scholarly journals Wind and Tide-Induced Hydrodynamics and Sedimentation of Two Tidal Inlets in Western Greece

2018 ◽  
Author(s):  
Nikolaos Th. Fourniotis ◽  
Georgios M. Horsch ◽  
Georgios A. Leftheriotis
Keyword(s):  
Sediment Transport ◽  
Simulation Models ◽  
Google Earth ◽  
Tidal Inlets ◽  
Horizontal Structure ◽  
Numerical Predictions ◽  
Combined Action ◽  
Mean Water Level ◽  
The Mean ◽  
Induced Currents

To quantify the detailed mechanisms that cause sedimentation at the tidal inlets in the Messolonghi-Aetoliko lagoonal system, the MIKE 21 FM (HD & ST) numerical simulation models were applied. The study focuses on the hydrodynamic circulation in the vicinity of the tidal inlets and the associated wind and tide-induced currents, as well as sediment transport, bed level evolution and total sediment load accumulation, with emphasis on the vicinity of two tidal inlets, where the problem is more acute. Based on the numerical predictions, which have been qualitatively corroborated via satellite images from Google Earth, it is shown that under the prevailing winds and tidal action, sandbars are formed in front or behind the tidal inlets depending on the wind direction, resulting in a gradual decrease of the mean water level at the mouths. Under the combined action of the tide and the wind the characteristic horizontal structure of the flow includes cyclonic and anti-cyclonic eddies that form at the near tip area of the jetties, which are associated with sediment transport mechanisms.

scholarly journals EVALUATION OF OVERALL ENTRANCE STABILITY OF TIDAL ENTRANCES

1974 ◽  
Vol 1 (14) ◽  
pp. 91 ◽  
Author(s):  
P. Bruun ◽  
F. Gerritsen ◽  
N.P. Bhakta
Keyword(s):  
Sediment Transport ◽  
Spring Tide ◽  
Tidal Prism ◽  
Material Transport ◽  
Tidal Inlets ◽  
Littoral Drift ◽  
Overall Stability ◽  
The Mean ◽  
Two Parameters

This paper is written in continuation of earlier published material (2, 4, 5) dealing with stability of tidal inlets on littoral drift shores. The experience available at that time was responsible for the introduction of two parameters: .vmean max/ defined as the mean max. velocity in the gorge at spring tide and the K/M-tot ratio (tidal prism at spring tide divided by material transport to the entrance from the adjoining shores) as the most pertinent parameters for description of overall stability. A more detailed justification for this choice is given in this paper, based on computation of the relative sediment transport at various tidal phases. Examples of earlier date (4) and twelve new examples from India are given.

scholarly journals Modelling of sediment transport and morphological evolution under the combined action of waves and currents

Ocean Science ◽  
2017 ◽  
Vol 13 (5) ◽  
pp. 673-690 ◽  
Author(s):  
Guilherme Franz ◽  
Matthias T. Delpey ◽  
David Brito ◽  
Lígia Pinto ◽  
Paulo Leitão ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Morphological Changes ◽  
Morphological Evolution ◽  
Research Effort ◽  
Beach Erosion ◽  
Model Complexity ◽  
Invariant Equilibrium ◽  
Waves And Currents ◽  
Combined Action ◽  
Modelling System

Abstract. Coastal defence structures are often constructed to prevent beach erosion. However, poorly designed structures may cause serious erosion problems in the downdrift direction. Morphological models are useful tools to predict such impacts and assess the efficiency of defence structures for different scenarios. Nevertheless, morphological modelling is still a topic under intense research effort. The processes simulated by a morphological model depend on model complexity. For instance, undertow currents are neglected in coastal area models (2DH), which is a limitation for simulating the evolution of beach profiles for long periods. Model limitations are generally overcome by predefining invariant equilibrium profiles that are allowed to shift offshore or onshore. A more flexible approach is described in this paper, which can be generalised to 3-D models. The present work is based on the coupling of the MOHID modelling system and the SWAN wave model. The impacts of different designs of detached breakwaters and groynes were simulated in a schematic beach configuration following a 2DH approach. The results of bathymetry evolution are in agreement with the patterns found in the literature for several existing structures. The model was also tested in a 3-D test case to simulate the formation of sandbars by undertow currents. The findings of this work confirmed the applicability of the MOHID modelling system to study sediment transport and morphological changes in coastal zones under the combined action of waves and currents. The same modelling methodology was applied to a coastal zone (Costa da Caparica) located at the mouth of a mesotidal estuary (Tagus Estuary, Portugal) to evaluate the hydrodynamics and sediment transport both in calm water conditions and during events of highly energetic waves. The MOHID code is available in the GitHub repository.

