Sediment Movement Mechanism around the Magome River Mouth based on Color Sand Tracer Experiments
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Abstract:
Mechanism of sand movement was investigated around of the Magome River mouth located on the Enshu-nada by the comparison of old geographical maps in about 200 years and by a color sand tracer experiment. The long term advancement of the shoreline as well as the rapid retreat in the last 20 years were identified. The movement of four color sands placed on the updrift and the downdrift sides of the river mouth jetty and in the jetty channel was monitored for three months. Entrapment of westward longshore transport by the jetty was found to be significant. A sand bypassing system was found to be feasible by utilizing an existing sewage discharge channel connecting the Tenryu River mouth to the Magome River.Keywords:
Jetty
River mouth
Longshore drift
Before the construction of Dachanwan Jetty Wharf,the mouth of Xixianghe River faced the Lingdingyang Bay directly.The strong tidal dynamic power facilitated the water environment to keep clean around the mouth area.The construction of the Dachanwan Jetty Wharf enclosed the open bay into a semi-closed one.Xixianghe River mouth is located at the furthest part of the wharf and the water exchange with the open sea was largely reduced.The dramatic hydrodynamic variation tampered with the full dilution of the polluted water from upstream and the pollutants were accumulated within the mouth area as well as the harbor basin,worsening the water environment.This situation was aggravated day by day.The various hydrodynamic control and guide schemes are figured out to improve the water quality of Xixianghe River.
Jetty
Wharf
River mouth
Open sea
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Anglet beach, located in the south of the French Atlantic coast, has been experiencing severe erosion for several decades, whereas recurrent dredging has been necessary to fight against the shoaling of the mouth of the Adour River. The channel entrance is protected from the very energetic wave climate by a main jetty, the effect of which on the system appears to be crucial. In this paper, we study the relationship between the two systems in terms of sedimentary exchanges. First, we determine the time history of volume of subtidal beach sand with a bathymetry dataset spanning 24 years. This analysis highlights continuous and large erosion affecting the subtidal part of Anglet beach. This phenomenon had been masked until 1990 thanks to dredged sand releases. However, after that date, the drastic reduction of artificial sediment intakes led to a drop in the sand volume. Numerical modeling is used to study the flow pattern around the mouth of the river. Different wave scenarios are simulated with the TOMAWAC spectral model. The flows induced by waves and tides are then computed with TELEMAC2D (EDF/DRD). The sheltering effect of the jetty on waves is found to generate cross-currents directed to the river mouth. The magnitude of these currents is strongly dependent on the wave class energy and sea level. Local sediment fluxes are then estimated at the limit between systems. This calculation shows that cross-currents induced by the three most energetic wave classes could be entirely responsible for the sediment motion from the coast of Anglet to the mouth of the Adour River.
Jetty
River mouth
Dredging
Shoal
Breakwater
Coastal erosion
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This paper describes diagnostic numerical simulations of waves, current, sediment transport, and morphology change at the mouth of the Colorado River; Texas. The simulations were performed with the Inlet Modeling System (IMS) developed by the Coastal Inlets Research Program at the Coastal and Hydraulics Laboratory, U.S. Army Engineer Research and Development Center. The IMS version applied consists of the circulation and sediment transport model M2D coupled with the wave spectral model STWAVE. The study site exhibits complex patterns of sediment transport over a weir jetty and deposition in an impoundment basin. Six alternatives are evaluated by comparison of calculated morphologic change and sediment impoundment coupled with the hydrodynamics over a 1-year simulation interval. Simulations are performed with and without a sediment training structure, different jetty lengths, and different weir lengths and elevations. The alternatives are examined for effectiveness in improving efficiency of the impoundment basin and in reducing sediment shoaling in the entrance channel to decrease dredging frequency.
Jetty
Dredging
Weir
Shoaling and schooling
Deposition
Sedimentary budget
Coastal engineering
Wave flume
Hydraulics
Flume
Breakwater
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Abstract One of the problems around estuaries with the wave-dominated combination of a small tidal range and low river discharges in the dry season was the mouth closed by a sand barrier. Longshore sediment flows silted up the river mouth while river flows were insufficiently large for flushing sand barriers. When the wet season started, river discharge suddenly enlarged. Discharge can’t flow through the river mouth due to being hindered by the sand barrier. The consequence was that the hinterlands were inundated. Yogyakarta International Airport (YIA) is located in a coastal area of Kulon Progo regency, between two river mouths (Bogowonto river and Serang River). The two rivers have unstable river mouths. The double Jetty had been built at the Bogowonto river, but its condition was damaged. Meanwhile, the breakwater was constructed at the river mouth Serang and called Tanjung Adikarto. Double Jetties will be built to stabilize the Bogowonto river mouth. The purpose of this paper is to provide an overview of the length of the Jetty to be more effective in stabilizing the Bogowonto river mouth. Therefore, so that more easily opened by river flow and does not cause excessive erosion on the one side of the Jetty.
