Hydraulic Transient Analysis and Discrete Blockage Detection on Distribution Pipelines: Field Tests, Model Calibration, and Inverse Modeling

The use of hydraulic transients for blockage detection has been suggested based on the results of numerical and laboratory based experiments using transient models in both the time and frequency domains. The use of hydraulic transients for block detection is attractive because other investigative techniques are limited to steady state pressure and flow (C-Factor) tests and CCTV camera investigation. However, the practical application of hydraulic transient based techniques to water distribution (and other pipelines) requires demonstration. This paper presents the results of transient tests performed on a water distribution pipeline in South Australia both without and with an artificially introduced discrete blockage (created using an in-situ in-line gate valve). The tests revealed that the laboratory systems investigated thus far do not replicate the effects of topological complexity and uncertainty, inelastic and mechanical losses at joints and soil/pipe interaction, regardless of whether a discrete blockage is present. It was found that blockage detection could not be successfully undertaken using inverse transient analysis using a traditional transient model that did not take the non-blockage related physical complexities into account. A novel transient model has been developed using Kelvin-Voigt viscoelastic mechanical elements to incorporate the effects of dispersion and damping by introducing (and calibrating) equivalent "viscous" damping through calibration to no-blockage measured responses. This new model required spatially distributed "viscous" elements to replicate the physical variability along the distribution pipeline that was tested. The location and size of the constriction formed using the in-line gated valve was able to be successfully determined using the new calibrated transient model and inverse analysis for a range of discrete blockages. In contrast to steady pressure and flow investigations, the use of hydraulic transients provided information regarding both the specific location and nature of the artificial discrete blockages with little extra practical effort required to conduct the tests relative to C-Factor tests.