Improved maintenance planning

City of Diemen saves with subsidence map

SkyGeo’s Subsidence Map plots subsidence of every road in the city of Diemen. Based on monthly satellite measurements from 1992, Hansje Brinker maps subsidence throughout the city over the past decades with millimeter accuracy. Road maintenance planners now know subsidence rates for every neighborhood based on thousands of measurements per square kilometer. For the first time ever, the planning for major repairs to roads and sewers is based on a complete set of quantitative data. With support from the City Council, the city is able to save € 200.000 annually on maintenance expenditures.

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Benefits of the SkyGeo solution

• Complete overview of subsidence over the whole city in one map
• Insight in subsidence dynamics on millimeter scale
• Retrospective surveying information going back to 1992
• Determine mean time before failure per street
• Basis for more efficient planning of infrastructure maintenance

Preventing damage due to subsidence

The municipality of Diemen is built on very “soft soil”; decomposition of peat leads to rapid subsidence up to 50 centimeters in 20 years. Differences in soil composition cause the subsidence rates to vary drastically between neighborhoods and even with- in streets. Maintenance in Diemen is urgent where subsidence exceeds 20 centimeters – the diameter of sewage pipes, which will not drain at this point any- more. To prevent city-wide service interruptions, the municipality has to perform periodic reconstruction and elevation of roads and drainage.

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Scheduling maintenance cycles

The municipality has an annual budget of €2,2 million to maintain roads and sewers for its 20.000 citizens. Until now, subsidence is measured by visual inspection, which is neither precise, nor repeatable, nor geographi- cally complete. In addition, differences in subsidence rates are difficult to quantify this way, making main- tenance in some neighborhoods either unnecessarily early or too late.

Mapping subsidence accurately

SkyGeo used over 100 radar images recorded by satellites from 1992 to construct the city-wide subsidence map. With our innovative methods, we determined subsidence in millimeters for thousands of locations throughout the municipality.

From the resulting map, the city determines the mean time before maintenance of roads and sewers – previously based on extrapolating the results from visual inspection into the future.

Efficient maintenance plans

Next, SkyGeo’s deformation map enables the city to accurately calculate maintenance cycles at every level (streets, neighborhoods and districts). The de- formation map shows the dynamics of the subsid- ence measured at each of the venues, so the city can better prevent possible sewer emergencies.

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“Problems we had for years with manual measurements were resolved at once”

Ron Kaptijn – Policy Officer Infra, City of Diemen

Better expenditure allocation

The deformation map also suggested that maintenance can be safely postponed in many neighborhoods. This leads to considerable savings in annual main- tenance expenditure and a reduction of impact of construction work in the neighborhood. Another result of the use of the deformation map is that the cost of subsidence is quantified for the first time ever with €1,4 million per year. This was the biggest line item in the maintenance budget for the city’s infrastructure. Thanks to the accurate mapping of subsidence, the city of Diemen saves over €200.000 per year through more efficient planning of maintenance of roads and sewers, while providing better service to citizens.

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