Aeolian sediment transport on a beach: Surface moisture, wind fetch, and mean transport

摘要: Abstract Temporal and spatial changes in wind speed, direction, moisture content are ubiquitous across sandy coastal beaches. Often these factors interact unknown ways to create complexity that confounds our ability model sediment transport at any point the beach as well capacity predict delivery into adjacent foredunes. This study was designed measure flow over a foredune Greenwich Dunes, Prince Edward Island National Park, with express purpose of addressing complex interactions. Detailed measurements reported for one stormy day, October 11, 2004, during which meteorological conditions were highly variable. Wind speed ranged from 4 ms − 1 20 ms , direction oblique varying between 60° 85° shore perpendicular, sand surface minimum about 3% (by mass) complete saturation depending on precipitation, tidal excursion, storm surge progressively inundated beach. The data indicate short-term variations (i.e., minutes hours) this arise predominantly because is expected, but also precipitation intensity, tide level. Even slight increases capable driving more intense saltation events, relationship mediated by other characteristically narrow As angle approach becomes oblique, fetch distance allows greater opportunity system evolve toward an equilibrium state before reaching Whether theoretically-predicted maximum rate ever achieved depends character (e.g., grain size, slope, roughness, vegetation, content) various attributes field average unsteadiness, angle, compression, boundary layer development). Moisture widely acknowledged important factor controlling release surface. All things being equal, wet lesser than dry On beach, effect has two influences: (a) temporal sense, typically decreases association rainfall when drying takes place; (b) spatio-temporal shoreline excursions associated nearshore processes (such wave run-up, surge, excursions) have constraining geometry beach—i.e., narrowing width Because saturated surfaces, such found swash zone, will only reluctantly yield sediments aeolian entrainment, available can occur narrower sea inundates Under constrained conditions, begins shut down unless (thereby increasing distance). In study, usually measured mid-beach rather upper closer foredunes). unusual finding likely internal development yields decrease near-surface (and hence, capacity) landward direction. Although recognized fluid mechanics literature, shear stress by-product developing downwind not been adequately investigated context geomorphology.