**3.1.3 Results and conclusions**

Site 1

The first site M1 was in the Buhairatil Khaleej, Figure 2, which is situated in the South of Buraidah City. The total line length of the survey was 360 meters with the unit electrode spacing of 5 meters using dipole-dipole configuration. The depth of investigation at this site was around 72 meters.

Fig. 2. Location map of Buhairatil Khaleej with the direction of the survey line

Result

132 Urban Development

Electrical Resistivity Survey was carried out at 4 locations (Figure 1) for investigating the depth of the wet zone in these localities. Based on the depth of the wet zones the

The resistivity survey was carried out using the multi-electrode resistivity technique. The surveys at all the 4 locations were carried out using the Dipole-Dipole configuration with the unit electrode spacing ranging from 2.5 meters to 5 meters depending upon the ground clearance using the SYSCAL-Pro 72 unit. RES2DINV Software, (Loke, 2002) was used for inverting the apparent resistivity values to a resistivity model section. The least square fitting technique (Loke and Barker, 1996) was used for getting the best fit for the resistivity

The first site M1 was in the Buhairatil Khaleej, Figure 2, which is situated in the South of Buraidah City. The total line length of the survey was 360 meters with the unit electrode spacing of 5 meters using dipole-dipole configuration. The depth of investigation at this site

approximate depths of injection bore wells were estimated.

Fig. 1. Location of the 4 localities in Buraidah, Qassim

**3.1.2 Methodology** 

model by iterations.

was around 72 meters.

Site 1

**3.1.3 Results and conclusions** 

Figure 3 shows the result of the resistivity survey. The resistivity values range from 7.07 ohm.m to 36.9 ohm.m.

#### Conclusion

The depth of investigation in the present case is about 72 meters. The resistivity value for the total depth of investigation does not show a very high contrast and in general is very low ranging from 7 ohm.m to 37 ohm.m. indicating the presence of a wet zone throughout the entire depth of investigation. However at a depth of about 30 meters from the surface the resistivity value increases indicating the presence of relatively dry zone. This boundary (Figure 4) can well be the contact zone between alluvium and weathered limestone as the site is situated in a stream channel. The 2 zones of relatively high resistivity shown in Figure 6 may be due to the presence of less weathered limestones.

Result

at this site was around 57 meters.

Assessing Hydrological Elements as Key Issue for Urban Development in Arid Regions 135

The second site M2 was in the Bohairatil Iskan Qadeema (Figure 5) which is situated in the Buraidah City Center. The length of the profile for this survey was 288 meters with the unit electrode spacing of 4 meters using Dipole-dipole configuration. The depth of investigation

Fig. 5. Location map of Bohairatil Iskan Qadeema with the direction of the survey line

The resistivity values range from 2.93 ohm.m to 7000.5.6 ohm.m.

Figure 6 shows the result of the resistivity survey carried out at Buhairatil Iskan Qadeema.

Fig. 3. Results of the resistivity survey at site M1

Fig. 4. Interpretation of the resistivity results at Site M1

134 Urban Development

Fig. 3. Results of the resistivity survey at site M1

Fig. 4. Interpretation of the resistivity results at Site M1

The second site M2 was in the Bohairatil Iskan Qadeema (Figure 5) which is situated in the Buraidah City Center. The length of the profile for this survey was 288 meters with the unit electrode spacing of 4 meters using Dipole-dipole configuration. The depth of investigation at this site was around 57 meters.

Fig. 5. Location map of Bohairatil Iskan Qadeema with the direction of the survey line

Result

Figure 6 shows the result of the resistivity survey carried out at Buhairatil Iskan Qadeema. The resistivity values range from 2.93 ohm.m to 7000.5.6 ohm.m.

Result

to 2258.20 ohm.m.

investigation at this site was around 57 meters.

