The Ecological Value and Economical Use of Soft (Cohesive) Material for Land Reclamation: Marker Wadden Case Study
Type:
Presented during:
WODCON XXII - Enhance the Harmony between Dredging and Ecology
Authors:
T. Vijverberg, R. Lievens, X. Bing and A. Rijsdorp
Abstract
"As sand, as a resource for land reclamations, is increasingly hard or costly to come by, alternative land fill methods are being explored worldwide, such as using softer sediments (clay, mud, fines), which may be more readily available locally. The use of these types of sediment as building material is innovative and not yet common practice. The behavior of soft sediment reclamations is difficult to predict. Pioneer projects improve our understanding on this topic. This paper presents a case study of the Marker Wadden project, which is situated in lake Markermeer in the center of the Netherlands. This project shows that it is possible to reclaim large volumes of fine cohesive material (the scale of the project is 800 ha with a final reclamation thickness of approximately 4,5 m) in an economical way, making use of state-of-the-art design and construction methods. Large quantities of fine sediments are available in lake Markermeer and the ecological functioning of the lake is low. The Marker Wadden project was set up to improve the ecological value of the whole lake system. The main challenges in building this large nature reserve are to build with soft mud in an economical way, to create elevation gradients, to promote biodiversity and to enable the catchment of fines. Starting points of Boskalis’ (design and construct contractor) design were: 1) Landscape design is leading to meet project goals (create habitat diversity for birds and fish); 2) Make use of natural processes as much as possible; 3) Smart design of operational work method with respect to self-weight consolidation, crust formation, atmospheric drying and effect of vegetation; 4) Apply state-of-the-art design tools: model, experiments, monitoring, adaptive working method during construction. In April 2016, Boskalis started the construction of the Marker Wadden. Almost 2 years later most of the islands are completed and in September 2018 a part of the area is opened to the public. Soft mud exhibits highly varying characteristics at each project, but the same construction (floating equipment) and design principles as applied for the Marker Wadden project can be applied to other projects around the world. This makes the Marker Wadden project a valuable pioneering example for how to reclaim large volumes of soft mud."
Keywords: Reclamation, Soft sediments, Nature reserve, Ecological restoration.