Filling out missing daily streamflow data using fuzzy rule-based models

Akgün, Ömer Burak
Daily streamflow observations are used for many purposes including analysis of current water-resources conditions in a basin, development of water-resources planning and management strategies and climate change adaptation measures. Streamgages are used to collect streamflow data; however, many streamgages suffer from a common problem: data-gaps. In this study, a Takagi-Sugeno Fuzzy RuleBased (TS_FRB) Model that uses Subtractive Clustering (SC) for rule generation is developed to fill out missing daily streamflow data due to a streamgage becoming inoperative for a long period. Fuzzy Rule-Based (FRB) model uses only daily streamflow data of neighboring streamgages, thus is very advantageous in terms of data requirement. Ergene Basin, Turkey is used as the case study and FRB models are developed to fill out missing daily streamflow data at four streamgages found in this basin. Numerous models are built to investigate the effect of the SC parameters (i.e., the number of cluster centers and the cluster radius) by which the rule-base of the FRB is identified, and the number of input variables on the performance of the models. Small cluster radius results in similar fuzzy rules to be devised, which vi reveals the needs for more rules. On the other hand, as the number of cluster centers increases, the risk of overfitting increases. Thus, selection of the best cluster radius and number of cluster centers combination is a challenging task and requires a trialand-error procedure. FRB models developed in this study provides good and robust ({u1D441}{u1D446}{u1D438} values around 0.67) estimations for the closely spaced streamgages located on the same tributary. On the other hand, FRB model performance is poor for the streamgage that is located far away from its neighboring streamgages and for the streamgage that is located on a different tributary than its neighbors. Moreover, anthropogenic effects in the Ergene Basin, makes the training of the FRB challenging and influences the model performance negatively.


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Citation Formats
Ö. B. Akgün, “Filling out missing daily streamflow data using fuzzy rule-based models,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Civil Engineering., Middle East Technical University, 2020.