A multi-criteria approach for asset management of waste water networks

1. A multi-criteria approach for asset management of waste water networks D2-Decision Deck project Workshop, February 21-22, 2007 , Paris-Dauphine. Amir NAFI,Vincent MOUSSEAU and Caty WEREY Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

2. Stakes and goals of the study • The context • The problematic • Proposed approach • Electre-Tri method • Implementation • Analysis of the results • Conclusion and outlook Plan Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

3. Stakes and goals • Long term policy for asset management • The use of available data in County Council of Bas-rhin • Respect of financial constraint by sewers selection • Proposing a way to select deteriorated sewers • Implementation of the approach in waste water utility • Identification of deteriorated sewers for rehabilitation • Considering possible improvment for Electre-tri method Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

4. Asset management Policy and goals Up date Inventory of asset Data collection Asset diagnosis and inspection Constraints Technical and financial Decision making , programming Short, mean et long terme Asset management Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

5. The context Context 152 sewerage utilities Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

6. Data on the pipe and its environment 5 100 km (4 600 km waste water) Defects noticed by CCTV inspectionsunder « local » codification 32 232 inspections 89 311 defects The context Sewers inventory in 2003: • Data base called CHIMERE Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

7. Assistance for sewers diagnosis Waste Water Utility Conseil général du Bas-rhin Subside, grant Inentory, data gathering, camera inspections Sewers networks The context Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

8. The problematic Camera Section Manhole Manhole Sewerpipe Soil Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

9. The problematic RERAU methodology • Defects:actual physical state of the pipe, observed by special cameras • Dysfunctions: consequences of defects • Impacts: effects of the dysfunctions if vulnerability: segment and environment. • Direct observation (O): it is the case of CCTV inspection • Observation-based estimations (E/O): some time results of defects observed by CCTV • Estimations based on risk factors (E/R): step before CCTV inspection. Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

10. Encoding of defaults EN 13508-2 standard codification (2003) Defect: Break/collapse Main Aditional information description code BAC characterisation The nature of the observation is: Break (A) – pieces of pipe visibly displaced - - Missing (B) – missing pieces of wall - Collapse (C) – complete loss of structural integrity quantification The length of the observation in millimetres Circumferential location The position of the observation Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

11. Main categories of dysfunctions Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

12. Problem formulation Criteria Sewers INF EXF HYD DEB DEV ... ENS Category Sewers S1 120 20 30 40 50 60ACC S2 120 20 30 40 50 60INT . . . . . . . . . . . . . . . . S90 120 20 30 40 50 60ABS Categories • 8 dysfunctions taken into account in decision making, number of • criteria equal to 8. • Density dysfunction is assessed according to RERAU methodology for each dysfunction corresponding to a criterion. • 3 categories for deterioration state: ABS, ACC and INT, 2 profiles • to determine • We consider an assignment problem of 90 sewers among 337

13. La méthode Electre-Tri Density C3, INT Category 3 Category 2 Profiles & thresholds C2, ACC C1, ABS Category 1 Criteria

14. Main categories of dysfunctions Camera inspections Encoding of defaults EN 13508-2 Data collection and problem formulation Density of dysfunctions RERAU methodology Table of Performance Electre-tri Elicitation Electre-tri method Expert Infering categories profiles and thresholds Results & analysis

15. Expert analysis, assignment example Chimer • Expert assignment • 7 sewers to category ABS • 37 sewers to category ACC • 47 sewers to category INT Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

16. Electre-tri elicitation, Profiles inference Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

17. Electre-tri implementation on example, IRIS Chimer Electre-tri implementation and expert assignment Weights inference obtained by IRIS Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

18. Results analysis Analysis of sewers not correctly assigned by Electre-tri • The sewers shown by the table above, are characterized by : • accumulation of minor dysfunctions that become the sewer deteriorate • presence of a major dysfunction specially infiltration • possible error from expert assignment, specially for sewer 49856 Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

19. Electre-tri implementation on 337 sewers Electre-tri implementation and sewers not correctly assigned because dysfunctions accumulation • Analysis of assignment • 27 sewers because of accumulation • 12 sewers because of a major dysfunction • 2 sewers because of possible error of expert Weighted sum for density Weighted sum for citeria Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

20. Weighted sum threshold determination Expert analysis of 15 sewers for threshold estimation Weighted sum for density Weighted sum for criteria Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

21. Implementation of filter defined by weighted sum Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.

22. Conclusion • Interactive approach between Expert and analyst • Defining of category frontiers according to assignment example • Assessing of weights for criteria handled in decision process • Interesting results, but inaccuracy due to the non consideration of the accumulation of minor dysfunctions • proposing filter with the help of weighted sum • reducing the inaccuracy by the use of ad-hoc filter • implementing the approach for sewers rehabilitation • up dating assignment example and category frontiers • improving Electre-tri to take into account accumulation phenomenon Joint Unit Research in Water Utilities Management Cemagref-Engees 1 quai Koch 67070 Strasbourg, France.