Aerodynamic roughness length of sandy beds and gravel beds

A physical model was developed for the aerodynamic roughness length of gravel beds and sandy beds under different atmospheric stability conditions based on Monin?CObukhov similarity theory and dimensional analysis. The relationship between the roughness length, the properties of the roughness elements, the characteristics of the airflow, and an atmospheric stability parameter (the bulk Richardson number) was then studied using the model. Results showed that the roughness length was not only functions of the shape, height, and coverage of the roughness elements and of the airflow, but also dependent upon atmospheric stability. These results were in agreement with results from wind tunnel experiments and field observations.