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Coastal erosion in the region of Thu Bon River mouth, Vietnam

Asplund, Eric and Malmström, Hanna LU (2018) In TVVR18/5007 VVRM05 20181
Division of Water Resources Engineering
Abstract
Coastal erosion has increased worldwide during the last decades, mostly due to human activities. Vietnam is not spared, where many places within the country suffer from beach erosion. This report focuses on the region around Thu Bon river mouth in the central part of Vietnam. The beaches next to the river mouth are experiencing severe erosion, especially Cua Dai Beach. The beach is totally eroded in some areas, and the erosion seems to move further away from the river mouth, which will affect the tourist business.

There is a lack of previous studies regarding nearshore wave climate and sediment transport along the coast. In the present investigation, field studies and simulations have been carried out to address this lack of knowledge.... (More)
Coastal erosion has increased worldwide during the last decades, mostly due to human activities. Vietnam is not spared, where many places within the country suffer from beach erosion. This report focuses on the region around Thu Bon river mouth in the central part of Vietnam. The beaches next to the river mouth are experiencing severe erosion, especially Cua Dai Beach. The beach is totally eroded in some areas, and the erosion seems to move further away from the river mouth, which will affect the tourist business.

There is a lack of previous studies regarding nearshore wave climate and sediment transport along the coast. In the present investigation, field studies and simulations have been carried out to address this lack of knowledge. Three different numerical models have been used to (1) calculate wave climate (EBED), (2) longshore sediment transport (LST Cascade), and (3) shoreline evolution (Cascade). The future shoreline evolution was simulated for 30 years, employing two different scenarios. The first scenario implied no change in sediment transport with the river flow, whereas in the second scenario the sediment transport was reduced to half of its initial value after 15 years. The results show a further retreat of the shoreline on the northern side of the river mouth, which already has an erosion problem. The erosion will move even more to the north in the future, if proper action is not taken. (Less)
Popular Abstract
Coastal erosion is an increasing problem worldwide, Vietnam is not spared. The study is conducted in the central part, in the Thu Bon river mouth, where a future evolution of the shoreline is simulated.

Cua Dai Beach is located on the north side of Thu Bon River mouth. It suffers severely from erosion, and the beach has eroded about 200 meters during a ten years period (Hung, et al., 2017). The beach is a popular place to visit among many tourists who travels to Hoi An Ancient Town, an UNESCO World Heritage site (UNESCO, 2018), 30 minutes away by bike. Along the coastline, there are several beach resorts that are now lacking a beach. One of the before popular resort has been forced to close down because the damages caused by erosion and... (More)
Coastal erosion is an increasing problem worldwide, Vietnam is not spared. The study is conducted in the central part, in the Thu Bon river mouth, where a future evolution of the shoreline is simulated.

Cua Dai Beach is located on the north side of Thu Bon River mouth. It suffers severely from erosion, and the beach has eroded about 200 meters during a ten years period (Hung, et al., 2017). The beach is a popular place to visit among many tourists who travels to Hoi An Ancient Town, an UNESCO World Heritage site (UNESCO, 2018), 30 minutes away by bike. Along the coastline, there are several beach resorts that are now lacking a beach. One of the before popular resort has been forced to close down because the damages caused by erosion and strong waves, and the lack of finances for restoration and protection. The tourism is highly valued in the area and finding a solution for the erosion problems is therefore crucial.

Before finding an effective solution, it is essential to identify the cause of erosion. The overall explanation for coastal erosion is due to disturbances in the natural sediment transport system (Rijn, 2011). Changes in the sediment budget can result in a transformation of areas functioning as sediment sinks respectively sources (Bird & Lewis, 2015). The reasons for the alterations are many and could be from both natural or man-made causes and be long-term or short-term (US Army Corps of Engineers, 1984). In the field area, a probable cause is man-made structures, were sand mining on the river bed and dams built upstream could be one of the reasons. Both sand mining and dams decrease the sediment concentration in the river, which eventually affect the beaches around the river mouth. Upstream Thu Bon River, there is a harbour. To maintain the passability to the harbour, dredging of the river mouth is needed. It creates a sinkhole which could also be a reason for the erosion at nearby beaches.

