Linking rapid erosion of the Mekong River delta to human activities.

Edward J Anthony,Manon Besset,Marc Goichot,Philippe Dussouillez,Guillaume Brunier,Van Lap Nguyen

doi:10.1038/srep14745

Abstract

As international concern for the survival of deltas grows, the Mekong River delta, the world’s third largest delta, densely populated, considered as Southeast Asia’s most important food basket, and rich in biodiversity at the world scale, is also increasingly affected by human activities and exposed to subsidence and coastal erosion. Several dams have been constructed upstream of the delta and many more are now planned. We quantify from high-resolution SPOT 5 satellite images large-scale shoreline erosion and land loss between 2003 and 2012 that now affect over 50% of the once strongly advancing >600 km-long delta shoreline. Erosion, with no identified change in the river’s discharge and in wave and wind conditions over this recent period, is consistent with: (1) a reported significant decrease in coastal surface suspended sediment from the Mekong that may be linked to dam retention of its sediment, (2) large-scale commercial sand mining in the river and delta channels, and (3) subsidence due to groundwater extraction. Shoreline erosion is already responsible for displacement of coastal populations. It is an additional hazard to the integrity of this Asian mega delta now considered particularly vulnerable to accelerated subsidence and sea-level rise, and will be exacerbated by future hydropower dams.

Highlights

River deltas crucially depend on sustained sediment supplies in order to maintain delta shoreline position and to balance subsidence
High-resolution satellite images show that the Mekong delta is largely prone to erosion, with shoreline retreat over the period 2003–2012 having affected over 50% of the > 600 km-long coast, and even up to 90% of the muddy South China Sea coast
An important recent decrease in mud supply to the coast during the high river-discharge season has been highlighted from MERIS staellite images[46], whereas decreasing rates of sandy shoreline progradation in the mouths sector of the delta are in agreement with large-scale sand mining in the delta channels, including in reaches very close to the sea

Summary

Introduction

River deltas crucially depend on sustained sediment supplies in order to maintain delta shoreline position and to balance subsidence. In the wake of this concern regarding the effects of dams, and, to a lesser extent, of river-bed mining, on fluvial sediment supply and on the future stability of the Mekong delta, erosion of the delta’s shoreline has become a important issue, highlighted in recent academic studies[25,26,27,28,29,30] and in numerous newspaper reports[31] It has been shown from analysis of maps and Landsat satellite images spanning the period 1950–2014 that delta erosion has progressively increased, especially along the muddy South China Sea coast, whereas the delta distributary mouths sector has shown a fluctuating trend tentatively attributed to shifts in flood discharge levels and associated sediment supply[29]. It poses threats to the safety and livelihood of subsistence farmers and fishers[33], as shown by the relocation of over 1200 households in coastal settlements affected by severe erosion in 201431, and the common recourse to the Vietnamese army in setting up hasty coastal defences along eroding sectors of the delta in the South China Sea

Methods

Findings

Discussion

Conclusion