İstanbul'un su kaynakları ve Büyük Melen sistemi'nin değerlendirilmesi

Abstract

Bugün nüfusu 10 milyonu geçen, Türkiye sanayi ve ticaretinin en önemli merkezi olan İstanbul'a içme kullanma ve sanayi suyu sağlanması her zaman kentin en büyük sorunlarından birisi olmuştur. Bu sorun kentin büyümesi ile orantılı olarak hergün biraz daha büyümektedir. İstanbul'un nüfus artış hızı 1955'ten 1990'a kadar ortalama yıllık %4.9 olmuştur. Bu büyüme hızı devam ettiği takdirde 2020 yılında nüfus 33 milyon, yıllık su ihtiyacı da 3.216 hmVyıl olacaktır. Bu durumda İstanbul'un mevcut (704 hmVyıl) ve planlanan (1.906 hm3/yıl) su kaynaklarının toplamı (2.610 hm3/yıl), 2020 yılında ihtiyacı karşılamayacaktır. Bu nedenle kentin nüfus artışında büyük rol oynayan göçün azaltılabilmesi için önlemler alınmalı, göç sebepleri ortadan kaldırılmalıdır. İstanbul'a yakın gelecekte su temin etmek için Sazlıdere Barajı, Kirazdere Barajı, Istranca Dereleri üzerindeki barajlar ve Yeşilçay Regülatörleri planlanmıştır. Emniyetli verimi 55 hmVyıl olan Sazlıdere Barajı'nın inşaatı 1996 yılında tamamlanmıştır. İzmit'in 10 km güneyinde yer alan Kirazdere Barajı'nın 2000 yılında tamamlanması ve 100 hm3/yıl suyun İstanbul'a verilmesi düşünülmektedir. Istranca Dereleri üzerinde inşa edilecek regülatör ve barajlarla 2000 yılma kadar toplam 14 dereden yılda 270 hm3 su sağlanması planlanmaktadır. Yeşilçay Regülatörleri ise İstanbul'un 60 km doğusunda yer alan Çanak ve Göksu Dereleri üzerinde inşa edilecek ve 2001 yılında 145 hmVyıl su şehre temin edilecektir. İstanbul'un uzun vadeli içme suyu ihtiyacını karşılamak amacıyla geliştirilmesi planlanan en önemli kaynak Büyük Melen Çayı'dır. İstanbul Boğazı'nın 170 km doğusunda yer alan Büyük Melen Çayı'ndan 4 kademede toplam 1.190 hmVyıl su temin edilmesi düşünülmektedir. 1. aşamada baraj yapılmadan bir regülatör (bağlama) ile 268 hmVyıl su alınması önerilmiştir. Melen Barajı 2. aşamada inşa edilecek ve 2005 yılında 307 hmVyıl su, 2010 yılında ek bir isale hattıyla yine 307 hmVyıl su ve 2020 yılında da 308 hmVyıl su şehre verilecektir. Bu çalışmada ise regülatör yapmadan, Melen Barajı'ndan önce inşa edilecek olan memba batardosundan daha fazla suyun çok daha az maliyetle alınabileceği gösterilmiştir. Ayrıca memba batardosu bir biriktirme haznesi olarak kullanılacağmdan suda bulunan iri daneler çökelecek, suyun bulanıklığı azalacak, dolayısıyla buradan alınacak suyun kalitesi, regülatörden almacak suyun kalitesinden daha iyi olacaktır.

