Stedin NV manages over 23,000 kilometer of gas distribution pipelines and 1.9 million connections into homes in the western part of The Netherlands. The company uses our ground-breaking door-by-door subsidence risk estimates to ensure that service pipelines with the highest risk are identified and maintained first. SkyGeo helps Stedin remove the most risk per invested dollar.

The weak link: gas service lines in subsiding cities

Most houses in the Netherlands’ soft soil are built on a foundation so they do not subside. Gas distribution pipelines on the other hand subside with the soil. This creates a hinge point where the gas service pipeline enters the building. These connections are prone to breaking.

The severity of subsidence directly correlates with problems in gas delivery service, as is well confirmed by inspection in the field. So subsidence-related maintenance is part of Stedin’s long-term planning.

Previously, Stedin’s knowledge of subsidence effects on risk was based on estimations from 1 soil sample per 10,000m2. This is not good enough, because ground subsidence in soft-soil delta areas is a heterogeneous process: within a street, one service line can be OK, and a few doors down, another service line can experience severe strain due to settlements.

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SkyGeo determined over 30,000 subsidence rate measurements in the Portland subdivision; at the left we show street-level data, based on Very High Resolution satellite data between 2009 and 2014. Next, an interpolated risk “heat” map was produced (whole image). The outlines of the houses and streets are shown in grey and Stedin could determine expected subsidence impact per front door. Individual homes, garages and streets are outlined in grey. Service lines going into homes in green (stable) areas are assigned low risk status, service lines in red areas subside rapidly and are assigned high risk. On the far right is a zoom-in of the interpolated subsidence risk map of Portland.

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Actual effects of subsidence on the most vulnerable part of a service line. On the right hand side, a house on foundation; on the left hand side of the photo a flexible service line connection outside of the house, “floating in” subsiding ground.

Real scheduled maintenance planning required more detailed information on subsidence. Now SkyGeo provides a direct estimate of subsidence effects on distribution lines from door to door, across Stedin’s entire service area.

Subsidence in the Portland area

Just south of the city of Rotterdam, the Portland subdivision was built in the 1990’s on four artificial islands. In this area, complaints about the gas delivery service were filed routinely in recent years. Visible signs of rapid subsidence in the roads coincided with high incidence of broken service lines.

Standard maintenance procedure was scheduled and would have dictated replacement of the majority of over 800 pipeline service connections. This scheduled maintenance would have progressed from connections in West Portland first, to the East last. Where no damage is found for several connections in a row, the maintenance is skipped. The operation was budgeted for more than €850.000.

Stedin’s asset manager decided to apply actual subsidence measurements as a proxy for risk in order to prioritize the maintenance activities. SkyGeo‘s satellite-based subsidence product started with 30,000 subsidence time series in the 3 km2 area. This very high resolution product shows 5 years of dynamic subsidence history of streets, buildings and other objects. The measurements were used to create a street-level deformation map. This showed subsidence rates up to 3 cm per year, distributed unpredictably over the area.

Ultimately, only 20% of the service lines in the area were found to be at high risk due to subsidence, including the area where the customer complaints originated. Stedin decided to prioritize maintenance on this 20% of the connections. The other parts of the area will be monitored.

As a test, Stedin dug out 5 random pipeline connections selected from the other, low risk 80%. These samples confirmed no damage from subsidence at all as predicted based on SkyGeo’s measurements.

Implementing the deformation maps

Realizing the importance of accurate and detailed subsidence measurements, Stedin has implemented these maps in their corporate asset management infrastructure. Asset Management and Network Operations Planning can access the data in a GIS environment, while field personnel can view data on a tablet. Specifically, service lines are identified where likely no subsidence occurs.

Nowadays, before scheduled maintenance gets done by a field crew, the planner assesses the subsidence risk.

Since digging up and checking an individual connection costs up to €1500, Stedin has saved hundreds of thousands of euros in Portland alone. Also, Stedin reduced customers’’ exposure to construction.

Based on the results in Portland, Stedin decided to use SkyGeo’s high resolution system to map subsidence risk for the rest of its service area with 1.9M subscribers. Stedin becomes the first gas distribution company in the world to have this innovative system operational for its network.

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