Noorderzijlvest uses early warning system for levee stability

The Lauwersmeerdijk protects the province of Groningen in the Netherlands from flooding by the North Sea. An erosion channel in this sea rapidly removes sand at the underwater part of the levee. In 2010 the Lauwersmeerdijk did not pass nationwide test of Levee Safety over a distance of 25 km; the underwater slope had become too steep, endangering levee stability. To prevent faulting in the levee, SkyGeo monitors the Lauwersmeerdijk by order of the local water board Noorderzijlvest since 2010. SkyGeo provides an effective early warning system to detect instabilities in the levee.

Advantages of early warning system

  • Deformation patterns of a large regional structure captured in one overview
  • Detailed monitoring for changes at hundreds of measurement points
  • Cost- effective method complementary to traditional surveying techniques
  • Quick assessment of levee stability based on satellite data

Levee instability

A strong tidal current in the North Sea causes rapid erosion of the underwater part of the Lauwersmeerdijk. The transportation of sand from the levee causes the underwater slope to become steeper over time. Eventually, this process can result in levee instability. The underwater depths were measured at cross-sections shown in the cartoon, but there were no historical surveying data of the levee prior to 2010.

A strong tidal current results in significant erosion of the toe of the Lauwersmeerdijk; a process which results in levee instability over time. The dashed lines show the original levee slope and an early stage of erosion.

Early warning system

SkyGeo reports deformation of the Lauwersmeerdijk on a quarterly basis. For accurate results, a large number of radar satellite images are combined that are acquired from 2004 to 2011. By following specific locations throughout the stack of imagery over time, deformation of these locations can be measured with millimeter precision.

An easy to read chart for each location shows the actual rate of subsidence — important information that would be too expensive to gain by using traditional measurement techniques over the entire length of the dike and that was not available prior to 2010 anyway.

This method provides Noorderzijlvest with an effective early warning system to identify sections on the levee that are potentially unstable.

Integral part of business operations

SkyGeo reports change to subsidence rates on a quarterly basis and helps Noorderzijlvest to prioritise locations for levee inspection. In this way, only specific locations that require attention are evaluated in the field, which results in a significant gain of time and money. Therefore, Noorderzijlvest has incorporated the early warning system as an integral part of their business operations.
The asset manager has decided that SkyGeo’s data need to be complemented locally by real-time deformation data and has installed a number of inclinometers inside of the dike in the areas where we detected rapid motion. Moreover, maintenance for this dike has been scheduled earlier by several years for this small section of the entire dike.

Deformation measurements of the Lauwersmeerdijk shows that potential instabilities are likely limited to a small section along the 12 km dike. The scale bar shows the average annual rate of subsidence; every point has a time series underlying it  (shown below).

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