Amman Silicified Limestone Formation is of Santonian-Campanian age and has a thickness of 50 m in the study area and covers a broad area of Amman city. It consists of dark brown to grey thick beds, chert, silicified limestone, chalk, marl, siliceous coqina and cherty phosphate, brecciated chert and Tripoli (Diabat and Abdelghafoor, 2004). It crops out in the northeastern part of the study area and was deposited in full marine to subtidal environments (Shawabkeh, 2001). See Fig. 2.10.
2.5 Hydrogeology
2.5.1 Aquifer systemsThe aquifer systems in Jordan have been divided to three main aquifer complexes according to their spatial distribution, lithology and the age of the geological units (Salameh and Bannayan, 1993; MWI and GTZ, 2004). The following is a brief geological description.
1. Deep Sandstone Aquifer Complex
Ram and Khreim Group (Paleozoic age: Cambrian-Silurian)
Zarqa and Kurnub Group (Mesozoic age: Jurassic-Lower Cretaceous) 2. Upper Cretaceous Aquifer Complex
Lower Ajlun Group (A1/6) which includes the Na‟ur aquifer (A1/2), Fuheis aquitard (A3), Hummar aquifer (A4), and Shueib aquitard (A5/6). (Mesozoic age: Upper Cretaceous).
Amman-Wadi As Sir aquifer (B2/A7), (Mesozoic age: Upper Cretaceous).
3. Shallow Aquifer Complex
Basalt Aquifer, sedimentary rocks, and alluvial deposits (Cenozoic age:
Tertiary-Quaternary).
Also these aquifers can be divided to two main types:
Bedrock (consolidated) aquifers: this includes the Deep Sandstone Aquifer Complex, the Upper Cretaceous Aquifer Complex and the basalt aquifer of the Shallow Aquifer Complex. These aquifers together compromise the main source of groundwater in Jordan.
Unconsolidated aquifers: limited to the aquifers in the Jordan Valley. Of minor importance compared with the Bedrock aquifers.
Fig. 2.10: Amman silicified limestone with chert layer north to the Kafrein dam. (310 52’ 40’’ N, 350 41’ 23’’ E)
The Deep Sandstone Aquifer Complex
The Ram Group Aquifer of Cambrian age is the oldest aquifer which belongs to this Complex. It is also known as the Disi Aquifer in Jordan and as Saq Aquifer in Saudi Arabia. It does not crop out in the catchment area of Wadi Kafrein and its outcropping is limited to the southern part of the country and to the lower slopes of the escarpment east of the Dead Sea. It extends beneath the whole country forming a large aquifer and the deepest aquifer in north Jordan (Fig. 2.11). It consists mainly of sandstones interbedded with siltstone, mudstone, limestone and dolomite. The thickness of this aquifer is around 1,000 m up to 2,500 m in the east of Jordan while its base is estimated to be more than 2,000 m below sea level (bsl) in the northern and eastern part of the country and around 4000 m (bsl) in the north western part of the country (WAJ and BGR, 1994; Hobler et al., 2001). The aquifer has been recharged during the last humid period before around 5,000 years and is being continuously drained, leading to a gradual depletion of groundwater (Hobler et al., 2001).
The Zarqa Group of Permian to Jurassic age has similar constituents to the underlying Ram Group Aquifer. The Zarqa Group Aquifer is characterized as a multi-layered bedrock aquifer with different permeability and storability, but the aquifer is considered as one hydraulic system because the aquifers are hydraulically connected to each other. The Zarqa Group crops out only in the lower Zarqa River basin and along the escarpment between the Rift and the Highlands to the east. Its thickness increases from the central part of Jordan toward north and east to reach 1800 m (MWI and GTZ, 2004).
The second group of this Complex is the Khreim Group Aquitard of Silurian age. It overlies the Ram Group and it consists of sandstone, siltstone, and shale. It has a low permeability and separates the Ram Group from the overlying aquifer forming a confining layer, leading it to be considered as an aquitard.
