REVITALIZATION OF HISTORICAL -ONÇEŞMELER WATER SYSTEM IN ,

Ahmet Dogan1, Eyüp Debik2

1Civil Engineering Department, Yildiz Technical University, , Istanbul 34220, Turkey, [email protected]

2Environmental Engineering Department, Yildiz Technical University, Esenler, Istanbul 34220, Turkey, [email protected]

Keywords: Water heritage, historic constructions, Onçeşmeler Fountain, Istanbul

Abstract Beykoz-Onçeşmeler is one of the best historical water fountains of Istanbul that was built during the Ottoman era of Turkey in 1746. This historical water system and its masterpiece water fountain survived until today. The fountain was built on a spring that actually discharges water collected from precipitations of Beykoz-Forestry region. The fountain structure is very important in terms of architecture and in historical perspective. People of Beykoz District in Istanbul have raised public awareness for protection and sustainability of this historical water system, therefore, Istanbul Great Metropolitan Municipality supported this research to investigate the hydrological properties of the water system to revitalize it according to its historical conditions. In the last couple of years, flow rates of the Onçeşmeler reduced significantly. A wastewater collection tunnel passed thorough Beykoz District along the Istanbul Straight at the depth of -5 m elevation below sea level. The tunnel was blamed to drain the groundwater that supplies water of the Onçeşmeler along the tunnel’s outer face. In this study, it was aimed to investigate the hydrological and hydrogeological properties of this historical water system in order to understand the relationship of the climate conditions, land use changes, and the wastewater tunnel passing underneath the water system with water of the Onçeşmeler fountain. At the end of the study, it was found out that the tunnel construction caused to increase hydraulic conductivity of the formation around the tunnel perimeter. Groundwater started flowing along the tunnel to follow this newly formed higher hydraulic conductivity zone along the tunnel instead of flowing towards the Onçeşmeler as it was used to flow formerly. This is especially true in dry and average seasons, however, in wet seasons, since groundwater levels are high, water is abundant to flow towards the Onçeşmeler as well as along the tunnel. Therefore, the effect of the tunnel is seen only in dry and partially in average seasons but not in wet seasons. The change of the precipitations, land use change, and other hydrological factors are not very effective in reducing the Onçeşmeler fountain.

1 Introduction Supplying water to Istanbul has been a problem throughout history. During the Byzantine period (364 - 378), two aqueducts and a big underground reservoir were constructed to bring water to the city [1]. During the , 16 water ways totaling 130 km and 33 aqueducts supplied water to a population of 150,000 - 200,000 people [2]. Onçeşmeler water fountain is one of the

9 unique historical structures built in 1746 to supply water to the Beykoz District of Istanbul [3]. In Ottoman culture, water was being supplied to the squares of the districts via fountains to have people access good quality spring water for free of charge. Most of the fountains are generally piece of the art and reflect the architecture characteristics of their time. In this perspective, the Onçeşmeler fountain is a good example, which is among the iconic historical structure of Beykoz with its unique architectural structure and modest identity (Figure 1). It is among the rare fountains of Istanbul and reflects its baroque style characteristics [4].

(a) (b) Figure 1: (a) Onçeşmeler Water Fountain; (b) Location of Onçeşmeler Water System in Istanbul

The Onçeşmeler fountain is technically a spring water (groundwater) emerging from the rocks (aquifer), on which a natural reservoir was carved into the rocks at the back of the fountain structure. The water collected in the reservoir freely flows out of ten nozzles made of bronze. Therefore, the structure is called as Onçeşmeler that literally means in Turkish “Ten-Fountains” (Figure 2).

Istanbul sets a good example of challenges faced with in water supply in heavily populated cities, where illegal settlements on watershed zones pose a threat to scarce water resources. Problems caused by lack of implementation of regulations could be compensated by engineering solutions. The Onçeşmeler fountain has been supplying spring water to the square of the Beykoz. Since it was built but in the last couple of years it was faced with the danger of getting dried or decreased its water level. This situation took the people’s attention and several protests took place to save the Onçeşmeler fountain and to urge water authority of Istanbul Great Metropolitan Municipality (IGMM) to find the cause of the problem and to take necessary measures to solve the problem.

