A computer model is mostly ineffective until it is calibrated. This is due to the fact that even though the engineer may have gone to great lengths of ensuring data accuracy, there will still exist subtle nuances in the distribution system that have gone undetected. Such nuances may consist of partially shut or closed valves, incorrect data on pumps and system valves (PRV's,etc.), or erroneous GIS data that was used in the model creation. None of these items will be discovered until the model has been through a series of calibration runs that effectively match what is occurring in the computer to what is occurring in the system. Depending on the system, a correlation of 5% to 10% between field data and simulation results is desired.
Ultimately, a calibrated model creates confidence by allowing the engineer to predict, with some level of certainty, how the system will react to operational changes. Such changes may include the addition of a pumping station, a new pressure zone, a new tank or the replacement of a well. Without a calibrated model, system modifications and the subsequent results generated from the hydraulic model will contain a variable degree of uncertainty.
The successful application of a hydraulic model in the analysis and design of a water distribution system is highly dependent upon how well the model is calibrated(1). Model calibration consists of fine tuning the model until it simulates field conditions to an established degree of accuracy. Fine tuning of the model entails making minor adjustments to the model input data to obtain the desired output data. The degree of accuracy refers to the difference between simulated and actual values and is used to establish a level of confidence in the model(2). It is normally expressed as a percent difference (typically 10 percent) between model predictions and actual measurements. Calibration is important to establish model credibility, create a benchmark, produce a predictive tool, increase knowledge and understanding of the system and its operations, and to discover errors or unknown conditions in the field(2).
The WQ Calibrator provides a fully automated approach to accurate and efficient pipe network calibration. The program makes use of a variation of the genetic algorithm optimization technology enriched with global search control strategies and closely coupled with the software for maximum efficiency, performance and reliability.