Determining the Best Way to Model Distribution Flushing

Modeling of distribution system flushing consists of adding demands to the model to simulate the open hydrants and observing the response of the system. However, the details of setting up flushing events bring up a number of issues that will be addressed in this paper. Most models do not explicitly include hydrants and their laterals in the model but simulate flushing as occurring at junction nodes near the hydrants. The paper shows that most of the head loss during flushing occurs in the hydrant itself, primarily as a conversion of pressure head to velocity head. As such, the error involved in simulating flushing at a junction node rather than at the location of the hydrant or hydrant tap is small. This paper discusses modeling practice in planning flushing operation. Conventional flushing (i.e. with no valve operation) is shown to do an adequate job in flushing a system in most cases and modeling can help engineers to identify situation where unidirectional flushing can yield significant improvement or flushing by operating hydrants alone will not be successful.