Estimation of hydraulic roughness of concrete sewer pipes by laser scanning

In sewer asset management, decision making on rehabilitation or replacement should preferably be based on the actual functionality of a sewer system. In order to judge the ability of a sewer system to transport wastewater, hydrodynamic models are used; in these, hydraulic roughness is one of the key parameters. For new pipes, this is well known, but for aged pipes with uneven deterioration along the cross section, information on the hydraulic roughness is lacking. In this article, the potential of laser scanning methods for accurate, noninvasive, and nonintrusive assessment of the hydraulic roughness of concrete sewer pipes is described, demonstrated, and discussed. Processing of raw scanned data consists of two steps: (1) spatial interpolation with uncertainty analysis, and (2) statistical analysis for estimating the hydraulic roughness. Moreover, a statistical analysis was carried out to determine the minimal scanning resolution required in order to yield results accurate enough for subsequent modeling uses. The results show a promising potential of the laser scanning approach for a simple and fast quantification of the hydraulic roughness in a sewer system.