Figure 14.  Wind flow over an embryo dune.  From measurements of wind velocity, the heights above the sand surface at which the wind reached the horizontal velocities from 0-10 m/sec were calculated.  In the central region of the transect, a reversal of the direction of air movement was noted and is represented as a negative velocity (-2 m/sec).  The topography and the position, height, and density of the dune grasses are depicted (from Willis et al. 1959).