been made in recent years in understanding the role of land use, hydraulic structures and climate in changing river flood hazards. It is crucial to consider all three factors of change in flood risk management and communicate them to the general public in a nuanced way. [ABSTRACT FROM AUTHOR]

Dissolved carbon has been widely investigated in natural rivers worldwide. However, it has been rarely studied in riverine system of farming regions, where small streams have been usually modified by a water gate and flood levee. This study was conducted to investigate dissolved organic and inorganic carbon (DOC, DIC) in artificially modified tributary streams, namely the Desheng and Shuangqiao-Shiba streams, in a farming region of the lower Yangtze River basin. The results showed that the DOC and DIC concentrations had remarkable temporal–spatial variability in the Desheng and Shuangqiao-Shiba streams. The mean DOC concentrations were 5.4 and 6.7 mg L−1 in the Desheng and Shuangqiao-Shiba streams during the period of about 1 year, while the DIC concentrations were 14.0 and 9.6 mg L−1 in both streams, respectively. The DOC and DIC concentrations mainly showed the linear decreasing trends from source through to export in the spring, summer, autumn, and winter. The DOC concentration was almost always lower than the DIC concentration. The DOC concentration was positively correlated with the DIC concentration in the Desheng stream over the four seasons, indicating that the DOC and DIC potentially had similar sources. The DOC and DIC concentrations increased with sewage discharge, which introduced a potential hazard to human health. The water gate and flood levee in the Desheng and Shuangqiao-Shiba streams were constructed for discharging floods and recharging irrigation in the farming region, and their effects on dissolved carbon require further research. [ABSTRACT FROM AUTHOR]

Sedimentary logging at outcrops remains a basic method of sediment description in the field. The area of sedimentological study in this work was the Slovak western part of the Magura Nappe, which is the largest tectonic unit of the Outer Western Carpathians. Sediments were deposited by gravity flows in the predominantly deep-sea environment of the foreland Magura Basin. The stratigraphic extent of the studied deposits is Late Cretaceous (Cenomanian) to Oligocene/early Miocene. Up to 113 sedimentological logs have been documented in detail with a total thickness of 2022 m. Simplified logging and interpretation of the depositional environment was additionally developed for 15 of the most interesting logs. Sedimentation by debris-flows, turbidity currents, slides, and slumps in the environment of the distributary channel, levee, inter-channel, and basin plain was also interpreted. An important element of the study was the inclusion of paleocurrent directions in the analysis of logs. The purpose of the study was to record the most important outcrops in the region and thus preserve them and make them accessible to the greater public, as well as supplement the characteristics of lithostratigraphic units and knowledge on the sedimentary evolution of the Magura Basin. [ABSTRACT FROM AUTHOR]

The question of whether the Mediterranean Sea desiccated during the Messinian salinity crisis (MSC) has been strongly debated for decades. In the Levant Basin, this debate was recently reignited in relation to the latest stage of the crisis after cessation of salt deposition. The desiccation supporters argue that salt truncation--and its subsequent burial by a latest Messinian, clastic-rich evaporitic unit--occurred subaerially on a desiccated seafloor. However, we show that this latest Messinian unit contains a dense net of channels with meanders, levees, and overspill deposits and is very similar to the turbidite channels observed on the modern seafloor. The aggradation characteristics of these buried channels (levee height, channel depth, and channel-floodplain coupling) indicate a marine rather than fluvial origin. Our conclusion adds to the findings of a previous study that salt truncation occurred in deep waters by dissolution. In a wider perspective, we suggest that the flush of clastics into the basin during the last stage of the MSC indicates a combination of wet climate and sea-level rise that started before the Zanclean (earliest Pliocene). [ABSTRACT FROM AUTHOR]

Flood prone areas are often protected against flooding by an extensive network of flood defenses. To ensure their structural integrity, these flood defenses are periodically assessed. Many levees have been functioning well for decades, and have survived several relatively high hydraulic loads within their lifetime. However, information on survived load conditions is seldom included in levee safety assessments. Observed degradation from levee inspections is also not taken into account. That way, information that is useful to improve the accuracy of estimations of the actual strength of the levee remains unexploited. This study proposes a pragmatic approach to include observations of survived loads and levee degradation in the levee safety assessment. This approach consists of three steps: (1) a prior estimation of the failure probability, based on levee characteristics, (2) a posterior estimation of the failure probability, based on observed hydraulic loads, and (3) correction of the posterior failure probability estimation, based on levee inspections. In a case study, the estimated failure probabilities using this approach were much lower than when information on levee performance was not included. This study demonstrates the value of levee performance observations and how they could be included to improve levee safety assessments. [ABSTRACT FROM AUTHOR]

