 |
| Titel |
Effect of environmental change on the morphology of tidally influenced deltas over multi-decadal timescale |
| VerfasserIn |
Balaji Angamuthu, Stephen Darby, Robert Nicholls |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250140742
|
| Publikation (Nr.) |
 EGU/EGU2017-4171.pdf |
|
|
|
|
|
| Zusammenfassung |
| An understanding of the geomorphological processes affecting deltas is essential to improve
our understanding of the risks that deltas face, especially as human impacts are likely to
intensify in the future. Unfortunately, there is limited reliable data on river deltas, meaning
that the task of demonstrating the links between morphodynamic and environmental change
is challenging. This presentation aims to answer the questions of how delta morphology
evolves over multi-decadal timescales under multiple drivers, focussing on tidally-influenced
deltas, as some of these, such as the Ganges-Brahmaputra-Meghna (GBM) delta are heavily
populated. A series of idealised model simulations over 102 years were used to
explore the influence of three key drivers on delta morphodynamics, both individually
and together: (i) varying combinations of water and sediment discharges from the
upstream catchment, (ii) varying rates of relative sea-level rise (RSLR), and (iii)
selected human interventions within the delta, such as polders, cross-dams and
changing land cover. Model simulations revealed that delta progradation rates are more
sensitive to variations in water discharge than variations in fluvial sediment supply.
Unlike mere aggradation during RSLR, the delta front experienced aggradational
progradation due to tides. As expected, the area of the simulated sub-aerial delta
increases with increasing sediment discharge, but decreases with increasing water
discharge. But, human modifications are important. For example, the sub-aerial
delta shrinks with increasing RSLR, but it does not when the sub-aerial delta is
polderised, provided the polders are restricted from erosion. However, the polders are
vulnerable to flooding as they lose relative elevation and can make the delta building
process unsustainable. Cross-dams built to steer zones of land accretion within the
delta accomplish their local goal, but may not result in net land gain at the scale
of the delta. Applying these results to the contemporary GBM delta implies that
cross-dams and polders have been a key control on the morphodynamic evolution
of the GBM delta over the last 60 years. However, with increased fluvial water
discharge and rates of RSLR likely under greenhouse gas (GHG) -driven warming, the
continuing use of sediment starved polders will only increase the vulnerability
of poldered areas from regular flooding, and eventually may lead to catastrophic,
permanent, inundation of the land. Hence, the future trend of morphological evolution of
the GBM delta depends on local human intervention, including measures to raise
the elevation of the land to cope with the continuing trend of RSLR and varying
fluvial discharges. The model findings provide a basis to establish guidelines for
planned future management interventions to prevent the delta from destruction. |
|
|
|
|
|
|