Roël de Leede – Senior Policy Maker Water and Sewerage at the municipality of Vlaardingen, the Netherlands.
Vlaardingen is a municipality in the Dutch province of South Holland, having approximately 72,000 inhabitants. The municipality is responsible for operating and maintaining the public space and requires insight in the state of its objects for fulfilling this task. Since the municipality is located in the soft soil region of the Netherlands, it is strongly affected by ground subsidence. This is impacting the speed with which the public space degrades, leading to frequent maintenance and heightening of the ground level.
An underground job
Roël de Leede is employed by Vlaardingen as Senior Policy Maker Water and Sewerage. In this fashion, he is jointly responsible for the prioritization of sewerage and road maintenance. Next to this, he is working on water management and mitigating climate change effects, such as the summertime droughts that are occurring more and more frequently in the Netherlands. His goal is to be the invisible force behind the scenes, taking care of the municipal maintenance in a way that the inhabitants experience the highest level of comfort with the lowest amount of inconveniences. So this is literally and figuratively an underground job!
Maintenance often causes inconvenience for the neighboring residents.
Insufficient information from soil maps
Subsidence is an important factor in the maintenance strategy of the municipality of Vlaardingen. They used to work with soil maps and models for their planning, based on low-frequent leveling measurements. Due the strong spatial variability in subsidence, these maps provide insufficient grounds for data-driven policy making. Because of this, the municipality was often in the dark and had to make rough estimations on the amount of subsidence in the past and towards the future. This led to higher maintenance costs and a larger amount of complaints by the residents. For example, settlements can cause broken pipes at house connections or lead to a decrease in quality of the main pipe due to fractures, cracks or open joints and connections.
An old sewer pipe that had to be replaced.
“Replacing one meter of sewer pipe easily costs €1,000 in Vlaardingen”, says Roël, “so this is something that we only want to do when it is absolutely necessary”. On top of this, the maps they used to have only provided them with an indirect indication of subsidence; they do not, for example, take into account the effects of the ground water table on the settlement rate.
“Ideally we replace sewer pipes the day before they collapse”
InSAR data for the municipality
Therefore, there is a great demand from Vlaardingen for data on the actual subsidence that occurred in the municipality. As Roël says: “Ideally we replace sewer pipes the day before they collapse.” This is the reason why Vlaardingen contacted Sensar. With our satellite-based measurements, Vlaardingen has access to detailed insights on the subsidence that occurred in the municipality since 2015, allowing them to make object-level decision on the future maintenance prioritization. Next to that, the data provides input on which fill material to use when raising the ground. The real estate department at Vlaardingen also uses the deformation map. They work on topics such as value estimation of buildings and signaling houses with potential foundation problems. On top of that, Vlaardingen wants to use this data to focus more on informing residents, as is described in the renewed Dutch environmental code.
The subsidence in the municipality of Vlaardingen, visualized per neighborhood.
Drought stress test
In order to improve the insights in the effects of drought on subsidence of the public space, Vlaardingen, Sensar and engineering firm Wareco joined forces in a drought stress test. In this test, the deformations that occurred during the extremely dry summer of 2018 were compared to the numbers during other summers. It appeared that the ground endured up to 5mm of additional subsidence due to the drought! This effect was not limited to strong subsiding neighborhoods, but was also visible in the normally relatively stable parts of the city. In some instances, it was even possible to correlate the water-extracting effect of trees with a higher settlement rate.
“By prioritizing only a few sewer pipes in a smarter way, I can already repay the costs of the service.”
All in all, satellite-based subsidence data saves Vlaardingen a lot of money and also ensures a better and more proactive service towards its inhabitants. The advantages are mainly in the more precise estimation of the moment of maintenance and the early detection of high-risk locations. “By prioritizing only a few sewer pipes in a smarter way, I can already repay the costs of the service”, says Roël. By using our data, the municipality of Vlaardingen now has a data-driven and smart prioritization for maintenance of the public space!