Trend Analysis of Low Flows

Determination of trends in low flows has a great importance in water resources planning and operation. Hydrological assessment on low flows is required in water quality control problems, water supply projects, irrigation, recreation, and ecological conservation. Trends in low flows could be seen as potential evidences of climate change, and significantly affect short-, medium-, and long-term future decisions. The main objective of this study is to identify low flow trends for gauging stations in four hydrological basins, Meriç-Ergene, Gediz, Ceyhan and Seyhan, from different regions in Turkey. For the analysis, 3, 2, 2 and 5 flow gauges were selected for Meriç-Ergene, Gediz, Seyhan and Ceyhan basins, respectively. In the study, data from gauging stations with either no or minimum anthropogenic activities are considered. Therefore, record period for each gauging station has been selected such that influence by any upstream dam or water structure is excluded. Stream gauges with common period of 27 years from 1988 to 2014 are used. In the study, the D-day average time series are obtained by taking the overlapping D-day average of the daily streamflow time series. Low flows of D = 1, 7, 14, 30, 90 and 273-day are considered. The non-parametric Mann-Kendall test which has found an effective and general use to assess the significance of trend in hydrological time series is applied. Results on the existence and the significance of trends in low flow characteristics of hydrological basins are obtained and discussed.