||Waterhammer models are used to design and analyze pressurized pipe flow systems and to locate leaks and other defects in water supply pipelines. This thesis analyses the importance of unsteady friction and visco-elastic damping as well as parameter uncertainty on the accuracy and reliability of waterhammer models. The analysis is performed by using analytical and numerical methods. It is found that unsteady friction damping has less effect on the damping rate of the transient envelope as the timescales of the wave travel period and radial diffusion becomes larger. The implication is that the role of unsteady friction on the damping rate of the transient envelope diminishes with system scales and that the results of laboratory experiments, which are limited to relatively small pipe lengths and diameters, have led researchers to overestimate the importance of unsteady friction on the damping of the transient envelope in real pipe systems. In addition, the pressure head attenuation attributable to unsteady friction is comparable to the visco-elastic effect during the initial transient stage while the visco-elastic effect becomes dominant both in terms of damping and phase shift at later stages. Moreover, the visco-elastic damping becomes more critical if the visco-elastic retardation time is less than the wave travel time along the entire pipeline length, indicating that the visco-elastic damping is important for long pipes. As far as leak and other pipe defect detection in pipelines, the role of transient wave reflections is found to be far more important than the transient damping. This finding has implications on the design of transient signals for pipe defects detection and suggests high bandwidth signals with clear reflections are preferable to this technology. The effects of uncertainties in geometric and dynamic parameters on wave envelope and wave scattering indicate that (i) traditional deterministic waterhammer models tend to overestimate the magnitude of the maximum pressure, but underestimate that of the minimum pressure and (ii) waterhammer waves can become localized along pipelines. As a result, understanding uncertainties is critical for analyzing the structural integrity of a pipe system as well as the development of transient-based leak and other defect detection methods. Finally, the transient-based leak detection method originally developed for single and elastic pipeline systems is extended and applied to more realistic pipelines such as visco-elastic pipe and series pipes in this thesis.