scholarly journals Influence of the Monsoon Trough on Westward-Propagating Tropical Waves over the Western North Pacific. Part II: Energetics and Numerical Experiments

2015 ◽  
Vol 28 (23) ◽  
pp. 9332-9349 ◽  
Author(s):  
Liang Wu ◽  
Zhiping Wen ◽  
Renguang Wu
Keyword(s):  
North Pacific ◽  
Numerical Experiments ◽  
Western North Pacific ◽  
Monsoon Trough ◽  
Water Model ◽  
Mean Flow ◽  
Horizontal Structure ◽  
Rotational Flows ◽  
The Mean ◽  
The Waves

Abstract Part I of this study examined the modulation of the monsoon trough (MT) on tropical depression (TD)-type–mixed Rossby–gravity (MRG) and equatorial Rossby (ER) waves over the western North Pacific based on observations. This part investigates the interaction of these waves with the MT through a diagnostics of energy conversion that separates the effect of the MT on TD–MRG and ER waves. It is found that the barotropic conversion associated with the MT is the most important mechanism for the growth of eddy energy in both TD–MRG and ER waves. The large rotational flows help to maintain the rapid growth and tilted horizontal structure of the lower-tropospheric waves through a positive feedback between the wave growth and horizontal structure. The baroclinic conversion process associated with the MT contributes a smaller part for TD–MRG waves, but is of importance comparable to barotropic conversion for ER waves as it can produce the tilted vertical structure. The growth rates of the waves are much larger during strong MT years than during weak MT years. Numerical experiments are conducted for an idealized MRG or ER wave using a linear shallow-water model. The results confirm that the monsoon background flow can lead to an MRG-to-TD transition and the ER wave amplifies along the axis of the MT and is more active in the strong MT state. Those results are consistent with the findings in Part I. This indicates that the mean flow of the MT provides a favorable background condition for the development of the waves and acts as a key energy source.

scholarly journals Analytical approach for determining the mean water level profile in an estuary with substantial fresh water discharge

2016 ◽  
Vol 20 (3) ◽  
pp. 1177-1195 ◽  
Author(s):  
Huayang Cai ◽  
Hubert H. G. Savenije ◽  
Chenjuan Jiang ◽  
Lili Zhao ◽  
Qingshu Yang
Keyword(s):  
Water Level ◽  
Fresh Water ◽  
River Discharge ◽  
River Flow ◽  
Water Discharge ◽  
Value Theory ◽  
Velocity Amplitude ◽  
Mean Water Level ◽  
The Mean ◽  
Fresh Water Discharge

Abstract. The mean water level in estuaries rises in the landward direction due to a combination of the density gradient, the tidal asymmetry, and the backwater effect. This phenomenon is more prominent under an increase of the fresh water discharge, which strongly intensifies both the tidal asymmetry and the backwater effect. However, the interactions between tide and river flow and their individual contributions to the rise of the mean water level along the estuary are not yet completely understood. In this study, we adopt an analytical approach to describe the tidal wave propagation under the influence of substantial fresh water discharge, where the analytical solutions are obtained by solving a set of four implicit equations for the tidal damping, the velocity amplitude, the wave celerity, and the phase lag. The analytical model is used to quantify the contributions made by tide, river, and tide–river interaction to the water level slope along the estuary, which sheds new light on the generation of backwater due to tide–river interaction. Subsequently, the method is applied to the Yangtze estuary under a wide range of river discharge conditions where the influence of both tidal amplitude and fresh water discharge on the longitudinal variation of the mean tidal water level is explored. Analytical model results show that in the tide-dominated region the mean water level is mainly controlled by the tide–river interaction, while it is primarily determined by the river flow in the river-dominated region, which is in agreement with previous studies. Interestingly, we demonstrate that the effect of the tide alone is most important in the transitional zone, where the ratio of velocity amplitude to river flow velocity approaches unity. This has to do with the fact that the contribution of tidal flow, river flow, and tide–river interaction to the residual water level slope are all proportional to the square of the velocity scale. Finally, we show that, in combination with extreme-value theory (e.g. generalized extreme-value theory), the method may be used to obtain a first-order estimation of the frequency of extreme water levels relevant for water management and flood control. By presenting these analytical relations, we provide direct insight into the interaction between tide and river flow, which will be useful for the study of other estuaries that experience substantial river discharge in a tidal region.

