**3. Geological and geomorphological framework**

According to Monnier and Guilcher, the morphological setting is characterized by the Tihamah littoral plain with a maximum width of 40 km, located at the foot of the highly dissected Precambrian granitic mountains of Alhijaz whose peaks reach several hundred meters. The plain is surmounted by a crest of basalts forming part of a set of castings called harrats (lava flows today in inversion of relief), coming from mouths located at a hundred kilometers inside and going back to the old Pleistocene based on their stratigraphic relations [5] in [6]. The existence of geomorphological phenomena related to the eustatic variations of the Red Sea during the Pleistocene is noted. The stability (or geological instability) of the coastal plain is related to the earthquakes associated with the formation of the Red Sea. Most faults, diaclases, and cracks take parallel and orthogonal directions to the Red Sea. Hydrologically, there are 24 watersheds in the context of the flooded area. Sixteen watersheds are directed toward the city of Jeddah to the west, and the rest flows in a southwesterly direction toward the great valley of *Wadi* Fatimah [7].

The study area is composed of Precambrian-Cambrian formations, overlain by a succession of Cretaceous-Tertiary sedimentary rocks and Tertiary-Quaternary basaltic lava flows and Quaternary-to-recent alluvial deposits (**Figure 3**).

**Figure 3.** *Geological map of Jeddah city.*

Volcanic lava tongues are associated with lineaments and ancient valleys. These lava formations follow the tracks of the paleovalleys and the direction of the movement of the water. The presence of volcanic languages and Quaternary sediments plays an important role in locating the population and human activities following the presence of springs and loose and fertile soil. The deltas of coastal *wadis* are affected by agricultural activities along the Red Sea coastal plain. **Figure 4** shows the geomorphological and topographic contexts of the city of Jeddah. This figure shows that the city extends on the outlet of several *wadis*, which in spite of the urbanization take back their old courses during strong and intense precipitations. Jeddah has developed all over the coastal plain and beyond, disrupting the normal flow of water.

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**Figure 6.**

**Figure 5.**

*Methodology of the study—Different stages of treatment.*

*Flood Risk and Vulnerability of Jeddah City, Saudi Arabia*

Remote sensing is a crucial tool for researching submersion areas and for assessing natural hazards. The present study is based on the processing of multisource and multidate satellite data, supplemented by cartographic documents and field observations. These different data were integrated in the same mapping projection system before proceeding to a series of digital treatments: digitalization, color composition, improvement, combined classifications using image texture, and fusion. **Figure 5** shows the different stages of treatment. Rainfall statistics were also used.

*Extract from Landsat ETM+ of February 1, 2011. There are only a few small water bodies (circled in yellow).*

*DOI: http://dx.doi.org/10.5772/intechopen.82073*

**4. Materials and methods**

**Figure 4.** *Geomorphological and topographic contexts of Jeddah city.*
