*GIS and Statistical Evaluation of Fluoride Content in Southern Part of Upper Rasyan Aquifer… DOI: http://dx.doi.org/10.5772/intechopen.91329*

sediments). In the west of the country, the sedimentary sequence is covered by Yemen volcanic (Cenozoic volcanic) [18]. The study area occupies the southwestern corner of the Arabian Shield, and the geological complexity of the region is mainly due to its position at the junction of the Red Sea and the Gulf of Aden rift systems. Geological map and geological cross sections for the study area were derived from the geological map of the upper Wadi Rasyan, scale 1: 100,000; that prepared by Dar Yemen Consulting Company [19]. As shown in **Figure 7**, the geomorphology of the study area is dominated by the tertiary volcano that covers most of the region.

Geomorphology of the study area was characterized as modern rock units, which was formed during the Cenozoic (Cenozoic volcanic group), which was formed by a series of eruptions and volcanic eruptions that were affected by Yemen in general and the province of Taiz, especially during the third geological age as a result of movements of the successive continental shelf separation tectonics along the fault line of large expanses of the Gulf of Aden, in the southern Dead Sea to north and the emergence of the Red Sea gorge and the separation of the Arabian plate from the African plate where it was accompanied by the emergence of streaks parallel to the axis of the Red Sea, which represented the levels of weakness and

**Figure 7.** *Geomorphology of study area (the source of basic map [19]).*

**Figure 8.** *Geology faults in the study area (the source of basic map [19]).*

area are illustrated in **Figures 5** and **6**. From the hydrology map of the study area, we found that the watershed drainage (the hydrology system) in the study area is dendritic and the direction of water surface is into the north-west corner of the study area. Based on hydrological characteristics, the study area has been divided

.

.

The geology of Yemen is a part of the Arab Shield which consists of a Proterozoic

.

3.Al-Burayhi and Hedran sub-basin (Central sub-basin) has 214 km<sup>2</sup>

crystalline subsoil covered by a Paleogene sedimentary sequence (Mesozoic

into three main sub-catchment area or sub-basins as shown below:

1.Al-Hawban sub-basin has 146 km<sup>2</sup>

*Main valleys and its tributaries in the study area.*

**Figure 6.**

**128**

**Figure 5.**

*Resources of Water*

*Hydrology system in the study area.*

2.Al-Dhabab sub-basin has 112 km<sup>2</sup>

*3.1.4 Geomorphology and geology of the study area*

#### **Figure 9.**

Alluvial aquifers form the highest and shallow aquifers in the region. These sediments exist along the Wadis path (**Figure 6**). The total thickness rarely exceeds 30– 40 m, but they can locally reach considerable thicknesses (up to 70 m). Hydraulic properties vary from site to other. Intergranular groundwater flow is dominant [19]. Volcanic aquifers consist of the tertiary volcanic sequence. The thickness of this sequence may exceed 600–700 m. Groundwater flows mainly in this type of aquifers through the cracks/faults. The sandstone aquifer includes Tawilah Sandstone, Southwest of the study area (Al-Dhabab), and this formation is soaked to an expected depth of more than 500 m. In general, sandstone is largely silicified and fractured, so that the dominant groundwater flow in this aquifer is of intergranular type and mixed

*GIS and Statistical Evaluation of Fluoride Content in Southern Part of Upper Rasyan Aquifer…*

Groundwater aquifers in the study area are recharged by many sources of water,

1. In Al-Hawban sub-basin, the aquifers are recharged with rainwater (either pure or loaded with wastewater that is disposed of in floodwaters), wastewater disposed of in sewers, industrial wastewater in the eastern part of the sub-

2. In Al-Burayhi and Hedran sub-basin, the aquifers are recharge with the floods coming from the Al-Hawban sub-basin that loaded with liquid and solid waste types, domestic wastewater that is transported from the city of Taiz across the sewerage network is deposited in sedimentation ponds in this sub-basin, wastewater used to irrigate crops in this sub-basin, irrigation water, which goes downloaded with high concentrations of salts, sedimentation ponds for industrial wastewater in the western part of the sub-basin, the floods that coming from the Al-Dhabab sub-basin to the south-west of the Al-Burayhi and Hedran basin, these floods reach the Al-Burayhi and Hedran sub-basin, which is mostly pure but soon to be contaminated by the remnants of industrial

3. In the Al-Dhabab sub-basin, rainwater is almost the only source of recharge for

activities located west of the Al-Burayhi and Hedran sub-basin.

fracture. The quality of this aquifer is excellent to good [19].

*Cretaceous Tawilah sandstone in the study area (the source of basic map [19]).*

*DOI: http://dx.doi.org/10.5772/intechopen.91329*

basin where there is an industrial food complex.

*3.1.5.1 Groundwater recharge*

the aquifers.

**131**

as follows:

**Figure 11.**

#### **Figure 10.**

pathways of magmatic systems [20]. A major crack extends from the east to the west of the study area. There are also local cracks stretching group north-west to south-east perpendicular to the main fault (**Figure 8**).

According to [19], the geology of the study area consists of Cretaceous Tawilah Sandstone (Kt), Lower Basalt (Tb1), Low Volcanic Acids (Tr1), Basic Volcanic Medium (Tb2), Second Volcanic Acids (Tr2), Granite (Tgr): *granite in the mountain of Sabir contains some older volcanic rocks* and finally Quaternary (QW): Wadi sediments are deposited by seasonal floods and wind-deposited soils derived from the alteration of volcanic ash and tufa mainly of (Tr1). Thickness can be up to 70 m. **Figures 9** and **10** illustrate geological cross-sections of some study areas.

### *3.1.5 Hydrogeology of the study area*

According to [19], groundwater in the study area is being produced from three aquifers: the Quaternary alluvium, the Tertiary fractured volcanic and the Cretaceous Tawilah Sandstone. Cretaceous Tawilah Sandstone in the study area is located in the lower classes, in the southwest of the study area and extends to the north, as shown in **Figure 11**.

*The geology cross-section of Jabal Sabir to Al-Hawban (the source of basic map [19]).*

*GIS and Statistical Evaluation of Fluoride Content in Southern Part of Upper Rasyan Aquifer… DOI: http://dx.doi.org/10.5772/intechopen.91329*

**Figure 11.** *Cretaceous Tawilah sandstone in the study area (the source of basic map [19]).*

Alluvial aquifers form the highest and shallow aquifers in the region. These sediments exist along the Wadis path (**Figure 6**). The total thickness rarely exceeds 30– 40 m, but they can locally reach considerable thicknesses (up to 70 m). Hydraulic properties vary from site to other. Intergranular groundwater flow is dominant [19].

Volcanic aquifers consist of the tertiary volcanic sequence. The thickness of this sequence may exceed 600–700 m. Groundwater flows mainly in this type of aquifers through the cracks/faults. The sandstone aquifer includes Tawilah Sandstone, Southwest of the study area (Al-Dhabab), and this formation is soaked to an expected depth of more than 500 m. In general, sandstone is largely silicified and fractured, so that the dominant groundwater flow in this aquifer is of intergranular type and mixed fracture. The quality of this aquifer is excellent to good [19].