Levees are the most frequently used flood protection measure worldwide. In central Europe, they have been built systematically since the beginning of the 19th century. After the extreme regional floods in 1997, 2002 and 2013, the need arose for a more systematic and optimised approach to levee design and management, including the decommissioning of ineffective dike reaches. In this paper, a multicriterial algorithm is presented for the optimisation of levee management. The aspects considered are flood risk, economy, technical conditions, environmental issues and the consistency with general documents and principles in water management. The method is demonstrated via a case study of a levee subsystem in the upper Morava River basin. [ABSTRACT FROM AUTHOR]

Addition of canals and levees to wetlands is common in hydrological management. Permanently flooded canals provide fishes with refuge from desiccation and corridors for long-distance movement, but also may present high risk of predation. Levees create barriers to movement. We evaluated the effect of canals and levees on the movement of fish in seasonally fluctuating marshes in Everglades National Park between 2003 and 2016. We used directional traps to quantify activity and directional movement of seven species of fishes moving through marshes near canals and levees, and farther into the wetland. Eastern mosquitofish (Gambusia holbrooki) were ubiquitous, were active at all sites throughout the year, and moved towards canals consistent with their use as refuge habitat. Sailfin mollies (Poecilia latipinna) and bluefin killifish (Lucania goodei) were also likely to swim towards canals as water levels dropped in the dry season. Flagfish (Jordanella floridae), golden topminnows (Fundulus chrysotus), and marsh killifish (F. confluentus) used wetlands associated with anthropogenic structures but showed no directional bias with respect to canals and these species did not appear to use them as a drought refuge. Non-native African Jewelfish (Hemichromis letourneauxi) displayed directed movement related to canals, but were most active at sites distant from canals. This study provides evidence for interspecific differences among seven fishes in how they move through a marsh near different anthropogenic structures and in different seasons of the hydrologic year. Modification of wetland landscapes with structures has implications for species sorting and metacommunity dynamics filtered by species-specific behavioral traits. Monitoring efforts like this support understanding how important members of the community, like small fishes, respond to environmental and anthropogenic factors that are subject to management decisions. [ABSTRACT FROM AUTHOR]

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 km 2 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. [ABSTRACT FROM AUTHOR]

Gravity-flow deposits form the northern part of the Crocker Formation (Oligocene–Early Miocene), with the most significant interpretation as a sand-rich system in the proximal and a mud-rich system in the distal area of the deep-water turbidite depositional setting. Seven outcrop localities in the northern-part area were selected for mapping and sampling, starting from Kota Kinabalu up to the Telipok area to evaluate the sedimentary sequence. This study used mapping, field observation, and log sketches in the field, as well as extensive analysis and interpretation of sedimentological methods to investigate the sequence of sediment outcrops in the Crocker Formation area of northwest Sabah. During the fieldwork, five main facies were found, namely, massive sandstone facies (f1), graded sandstone facies (f2), laminated sandstone facies (f3), interbedded sandstone and mudstone facies (f4), and mudstone facies (f5). These northern-part outcrops are interpreted as being deposited from the highest to the lowest turbidity currents and the actuality of pelagic mudstone deposition, based on their fining-coarsening-upward pattern. The five geometrical bodies were proposed as laterally contiguous depositional environments, namely, (1) inner fan channel, (2) inner fan channel–levee complex, (3) mid-fan channelized lobes, (4) non-channelized lobes/distal lobes, and (5) basin plains. The facies interpretation shows that the study area consists of lobes, channel–levee complexes, and levees formed in a fan of a deep-water basin setting, with the basinal plain enveloped by thick mudstone deposits. This northern part of the Crocker Formation is interpreted as a multiple-sourced sediment, shelf-fed, Type II, low-efficiency, and sand-rich turbidite depositional system. [ABSTRACT FROM AUTHOR]

