Long-term varations in beach width of Alexandria Governorate have ben analyzed using two sets of aerial photos taken in 1955 and 1983. The analysis reveals that a major part of most beaches has been subjecded to coast...Long-term varations in beach width of Alexandria Governorate have ben analyzed using two sets of aerial photos taken in 1955 and 1983. The analysis reveals that a major part of most beaches has been subjecded to coastal erosion except for only beaches. The esthated long-term rate of erosion is approximately 0. 20 m/a.El Maamoura, located east of Alexandria is selected to evaluate seasonal vacations. 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.展开更多
Major differences in beach erosion between two neighboring artificial beaches Xiangluwan Beach(XL beach)and Meiliwan Beach(ML beach)in Zhuhai,China,were studied after Super Typhoon Hato.In this study,a fully nonlinear...Major differences in beach erosion between two neighboring artificial beaches Xiangluwan Beach(XL beach)and Meiliwan Beach(ML beach)in Zhuhai,China,were studied after Super Typhoon Hato.In this study,a fully nonlinear Boussinesq wave model(FUNWAVE)-Total Variation Diminishing(TVD)was used to distinguish the main impact factors,their relative contributions,and the hydrodynamic mechanisms underlying the different beach responses.Results show that compared to the ML beach,the main reason for the relatively weak erosion on Xiangluwan(XL)beach was the smaller beach berm height(accounting for approximately 75.9%of the erosion response).Regarding the beach with a higher berm,the stronger wave-induced undertow flow,along with the higher sediment concentration,led to a higher offshore sediment transport flux,resulting in more severe erosion relative to the beach with a smaller berm height.The second most important reason explaining the weak erosion on XL beach was the absence of seawalls(accounting for approximately 17.9%of the erosion response).Wave reflection induced by the seawall could cause higher suspended sediment concentration,resulting in a toe scouring near the seawall.The offshore submerged breakwater protected XL beach slightly(accounting for approximately 6.1%of the erosion response).Due to the higher water level induced by storm surge,most of the wave energy could penetrate through the submerged breakwater.The effect of the larger berm width of XL beach was negligible.Compared to the beach with a larger berm width,the erosion/deposition regions in the beach with a narrower berm width showed shoreward migration,without significant changes in the erosion/deposition extent.Despite of this,the larger berm width could reduce the wave energy reaching the shoreline.This study of the storm stability of artificial beaches may be applied to beach restoration design.展开更多
River training walls have been built at scores of locations along the NSW coast and their impacts on shoreline change are still not fully understood. In this study, the Brunswick River entrance and adjacent beaches ar...River training walls have been built at scores of locations along the NSW coast and their impacts on shoreline change are still not fully understood. In this study, the Brunswick River entrance and adjacent beaches are selected for examination of the impact of the construction of major training walls. Thirteen sets of aerial photographs taken between 1947 and 1994 are used in a GIS approach to accurately determine the shoreline position, beach contours and sand volumes, and their changes in both time and space, and then to assess the contribution of both the structures and natural hydrodynamic conditions to large scale (years-decades and kilometres) beach changes. The impact of the training walls can be divided into four stages: natural conditions prior to their construction (pre 1959), major downdrift erosion and updrift accretion during and following the construction of the walls in 1959～1962 and 1966, diminishing impact of the walls between 1966 and 1987, and finally no apparent impact between 1987～1994. The impact extends horizontally about 8 km updrift and 17 km downdrift, and temporally up to 25 years.展开更多
Severe weather systems can generate large waves and storm surges which can cause many fatalities in coastal areas.In extreme circumstances a single cyclone caused up to 500,000 fatalities in the Bay of Bengal in 1970....Severe weather systems can generate large waves and storm surges which can cause many fatalities in coastal areas.In extreme circumstances a single cyclone caused up to 500,000 fatalities in the Bay of Bengal in 1970.Adaption by authorities in that region from evacuations and construction of storm shelters have significantly reduced the number of such fatalities there.The effects of Hurricane Sandy in 2012 in New York City and surrounding areas is examined to show how ocean effects can cause many casualties.Scrutiny of a European storm shows how a slight error in analysis can fail to detect a deadly increase in intensity which caused many fatalities.World record wave height events are examined,and the historical Australian east coast events are investigated.The impacts from long period waves emanating from distant storms are shown to be a forecasting problem.展开更多
The Longfengtou Beach in the Haitan Bay, located in Fujian Province of China and facing the Haitan Strait, has been suffering severe erosion due to the construction of seawalls. A simple beach nourishment project impl...The Longfengtou Beach in the Haitan Bay, located in Fujian Province of China and facing the Haitan Strait, has been suffering severe erosion due to the construction of seawalls. A simple beach nourishment project implemented has not achieved the anticipated beach restoration. Thus a practical solution has to rely on a combination with near-shore marine structures. In this study, a 2-D calibrated flow model is set up to investigate the effects of three different layouts of near-shore marine structures on the tidal current. It is shown that the breakwaters situated in both the north and south ends play a vital part in the protection against erosion. The offshore breakwaters can serve as a barrier to obstruct the current circulation then reduce the current velocity. The groyne linking the Guimo islet and the coast significantly reduces the south-to-north water exchange through the channel and redirects the current direction nearly perpendicular to the north breakwater, which cuts off the longshore transport that may have a negative influence on the beach, especially, the northern part. It is also noted that the monsoon at the site with different directions increases the current velocity. In general, proper layouts of marine structures can reduce the current velocity thus lead to less intense sand transport near the beach.展开更多
文摘Long-term varations in beach width of Alexandria Governorate have ben analyzed using two sets of aerial photos taken in 1955 and 1983. The analysis reveals that a major part of most beaches has been subjecded to coastal erosion except for only beaches. The esthated long-term rate of erosion is approximately 0. 20 m/a.El Maamoura, located east of Alexandria is selected to evaluate seasonal vacations. 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.
