Validation of a reduced-complexity numerical model for resolving deltaic dynamics : internal consistency and morphodynamics

Abstract

River deltas are fragile ecosystems that have immense ecological, economic, and social importance. The ability to understand them is facilitated by numerical models that can resolve the complex hydrodynamics and morphodynamics of deltas. DeltaRCM is one such model, and to validate its behavior, internal consistency is tested with variable input parameters; results indicate realistic growth with predictable patterns. The morphodynamics are tested against experimental and real deltas with the use of metrics: specifically, delta growth metrics like shoreline-to-area ratio and relative shoreline roughness, channel overlap, and avulsion behavior. DeltaRCM performs very well when compared to real systems with growth rate and relative shoreline roughness, and fairly well for shoreline-to-area ratio. The channel overlap metric suggests DeltaRCM displays a slightly higher degree of channel stability than an experimental delta, though the general trend of memory decay remains the same. A similar link exists between DeltaRCM and reality for the wetted fraction, in that general trends are similar but comparison breaks down at finer scales. Furthermore, based on DeltaRCM results, wetted fraction is an imperfect tool for determining avulsion timescale. A new metric, the sedimentograph, is introduced as a way of describing delta growth at the subsurface level; DeltaRCM gives reasonable results for this metric, though comparison to real systems is difficult.