The Lower Cretaceous Kurnub Group consists of white, multi-colored, and grey sandstone, mostly medium to coarse grained, with thin beds of grey and brownish siltstone. The thickness of the Kurnub Group decreases gradually from the northwestern to the southeastern part of Jordan with lowest thicknesses in the east which reaches 100-200 m in Azraq and 40-100 m in Hamad (Margane et al., 2002). In addition to its outcropping along the Rift escarpment of Wadi Zarqa River toward the south, it crops out in the catchment area of Wadi Kafrein in the southern and southeastern part; in Wadi Na‟ur and Wadi Bahhath (Fig. 2.5). Other out crops of the Kurnub Group is found in the deeply eroded cores of anticlines in Baq‟a area, and in Wadi Hisban which is located to the south of Wadi Kafrein.
Fig 2.11: Hydrogeological map of the main aquifers and aquitards in Jordan with their spatial distribution (MWI and GTZ, 2004).
Salameh and Udluft (1985) detected three different directions of the groundwater flow in Zarqa and Kurnub aquifers; in the southern part of Jordan it flows towards the northeast, in central Jordan towards west and in the northern Jordan towards the southwest.
Upper Cretaceous Aquifer Complex
This Aquifer Complex includes the Upper Cretaceous Ajlun and Belqa Groups and is divided to several hydrological units (Table 2.1). It consists of alternating sequences
of marl, limestone, dolomite and shale. It is divided to two main aquifer systems; the Lower Ajlun Group aquifers (A1/6) and Amman-Wadi As Sir aquifer (B2/A7).
The Lower Ajlun Group aquifers (A1/6) overlie the Kurnub Group with a disconformity and extend all over Jordan except its southern parts. It is dominated by sequences of marl, limestone, dolomite, and shale and it is divided into the following four hydrological units:
1. The Na‟ur aquifer/aquitard (A1/2) forms the lower part of this sequence and consists mainly of marls forming a confining layer which separates the aquifer from the underlying Kurnub Group Aquifer.
2. The Fuheis aquitard (A3) consists of about 80 m of marl and shale, which separates the A1/2 aquifer/aquitard from the overlying A4 aquifer (Salameh, 1996).
3. The Hummar Aquifer (A4) consists of marl and shale and crops out along the highlands. In the study area it crops out in the central and eastern part.
4. Wadi Shueib aquitard (A5/6) which consists of fossiliferous limestone, massive crystalline and thinly bedded porcellaneous limestone with a thickness ranging from 30 to 130 m (MWI and GTZ, 2004).
Amman-Wadi As Sir aquifer (A7/B2) represents the most important aquifer in Jordan because of its wide extent and relatively high permeability. It is the uppermost unit of Ajlun Group (A7) and the lower unit of Belqa Group (B2); together they form one hydrogeological unit consisting of limestone, chert-limestone, sandy limestone, and marly limestone and crop out along the highland where the Formation is being recharged. In Wadi Kafrein it crops out in the northern part and in the middle part along Wadi Bahhath (Fig. 2.5). Another outcropping of this Formation is found in the lower part of the study area near Kafrein Dam and along the Kafrein Syncline. Wadi As Sir Formation is folded and partially overturned in the western limb of the syncline (Fig. 2.4a).
Wadi As Sir Aquifer together with Na‟ur and Hummar aquifers are of local importance in the study area. All springs issue from these hydrological units except Wadi Kafrein spring, which issues from the Kurnub Group.
Shallow Aquifer Complex
This aquifer complex can be divided into four systems; the Basalt Aquifer, the Alluvial Deposits of the Jordan Valley, Wadi Araba, and the Eastern Shore of the Dead Sea.