This study aimed to investigate those reasons that cause the flow reduction or even drying of the historic fountain and to find possible solutions to revitalize and make it available for public usage again. Possible reasons for reduced flow rates are (i) climate change and reduced recharge due to less rainfall compared with historical situation, (ii) new illegal groundwater wells opened in the area that interfere with the source of Onçeşmeler water, (iii) land use changes because of increas- ing urban area and decreasing forest area, and (iv) groundwater loss due to the tunnel construc- tion of "Kavacık-Paşabahçe-Beykoz Wastewater Tunnel" passing underneath the recharge area of the fountain. This tunnel is suspected to create a loose-cracked formation around the tunnel peri-

10 meter by deforming the geological formation around the tunnel during tunnel construction, which may forces groundwater flowing along the tunnel instead of flowing towards the Onçeşmeler fountain.

(a) (b) Figure 2: (a) Water flows out of TEN-NOZZLES coming from the (b) natural reservoir carved into rocks behind the fountain

2 Materials and Methods 2.1 Description of the study area The Onçeşmeler fountain is located in the main square of Beykoz district of Istanbul next to Bosphorus. The area is relatively protected from urban developments because of its historical characteristics and forest cover. The area is bounded by Bosphorus from west and forest region from east hilly area. It has steep slopes with natural forest cover. The climate in the region is described as "Transition Type Climate", which is a mixture of Mediterranean and climate. The summers are not as hot as the Mediterranean climate and not as rainy as the Black Sea climate. The annual precipitation is around 800 mm. The maximum rainfall is observed between November and February, and the lowest in July. The average temperature of summer months is 20-23 °C.

2.2 Water catchment area The surface watershed area of the Onçeşmeler fountain encompasses the north-eastern and eastern slopes of the valley, where the fountain is located. Those slopes are very steep and short, therefore, it is clear that the source of the Onçeşmeler is not from surface water but from ground- water. The groundwater catchment area is much larger than the surface water catchment area of the fountain (Figure 3).

2.3 Geology and hydrogeology of the region There are numerous studies on the general geology of the region [5-8]. The fountain is located on a hill slope with gravel and alluvium deposits, but the dominant formation of the region is Dolayoba limestone. Geophysical studies were performed in the region in order to investigate the possible aquifer formations and groundwater availability before the location of observation wells were determined. Geophysical studies showed that the Onçeşmeler watershed area consists of 3-4 m thick clay units and sandstone alternation with fractured cracked limestone in between 4-60 m.

11 It is also estimated that the average groundwater depth is around 20-30 m. In the northern part of Onçeşmeler, 30-43 m limestone formation is overlaid by 28-30 m of impermeable clay unit. These results were proved to be true after analyzing the well logs obtained during the geological study in the region.

Figure 3: Water catchment area of the Onçeşmeler

Hydrogeological investigation was carried out by drilling 6 observation wells on the recharge area of Onçeşmeler based on geophysical studies. Bore holes of the observation wells were used to understand the geological structure of the region. The drilling locations are chosen such a way that four of them are located along the wastewater tunnel passing through the recharge area of Onçeşmeler. These four observation wells are used to understand the effect of tunnel construction on groundwater flow characteristics in the region. Other two of the wells together with further wells are located such a way that helps to obtain a groundwater map of the region. The locations of the wells and the tunnel lines are shown in Figure 4.

Figure 4: The location of the observation wells and tunnel lines

12 The hydrogeological properties of the water catchment area of Onçeşmeler are interpreted by examining the well logs and published geological-hydrogeological maps. In order to determine the hydraulic conductivity of the limestones in the study area, slug tests for each observation well were performed. Well logs, the experimental results and field observations showed that the region has an aquifer structure consisting of cracked, fissured, porous limestones that proves the accuracy of the available hydrogeology and geological maps. Well logs also showed that the cracked rock structure in the region has an average joint spacing of 10 cm and a crack spacing of 0.3-1 mm. Based on this structure and type of rock, it is estimated that the hydraulic conductivity of this karstic formation in the study area can be taken as between 10-2 and 10-4 m/s.

