Sediment Dynamics in Mangrove areas, Mekong River- and Ho Chi Minh - Dong Nai River Delta
Final Report Abstract
The SE-Asian region imply many locations and megacities which will be highly affected by sea level rise by the end of the 21st century of which Ho Chi Minh city belongs to the 20 cities with a population most exposed to coastal flooding in the 2070s assuming 0.5 m sea level rise and with highest economic average annual losses due to marine flooding in the 2050s. At the same time the ecological important mangrove belts, which are common along these coastlines. will retreat. Therefore improved understanding of temporal and spatial water level fluctuations and knowledge about processes of coastal retreat along deltaic systems is needed for a better coastal resource planning and management. Our data show that there is no difference to global mean sea level rise along the Mekong Delta. The observed differences of relative sea level rise along the Mekong Delta coast are related to non climatic components, as they are manifold in deltaic systems. Subsidence is due to delta development and often uneven within a delta. Besides natural compaction, sinking due to exploitation of resources like groundwater or shortage in sediment discharge to the open coast due to sediment mining in the distributaries of the Mekong River are contributors. This subsidence can be significantly higher than the rate of eustatic sea level rise. In our study it was not possible to distinguish between the different causes creating the subsidence as no precise data about the different interventions exist. We only show the product of all the components. Relative sea level rise for some areas at the Mekong Delta coastline (Binh Dai, My Thanh) is higher than general estimates with 2,8 – 8,8 mm/Year. Syvitsky et al. (2009) calculated a relative sea level rise of 6 mm/yr for the MD based on a 22 years data set from Vung Tau tide gauge. This value cannot be confirmed by the data we used in our study as Vung Tau, regarded as a stable area, shows a sea level rise of only 3.5 mm/yr. Coastlines showing cliffs composed of mangrove soil are an indicator for rapid erosion. This shoreline retreat is controlled by three major hydrological factors, • the inundation due to tides, • the energy impact from waves, • the tidal flow asymmetry. Among these three impacting factors, tides plays a key role as they control the time of inundation. Waves need the guide by tides as they can only act on the base of the cliff, hence the wave is the second significant factor accelerating the cliff recession. As results of the tidal flow asymmetries, in the studied areas ebb currents are faster than flood currents. These tidal flow asymmetries prevent the accumulation of eroded material in front of cliffs and therefore it is considered as the third important factor maintaining the recession process. Additionally soil composition of mangrove shoreline can effect erosion in reducing the speed of retreat.
Publications
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2008. Suspended sediment dynamics in mangrove areas, Dong Tranh estuary, Can Gio mangrove forest, Ho Chi Minh City, Southern Vietnam. Annual Report of FY 2007, The Core University Program between Japan Society for the Promotion of Science (JSPS) and Vietnamese Academy of Science and Technology (VAST), 439 – 450
La Thi Cang, Czerniak, P., Nguyen Cong Thanh, Schwarzer, K., Ricklefs, K.
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Some aspects of processes driving the retreat of mangrove-coasts; examples from Vietnam. JSPS and CCOP/GSJ/AIST Seminar on Coastal Erosion in the Deltas, 2nd Annual Meeting of JSPS AA Science Platform: Mega-Delta Watching in Asia, 2nd Annual Meeting of CCOP DelSEA-II Project, Bangkok (Thailand), 02. - 03. Nov., 2009
Schwarzer, K., Nguyen Cong Thanh, K. Ricklefs, La Thi Cang, Le Xuan Thuyen
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2010. The influence of tropical rainfall on sediment redeposition in mangrove environments – examples from Can Gio, SE- Vietnam. JSPS and CCOP/GSJ/AIST Seminar on Coastal Erosion in the Deltas, 2nd Annual Meeting of JSPS AA Science Platform: Mega-Delta Watching in Asia, 2nd Annual Meeting of CCOP DelSEA-II Project, Haiphong (Vietnam), 24. - 29. Nov., 2010
Schwarzer, K., Nguyen Cong Thanh, K. Ricklefs, La Thi Cang
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2016. Sediment re-deposition in the mangrove environment of Can Gio, Saigon River estuary (Vietnam). Journal of Coastal Research, SI 75 (1), 138 – 142
Schwarzer, K., Thanh Cong Nguyen, Ricklefs, K.
