İstanbul iline içme-kullanma suyu temini amacıyla Sapanca Gölü Havzası'nın incelenmesi

Abstract

İstanbul'un su sorunu 1990 yılının son aylarında büyük bir boyut kazanmıştır. İstanbul'un su sıkıntısında en önemli nedenler, nüfusun olağanüstü artışı ve kaynaklardaki artışın nüfus artışının gerisinde kalması, iklim koşullarının tüm dünyada olduğu gibi Türkiye'de de eskiye göre daha düzensizleşmesi, su kaynaklarının yeterince korunmaması nedeniyle elden birer birer çıkmaları ve yanlış planlama ve programlama stratejileri sonucu su kaynaklarının geliştirilememesidir. Ayrıca İstanbul'un gerek temiz su, gerekse pis su şebekelerinin yeterli olmayışı nedeniyle şebeke kayıpları çok yüksektir. Nüfusu devamlı ve yüksek bir oranda artan İstanbul'un su gereksinimini karşılamak için önce kendisinin yerüstü ve yeraltı sularından yararlanılmıştır. Bu yeterli olmayınca komşu illerden su getirilmesi gündeme gelmiştir. Planlama aşamasında olan ve İstanbul'a su temini için uzun vadeli bir çözüm olarak öngörülen Büyük Melen Sistemi ise, gelecekte İstanbul ilinin su ihtiyacını karşılayacak kapasitedir. İSKİ tarafından İstanbul'a verilen su, şehrin Asya ve Avrupa yakasında bulunan yağış havzalarından sağlanmaktadır. Yağış havzaların yıllık su potansiyelleri, mevcut su kaynaklarına yıllık ortalama su girişi, yağış havzalarının alanları, ortalama yıllık yağışları ve akış katsayıları dikkate alınarak hesaplanmıştır. İSKİ tarafından belirlenen emniyetli verimlerin İstanbul ilinin ihtiyacım karşılayıp karşılayamayacağının belirlenmesi amacıyla İstanbul ilinin nüfus ve su ihtiyacı tahmini yapılmış ve sonuçta İstanbul ilinin ne kadar su açığının bulunduğu hesaplanmıştır. 203 1 yılında devreye girecek olan Büyük Melen Sistemi tamamlanıncaya kadar yakın çevredeki temiz su kaynaklarının etüd edilmesi gerekmektedir. Bu amaçla İstanbul'a yakınlığı ve kaynaklarının büyüklüğü nedeniyle Aşağı Sakarya Havzası' nda yeralan Sapanca Gölü ve Mudurnu Çayı hidrolojik açıdan incelenmiştir. Sapanca Gölü'nden su temin eden belediyelerin ve endüstri kuruluşlarının su ihtiyaçları saptanmıştır. Su potansiyeli açısından oldukça zengin olan Mudurnu Çayı, Sapanca Gölü'nde gerekli aktif hacmin oluşturulması koşuluyla, İstanbul ilinin içme ve kullanma suyu ihtiyacım karşılayacak durumdadır. Bugün İstanbul'a yılda 550 milyon m3 su verildiği gerçeği dikkate alınacak olursa, Mudurnu Çayı sularının 207x1 06 m3'lük bir kısmının İstanbul'a tahsis edilmesi hiç de küçümsenmeyecek bir olaydır. Sapanca Gölü'nde herhangi bir aktif hacim yaratılmadan, Mudurnu Çayı'nın % 95 garantili akımı olan 2.5 m3/sn su ilk planda İstanbul'a tahsis edilebilir. 10, 15, 20, 25 m3/sn'lik aylık ortalama değerler esas alınarak, sırası ile bu debilere eşit ve daha küçük olan debilerin, Sapanca Gölü tarafından regüle edilerek İstanbul'a tahsis edilmek üzere Sapanca Gölü' ne derive edilmesi hususu incelenmiştir. 10 m3 /sn debiye göre boyutlandırılan Mudurnu-Sapanca isale hattı inşa edilerek Sapanca Gölü vasıtası ile İstanbul'a 2.5 m3/sn'lik Mudurnu Çayı suları tahsis edilmeli ve daha sonra ise gölde aktif hacim kazanılmasını sağlayacak tesisler yapılarak İstanbul'a tahsis edilen su miktarı 6.5 m3/sn'ye çıkartılmalıdır.