Historical Development Established 4500 years ago and urbanized for over 2600 years, Istanbul is the first metropolis in the world having a population over a million in the 1 1 th century. The city of Istanbul is located on both sides of Bosphorus and along the Sea of Marmara, and is the largest city in Turkey. It is the industrial, commercial, tourism and cultural center of Turkey. Today Istanbul's population alone is more than some European countries. Ever since its establishment, administrators have dealt with the problem of providing a safe and healthy water to the city. Arches, cisterns and fountains were constructed for supplying water. The first facilities were Kırkçeşme and Halkalı whose construction began in the Roman and Byzantium period. Some parts of these faculties near to Cebeci Village, were built in the 4 th century (AD). Other parts near Kemerburgaz were built in the 6 th century (AD). In the Ottoman period the old faculties were repaired and the new ones were constructed by architect Sinan. Taksim water works, built in 1730, gave water to Beyoğlu and Galata regions. Some small dams like Valide Dam, Elmalı Dam, etc. which we still supply water were built in the Ottoman period. The job of bringing water from Terkos Lake was given to a French company. In 1881, when the water demand of the city could not be met, the company known as Terkos commonly among the population built a pumping station for supplying water to Istanbul This facility is the first system of Turkey working under pressure. Providing water to Istanbul by French companies lasted until 1932. Finally, Terkos company was turned over to the Istanbul Water Administration which was established under law no: 2226 in 1933. Existing Water Sources The existing water sources of the Istanbul water supply system are Terkos Lake, Alibeyköy Dam, Büyükçekmece Dam, Ömerli Dam, Darlık Dam, Elmalı Dams, dams on the Istranca Rivers and Şile Wells. Terkos is Istanbul's oldest reservoir. It is situated 40 km northwest of Istanbul and has been a major source of water since late 19 th century. Terkos has a drainage area of 619 km2 and its annual average yield is 142 million m3. Water of Terkos Lake is purified in the Kağıthane Treatment Plant. The Alibeyköy Dam was constructed at about 10 km northwest of Istanbul in 1972 as a back-up reservoir of Terkos. A part of the Terkos water is fed to the Alibeyköy reservoir. Alibeyköy has a drainage area of 160 km2 and its annual average yield is 36 million m3. The Büyükçekmece Lake, located at about 30 km west of Istanbul close to the Sea of Marmara, was developed in 1987 as a water source to Istanbul. The annual average yield of Büyükçekmece Dam is evaluated to be 100 million m3. The Ömerli reservoir, located at about 25 km east of Istanbul, was developed in 1972 as a master reservoir on Riva River, on the Anatolian side of Istanbul. The effective capacity of the Ömerli reservoir is 235 million m3 and the annual average yield is 220 million m3. Ömerli has a drainage area of 634 km2. Ömerli water is pumped to Emirli Treatment Plant for purifying. The Darlık Dam, located at about 40 km east of Istanbul on the Black Sea side, was constructed in 1988 and put into service in 1989 as a back-up reservoir of Ömerli. Darlık has a drainage area of 207 km2 and the annual average yield is evaluated to be 97 million m3. Water of Yeşilvadi Weir which was constructed in 1992 and water of Şile Wells are pumped into the Darlık reservoir. All of the Darhk water is pumped up into the Ömerli reservoir for water supply to Istanbul. The Elmah reservoir, located at about 10 km northeast of Istanbul, has long been a major water source to the Anatolian side of Istanbul since its first stage development in 1893. The second stage development was made in 1956 to cope with an increasing water demand on the Anatolian side of Istanbul. Elmah has a drainage area of 76 km2 and the annual average yield is estimated to be 15 million m3. The Istranca System, located at around 40 km northwest of the Terkos Lake, has been proposed to feed Terkos with additional water through a pipeline system along the northern coast facing the Black Sea. ISKI has a plan to develop the Istranca System in four phases. Phase 1 was completed in 1995 and Düzdere, Kuzuludere and Büyükdere Dams were constructed. 44 million m3/year water is provided from these three dams. xt Potential Water Resources Sazbdere Dam, Kirazdere Dam, Yeşilçay Weirs and the second, third and fourth stages of Istranca System has been proposed as a short-term solution to the habitual water shortage in Istanbul. The Sazhdere Dam is located at about 6 km upstream of the Büyükçekmece Lake on the European side of Istanbul. The construction of the dam was completed in 1996 but the pipeline has not been constructed yet. The average yield of Sazhdere is estimated to be 55 million m3/year. The Kirazdere Dam, located at about 10 km south of Izmit, is under construction with a target completion date at the end of 2000. Out of the average yield of 140 million m3/year, 40 million m3/year is planned to be consumed in Izmit and its vicinity which is out of the project area for Istanbul water supply, and the remaining 100 million m3/year is planned to be supplied to Istanbul. In the first stage of Yeşilçay System, Sungurlu and Isaköy Weirs will be constructed on the Çanak and Göksu Rivers. The annual average yield of these weirs is 145 million m3. DSI proposes Yeşilçay Dam with an average yield of 335 million m3/year to be constructed at the river mouths of two rivers in 2020. In the final three stages of Istranca System, ISKI plans to supply 226 million m3/year water from 1 1 rivers to Istanbul. The Büyük Melen System