The effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach

This paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement, intensity of sand transport by wind and mass flux. The experiment was carried out over a period of five weeks at Greenwich Dunes, Prince Edward Island, Canada in May and June 2002. Moisture content was measured with a Delta-T moisture probe over a 50 m by 25 m grid established on the beach. Measurements of wind speed and direction were made with arrays of cup anemometers and a two-dimensional sonic anemometer. Transport intensity was measured at a height of 2–4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal. Anemometers and saltation probes were sampled at 1 Hz. Sand transport was measured with vertical integrating sand traps over periods of 10–20 minutes. Results show that where there is a considerable supply of dry sand the saltation system responds very rapidly (1–2 s) to fluctuations in wind speed, i.e. to wind gusts. Where sand supply from the surface is limited by moisture, mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent. Threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch, but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind. Mass flux increases with increasing fetch length and the relationship is described best by a power function. Further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance. Copyright © 2007 John Wiley & Sons, Ltd.

[1]  Andrew Baird,et al.  Inter-tidal Dynamics of Surface Moisture Content on a Meso-tidal Beach , 2001 .

[2]  Z. Dong,et al.  The blown sand flux over a sandy surface: a wind tunnel investigation on the fetch effect , 2004 .

[3]  R. Davidson‐Arnott,et al.  Rapid Measurement of Surface Moisture Content on a Beach , 2005 .

[4]  Wim Cornelis,et al.  The effect of surface moisture on the entrainment of dune sand by wind: an evaluation of selected models , 2003 .

[5]  Bernard O. Bauer,et al.  A general framework for modeling sediment supply to coastal dunes including wind angle, beach geometry, and fetch effects , 2003 .

[6]  R. Bagnold,et al.  The Physics of Blown Sand and Desert Dunes , 1941 .

[7]  R. Davidson‐Arnott,et al.  The effect of wind gusts, moisture content and fetch length on sand transport on a beach , 2005 .

[8]  D. Gillette,et al.  CAUSES OF THE FETCH EFFECT IN WIND EROSION , 1996 .

[9]  W. Cornelis,et al.  A Parameterisation for the Threshold Shear Velocity to Initiate Deflation of Dry and Wet Sediment , 2004 .

[10]  K. Nordstrom,et al.  Effect of source width and tidal elevation changes on aeolian transport on an estuarine beach , 1992 .

[11]  R. Davidson‐Arnott,et al.  Measurement and Prediction of Long-Term Sediment Supply to Coastal Foredunes , 1996 .

[12]  R. Davidson‐Arnott,et al.  Topographic Steering of Alongshore Airflow over a Vegetated Foredune: Greenwich Dunes, Prince Edward Island, Canada , 2006 .

[13]  P. Belly,et al.  Sand movement by wind , 1964 .

[14]  K. Nordstrom,et al.  Aeolian transport of sediment on a beach during and after rainfall, Wildwood, NJ, USA , 1998 .

[15]  A. Baas.  Evaluation of saltation flux impact responders (Safires) for measuring instantaneous aeolian sand transport intensity , 2004 .

[16]  William G. Nickling,et al.  The initiation of particle movement by wind , 1988 .

[17]  Ian J. Walker,et al.  Flow dynamics over a foredune at Prince Edward Island, Canada , 2005 .

[18]  Andrew Baird,et al.  Thresholds of aeolian sand transport: establishing suitable values , 2004 .

[19]  C. Neuman,et al.  A wind tunnel study of the influence of pore water on aeolian sediment transport , 1998 .

[20]  K. Horikawa,et al.  SAND TRANSPORT BY WIND ON A WET SAND SURFACE , 1984 .

[21]  Thomas J. Jackson,et al.  Calibration and modification of impedance probe for near surface soil moisture measurements , 2004 .

[22]  P. D’Odorico,et al.  On the effect of moisture bonding forces in air‐dry soils on threshold friction velocity of wind erosion , 2006 .

[23]  D. Sherman,et al.  A Review of the Effects of Surface Moisture Content on Aeolian Sand Transport , 1995 .

[24]  William G. Nickling,et al.  Wind tunnel evaluation of a wedge-shaped aeolian sediment trap , 1997 .

[25]  J. N. Svasek,et al.  Measurements of sand transport by wind on a natural beach , 1974 .

[26]  Cheryl McKenna Neuman,et al.  Measurement of water content as a control of particle entrainment by wind , 2006 .

[27]  K. Nordstrom,et al.  Effects of time-dependent moisture content of surface sediments on aeolian transport rates across a , 1997 .

[28]  William G. Nickling,et al.  A THEORETICAL AND WIND TUNNEL INVESTIGATION OF THE EFFECT OF CAPILLARY WATER ON THE ENTRAINMENT OF SEDIMENT BY WIND , 1989 .

[29]  A. Baas,et al.  Formation and behavior of aeolian streamers , 2005 .

[30]  Andrew Baird,et al.  The dynamic effects of moisture on the entrainment and transport of sand by wind , 2004 .

[31]  D. Wal.  Effects of fetch and surface texture on aeolian sand transport on two nourished beaches , 1998 .

[32]  J. Stout.  Effect of averaging time on the apparent threshold for aeolian transport , 1998 .

[33]  R. Davidson‐Arnott,et al.  SPATIAL AND TEMPORAL VARIABILITY IN INTENSITY OF AEOLIAN TRANSPORT ON A BEACH AND FOREDUNE , 2003 .