Anisotropic flow resistance theory and experimental verification on partially submerged crop vegetation

The presence of orderly arranged rows and spacing of crop vegetation increases the anisotropy of the Earth's surface, and affects the resistance of the surface to overland flow. However, few studies have addressed how the orderly arrangement of crop vegetation affects the resistance of the surface to overland flow. In the present study, we consider that flow resistance has anisotropic attributes. We have also performed a flow resistance experiment using rigid and simulated partially submerged crop vegetation. The simulation replicated water flow in different directions over the same crop vegetation and overland surface. The angles of flow direction and the crop rows were arranged as 15 °, 30 °, 45 °, and 90 °. The results show that the flow resistance of partially submerged crop vegetation is composed of surface resistance n_s and vegetation resistance n_p. Vegetation resistance n_p is linearly proportional to the submerged vegetation height h, and the proportionality coefficient α (Δn/Δh) varies with the angle θ of the flow direction and the crop rows under the same water depth conditions, n₁₅ > n₃₀ > n₄₅ > n₉₀. Further regression analysis revealed that the relationship between the coefficient α and vertical projection width of crop stems in the flow direction is a power function.