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On the Calibration of Hydrologic Models

by Baolin Wu, Contra Costa County Flood Control, District, Martinez, United States,



Document Type: Proceeding Paper

Part of: Engineering Hydrology

Abstract:

A procedure is proposed to calibrate hydrologic models to generate representative design flows and flood hydrographs. This procedure includes two calibration steps; event calibration and frequency calibration. An event calibration uses concurrently recorded rainfall data and runoff data to calibrate model parameters. Additional rainfall data is then input into the model to generate the simulated runoff. If the difference between the recorded and simulated runoff is within a given tolerance level, the model is assumed to be calibrated. However, a model calibrated by this conventional approach might not be suitable for producing design flows with high return periods, such as 50 years and 100 years design flows. This is because in an event calibration, the model usually is calibrated using only events with low return periods. There is no assurance that a model calibrated using low return period events can accurately generate design flows with high return periods. In addition, a design storm is introduced into this process and this critical parameter has never been calibrated with the model. Frequency calibration is proposed to re-calibrate the model with an adopted design storm. In this step, reliable runoff frequency curves, one for peak flow and one for runoff volume, are developed from recorded runoff data. The total storm rainfall amount for a given return period is distributed by an adopted design storm pattern and input into the model which has been previously calibrated using event calibration. The generated peak flow and runoff volume are then compared against those of frequency curves with the same return period. Adjustments can be made to the design storm and model parameters to ensure satisfactory reproduction of peak flow and runoff volume.

Subject Headings: Calibration | Runoff | Hydrologic models | Storms | Hydrologic data | Rainfall-runoff relationships | Mathematical models

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