Special Issue "The Application of Hydraulic and Sediment Transport Models in Fluvial Geomorphology"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics".

Deadline for manuscript submissions: closed (15 December 2019).

Special Issue Editors

Prof. Dr. PE Artur Radecki-Pawlik
E-Mail Website1 Website2
Guest Editor
Institute of Structural Mechanics, Faculty of Civil Engineering, Cracow University of Technology, 31-155 Kraków, Warszawska 24 street, Poland
Interests: rivers and mountain streams hydraulics; low head hydraulic structures; river engineering; river morphology; sediment transport
Dr. Tomáš Galia
E-Mail Website
Guest Editor
Department of Physical Geography and Geoecology, Faculty of Science, University of Ostrava, 710 00 Ostrava, Chittussiho 10 street, Czech Republic
Interests: morphology and sediment transport in mountain streams; instream wood; grade-control structures; modelling of bedload transport; river restorations

Special Issue Information

Dear Colleagues,

After publishing the famous “Fluvial Processes in Geomorphology” in the early 1960s, the work of Luna Leopold, Gordon Wolman and John Miller became a key for opening the door for understanding river and streams. They firstly showed the problem to geomorphologists and geographers. Later, Chang in his “Fluvial Processes in River Engineering” gave the basis for engineers, showing how this group of professionals could deal with rivers and to try to understand them. In the meantime, more decent studies have been published. Many of them started to combine fluvial geomorphology knowledge and river engineering needs, such as “Tools in Fluvial Geomorphology” by G. Mathias Kondolf and ‎Hervé Piégay; or even more focused on river  engineering tasks, such as “Stream Restoration in Dynamic Fluvial Systems: Scientific Approaches” by Andrew Simon, Sean Bennett, and Janine Castro. Finally, Luna Leopold summarized rivers and streams morphologies in a beautiful “A view of the river”. It appears that we continue to explore the subject in the right direction. We better understand rivers and streams and we can find, as engineers and fluvial geomorphologists, some tools also help to make rivers alive. However, there is still a hunger for more scientific tools that we could use to understand more about rivers, to aide in having healthy streams and rivers with a high biodiversity in the present world, which has started to face water scarcity. Thus, the aim of this of this Special Issue is to improve knowledge of our streams and rivers, showing how modeling can help (or disturb) in understanding fluvial processes. There have already been attempts, showing the cooperation between hydraulic engineers and fluvial geomorphologists. This Special Issue is directed to show how we could further serve our rivers using different kinds of modelling: Computer models, conceptual models, intellectual models, sophisticated software and/or analytical models. Thus, we seek works that help to build such tools, showing what we are already done, and to also show what direction we are supposed to move towards in the future for the sake of protecting our streams and rivers. Most of all, this Special Issue is directed to practical and theoretical platforms for the discussion of our understanding of rivers. It is not only for our professionals but also for the students we teach to prepare for continuation of such important work for all the people in the world. Thank you in advance for your very important contributions.

Prof. Dr. PE Artur Radecki-Pawlik
Dr. Tomáš Galia
Guest Editors

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Keywords

  • Fluvial processes
  • Hydraulic modeling
  • River hydraulics
  • Mountain streams
  • Fluvial geomorphology
  • Hydraulic structures
  • Modeling in geomorphology
  • River engineering
  • River channel management
  • River restorations

Published Papers (14 papers)

