AWWA DSS58717

No scientific database is available to guide utilities in determining the appropriate flushing velocity that will create a shear force capable of dislodging and transporting specific types of particles, film, or scale. Often, criteria used to decide when flushing is adequate include visual observation of "clear" water coming from the hydrant, a pre-selected time period (sometimes related to calculations on volume of water displaced), the ability of the zone to maintain pressure, or samples collected and analyzed for standard water quality analyses. Onsite water quality analyses may be valid indicators of effective flushing but still leave the estimated velocity, duration, and frequency of flushing to guesswork or generalization. The objective of this project was to determine the range of flushing velocities required to dislodge and remove various accumulated materials from water distribution mains. Includes tables, figures.