A Streamflow Threshold Determination Method for Hydrologic Model Calibration and Verification

Identification of the type and characteristics of streamflow in a watershed is the key to the development of most appropriate water infrastructure. Though these features are watershed specific, the current practice is to capture the details using generalized thresholds. Considering the importance of optimal resource use, present-day water engineers must resort to methodologies that enable the determination of streamflow thresholds of a watershed by making use of watershed signatures. In the present work, a watershed hydrology-based method to capture the high, intermediate and low streamflow thresholds is presented with a demonstration using data of the Kalu. Ganga basin of Sri Lanka. The acceptability of thresholds is established by application and supported with literature quoted practice. Repeatability of the method is successfully confirmed by application at Gin Ganga basin of Sri Lanka for two different data lengths and two temporal resolutions. Described method conjunctively evaluates the consistent streamflow segments and average slope of the flow duration curve to determine the thresholds which are watershed signatures for a particular temporal resolution. This dependence on temporal resolution while highlighting the importance of using appropriate thresholds for meaningful hydrologic model evaluations, cautions the use of traditional methods based on generalized thresholds. Proposed method is a versatile tool for model development with specific objectives such as water allocation, regulation, flood management, water extraction or environmental flow maintenance. Identification of thresholds using this method builds the confidence of practicing engineers when using design safety factors for streamflow.