Quantifying Sand Transport Sensitivity to Dune Shape: Field-Validated CFD with AirSketcher

Coastal dune management often alters crest and lee geometry, yet quantifying the transport impact of small shape changes is difficult without heavy models. This paper presents a streamlined, field-anchored CFD workflow (AirSketcher) that ingests a side-profile image, auto-detects the dune outline, and computes near-surface flow. A neutral ABL power law inlet (𝛼 = 0.16) is applied consistently across scenarios; turbulence is closed with a one-equation eddy-viscosity model. Model skill is established against multi-height mast measurements at Tomahawk Beach (Dunedin, NZ): height-matched profile correlations are strong (𝑟2 ≈ 0.985, 0.968, 0.840, 0.951), and the solver reproduces stoss speed-up, crest amplification, and lee-side recovery. For design comparison, a geometry-aware transport proxy is formed as a cubic line-integral of speed along a near-surface polyline (Bagnold-type scaling). Three shapes are evaluated under the validated wind: baseline, top-cut, and back-cut. Integrated proxies (∫ 𝑈3 d𝑠) are 804,446, 667,430, and 484,779 m4 s−3, implying ≈ −17% (top-cut) and ≈ −40% (back-cut) vs. baseline. Flow patterns explain the reductions—crestpeak attenuation, muted lee jets, earlier reattachment—concentrating deposition nearer the crest, especially for the back-cut. The approach offers a rapid, interpretable metric for screening dune modifications before committing to fully coupled morphodynamic modeling. Keywords— Coastal dunes; CFD; Aeolian transport; dune shape; morphodynamics; wind flow modeling; AirSketcher