A Study on the Delineation of Flushing Sections and Simulation Method to Verify Appropriate Flushing Velocity for Applying Flushing

Abstract

Recently, water supply networks have experienced deterioration because of various factors, which result in the accumulation of a large amount of scale on the inside surface of pipes. The scale may enter houses when a surge occurs owing to abrupt velocity or flow direction change in pipes, and eventually, water quality accident such as red-water can occur. The scale should be removed by applying pipe-cleaning practices, such as flushing, to prevent this type of accident. Currently, most studies have suggested only the desirable flow velocity to remove the scale through flushing. In our opinion, it will be more critical to develop a method for determining whether it would be possible to achieve the desired flow velocity. Hence, we developed a method to delineate a flushing section and modify a water supply network in considering the minor loss on the hydrant using the head loss-flow rate curve for the hydrant. Next, we simulated a flow condition using the emitter coefficient to achieve the desired flow velocity for flushing each section. The proposed method was applied to a part of the water supply network of a city in Korea. From the results, the pressure head at the primary water source point of the network was sufficient such that each flushing section experienced the desired flow velocity to complete the flushing process. We lowered the pressure head by 20 m at the primary water source point and simulated a flow condition for insufficient pressure head. Under these conditions, some of the flushing sections could not experience the desired flow velocity, and hence, the scale could not be removed as desired. In this case, we believe that the utility authority should decide whether flushing is still a suitable option for cleaning the pipe, or whether other cleaning methods should be considered.