Water resource management and flood forecasting are crucial societal and financial stakes requiring reliable predictions of flow parameters (depth, velocity), the accuracy of which is often limited by uncertainties in hydrodynamic numerical models. In this study, we assess the effect of two uncertainty sources, namely breach characteristics induced by overtopping and the roughness coefficient, on water elevations and inundation extent. A two-dimensional (2D) hydraulic solver was applied in a Monte Carlo integration framework to a reach of the Loire river (France) including about 300 physical parameters. Inundation hazard maps for different flood scenarios allowed for the highlighting of the impact of the breach development chronology. Special attention was paid to proposing a relevant sensitivity analysis to examine the factors influencing the depth and extent of flooding. The spatial analysis of the vulnerability area induced by a levee breach width exhibits that, with increasing the flood discharge, the rise of the parameter influence is accompanied by a more localized spatial effect. This argues for a local analysis to allow a clear understanding of the flood hazard. The physical interpretation, highlighted by a global sensitivity analysis, showed the dependence of the flood simulation on the main factors studied, i.e., the roughness coefficients and the characteristics of the breaches. [ABSTRACT FROM AUTHOR]

In recent years, levees have been collapsing and residents have been being robbed of their lives and properties almost every year in Japan. For soil levees, the fluctuation of the pore water pressure in the ground is a dominant parameter of their weakening. The multipoint monitoring of the pore water pressure in a levee allows us to grasp the risk of levee collapse directly. In this study, we developed a new ultrasmall-pore water pressure gauge (UPWP gauge) whose production cost and power consumption are lower and whose installation is easier than those of commercially available pore pressure gauges. We performed basic laboratory experiments for this UPWP gauge and pooling experiments for a full-scale-model levee and assessed their performance. Our results revealed that the errors of the values measured using the UPWP gauge in the laboratory test were within ±15 mm for the set water levels. Furthermore, in the verification of the full-scale test levee, the elevation process, and the maximum pore water pressures of the UPWP and the existing pore pressure gauges were in good agreement. [ABSTRACT FROM AUTHOR]

Sandy natural levee deposits have been pointed out to provide seepage paths under river levees, which are largely related to the underseepage problems. However, few attempts have been taken to quantitatively study the relationship between the natural levees and the leakages in river levees. To capture the features of real natural levees, statistical studies are performed on the geometry and hydraulic conductivity of the micro-topographies along the Kinu River in Japan. By setting cases based on the retrieved data, a parametric study on the geometric and hydraulic parameters is performed by finite element seepage analysis. As a result, the embankment sitting on the landside of the natural levees is identified to be susceptible to leakages. In addition, rainfall and flooding are distinguished as the two driving forces of leakages depending on the hydraulic conductivity of the embankment bodies and the underneath foundations. The sandy natural levee deposits, with relatively high hydraulic conductivity, providing seepage paths for the under seepage, may magnify the effects of the seepage driven by the flooding, and lead to the classical backward erosion piping. Discussion and comments are addressed for the existing engineering practice in Japan. [ABSTRACT FROM AUTHOR]

Rivers play an integral part in the sustenance of life on earth. The river or natural channel's sinuous nature causes erosion of its outer wall and silt deposition on its inner wall. These changes in the terrain make it vital to design the meandering compound channel. Levees, both straight and meandering, can be constructed on both sides of the channel to guard the surrounding lands. For doubly meandering levee alignment, the momentum transfer between the main channel and the adjoining floodplains affects the velocity distribution across the channel cross-section. So, hydraulic engineers must investigate this complex flow phenomenon in the case of a doubly meandering compound channel. This study investigates the flow in meandering compound channels using numerical and physical modelling, both of which are important in understanding non-uniform flow and its behaviour. As a result, a research is presented on the sharing of velocity over the cross section of the main channel and the floodplains of meandering compound channels. The geometry of meandering compound channels, having straight as well as sinuous floodplain levees, is chosen for this study. Unlike the experimental models, numerical hydraulic models are remarkably economical. So, in this research, the numerical hydraulic model is adopted to determine the different flow characteristics of compound meandering channels. In this paper, a complete three-dimensional and two-phase Computational Fluid Dynamics (CFD) model of the meandering compound channels is analyzed making use of the RNG K-ɛ turbulence model as well as Volume of Fluid (VOF) methodology. A comparison study between numerical results and experimental results are represented, considering the two different experimental data of compound meandering channel having the main channel meandered with sinuosity (ratio of channel length to the down valley length) of 1.37 and were flanked by straight floodplains as well as meandering floodplains having sinuosity 1.06 on both sides. By error analysis, it is observed that the numerical results agree with that of the experimental ones. [ABSTRACT FROM AUTHOR]