Jetty
River mouth
Breakwater
Dry season
Bank
Wet season
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Beach changes related to human activities, such as the effect of construction of groynes and detached breakwaters on a coast with prevailing longshore sand transport, and offshore sand mining, which have engineering importance, were predicted using the Types 1 and 2 BG model. When a long port breakwater is extended, a large wave-shelter zone is formed and dominant longshore sand transport is induced from outside to inside the wave-shelter zone, resulting erosion outside the wave-shelter zone and accretion inside the wave-shelter zone. These beach changes were also predicted using the Type 2 BG model with the evaluation of the effect of a jetty extended at the port entrance to reduce sand deposition inside the port.
Jetty
Breakwater
Longshore drift
Coastal erosion
Deposition
Port (circuit theory)
Plage
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A one-dimensional numerical model for predicting the cross-shore distribution of the longshore sediment transport rate was developed. The model predicts the suspended load due to wave breaking and bed load due to longshore current velocity and velocity skewness and atiltness. The model validity was examined for steady flows and for waves and wave-induced longshore currents. The sediment transport rates for steady flows estimated by the present model agreed with those by Ribberink's formula. The total longshore sediment transport rates estimated by the present model were smaller than those estimated by CERC's formula. However, because CERC's formula was found to overestimate the total longshore sediment transport rate, the present model likely predicts the longshore sediment transport in the field properly.
Longshore drift
Surf zone
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The US Army Corps of Engineers (USACE) has undertaken a thorough study of coastal processes in and around the entrance to Grays Harbor, WA, in order to optimize the performance of the North Jetty. As part of this study, detailed numerical modeling of 2D nearshore circulation and sediment transport was conducted to evaluate the impacts of a number of structural alternatives on waves, water levels, nearshore circulation and the resulting sediment transport relative to existing conditions (MacDonald et al., 2003). This work was done to examine the sensitivity of these impacts to variations in nearshore bathymetry. This paper summarizes the approach and findings of this fine-scale nearshore modeling work. Five structural alternatives were investigated along with two sets of bathymetric conditions in order to account for the year-to-year variability in nearshore morphology. Several numerical models were used to study the waves, circulation patterns, sediment transport potential and sediment bypassing. Ninety-six simulations were performed for each structure-bathymetry combination to represent the local tide and wave climate. A novel approach of this work was the analysis of the results in terms of an annualized climate. The results of this fine-scale nearshore modeling work showed that all alternatives were successful, to varying degrees, in promoting sediment retention on the adjacent beach and in reducing sediment bypassing into the inlet.
Jetty
Coastal engineering
Sediment control
Breakwater
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AbstractAt the Shiribetsu River mouth located in Hokkaido, Japan, a jetty has been constructed on the right hand side of the mouth from July to October 1999. In this study, the effectiveness of the jetty construction is studied by analyzing field data of river mouth morphology and water level variation. Before the jetty construction, water level rise due to wave set-up has frequently been observed every year from October to March. It is found that the height of the wave set-up increased in winter with the development of sand spit at the river mouth. After the construction, it is confirmed that the interruption of longshore sediment movement due to the construction of the jetty led to the stability of the river mouth opening. Furthermore, it reduces the wave set-up in the river mouth.Keywords: River mouthShiribetsu Riverjettysand spittopography changewave set-up
Jetty
River mouth
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At the Shiribetsu River mouth located in Hokkaido, Japan, water level rise due to wave set-up has frequently been observed every year from October to March, and it is reported that the magnitude of water level rise shows very close correlation with sand spit length at the river mouth. Ariver mouth jetty has been constructed at the right hand side of the river mouth during the period from July 1999 to October 1999. In this study, the effectiveness of the jetty construction is studied from aviewpoint of river mouth morphology and water level variation. It is confirmed that the prevention of longshore sediment movement caused by construction of the jetty led to stability of the river mouth topography. Furthermore, the water depth at the river entrance has increased, resulted in the reduction of water level rise in the river mouth caused by wave breaking.
Jetty
River mouth
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