VARIDATION OF EFFECT OF RIVER-MOUTH JETTY AT MAITE RIVER FLOWING INTO NAKATSU TIDAL FLAT
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中津干潟に流入する舞手川の河口では，2019年3月までに長さ54mの河口導流堤が延ばされた．河口導流堤の建設後，様々なモニタリング調査が行われた．2019年9月18日のドローン画像によれば，この河口導流堤は河口流路の固定化，河口砂州の形成抑制，河口左岸の砂丘地の侵食防止，河口導流堤の西側隣接部でのカブトガニ産卵のための砂州形成などに役立ったことが分かった．河口導流堤の延伸後，河口の西側に隣接する砂丘地の侵食が止まっただけでなく，砂丘地前面の砂浜が大きく広がった．また，河口左岸沖に粗砂が堆積して砂州が形成され，それがカブトガニの産卵地となったことが分かった．Keywords:
Jetty
Tidal flat
River mouth
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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연안에서 표사문제의 대책을 장기적인 관점에서 수립하기 위해서는 연안에서의 표사뿐만 아니라 배후지 하천으로부터 유출되는 유사량을 포함한 종합적인 토사관리 필요성이 증가하고 있다. 이와 같은 관점에서 본 연구에서 연안해역으로 유출되는 하천 유사의 이송, 하구에서 사주발생과 발달 및 하구폐색, 연안으로 유출된 유사의 저류문제, 홍수 시 외해로 유출되는 유사의 특성 등에 대해 검토하였다. 최근 울산 회야강 하구에 하구폐색과 하구사주의 발생에 따른 대책으로 1997년부터 2004년에 걸쳐 총연장 156m의 도류제를 건설하였다. 이에 따라 회야강 하구에서 도류제 건설에 따른 토사이동 특성이 변히고 있음에 따라 해저지형 변동과 표사이동을 해석하기 위하여 1차원 수치해석을 수행하였다. 이를 위해 먼저 울산 회야강 하구역에서 유출하는 유사량을 3가지 모래가 혼합되어 있다고 가정한 혼합입경의 관점을 가정하였다. 그리고 회야강 하구인근의 파동장, 해빈류장 및 표사이동 특성을 Bailard(1981)의 에너지 모형에 의해 해저지형 변동 특성을 해석하였다. 또, 하구폐색의 변동특성을 확인하기 위하여 항공사진을 통한 회야강 하구 및 진하 해수욕장 인근 지형변화를 비교하였다. Integrated sand control including sediment discharge from hinterland rivers is necessary to maintain coastal sand resources over a long term. In this regard, the following subjects should be considered; efficient ways to transfer discharged sand from a river to the neighboring coast, measures to improve storage efficiency of the discharged sand at the river delta and/or river terrace, measures to prevent the sand resources from being discharged into the deep sea during flooding. From the 1997 to January 2004, the jetty of 156 m length was constructed the Heoya-river mouth to protect the blockade of river mouth. Several tests were carried out to investigate the characteristics of sediment transport and morphological change due to the construction of the jetty at the Heoya-river mouth. Firstly, The sand discharge from Heoya river is quantified by one-dimensional numerical analysis assuming the mixed sand of three different particle diameters. Also the numerical mode system, which predicts the sea bed changes obtained from the Bailard's energy model(1981), was combined with the wave, wave-induced currents and sediment transport models. Then, to understand the changes to the blockade of the river mouth, several aerial photographs were compared, which showed that the changes were significant.
Jetty
River mouth
River delta
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中津干潟に流入する舞手川の河口では，2019年3月までに長さ54mの河口導流堤が延ばされた．河口導流堤の建設後，様々なモニタリング調査が行われた．2019年9月18日のドローン画像によれば，この河口導流堤は河口流路の固定化，河口砂州の形成抑制，河口左岸の砂丘地の侵食防止，河口導流堤の西側隣接部でのカブトガニ産卵のための砂州形成などに役立ったことが分かった．河口導流堤の延伸後，河口の西側に隣接する砂丘地の侵食が止まっただけでなく，砂丘地前面の砂浜が大きく広がった．また，河口左岸沖に粗砂が堆積して砂州が形成され，それがカブトガニの産卵地となったことが分かった．
Jetty
Tidal flat
River mouth
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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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The coastal zone of Niigata Prefecture is severely affected by erosion. This study was developed to investigate the relationships between river regulation and changes to the coastal zone. Regulation of the Shinano River began during the Meiji Period with the construction of a long jetty. The jetty was built to avoid the silting of the river mouth, and allow the significant maritime trade to continue with inland transport via the Shinano River. Additional regulation involved the dredging of two channels southward from the mouth of the Shinano River, the Sekiya and the Ohkozu, for the purpose of flood mitigation in the Niigata Plain. To evaluate changes to the coastline, several approaches were used. Firstly, six sets of aerial photographs were examined. Then, the sediments grain-size parameters and mineral variation were analyzed to find the correspondence with shoreline changes. As a third approach, field surveys were conducted and historical data on the coastal process was assessed. The coast in the vicinity of the artificial channels accreted and there was erosion on the down-drift side of the river mouth.
Jetty
River mouth
Siltation
Dredging
Coastal erosion
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Muara Sungai Serayu is located in the Cilacap district, precisely in the Adipala and Kesugihan districts. When the flow of water enters the estuary there will be a change or transition in the speed of the water flow. Slowing water flow causes sedimentation in the river mouth so that sedimentation occurs at the mouth of the river mouth. The mouth of the Serayu river estuary has undergone a morphological change due to the presence of a sand spit that covers the mouth of the river estuary so that it experiences a diversion to the area. From the results of the SED2D modeling there was a change in the base elevation in the mouth of the river mouth with the existing conditions of 11.79% - 30.20%. In the groundsill planning conditions an increase of 0.35%, resulting in a decrease in elevation of 11.56% - 30.55%. Changes in the base elevation in the jetty planning conditions decreased by 0.47% from the existing conditions, so there was a change in evelation for 1 year amounting to 0.06% - 29.73%. Based on the sedimentation pattern that has been modeled on the groundsill planning conditions and jetty planning conditions by considering changes in the base elevation, then what is used as an estuary safety building is a long type jetty. Before planning the jetty, dredging is needed around the mouth of the Serayu River estuary to a depth of -3.00 m. Keywords — Groundsill, jetty, river estuary mouth Serayu, sediment
Jetty
River mouth
Dredging
Sedimentation
Elevation (ballistics)
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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.
Jetty
River mouth
Longshore drift
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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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