The role of sedimentation and natural compaction in a prograding delta: Insights from the mega
Mekong delta, Vietnam
C. Zoccarato, P. Teatini
Dept. of Civile, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
P. S. J. Minderhoud
Utrecht University, Physical Geography, Utrecht, The Netherlands
ABSTRACT
The Vietnamese Mekong Delta was formed by rapid transgression during the second half of the
Holocene by deposition of mainly unconsolidated, fine-grained (clayey) sediments undergoing high
compaction rates. The natural subsidence can seriously impact the already vulnerable delta plain as its
low elevation exposes the delta to global sea level rise, flooding, salinization. Human activities such as
groundwater pumping, infrastructural loading, sand mining and dam construction have exacerbated
the effects of natural consolidation. Here we present a novel modeling study that has allowed to
reproduce the formation and evolution of the Mekong delta over the past 4000 years. Using an adaptive
finite-element mesh, the model properly simulates accretion and natural consolidation characterizing
the delta evolution. Large soil grain motion and the delayed dissipation of pore-water overpressure are
accounted for. We find that natural compaction of Holocene deposits following delta evolution exceeds
predicted values of absolute sea level rise. The unprecedented high rates (up to ~20 mm/yr) threaten
the lower delta plain with permanent inundation and inevitably reduce the designed service life of
flood defense structures along the coast. Total subsidence and sediment delivery to the delta plain will
determine its future elevation and vulnerability to relative sea level rise.