scholarly journals SIMULASI WAKTU TUNGGU MAHASISWA DAN DOSEN DI LAYANAN AKADEMIK UNIVERSITAS BUNDA MULIA

2017 ◽  
Vol 10 (1) ◽  
Author(s):  
Rudy Santosa Sudirga
Keyword(s):  
Response Time ◽  
Waiting Time ◽  
Operations Management ◽  
Heavy Traffic ◽  
Simulation Models ◽  
Operation Performance ◽  
Service Operation ◽  
Mean And Variance ◽  
The Mean ◽  
Time In Service

<p>The Management of Academic Service continues to be a major challenge for many college, high school and college organizations in providing better services with fewer resources. The allocation of service staffs and response-time in service involve many challenging issues, because the mean and variance of the response-time in service can be increased dramatically with the intensity of heavy traffic. This study discusses how to use simulation models to improve response time in service operation. Performance at the Academic Service as a whole can be considered very good and is still idle due to utilization of Academic Service, which is still equal to an average of 17%, or it can be said that the workload is not too excessive and deemed to be able to serve the students and lecturers. The performance of Academic Sevice University Bunda Mulia can be considered excellent in terms of operations management, as indicated by the average waiting time, which is very short at only 9.10 seconds.<br />Keywords: Queueing System, Waiting Time, and Simulation</p>

scholarly journals Dynamics of fortnightly water level variations along a tide-dominated estuary with negligible river discharge

2021 ◽  
Author(s):  
Erwan Garel ◽  
Ping Zhang ◽  
Huayang Cai
Keyword(s):  
Water Level ◽  
Phase Difference ◽  
River Discharge ◽  
Water Levels ◽  
Level Increase ◽  
Upstream Direction ◽  
Water Level Variations ◽  
Mean Water Level ◽  
The Mean ◽  
Guadiana Estuary

Abstract. Observations indicate that the fortnightly fluctuations in mean water level increase in amplitude along the lower half of a tide-dominated estuary (The Guadiana estuary) with negligible river discharge but remain constant upstream. Analytical solutions reproducing the semi-diurnal wave propagation shows that this pattern results from reflection effects at the estuary head. The phase difference between velocity and elevation increases from the mouth to the head (where the wave has a standing nature) as the high and low water levels get progressively closer to slack water. Thus, the tidal (flood-ebb) asymmetry in discharge is reduced in the upstream direction. It becomes negligible along the upper estuary half, as the mean sea level remains constant despite increased friction due to wave shoaling. Observations of a flat mean water level along a significant portion of an upper estuary, easier to obtain than the phase difference, can therefore indicate significant reflection of the propagating semi-diurnal wave at the head. Details of the analytical model shows that changes in the mean depth or length of semi-arid estuaries, in particular for macrotidal locations, affect the fortnightly tide amplitude, and thus the upstream mass transport and inundation regime. This has significant potential impacts on the estuarine environment.

scholarly journals Discharge and Sediment Transport in a River Basin. Assessment Before and After the Construction of a Dam at the Upper Basin Boundary

2021 ◽  
Author(s):  
George Paschalidis ◽  
Ilias IIordanidis ◽  
Petros Anagnostopoulos
Keyword(s):  
Sediment Transport ◽  
Meteorological Data ◽  
Climatic Data ◽  
Northern Greece ◽  
Basin Boundary ◽  
Software Packages ◽  
Before And After ◽  
The Mean ◽  
Gis Interface ◽  
Good Agreement