基金Supported by the National Natural Science Foundation of China(Nos.42006176,42330406,U1706220,41901006)the Basic Research Project of the Science and Technology Innovation Development Program of in Yantai(No.2022JCYJ028)。
文摘Major differences in beach erosion between two neighboring artificial beaches Xiangluwan Beach(XL beach)and Meiliwan Beach(ML beach)in Zhuhai,China,were studied after Super Typhoon Hato.In this study,a fully nonlinear Boussinesq wave model(FUNWAVE)-Total Variation Diminishing(TVD)was used to distinguish the main impact factors,their relative contributions,and the hydrodynamic mechanisms underlying the different beach responses.Results show that compared to the ML beach,the main reason for the relatively weak erosion on Xiangluwan(XL)beach was the smaller beach berm height(accounting for approximately 75.9%of the erosion response).Regarding the beach with a higher berm,the stronger wave-induced undertow flow,along with the higher sediment concentration,led to a higher offshore sediment transport flux,resulting in more severe erosion relative to the beach with a smaller berm height.The second most important reason explaining the weak erosion on XL beach was the absence of seawalls(accounting for approximately 17.9%of the erosion response).Wave reflection induced by the seawall could cause higher suspended sediment concentration,resulting in a toe scouring near the seawall.The offshore submerged breakwater protected XL beach slightly(accounting for approximately 6.1%of the erosion response).Due to the higher water level induced by storm surge,most of the wave energy could penetrate through the submerged breakwater.The effect of the larger berm width of XL beach was negligible.Compared to the beach with a larger berm width,the erosion/deposition regions in the beach with a narrower berm width showed shoreward migration,without significant changes in the erosion/deposition extent.Despite of this,the larger berm width could reduce the wave energy reaching the shoreline.This study of the storm stability of artificial beaches may be applied to beach restoration design.
文摘River training walls have been built at scores of locations along the NSW coast and their impacts on shoreline change are still not fully understood. In this study, the Brunswick River entrance and adjacent beaches are selected for examination of the impact of the construction of major training walls. Thirteen sets of aerial photographs taken between 1947 and 1994 are used in a GIS approach to accurately determine the shoreline position, beach contours and sand volumes, and their changes in both time and space, and then to assess the contribution of both the structures and natural hydrodynamic conditions to large scale (years-decades and kilometres) beach changes. The impact of the training walls can be divided into four stages: natural conditions prior to their construction (pre 1959), major downdrift erosion and updrift accretion during and following the construction of the walls in 1959～1962 and 1966, diminishing impact of the walls between 1966 and 1987, and finally no apparent impact between 1987～1994. The impact extends horizontally about 8 km updrift and 17 km downdrift, and temporally up to 25 years.
文摘Severe weather systems can generate large waves and storm surges which can cause many fatalities in coastal areas.In extreme circumstances a single cyclone caused up to 500,000 fatalities in the Bay of Bengal in 1970.Adaption by authorities in that region from evacuations and construction of storm shelters have significantly reduced the number of such fatalities there.The effects of Hurricane Sandy in 2012 in New York City and surrounding areas is examined to show how ocean effects can cause many casualties.Scrutiny of a European storm shows how a slight error in analysis can fail to detect a deadly increase in intensity which caused many fatalities.World record wave height events are examined,and the historical Australian east coast events are investigated.The impacts from long period waves emanating from distant storms are shown to be a forecasting problem.
基金supported by the Marine Public Welfare Pro-gram of China(Grant No.201305003)
文摘The Longfengtou Beach in the Haitan Bay, located in Fujian Province of China and facing the Haitan Strait, has been suffering severe erosion due to the construction of seawalls. A simple beach nourishment project implemented has not achieved the anticipated beach restoration. Thus a practical solution has to rely on a combination with near-shore marine structures. In this study, a 2-D calibrated flow model is set up to investigate the effects of three different layouts of near-shore marine structures on the tidal current. It is shown that the breakwaters situated in both the north and south ends play a vital part in the protection against erosion. The offshore breakwaters can serve as a barrier to obstruct the current circulation then reduce the current velocity. The groyne linking the Guimo islet and the coast significantly reduces the south-to-north water exchange through the channel and redirects the current direction nearly perpendicular to the north breakwater, which cuts off the longshore transport that may have a negative influence on the beach, especially, the northern part. It is also noted that the monsoon at the site with different directions increases the current velocity. In general, proper layouts of marine structures can reduce the current velocity thus lead to less intense sand transport near the beach.
