Hydraulic Model–Based Prediction for the Flushing Velocity of Water Distribution Systems

Flushing is a widely used method for cleaning water pipes, demanding the achievement of optimal flushing velocity for effectiveness. A prior examination of flushing condition including velocity, duration, and flow rate is crucial to minimize water and economic losses while maximizing the impact of flushing. Although simulation models are commonly employed for this purpose, they often overlook potential head loss during flow through hydrants or drain valves, compromising the effectiveness of flushing. This study investigated the impact of different simulation methods on estimating flushing conditions through hydrants and drain valves. The structural layout (minor loss coefficient) and specifications (emitter coefficient) of each flushing path were incorporated into traditional models. Applying this method to a hypothetical network and the water distribution system of G-City in Gyeonggi Province of South Korea, we compared the flushing effects of four different modeling approaches. Results reveal that drain valves tend to exhibit higher velocity than hydrants under the same conditions, mainly due to their structural layout. However, both drain valves and hydrants may experience overestimation of flow rate and velocity if the minor loss coefficient is disregarded. Practitioners should exercise caution regarding potential low flushing efficiencies. The limited numbers and locations of drain valves compared to hydrants constrain their field application, emphasizing the need for comprehensive consideration of various field conditions when developing a suitable flushing plan.