VOGEL, S.; Duke Univ. : Drag reduction by aquaplaning in broad leaves during floods

Leaves of an especially flood-tolerant, forest-floor plant, Hexastylis arifolia, were subjected to rapid water movement at shallow depths to approximate sheet flow conditions during flooding. When held by the basal ends of their petioles, 20 mm down, leaves surfaced, apparently through hydrodynamic lift, and aquaplaned, with very low drag relative to surface area. Held deeper, they curled into cones, with higher, although still relatively low drag. Whether aquaplaning or submerged, both measured and extrapolated drag remained well below petiole breaking strength as measured with a tensometer. Leaves of some other plants that might occasionally feel sheet flow behaved similarly; most had upwardly curved basal blade lobes and fairly long petioles. But leaves from trees with similar basal lobes and long petioles could not be persuaded to aquaplane. Significance of the low drag during aquaplaning remains uncertain, since petiole and attachment strength should suffice even without it, and since flooding with sheet flow will be only a rare event for most of these plants.