has been proposed by DSI as a long-term solution to the water shortage in Istanbul. The proposed Melen damsite is located on the downstream reach of the Büyük Melen River at about 170 km east of the Bosphorus and about 7 km south of the Black Sea which the Büyük Melen River drains into. The drainage area at the damsite is 2317 km2. The Büyük Melen System is proposed to be developed in five phases. In the first phase Melen intake without dam construction, and transmission line from Melen to Ömerli will be constructed. In the second phase new water treatment plant receiving raw water from Ömerli or directly from Melen, and transmission line from the new treatment plant to Kağıthane distribution center on the European side including Bosphorus crossing will be constructed. In the third phase Melen Dam and an additional transmission line from the Melen Dam to Kağıthane through Ömerli, including expansion of the new treatment plant will be constructed. In the fourth phase another additional transmission line from the Melen Dam to Kağıthane through Ömerli, including further expansion of the new treatment plant will be constructed. In the final phase another transmission line will be constructed and 1. 190 million m3/year water vWll be supplied to Istanbul Supplying domestic water to Istanbul, which is Turkey's most important center of industry and commerce with a population over 10 million, has always been an important problem. This problem is continuously growing in proportion with the city's population. The total existing and proposed water resources of Istanbul will be 2.610 million m3/year in 2020. When we look at the population censuses which have been made since 1955 we can see that the growth rate of Istanbul is 4.9%. If Istanbul's population increased with 4.9% growth rate, the population would be 33 million in 2020 and the water resources would not cope with the demand. The growth rate of Istanbul is twice the Turkey's average. The emigration to Istanbul xn must be prevented for solving the water problem as well as the other problems like traffic, air pollution etc. Büyük Melen System The stream gauging stations on the Büyük Melen River were examined for calculating the discharge at the Melen Weir site. The stream values had been observed since 1981 till 1991 at two stations belonging to Electrical Power Resources Survey and Development Administration. Ortaköy station has a drainage area of 104.8 km2. Beyler station's drainage area is 2174 km2. The drainage area at the weir site is 2317 km2. The stream values which had been observed at the two stations were multiplied by the ratio of drainage areas. By this way the stream values at the weir site were found. The average of the discharges is 5 1.78 m3/s. The discharges, from the biggest value to the smallest and the time percentages were arranged as a graph. From this graph it is seen that the average discharge, 51.78 m3/s can be observed only 44% of the time in the river. If we want to bring the average discharge 100% of the time we must construct a dam. For calculating the volume of the Melen reservoir, two methods were used. In the first method named as Ripple method, the volume of the reservoir was calculated from the total discharge graph and was found 1.020 million m3. In the second method named as Sequent Peak method, the volume of the reservoir was found 943.4 million m3. The difference between these two methods is the reading mistake of the graph. Both of these volumes were calculated for the 100% regulation. Nippon Koei, the Japan company, made a feasibility study on Büyük Melen System in 1991. In this study the company proposed to develop the Melen System in five phases. In the first phase a weir construction was proposed. By the construction of the weir, 8.5 m3/s water will be supplied to Istanbul in 2002. In this thesis it is shown that water can be provided from upstream cofferdam of the Melen Dam instead of from the weir. Upstream cofferdam will be constructed to divert the water for XHl constructing the dam on a dry ground. For finding the crest elevation of the upstream cofferdam hydraulic calculations of the diversion tunnels which were proposed in the feasibility study were made. The hydraulic losses formed in the tunnels like entrance losses, friction losses and bend losses were found. Outfall curve of the two diversion tunnels, each with 7 m diameter was drawn. We can see the discharge values of the diversion tunnels at any reservoir water elevation from the outfall curve. Flood routing calculations were made for finding the water surface elevation in the cofferdam reservoir. These calculations were made by a computer program. Flood hydrographs of 50 years return period and 100 years return period, outfall curve of tunnels and area-capacity curve of the Melen Dam were used in this program. The crest elevation of the upstream cofferdam was found as 28 m. It is proposed to provide 268 million m3/year water from the Melen Weir. For supplying this water from the upstream cofferdam, a reservoir operation study was made. It was seen that if the crest elevation of the cofferdam was raised to 34.5 m, 306 million m3/year water would be supplied. The cost of raising the cofferdam elevation is estimated to be 500.000 $, but the Melen Weir will cost 8.000.000 $. When water is supplied from a reservoir, the quality of the water becomes well and the solid particles in the water settle down. If the water was supplied from the cofferdam there would be economy in the energy, because the normal water surface elevation of the weir is 17.40 m but in the cofferdam reservoir it is 28.10 m. So water will be pumped to a height 10.7 m less than the weir water pumping height.