The demand for reliable piped water supplies in Istanbul is increasing rapidly. To assist in meeting this demand it is proposed that the feasibility of supplying the city from the Sapanca Lake be investigated. The concept of using the water resources in the Lower Sakarya Project Area to supply Istanbul is not new. The proposal of using the Sakarya River for that purpose was investigated by TAMS in 1965 and in 1970 by the DAMOC Consortium. Water would be diverted from the Sakarya River into the east end of Sapanca Lake, allowing the same amount to be abstracted from the west end of Sapanca Lake (thereby saving about 16 kilometers of pipeline). This water would then be transferred by the most economic of several possible routes to the Ömerli Reservoir Treatment Works site and from there into service reservoirs in Istanbul DAMOC rejected the use of the Sakarya because of concern about the quality of the water in the River. It was dirty with high colour, high solids content, high turbidity and high hardness and they feared it would become polluted because of effluent discharge upstream. Treatment of this water would be possible though the processes would be more complex than those practised currently using the cleaner reservoir source waters. The Sapanca Lake water quality will also deteriorate by mixing with the Sakarya River water. The communities within the Outside Greater Istanbul Project Area have always relied on nearby streams and springs as their sources of water supply. However, the populations of these communities have grown to the point where these local sources are completely utilized. The shift in land use from agriculture to heavy industry is creating water demands far in excess of the existing supply capability. The need for development of additional sources of supply is clear. This report contains a detailed review of the existing and potential sources of supply for the Istanbul Project Area and makes a preliminary examination of the feasibility of a project to transfer water to the Istanbul water supply system from the Sapanca Lake. The objective of this report is to examine the feasibility of the proposal and make appropriate recommendations. This review consists of a discussion of the hydrologic characteristics, physical features, yield of the existing, lasting and planned surface water sources, the estimated population and water demand in the Istanbul Project Area and the Sapanca Lake Basin. In the second section, the hydrologic characteristics, the existing, lasting and planned water sources of the Istanbul Project Area are investigated. In order to find out the growth in demand for water in Istanbul, the predicted population in Istanbul is provided by ISKI. Comparing the water demand with the yield of the existing surface water sources, it becomes possible to find out whether there is enough water to supply the city. Based on the last population estimates, it is clear that the water sources in xii Istanbul will not meet the growth in demand for water until the Yeşilçay System would be completed in 1999. In this transition period, ISKI and DSI carry out some water development programmes, for example the Istranca Streams Project. The Melen River will be used as the main source of water in 2032, which will meet the rising demand for water in Istanbul Until the Great Melen Project would be completed in 2032, some adjacent clean water sources have to be examined. As the Lower Sakarya Project Area has ample surface water resources to meet the needs for regional water supply, it will be appropriate to examine two of the available water sources, the Sapanca Lake and the Mudurnu Creek. Two major sources of supply in the Lower Sakarya Project Area are the Sapanca Lake and the Mudurnu Creek which is one of the most important branches of the Sakarya River. Sapanca Lake is a large natural lake situated in the eastern part of the Lower Sakarya Project Area. It is roughly elliptical in shape with an east-west orientation to its long axis, which is 16 kilometers long. The east end is about 5 kilometers west of Sakarya River, and the west end is about 20 kilometers east of Izmit. The lake surface varies from approximately 31 to 33 meters in elevation and from 46 to 52 square kilometers in area due to normal seasonal variations. This range in elevation results in an annual variation in storage of about 100 million m3. A survey of existing buildings, railroads and recreation facilities located along the shores of the lake showed that the maximum water surface of the lake should not be allowed to rise for prolonged periods above elevation 32.0 m. The east and west shores of the lake are shallow swamps. The maximum depth of Sapanca Lake is about 52 meters, which