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Location
ArRiyadh lies in the center of Arab Peninsula on latitude 34° - 38 northand longitude 46 – 43 east 600 m above sea level. This
location has given ArRiyadh strategic dimension where it is considered the
connecting link between the east and the west North and south in addition to
deriving the strategic importance of the Arab Peninsula which is linking the
two biggest continents. The distance between ArRiyadh and the center of
administration regions is as follows:
ArRiyadh is 389 km from Dammam in the Eastern Province, 1,049
km from Arar in the Northern Province, 1,207 km from Sakaka in Juf Region,
1,310 km from Tabuk, 1,040 from Baha,641 km from Jizan, 641 km from
Hail, 338 km from Buraidah in Qassim Region, 869 km from Madinah, 880 km from
Makkah, 1,051 km from Abha in Asseir Region, and 979 km from Najran.
Geological Formation
The Arab Peninsula is formed of two types of rocks: The solid
granite Arab shield rocks (basal rocks) constitute two fifth of the area of
the Peninsula while the sedimentary formations constitute the remaining area
of Peninsula where ArRiyadh lies. This area could be classified as :
Jubailah Formation
The exposed formation lies west of ArRiyadh. It is composed of
fire limestone overlapping with coarse limestone. The rocks of this layer are
cracked by the effect of erosion.
Arab Formation
Arab Formation comes after Jubaila formation on the east. The
exposed port appears along 10 km. This formation extends from the north west
to south east.
Hait Formation
This formation is
found to the east of Arab formation overlying Arab formation. This formation
is gently sloping eastward. The maximum thickness of this formation reaches
up to 90m below Al Sulay formation.
Al-Sulay Formation
This limestone formation
extends from the north west to south east and protrudes in the form of high
lands Known as Sulay verge.
Al-Kharj Formation
This formation
appears in horizontal layers enclosed in marine sedimentations. It is
composed of lime stones overlapping with gypsum and gravel layers.
Valley Sedimentations
These
sedimentations are found in valley streams around and inside Riyadh City. Two
types of these sedimentations were identified: the first one is composed of
clay mixed with layers of silt and gravel in the stream of Wadi Hanifa, Alsen
and Batha valleys, while the other sedimentation is composed of silt sand and
sandy clay mixed with gravel layers in Sulay valley.
Surface Appearance
Riyadh is located
on sedimentary plateau 600m over marine level to the east of Najd Knoll.
Valise, major topographic features of the city such as Wadi Hanifa that goes
through from the north west to south east. Length of this valley is
approximately 120km, depth varies between less than 100m to around 1000m.
Wadi Hanifa is fed by number sub-valleys such as Batha with around 25km
length starting north Mujainah and streaming South wards to Join Wadi Hanifa.
The other sub-valley is Aisen valley of about 35km length streaming parallel
to Batha valley and joining Wadi Hanifa. Many other subsidiaries join Wadi
Hanifa on the west and south west such as Ammariyah Wobair, Al Kudiah, Laban
and Namar valleys.
Hait Verge
Taking the form of
Highlands extruding in Zigzagging line from the south east of the city to the
east and north east. Maximum height of these highlands reaches approximately
700 m over Sea level.
Twaik Verge
It
comprises a part of Twaik verges that run through Najd highlands making an
arch from southwest & the north east other to the North West, of 1,100 km
length.
Muaizeelah Nafud
Comprises of dunes to the north of city and
becomes much denser to the north and join Banban sands.
Soil
Valley
sedimentation soil which is mostly
composed
of silt sands that are linked by
Carbon
substance of different levels. Test
Results showed that
soaking of soil reates further downfalls. Since data of Al-Kharj formation
soil and gravel is very scarce, it May cause similar down falls though with
minor effect because of the age of Al-Kharj formation and its stronger
adherence. Soil at the east is clay soil that keeps high level of water due
to low porosity in addition to bad slope. Density of granule soil at the
northern part of Riyadh valleys varies between moderate to high density. In
the case of water level fluctuation, this dense granulose soil causes slight
earth down fall in clay soil and thus causes surface soaking when ground
water rises. While decrease of water results in slight down fall that may
affect buildings and roads at City-center.
Sedimentary soil
and high weathering rocks are characterized by varying density and high water
level that may cause down falls and sedimentation of harmful salts due to
evaporation action. Exposed rocks composed of Jubailah formation west of the
city. Arab formation is found to the east of these rocks. Also there exist
hidden cavities concentrated in Arab formation soil, followed by cracks to
the east that are widely spreaded in Arab and Al-Sulay formations. Jubailah
formation has low porosity while porosity in Arab and sulay formation is
highly various due to the existence of substances that fill cavities and
cracks. When water level rises up, these substances moves due to solvency and
drifting and hence increases the porosity of soil. Dumping area: varies
according to dumping materials from granulose materials to fine materials.
Mostly found in valleys. Mostly coming from quarries existing at Wadi Hanifa
and its subsidiaries.
