Sand transport and deposition within arrays of non-erodible cylindrical elements

Abstract

The study concerns sand deposition within a regular array of vertical cylinders placed in the path of a sand-laden wind. Twelve wind tunnel experiments using three preselected shear velocities (28Á78, 32Á86 and 45Á1 cm s À1 ), with associated rates of sand feed (0Á3, 2Á0 and 3Á8 g cm À1 s À1), and four roughness element concentrations (! = 0Á046, 0Á092, 0Á184 and 0Á369) were carried out to evaluate the factors that affect sand deposition and sand flux in the presence of immobile rough elements. The measurements showed that as the concentration of non-erodible elements increased, the percentage reduction in the initial sand flux increased and a particularly sharp reduction occurred when ! ! 0Á18. The pattern of reduction was found to be q red = q eq (d/H) [Áy/(ÁyÀd)](0Á68 À3Á5!) when ! 0Á18, and q red = q eq (d/H)[Áy/(ÁyÀd)](0Á025) when ! b 0Á18, where q eq is the equilibrium rate of sand transport arriving at the best bed, d is the diameter of the cylinder, H is the height of the cylinder, and Áy is the width of unit area associated with a cylinder.The experimenal results also showed that the sand flux downstream of the array started to increase immediately upon the commencement of burial of the array's cylinders. Thus the sand deposition and sand flux along an array consisting of regularly distributed, non-erodible elements were shown to be neither uniform nor steady.

Large roughness element effects on sand transport, Oceano Dunes, California

“…() (their figure 7) and the Oceano data, the element height effect on transport efficiency can be demonstrated. For λ = 0·022, the NSF and λ relationship for the Al‐Awadhi and Willetts () (average element height = 0·035 m) and Lancaster and Baas () (average element height = 0·1 m) data sets, would predict essentially no measureable effect of element height on sand transport efficiency. For the Gillies et al .…”

“…Field and wind tunnel data measurements of sand transport through roughness that is on the order of a few centimeters (Al‐Awadhi and Willetts, ) to tens of centimeters in height (e.g. Lancaster and Baas, ; Gillies et al ., ) have revealed that the reduction in sand transport scales as a power function of the roughness density ( λ ), which is defined as: where n is the number of elements, b the element breadth, h the element height, S the area of the surface that contains all the elements.…”

Variation in bed level shear stress on surfaces sheltered by nonerodible roughness elements

“…Validation of the model (Figure 2) has been carried out in numerous field and lab studies, as by, for example, McKenna‐Neuman and Nickling [1995], Nickling and McKenna‐Neuman [1995], Musick et al [1996], Wolfe and Nickling [1996], Grant and Nickling [1998], Sterk et al [1998], Al‐Awadhi and Willetts [1999], Crawley and Nickling [2003], and Wyatt and Nickling [1997]. While the basic form of the model has been widely adopted, its parameterization remains controversial and challenging to carry out in practice [ Crawley and Nickling , 2003], with reported measurements for m ranging from as little as 0.16 for sparse shrubs [ Wyatt and Nickling , 1997] to values possibly in excess of 1 for a developing lag surface [ Nickling and McKenna‐Neuman , 1995].…”

Experimental Study of Blown Sand in a Vegetated Area

“…Artificial plants with complicated shapes and varying flexibility were employed in this study, whereas simple stick-type plant models without flexibility were employed in previous studies (e.g., AL-AWADHI and WILLETTS, 1999;MUSICK, TRU-JILLO, and TRUMAN, 1996;TSUJIMOTO and NISHIZAWA, 1999). Simulations of Calystegia soldanella and Carex kobomugi plants, which grow on sandy beaches, were adopted as flexible vegetation models in addition to stick-type models (see Figure 2).…”