The secret art of model calibration

David Edgren


I’ve always thought calibration is the single most important step in hydraulic modeling. Not only is it the bridge between having a model that just shows what’s physically there with some initial guesses at hydrology, and one that’s ready for simulating whatever kind of alternative analysis you’re going to throw at it. But most importantly it’s the phase in which you develop your mental model to really understand the system and how it interacts. By the time you’re done with calibration you should understand better than anybody else how the existing system actually operates from a big picture.

Calibration is needfully a science. We use metrics and specific standards (such as the well-known CIWEM Code of Practice) to evaluate the quality of a calibration. But it’s also an art. It requires modeler’s judgment, compromise, and big picture thinking and is not easily captured in an algorithm. This side of calibration is often neglected in discussion and underappreciated. Enough that we might even call it secret?

At RJN we’ve developed a framework or culture emphasizing the art of model calibration that’s been refined over many years and models. It has recently become more apparent to me that a couple pieces of our calibration process that regularly lead us to powerful insights are distinctive, possibly even unique, and not yet commonly recognized as part of the calibration process by many modelers.

This presentation will be some reflections and suggestions for model calibration based on my experience calibrating models and training others in the calibration process. In it I will classify some goals of model calibration, highlight the importance of calibrating hydraulics as well as hydrology and the most important tool to do so, identify the ability to find system anomalies during the calibration process, and suggest the least helpful (and most overrated) parameters to calibrate, all illustrated with real-life examples. It will focus primarily on urban, 1D, SWMM-based models of combined or high-RDII sanitary systems with existing SSOs, CSOs, or basement backups.

 Click here to watch recorded presentation on YouTube.

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