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Research

Open AccessArticle
Modeling of River Channel Shading as a Factor for Changes in Hydromorphological Conditions of Small Lowland Rivers
Water 2020, 12(2), 527; https://doi.org/10.3390/w12020527 (registering DOI) - 13 Feb 2020
Abstract
The ecological water quality in rivers and streams is influenced both by the morphological factors (within the watercourse channel and by the dynamic factors associated with flow), as well as biological factors (connected with the flora and fauna characteristic of its specific area). [...] Read more.
The ecological water quality in rivers and streams is influenced both by the morphological factors (within the watercourse channel and by the dynamic factors associated with flow), as well as biological factors (connected with the flora and fauna characteristic of its specific area). This paper presents an analysis of the effect of river channel shading by trees and shrubs on hydromorphological changes in a selected reach of the Wełna River, Poland. The analysis was conducted on two adjacent cross-sections (one in a reach lined with trees, the other in an open area with no tree or shrub vegetation). Data were collected during field surveys in the years 2014 and 2019. According to the Water Framework Directive, the Wełna River represents a watercourse with small and average-sized watershed areas, with sand being the dominant substrate of the river bottom. Flow volume, distributions of velocity in the sections, as well as substrate grain-size characteristics and river bottom morphology, were determined based on field measurements. In the study, the leaf area index (LAI) of vegetation was measured in the reach lined with trees, while the number and species composition of macrophytes were determined in the investigated river reaches. Moreover, a digital surface model (DSM) and Geoinformation Information System GIS tools were used to illustrate variability in shading within the tree-lined reach. The DSM model was based on Light Detection and Ranging (LIDAR) data. The results of this study enable us to establish the relationship between river shading by vegetation covering the bank zone, and changes in hydromorphological parameters of the river channel. Full article
Open AccessFeature PaperArticle
A Non-Tuned Machine Learning Technique for Abutment Scour Depth in Clear Water Condition
Water 2020, 12(1), 301; https://doi.org/10.3390/w12010301 - 20 Jan 2020
Abstract
Abutment scour is a complex three-dimensional phenomenon, which is one of the leading causes of marine structure damage. Structural integrity is potentially attainable through the precise estimation of local scour depth. Due to the high complexity of scouring hydrodynamics, existing regression-based relations cannot [...] Read more.
Abutment scour is a complex three-dimensional phenomenon, which is one of the leading causes of marine structure damage. Structural integrity is potentially attainable through the precise estimation of local scour depth. Due to the high complexity of scouring hydrodynamics, existing regression-based relations cannot make accurate predictions. Therefore, this study presented a novel expansion of extreme learning machines (ELM) to predict abutment scour depth (ds) in clear water conditions. The model was built using the relative flow depth (h/L), excess abutment Froude number (Fe), abutment shape factor (Ks), and relative sediment size (d50/L). A wide range of experimental samples was collected from the literature, and data was utilized to develop the ELM model. The ELM model reliability was evaluated based on the estimation results and several statistical indices. According to the results, the sigmoid activation function (correlation coefficient, R = 0.97; root mean square error, RMSE = 0.162; mean absolute percentage error, MAPE = 7.69; and scatter index, SI = 0.088) performed the best compared with the hard limit, triangular bias, radial basis, and sine activation functions. Eleven input combinations were considered to investigate the impact of each dimensionless variable on the abutment scour depth. It was found that ds/L = f (Fe, h/L, d50/L, Ks) was the best ELM model, indicating that the dimensional analysis of the original data properly reflected the underlying physics of the problem. Also, the absence of one variable from this input combination resulted in a significant accuracy reduction. The results also demonstrated that the proposed ELM model significantly outperformed the regression-based equations derived from the literature. The ELM model presented a fundamental equation for abutment scours depth prediction. Based on the simulation results, it appeared the ELM model could be used effectively in practical engineering applications of predicting abutment scour depth. The estimated uncertainty of the developed ELM model was calculated and compared with the conventional and artificial intelligence-based models. The lowest uncertainty with a value of ±0.026 was found in the proposed model in comparison with ±0.50 as the best uncertainty of the other models. Full article
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Open AccessArticle
The Evolution of Gravel-Bed Rivers during the Post-Regulation Period in the Polish Carpathians
Water 2020, 12(1), 254; https://doi.org/10.3390/w12010254 - 16 Jan 2020
Abstract
This study provides a conceptual model of the functioning of gravel-bed rivers during the post-regulation period in Poland and forecasts their subsequent evolution. The main difference between fluvial processes during the pre-regulation and post-regulation period is that they are limited to a zone [...] Read more.
