Geomorphology of Jeddah Governate, with emphasis on drainage systems

الملخص EN

Jeddah Governate comprises three distinct geomorphological zones ; the Red Sea and shore features, the coastal plain, and coastal hills and pediments.

The last zone lies east of the municipal Jeddah city and consists of low lying hills, and an elongated N-S oriented depression, forming a basin that lies within the coastal hills.

The Red Sea displays landforms that characterize prograde shorelines ; implying that the Red Sea is recently in regression.

Such features include flat lying sandy beaches, lagoons, sabkhas, sea islands, bars and spits, as well as the raised dead coral terraces and marine limestones exposed inland.

The drainage in the area consists of a large number of systems twelve of which were considered to be major systems that were delineated, described and analyzed morphometrically.

These systems are, from north to south : Wadi Al-Kura’, Wadi Muraygh and Wadi Ghuraiyah, Wadi Um Hablayn, Wadi Burayman, Wadi Hutayl, Wadi Bani Malik, Wadi Mirayyikh, Wadi Quwayzah, Wadi Ushayr, Wadi Ghulayl, Wadi Al-Khumrah and Wadi Fatimah.

All of these systems drain westwards towards the Red Sea, except Wadi Fatima that abruptly diverts direction to the north at its lower course along the coastal plain and this could be attributed to active faulting.

A large number of wadi channels, both major and minor, terminate within the coastal plain at a distance from the Red Sea shore.

This phenomenon could be attributed to one or more factors, such as active neotectonics, human activities and shore drift.

Almost all of the drainage systems in the area exhibit parallel patterns along the coastal plain, whereas they display dendritic to subdendritic and radial pattern upstream.

The drainage density of the wadi systems varies in the previously mentioned geomorphologic zones of Jeddah Governate, being the highest along the coastal hills zone.