Caty Werey

Bio: Caty Werey is an academic researcher. The author has contributed to research in topics: Asset management & Sewerage. The author has an hindex of 6, co-authored 16 publications receiving 106 citations.

Sewer asset management – state of the art and research needs

Abstract: Sewer asset management gained momentum and importance in recent years due to economic considerations, since infrastructure maintenance and rehabilitation directly represent major investments. Becau...

Condition grading for dysfunction indicators in sewer asset management

Abstract: Asset management is an increasing concern for the water and wastewater industry. Condition assessment of sewer segments is an important component of sewer asset management and relies mostly on visual inspection. Observed defects are translated into a score for each segment. Although most protocols give a segment a condition grade by comparing its score with a subjective scale of numerical values, we propose a protocol to calibrate thresholds for each asset stock. Thresholds are calculated according to two sets of parameters: overall condition of the asset stock in question (estimated by a representative sample or provided by the utility manager) and assignment-error weighting (determined by the utility manager) linked to either over-estimation or under-estimation of condition grade. This method is applied to 150 km of sewers from the Greater Lyon asset stock. Sensitivity analyses of these parameters are then implemented. Three hypotheses about overall condition of the asset stock are combined with three m...

Transitioning to sustainable urban water management systems: how to define expected service functions?

Abstract: Sustainable water management is a worldwide challenge for the twenty-first century. It involves replacing traditional management approaches with a new concept, often referred to as sustainable urban water management (SUWM). This paradigm shift means that SUWM systems must include new services, some of which have already emerged. However, no publications have presented the expected SUWM system in terms of the full range of services it would need to include, and no publications have proposed a method for identifying the services the system must provide. This paper proposes a method for identifying these services and presents a generic petal diagram to represent the service functions of the SUWM system. Moreover, this paper presents a new method for defining these services in a specific territory. This method is based on the confrontation between a general representation and the objectives of the stakeholders in a given system in a given territory. The method is illustrated with a full-scale case study on th...

Sewer asset management: from visual inspection survey to dysfunction indicators

Abstract: Asset management is an increasing concern for wastewater utilities and companies. Criteria are developed for supporting the definition of investigation and rehabilitation programs. Dysfunction indicators contribute to the calculation of criteria, using expert rules. These indicators are mostly based on visual inspections, which provide major information. However, difficulties remain in the translation of visual inspection survey into dysfunction indicators. This article presents a methodological approach aiming to fill this lack. In the framework of the French RERAU program (Rehabilitation of urban sewer networks) a methodological approach has been developed in order to convert visual inspections of sewer segments into four possible condition grades {1, 2, 3, 4}, grade 4 corresponds to the worse condition. Three complementary procedures are thus executed: (a) expert rules based on sequences of observation codes, (b) comparison of single score to threshold and (c) rules based on analysis of segment profiles (scores distribution). An experiment lead in the Bas-Rhin (France) illustrates the different steps of the methodological approach and the applicability of the RERAU methodology on CCTV data. Moreover, confrontation between expert assessment of sewer segments (condition grade) and calculated scores has demonstrated the necessity of considering diagnosis imperfection, which may lead to misclassification in some cases. The algorithm proposed in this article aims to minimize a cost function with costs assigned to false positive diagnosis test (segment classified in worse condition than experts' opinion) and false negative diagnosis test (segment classified in better condition than experts' opinion). The algorithm is described in detail and applied to an example. Thus imprecision of assessment is taken into account: the threshold is chosen as to be the most efficient (in term of cost). This approach is generally applicable to numerous domains, when levels of performance need to be defined.

Sewer asset management tool: dealing with experts' opinions

Abstract: Asset management requires the development of performance indicators (PIs) and decision procedures. Within the French RERAU methodology each rehabilitation criterion is assigned a grade out of four possible ones. This grade results from an aggregation of complementary PIs that use information derived from various sources: visual inspection, OM 2) one expert disagrees with a majority, a consensus may be defined; 3) major conflicts between answers.

The consistency of visual sewer inspection data

Abstract: In common with most infrastructure systems, sewers are often inspected visually. Currently, the results from these inspections inform decisions for significant investments regarding sewer rehabilitation or replacement. In practice, the quality of the data and its analysis are not questioned although psychological research indicates that, as a consequence of the use of subjective analysis of the collected images, errors are inevitable. This article assesses the quality of the analysis of visual sewer inspection data by analysing data reproducibility; three types of capabilities to subjectively assess data are distinguished: the recognition of defects, the description of defects according to a prescribed coding system and the interpretation of sewer inspection reports. The introduced uncertainty is studied using three types of data: inspector examination results of sewer inspection courses, data gathered in day-to-day practice, and the results of repetitive interpretation of the inspection results. After a thorough analysis of the data it can be concluded that for all cases visual sewer inspection data proved poorly reproducible. For the recognition of defects, it was found that the probability of a false positive is in the order of a few percent, the probability of a false negative is in the order of 25%.

Sewer asset management – state of the art and research needs

Abstract: Sewer asset management gained momentum and importance in recent years due to economic considerations, since infrastructure maintenance and rehabilitation directly represent major investments. Becau...

Integrated rehabilitation planning of urban infrastructure systems using a street section priority model

Abstract: Due to the changes in water management, from the construction of new systems to the rehabilitation of existing networks, integrated strategic rehabilitation management has become more and more important. Consequently, this paper shows a method that considers sewer and water distribution networks against environmental factors (e.g. street network and connected buildings) in a priority model. This approach aids in not only identifying areas where rehabilitation is technically necessary but also economically recommendable (e.g. completely depreciated). This is achieved by implementing factors of structural resiliency, vulnerability of the network, capital value and other network components (e.g. manholes, house connections). This model is applied to a medium sized case study in which the rehabilitation areas identified by the developed model are compared to the actual rehabilitation plans of the water and sewage companies. Results also show the application of the estimated ranking for rehabilitation ...