This study provides a conceptual model of the functioning of gravel-bed rivers during the post-regulation period in Poland and forecasts their subsequent evolution. The main difference between fluvial processes during the pre-regulation and post-regulation period is that they are limited to a zone that is currently several times narrower and trapped in a deep-cut channel. During the river post-regulation period, the construction of additional river training works was significantly limited in river channels. Moreover, all forms of economic activity were significantly reduced in the channel free migration zone, particularly bed gravel extraction operations. As a result of these changes, a limited recovery of the functioning and hydromorphology of the river channel occurred via a return to conditions in effect prior to river regulation. In recovering sections of river, the channel gradually broadens, and its sinuosity and number of threads increase. The overall process can be called spontaneous renaturalization, which yields a characteristic post-regulation river channel. The conceptual model was developed on the basis of the evolution of the gravel-bed river, the Raba River, during the post-regulation period in the Polish Carpathian Mountains. Full article
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Open AccessArticle
Hydrogeomorphic Impacts of Floods in a First-Order Catchment: Integrated Approach Based on Dendrogeomorphic Palaeostage Indicators, 2D Hydraulic Modelling and Sedimentological Parameters
Water 2020, 12(1), 212; https://doi.org/10.3390/w12010212 - 12 Jan 2020
Abstract
Floods represent frequent hazards in both low- and first-order catchments; however, to date, the investigation of peak flow discharges in the latter catchments has been omitted due to the absence of gauging stations. The quantification of flood parameters in a first-order catchment (1.8 [...] Read more.
Floods represent frequent hazards in both low- and first-order catchments; however, to date, the investigation of peak flow discharges in the latter catchments has been omitted due to the absence of gauging stations. The quantification of flood parameters in a first-order catchment (1.8 km2) was realised in the moderate relief of NE Czechia, where the last flash flood event in 2014 caused considerable damage to the infrastructure. We used an integrated approach that included the dendrogeomorphic reconstruction of past flood activity, hydraulic modelling of the 2014 flash flood parameters using a two-dimensional IBER model, and evaluation of the channel stability using sedimentological parameters. Based on 115 flood scars, we identified 13 flood events during the period of 1955 to 2018, with the strongest signals recorded in 2014, 2009 and 1977. The modelled peak flow discharge of the last 2014 flood was equal to 4.5 m3·s−1 (RMSE = 0.32 m) using 26 scars as palaeostage indicators. The excess critical unit stream power was observed at only 24.2% of the reaches, representing predominantly bedrock and fine sediments. Despite local damage during the last flood, our results suggest relatively stable geomorphic conditions and gradual development of stream channels under discharges similar to that in 2014. Full article
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Open AccessArticle
The Role of Gate Operation in Reducing Problems with Cohesive and Non-Cohesive Sediments in Irrigation Canals
Water 2019, 11(12), 2572; https://doi.org/10.3390/w11122572 - 06 Dec 2019
Abstract
Sediments cause serious problems in irrigation systems, adversely affecting canal performance, driving up maintenance costs and, in extreme cases, threatening system sustainability. Multiple studies were done on the deposition of non-cohesive sediment and implications for canal design, the use of canal operation in [...] Read more.
Sediments cause serious problems in irrigation systems, adversely affecting canal performance, driving up maintenance costs and, in extreme cases, threatening system sustainability. Multiple studies were done on the deposition of non-cohesive sediment and implications for canal design, the use of canal operation in handling sedimentation problems is relatively under-studied, particularly for cohesive sediments. In this manuscript, several scenarios regarding weirs and gate operation were tested, using the Delft3D model, applied to a case study from the Gezira scheme in Sudan. Findings show that weirs play a modest role in sedimentation patterns, where their location influences their effectiveness. On the contrary, gate operation plays a significant role in sedimentation patterns. Reduced gate openings may cause canal blockage while intermittently fully opening and closing of gates can reduce sediment deposition in the canal by 54% even under conditions of heavy sediment load. Proper location of weirs and proper adjusting of the branch canal’s gate can substantially reduce sedimentation problems while ensuring sufficient water delivery to crops. The use of 2D/3D models provides useful insights into spatial and temporal patterns of deposition and erosion but has challenges related to running time imposing a rather coarse modelling resolution to keep running times acceptable. Full article
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Open AccessArticle
Numerical Study of Remote Sensed Dredging Impacts on the Suspended Sediment Transport in China’s Largest Freshwater Lake
Water 2019, 11(12), 2449; https://doi.org/10.3390/w11122449 - 21 Nov 2019
Abstract
As the largest freshwater lake in China, Poyang Lake plays an important role in the ecosystem of the Yangtze River watershed. The high suspended sediment concentration (SSC) has been an increasingly significant problem under the influence of extensive sand dredging. In this study, [...] Read more.
