First results of geophysical and geotechnical investigations along the Hedwige- and Prosperpolder dykes
S.N. Elgün, G. De Backer, J. Bink, W. Zomer and P. Peeters
Journal name: First Break
Issue: Vol 37, No 8, August 2019 pp. 63 - 68
Special topic: Legacy Data
Info: Article, PDF ( 554.28Kb )
Price: € 30
The Hedwige- and Prosperpolders are situated on the border of Belgium and the Netherlands near Antwerp, as presented in Figure 1. A polder is a low-lying tract of land that forms an artificial hydrological entity, enclosed by embankments known as dykes. It is decided that the two polders will be turned into an area with intertidal nature (managed realignment). Together with the ‘Drowned Land of Saeftinghe’ they will be part of the largest intertidal nature area in Western Europe. The reconstruction means that the current dyke along the river Scheldt will become obsolete and partially removed. This presents a unique opportunity to perform full-scale tests on this dyke, which has been in service for several decades. BZ Engineers & Managers commissioned by The Dutch Foundation for Applied Water Research (STOWA) and the Belgian Flanders Hydraulics Research (FHR, Department of Mobility and Public Works) have joined forces to organize these experiments. Together with several other partners, including knowledge institutes, universities and flood managers, the test and experiments will improve understanding of the impact of floods incidents and of climate change. Field experiments on the Scheldt dykes form the core of the collaboration. In order to design the field experiments, including their scope and location, a reliable 3D model of the dyke body is required. In particular, it is considered important to test and compare several different scenarios and outcomes of a dyke breach. In order for these tests to be useful in a predictive sense, it is necessary to characterize the test dyke body structure for comparison with dykes elsewhere. The experiments in the Hedwige- and Prosper polder will also be an inspiration to use area covering measurement techniques on a wider scale on dykes factually protecting the hinterland from flooding. The application of such measurement techniques is now limited, but it is expected that these techniques can help to give insight into the whole volume of the dyke and its subsoil. Since most failure mechanisms occur on a local or micro scale, the translation from point measurements to volume increases our understanding of failure mechanisms related to dyke strength. It is important to establish that dyke composition is reasonably homogeneous along the section under investigation if meaningful comparison of various breach scenarios is to be achieved. Ideally, the three-dimensional composition of the dyke body needs to be determined. Geotechnical measurements based on point sampling techniques including CPTEs (Lunne and Robertson, 1997; Robertson, 1990) provide precise, localized information but leave much of the ground unsampled. This reduces the reliability of any ground models based on the results. Engineering geophysics provides a means to populate a more reliable ground model with continuous or quasi-continuous information.