To comprehend the reasons for coastal erosion, it is necessary to examine and understand the different coastal processes taking place in the studied system. Field surveys can be useful and for example, numerical modelling. It is the chosen method in this study. Three different models are used to describe the wave climate, the sediment transport along the shoreline, and to simulate the future evolution of the coast. A clear perception of the system will help find the right solutions for the erosion problem (US Army Corps of Engineers, 1984). Lack of knowledge of the studied system can have a negative effect and make the situation even worse (Rijn, 2011).

The future does not look bright for Cua Dai Beach. 30 years ahead, the erosion will get worse. It will most likely travel further north away from the river mouth and affect the next beach. At Cua Dai coastline, the beach is found to be totally eroded, forcing the sand to be taken elsewhere. The movement of the erosion to the north is confirmed by both sediment transport patterns in the model results and field observations. A significant factor for the erosion at Cua Dai Beach is found to be the sediment supply coming from the river. Therefore, it is important to consider the activities upstream the river when trying to find the right solution.

The result of this study can be used to help to look at the problem in a long-term perspective. It can be seen action is needed to keep the sandy beaches on the north side of the Thu Bon river mouth. A solution is of great importance for the people who depend on tourism, since it could have significant consequences on their livelihoods’.

References
Bird, E., & Lewis, N. (2015). Beach Renourishment. Springer International Publishing.
Hung, N. T., Vinh, B. T., Nam, S. Y., & Lee, J. L. (2017). Cause Analysis of Erosion-Induced Resort Washout on Cua Dai Beach, Vietnam. . Journal of Coastal Research, 79, 214-218.
Rijn, L. v. (2011). Coastal erosion and control. Ocean & Coastal Management, vol.54. iss.12. p. 867-887.
UNESCO, W. H. (2018, 01 17). UNESCO World Heritage Centre. Retrieved from Hoi An Ancient Town: http://whc.unesco.org/en/list/948
US Army Corps of Engineers. (1984). Shore Protection Manual,. Washington D.C.: US Army Corps of Rngineers, Coastal Engineering Research Center. (Less)
Please use this url to cite or link to this publication:
author
Asplund, Eric and Malmström, Hanna LU
supervisor
organization
alternative title
Kusterosion i området vid Thu Bon floden mynning i Vietnam
course
VVRM05 20181
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Coastal erosion, Cua Dai Beach, longshore sediment transport, EBED, Cascade
publication/series
TVVR18/5007
report number
18/5007
ISSN
1101-9824
language
English
additional info
Examinator: Hans Hanson
id
8954557
date added to LUP
2018-07-10 09:16:05
date last changed
2018-07-10 09:16:05
@misc{8954557,
  abstract     = {Coastal erosion has increased worldwide during the last decades, mostly due to human activities. Vietnam is not spared, where many places within the country suffer from beach erosion. This report focuses on the region around Thu Bon river mouth in the central part of Vietnam. The beaches next to the river mouth are experiencing severe erosion, especially Cua Dai Beach. The beach is totally eroded in some areas, and the erosion seems to move further away from the river mouth, which will affect the tourist business.

There is a lack of previous studies regarding nearshore wave climate and sediment transport along the coast. In the present investigation, field studies and simulations have been carried out to address this lack of knowledge. Three different numerical models have been used to (1) calculate wave climate (EBED), (2) longshore sediment transport (LST Cascade), and (3) shoreline evolution (Cascade). The future shoreline evolution was simulated for 30 years, employing two different scenarios. The first scenario implied no change in sediment transport with the river flow, whereas in the second scenario the sediment transport was reduced to half of its initial value after 15 years. The results show a further retreat of the shoreline on the northern side of the river mouth, which already has an erosion problem. The erosion will move even more to the north in the future, if proper action is not taken.},
  author       = {Asplund, Eric and Malmström, Hanna},
  issn         = {1101-9824},
  keyword      = {Coastal erosion,Cua Dai Beach,longshore sediment transport,EBED,Cascade},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVVR18/5007},
  title        = {Coastal erosion in the region of Thu Bon River mouth, Vietnam},
  year         = {2018},
}