Why and how can there be a water shortage in Istanbul this summer?

Water supply to Istanbul, a very unique city where 19% of our country's population lives, has historically always been on the agenda. Today, Istanbul is still experiencing some problems in terms of water supply security. This year, many regions of Turkey experienced regional winter drought and precipitation decreased by up to 40% compared to normal. In this water year, precipitation in Istanbul has also decreased. ISKI Deputy General Manager Bülent Solmaz explained this situation as follows: "When we look at the regular records of the last 20 years, we are experiencing the period in which we have received the least rainfall in our history in the 5-month period since October, which we define as the water period".

Currently, the average occupancy rate of Istanbul's dams is at its lowest level in the last 9 years. As a natural consequence of these conditions, there is a possibility that Istanbul's water management will be challenged in terms of quantity and quality security of water supply this summer. In this article, we have tried to present the root causes and possible consequences of this water tension, which occurs almost every year, with a brief analysis based on data 

What is the root cause of the jeopardized water supply security in Istanbul?

Istanbul is currently supplied with approximately 3 million m3 of water per day from 11 dams and the Melen system since the Melen Dam cannot be put into operation. The total storage capacity of the dams supplying water to Istanbul is approximately 868 million m3 . If the Melen Dam had been commissioned, this storage capacity would have increased approximately 1.8 times.

The fact that Melen Dam could not be put into operation due to body cracks and that this issue has been pending for a long time has disrupted Istanbul's Water Supply Plan and increased the unit water supply cost. Because Melen water must first be pumped to a height of 196 meters by pumps. As the amount of water to be transmitted increases, the already high energy cost increases even more. 

Due to the inability to retain water in the dam as a result of cracks in the body of Melen Dam, ISKI constructed additional water relief structure and Pumping Stations in B. Melen Stream in order to ensure the water supply and quality security of Istanbul, especially in summer months. Thus, it has become possible to pump more water from Melen Stream especially to the European side of Istanbul. 

In addition, due to the lack of water retention in the Melen Dam, the capacity of the pumping station at the Melen Dam site had to be increased, as well as the capacities of the Ömerli Dam pumping station and the Cumhuriyet drinking water treatment plant, where water will be pumped to the European side, had to be increased by approximately 20%.

In summary, the capacity of the Melen Pumping Station was increased along with the capacities of other facilities in order to transfer more water from the Asian Side to the European Side where the Melen and Yeşilçay basins are located. Thus, an additional 590,000m³/day of water was transferred to Ömerli Dam and Cumhuriyet Treatment Plant. However, this infrastructure will be used mostly in winter and spring months.

Due to insufficient water supply to the pump stations in Melen Stream in summer months, the water transfer opportunity decreases. For this reason, this facility contributes to the transfer of water during the rainy season in winter and spring.  

Istanbul's water supply plan has become very fragile due to the lack of water storage in the Melen Dam and water supply from Melen through pumps. Therefore, in case of 2 consecutive years of drought in Istanbul and especially in the Melen basin, water supply to the European side of Istanbul in the summer months will be at risk. 

The monthly water supply of the Great Melen Basin varies over the years 

The flow rates of the Büyük Melen Stream drop very low between June and November and the monthly flow rates vary greatly between years. This situation can be seen in Figure 1 and Figure 2. 

Figure 1. Monthly total flows at the Melen Regulator site 

When Figure 1 is examined, it is seen that the monthly total flow rates measured in the Melen regulator area vary according to the years, decreasing significantly in July, August, September and October, and these amounts may not be sufficient for the flows planned to be discharged from Melen in dry years.

Figure 2. Lowest instantaneous currents measured at the Melen Regulator site 

In addition, the lowest instantaneous flows measured at the Melen Regulator site for many years are also variable according to the years. In case of the lowest flows, especially in July, August, September, October and November, it is seen that the flows planned to be drawn from here for the European side may not be met instantaneously (Figure 2). 

For this reason, it may be difficult to transfer sufficient water from Melen and Yeşilçay systems to the European side in the summer months of dry periods such as this year. Considering this situation, water is transferred to the European side from the Melen and Yeşilçay systems at full capacity in March, April and May, when water is more abundant in the Melen stream, and efforts are made to prevent the decrease in the dam levels there.

As a result, the root cause of the jeopardization of water supply security in Istanbul is the cracks in the body of the Melen Dam as a result of project and construction errors, and therefore its inability to hold water. 

In addition to this, Istanbul's water management has failed to transition to Demand Management. 

Why is Istanbul's water shortage on the European side?  

The water resources and reservoirs on the European side of Istanbul are not sufficient to meet the water demand of the population on this side. In Istanbul, 60% of the population lives on the European side, but 40% of the water resources are located on this side. In addition, according to the data, the Anatolian side receives more rainfall. As the water demand on the European side of Istanbul is more intense and the storage volumes of some dams are small, the first thing that comes to the fore in a dry period is the news that these dams are empty. This was the case this year, and the water in the Istranca dams and Alibeyköy Dam rapidly decreased and the dams emptied.

Istanbul's water supply system is based on three main dams, Ömerli, Büyükçekmece and Terkos, and the water supply to Istanbul is integrated with these dams. 

ISKI Deputy General Manager Mr. At the beginning of this March, Mr. Bülent Solmaz made the following statement with a very accurate observation;

"We need to try to transfer more water to the European side than we can from Asia, and in this way we will balance the drought in Europe. According to our current simulations and projects, we calculate and think that if we transfer enough water from the Asian side to the European side, we will not face any water cuts or any problems."

The fact that there is much less precipitation in our European Region puts us in difficulty in terms of water supply, and we try to solve this deficit by transferring much more water from the Asian Side.

As Mr. Solmaz stated, the European side needs to be continuously supplied from the Melen and Yeşilçay systems during the rainy season. However, this supply may not be realized sufficiently in the summer months due to the decrease in flow. In this case, the water supply and quality security of the European side may be at risk. In fact, Mr. Solmaz clearly stated in his statement that "the prerequisite for not facing a water shortage or any other problem is to transfer sufficient water from Asia to Europe". 

Conclusion

Melen Dam is the most important part of the Melen water supply system and the insurance of Istanbul's water security. Failure to store water in Melen Dam threatens Istanbul's water supply and quality security, disrupts the water supply plan and increases the energy cost of water supply.

This year, due to the inability to store water due to cracks in the body of the Melen Dam, there may be difficulties in ensuring the water supply security of the European side of Istanbul, especially in the summer months. ISKI management is carrying out various works to prevent this problem. However, as long as Melen Dam remains out of operation, it will be difficult to ensure water supply and quality security in Istanbul during dry periods.  The most fundamental solution in this regard is to rapidly start the construction of a new dam on the site of Melen Dam. Along with this, demand management of water in Istanbul should be initiated. 

To summarize; as the commissioning of the Melen Dam is delayed, not only the security of water supply and quality will be at risk, but also the energy cost will continue to put an additional burden on the budget of ISKI. Currently, this energy cost is close to the cost of reconstructing the Melen Dam. There is a growing need for an innovative water management and water use approach that addresses water and wastewater management together in Istanbul.