**3.1.4 Discussion**

140 Urban Development

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

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

Result

0.81 ohm.m to 137.60 ohm.m.

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

Conclusion

as well.

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 during rainfall.

#### **3.2 Assessing elements of surface hydrology for environmental quality characterization of a site northwest of Riyadh, Saudi Arabia (M. T. Hussein et al, 2009)**

#### **3.2.1 Introduction**

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 assessment for urban development.

The tasks undertaken to achieve this purpose were:


Assessing Hydrological Elements as Key Issue for Urban Development in Arid Regions 143

The site is comprised of three blocks and it is bounded to the east by the Riyadh-Al Qassim highway and to the south by the North ring road. To the north and west, the site is bounded

The Jurassic Arab Formation limestone underlies most of the site (Vaslet et al., 1991). Unconsolidated deposits of silt, sand and gravels are observed on the wadies. The only hydraulic connections in between the site and its surroundings are the culverts under the roads surrounding the area. Dumped fill material and construction debris covers about 3%

GPS locations, types, dimensions of all culverts within the project site were measured (Table 1). The coordinates were measured by a hand held Garmin GPS and are reported in degrees, minutes, and seconds. The culverts in the site include three types: multispan box, double tube and single tube pipe culverts. Table 2 shows locations, and dimensions of existing

1 24.76898 46.74325 Multispan box (3) 18X1.25 m Block A in 2 24.76843 46.64344 Single pipe 0.9 m Block A in 4 24.76392 46.64519 Single pipe 0.9 m Block A in 5 24.75934 46.64331 Single pipe 0.9 m Block A in 9 24.75852 46.64165 Single pipe 0.9 m Block B in 6 24.75905 46.63718 Multispan box (3) 7.4X1 m Block A out 7 24.76052 46.63682 Multispan box (5) 22.1X 1.4 m Block A out 8 24.77024 46.63979 Double pipe 2.0X0.8 m Block B in 3 24.76792 46.63875 Single pipe 0.8 m Block A in

24.76898 46.74325 20X40 m Block A wet 24.76354 46.64509 22X30 m Block A dry 24.75866 46.64159 20X25 m Block A Partially wet 24.75856 46.6416 30X35 m Block A dry 24.75939 46.63317 15X20 m Block A dry

Culvert Type Dimensions Location Remarks Latitude Longitude

Dimensions Location Remarks

Site description

of the site area.

**3.2.3 Results** 

Culvert No.

Field observations

ponding areas in the site and potential ponding areas.

Coordinates

Table 1. Culvert types and dimensions

Longitude Latitude

Coordinates Approximate

Table 2. Pounding and potential pounding areas

by residential areas.


Fig. 14. Location map of the study area

#### **3.2.2 Methodology**

A field visit to the site was made, in which the boundaries of the study area was walked over and major features on the area were noticed, ground conditions including rock and soil type were identified. Ponding areas and potential ponding areas were figured- out and located. Meteorological data (precipitation, temperature, evaporation, wind speed and directions) and topographic maps were collected. The meteorological data were then treated for statistical analysis

The collected topographic maps and data were used for the identification of natural drainage of the site and the surrounding areas, and delineation of the catchments boundary.

The above mentioned accomplishments were subject to detailed desk study, and data analysis. The acquired data were analyzed and presented using Microsoft EXCEL, Global Mapper V. 6 (Global Mapper Software LLC), and WMS V. 7 (Environmental Modeling Systems, Inc.) GIS V. 8 (ESRI).

Site description

142 Urban Development

 Collate and review any existing data relevant to the site and the immediately surrounding area were reviewed and collated. This included but was not limited to ground conditions, meteorological records, historic records and/or photographs of

 Identification the approximate extent of catchments contiguous with the site, and estimate the approximate flow rates, flow directions and pounding levels in typical and

A field visit to the site was made, in which the boundaries of the study area was walked over and major features on the area were noticed, ground conditions including rock and soil type were identified. Ponding areas and potential ponding areas were figured- out and located. Meteorological data (precipitation, temperature, evaporation, wind speed and directions) and topographic maps were collected. The meteorological data were then treated

The collected topographic maps and data were used for the identification of natural drainage of the site and the surrounding areas, and delineation of the catchments boundary. The above mentioned accomplishments were subject to detailed desk study, and data analysis. The acquired data were analyzed and presented using Microsoft EXCEL, Global Mapper V. 6 (Global Mapper Software LLC), and WMS V. 7 (Environmental Modeling

flooding or pounding.

severe rainfall events.

Fig. 14. Location map of the study area

**3.2.2 Methodology** 

for statistical analysis

Systems, Inc.) GIS V. 8 (ESRI).

Site visit to assess broad surface hydrology.

Identification of relevant standards and guideline values.

The site is comprised of three blocks and it is bounded to the east by the Riyadh-Al Qassim highway and to the south by the North ring road. To the north and west, the site is bounded by residential areas.

The Jurassic Arab Formation limestone underlies most of the site (Vaslet et al., 1991). Unconsolidated deposits of silt, sand and gravels are observed on the wadies. The only hydraulic connections in between the site and its surroundings are the culverts under the roads surrounding the area. Dumped fill material and construction debris covers about 3% of the site area.