As the largest freshwater lake in China, Poyang Lake plays an important role in the ecosystem of the Yangtze River watershed. The high suspended sediment concentration (SSC) has been an increasingly significant problem under the influence of extensive sand dredging. In this study, a hydrodynamic model integrated with the two-dimensional sediment transport model was built for Poyang Lake, considering sand dredging activities detected from satellite images. The sediment transport model was set with point sources of sand dredging, and fully calibrated and validated by observed hydrological data and remote sensing results. Simulations under different dredging intensities were implemented to investigate the impacts of the spatiotemporal variation of the SSC. The results indicated that areas significantly affected by sand dredging were located in the north of the lake and along the waterway, with a total affected area of about 730 km2, and this was one of the main factors causing high turbidity in the northern part of the lake. The SSC in the northern area increased, showing a spatial pattern in which the SSC varied from high to low from south to north along the main channel, which indicated close agreement with the results captured by remote sensing. In summary, this study quantified the influence of human induced activities on sediment transport for the lake aquatic ecosystem, which could help us to better understand the water quality and manage water resources. Full article
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Open AccessArticle
Validation of a Novel, Shear Reynolds Number Based Bed Load Transport Calculation Method for Mixed Sediments against Field Measurements
Water 2019, 11(10), 2051; https://doi.org/10.3390/w11102051 - 30 Sep 2019
Abstract
In this study, the field measurement-based validation of a novel sediment transport calculation method is presented. River sections with complex bed topography and inhomogeneous bed material composition highlight the need for an improved sediment transport calculation method. The complexity of the morphodynamic features [...] Read more.
In this study, the field measurement-based validation of a novel sediment transport calculation method is presented. River sections with complex bed topography and inhomogeneous bed material composition highlight the need for an improved sediment transport calculation method. The complexity of the morphodynamic features (spatially and temporally varied bed material) can result in the simultaneous appearance of the gravel and finer sand dominated sediment transport (e.g., parallel bed armoring and siltation) at different regions within a shorter river reach. For the improvement purpose of sediment transport calculation in such complex river beds, a novel sediment transport method was elaborated. The base concept of it was the combined use of two already existing empirical sediment transport models. The method was already validated against laboratory measurements. The major goal of this study was the verification of the novel method with a real river case study. The combining of the two sediment transport models was based on the implementation of a recently presented classification method of the locally dominant sediment transport nature (gravel or sand transport dominates). The results were compared with measured bed change maps. The verification clearly referred to the meaningful improvement in the sediment transport calculation by the novel manner in the case of spatially varying bed content. Full article
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Open AccessArticle
Secondary Flow Effects on Deposition of Cohesive Sediment in a Meandering Reach of Yangtze River
Water 2019, 11(7), 1444; https://doi.org/10.3390/w11071444 - 12 Jul 2019
Abstract
Few researches focus on secondary flow effects on bed deformation caused by cohesive sediment deposition in meandering channels of field mega scale. A 2D depth-averaged model is improved by incorporating three submodels to consider different effects of secondary flow and a module for [...] Read more.
Few researches focus on secondary flow effects on bed deformation caused by cohesive sediment deposition in meandering channels of field mega scale. A 2D depth-averaged model is improved by incorporating three submodels to consider different effects of secondary flow and a module for cohesive sediment transport. These models are applied to a meandering reach of Yangtze River to investigate secondary flow effects on cohesive sediment deposition, and a preferable submodel is selected based on the flow simulation results. Sediment simulation results indicate that the improved model predictions are in better agreement with the measurements in planar distribution of deposition, as the increased sediment deposits caused by secondary current on the convex bank have been well predicted. Secondary flow effects on the predicted amount of deposition become more obvious during the period when the sediment load is low and velocity redistribution induced by the bed topography is evident. Such effects vary with the settling velocity and critical shear stress for deposition of cohesive sediment. The bed topography effects can be reflected by the secondary flow submodels and play an important role in velocity and sediment deposition predictions. Full article
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Open AccessArticle
River Model Calibration Based on Design of Experiments Theory. A Case Study: Meta River, Colombia
Water 2019, 11(7), 1382; https://doi.org/10.3390/w11071382 - 05 Jul 2019
Abstract
Numerical models are important tools for analyzing and solving water resources problems; however, a model’s reliability heavily depends on its calibration. This paper presents a method based on Design of Experiments theory for calibrating numerical models of rivers by considering the interaction between [...] Read more.
