Sustainable dike design ideas prove their worth against floods

Challenge

Substantial improvement works were carried out in the North Limburg area of the Netherlands between September 2016 and February 2021. They included constructing around 20 km of new dikes, excavating two new high-water channels for the River Meuse and reactivating its former tributary.

The work released millions of cubic metres of muddy and silty clay soil that the Limburg Province wanted to reuse to construct a steep-sided dike and a high-ground dike at Ooijen-Wanssum. This approach would improve safety, reduce the project’s carbon footprint and help the dike structures blend into the landscape. However, the challenge was that the soil did not meet the standard requirements for dike clay, so our task was to test the soil and ensure it was strong and safe enough to construct the new dikes.

Solution

The project involved the design and construction of around 20 km of dikes in Ooijen-Wanssum. This was a multidisciplinary collaboration between the client Mooder Maas (a combination of Dura Vermeer and Ploegam), the landscape architect (H+N+S) and Fugro’s own specialist dike designers and soil-driven levee design and laboratory experts.

Our team’s tasks were many and varied, including:

• Designing, preparing, supervising and analysing the development of large-scale wave and stream flume testing. We worked out the strength and erosion resistance of the area’s own local materials for the dike design. We also determined the soil’s properties and behaviour, based on large-scale field testing;

• Drafting a design protocol and safety philosophy for the two dikes, based on a soil-controlled process;

• Designing cut-off walls made of clay. By using Fugro Aquisense® soil penetration tests we proved that the cut-off walls should be short, with a clay finish (rather than steel);

• Conducting design sessions with asset managers to improve their understanding of this new concept, implement their maintenance strategy and gain their acceptance of the innovative design concepts and the use of local materials

• Drafting the design for 18 km of sustainable dikes. The design included a steep-sided and a high-ground dike, as well as 2 km of soil retaining constructions along Wanssum harbour;

• Determining the material requirements and developing a project-specific protocol for classifying and identifying the area’s own soils. Our work helped move the project from design to implementation;

• Providing insights into the future management requirements. During the design phase we built a scale model of the steep-sided dike to improve stakeholders’ understanding about using different materials from the local area, the risk of erosion caused by the river flows and the need for careful monitoring of the dike profile;

• Supervising the implementation. We monitored subsidence and the design stability of the embankments. We also performed the preliminary investigation and onsite material testing.

Innovative highlight

Utilising an area’s own (clay) soil to construct dikes is unique and working together with H+N+S Landscape Architects we designed an innovative approach that included:

• Using large-scale gully testing, laboratory testing, our material knowledge and dike expertise to achieve a demonstrably safe, soil-controlled design;

• Performing Aquisense® soil penetration tests to determine the permeability variation of the soil under the dikes. The findings resulted in a slimmer design, with shorter cut-off walls which could now be made out of local clay soil – a more cost efficient and environmentally friendly alternative to steel walls;

• The project won three national industry awards: Spatial Quality Award 2018 for the dikes’ integration in the landscape; Water Innovation Award 2019 for Flood Defence; Golden Pyramid 2020 for inspirational entrepreneurship.

Impact

• Performing a closed-ground assessment – high qualified performance of excavating material – our Geo-data expertise supported the design of safe, sustainable, wider dikes that blend into the local landscape and offer more possibilities for shared use;

• Reducing CO2 emissions by more than 50% – rather than removing around 3.5 million cubic metres of soil, we worked with locally available materials and assessed their strength through extensive laboratory and gully testin, so that the soil could be reused to build the new dikes;

• Optimising dike design – our cutting-edge measurement techniques such as Fugro Aquisense® soil penetration tests resulted in an optimised design with shorter cut-off walls under the dikes, built using cheaper and more environmentally friendly local clay;

• Flood defence – when high water ravaged Limburg in July 2021, the Ooijen-Wanssum dikes held firm.