Condition grading for dysfunction indicators in sewer asset management

Abstract

Asset management is an increasing concern throughout the global water and wastewater industry. Condition assessment of sewer segments is a main step of asset management and relies mostly on visual inspection. Observed defects are then translated into a score for each sewer segment. While most protocols assign a segment to a condition grade by comparing its score with a subjective scale of numerical values, this paper proposes a protocol to calibrate thresholds for each asset stock. The proposed calibration criterion allows thresholds calculation according to two sets of parameters: overall condition of the considered asset stock and weights (fixed by the utility manager) associated to over-estimation and under-estimation of condition grade. The overall condition of the considered asset stock may be estimated by a representative sample or provided by utility manager as a hypothesis. This method is applied on a portion of 152 kilometers of the asset stock of the Greater Lyon (4471 segments). Sensitivity analyses are implemented. Three hypotheses about overall condition of the asset stock are combined with three matrices of assignment-error weights. Both parameters gradually influence thresholds and therefore change the assessment of the studied sewer segments. The synthesis of such sensitivity analyses can be used to prioritize complementary investigations and/or rehabilitation actions.