THE MECHANISM AND INFLUENCE ON KARSTIC SPRING FLOW OF THE SARCHINAR SPRING CASE EXAMPLE, SULAIMANIYA,NE IRAQ
Salahalddin Saeed Ali, Zoran Stevanovic and Igor Jemcov,/University of Sulaimani
Published in: Iraqi Bulletin of Geology and Mining, Vol.5, No.2, 2009, p.87 -100.
ABSTRACT
The Sarchinar spring one of the largest springs in northern Iraq, supplies municipal water for the Sulaimani city of 700000 inhabitants. The outlet drains a large catchment area, some 200 km2 of the Sarchinar – Chaq Chaq karstic system.The recharge of the spring is based on: A) the diffuse infiltration of rainfall through the exposed outcrops of Jurassic and Cretaceous (Qamchuqa – Kometan or Balambo Formations thickly-bedded and highly fractured limestone layers; B) the percolation of runoff and intermittent stream water of Chaq Chaq Valley through tectonically active zones. During the recession periods of the extremely dried 1999 and 2000 the minimal discharge of the system was around 600 l/sec. The recorded maximum during period 1999-2005 was 7454 l/sec (March, 2003).
For the characterization of karstic aquifer and discharge regime evaluation the analyses of input – output relationship were applied including the autocorrelation, cross-correlation and spectral density methods. The main characteristics are cyclic variations and significant aquifer storage capacity. During wintertime, the system reacts to rainfall events with a delay of a few days representing the minimum travel time for the recharging inputs. Meanwhile, a slow reaction could be observed during low water period after approximately one month (rainfall at the beginning of May transferred as output at the beginning of June). Regime of this spring is determined by several factors. The principals are: arid climate and unstable recharge (six months without rainfall), well karstified and fractured aquifer system, recharge by seepage from the nearby Chaq Chaq Valley.
INTRODUCTION
Sarchinar spring is well known in the region by its very large discharge and great resort area formed around the spring. It is locally considered as one of the natural beauties, but in the same time it is the main source of drinking water of entire city of Sulaimaniya.
The general water demands of the Sulaimaniya city is rapidly increasing along with its population and industry growth. The number of inhabitants has increased from 20000 in 1930 to 53000 in 1960, 200000 in 1980 and 700000 in 2005. The total water demand of the city is reaching 200000 m3 per day; %70 of this amount is covered by the spring water from mid November till June, while the surface water pumped from Dokan reservoir some 50km far from the city is ensuring supply for the rest of the year.
The water of Sarchinar drains out not only from the main discharge point (Fig. 1), but also from a cluster of small springs. During the high water period the system overflow is clearly outlined by these temporary springs located 900 m upstream of the main outlet. According to Maulood and Hinton (1978) there are 16 such small springs.
PREVIOUS STUDIES
Until present the spring was the object of several studies and investigations but mostly related to some specific aspects of its utilization. Therefore, still no complete survey of this important spring is undertaken.
The authors of the Parsons Co.’s study (Anon, 1957), described Sarchinar spring as “one of the larger springs, supplies municipal water for the 43000 inhabitants of Sulaimani. In June 1957, the yield of the spring was calculated to be 56000 US gallons per minute. Water is also diverted from this spring and used extensively for irrigation…”
Fig.1 Pumping station at Sarchinar spring in Sulaimaniya city
Cwiertniewski (1961) reported that groundwater which Sarchinar spring drains “is flowing through open solution channels”. During seventies, El-Yossif and Al-Najim, (1977) published the paper on the hydrological and chemical properties of the spring, followed by the study of Maulood and Hinton (1978) on the ecology of Sarchinar Spring. Al-Rawi et al (1990) performed geoelectrical and hydrogeological survey in wider area. Al-Manmi (2002) conducted an environmental and hydrological study of groundwater in Sulaimaniya area that also included Sarchinar spring. Mohammed (2004) studied the ecology and aquatic life of the spring water. Recently, Stevanovic and Iurkiewicz (2004) completed hydrogeological study of the entire region. The Sarchinar spring flow regime and its importance were also emphasized in their work.
