Onshore sediment transport on a sandy beach under varied wave conditions: Flow velocity skewness, wave asymmetry or bed ventilation?

Abstract. A modeling system for the estimation of flash flood flow velocity and sediment transport is developed in this study. The system comprises three components: (a) a modeling framework based on the hydrological model HSPF, (b) the hydrodynamic module of the hydraulic model MIKE 11 (quasi-2-D), and (c) the advection–dispersion module of MIKE 11 as a sediment transport model. An important parameter in hydraulic modeling is the Manning's coefficient, an indicator of the channel resistance which is directly dependent on riparian vegetation changes. Riparian vegetation's effect on flood propagation parameters such as water depth (inundation), discharge, flow velocity, and sediment transport load is investigated in this study. Based on the obtained results, when the weed-cutting percentage is increased, the flood wave depth decreases while flow discharge, velocity and sediment transport load increase. The proposed modeling system is used to evaluate and illustrate the flood hazard for different riparian vegetation cutting scenarios. For the estimation of flood hazard, a combination of the flood propagation characteristics of water depth, flow velocity and sediment load was used. Next, a well-balanced selection of the most appropriate agricultural cutting practices of riparian vegetation was performed. Ultimately, the model results obtained for different agricultural cutting practice scenarios can be employed to create flood protection measures for flood-prone areas. The proposed methodology was applied to the downstream part of a small Mediterranean river basin in Crete, Greece.

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Spatial and temporal trends for water-flow velocity and bed-material sediment transport in the lower Mississippi River

Geological Society of America Bulletin ◽

10.1130/b30497.1 ◽

2011 ◽

Vol 124 (3-4) ◽

pp. 400-414 ◽

Cited By ~ 118

Author(s):

J. A. Nittrouer ◽

J. Shaw ◽

M. P. Lamb ◽

D. Mohrig

Keyword(s):

Sediment Transport ◽

Flow Velocity ◽

Water Flow ◽

Mississippi River ◽

Temporal Trends ◽

Water Flow Velocity ◽

Lower Mississippi River ◽

Bed Material ◽

Spatial And Temporal Trends

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Investigation of Wave Conditions in the Paranagua´ Estuarine Complex in the South of Brazil

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 4 ◽

10.1115/omae2010-20721 ◽

2010 ◽

Author(s):

Farhad Nazarpour ◽

Roberto Mayerle

Keyword(s):

Sediment Transport ◽

Wave Model ◽

Wave Generation ◽

The South ◽

Tidal Variation ◽

Joint Research ◽

Joint Research Project ◽

Wave Heights ◽

Wave Conditions ◽

South Of Brazil

This paper summarises results of investigations aiming at the improvement of the understanding about the wave conditions in the Paranagua´ Estuarine Complex (PEC) in the South of Brazil. The investigations were carried out in the framework of a joint-research project funded by the German Ministry of Education and Research and the Ministry of Science and Technology in Brazil. In this study a phase-averaged wave model was set-up and applied to the study area. The relevance of the main processes affecting wave generation and dissipation were investigated. Focus was given to the wave conditions in the vicinity of the harbour some 25km within the PEC. The fetch was found to have a major effect on wave generation in the study area. Significant wave heights up to about 0.6m resulted near the harbour during storms. The results obtained helped in advancing the development of the coupled process-based models for simulation of flow, waves and sediment transport in the PEC. It was found that although currents have a certain influence on the wave heights, the effect of the tidal variation resulted more significant. Moreover waves were found to affect the current velocities in shallow water areas and should therefore be included for enhancing the predictions of sediment transport rates particularly for more adverse wind conditions.

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WAVE-INDUCED FLOW AND NEARSHORE SUSPENDED SEDIMENT

Coastal Engineering Proceedings ◽

10.9753/icce.v21.108 ◽

1988 ◽

Vol 1 (21) ◽

pp. 108 ◽

Cited By ~ 3

Author(s):

J.C. Doering ◽

A.J. Bowen

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

Suspended Sediment Concentration ◽

Sediment Concentration ◽

Accurate Prediction ◽

Wave Crest ◽

Wave Trough ◽

Induced Flow ◽

Wave Induced ◽

Velocity Skewness

It has been realized for nearly one hundred years that the transport of sediment is related to the characteristics of a wave, in particular its shape. Cornish (1898) noticed that the shoreward velocity associated with a wave crest was more effective at moving coarse sediment than was the seaward velocity associated with the wave trough. Cornish's observation was consistent with the theory of Stokes (1847), which predicts the onshore velocity associated with the wave crest is stronger and of shorter duration than the offshore velocity associated with the wave trough. This horizontal asymmetry of the cross-shore flow, which is a reflection of the wave shape, is known as velocity skewness. It has been suggested that "the existence of the beach depends on small departures from symmetry in the velocity field balancing the tendency for gravity to move material offshore"(Bowen, 1980). Although the concept of velocity skewness has been incorporated into detailed predictors of sediment transport (Bowen, 1980; Bailard and Inman, 1981) it is only one of many facets that needs to be understood in order to make the accurate prediction of sediment transport realizable. A comprehension of sediment transport is hampered by both an incomplete knowledge of the hydrodynamics and a lack of instrumentation to directly measure instantaneous sediment concentration and the accurate prediction of sediment transport is probably the most enigmatic problem in coastal engineering. Occasionally, suspended sediment concentration has been inferred from in situ pumps and hand-held tubes, but these methods lack the temporal and spatial resolution necessary to elucidate the details of the interaction between the waveinduced flow and the sediment. Recently, a miniature optical backscatter sensor (MOBS), which provides a time series of suspended sediment concentration at a "point", was developed by Downing et al. (1981). During a recent field experiment a vertical array of 5 of these optical backscatter sensors and a colocated flow meter was deployed close to the sea bed. These colocated measurements provide a unique opportunity to investigate the response of near-bed suspended sediment concentration to the wave-induced flow.