2.4 Hydraulic characteristics of Onçeşmeler The average flow rate of the Onçeşmeler in 1994 was 789 m3/d. In the same year, the flow rate decreased to almost 100 m3/d due to newly opened groundwater production wells in the region. Flow rate of the fountain was measured as 165 m3/d on March 20, 2013. Recently, it was recorded that the fountain does not flow most of the time but only in small amounts at rainy seasons. Based on the monthly measurements in the period of 2015-2016, the average flow rate of the fountain in winter of 2015 was about 400 m3/d, and it was dry in summer 2015.

2.5 Tunnel passing through the recharge area of the Onçeşmeler Kavacik-Beykoz wastewater tunnel was constructed between 2007 and 2009. The tunnel is 4,267 m in length and 3,175 mm in diameter. The rock formations generally are carbonate shale, sandstone, mudstone, clayey limestone, marine limestone, and frequently encountered quartz veins as seen in Figure 5. During the tunnel construction works, it was reported that groundwater came into the tunnel from some points [9]. Geological and hydrogeological aspects of the Kavacık- Beykoz wastewater tunnel were obtained during TBM drilling. This wastewater tunnel passes through the upstream recharge area of Onçeşmeler at an elevation of -5 m below sea level. By considering the groundwater levels are around +2 to +6 m, it is suspected that this tunnel might have affected the Onçeşmeler flow rates.

Figure 5: An example from the section of Kavacık-Beykoz Wastewater Tunnel [9]

13 All hypotheses about the possible causes of flow decrease in Onçeşmeler were investigated; precipitation and ET records were correlated with the flow rates of the fountain to see the effects of climate conditions on the flow rates of Onçeşmeler. Land use changes and residential areas’ developments were also evaluated. To investigate the effect of the tunnel on the water system, groundwater levels at monitoring wells were collected every 15 days. Water quality samples were also taken every month in order to investigate the possible effects of residential areas on water quality. Groundwater flow mechanism around the tunnel and towards the Onçeşmeler was analyzed to see the probable effects of the tunnel on groundwater system.

3 Results and Discussion The main purpose of this study was to review the hydrological and hydrogeological characteristics of the historical Beykoz Onçeşmeler fountain in order to determine the recharge area, to investigate the quantity and quality of groundwater that is the source of the fountain water, and to investigate the possibilities of revitalizing the Onçeşmeler to its historical flow conditions by solving the problems decreasing the flow rates of Onçeşmeler or even drying totally in summer periods. As it was summarized before, the possible reasons for reduced flow rates are climate factors, new groundwater production wells opened in the area, increasing impervious areas due to urbanization, and groundwater loss due to tunnel construction passing underneath the recharge area of the fountain.

3.1 Groundwater - precipitation relationship First, precipitation, groundwater levels and the flow rates of the fountain are compared. The groundwater levels and the flow directions are visually analyzed in order to determine the source of fountain’s water and its dependency on the precipitation.

Rainfall recordings, groundwater levels and flow rate of Onçeşmeler are analyzed in order to see the interaction of groundwater levels and Onçeşmeler flow rates with rainfall. It was seen a relatively rapid correlation between 15-Days total precipitation and the groundwater levels. The groundwater levels have risen after substantial rains. The flow rates of the Onçeşmeler also respond to precipitation rather quickly similar to observation well elevations as seen in Figure 6. This shows that Onçeşmeler water is supplied solely from groundwater, which in turn is recharged by precipitations. Rapid recharge rates after rainfall show that the aquifer and overlying alluvial layer are highly permeable. This observation complies with the results of hydrogeological investigations that indicate the existence of fractured limestone aquifer in the region.

