The Effect of a Single Shrub on Wind Speed and Nabkhas Dune Development: A Case Study in Kuwait

Jasem M Al-Awadhi

doi:10.4236/ijg.2014.51004

Abstract

Thirty coastal nabkhas were selected for morphometrical measurements. The studied nabkhas were mostly elongated, with an average total length of about 12.9 m, an average width of 3.4 m, and an average height of 1.2 m. Optical porosity of nabkha shrub crown was measured and no apparent relationship with the horizontal size of trapped wind laden sand was found. A simple wind tunnel experiment was carried out to investigate the horizontal wind-flow distribution across a pro-typed shrub. The results of the experiment revealed that the degree of wind sheltering might extend up to a downwind distance approximately equal to 4.5 times the height of the shrub, where an effective velocity recovery started.

Highlights

Nabkha is a type of Aeolian landforms, which is commonly developed as a result of sand accumulation around coastal and desert shrubs [1]
The study area is well described by Al-Awadhi and Al-Dousari [13]. Another attempt was made to investigate the effect of shrub crowns porosity (p) of nabkhas on the horizontal dimension of sand trapped using image processing technique built in PAX-it software
Nabkha dunes are formed as a result of significant variations in wind velocity caused by the interaction of the shrub with airflow carrying Aeolian sand

Summary

Introduction

Nabkha is a type of Aeolian landforms, which is commonly developed as a result of sand accumulation around coastal and desert shrubs [1]. Other important factors controlling nabkhas morphology include type of sediment supply and climate [5] as well as the porosity of the shrub crown (e.g., [2]). Grant and Nickling [9] carried out a field study to investigate the effect of vegetation porosity (leaf density) on the drag coefficient of small conifer trees (1.4 m in height). More than 50% of the Kuwait surface is covered by 13 mobile sandy bodies These are continually drifted along the surface by wind, mainly during the summer season (May to September), to form different land forms including coastal nabkhas [12]. To provide a better understanding of the mechanism of nabkha development, this paper discusses the results of the horizontal windflow distribution across a pro-typed shrub, obtained from a wind-tunnel experiment and supported by field measurements of horizontal size of trapped wind laden sand.

Materials and Methods

Morphometrical Parameters of the Studied Nabkhas

Wind Flow Pattern across a Shrub

Discussions

Findings

Conclusions