A Lagrangian wave characteristic method for simulating transient water column separation

ydraulic transient simulation models are widely used by water utilities and engineering firms around the world in the planning, analysis, and design of water distribution piping systems (Boulos et al, 2006; Walski et al, 2003). These models are used to both evaluate potentially objectionable pressure transients (surges), which could lead to unacceptable operating conditions developing in the system and compromising its integrity, and to investigate “what if” scenarios associated with decisions regarding safe system operation. Examples of unacceptable conditions include pressures that are too high or too low and are created by unsteady or rapidly changing flow rates within the system. Such conditions can cause breaches in the hydraulic and physical integrity of the distribution system that increase the risk of negative public health outcomes. High-pressure transients (upsurges) can lead to system failure and excess leakage. Low-pressure transients (downsurges) can create vacuum conditions and pipeline collapse as well as opportunities for contaminated groundwater to intrude into the distribution system at a leaky joint or break, with possible consequences to public health. Depending on the size of the leaks, the volume of intrusion can range from a few gallons to hundreds of gallons (Boyd et al, 2004a; Boyd et al, 2004b; Funk et al, 1999). Recent studies by the National Research Council, the Water Research Foundation, and the US Environmental Protection Agency confirmed the potential for pathogen intrusion in drinking water distribution networks during low-pressure transients (Besner, 2007; Boulos et al, 2006; Fleming et al, 2006; NRC, 2006; Friedman et al, 2004; LeChevallier et al, 2003, 2002; Kirmeyer et al, 2001). H