GEOLOGICAL SETTING OF THE CATCHMENT
The northern part of Iraq (including Sulaimaniya Governorate) as part of Western Zagros Fold-Thrusted belt is represented by high mountains, most of them more than 2000 m a.s.l. (Eastern Taurides and Western Zagros). From north to south the three major tectonic zones that occur are: Thrust Zone, High Folded Zone, and Low Folded Zone (Buday, 1980 and Buday and Jassim, 1987). The Sarchinar catchment area belongs to the High Folded zone with dominant presence of carbonate and clastics rock of Cretaceous age.
Balambo, Sarmord and Qamchuga formations date from the late phase of Early Cretaceous (Aptian, Albian). The thick layers (often massive and in the banks) are dominantly carbonate (limestones and dolomitized limestones). Lower and the middle part of Late Cretaceous rocks are also consisted of carbonates (Kometan, Dokan formations), or “impure” carbonates (Shiranish formation) and clastic rocks (Tanjero formation).
Fig.2. Geological map of part of Sharazoor-Piramagroon Basin.along which the catchment area of Sarchinar spring is shown , Ali(2007).
The total thickness of each indicated is between 100 and 500m respectively, but is largely variable and is rather reduced (upper part is often eroded). Great inclination of layers, sometimes sub-vertical slope, which is descending generally to the SW direction, is the result of intensive orogenic movements (Stevanovic and Markovic, 2003). Sarchinar groundwater basin includes part of Pira Magroon and Azmir anticlines with several smaller modulated folds, all separated by the narrow syncline of Chaq Chaq Valley (Figs. 2, 3 and 4).
The Sarchinar spring and Chaq Chaq valley are located within northern part of larger watershed of Tanjero stream, which finally collect all surface and subsurface water to the Darbandikhan reservoir. The Sarchinar basin alone extends for a distance of nearly 25 Km to the north and about 3 km to the south from the spring site. Its width between bordering divides is about 8 km, whereas total catchment area is assessed on approximately 200 Km2.
The spring is located in the lowest and last elevation of the southeast plunge of Pira Magroon Mt. where the Kometan formation is exposed to the surface (Fig.3, 4 and 5). It is marking the contact between karstified and fractured limestone of Kometan with the Shiranish marls (Upper Cretaceous). The late unit acting as impervious barrier and directs water to ascedentally flowing out. Therefore, the location of the spring is controlled by both, morphology and stratigraphy of the area.
Fig.3 General view of Chaq Chaq valley, showing the exposed Cretaceous formations:
Ta:Tanjero, Sh:Shiranish, Ko: Kometan , Ba: Balambo , Qa: Qamchuqa.
HYDROGEOLOGICAL PATTERN
The recharge areas of two parallel anticlines (Pira Magroon and Azmir) are consisting of Kometan, Qamchuqa limestones and the upper part of Balambo Fns. Kometan Fn. consists of well-bedded and fine crystalline limestone, which has the thickness of 120m. In Qamchuqa Fn. massive dolomitic limestone is prevailing, with a thickness that can reach some 600 m. The formation crops out along upper limb and crest of the anticlines that surrounding the Chaq Chaq valley (Fig.3). The upper part of Balambo Formation consists of about 200m of yellowish white well-bedded limestone. This part is very similar to Kometan; the only differences are the stratigraphic position and higher content of marl; component. This unique karstic aquifer also called as “Bekhme” by Stevanovic and Iurkiewicz, (2004); is characterized by great thickness and large surface extension. It is highly fissured, well-karstified with many channels and caverns that were registered on the surface (Karim et al, 2003) or during the drilling.