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Applicability of acoustic Doppler devices for flow velocity measurements and discharge estimation in flows with sediment transport

Journal of Hydrology ◽

10.1016/j.jhydrol.2013.11.020 ◽

2014 ◽

Vol 509 ◽

pp. 504-518 ◽

Cited By ~ 12

Author(s):

Guillaume Nord ◽

Francesc Gallart ◽

Nicolas Gratiot ◽

Montserrat Soler ◽

Ian Reid ◽

...

Keyword(s):

Sediment Transport ◽

Flow Velocity ◽

Velocity Measurements ◽

Discharge Estimation

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A RANS numerical model for cross-shore beach profile evolution

10.5194/egusphere-egu2020-10501 ◽

2020 ◽

Author(s):

Julio Garcia-Maribona ◽

Javier L. Lara ◽

Maria Maza ◽

Iñigo J. Losada

Keyword(s):

Sediment Transport ◽

Numerical Model ◽

Transport Model ◽

Numerical Models ◽

Computational Cost ◽

Physical Modelling ◽

Computational Effort ◽

Beach Profile ◽

Time Step ◽

Wave Conditions

The evolution of the cross-shore beach profile is tightly related to the evolution of the coastline in both small and large time scales. Bathymetry changes in extreme maritime events can also have important effects on coastal infrastructures such as geotechnical failures of foundations or the modification of the incident wave conditions towards a more unfavourable situation.The available strategies to study the evolution of beach profiles can be classified in analytical, physical and numerical modelling. Analytical solutions are fast, but too simplistic for many applications. Physical modelling provides trustworthy results and can be applied to a wide variety of configurations, however, they are costly and time-consuming compared to analytical strategies. Finally, &#160;numerical approaches offer different balances between cost and precision depending on the particular model.Some numerical models provide greater precision in the beach profile evolution, but incurring in a prohibitive computational cost for many applications. In contrast, the less expensive ones assume simplifications which do not allow to correctly reproduce significant phenomena of the near-shore hydrodynamics such as wave breaking or undertow currents, neither to predict important features of the beach profile like breaker bars.In this work, a new numerical model is developed to reproduce the main features of the beach profile and hydrodynamics while maintaining an affordable computational cost. In addition, it is intended to reduce to the minimum the number of coefficients that the user has to provide to make the model more predictive.The model consists of two main modules. Firstly, the already existing 2D RANS numerical model IH2VOF is used to compute the hydrodynamics. Secondly, the sediment transport model modifies the bathymetry according to the obtained hydrodynamics. The new bathymetry is then considered in the hydrodynamic model to account for it in the next time step.The sediment transport module considers bedload and suspended transports separately. The former is obtained with empirical formulae. In the later,the distribution of sediment concentration in the domain is obtained by solving an advective-diffusive transport equation. Then, the sedimentation and erosion rates are obtained along the seabed. Once these contributions are calculated, a sediment balance is performed in every seabed segment to determine the variation in its level.With the previously described strategy, the resulting model is able to predict not only the seabed changes due to different wave conditions, but also the influence of this new bathymetry in the hydrodynamics, capturing features such as the generation of a breaker bar, displacement of the breaking point or variation of the run-up over the beach profile. To validate the model, the numerical results are compared to experimental data.An important novelty of the present model is the computational effort required to perform the simulations, which is significantly smaller than the one associated to existing models able to reproduce the same phenomena.

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Experimental study of sediment transport processes and size selectivity of eroded sediment on steep Pisha sandstone slopes

10.5194/egusphere-egu2020-2269 ◽

2020 ◽

Author(s):

Pan Zhang ◽

Pingqing Xiao ◽

Chunxia Yang

Keyword(s):

Sediment Transport ◽

Flow Velocity ◽

Overland Flow ◽

Yellow River ◽

Transport Processes ◽

The Yellow River ◽

Size Selectivity ◽

Coarse Sediment ◽

Sediment Particles ◽

Slope Flow

The Pisha sandstone area on the Ordos Plateau of China is the primary source of coarse sediment of the Yellow River. Sediment size distribution and selectivity greatly affect sediment transport and deposition. Hence, sediment transport processes and size selectivity by overland flow on Pisha sandstone slopes were investigated in this study. Experiments were run with Pisha sandstone soil (bulk density of 1.35 g/cm3) under rainfall intensities of 87 and 133 mm/h with a 25&#176; slope gradient, and the duration of simulated rainfall is 1 h. Sediment and runoff were sampled at 2-min intervals to examine the size distribution change of the eroded sediment. The particle composition, enrichment rate, fractal dimension, and time distribution characteristics of median grain size (d50) of eroded sediment were comprehensively analyzed. Statistical analyses showed that the erosion process of Pisha sandstone slope mainly transported coarse sediment. More than 40% of eroded sediment particles were coarse sediment, which will become the main sediment in the lower reaches of the Yellow River bed. The particle size of eroded sediment tended to gradually decrease with the continuous rainfall but remained larger than the background value of Pisha sandstone soil after refinement. The fractal dimension was positively correlated with the slope flow velocity, while the d50 was negatively correlated with the slope flow velocity. Overall, these findings show a strong relationship between the sediment transport and flow velocity, which indicates that the selectivity and transportation of sediment particles on the Pisha sand slopes is mainly influenced by the hydrodynamic parameters of overland flow. This study provides a methodology and data references for studying the particle selectivity characteristics of eroded sediment and provides a scientific basis for revealing the mechanism of erosion and sediment yield in the Pisha sandstone area of China.

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