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The observations of seabed sediment erosion and resuspension processes in the Jiaozhou Bay in China
LIU Xiaolei, ZHU Chaoqi, ZHENG Jiewen, GUO Lei, YIN Ping, JIA Yonggang
2017, 36(11): 79-85. doi: 10.1007/s13131-016-1072-5
Keywords: seabed sediment, erosion, resuspension, tripod, Jiaozhou Bay
In estuarine and coastal areas, the seabed is in a constant process of dynamic change under marine conditions. Seabed sediment erosion and resuspension are important processes that safely control the geological environment. Field tripod observations conducted in the Jiaozhou Bay in China are reported, to investigate the effects of hydrodynamic conditions on the erosion and resuspension processes of the seabed. The observational results show that the maximum shear stress created by tidal currents can reach 0.35 N/m2, which is higher than the wave-induced shear stress during fair weather conditions. A seabed erosion frequently occurs during the flood tide, whereas a seabed deposition occurs during ebb tide. Waves can produce a bottom shear stress approximately equivalent to that induced by currents when the local wind reaches Force 4 with a speed of 5 m/s. When the wind reaches 7 m/s and the significant wave height reaches 26 cm, waves play a more significant role than currents in the dynamic processes of the seabed sediment resuspension and lead to a high value of turbidity that is approximately two to eight times higher than that in fair weather. These analyses clearly illustrate that periodic current-induced sediment erosion and resuspension are dominant in fair weather, whereas episodic high waves are responsible for significant sediment resuspension. Additional work is needed to establish a more thorough understanding of the mechanisms of sediment dynamics in the Jiaozhou Bay.
A model for calculating the erosion distance of soft sea cliff under wave loading
CHANG Fangqiang, SHU Zhonglei
2018, 37(7): 69-77. doi: 10.1007/s13131-018-1245-x
Keywords: wave, soft sea cliff, erosion
A model for calculating the erosion distance of soft sea cliff under wave loading is established based on the erosion mechanism of soft sea cliff under wave loading and for considering wave hydrodynamic and sea cliff material parameters. The model is verified, and the parameters are regressed using an indoor flume experiment. The erosion distances of the sea cliff in the northeast of the Pingtan Island are calculated by the model, and the results are compared with the measured data. The maximum erosion occurs in static water level, the location of the maximum erosion moves up as the wave continues, and the erosion stops when the wave lasts for a period of time. The erosion does not occur until the wave height exceeds a critical value; however, the contribution of large waves to the erosion is not relatively substantial. The calculated erosion distances at two places in the northeast of Pingtan Island are 0.32 m and 0.26 m.
Sea-level rise impact on the evolution of a microtidal Mediterranean coastline without human-made structures—a case of the Port aux Princes-Sidi Daoued coastline, Gulf of Tunis, NE-Tunisia
SAÏDI Hanen, ZARGOUNI Fouad
2019, 38(3): 72-77. doi: 10.1007/s13131-018-1331-0
Keywords: Mediterranean coastline, erosion, sea level rise, littoral cell, Gulf of Tunis, Tunisia
The evolution of the natural and pristine Mediterranean coastline Port aux Princes-Sidi Daoued (Gulf of Tunis, NE-Tunisia) is studied during the period of 1887-2010 on the basis of an ancient minute of bathymetry (1887) and aerial photographs treated by numerical photogrammetric methods. Morphological changes of the coastline shows a general retreat despite the absence of the various anthropogenic actions. Adding to the drift currents and the currents of high energy that are generated by the N-W dominant waves along steeply sub-marine funds, the erosion is mainly due to the sea level rise which increased since the beginning of the 2000s. The Port aux Princes-Sidi Daoued coastline works as a single littoral cell limited by Jbel Korbous to the SW and the fishing harbor of Sidi Daoued to the N-E.
Wave flume experiments on the contribution of seabed fluidization to sediment resuspension
ZHANG Shaotong, JIA Yonggang, WANG Zhenhao, WEN Mingzheng, LU Fang, ZHANG Yaqi, LIU Xiaolei, SHAN Hongxian
2018, 37(3): 80-87. doi: 10.1007/s13131-018-1143-2
Keywords: erosion, shear stress, seepage flows, pore pressure build up, fine-grained particles, Huanghe Delta
Sediment resuspension is commonly assumed to be eroded from the seabed surface by an excess bottom shear stress and evolves in layers from the top down. Although considerable investigations have argued the importance of wave-induced seabed fluidization in affecting the sediment resuspension, few studies have been able to reliably evaluate its quantitative contribution till now. Attempt is made to preliminarily quantify the contribution of fluidization to resuspension using a series of large-scale wave flume experiments. The experimental results indicated that fluidization of the sandy silts of the Huanghe Delta account for 52.5% and 66.8% of the total resuspension under model scales of 4/20 and 6/20 (i.e., relative water depth: the ratio of wave height to water depth), respectively. Some previously reported results obtained using the same flume and sediments are also summarized for a contrastive analysis, through which not only the positive correlation is confirmed, but also a parametric equation for depicting the relationship between the contribution of fluidization and the model scale is established. Finally, the contribution of fluidization is attributed to two physical mechanisms: (1) an attenuation of the erosion resistance of fluidized sediments in surface layers due to the disappearing of original cohesion and the uplifting effect resulting from upward seepage flows, and (2) seepage pumping of fines from the interior to the surface of fluidized seabed.
