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Turkey is divided into 26 hydrological basins with large differences in specific discharge (Table 2) (GDRS, 2003). Most rivers originate in Turkey and there are more than 120 natural lakes and 579 artificial lakes. Total internal renewable water resources are estimated at 227 km3/year (Table 3). About 186 km3 is surface water and 69 km3 groundwater, while 28 km3 is considered to be the overlap between surface water and groundwater. Average surface runoff entering the country from Bulgaria and the Syrian Arab Republic is 1.8 km3/year, of which 0.6 km3 from the Tunca River coming from Bulgaria and 1.2 km3 from the Asi-Orontes coming from the Syrian Arab Republic. The Meriç River, originating in Bulgaria, forms the border between Greece and Turkey with a flow of 5.8 km3/year and therefore the part accounted for by Turkey is considered to be half of the total flow or 2.9 km3/year. This gives a total inflow of 4.7 km3/year. Adding the incoming flow to the internal renewable water resources brings the total natural renewable water resources to 231.7 km3/year. Of the total flow of 53.74 km3/year leaving the country, 28.1 km3 flows to the Syrian Arab Republic (of which 26.29 km3 is the natural outflow of the Euphrates), 21.33 km3 to Iraq (Tigris and affluent), and 4.31 km3 to Georgia. Groundwater flows to other countries are estimated at 11 km3/year, of which 1.2 km3/year to the Khabour Springs feeding the Khabour River, situated in the Syrian Arab Republic, with a runoff of 1.2 km3/year, have their origin in groundwater coming from Turkey. Taking into consideration the outflow and the flows reserved between countries (see international water issues below), the total actual renewable water resources are equal to 213.56 km3/year.
Turkey contributes about 90 percent of the total annual flow of the Euphrates, while the remaining part originates in the Syrian Arab Republic and nothing is added further downstream in Iraq. Turkey contributes 38 percent directly to the main Tigris River and another 11 percent to its tributaries joining the main river further downstream in Iraq. In general, the streams and rivers vary greatly in their flow from season to season and from year to year. For example, the Euphrates annual flow at the border with the Syrian Arab Republic ranged from 15.3 km3 in 1961 to 42.7 km3 in 1963.
A trend analysis of annual minimum, maximum and mean stream-flow variables in Turkey showed that there was a significant decreasing trend seen mostly in the basins in western Turkey, whereas some basins draining to the Black Sea exhibited significant increasing trends. Almost no evidence of any significant change was experienced in the rest of the country (Topaloglu, 2006).
A significant part of the water in mountainous coastal areas finds its way to the sea without forming any large groundwater reservoir. Hydrogeological surveys carried out in 342 plains in order to assess groundwater potential, estimated the reliable groundwater reserves or exploitable groundwater at 14 km3/year (Kirmizitas, 2006). The legislation on groundwater reserves taking effect in 1960 mandated the DSI (General Directorate of State Hydraulic Works) to carry out work for the exploration, utilization, maintenance and registration of groundwater reserves in Turkey. Under this mandate, it conducts surveys on groundwater reserves and makes the necessary arrangements for the utilization of identified reserves. So far the DSI has allocated an annual 11.44 km3 of this reliable reserve, of which 5.20 km3 for municipal and industrial purposes, 3.90 km3 for state administered irrigation and 2.34 km3 for private irrigation schemes (DSI, 2006).
Turkey is a country rich in wetlands, ranking first in this respect among the Middle Eastern and European countries. There are more than 250 wetlands in the country with a total area of approximately one million hectares. Almost 75 wetlands are larger than 100 hectares (TÇV, 1995). Of all Turkish wetlands, 60 percent has freshwater, 20 percent brackish water and 20 percent salt water. Turkeys wetlands are important because they are concentrated in Anatolia, which is crossed by two major bird migration routes. There are four major wetlands: Göksu Delta, Kizilirmak Delta, Sultan Marshes and Kus Cenneti. Five wetlands are identified as Ramsar sites: Göksu Delta, Manyas Bird Sanctuary, Sultan Marsh, Lake Burdur and Lake Seyfe. Based on international criteria, 18 wetlands have been classified as first class areas (Class A) that can offer refuge and food to over 25 000 birds at a time. An additional 45 wetlands have been identified as Class B, accommodating 10 000-25 000 birds.
The most serious negative development encountered in the preservation of wetlands is intentional draining. Swamps and marshes have been drained and reclaimed for agriculture and for malaria control (Harmancioglu et al, 2001). A second important threat to the wetlands is pollution, both directly and indirectly by the rivers that feed them. In particular, sediments in contaminated rivers accumulate in wetlands. The heavy metals and pesticides cause mass deaths of fish, frogs and waterfowl. Another threat to wetlands is the collection of bird eggs and frogs, cutting and burning of grasses, grazing cattle, especially water buffalo, in the shallow areas.
By 2006, 208 large dams, mostly rock-fill or earth-fill, had been constructed. In total 579 dams have been completed and put into service for water supply, irrigation, hydropower and flood control (DSI, 2006). Almost 210 dams are under construction. The 208 large dams were constructed in large irrigation schemes (>1 000 ha, with 70 percent >10 000 ha), the rest are in the small irrigation schemes (<1 000 ha). The large dams have a total reservoir capacity of almost 157 km3, whereas the total capacity of all dams is 651 km3.
The Ataturk dam on the Euphrates River in the south-eastern part of the country, with a total storage capacity of 48.7 km3, is one of the 10 largest dams in the world. In the beginning of 1990, the filling of the reservoir behind the dam started and was completed in 1992. The surface area of the reservoir is about 817 km2. The water obtained from the Ataturk dam is carried to the Harran Plain by the Sanliurfa tunnel system, which is the largest tunnel system in the world in view of its length and flow rate. The water passes through banners which are 26.4 km in length and 7.62 m in diameter with an estimated flow of about 328 m3/s, which is one-third of the total flow of the Euphrates.
There are 3 215 municipalities in Turkey, 1 327 of which have their own sewage system. About 60 percent of the population is connected to a wastewater treatment plant. Today, almost 1.68 km3 of municipal wastewater per year is treated using extended aeration, biological nutrient removal (BNR) and trickling filters system (TÜIK, 2003). In 1994 treatment of municipal wastewater was estimated at 0.1 km3/year. In the year 2000, the GDRS (General Directorate of Rural Services) of the Ministry of Agriculture, Forestry and Village Affairs ordered every village to have a wastewater treatment plant which uses special absorbent crops, such as reed and grass, for treating municipal wastewater. Whereas this project is successful in some regions, no reliable statistically data are available as the GDRS were discontinued following a government reorganization.