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Coupled morphodynamic and hydrogeologic modeling for evaluating the salinization of groundwater resources in coastal deltas resources in coastal deltas
Anthropogenic activities associated with climate change and urbanization in coastal deltas (i.e.
groundwater extraction, coastal engineering and urban loading) have resulted in freshwater
degradation through the upwelling of saline paleowater. Factors controlling the preservation of
paleowater, and the initiation of exfiltration and subsequent upwelling of saline water are not yet
well understood. This research uses coupled morphodynamic-hydrogeologic modeling to
evaluate the groundwater response to geomorphic change. Delft3D is used to model the
formation of coastal deltas throughout the Holocene and create generic three-dimensional
distributions of sediment deposits characteristic of fluvial, wave, and tidal dominated deltas. The
generated sediment deposits are used to create three-dimensional effective grain-size maps by
convoluting the spatial distribution of each grain-size. This accounts for the combined effect of
multiple grain-sizes while preserving basin-scale heterogeneity commonly seen in highly
heterogeneous depositional environments. The effective grain size maps are used as the
geologic input for density-dependent groundwater flow and solute transport modeling. Results
are expected to show that the degree of aquifer heterogeneity correlates to the balance of fluvial
and marine morphological forces shaping sediment deposition. Spatial variability in basin-scale
aquifer heterogeneity is anticipated to control the exfiltration and upwelling patterns of saline
paleowater in deltaic environments. The modeling approach taken in this research is novel and
allows for the investigation of evolving groundwater systems with changes in landscape. Results
of this study will allow for the assessment of delta vulnerability to freshwater degradation from
upwelling saline paleowater, based on morphological classification. In the future, this research
may be used to help determine which deltas are most at risk for salinization and where science
and engineering efforts can be most beneficial to society.
