Date

2021-5

Author

Özcan, Cansu

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In this study, a holistic environmental flow assessment (EFA) adopted from the ELOHA framework is performed for the Sakarya Watershed. The most significant environmental flow events were quantified using natural streamflow data estimated at the selected target streamflow gages. Also, hydrologic alterations due to several human pressures were assessed. The U.S. Geological Survey approach was adopted as the streamflow naturalization methodology. 18 FDC exceedance probability percentile flows (i.e., Q0.1-Q99.9) were naturalized combining three approaches. Multiple linear regression models were developed using SPSS software to calculate Q1-Q85; Drainage Area Ratio (DAR) method was used to calculate <Q1; and regressions against the flow values was performed to calculate >Q85. The QPPQ method was implemented to interpolate these 18 estimated percentile flows to generate daily natural streamflows. The model performance was evaluated by R2, NSE and PBIAS calculated from the FDC percentile flows. The predictive performance of the entire naturalization methodology (i.e., regional regression modeling + QPPQ method) was evaluated by NSE between the estimated and measured daily natural streamflows. The NSE values indicated the source gauge selection procedure is critical because the difference between gauge characteristics and the prediction performance are inversely correlated. The hydrologic alteration assessment was performed by the Indicators of Hydrologic Alteration (IHA) – Range of Variability Approach (RVA). The 32 IHA/RVA indicators demonstrated that all anthropogenic pressures have significantly changed the natural streamflow dynamics. With this regard, the environmental flow requirements of the Sakarya River were proposed using 34 Environmental Flow Components (EFCs) parameters.

Subject Keywords

Hydrologic Alteration Assessment, Environmental Flows (EFs), Streamflow Naturalization, ELOHA, Regression Modeling, QPPQ Method

URI

https://hdl.handle.net/11511/90920

Collections

Graduate School of Natural and Applied Sciences, Thesis