Providing clean water at relevant quality and quantity is a challenge that regulatory authorities have to face in metropolitan cities that seem to develop at their limits of sustainability. Istanbul strives to face such a challenge for its population of over 10 million, through six surface water resources.
Nearly all of Istanbul’s drinking water (97%) comes from surface water collected in reservoirs. Its most important water sources are the Omerli-Darlik system on the Asian side and the Terkos-Alibeykoy system on the European side. Both systems consist of dams, reservoirs, water treatment plants and pipelines. Many of the reservoirs that supply Istanbul are located within the metropolitan area and are exposed to pollution from settlements without adequate sanitation.
Water quality is theoretically controlled by conservation zones around the reservoirs which limit construction and industrial activities in four concentric buffer zones with increasingly strict regulations the closer the zones are to the reservoirs. However, there is litte enforcement of these regulations in the face of rapid and often unplanned urbanization. Illegal settlements sprang up around the reservoirs, fueled by land speculation. Subsequently they became de facto legalized with their own municipal administrations elected mayors.
Istanbul water supply system is currently being operated by the Istanbul Water and Sewage Authority (ISKI) with empirical methods. These trial and error methods based on past experiences cannot solve the long term operation problem of the system as was seen in the drought periods of the last two decades where the inhabitants suﬀered serious water shortages. Planning new resources as soon as a similar crisis arises is generally a high priced, non- feasible and premature decision. Primarily the operation policy of the system must be optimized for the present conditions. It is seen from the results of this study that an operating rule based on the system concept can provide a considerable increase in the yield of the water supply system. It can be concluded that if the Istanbul water supply system had an optimum dynamic operating rule, the crisis would not be so terrifying.
However, given the growth of Istanbul, additional water resources were still needed. Therefore the Melen System is being developed to cover the long term water demand of İstanbul. The first stage supplying 268 million m3 was completed in 2007 with Japanese financing. A second and third stage are expected to bring a total of 1,180 billion m3 for all three phases to meet the water demand of the city until the year 2040, doubling the amount of water supplied prior to the Melen system.
Although the data do not indicate a clear declining trend in rainfall, extreme events – especially droughts – seem more pronounced than in the past. In 2006, rainfall of 67 mm was the record low for the previous 50 years, a period during which the average was 257 mm per year. Furthermore, the water level in reservoirs serving the city plummeted to around 25% of full capacity in 2007 and 2008. ISKI, using a scenario of a 2°C temperature increase by 2030, estimated that the city’s water supply may decline by as much as 14% over the next two decades because of higher evaporation from reservoirs.
Extract from a page of the website MappingTheCommons