EXPERIMENTAL TIDE-DOMINATED DELTA EVOLUTION: MORPHOLOGIC RESPONSE TO SEA-LEVEL RISE AND NET DEPOSITION

The effect of sea-level variation on ancient deltas has generally been interpreted by stratigraphic analysis and provides insight as to how these systems respond to allogenic forcing. However, inherent in the natural sedimentary record are uncertainties associated with, for example, missing strata, unknown forcing conditions, and multiple superimposed effects. As modern day deltas are some of the most populated places on the planet, understanding their response to relative sea-level (RSL) rise is critical. Using an experimental basin, we investigated tide-dominated deltas (TDD) with varying sediment supply conditions under a steady base level-rise. We carried out three experiments using different parameters for tidal and fluvial input to better define their mutual influence on TDD evolution. Qualitative analysis of the delta profiles proved that the experimental setup reproduces numerous features typically observed in TDD stratigraphy such as tidal ravinement surfaces and slope-break trajectories. Shoreline position measured from high resolution DEM data shows that tides can enhance marine transgression when fluvially supplied sediment is limited. Conversely, shoreline retreat is slowed overall when sediment supply is increased to counterbalance base-level rise. Discretizing a TDD into areas of varying tidal and fluvial influence shows disparity in shoreline migration across these zones. Finally, we developed two methods to quantify how a TDD subjected to RSL rise evolves through time. Both methods were able to capture the observed depositional variance between tidal- and fluvial-dominated zones. Despite the erosional behavior of tides, sharpened by the lack of both organic deposition and longshore sediment transport, results show that a sufficiently high sediment input can counterbalance the effect of RSL rise.