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The existence of the Mississippi River (MR) and Tributaries' levees in coastal Louisiana could block storm surge and cause surge setup in adjacent basins. In order to reduce storm surge amplification caused by these barriers, one possible solution is to build "floodways" through the mainstem MR levees to allow surge during tropical events to cross. The primary purpose of this study is to examine if these floodways/openings can help reduce storm surge in adjacent basins. Using Hurricane Isaac (2012) as an example, a pre-validated Delft3D-based hydrodynamic model was applied to study the effect of levee openings on storm surge. Model results and flux analysis show that these levee openings were not effective in reducing storm surge in Barataria Basin and Breton Sound due to the complex interaction between the cross flow from the surge and the MR flow. During Isaac, the MR water could be diverted to Barataria and/or Breton, which resulted in an increase in storm surge, essentially defeating the primary objective of the levee openings. Overall, the impact of levee openings at the selected locations on storm surge reduction in adjacent basins of coastal Louisiana was minor and very limited. [ABSTRACT FROM AUTHOR]

Backward erosion piping accounts for one of the leading threats to dams and levees throughout the world. A laboratory modeling program has been conducted to interpret pore pressure data and observations collected during backward erosion piping (BEP) initiation and progression in sandy soils. An analytical model has been applied to assess the development of BEP mechanisms as well as calculating the critical hydraulic conditions required for various BEP stages to initiate and progress. The results with the predicted model are produced by successively matching the hydraulic head regime surrounding the developing BEP stages based on observations and pore pressure measurements obtained from the laboratory models. Interpretation based on an analytical model allows assessment of the processes governing BEP initiation and progression, including: (1) substantial concentrations of seepage flow around the edge of the exit area resulting in increased gradients and BEP initiation (i.e., sand boiling); (2) soil particles collapsing leading to BEP progression (i.e., channel development). The findings of the study identified the criterion for governing channel progression that can be applied to the assessment of BEP mechanics. [ABSTRACT FROM AUTHOR]

Impacts of climate change and human-made interventions have altered the fluvial regime of most rivers. The increasingly uncertain floods would further threaten the flow delivery system in regions such as Pakistan. In this study, an alluvial reach of the Indus River below Kotri barrage was investigated for the geomorphologic effects of sediments deposited over the floodplain as well as the influences on the downstream flood-carrying capacity. The hydrodynamic modeling suite HEC-RAS in combination with ground and remotely sensed data were used to undertake this analysis. Results suggest that the morphology of the river reach has degraded due to depleted flows over a long period and hydrological extremes that have led to excessive sediment deposition over the floodplain and an enhancement in flood water extension possibility over the banks. A deposition of 4.3 billion cubic meters (BCM) of sediment increased the elevation of the channel bed which in turn reduced a 17.75% flood-carrying capacity of the river reach. Moreover, the excessive deposition of sediments and the persistence of low flows have caused a loss of 48.34% bank-full discharges over the past 24 years. Consequently, the river's active reach has been flattened, with a live threat of left levee failure and the inundation of the populous city of Hyderabad. The study would gain insights into characterizing the impacts associated with a reduction in the flood-carrying capacity of the alluvial channel on account of the inadequate sediment transport capacity after heavy flow regulations. [ABSTRACT FROM AUTHOR]