Abstract The purpose of this study is the evaluation of runoff and sediment transport in the basin of the Nestos River (Northern Greece) downstream of the dam of Platanovrisi, constructed in 1998. The model used for the simulation was AGNPS, which is based on the Revised Universal Soil Loss Equation (RUSLE), combined with a GIS interface. Two different simulations were conducted, one for the years 1980-1990 and another for the period 2006-2030, before and after the construction of the dam respectively. For the simulation for the period 1980-1990 existing meteorological data were employed, and the results were in good agreement with those of a different study (Hrissanthou, 2002). The simulation for the period 2006-2030 was based on rainfall and climatic data generated from the software packages GlimClim and ClimGen. The mean runoff was by 5% lower and the mean annual sediment yield by 20% lower than the corresponding values for the period 1980-1990.

A Statistical Discourse of the Climate of the Niger Delta Region of Nigeria

2020 ◽  
Vol 1 (1/2) ◽  
pp. 15-33
Author(s):  
M Odigwe ◽  
S. I. Efe ◽  
A. O. Atubi
Keyword(s):  
Niger Delta ◽  
Google Earth ◽  
Annual Rainfall ◽  
Series Data ◽  
Trend Test ◽  
Delta Region ◽  
Niger Delta Region ◽  
Ex Post ◽  
Significant Difference ◽  
The Mean

The study aimed at investigating the climate of the Niger Delta Region (NDR) of Nigeria. This is to ascertain the variations in rainfall and temperature in the Niger Delta Region. The study utilized the ex-post facto research design. The study utilized the annual rainfall and temperature time series data from 1925 – 2018 periods. That was generated from the archive of the Climate Research Unit (CRU) Ts 4.03 using Google earth. The grided points of 5ox5o high resolution of thirty-two (32) CRU Ts 4.03 stations were utilized for the study. In order to analyse the data on rainfall and temperature the descriptive statistical techniques were employed. While testing the formulated hypotheses, the one-way analysis of variance (ANOVA) was utilized to decide the significant difference in stations, additionally the Turkey Test was utilized to decide were the difference in the mean lies, while the Mann-Kendell Trend Test was used to determine the upward and downward trends in rainfall and temperature. Thus, the study revealed that the mean distribution of rainfall and temperature in the Niger Delta region for the past ninety-four (94) years showed a downward and upward trend with a mean of 2238.3mm and 26.7oC in rainfall and temperature respectively. While, the highest and lowest rainfall (2600.7mm and 1854mm), was recorded in 1955 and 1984 which indicates an increase of 746.7mm. The highest and lowest temperature (27.4oC and 25.9oC) was recorded in 2017, 1976 and 1977 respectively which indicate a rise of 1.5oC. Furthermore, the study revealed that there is a statistically significant variation in rainfall in the Niger

Numerical Simulation of Wave Breaking Over a Submerged Step with SPH Method

2018 ◽  
Vol 01 (02) ◽  
pp. 1840005 ◽  
Author(s):  
Hongjie Wen ◽  
Bing Ren ◽  
Guoyu Wang ◽  
Yumeng Zhao
Keyword(s):  
Wave Breaking ◽  
Sph Method ◽  
Vertical Distributions ◽  
Sph Model ◽  
Smoothed Particle ◽  
Mean Water Level ◽  
The Mean ◽  
Wave Maker ◽  
Wave Induced ◽  
Smoothed Particle Hydrodynamic

Wave breaking over a submerged step with a steep front slope and a wide horizontal platform is studied by smoothed particle hydrodynamic (SPH) method. By adding a momentum source term and a velocity attenuation term into the governing equation, a nonreflective wave maker system is introduced in the numerical model. A suitable circuit channel is specifically designed for the present SPH model to avoid the nonphysical rise of the mean water level on the horizontal platform of the submerged step. The predicted free surface elevations and the spatial distributions of wave height and wave setup over the submerged step are validated using the corresponding experimental data. In addition, the vertical distributions of wave-induced current over the submerged step are also investigated at both low and high tides.

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