360 I PART 3 I THE MEKONG URGENCY
et al., 2014; Minderhoud et al., 2020b) (Chapter 9 deals with delta elevation and land subsidence in greater detail). In addition to causing land subsidence, groundwater pumping also increases groundwater salinization, as freshwater reserves are being replaced by salt water, causing additional loss of freshwater. As a result, fresh groundwater reserves are rapidly decreasing.
4.3 Elevation loss in the delta Over the past decades, the factors controlling the natural dynamics of relative delta elevation have changed drastically in the VMD. This is the result of a combination of climatic and anthropogenic impacts. Increased flood control and sediment starvation have decreased the amount of sediments delivered to channels and
5. Discussion and conclusions The VMD has extensive experience in mitigating and adapting to environmental changes. Figure 7.15 presents the evolution of adaptation to environmental problems in agricultural production since 1986 after the introduction of the “doi moi” (renovation) policy. Water management in the VMD has historically followed the “Dutch dyke” strategy. It includes structures of dykes that encircle settlement and rice fields [ Biggs et al., 2009 ]. In the “doi moi” policy, agriculture and aquaculture were intensified and grown rapidly to supply food for local inhabitants and Viet Nam. A dense canal network was developed [ Fi-
then to flood plains [ Kondolf et al., 2014; Li et al., 2017 ], while global warming increases global sea level rise. Meanwhile, human activities in the delta have enhanced natural subsidence [ Zoccarato et al., 2018 ] and created additional human-induced subsidence [ Minderhoud et al., 2017, 2018 ] [ see Chapter 9 ]. Subsidence is occuring throughout the Delta, at rates of up to several centimetres per year, and up to 5 cm/ year in places [ Erban et al., 2014; Minderhoud et al., 2020a ]. And this subsidence is no longer counterbalanced by the deposition of new sediments. In consequence, the Delta is currently experiencing rapid elevation loss [ Minderhoud et al., 2020b ]. As subsidence and consequential relative sea level rise act as amplifiers of other processes — including flood exposure — erosion and salinization are occuring at increasing rates in the Delta [ Tamura et al., 2020 ].
gure 7.2 ] in order to drain floods to the West Sea, and to clean acid sulphate soils. However, despite this strategy, the rice crops in the upper VMD were still damaged and destroyed by annual floods from August to October. The historic flood of 2000, in particular, caused enormous damage to infrastructure, residents’ properties and agricultural crops. After this hugely damaging flood, rice crops were protected by a dyke system that consists of both low dykes and high dykes [ Thanh et al., 2020 ]. The VMD provinces rarely constructed high dykes before 2000 [ Duong et al., 2016 ]. Since 2000, the upper VMD (An Giang and Dong Thap provinces) has built and planned high dykes to protect rice crops in the entire provincial area. Until 2009, the area protected by high dykes was about 1,222 km2, covering around 35% of the An Giang province area, and