Not all rocks located in the Chaq Chaq valley are taking part in recharging of the aquifer. More than half of the valley surface is covered by impervious Tanjero and Shiranish Formations. Tanjero formation is characterized by rhythmic alternation (succession) of thin beds of sandstone with very thin interbeds of calcareous shale. These types of lithology are all act as thick impervious succession except where they are intensely deformed then may form shallow and local aquifer (or aquitard). The sandstone shale beds are completely barren of porosity but some recently drilled shallow wells showed that the sandstone succession can be a local aquifer when is deformed (fractures and jointed). Shiranish Formation is consisting of thick succession of marl and marly limestone. These two formations thus have very low infiltration coefficients so large portion of runoff water leave the Chaq Chaq valley without recharging Sarchinar, particularly during winter months. During spring and summer period before Chaq Chaq is completely drying out lower velocity cause that seepage towards karstic aquifer in both, vertical and lateral contacts, is somehow increased.
Fig. 4. Transversal geological cross section across Chaq Chaq valley (syncline)
STRUCTURAL CONTROL OF THE SPRING
The infiltrated water within karstic aquifer from the crest and upper parts of both limbs is flowing towards lower part of both southwestern and northwestern limbs of anticlines and then became diverted toward the plunge where the spring is located. There is an important reverse high angle fault (named North Sarchinar fault) striking NNW-SSE, which crosses the Chaq Chaq wadi nearly 1.5 Km to the north of the spring. A good amount of water enters this fault zone and infiltrates vertically downward (Al-Rawi, et al, 1990). By this fault the southeastern end of the plunge (locally called Girdy Sarchinar) is suddenly subsided. The role of the fault was even more significant during past before enhancement of the flow direction by karstification.
Slightly south of the Sarchinar spring there is a major transverse fault, which has been named as Sarchinar Tear fault (Al-Rawi, et al, 1990). The southern block of this fault has relatively moved about 20m downward and 200m eastward. The fault is actually made up of a number of parallel fractures. Due to this fault, the whole area due south has been tilted towards NW, thereby forming a topographic saddle, (Al-Rawi, et al, 1990).
Fig. 5. Geological cross section crossing Azmir anticline and the spring site.
GROUNDWATER BUDGET
The recharge area is characterized by mean annual precipitation of about 700mm in the foothills, but it may even reach about 1000mm in higher altitude areas. The maximum rainfall is during the winter months when the snow covers higher peaks. The annual rainfall in north Iraq is not much less than the annual rainfall in most of Europe, but the difference is in its distribution. Almost by a rule, there is no rainfall between June and September. Taking the average rainfall for the whole basin area as about 800 mm per year and the basin surface, the total recharge potential is cca 160 x 106 m3 per annum (Al Rawi et al, 1990). There are a number of longitudinal and transversal faults and fracture zones, which should facilitate the percolation of water from the surface into the subsurface. The basin configuration is also quite favorable (wide valley and gentle slopes) for higher percentages of filtration surface water into the subsurface, within the karstic outcrops. It is assumed that all these factors may be allowing more than 55% of the annual rainfall to percolate down into the ground. Thus, the annual recharge of the groundwater basin should be around 80 x106 m3.
KARSTIFICATION
During the long geological history of the Territory of Northern Iraq, especially in the Mesozoic and Tertiary periods, a lot of soluble rocks like limestone, dolomite and evaporite were deposited. This enabled the development of strong karstification and the formation of both surface and underground karstic morphology. Alpine folding and uplifting of mountains built of carbonate rocks continuing until the present, has caused stronger penetration of surface water underground. This was reinforced by numerous fissures, joints and fault surfaces, and deepening of the basis of karstification. Two different levels of karst formed in different phases could be connected in some places, offering a false picture of the unique process of karstification, (Stevanovic and Markovic,2003).Carbonate rocks in general show non-homogeneity with the prevailing presence of limestone, but also with insoluble varieties such as interstratified clays. In Balambo Fn. or in marly limestone in Shiranish Fn., uplifting of carbonate massifs and their intensive folding and faulting, repeated in several phases, caused the complex systems of faults and fractures as privileged ways for the water circulation (Stevanovic and Iurkiewicz, 2004).