Numerical models are important tools for analyzing and solving water resources problems; however, a model’s reliability heavily depends on its calibration. This paper presents a method based on Design of Experiments theory for calibrating numerical models of rivers by considering the interaction between different calibration parameters, identifying the most sensitive parameters and finding a value or a range of values for which the calibration parameters produces an adequate performance of the model in terms of accuracy. The method consists of a systematic process for assessing the qualitative and quantitative performance of a hydromorphological numeric model. A 75 km reach of the Meta River, in Colombia, was used as case study for validating the method. The modeling was conducted by using the software package MIKE-21C, a two-dimensional flow model. The calibration is assessed by means of an Overall Weighted Indicator, based on the coefficient of determination of the calibration parameters and within a range from 0 to 1. For the case study, the most significant calibration parameters were the sediment transport equation, the riverbed load factor and the suspended load factor. The optimal calibration produced an Overall Weighted Indicator equal to 0.857. The method can be applied to any type of morphological models. Full article
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Open AccessArticle
Hydraulic Parameters for Sediment Transport and Prediction of Suspended Sediment for Kali Gandaki River Basin, Himalaya, Nepal
Water 2019, 11(6), 1229; https://doi.org/10.3390/w11061229 - 12 Jun 2019
Cited by 1
Abstract
Sediment yield is a complex phenomenon of weathering, land sliding, and glacial and fluvial erosion. It is highly dependent on the catchment area, topography, slope of the catchment terrain, rainfall, temperature, and soil characteristics. This study was designed to evaluate the key hydraulic [...] Read more.
Sediment yield is a complex phenomenon of weathering, land sliding, and glacial and fluvial erosion. It is highly dependent on the catchment area, topography, slope of the catchment terrain, rainfall, temperature, and soil characteristics. This study was designed to evaluate the key hydraulic parameters of sediment transport for Kali Gandaki River at Setibeni, Syangja, located about 5 km upstream from a hydropower dam. Key parameters, including the bed shear stress (τb), specific stream power (ω), and flow velocity (v) associated with the maximum boulder size transport, were determined throughout the years, 2003 to 2011, by using a derived lower boundary equation. Clockwise hysteresis loops of the average hysteresis index of +1.59 were developed and an average of 40.904 ± 12.453 Megatons (Mt) suspended sediment have been transported annually from the higher Himalayas to the hydropower reservoir. Artificial neural networks (ANNs) were used to predict the daily suspended sediment rate and annual sediment load as 35.190 ± 7.018 Mt, which was satisfactory compared to the multiple linear regression, nonlinear multiple regression, general power model, and log transform models, including the sediment rating curve. Performance indicators were used to compare these models and satisfactory fittings were observed in ANNs. The root mean square error (RMSE) of 1982 kg s−1, percent bias (PBIAS) of +14.26, RMSE-observations standard deviation ratio (RSR) of 0.55, coefficient of determination (R2) of 0.71, and Nash–Sutcliffe efficiency (NSE) of +0.70 revealed that the ANNs’ model performed satisfactorily among all the proposed models. Full article
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Open AccessArticle
A Combined Field and Numerical Modeling Study to Assess the Longitudinal Channel Slope Evolution in a Mixed Alluvial and Soft Bedrock Stream
Water 2019, 11(4), 735; https://doi.org/10.3390/w11040735 - 09 Apr 2019
Cited by 2
Abstract
A study approach is developed to assess the longitudinal channel slope under the equilibrium condition as well as the transient evolution of a mixed alluvial-soft-bedrock stream. Both the historical field data and 2D mobile-bed numerical modeling are adopted. The proposed approach is applied [...] Read more.
A study approach is developed to assess the longitudinal channel slope under the equilibrium condition as well as the transient evolution of a mixed alluvial-soft-bedrock stream. Both the historical field data and 2D mobile-bed numerical modeling are adopted. The proposed approach is applied to a 14 km reach downstream of the Ji-Ji Weir, Chuo-Shui River, Taiwan, where continuous maintenance works have been carried out to stabilize this reach. In this study, the temporal evolution of the longitudinal channel profile is assessed numerically with three spatial scales: The large (the entire study reach), the medium (four sub-reaches), and the local (cross-sections) scale. The large scale analysis is the approach for purely alluvial streams and is shown to be difficult to use to characterize mixed alluvial-bedrock streams. The local scale analysis shows that the soft-bedrock incision has a widely fluctuating slope, reflecting the compound environmental forcing and complex riverbed setting. With the medium scale analysis, the longitudinal channel profile is found to follow a predictive trend if the reach is partitioned into four distinctive sub-reaches. Characteristics of the dynamic channel slope evolution in different spatial scales are computed and presented. The study results can be used to select the proper locations and types of the engineering stabilizing structures in a mixed alluvial and soft bedrock stream. Full article