Assessing Hydrological Elements as Key Issue for Urban Development in Arid Regions 137

The third site M3 was in the Bohairatil Iskan Jadeeda (Figure 8) which is situated about 1 km North East of the site M2. The length of the profile for this survey was 288 meters with the unit electrode spacing of 4 meters using dipole-dipole configuration. The depth of

Fig. 8. Location map of Bohairatil Iskan Jadeeda with the direction of the survey line

The cross sections of the lake walls showed the presence of weathered Limestones with calcrete infillings and the presence of folds. Figure 9 shows the result of the resistivity survey carried out at Buhairatil Iskan Jadida. The resistivity values range from 0.17 ohm.m

Fig. 6. Results of the resistivity survey at site M2

#### Conclusion

The results (Figure 7) clearly indicate the presence of an approximately 40 meters thick wet zone starting from 6 meters below ground level up to 46 meters below ground level. The resistivity values within this zone range from 2.93 ohm.m to about 30 ohm.m. The lake still had some water and this probably explains the presence of a thick wet zone. Bore wells drilled to a depth greater than 45 meters could be helpful in injecting the water collected in this lake during rains.

Fig. 7. Interpretation of the resistivity results at Site M2

136 Urban Development

The results (Figure 7) clearly indicate the presence of an approximately 40 meters thick wet zone starting from 6 meters below ground level up to 46 meters below ground level. The resistivity values within this zone range from 2.93 ohm.m to about 30 ohm.m. The lake still had some water and this probably explains the presence of a thick wet zone. Bore wells drilled to a depth greater than 45 meters could be helpful in injecting the water collected in

Fig. 6. Results of the resistivity survey at site M2

Fig. 7. Interpretation of the resistivity results at Site M2

Conclusion

this lake during rains.

The third site M3 was in the Bohairatil Iskan Jadeeda (Figure 8) which is situated about 1 km North East of the site M2. The length of the profile for this survey was 288 meters with the unit electrode spacing of 4 meters using dipole-dipole configuration. The depth of investigation at this site was around 57 meters.

Fig. 8. Location map of Bohairatil Iskan Jadeeda with the direction of the survey line

Result

The cross sections of the lake walls showed the presence of weathered Limestones with calcrete infillings and the presence of folds. Figure 9 shows the result of the resistivity survey carried out at Buhairatil Iskan Jadida. The resistivity values range from 0.17 ohm.m to 2258.20 ohm.m.

Assessing Hydrological Elements as Key Issue for Urban Development in Arid Regions 139

The fourth site M4 was in the Bohairatil Riyan (Figure 11) which is situated in the North Western part of Buraidah City. The total line length of the survey was 180 meters with the unit electrode spacing of 2.5 meters using dipole-dipole configuration. The depth of

Fig. 11. Location map of Bohairatil Riyan with the direction of the survey line

Fig. 10. Interpretation of the resistivity results at Site M3

investigation at this site was around 36 meters.

Site 4

Fig. 9. Results of the resistivity survey at site M3

#### Conclusion

The wet zone thickness in the present locality is about 35 meters with some local variations as seen in the middle of the section where the wet zone extends up to the entire depth of investigation. This fact could be explained by the presence of structural features which might have resulted in partial weathering of the limestones thus resulting in varying degree of water saturation. The difference in water saturation around this zone is clearly reflected in the resistivity contrasts in the cross-section in figure 16. In the Eastern part of the profile some fresh limestone outcrops were present and it has been reflected in the form of high resistivity in the right side of the profile, (Figure 10). In general the wet zone thickness in the section varies from about 6 meters below ground level to about 40 meters below ground level. Injections well drilled to a depth of around 45 meters could solve the purpose of getting rid of excess water at this site.