Climate
Riyadh climate is
dry with big variation in temperature, irregular rains with much variation in
quantity. During 1964-1992, the lowest measures were recorded in 1966 did not
exceed 12.6 m m, while the highest recorded level was in 1976 amounted to 176
mm. Average level for the same period was recorded as 82.2 mm. The rainy
season is often between November and May. Spring months (March, April and
May) and winter season (DecemberJanuary and February) are the
rainiest months.
The main feature of
Riyadh temperature is the extreme increase in Summer and decrease in winter.
By reviewing climatic data during 1382- 1417H it is quite evident that the
highest temperature in summer goes up to 42° while in winter decrease to 11°.
January is the coldest month while July is the highest temperature. Due to
this variation in temperature, the average temperature reaches 25°. Because
of absence of water surface and low rate of rains, the relative humidity in
Riyadh is very low, where the average humidity during 1382- 1417H was only
23% while relative humidity in winter season is 47% and 19% in Summer.
Dominant wind direction
in Riyadh is from north, northeast and northwest sides. Average wind speed
during 1318-1417H was around 5 knots/hour (approximately 8 miles/hour), while
the highest speed during the same period was about 25 knots/hour. Mostly wind
runs from north. The lowest rate of wind speed was 1.6 knots/hour, and the
lowest recorded wind speed was 0.8 knots/hour.
Water Resources
Supply of water
into the Riyadh City comes from three major sources, which are as follows:
Ground Surface Water
A-Wadi Hanifa and Subsidiaries:
In coming rain
water to Wadi Hanifa is estimated to be 15 million cubic meter per year. The
city is benefiting from this quantity of water in this valley. Most of this
water comes from Al–Hair area where number of wells were made for producing about 18 thousand cubic
feet per day. Water analysis performed, revealed that Wadi Hanifa water
contains low quantity of salts, so water is pumped out directly after primary
treatment.
B- Wadi Nisah:
Ground water is
found in three surface layers, Valley clay, Dhurma lime formation and the
sand stone layer. Number of wells in Wadi Nisah are 16 wells that produce 54
cubic meter/day. The natural annual recharge varies between 3-7 million cubic
meters. Water of Wadi Hanifa is of good quality, where salinity is not
exceeding 400 mg/L.
Ground Water
A- Al Manjour Formation:
The annual recharge rain water in this layer is
estimated to be 85 million cubic meters, this layer retain considerable
amount of water that reach up to 750 billion cubic meters. Al Manjour water
is highly saline where as salinity is estimated as 1500mg/L. Water is drawn
from this formation through the two fields of Bowaib and Salboukh 108
thousand and 86 thousand cubic meter respectively. Due to high salinity of Al
Manjour water, five water treatment plants were established in Malaz,
Shumaisi and Manfouha, and two in Bowaib and Salboukh.
B- Al
Waseea Formation:
Water of Waseea
formation is estimated to be around 57 billion cubic meters while the annual
recharge is approximately 420 million cubic meters. Water salinity in this
formation varies between 1000- 3000mg/L. Al Waseea water is pumped to a water
treatment plant 30 km east of Riyadh to be mixed with treated sea water.
Treated Sea Water
It is the most
modern and important water source in Riyadh. Water of this source is
estimated to provide around 830 thousand cubic meters per day. It is pumped
from the water conversion plant on the Arab gulf near Al-Jubail City through
two giant ducts, the radius of each is 60" (sixty inches) for a distance
of 466 km.
Wadi Hanifa
Wadi Hanifa is
sloping of the verge of Twaik in the north west of this valley which is
characterized by small lime soil valley, different types of wild trees and
green belt give you a feeling of wild life. Wadi Hanifa is existing at the
center of Najd platuea which is considered as the most prominent feature of
Riyadh location. Wadi Hanifa is flowing from north to south for about 120 km.
It is acting as a natural drainage of rainwater for an area of 4000 sq.km.
This valley is the major drainage of Riyadh city where 40% of the city lies
within the basin of this valley. Wadi Hanifa Basin is composed of more than
40 sub-valleys on both western and eastern sides. The length of most of these
sub-valleys reaches up to 25 km.
Topography of this
valley comprises five major sections starting valley bed, the plain green
lands on both side adjacent to flood drainage Channel which is composed of
five clay and alluvial deposits, the sedimentary horizontal shelves that is
suitable for agricultural and grazing purposes, cliffs on both sides
following the plains and finally the sub-valley that constitute water flow of
the valley. Wadi Hanifa is characterized by residential compounds of
villages, agricultural activities such as nurseries, palm gardens, vegetables
and fruits. Valley is also including antiquities and historical remains of
old human civilizations such as houses, dams and so forth.
This valley is
still representing wild lands and agricultural forms that are very rich with agricultural
and pasture resources having recreation spaces, particularly at the
subsidiary branches in the north. Due to the extended leveled plains in
center land use is very much diversified and that building activities are
actively creeping on both sides of the valley. The southern part of this
valley constitutes the permanent water stream that contributes in diversity
of the land that is characterized by agriculture on both banks from source up
to its estuary in Sahba'a.
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