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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 19 6.2 Calibration Results Every model will have some level of inaccuracy because of the ambiguity in assumed conditions and available modeling techniques. It is unreasonable to expect a model to agree exactly with field data for every condition. The objective of creating a model is to generate a tool for predicting a network’s behavior to an acceptable accuracy level, not to perfection. 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. 6.2.1 Fire Hydrant Flow Test Calibration Results Completion of fire hydrant flow tests allows for collection of data over a wide range of operating conditions, including peak (high) demand periods. The results of testing for static and residual pressures during the fire flow tests are presented below. 6.2.1.1 Static Pressure Test Results Static pressures were taken at the pressure hydrant prior to initiating the fire hydrant flow tests. The observed static pressures along with the simulated pressure from the hydraulic model are shown in Appendix A. Comparison of static pressures from field test results with simulated hydraulic model results showed that 18 tests (92 percent) were within 5 feet (≈2 psi) of the field test measurement, and all of the tests were within 10 feet (≈5 psi). This level of accuracy is considered acceptable in accordance with criteria established above. 6.2.1.2 Residual Pressure Test Results During each fire hydrant flow test, residual pressures were recorded at a hydrant near the flowing hydrants. The observed residual pressures along with the simulated pressure from the hydraulic model are shown in Appendix A. Comparison of the observed field pressures and the simulated pressures obtained from the hydraulic model showed that 15 of the 24 tests (63 percent) were within 5 feet (≈2 psi) of the observed field reading, and 22 of the 24 tests (92 percent) were within 10 feet (≈5 psi). Note that the model results presented here reflect adjustments made from Fire Flow, HGL, and EPS calibration. As stated in the comments listed in the results table, the differences for Tests No. 6 and 21 are likely caused by fully or partially closed valves located within or near the subdivision that the test occurred.