As seen in Figure 6, the Onçeşmeler is dry in summer months, when there is no precipitation. Contrary to this, although there was no precipitation in the summer of 2016, considerable amount of flow rates were observed in Onçeşmeler. This can be explained by the pumped water supply from two deep groundwater production wells, drilled by Istanbul Water Authority (ISKI). In 2016, ISKI took measures to prevent public outrage because of decreased flow rates of the fountain and drilled two wells at upper part of the aquifer to supply water to the Onçeşmeler fountain. With this boosting, Onçeşmeler started flowing around 300 m3/d in summer 2016, which is almost equal or higher than its historical values. In rainy winter 2016, flow rate of Onçeşmeler reached 800 m3/d,

14 approaching the measured values in 1994. Water pumped to supply Onçeşmeler is actually coming from the same aquifer that is the main source of Onçeşmeler itself.

From the analysis, it was also understood that the rainfall contribution to the recharge has apparently 15 days delay time. Onçeşmeler flow rates are directly related to precipitation. About 10% of the total rainfall in the basin area recharges the aquifer. Consequently, it can be concluded that rainfall-recharge relationship has also minimal effects on the decreased flow rates of Onçeşmeler due to hydrological or climate factors.

Onçeşmeler flow rates show seasonal variation. To understand the tunnel effect on groundwater flow and on Onçeşmeler flowrates, groundwater elevation maps were plotted to see the flow direction at every season (Figure 7). The loose, deformed, highly conductive formation that occurred during the construction around the perimeter of the tunnel causes the groundwater flow along the tunnel that in turn reduces the Onçeşmeler flow rates significantly.

The geological structure of Beykoz region consists of 5-10 m clayey depositions on the surface and urban areas that significantly reduces the permeability. The frequency of intense rainfalls is increased because of climate change that increases the surface runoff and decreases the infiltra- tion compared to moderate intensity rainfalls. This in turn decreases the groundwater recharge in the region that may cause the flow rates of Onçeşmeler reduced.

Figure 6: Onçeşmeler Flowrates and 15-Days Total Precipitations

Although the Beykoz region is under the stress of urbanization, the forests and green areas are relatively well protected, where rainfall can still recharge the groundwater. This is obviously seen in winter months, when the groundwater levels rise the Onçeşmeler starts flowing at its maximum rates. Because of this, it can be stated that the impact of land use change and climate change on groundwater recharge remained minimal to moderate.

15 Groundwater level measurements were made every 15 days in the observation wells, of which four ones are located on both sides of the Kavacık-Beykoz wastewater tunnel (Figure 4). Based on these measurements, the groundwater level map and associated groundwater flow directions have been determined. Groundwater maps and flow directions are obtained for summer months and winter months, separately. The tunnel crosses the region in the north-south direction at an elevation of -5 m. The groundwater of the region was used to flow towards Bosphorus in east-west direction before the tunnel construction. The tunnel caused the groundwater flowing along the tunnel instead of flowing towards Onçeşmeler in dry seasons. It was seen from the groundwater maps that during the low rainfall season the lose formation around the tunnel drains most of the groundwater and causes the Onçeşmeler to dry. On rainy seasons, the tunnel causes groundwater levels to decline, but it is not able to stop groundwater flow towards Onçeşmeler. As an inevitable result of tunnel construction, fractures, cracks and deformations took place around the tunnel. The hydraulic conductivity in this deformed zone can reach up to 10 times the original hydraulic conductivity [10]. For this reason, groundwater prefers to flow along this loose highly conductive formation that is called preferential flow.

To investigate the effects of the tunnel on groundwater and Onçeşmeler flow rates, groundwater elevation maps and flow directions are plotted on the same graphics as seen in Figure 7. Observa- tion wells were intentionally located on both sides of the wastewater tunnel passing through Onçeşmeler recharge basin. If there is a sudden drop in groundwater head over the tunnel that would be considered as the effect of tunnel on groundwater flow characteristics. A sudden drop up to 5 meter in the groundwater level as the tunnel passes was observed. This clearly shows the effects of tunnels on groundwater and Onçeşmeler flow rates.

