Effect of Flow Proportions on HSPF Model Calibration Accuracy

Abstract

Automatic calibration of complex models, which includes continuous hydrograph models, requires sophisticated calibration methods. Also, these model-independent-parameter estimators require complex objective functions to ensure that the final parameter values reflect the hydrologic flow components (surface runoff, interflow, and baseflow) that the models are designed to represent. A multicomponent objective function should include components to represent each of the important physical processes represented in the model. The goal of this investigation was to develop a weighted multicomponent objective function and a method that can be used to provide estimates of the weights. For best calibration accuracy, the weights of the objective function should reflect the flow proportions of the streamflow record. A properly weighted objective function will enhance the accuracy of a watershed model such as the Hydrological Simulation Program–FORTRAN (HSPF). Methods of weighting were first made using data from eight hypothetical watersheds that had varying proportions of flow components (surface runoff, interflow, and baseflow). Then, the methods were tested with data from two watersheds from Delaware and Maryland. The components of the objective function include baseflow separation and autoregression equations to represent hydrologic processes. The results indicated that the calibration accuracy greatly improved when the objective function weights were set based on flow proportions. Also, a conceptual baseflow separation was superior to hydrograph separation based on a Laplace transform filter. Two weighted multicomponent objective functions were compared and shown to provide different levels of accuracy, which suggests that the structure of the objective function is important.