Coastal erosion risk assessment of Hainan Island, China
Qianxin Su, Zhiqiang Li, Gaocong Li, Daoheng Zhu, Pengpeng Hu
2023, 42(7): 79-90. doi: 10.1007/s13131-022-2122-1  Published:2023-07-25
Keywords: coastal erosion, Coastal Erosion Risk Assessment (CERA), vulnerability, risk, influence factor
Coastal erosion on islands is increasing due to sea level rise, frequent extreme events, and anthropogenic activities. However, studies on the multifactorial coastal erosion risk and the vulnerability of islands are limited. In this study, the Coastal Erosion Risk Assessment (CERA) method was applied for the first time to the study area in China to assess the erosion risk on the coast of Hainan Island; to explore the effects of coastal ocean dynamics, sediment movement characteristics, and anthropogenic construction; and to discuss the suitability of the method and countermeasures for coastal protection. The results show that the coast of Hainan Island shows high sensitivity, high value, low exposure, and moderate erosion. The whole island showed high vulnerability but low erosion risk, with the eastern region being more affected by erosion, particularly the eastern side of Wulong Port and Yalin Bay in Wenchang, and the shore section of Yalong Bay in Sanya, having a very high risk of coastal erosion. In addition, Monte Carlo simulation was used to check the applicability of the CERA method, and it was found that the rate of shoreline change, population density, and number of storms significantly contributed to coastal erosion, but only the short-term effects of sea level rise were considered. The effects of sea level rise and sediment grain size were primarily analyzed as influencing factors. The effects of sea level rise continue to strengthen, with coastal retreat expected to be greater than 2 m by the mid-21st century. Moreover, Hainan Island is primarily composed of the fine and medium sand types, which have little resistance to coastal erosion. Currently, the impact of sediment grain size is rarely considered in coastal erosion risk assessment studies. However, it can be incorporated into the indicator system in the future, and the spatial variation of indicators can be fully considered to strengthen the refinement study.
Beach erosion along the coastline of Alexandria, Egypt
Omran E. Frihy, Samir M. Nasr, Khalid Dewidar, Mohamed El Raey
1994(2): 243-251.
Long-term vacations in beach width of Alexandria Governorate have been analyzed using two sets of aerial photos taken in 1955 and 1983.The analysis reveals that a major part of most beaches has been subjected to coastal erosion except for only beeches.The estimated long-term rate of erosion is approximately 0.20 m/a.
El Maamoura beach, located east of Alexandria,is selected to evaluate seasonal variations.Sand volume losses are found to be 450 m3/(m·a) for the entire beach length (1.2 km).The annual sand transport by wind is estimated as about 37.7 m3.Subtracting this amount of sand from the net sand loss 450 m3/(cm·a) yields 412.3 m3/(cm·a) of eroded sand caused by the action of currents and waves.
Erosion hotspot identified along the sandy coast of Shanwei: characteristics and origin
Jitao Yu, Yuanting Ding, Lin Zhang, Pei Liu, Renfu Fan
2023, 42(7): 91-102. doi: 10.1007/s13131-022-2124-z  Published:2023-07-25
Keywords: erosion hotspot, shoreline, non-linear behavior, artificial sand mining, beach morphodynamic equilibrium, Landsat images
Based on the measured beach profile data of Sanzhou Bay from 2015 to 2019, an erosion hotspot was identified along the Shanwei coastline of eastern Guangdong, where the maximum retreat distance of the shoreline exceeded 80 m and the erosion rate was more than 20 m/a. To determine the time at which the erosion hotspot started and the potential causes of its formation, this study used 63 Landsat satellite images from 1986 to 2019 to construct a time series of shoreline positions over the past 30 years by extracting their high-tide shorelines. Next, the M-K trend test method was introduced to evaluate the non-linear shoreline behavior based on the single-transect method. The results showed that the time of approximately 2013 marked the start of the erosion hotspot, the erosion hotspot was characterized by erosion rates of more than 2 m/a (a maximum rate of 31.6 m/a), and the affected shoreline more than 4.3 km from 2013 to 2019. Furthermore, this erosion hotspot was proved to be caused by artificial sand mining in the nearshore zone, which destroyed the original beach’s morphodynamic equilibrium. With the aid of storm events, soil cliffs composed of loose sediment on the backshore were sacrificed to achieve a new equilibrium, resulting in an extremely significant retreat parallel to the coast on the west side of the study area, which reflects the combined effect of human and natural processes. This study provides a concrete example of the rapid response of shorelines to artificial sand mining activities, and the associated finding is a stark warning about the cautious development and utilization of coastal zones and the strict regulation of human activities.