Fig. 10. Interpretation of the resistivity results at Site M3

138 Urban Development

The wet zone thickness in the present locality is about 35 meters with some local variations as seen in the middle of the section where the wet zone extends up to the entire depth of investigation. This fact could be explained by the presence of structural features which might have resulted in partial weathering of the limestones thus resulting in varying degree of water saturation. The difference in water saturation around this zone is clearly reflected in the resistivity contrasts in the cross-section in figure 16. In the Eastern part of the profile some fresh limestone outcrops were present and it has been reflected in the form of high resistivity in the right side of the profile, (Figure 10). In general the wet zone thickness in the section varies from about 6 meters below ground level to about 40 meters below ground level. Injections well drilled to a depth of around 45 meters could solve the purpose of

Fig. 9. Results of the resistivity survey at site M3

getting rid of excess water at this site.

Conclusion

The fourth site M4 was in the Bohairatil Riyan (Figure 11) which is situated in the North Western part of Buraidah City. The total line length of the survey was 180 meters with the unit electrode spacing of 2.5 meters using dipole-dipole configuration. The depth of investigation at this site was around 36 meters.

Fig. 11. Location map of Bohairatil Riyan with the direction of the survey line

Assessing Hydrological Elements as Key Issue for Urban Development in Arid Regions 141

The probable presence of alluvium was detected only at the first site M1 at Bohairatil Khaleej with a sharp contrast in resistivity value at around 30 meters from the surface and is in accordance with the field observation which shows that this site is located in the course of a Wadi. The resistivity values are low at the other 3 localities as well indicating the presence of wet and weathered limestones. Presence of alluvium in these localities can be ruled out based on the exposed wall sections in the lakes which show beds of limestones intercalated with calcrete infillings. At the locations M2, M3 and M4 a contrast in resistivity values are observed at a depth ranging from 30 meters to 45 meters below ground level. It is recommended that wells drilled up to depths ranging from 45 meters to 55 meters in all the 4 localities can be efficient in getting rid of the excess rain water collected in these lakes

**characterization of a site northwest of Riyadh, Saudi Arabia (M. T. Hussein et al, 2009)** 

Elements of surface hydrology, specially rainfall and surface runoff, are important factors in environmental quality characterization for urban development. In arid regions, these elements are difficult to forecast and may cause negative complications, especially in planning and design, if not been aware of. The study area under consideration lies within an urban center in the north west of Riyadh City, Saudi Arabia (Figure 14), between longitudes 46º 37´ 26" E- 46º 39´ 20" E, and latitudes 24º 45´ 00" N- 24º 46´ 45" N. The main purpose of this study was to workout elements of surface hydrology as part of an environmental

 Review of the published topographical information to identify significant hydrological features such as, current and historic stream flow paths and potential ponding areas. Review of the already existing infrastructure to identify significant features such as

**3.2 Assessing elements of surface hydrology for environmental quality** 

Fig. 13. Interpretation of the resistivity results at Site M4

**3.1.4 Discussion** 

during rainfall.

**3.2.1 Introduction** 

assessment for urban development.

The tasks undertaken to achieve this purpose were:

culverts and any potential surface flow restrictions.

#### Result

The cross sections of the lake walls showed the presence of weathered limestones with calcrete infillings and the presence of nodal structures. Figure 12 shows the result of the resistivity survey carried out at Buhairatil Riyan Jadida. The resistivity values range from 0.81 ohm.m to 137.60 ohm.m.

Fig. 12. Results of the resistivity survey at site M4

#### Conclusion

As mentioned earlier the resistivity values for this site ranges from 0.81 ohm m to 36.9 ohm.m. which is very low. In general the section shows the presence of wet zone through the entire depth of investigation. However the depth of investigation in the present case is limited only to 36 meters due to the unavailability of open space for laying the resistivity cables. On the lower left portion of cross section in Figure 13 the probable contact between the dry and wet zone is shown at about a depth of 25 meters. From the general depth of the dry zone in the previous 3 sections it can be concluded that drilling injections wells to the depth of about 45 meters may solve the purpose of getting rid of the excess water at this site as well.

Fig. 13. Interpretation of the resistivity results at Site M4
