Content - Rise and Fall project

Subsidence in coastal areas of
the Vietnamese Mekong Delta:
challenges and possibilities for
adaptation
Nguyen Hieu Trung, Van Pham Dang Tri
Can Tho University, Vietnam
Email: nhtrung@ctu.edu.vn
Content
• Land Subsidence (LS) - the ongoing processes
in the Vietnamese Mekong Delta (VMD)
• Impacts of LS to the sustainable development
of the VMD
• Possible adaptation measures
Content
• Land Subsidence (LS) - the ongoing processes
in the Vietnamese Mekong Delta (VMD)
• Impacts of LS to the sustainable development
of the VMD
• Possible adaptation measures
Background
• Located at the end of the
Mekong River. Low and
flat area.
• Land areas: ~39,000 km2
(shared 12% nation areas)
• Population: ~18,6 mil
people (22% of nation)
• > 50% national rice
production (90% of
exporting rice of VN)
• 70% national fruit trees
production
• 80% national aquaculture
production
Source: Mehdi Saqalli and Mireille Dosso, 2011
LS - the ongoing processes in the VMD
•
•
Natural subsidence by natural compaction, alluvial and marine processes (e.g.
leaking drains softening soil, clay shrinkage, natural loading)
Intensive flood and salinity control system for agriculture  Reduce of wetlands
 reduce GW recharge (IUCN, 2011).
Source: JIRCAS, 2013
LS - the ongoing processes in the VMD
•
Upstream hydropower development will reduce
stream flow and sediment load to the MD.
(Nguyen Van Manh, et. al, 2015)
(Source: www.mekongflows.org - Mekong Flows team,
University of Canterbury. Data source: Mekong River
Commission, 2010)
LS - the ongoing processes in the VMD
• Poor surface water quality or lack of fresh water in the dry season in
coastal provinces  over exploitation of ground water  land
subsidence.
(Source: Erban et al., 2014)
Content
• Land Subsidence (LS) - the ongoing processes
in the Vietnamese Mekong Delta (VMD)
• Impacts of LS to the sustainable development
of the VMD
• Possible adaptation measures
Impacts
– Different level of subsidence along river/canal  change of
river morphology  change of flow  increase erosion.
Severe landslide happens in Cai Rang district, Can Tho city. (Photo: SGGP)
Impacts
– Increase flooding depth and
duration.
Relative SL = Absolute
SL + Subsidence
1-4 cm/year
Source: Deltares 2013
(Van Pham Dang Tri, et.al. 2012)
Impacts
• Increase saline intrusion
(Source: Deltares)
(Trần Quốc Đạt, et. al., 2010)
Scenario of absolute SLR 20cm (2030s), upstream discharge reduce 38% with
upstream agriculture development.  happen earlier with relative SLR  impacts
to rice production of the delta.
Content
• Land Subsidence (LS) - the ongoing processes
in the Vietnamese Mekong Delta (VMD)
• Impacts of LS to the sustainable development
of the VMD
• Possible adaptation measures
Possible adaptations
Delta scale, provincial scale
Delta plan
Possible adaptations
Delta scale, provincial scale
- To have better water governance  quantify the interaction of
surface water, ground water and land subsidence in the Mekong
Delta  need a new integrated Delta modeling toolbox:
• to incorporate the different models and
• to enable integrated scenario (e.g. upstream dev., relative SL, land
uses) evaluation and comprehensive presentation of results to water
managers and policy makers
Rise and Fall project.
Possible adaptations
Delta scale, provincial scale
- To increase surface water storing (e.g. in canals, wetlands).
- To recharge ground water (during the flood season).
room for river (Netherlands) `
Possible adaptations
Delta scale, provincial scale:
• To reduce ground water extraction 
Alternative sources for water supply
(e.g. surface water and rain water).
Possible adaptations
Local scale adaptation
• To save water  apply water saving techniques in agriculture (e.g.
Alternative Wet and Dry).
• To reduce fresh water shortage risks  use salinity tolerance rice
varieties, adjust cropping calendar or change to upland crops.
(Project: Developing agriculture, aquaculture and environment based climate adaptation strategies for the
Mekong Delta Plan in Vietnam)
Possible adaptations
Local scale adaptation
• To reduce surface water pollution:
– Recycling nutrient in farming
– Combine centralize and decentralize treatment system (e.g. contructed
wetland)
Thank you for your
attention