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Open AccessArticle
Analysis of Shear Stress and Stream Power Spatial Distributions for Detection of Operational Problems in the Stare Miasto Reservoir
Water 2019, 11(4), 691; https://doi.org/10.3390/w11040691 - 04 Apr 2019
Cited by 2
Abstract
In this paper an analysis of the lowland reservoir operation in atypical conditions is presented. The chosen study object is the Stare Miasto reservoir in the Powa river (Poland), which has been in operation since 2006. It is a two-stage reservoir, consisting of [...] Read more.
In this paper an analysis of the lowland reservoir operation in atypical conditions is presented. The chosen study object is the Stare Miasto reservoir in the Powa river (Poland), which has been in operation since 2006. It is a two-stage reservoir, consisting of an upper sedimentation part and a lower main reservoir. The upper part is separated from the main part by an internal dam with a sluice gate. Such a construction enabled better control of sediment deposits and their removal. The atypical conditions were caused by flood wave propagation in the Powa river and the reservoir in 2014. In the research, three reservoir bathymetries are analyzed—from 2006, 2013, and 2018. Two-dimensional (2D) hydrodynamic modeling is applied to analyze spatial variability of investigated hydraulic parameters. Such an approach enabled better recognition of the changes observed in the reservoir during 2006–2018. In the research, the spatial distributions of the velocities, the shear stresses, and the stream power are the basis for the analyses and comparisons. The simulations enabled identification of the main elements prone to collapse during flood wave propagation. The presented results and approach may be applied for improvement of reservoir design, with special emphasis on specific structures located in a reservoir basin. Full article
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Open AccessFeature PaperArticle
Hydraulic Modeling and Evaluation Equations for the Incipient Motion of Sandbags for Levee Breach Closure Operations
Water 2019, 11(2), 279; https://doi.org/10.3390/w11020279 - 06 Feb 2019
Cited by 3
Abstract
Open channel levees are used extensively in hydraulic and environmental engineering applications to protect the surrounding area from inundation. However, levees may fail to produce an unsteady flow that is inherently three dimensional. Such a failure may lead to a destructive change in [...] Read more.
Open channel levees are used extensively in hydraulic and environmental engineering applications to protect the surrounding area from inundation. However, levees may fail to produce an unsteady flow that is inherently three dimensional. Such a failure may lead to a destructive change in morphology of the river channel and valley. To avoid such a situation arising, hydraulic laboratory modeling was performed on an open channel levee breach model capturing velocity, in x, y and z plans, at selected locations in the breach. Sandbags of various shapes and sizes are tested for incipient motion by the breach flow. We found that a prism sandbag has a better hydrodynamic characteristic and more stability than spherical bags with the same weight. Experimental results are then used to evaluate existing empirical equations and to develop more accurate equations for predicting critical flow velocity at the initial stage of sandbag motion. Results showed the superior predictions a few of the equations could be considered with an uncertainty range of ±10%. These equations explained the initial failed attempts of the United States Army Corps of Engineers (USACE) for breach closure of the case study, and confirmed the experimental results are simulating the case study of breach closure. Full article
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Open AccessArticle
Comparison of Hydrodynamics Simulated by 1D, 2D and 3D Models Focusing on Bed Shear Stresses
Water 2019, 11(2), 226; https://doi.org/10.3390/w11020226 - 29 Jan 2019
Cited by 4
Abstract
For centuries, scientists have been attempting to map complex hydraulic processes to empirical formulas using different flow resistance definitions, which are further applied in numerical models. Now questions arise as to how consistent the simulated results are between the model dimensions and what [...] Read more.
For centuries, scientists have been attempting to map complex hydraulic processes to empirical formulas using different flow resistance definitions, which are further applied in numerical models. Now questions arise as to how consistent the simulated results are between the model dimensions and what influence different morphologies and flow conditions have. For this reason, 1D, 2D and 3D simulations were performed and compared with each other in three study areas with up to three different discharges. A standardized, relative comparison of the models shows that after successful calibration at measured water levels, the associated 2D/1D and 3D/1D ratios are almost unity, while bed shear stresses in the 3D models are only about 62–86% of the simulated 1D values and 90–100% in the case of 2D/1D. Reasons for this can be found in different roughness definitions, in simplified geometries, in different calculation approaches, as well as in influences of the turbulence closure. Moreover, decreasing 3D/1D ratios of shear stresses were found with increasing discharges and with increasing slopes, while the equivalent 2D/1D ratios remain almost unchanged. The findings of this study should be taken into account, particularly in subsequent sediment transport simulations, as these calculations are often based on shear stresses. Full article
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