Sand mining in the Mekong Delta revisited - current scales of local sediment deficits

Abstract

The delta of the Mekong River in Vietnam has been heavily impacted by anthropogenic stresses in recent years, such as upstream dam construction and sand mining within the main and distributary channels, leading to riverbank and coastal erosion. Intensive bathymetric surveys, conducted within the Tien River branch during the dry and wet season 2018, reveal a high magnitude of sand mining activities. For the year 2018, an analysis of bathymetric maps and the local refilling processes leads to an estimated sand extraction volume of 4.64 0.31 Mm/yr in the study area, which covered around 20 km. Reported statistics of sand mining for all of the Mekong’s channels within the delta, which have a cumulative length of several hundred kilometres, are 17.77 Mm/yr for this period. Results from this study highlight that these statistics are likely too conservative. It is also shown that natural sediment supplies from upper reaches of the Mekong are insufficient to compensate for the loss of extracted bed aggregates, illustrating the non-sustainable nature of the local sand mining practices.

Assessment of the Impact of Sand Mining on Bottom Morphology in the Mekong River in An Giang Province, Vietnam, Using a Hydro-Morphological Model with GPU Computing

“…SC4A: During this period, alluvial sediment was reduced by two-thirds compared to the previous period [14], and, accordingly, the sediment boundary was also reduced. The calculation results show that the whole study area tended to erode, even at the site of Tan An mine (which has stopped operating), which gradually eroded (see Figures 16f,h).…”

“…The lower Mekong morphology is created by bedrock-controlled and alluvial reaches [12]. There are many causes of continuous and severe erosion in the area, such as excessive sand mining and sediment imbalances leading to erosion [13,14]. The annual extraction, according to the estimation of Bravard et al (2013), is 34 Mm 3 (approximately 54 MT/year for an aggregate density of 1.6 t/m 3 ), featuring mostly (90%) sand and, to a smaller degree, gravel (8%) and pebbles (1%).…”

Long-term sediment decline causes ongoing shrinkage of the Mekong megadelta, Vietnam

“…This declining sediment supply has led to enhanced coastal erosion with high-resolution satellite images from 1993 to 2013 indicating a substantial increase in the last 10 years 12 . Longer-term analysis covering 1973-2015 also confirmed accelerated coastal erosion in the last few decades, particularly after 2005, in response to the increased capacity of hydropower dams in the Mekong's catchment 13 and intensive sand mining in the deltaic channels [6][7][8][9] .…”

“…The Mekong delta, southern Vietnam, is the third largest delta in the world and has been characterized by long-term large sediment supply in its extensive catchment under the influence of the rainy Asian monsoon climate. However, recent anthropogenic catchment disturbances such as upstream hydropower dam construction 4,5 and fluvial sand mining [6][7][8][9] , possibly along with climate change-induced discharge reduction 10 , are considered to have caused severe decline in the sediment discharge to the coast, compounding concerns raised by exacerbated subsidence due to accelerated groundwater extraction 11 and thus leading to alarms being raised regarding the increasing vulnerability of this populous megadelta. This declining sediment supply has led to enhanced coastal erosion with high-resolution satellite images from 1993 to 2013 indicating a substantial increase in the last 10 years 12 .…”

Anthropogenic sediment starvation forces tidal dominance in a mega-delta

“…These declining rates of fluvial sediment supply have been attributed to the effects of shifting tropical cyclonic tracks 31 as well as extensive river impoundment and hydropower development across the Mekong's catchment 18 . Furthermore, sections of the river and its delta have been subject to intensive sand mining, some of which is not regulated 32 , with official statistics alone documenting annual removal rates in excess of 50 Mt yr -1 (33) compared to sand influx rates of 6.2±2.0 Mt yr -1 at the delta apex 20 . As a result, similar to other large deltas such as the Chao Phraya 34,35 , Pearl 36 , Yangtze 37 and Yellow 38 , the Mekong is subject to severe, anthropogenically-driven, sediment starvation, resulting in rapid and extensive channel erosion 39 .…”