Experimental study of wind directional variability in the vicinity of a model valley

This paper reports the results of a preliminary study examining the effects of valley presence on airflow direction and focuses on valleys situated in areas of low relief. Wind tunnel experiments are used to visualise near-surface airflow over a series of models representing valleys oriented at different angles to mean airflow. Results indicate that the presence of a valley has no significant influence on airflow direction when the approach angle of the wind is perpendicular to the valley strike. However, any wind approach-angle less than 90 degrees is found to cause marked deflection of airflow to become more parallel to the valley. Analogies can be drawn between the surface streamlines recorded on the negative terrain of the valley models and those around positive terrain such as hills. A discussion of air pressure perturbation over both positive and negative terrain concludes that valley structures can have a significant effect on overlying synoptic windflow. The nature and magnitude of this effect is dependent upon a complex range of environmental parameters including valley morphometry, wind speed and the thermal stability of the airflow. The findings outlined have implications for the development of aeolian bedforms and processes of aeolian sedimentation in the vicinity of valleys. (C) 2000 Elsevier Science B.V. All rights reserved.