(a) Average Conditions (b) Wet Season

Figure 7: Groundwater Elevations and Flow Direction

(c) Dry Season

16 3.2 Water Quality Study Residential development in the region can reduce the water quality slightly. To investigate the water quality of Onçeşmeler, water samples were taken monthly from observation wells and Onçeşmeler. The following parameters were analyzed according to Turkish Standard for “Water Intended For Human Consumption” at monthly periods [12]: pH, Turbidity, Conductivity, Color, Appearance, Taste, Odor, Alkalinity, Bicarbonate, Total Dissolved Solids (TDS), Ammonia, Total Hardness, Calcium, Magnesium, Sodium, Potassium, Iron, Manganese, Aluminum, Boron, Copper, Zinc, Cobalt, Antimony, Arsenic, Selenium, Mercury, Cadmium, Chromium, Lead, Nickel, Beryllium, Silver, Chloride, Sulfate, Nitrate, Cyanide, UV 254, Total Organic Carbon (TOC), Total Coliform Bacteria, and Fecal Coliform. Analytical results of the parameters turbidity, total hardness, nitrate, ammonia, iron, manganese, aluminum, and lead did not meet the limit values in some samples.

For the turbidity, the standard requires max. 5 NTU, but the turbidity of many samples exceeded this limit. On the other hand, samples taken from the Onçeşmeler reservoir met the limits luckily. For the hardness, there is no limitation, but waters are classified as hard water above 150 mg

CaCO3/L [11]. According to this, almost all samples have hardness higher than 150 mg/L.

While the Turkish Standard requires ammonium contents less than 0.5 mg/L, just four samples in the study had ammonia concentrations higher than this limit. For nitrate, the standard limits the concentration to less than 50 mg/L. Just nitrate concentration in 3 samples from observation wells exceeded this limit. However, the Onçeşmeler reservoir quality met this limit for all the samples.

Some parameters such as lead, aluminum, iron and manganese were analyzed just for selected months during the study. While drinking water should contain lead lower than 10 μg/L, some samples have more than that. For aluminum, the standard limits the concentration to less than 200 μg/L, and just some samples exceeded the limit in two observation wells, while Onçeşmeler reservoir quality met this limit for every sample. While the standard requires less than 200 μg/L iron, many of the samples during the study have more than this concentration. However, all samples from the Onçeşmeler reservoir met this limit. For manganese, the standard limits the concentration to less than 50 μg/L; just 6 samples from three observation wells exceeded this limit. On the other hand, Onçeşmeler reservoir quality met this limit for every sample. The analytical results show that some samples from some wells do not meet the desired limits in some periods. On the other hand, the results for samples taken from the Reservoir of Onçeşmeler are not similar to those of the parameters measured in the wells; they met the desired limits for all parameters except hardness and bacterial properties according to Turkish Water Quality Standards.

The collection of water at a large area causes a dilution of the pollutants, and the measured values meet the desired limits in the reservoir. On the other hand, the collected water from the reservoir is in the hard water class, but does not pose any health risks. For that reason, it is possible to supply the water to the public after good disinfection.

17 As the fountain is a historical structure, it is not possible to install any purification system within the area of Onçeşmeler. Because of this, it is considered that just disinfection process can be sufficient to supply water to public. Taking into account that water is put into use immediately after the storage reservoir, disinfection process must be carried out by UV disinfection process. Moreover, it would be useful to inform the public that it is hard water. If the hardness is wanted to be removed, it may be possible to make an ion exchange process at a reliable distance to the fountain and a suitable location after collecting the water from the wells. A cation exchanger can be used to remove the (heavy) metal ions from water.

4 Conclusions and Suggestions Analysis of the hydrological data by considering the groundwater and tunnel interaction shows that the main cause for the reduction of Onçeşmeler flow rates is the effect of tunnel on ground- water the flow mechanism. Climate effects and land use change have minimal impact on the flow rates of Onçeşmeler [13] . Given this conclusion, several alternative solutions are considered to revitalize the Onçeşmeler to its historical conditions. The first solution might be creating an impermeable buffer zone around the tunnel as wide as the diameter of the tunnel by jet-grouting. In this case, the cement injection should be made from the inside of the tunnel to the outside. Because the tunnel is in continuous use, this solution seems not to be suitable and is expensive. The second alternative is to create impermeable diaphragms at several points along the tunnel with cement injection from outside of the tunnel. Although these solutions can solve the problem in summer months, when groundwater level decrease, they are both expensive and difficult to implement.