results in a bottom elevation of approximately 20 meters below sea level. The natural basin of Sapanca Lake located at the southern and higher end of the project offers several alternative uses as a storage reservoir. The storage capacity is limited in part by the existing buildings, road and railroad on its shores and by the effect wide fluctuation of the Lake level would have upon recreation. A reasonable fluctuation in the lake surface would provide a reservoir capacity of about 150 million m3. This capacity is adequate to provide carry-over storage for development of about 4.8 mVsec or nearly all of the inflow into the Lake. The area of the Sapanca Lake water shed is 31 1 square kilometers, including the area of the lake. Drainage to the lake is primarily from the steep hills to the north and south of the lake. The streams which discharge into Sapanca Lake from the north ad south are relatively short. The area experiences short duration, high intensity storms, which cause flash flooding and storm runoff that carrier large quantities of detritus. Some inflow can be attributed to springs and groundwater discharge from the Sapanca aquifer, which underlies the alluvial plain along the south side of the lake. This situation causes a relatively high dry season inflow. The only outlet from the lake is the Çarksuyu, a tributary to the Sakarya River. The Carksuyu has become heavily polluted both from domestic sewage and industrial wastes. For example, it was estimated that the three factories in Adapazarı, that manufacture starch, release some 150 m3 per day of waste water containing sulphur xni dioxide and hydrocloric acid. An acetic acid factory releases about 600 m3 per day. Four leather tanning factories release acids to the stream. Similarly, disposal of animal waste from slaugther houses is released into the stream. The only known attempt to control unrestricted wasting into the Çarksuyu exists at the sugar factory where wastes from processing sugar beets are collected in stilling pools to settle out the high lime and acid contents in waste waters before releasing these waters to the stream. The Çarksuyu was the principal source of water supply in the vicinity of Adapazarı. As the quality of the Çarksuyu deteriorates, withdrawals are made neither directly from the creek nor from wells on its bank any longer. Sapanca Lake has sufficent undeveloped water, when added to existing surface resources and projected groundwater development, to meet the projected Near Term (1996 to 2031) domestic requirements of its surrounding municipalities. The water demand of the industrial facilities in Izmit have to be satisfied from another water source, for example from the planned Yuvacik Dam. The average annual inflow of the Lake is 185.63 million m3. The maximum and minimum annual inflows were 312.30 and 114.17 million m3 in 1969 and 1966, respectively. The average annual inflow volume is equivalent to a rate of 5.89 m3/sec. The average storage in the Sapanca Lake under natural conditions (100 million m3) is about 54 percent of the average annual inflow (185.63 million m3). The inflow records of the Sapanca Lake are provided from the "Hydrologic Report of the Sapanca Lake" prepared by DSI in 1983. The computed records covering a period of 16 years are used as a basis for determining the total annual yield of the Sapanca basin. The mass curve of the Lake has been obtained, based on the records from 1963 to 1978. In the light of the mass curve of the computed useable inflow, some results are obtained :. The required storage is 64xl06 m3 to produce 124.25xl06 m3/year (3.94 mVsec) draft from the lake to supply Adapazarı and Izmit. The water demand of the industrial facilities in the vicinity of Adapazarı that drew water from the Çarksuyu must be satisfied by pumping from the Sakarya River.. In the case of using all of the average annual flow of the Sapanca Lake (185.63 million m3), 61.38xl06 m3/year (1.95 m3/sec) would be available to use for different purposes with an active capacity of 234x1 06 m3. This amount of water could be used to transfer water to Istanbul water supply system or to meet the future needs for the regional water supply. Sapanca Lake is a valuable resource and its waters are well suited from standpoints of both quality and clarity for domestic and industrial water supply, fish culture and recreation, as well as irrigation. It is advisable to conduct supplemental water quality analyses; however the waters of Sapanca Lake are considered to be within acceptable limits for the purposed use. Sapanca Lake water will probably deteriorate even further as nearby development takes place. The uncontrolled discharge of household and sanitary waste liquids from the