Investigation of Long-Term Monthly Total Streamflow Trends in Bolu City with the IPTAR and IPTA

Abstract

This study investigates the long-term monthly total streamflow trends in Bolu City by using a new graphical method called Innovative point trend analysis with a radar graph (IPTAR). This method uses the differences between the long-term statistic values to plot a radar graph, a no trend polygon to determine trend directions and critical trend polygons to identify trend significances. Also, the IPTAR was compared with the Innovative polygon trend analysis (IPTA). Bolu is neigbour to Ankara, the capital of Türkiye. It is thought that Ankara water demand up to 2050 can be met via an interbasin water transfer project called the Gerede system on Ulusu Stream. On the other hand, Koprubası Dam is located in Bolu city for the aims of energy production and flood prevention. In this study, long-term streamflow data related to the Gerede system and Koprubası Dam are used for trend analysis. Run test is used to test the homogeneity of data. It is determined that the data are homogeneous within the 99.9 % confidence interval. The IPTAR observed statistically significant decreasing or increasing trends. According to the results of the IPTAR, (1) monthly total flow for April when the highest flow is observed for three stations shows a decreasing trend and the rate of decrease is higher than 10% for two stations. (2) statistically significant increasing or decreasing trends are observed for the monthly total flows for summer months. Comparison of two methods shows that (1) the IPTAR determines trend significance with the critical trend polygons on radar graph while the IPTA assess trends with the trend length and trend slope. (2) trend analysis with the IPTAR is simpler than that of the IPTA due to usage of a radar graph. (3) the IPTAR can start trend analysis from a selected time but the IPTA cannot.

Keywords

• Innovative point trend analysis with a radar graph (IPTAR)
• Innovative polygon trend analysis (IPTA)
• Trend analysis
• Gerede system
• Ankara water demand
• Koprubası Dam
• Bolu

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