Surface karstic small forms, dimensions from cm to dm, occur in practically the whole limestone area. Compared with other karstic Euro-Asian mountainous ranges formed during the Alpine orogenic cycle (Alpides, Dinarides, Helenides, Taurides), typical larger surface forms, such as sinkholes or dolines, are not as frequent in this region. Some large depressions resemble the polje forms, but they are always open in the direction of the main drainage stream. Even if they are formed by karstic process, they have been strongly modified by surface fluvial process,(Stevanovic and Markovic,2003).
In the study area, limestone rocks of Qamchuqa formation responded more to karstification processes than the other Cretaceous rocks, and many dry caves (small diameters from less than one meter to more than 3 meters of previous groundwater tables now exist in these rocks. Due to relatively thin bedding layers of Kometan formation no great opportunity for karstification process occurred, but lot of relatively large shallow subsurface cavities and open channels have been detected 200m upstream of Sarchinar spring by (Al-Rawi, et al, 1990), beside similar cavities found during drilling wells in these rocks.
DISCHARGE REGIME AND TIME SERIES ANALYSIS
The karstic properties can be inferred from the discharge fluctuation of the spring. The spring discharge increases several times after each storm with more than 30mm of rainfall and is rapidly decreased after few days.
According to analysis of data from the pumping station that supply the city, during the recession periods of 1999 and 2000 the minimal discharge of the system was evaluated to be around 600 l/sec. Application of the recession coefficient method was attempted for the spring and based on the spring hydrograph recorded during April 1999 – March 2000. By using the Mailet recession curve, two recession coefficients were obtained:
•1 = 0.0068 (discharge reduced from 1.36 to 0.94 m3/s within 36 days), and
•2 = 0.00018 (discharge additionally reduced to 0.67 m3/s within 122 days)
Considering that the second recession coefficient 2 characterizes a very slow drainage through the well-karstified and rich aquifer of Pira Magroon/Azmir Mountains. It was inferred that complete exhausting of dynamic resources of Sarchinar reservoir would theoretically require a period of almost ten years of continuous discharge without any additional recharge (Stevanovic and Iurkiewicz, 2004).
Fig.6 Sarchinar spring discharge during recession period of 1999.
After the short drought cycle that affecting entire region, during the years 2001/2002 the following spring discharges were recorded (Table 1):
Table 1 – Characteristic data recorded for Sarchinar spring
Fig. 7 – Correlation chart: rainfall (Sulaimani) – Sarchinar Spring
The system reacts to rainfall events with a delay of 2-3 days representing the minimum travel time for the recharging inputs (Fig.7). Meanwhile, a slow reaction could be observed after approximately one month (rainfall at the beginning of May transferred as output at the beginning of June).The analysis of spring hydrographs may provide valuable indirect information on the structure of the karst hydrogeological system (Bonacci 1993; Krešić, 1997, Larocque et al. 1998). For this purpose the method of implementing systematic (time series) analyses was developed (Mangin, 1984). As an initial step for characterization of a karst aquifer, the results of autocorrelation, spectral density and cross-correlation should be taken into consideration (Jemcov, 2006). According to such analysis applied in case of Sarchinar hydrogram for the year 2003, auto-correlogram of discharges rates of the spring exceeds the confidence limits for approximately 85 days (Fig. 8). This implies that aquifer storage is significant and that it releases water gradually. Also the very slow decline of the auto-correlogram shows a relatively stable discharge regime, conditioned by the limited dimensions of the karst channel, which also confirmed earlier made statement of large groundwater reserves (for drought year of 1999).
Fig.8 Auto-Correlogram and Cross-correlogram of Sarchinar Spring
The spectral density function of the spring discharges show high peaks at a low frequency of 0.003165 (above 300 days), which confirms the presence of an annual cycle (Fig. 9). Considerable peaks at the frequencies (from about 120-90 days) show seasonal cycle of spring. Beside peaks at the middle frequencies (from about 40 days), which show relatively low densities, at high frequencies even the low density does not exist. This analysis confirms that Sarchinar spring is characterized by seasonal recharge and discharge cyclicity.
Fig.9 Simple spectral analysis of Sarchinar spring discharge.
