Sources of error in network modeling: a question of perspective

This article explores and provides an overview of several important issues of uncertainty and error that arise in modeling water distribution systems. Initial emphasis is given to the ability and role of both the Hazen‐Williams and Darcy‐Weisbach friction models to describe hydraulic losses in a pipeline. Notwithstanding the suitability of these friction models, there exists a multitude of other uncertainties that can affect the accuracy of a hydraulic solution. A source of error often ignored during extended period simulation arises through the reservoir routing scheme used at storage elements. Other uncertainties stem from the way demands are represented (in both space and time), how the behavior of various hydraulic devices (such as valves and pumps) is emulated in simulation programs, and how the system's behavior is assumed to evolve in time. Persistent problems are also associated with aggregating demands, calibrating and skeletonizing systems, and gathering reliable field data. The problems associated with reservoir routing and system calibration are elucidated through more detailed numerical examples.