A Study on Sand Dune Forms Southeast of Jeddah, Saudi Arabia
W.M. SHEHATA, A.A. SABTAN and M.M. GHAZAL
Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia
JKAU: Earth Sci., vol. 10, A Study on Sand Dune... pp. 91-103 (1419 A.H. / 1998 A.D.)
ABSTRACT.
The drifting sand and dune movement pose serious geohazard on urban development and road construction in the Kingdom of Saudi Arabia.
This fact initiated several research projects in a number of universities and research institutes in the Kingdom.
Two locations of inter mountain dune fields east and southeast of Jeddah were investigated and the dune forms were identified. In addition to the sand sheets, the major dune type is the reversal linear dunes coexisting with few small barchan dunes.
Detailed investigations on the linear dunes indicated that the ultimate direction of movement of the dunes is downwind along their crest line. However, during their migration, the dunes wander laterally in both directions but more in one direction than the other depending on the frequency of the prevailing wind and configuration of the surrounding mountains.
The sand from the two locations was found to be similar in their grain size parameters. Some variations, however, were observed both along the crest line and across the dune body. Mineralogically, the sand reflects the composition of the surrounding igneous, metamorphic and sedimentary rocks. The results of cone penetration tests were used to reconstruct a possible cross section for the linear dune which is slightly different from the existing hypothetical sections.
A reasonable similarity was obtained between the studied dunes and the linear dunes existing in Al Nufud but some differences were found between the sand from these dunes and the other dune forms in Al Jafurah and Ad Dahna sand seas.
The sections of the highways crossing these dune fields are either parallel or intersect the dune crest lines at small angle. The dunes, therefore, pose only minor sand drifting hazard on these highways. A forest is suggested to be established to control this hazard and minimize the waste water ponding problems.
1. Introduction
The eolian sand areas cover approximately one third of the Arabian Peninsula and form an important physiographic province in Saudi Arabia. Sand exists in the form of sand seas in the north (Al Nufud sand sea), in the east (Al Jafurah and Ad Dahna sand seas), and in the south (Al Rub al Khali). In the western part of Saudi Arabia, sand exists as dunes and sand sheets scattered along the Red Sea coast or between the mountains of Tihama along the western part of the Arabian Shield. Since sand poses natural erosional-depositional hazards on the existing structures, roads and urbanized areas, it became necessary to study the behavior of the sand forms in the different parts of the country.
Several investigations have been made on the Nufud sand sea (Whitney, 1981; Whitney et al., 1983; Vincent, 1984), Al Jafurah sand sea (Fryberger et al., 1984; Anton and Vincent, 1986; Shehata et al., 1992), Ad Dahna sand sea (Al-Saud, 1988 and ElNozahy, 1993), and Al Rub al Khali sand sea (McClure, 1978, 1984; Edgell, 1990). Limited studies have been performed on the dunes in the western area (Binda, 1983; Zaidi, 1983), probably because of their limited severity as a natural hazard.
The objectives of this work are to present the dune types, mode of movement and properties of the dune forming sand in the central Tihama area represented by two inter mountain dune fields to the east and southeast of Jeddah. These findings will also be compared with the results of the several investigations performed on Al Jafurah and Al Nufud sand seas. A remedial measure will be suggested to solve the problem associated with the dunes and minimize the hazard related to the existing waste water flow along Jeddah-Taif road.
7. Conclusions and Recommendations
The main sand dune type in the inter-mountain areas in central Tihama is the reversible linear as encountered in two inter mountain dune fields. These dunes follow a winding movement as they move along their crest lines. The reversal nature of the dunes was substantiated by the cone penetration resistance tests and by some of the grain size parameter values.
The mineralogy of the dunes is different than that of the other sand seas and the high percentage of heavy minerals content worth further investigation and economic evaluation. It is also recommended for the engineers to use some of the geological grain size distribution parameters as they better describe the sand.
The mineralogy of the dunes is different than that of the other sand seas and the high percentage of heavy minerals content worth further investigation and economic evaluation. It is also recommended for the engineers to use some of the geological grain size distribution parameters as they better describe the sand.
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