Study on Wave-influenced resistance to erosion of silty soil in Huanghe (Yellow) River Delta
QIN Hao, CHEN Fang, LIU Yalin
2010(2): 53-57. doi: 10.1007/s13131-010-0021-3
Keywords: wave load, resistance of soils to erosion, disintegration test, liquefaction
Along with the reduction of sediment yield of the Huanghe (Yellow) River, the erosion of the Huanghe River Delta aggravates, which has becomes an important factor that threatens the coastal protection structures. Starting from the study of the erosion resistibility of the sediment, this paper explores the internal mechanism of erosion phenomenon. This paper takes Diaokou as the study area and takes soils as samples which are mixed with clay into reconstructed samples whose ratio of clay content are 5%, 10%, 15%, 20% respectively, then dynamic tri-axial apparatus is applied to simulate wave loads of different intensity; then the resistibility of soil to erosion is determined via concentrated flow test and the structural property is determined via the disintegration test. Finally, the resistibility to erosion and the structural property of the non-compressed soil samples are compared with the compressed data. The results indicates that liquefaction failure exerts significant influence on the resistibility to erosion and the structural property of the silty soil in the Huanghe River Delta. Therefore, in the future erosion studies, the liquefaction phenomenon shall be fully considered.
Simulation of three-dimensional cohesive sediment transport in Hangzhou Bay, China
DU Panjun, DING Pingxing, HU Kelin
2010(2): 98-106. doi: 10.1007/s13131-010-0028-9
Keywords: waves, currents, suspended sediment, deposition, erosion, Grant-Madsen Model
Sediment transport in the Hangzhou Bay is extremely complicated due to its bathymetry and hydrodynamic conditions. The ECOMSED model is employed to simulate three-dimensional (3-D) cohesive sediment transport in Hangzhou Bay. Dynamical factors such as Coriolis force, tides, salinity, river discharges, and waves are considered in the model. The wave parameters, including the significant wave height, period, and direction, are calculated with the SWAN model. The Grant-Madsen model is introduced for the bed shear stress due to the combined effect of waves and currents. The formulation of bed shear stress used to calculate the sink/source terms is modified based on previous research that sufficiently validated the formulation with measurement data. The integrated model of the above-mentioned models is applied to simulate sediment transport in Hangzhou Bay. The results of the simulation agree well with field observations concerning the distribution of suspended sediment, indicating that the sediments are remarkably suspended in Hangzhou Bay under the action of waves and currents.
Tidal flat erosion of the Huanghe River Delta due to local changes in hydrodynamic conditions
JIA Yonggang, ZHENG Jiewen, YUE Zhongqi, LIU Xiaolei, SHAN Hongxian
2014, 33(7): 116-124. doi: 10.1007/s13131-014-0501-y
Keywords: hydrodynamic conditions
An ideal nature system for the study of post-depositional submarine mass changing under wave loading was selected in the inter-tidal platform of the subaqueous Huanghe River Delta, a delta formed during period from 1964 to 1976 as the Huanghe River discharged into the Bohai Gulf by Diaokou distributary. A road embankment constructed for petroleum recovery on the inter-tidal platform in 1995 induced the essential varieties of hydrodynamic conditions on the both sides of the road. With both sides sharing similarities in (1) initial sedimentary environment, (2) energetic wave loading, (3) differential hydrodynamic conditions in later stages, (4) enough long-range action, and (5) extreme shallow water inter-tidal platforms;the study is representative and feasible as well. Two study sites were selected on each side of the road, and a series of measurements, samplings, laboratory experiments have been carried out, including morphometry, hydrodynamic conditions, sediment properties, granularity composition, and fractal dimension calculation of the topography in the two adjacent areas. It was observed that in the outer zone, where wave loading with high magnitude prevailed, the tidal flat was bumpy and exhibited a high erosion rate and high fractal dimension. Further, the fractal dimension diminished quickly, keeping with the enlarging of calculative square size. However in the inner zone, where the hydrodynamic condition was weak, the tidal flat was flat and exhibited a low erosion rate and low fractal dimensions;the fractal dimension diminished with the enlarging of calculative square size. The fractal dimensions in the different hydrodynamic areas equalized increasingly as the calculative square size accreted to threshold, indicating that the hydrodynamic condition plays a significant role in topography construction and submarine delta erosion process. Additionally, the later differentiation of sediment properties, granularity composition, microstructure characteristics, and mineral composition induced by the different hydrodynamic conditions can also contribute to the variation of topography and sea-bed erosion in the two adjacent areas.
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