The final solution is actually the solution that has already been applied by Istanbul Water Authority (ISKI) according to the suggestion of the authors of this study. Two wells in depths of 192 m and 241 m were drilled in the upper part of the aquifer in 2016. The groundwater pumped from these wells supplies Onçeşmeler.

The natural flow rate of Onçeşmeler in summer months varies from 0 to 300-500 m3/d. Average flow rate is 550 m3/d under typical groundwater recharge conditions. In wet seasons, there will be no problems with the flow rates. Considering these situations, most appropriate amount of water to transfer from the upper parts of the aquifer to the Onçeşmeler is 500 m3/d by-passing the tunnel line, which crosses thorough the groundwater recharge area. A float control system should be placed in the reservoir to manage the supply of 500 m3/d to the Onçeşmeler. When the flow rate is lowered from the target level, then the pumps of ISKI wells will be turned on automatically.

5 Acknowledgements This work was partially supported by İstanbul Great Metropolitan Municipality Water Administra- tion (ISKI) and ÇEVMED Company at the Yildiz Technical University, Technology Development Area. The authors would like also to thank DAAD and the Exceed SWINDON project for providing them financial support to participate at this workshop.

18 6 References [1] Saatci, A.: Solving Water Problems of a Metropolis. Journal of Water Resource and Protection 2013, 5/44, 7-10. doi: 10.4236/jwarp.2013.54A002.

[2] ISKI, Istanbul Water and Sewerage Administration: History of water management in Istanbul, 2017, available at http://www.iski.istanbul/web/en-US/kurumsal/iski-hakkinda/history-of- water-management-in-istanbul.

[3] Ayvansarayı, I.I.H.H.: (Hâfız Hüseyn, İbnü’l-Hâcc İsmâîl Ayvansarâyî), Hadîkatü’l-Cevâmi, Matbaa-i Âmire, Istanbul. 1865, vol. 2, p. 152.

[4] Dünden Bugüne İSTANBUL Ansiklopedisi ‘İshak Ağa Çeşmesi’, 1994, vol. 4, pp. 194-195.

[5] Dalgic¸S.: The influence of weak rocks on excavation and support of the Beykoz Tunnel, Turkey, Engineering Geology 2000, 58, 137–148.

[6] Özgül, N.: Istanbul il alanının jeolojisi, Istanbul Kent Jeolojisi Projesi, IBB, Istanbul 2011.

[7] Özgül, N.: Stratigraphy and Some Structural Features of the Istanbul Palaeozoic. Turkish Journal of Earth Sciences 2012, 21, pp. 817–866.

[8] Ündül, Ö., Tuğrul, A.: The Engineering Geology of Istanbul, Turkey, IAEG 2006 Engineering Geology for tomorrow’s cities, Nottingham, UK, September 6-10, 2006, pp. 34-34

[9] Guclucan, Z., Meric, S., Palakci, Y., Bilgin, N., Balci, C., Copur, H., Namli, M., Bilgin, A.R., and Kandemir, E.: The Use of Theoretical Rock Cutting Concepts in Explaining the Cutting Performance of a TBM Using Different Cutter Types in Different Rock Formations and Some Recommendations. In: Proc. World Tunneling Congress, Safe Tunneling for the City and for the Environment, Budapest, Hungary May, 2009, pp. 487-489.

[10] Butscher, C., Einstein, H.H., Huggenberger, P.: Effects of tunneling on groundwater flow and swelling of clay-sulfate rocks. Water Resources Research 2011, 47, 11.

[11] Davis, M.L.: Water and Wastewater Engineering, McGraw Hill Companies Inc., N.Y., USA, 2010, pp 1268

[12] Turkish Standards Institution: Turkish Standards for Water Intended for Human Consumption, Ankara, 2005

[13] Musaoglu, N., Tanik, A., Kocabas, V.: Identification of land-cover changes through image pro- cessing and associated impacts on water reservoir conditions. Environmental Management 2005, 35(2), 220-230.

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