How Obstacles Create Sand Dunes: Wind Disruption and Deposition

Obstructions—vegetation, rocks, fences, buildings—are catalysts for dune initiation and shaping. They manipulate wind flow to accumulate sand.

Mechanisms

Flow Disruption & Deposition: Wind slows on the windward side, dropping sand. This forms a nucleus.

Lee-Side Eddies: Vortices in the wake lift and transport sand to the leeward side, building the dune's slip face.

Windward Accumulation & Avalanching: Sand piles on the windward slope until it exceeds the angle of repose (~34°), then avalanches down the lee face, advancing the dune.

Sand Trapping: Obstacles act as fences; sand drifts around and over them, elongating the deposit.

Flow Deflection: Alters local wind direction, creating secondary deposition zones that shape dune orientation (transverse vs. longitudinal).

Obstacle Type Matters

• Isolated bushes → coppice dunes (mounds).
• Linear ridges → longitudinal dunes.
• Fences → artificial foredunes for coastal protection.

Without obstacles, sand sheets migrate uniformly. Obstacles break symmetry, creating the dune field's architecture. This principle is used in desert stabilization and coastal management.