The Basalt Aquifer of Oligocene-Pleistocene age is composed of massive alkali basalt and forms a good aquifer with significant hydrogeological importance. It crops out along the eastern margin of the Dead Sea, at the rims of and on the plateau facing the Yarmouk Valley and in the lower Wadi el Arab, in the subsurface of the Jordan Valley and in Harrat-Ash Shaam basaltic province north and east of Azraq (Hobler et al., 2001; Margane et Al., 2002). The maximum observed thickness of basalt is 479 m
in Harrat-Ash Shaam area with a general increase towards Jebel Druze in Syria where it may reach around 1,500 m (Wolfart, 1966).
The Alluvial Deposits of the Jordan Valley extends from the northern shore of the Dead Sea up to the downstream of the Yarmouk River with total length of 100 km and a width ranging from 4.5 km in Al Karameh area to 13 km in Wadi Hisban (MWI and GTZ, 2004). It is recharged from the eastern and western boundaries of the Dead Sea and the Jordan River. It consists of sand, gravel, conglomerate, marl, travertine, limestone, and evaporates. The thickness of the alluvium ranges from zero in the eastern boundary to 750 m in the deepest part of the basin near the Jordan River.
Wadi Araba Alluvial Aquifer extends from the southern shore of the Dead Sea to the northern shores of the Gulf of Aqaba and presents the main source of groundwater in Wadi Araba basin. The aquifer consists of conglomerates, gravels, sands, silts, and clays.
The Eastern Shore of the Dead Sea consists of the Lisan Formation and Holocene gravel and boulders. It is recharged from stream runoff, lateral flows of adjacent aquifers, or from the underlying basalt aquifer (Salameh and Bannayan, 1993; MWI and GTZ, 2004).
2.5.2 Springs
In Jordan, around 800 springs are monitored by the Ministry of Water and Irrigation-Surface Water Monitoring Division, with oldest spring discharge records dating back to 1937. Several reports and publications are available about spring locations, discharges, and abstraction amounts (NRA, 1966; WAJ, 1986; UNDP, 1994; WAJ and BGR, 1996).
Spring discharge represents an important source of water in the study area; it is used for irrigation by local people and for domestic purposes as well. Twenty-two springs discharge in the catchment area of Wadi Kafrein with an average volume of 12.3 MCM/yr; Fig. 2.12 shows the spring locations and the issuing aquifer of each spring.
The average discharge volumes of the springs range from 0.66 m3/hr of El Kashabeh spring in Wadi Na‟ur up to 397 m3/hr from Al Bahhath spring in Wadi Al Bahhath, (calculated from monthly measurements records, 1980-2006).
Almost half of the total spring flow volumes issue from Hummar (A4) aquifer (47.6%), with a total annual volume of 5.8 MCM, among which Al Bahhath spring discharges a total amount of 3.5 MCM/yr . The water of Al Bahhath spring used to be collected in water tanks for different purposes without any control (Fig. 2.13a).
Recently and in the summer of 2009 a decision was issued which prevents the use of the spring water by these tanks to protect the water resources and to increase the amount of water reaching the Kafrein dam used for irrigation purposes in the Jordan Valley.
Fig. 2.12: Classification of Kafrein spring discharges according to their aquifers.
The second big and important spring in the catchment area is Wadi As Sir spring (Fig.
2.13b) with average discharge of 380m3/hr. A water purification plant was established near the spring during the 1950s and in 1999 modern filters were installed to treat around 9,000m3/day to supply the city of Wadi As Sir with the daily needs of water (Verbal information, Mr. Hani Median /station operator, also records of the station).
The springs of Wadi Kafrein emerge from four main hydrological units; Kurnub Group, Na‟ur (A2/A1), Hummar (A4) and Wadi As Sir (A7), the volume percentages are given in Fig. 2.14 where it is illustrated that more than 80% of the springs emerge from Wadi As Sir and Hummar aquifers.
Fig. 2.13a: Al Bahhath spring with an annual discharge of 3.5 MCM presents a main source of baseflow in the study area.
Fig. 2.13b: Wadi As Sir spring, the water is pumped to Wadi As Sir Water Purification Plant supplying the city of Wadi As Sir with its water needs.
Fig. 2.14: Volume percentages of total spring discharge from the hydrological units.