communities could seriously impair the quality of the water in Sapanca Lake. Pollution of the lake from sewage, industrial processes and agricultural fertilisers may result in high nitrat levels. Recent legislation requiring industry to treat effluent prior to discharging it into the lake and the development of xrv sewerage and sewage treatment in towns will assist in maintaining quality standards in future. Mudurnu Creek is the second largest potential water source available in the Lower Sakarya Project Area, which enters the Sakarya River from the east. Its source is in the mountains east of the town of Mudurnu. The course of the creek is generally from east to west through the mountainous terrain until it reaches the Adapazarı Plain. The creek channel men turns in a northerly direction until it enters the Süleymaniye Swamp. The outlet from the swamp enters the Sakarya River 66 kilometers from the Black Sea. The channel capacity through the swamp is inadequate. Mudurnu waters pass through the swamp in numerous small channels; most of these are interconnected with Dinsiz Creek which enters the swamp from the east. A network of many small channels has resulted. The total drainage area of Mudurnu Creek is 1718 square kilometers and its length is 130 kilometers. The average gradient of the channel is 15 kilometers in the mountains and 0.5 m. per km in the plain. Two gaging stations have been operated on the Mudurnu Creek. The uppermost gaging station operated on Mudurnu Creek is at Dokurcun and was established by EIE in 1956. The drainage area at this point is 1059 square kilometers. The records of this station are considered to be accurate and have been valuable in these studies since they include records of the driest year in 26 years. The average depth of runoff of 222 mm. from Mudurnu Creek is relatively low in comparison with Dinsiz Creek (467 mm.) and Sapanca Lake (706 mm.). The average annual runoff in the Creek is 256 million m3. The minimum flow, which occurs during the irrigation season, is 1.52 m3/sec. Studies of the possibilities for storage of water on this stream and derivaring it into the Sapanca Lake were carried out as alternative solutions to transfer water to Istanbul The feasibility studies are made to supply water to Sapanca Lake, thereby increasing its potential yield, from the Mudurnu Creek, a major east bank tributary of the Sakarya River. The proposal is to feed Mudurnu Creek into the eastern end of the lake and to abstract an equal amount from an intake at the western end. This water would then be transferred by the most economic of several possible routes to the Ömerli Reservoir Treatment Works site and from there into service reservoirs in Istanbul The quality of Mudurnu water is said to be good and problems on mixing with Lake water are not foreseen. The present urban and industrial use of water in and adjacent to the project area is centered around the cities of Adapazarı and Izmit. The tendency is for industries to locate along the railroad and the Istanbul-Ankara highway which passes through the north of the Lake. Industrial installations extend from 18 km. west to 6 km. east from Izmit and 6 km. southwest from Adapazarı toward izmit. Sapanca Lake, the most promising source of future water supply, is situated between these two ernes. In the vicinity of Izmit the present industrial use of water from the Sapanca Lake is about 66 million m3 per year. The largest individual user is a paper company at Izmit (SEKA) which obtains its supply by pumping from the Sapanca Lake. This diversion is at a continuous rate of 1 m3/sec and totals approximately 30 million m3 per year. xv The present water supply for the surrounding communities of Sapanca Lake is entirely adequate. With the present population of about 300.000, the potential water demand with adequate facilities would be about 70.000 m3 per day. The estimated municipal water demand in 2031 is about 360.000 m3 per day or 132 million m3 per year assuming an increase in population to 1.210.000 in that year, based on ratios developed for adjacent areas. The present water supply of 66 million m3 per year in the limit area should be increased if the city continues to grow at the present rate. It is estimated that the total industrial water demand of Izmit in 2031 will be about 80 million m3 per year. The total demand is estimated to be about 212 million m3 in 203 1. It can be easily seen that the Sapanca Lake will be inadequate to meet the future water demand of its surrounding municipalities and industrial facilities because it would exceed the supply by some 26 million m3. If the industrial facilities supply the required amount of water from another water source, the Sapanca Lake will be