II.4.3 Breda’s case study 103 8.0 24.5 41.0 57.5 74.0 Pipe age (in 2024) (a) (c) (d) (b) 0 25 50 75 100 Pipe length (meters) Concrete PVC Other 0.00 0.25 0.50 0.75 1.00 Pipe diameter (meters) Figure II.4: Covariates in Breda’s sewer network: (a) pipe age computed by 2024, (b) pipe diameter in metres, (c) pipe length in metres, (d) pipe material. Figure II.6(a) presents a histogram of inspections over the years, showing an increasing trend. Figure II.6(b) illustrates the maximum number of inspections per pipe, with approximately 85% inspected only once, 12% twice, and less than 3% three or more times. Figure II.6(c) illustrates the percentage of the network inspected over the years. From approximately 2010 onwards, about 10% of the network is inspected annually. Details on the design and execution of the inspection campaigns are unavailable and beyond the scope of this case study.
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