GEOTECHNICAL HAZARDS ASSOCIATED WITH DESERT ENVIRONMENT

The aridity of the Arabian Peninsula's deserts ranges between arid to hyperarid with hot dry climate, scarce precipitation and sparse vegeta tion. These harsh environmental conditions enhance some geomorphologic processes more than others, cause specific geotechnical problems, and increase desertification. From west to east, the general physiography of Saudi Arabia shows the Red Sea coastal plains and the escarpment f oothills called Tihama followed by the Arabian Shield mountains, the A rabian Shelf plateau and finally the Arabian Gulf coastal plains. Sand moves by wind either as drifting sand or migrating dunes in four majo r sand seas, over the Arabian Shelf, and in the inter-mountain valleys , in the Arabian Shield causing problems of erosion and deposition. Hu man activities in the deserts may cause more instability to the sand b odies, enlarging the magnitude of the problem. Fine silty soil particl es also move by wind, depositing loess mainly in selected areas downwi nd in the Tihama. These loess deposits subside and may form earth fiss ures by the process of hydrocompaction upon wetting. The addition of w ater can be either natural through storms or man-made through human ag ricultural or civil activities. Extensive sabkhas exist along the coas tal plains of both the Red Sea and Arabian Gulf. The sabkha soil may a lso heave by salt re-crystallization or collapse by wetting. The shall ow groundwater brines present in sabkhas also attack and corrode civil structures. Urbanization and excessive groundwater pumping may also d eplete the fresh groundwater resources and may cause subsidence, groun d fissuring and surface faulting as observed in some locations in the Arabian Shield. Although the average annual precipitation is very low, rain usually falls in the form of torrential storms, collected by dry valley basins and causing floods to unprotected downstream areas on t he coastal plains of the Red Sea. The desert environment, being a frag ile echo system, needs to be treated with care. Intercommunications be tween different national and international agencies and education of t he layman should help to keep the system balanced and reduce the resul ting environmental hazards. In addition, any suggested remedial measur es should be planned with nature and engineered with natural materials .