Cross-correlograms for spring flow and precipitation shows a very minor level of significance from 3 to 11 days, but after that is insignificant. Low cross-correlation values show that the influence of infiltration is significantly attenuated by the karst hydrogeological system.
The statistically test of the data of rainfall- discharge for four days lag time shows high correlation and response between rainfall and discharge,(Fig.10). Accordingly very minor differences was found between observed and simulated discharge.
Fig.10 Diagram of observed and simulated discharge of Sarchinar spring.
Altogether, the analysis shows large storage capacity for the Sarchinar aquifer. Water is store within this karst hydrogeological system during the recharge period and is later slowly release during the dry season. Dynamic resources are the consequence of small fissures and matrix porosity (slow subsequent water release following de-saturation of larger fractures) as well as the large subsurface reservoir extended from Pira Magroon anticline towards the outlet.
ENVIRONMENTAL IMPACT
The spring is located in NW suburban area. Very close to the spring, at the distance of some 200m there is a cement factory (which auspiciously is now closed and planned to be abandoned), and a small quarry which both have had significant impact on the water quality and disturb the environment.
The spring is also suffering from several other problems; the first one is the continuously spread of urbanization toward the recharge area in addition to increase population of the densely distributed villages in the upstream valley of Chaq Chaq. The second source of pollution was attributed to the newly built dam of 13m heights. This dam was constructed at 1Km to the north of the spring on the temporary stream (wadi), (Fig.11). In spite that hydraulic connection has never been confirmed by tracing tests, it is certain that surface water is percolating near the spring after left impervious rocks of Tanjero and Shiransh, through aforementioned large faults and numerous fractures and caverns within Kometan karstic aquifer.
The Chaq Chaq dam was built by support of one NGO in late 2002, but without feasibility or previous research. Furthermore, the dam design and construction was inadequate to properly maintain the water storage, thus the first happened serious flood in 2006 caused that dam collapse, (Fig.12).
Fig.11 Geological sketch map of the mouth of Chaq Chaq valley (syncline),
Showing the locations of Sarchinar spring and recently constructed earth dam.
Fig.12: Detroyed right side of the Chaqchaq dam, the geologists in the photo was against its construction at this locality.
The idea to build a dam with a reservoir in Chaq Chaq valley had nothing with hydrogeology or controlling of aquifer. The primary aim was to store temporary stream flow. But, shallow reservoir in an area such as Iraqi Kurdistan where daily evaporation rate during summer is reaching 1,5 cm/day is not sounding favorable. However, such kind of dam in narrow spring outlet area theoretically could have some positive implications concerning reduction of water velocity and more extended aquifer recharge throughout the year. To confirm such statement, some evidences of more stable discharge were identified on the spring hydrogram for the year 2003 comparing the previous ones.
There are two other facts that confirm deeper circulation within karstic aquifer: First, relatively constant temperature of the spring water throughout the year (±17 C0), while air temperature varying from less than 0 C0 to more than 40C0. Second: seldom recorded increased turbidity values of the spring even after heavy rainfalls. The blasting processes which had been performing for more than 40 years for quarrying limestone to supply the cement factory located directly 200m north of the spring, on the neighboring hill has had a great impact in the widening of the existing joints and fractures and even creating of new ones. These fractures that have direct connection with surface are extended as open channels and even caves to the spring location (Al-Rawi et al, 1990).
INSTEAD CONCLUSION- TOWARDS AQUIFER CONTROL
Sarchinar spring is of essential importance for future development of Sulaimani city. Its ascedential flow, large catchment and huge groundwater resources provide an opportunity for better utilization and control of karstic aquifer. The precondition is systematic hydrogeological research that should include geophysics, drilling, tracing and permeability tests, and several other methods in order to determine most suitable tapping structures and methods of possible artificial control of the discharge.
Recently conducted hydrochemical and biological analysis (performed in Sulaimani University laboratories) during late 2005 proved that the spring water is still meeting WHO and Iraqi standards. However, permanent monitoring and preventive measures against pollution are order of the day concerning existing open karstic system, narrow highly populated area and several potential polluters.
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