- Water Board in The Netherlands
- Responsible for ground water table, water quality and levee safety
Water Board ‘De Stichtse Rijnlanden’ (HDSR) uses the Sensar LeveeScan to gain insights into the historical settlements per levee segment. This allows for making a smart and more detailed design for the levee reconstruction of project Sterke Lekdijk. This project is part of the Dutch national program for flood defense (HWBP).
Current soil models lack detail
The soil condition on and around a levee is of major importance during a reconstruction project. An accurate estimation of future settlements allows for taking measures during the design phase. In this way, it can be ensured that the levee remains at height towards the future and offers proper protection against high water scenarios. For estimating future settlements, HDSR used to work with the subsidence map from the Dutch government; a relatively coarse map based on publicly available data. Unfortunately, using this map, one cannot distinguish the levee from its hinterland. Therefore, the map lacks the detail needed to assess the heterogeneous soil profile that is expected around rivers.
The subsidence map of the Dutch government that HDSR used to work with.
Project Sterke Lekdijk
- Reinforcement of 55km primary levee
- Protects a large part of the big Dutch cities from floods
- Expected works: 2021-2029
Next to this, the interpolated map only offers an indirect indication of settlements, based on the soil type. This approach neglects other potential causes of subsidence and is therefore incomplete. Because of this, the water board had to take a conservative number into account for the future settlements of 0.5 to 1 cm/yr for the whole levee, even though large parts were construct on historical sand bodies. An increase in the level of detail could greatly improve the efficiency of the project and prevent unnecessary disturbances for the environment.
“We can now determine the best approach per levee segment. This saves us a lot of money.”
- National reinforcement plan for 1300km of primary flood defense before 2050
- Goal: matching the new Dutch flooding safety standards
Insight in settlements per levee segment
This is why HDSR approached Sensar. Our LeveeScan product is based on InSAR satellite data and provides the water board detailed and accurate information on the historical and actual subsidence rates of the levee and its direct environment. We can look back in time as far as 1992. The Sensar LeveeScan provides direct input for assessing the future subsidence of the levee and thereby the parameters for the levee reconstruction design. “With this method we can now determine the best approach per levee segment. This saves us a lot of money”, says Waldo Molendijk – contract manager of project Sterke Lekdijk.
Historical settlements on a part of the levee, visualized in the Sensar LeveeScan per segment as 25th percentile.
Sensar LeveeScan detects less subsidence than expected
A part of the levee that is being reconstructed.
The water board was initially accounting for 1 cm/yr of settlements over the total 55km of levee. The Sensar LeveeScan showed that there was no segment where this amount has occurred in the past. This allowed HDSR to ease the reconstruction requirements on many parts of the levee. It turned out that the levee did not have to be raised for the coming 50 years on several segments. This led to great cost savings for the reconstruction project. Next to this, HDSR used the Sensar LeveeScan to map out the reference situation of neighboring buildings. This allows to put potential building damages that might occur during the works in perspective.
“Fellow water boards, take advantage of this product!”
More than €1,000,000 cost savings
HDSR estimate that the use of the Sensar LeveeScan has led to a total cost saving of more than 1 million euros. This can be ascribed to the smarter definition of the approach per levee segment and a better risk mitigation towards the future. And next to the monetary savings, the product also leads to savings for the climate and the environment. By making better use of the space, reducing the use of materials and having a lower amount of construction activities, the CO2 emissions on this project are reduced. Satellite data therefore contributes both to the financial aspect, as well as to the sustainability. “Fellow water boards, take advantage of this product!”, says Waldo.