404 I PART 3 I THE MEKONG EMERGENCY
1. Introduction The Vietnamese Mekong Delta (VMD) is the third largest delta in the world, covering 48,900 km2. The Mekong River branches out into 7 main VMD distributary channels before draining to the sea. In addition to these natural river branches, a large network of canals of varying sizes have been built over centuries, enabling navigation and irrigation [ Chapter 7 ]. The sub-aerial delta plain of the VMD is one of the most fertile regions in the world, home to ~17 M people, and produces 50% of Viet Nam’s food supply. Over the past decades, rapid urbanization and intensified agri-/aquacultural production have put significant stress on the delta’s natural resources, such as sand and fresh ground/surface water. Life and live-
lihood in the delta are punctuated by the tropical monsoon, with a wet season from July to October and a dry season from December to May, driving large seasonal variations of the hydrology [ Chapter 7 ]. The average monthly discharge of the Mekong measured upstream (Kratie, Cambodia) ranges from 2 103 m3s-1 in the dry season to 36 103 m3s1 during the wet season. During the latter season, the strong fluvial discharge drives a flood pulse that inundates the floodplains and brings new sediments and nutrients to the delta. The fluvial forces limit the salt intrusion from the sea in the estuary channels to only a few kilometres, whereas during the dry season ocean forces drive up-channel salt intrusion over tens of kilometres.
[ Figure 9.1 ] Changes in the Mekong delta
Drivers (italic) and consequences (bold) of changes in the Mekong delta. Relative sea level rise is the combined effect of global sea level rise and land subsidence. Source: P. Minderhoud (2019).