sufficent to meet the projected demand until 203 1. However, through diversion from Mudurnu Creek an additional 79 million m3 can be made available without a reduction in water quality and without an increase of the active storage capacity of the Lake. The values obtained from the Dokurcun gaging station are indicative of the dependable range in flow 2.50 m3/sec (79xl06 m3/year). This amount of water of the Mudurnu Creek can be transferred to Istanbul without storage. The 26 years of available records at the Dokurcun gaging station are carried to the regulator axis by multiplying the values with the correlation factor (1.2). The average monthly flows which are equal or smaller than 10, 15, 20 and 25 m3/sec are taken into account and thus the amount of water to be transferred to Istanbul and the required active capacity in the Sapanca Lake are calculated by using the mass curves. These active capacities are added to the before-mentioned active capacity of the Sapanca Lake to determine the total active capacity to meet the demand for water in the vicinity of the Lake and to supply water to be transferred to Istanbul. The minimum and maximum operating levels are determined by using the volume-area curve of the Lake. The most appropriate solution is the diversion of the flows which are equal or smaller than 10 m3/sec by using a transfer system with 10 m3/sec capacity to the Sapanca Lake. The required active capacity is 313xl06 m3 in order to transfer 6.5 m3/sec (207xl06 m3) water to Istanbul The active capacity will decrease to 140xl06 by transferring water in 24 months of the dry season (1957-1963) at rates varying between 1.77 m3/sec and 5.60 m3/sec. If 1.94 m3/sec of the Sapanca Lake water is transferred to Istanbul and the demand of the vicinity of the Lake is satisfied by the Lake, the required active capacity will be 374x1 06 m3. Therefore the minimum and maximum operating level have to be 24.50 m. -32.50 m., respectively. So it will be possible to transfer 270x1 06 m3 per year to Istanbul In the case of using only the Mudurnu Creek water (6.5 m3/sec) to supply Istanbul, the active capacity will be 204x1 06 m3 and the corresponding minimum and maximum operating levels will be 28.00 m.-32.50 m A transfer system would be appropriate to transfer water at rates varying between 2.5 and 10 m3/sec. This would make an additional 207 million m3/year available to consumers supplied from the Lake. The Mudurnu Creek is a relatively small river and such quantities are not continuously transferable. The proposal therefore envisages making use of the Lake as a reservoir, satisfying demand from users of Sapanca xvi waters by reducing Lake levels at times of low flow in the Mudurnu Creek. The water levels will be much reduced in low flow periods and raised above present levels in high flow periods. The effect of these fluctuations on the water quality and ecology of the Lake and its surroundings has to be examined. The lake waters should be conserved to serve as the principal source of supply for Izmit and the adjacent industrial area. The total yield of Sapanca Lake could be increased by 79 million m3 per year by diverting the Mudurnu Creek into the Sapanca Lake. This project could provide about 8.5 m3/sec of water to Istanbul It will meet the rising demand for water in Istanbul The dependable low flow in the river would be sufficient to allow abstraction of up to 8.5 m3/sec for supplies to Istanbul. A flow of 8.5 m3/sec would be sufficient to satisfy projected demand to the year 2030. The Sapanca Transfer Project has been examined at pre-feasibility level. This seems reasonable given the considerable distance of the Sapanca Lake from Istanbul, which in addition to increasing costs also presents considerable technical challenges. However, no consideration of detailed operational requirements has been made. As there is 120 kilometers of route to be controlled and operated, the problems will be considerable. If the proposal to transfer water from Sapanca Lake into the Istanbul water supply system is feasible, the transfer system must be investigated technically. Communication systems will have to be provided and safety devices provided along the routes. Energy use and control would have to be carefully examined. The existing distribution system in Istanbul also requires attention. In addition to problems of leakage from the existing mains, the distribution system capacity will require progressive enlargement and expansion in order to provide the growing population with water at their taps. The water distribution network within Greater Istanbul is said to be inadequate and a project to improve it by participation in extending it and undertaking leak detection could be attractive.