İklim Değişikliğinin Havza Ölçeğinde Akım ve Sediman Miktarına Etkilerinin Değerlendirilmesi: Yuvacık Baraj Gölü Havzası

Quantitative estimations of climate changes on hydrological processes help to understand and manage water resource problems such as floods and droughts in the future. This study aims to present the preliminary results of a study to determine the impact of climate change on river flow to develop sustainable watershed management plans and to evaluate the possible urban water use and environmental impacts to prepare policies to mitigate its negative impacts. In this study, the Soil and Water Assessment Tool (SWAT) was used as a hydrological model to predict hydrological effects of climate change to better understand and solve future water resource problems. In this context, firstly the Soil and Water Assessment Tool (SWAT) was operated on the Yuvacık Dam Basin in Marmara Region to reveal the present hydrological situation. The hydrological model was then simulated by using the climate change data that have 20 km spatial resolution between 2021-2099 years based on RCP 4.5 and RCP 8.5 scenarios that were produced by the General Directorate of Meteorology. Thus, the effects of climate change on the amount of water and sediment were estimated between these years. According to the RCP 4.5 and RCP 8.5 scenarios, 2.23% and 2.062% decrease in the average annual rainfall, and 1.24 and 0.03 of increase in temperature values were predicted, respectively. However, an increase in precipitation was expected between April and August. The average monthly flows (between 2006-2014) of the Kazandere, Kirazdere and Serindere rivers recharging the Yuvacık Dam in the basin is 0.55, 1.28 and 1.94 m3/s, respectively. Corresponding modelled flow values based on RCP 4.5 and RCP 8.5 scenarios for 2021-2099 period, for Kazandere, Kirazdere and Serindere are 0.14 and 0.17 m3/s, 0.41 and 0.33 m3/s, 0.86 and 0.68 m3/s, respectively. These values show significant decrease in flow rates of the rivers in the future. Moreover, the peak flow values of the streams especially for Kazandere and Kirazdere decrease from 8 to 2 m3/sec. The amount of the monthly average of sediment measured at the Serindere stream station for the years 2010-2013 was 49 tons, while it was calculated as 247.58 tons based on RCP 4.5 and 332.21 tons based on RCP 8.5 for 2021-2099 period. According to both scenarios, an increase in the predicted rainfall between April and August, and an increase in temperature will cause mechanical erosion in the basin. Thus, the amount of sediment carried by flow is expected to increase. The Yuvacık Dam is used for providing irrigation and drinking water requirements of Sakarya and Izmit provinces, and for the prevention of flood as well as for water management during drought periods. Therefore, the decrease in the flow rates of the streams recharging the dam will cause a decrease in the water volume of the dam, hence the future water management planning should be made for the crop pattern in the irrigated areas of the dam and for the drinking water usage. Furthermore, the decrease in the flow rates will cause to decrease the forest areas in the basin and which in turn will lead to an increase in the amount of erosion. This will cause an increase in the amount of sediment coming to the reservoir thus the service life time of the reservoir will be shortened.