Negative Diffusivity of Shorelines via the Littoral Drift Rose Concept

Abstract

Conventionally, long-term coastline evolution is usually described using the diffusion equation. Particularly, the diffusion coefficient, ε, is a function of the wave angle: this implies that the diffusivity can assume negative values when wave angles are >45°. The negative-diffusivity concept is often unfamiliar to engineers; therefore, the main purpose of this study is to further investigate its possible implications on shoreline evolution. Practically, negative diffusivity leads to the instability of the coast: any existing perturbation indefinitely grows, and periodic fluctuations of the coast (sand waves) are detected. This research will document the presence of unstable behaviors in some areas of the Adriatic coast, corroborated by the concept of Littoral Drift Rose (LDR).

Keywords

• negative diffusion
• Littoral Drift Rose
• one-line theory