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Water Distribution System Hydraulic Model Calibration and System Evaluation Report Chapter 6 – Hydraulic Model Calibration December 2019 P05049-2019-000 Page 18 CHAPTER 6 HYDRAULIC MODEL CALIBRATION The objective of creating a model is to generate a tool for predicting the distribution system network’s behavior within an acceptable level of accuracy. Upon completion of adjustments to pipe roughness coefficients and system demands, final simulated results from the hydraulic model were compared with the observed field results in order to determine the calibration level achieved. The results were incorporated into the following sections. The hydraulic model can be considered calibrated when the results produced by the hydraulic model can be used with confidence to make decisions regarding the design, operation, and maintenance of the water distribution system. The guidelines presented below by the authors of Water Distribution Modeling (Haestad 2001) give some numerical guidelines for calibration accuracy: however, they are not meant to be definitive. “The model should accurately predict hydraulic grade line (HGL) to within five to 10 feet at calibration data points during fire flow tests and to the accuracy of the elevation and pressure data during normal demands. It should also reproduce water storage level fluctuations to within three to six feet for EPS runs and match treatment plant/pump station flows to within 10 to 20 percent.” 6.1 Calibration Process Because significant efforts were made in properly allocating demands throughout the water distribution system, most of the calibration effort focused on adjusting pipe roughness coefficients to match field data collected during the fire hydrant flow tests. Fire hydrant flow test data was entered into the hydraulic modeling software for the 24 flow tests. Simultaneous operating data such as water storage levels, Booster Station pump flows, and estimated demands were also entered into the software program for each of the flow tests. The SCADA data for the South Water Tower and North Water Tower levels was measured to the nearest tenth of a foot. It was desirable to have more precision in measuring the change in the tank levels in order to more accurately calibrate the model. As such, the data collected by the HPR’s that were placed near each of the water towers was used as input data for each of the two tank levels. After the background data was entered and the fire flow tests were simulated, model results were compared with field measurements. When model results varied from the observed field measurements, the pipe roughness coefficients were adjusted. Similarly, this adjustment process was performed for the HGL tests and the EPS tests.