In low-lying coastal areas floods occur from (combinations of) fluvial, pluvial, and coastal drivers. If these flood drivers are statistically dependent, their joint likelihood might be misrepresented if dependence is not accounted for. However, few studies have examined flood risk and risk reduction measures while accounting for so-called compound flooding. We present a globally-applicable framework for compound flood risk assessments using combined hydrodynamic, impact and statistical modeling and apply it to a case study in the Sofala province of Mozambique. The framework broadly consists of three steps. First, a large stochastic event set is derived from reanalysis data, taking into account co-occurrence of, and dependence between all annual maxima flood drivers. Then, both flood hazard and impact are simulated for different combinations of drivers at non-flood and flood conditions. Finally, the impact of each stochastic event is interpolated from the simulated events to derive a complete flood risk profile. Our case study results show that from all drivers, coastal flooding causes the largest risk in the region despite a more widespread fluvial and pluvial flood hazard. Events with return periods larger than 25 year are more damaging when considering the observed statistical dependence compared to independence, e.g.: 12% for the 100-year return period. However, the total compound flood risk in terms of expected annual damage is only 0.55% larger. This is explained by the fact that for frequent events, which contribute most to the risk, limited physical interaction between flood drivers is simulated. We also assess the effectiveness of three measures in terms of risk reduction. For our case, zoning based on the 2-year return period flood plain is as effective as levees with a 10-year return period protection level, while dry proofing up to 1 m does not reach the same effectiveness. As the framework is based on global datasets and is largely automated, it can easily be repeated for many other regions for first order assessments of compound flood risk. [ABSTRACT FROM AUTHOR]

In this study, weathering intensity, provenance and tectonics setting of Quaternary sediment deposits of the Ganga river, the Yamuna river and their tributaries in and around Haridwar area, Uttarakhand, India is explicated. The channel and levee sediments are well preserved along these rivers. For the purpose, the concentration of major oxides in the channel and levee sediments of rivers were analysed and chemical indices and discriminant functions were determined to understand the mobility pattern of different chemical constituents under various climatic conditions. An overall view of variation in provenance, shifting of channels and mechanism of river sediments transportation and accumulation in varying energy conditions is emphasised and validated from the field evidences and the present condition. Geomorphologically, the area comprises of bedrock strata of various lithologies, small sediments mounds and high hills, and fault scarps. The accumulated sediments and debris in channel bars and levees, and deviated drainages are the prominent features observed along the catchment of studied rivers. The results reveal the distinct concentration of heavy minerals derived from multiple provinces under low to intermediate weathering intensity, due to frequent climatic changes, migration of river channels, activation of thrusts and neotectonic activities. The integrated outcome of the present study can be used to predict the dynamics of the Ganga and Yamuna rivers and their tributaries which may provide a holistic management of headwater region above the area and its influence in lower parts of river sediment deposits in plains. [ABSTRACT FROM AUTHOR]

Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip. We present small-scale experiments with local pressure measurements in the pipe during equilibrium and pipe progression for different sands and degrees of hydraulic loading. The experiments confirm a positive relation between progression rate and grain size as well as the degree of hydraulic overloading. Furthermore, the analysis of local hydraulic conditions shows that the rate of BEP progression can be better explained by the bed shear stress and sediment transport in the pipe than by the seepage velocity at the pipe tip. The experiments show how different processes contribute to the piping process and these insights provide a first empirical basis for modeling pipe development using coupled seepage-sediment transport equations. [ABSTRACT FROM AUTHOR]

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 F o S 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 F o S 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 F o S threshold. [ABSTRACT FROM AUTHOR]

The liquefaction-induced river levee failures observed at micro-scale landforms of an old river course during the 2011 Tohoku earthquake were investigated by means of weight sounding and soil sampling. An empirical procedure to evaluate the liquefaction resistance of soils using weight sounding and soil sampling is proposed, which explicitly incorporates the effect of the fines content of soils. Case studies were carried out at three locations along Kokaigawa River. The use of weight sounding and soil sampling proves effective in discerning the geotechnical reasons behind the occurrence of the river levee failures observed at the old river course. [ABSTRACT FROM AUTHOR]

Accurate prediction of levee breach flow is crucial to the mitigation of floods, and for timely breach closure. In this work, flow in an idealized levee breach has been studied for the case of a trapezoidal embankment. Flow data including water depths, surface velocities, and flow discharges were obtained from 28 experiments considering different cases of breach width and main channel downstream water depth. Ultrasonic sensors were used to record the water depth in the channel and the breach. The water surface velocity was measured using a particle tracking velocity method. A one-dimensional dynamic model based on the conservation of mass and momentum in two control volumes was developed by drawing similarities between levee breach flows and diverging open channel junction flows. The proposed model shows satisfactory performance against two independent datasets. [ABSTRACT FROM AUTHOR]