One of the failure mechanisms for water retaining structures is piping. Piping is an internal erosion mechanism creating hollow spaces (pipes) underneath, for example, a dike as a result of the transport of soil particles due to seepage. The formation of pipes can cause collapse of the structure once the erosion process reaches the outside of the dike. This study focusses specifically on the possibility of the occurrence of this failure mechanism in the Maasvallei area. The Maasvallei covers the area of the Maas roughly between the Dutch towns Roermond and Mook. The early signs of piping in the form of sand boils are frequently observed during periods of high water levels in the Dutch rivers. Although the total collapse of a dike in the Netherlands due to piping has not occurred in the past decades, the frequent observation of the early signs of the piping process has resulted in the inclusion of the piping failure mechanism in the Dutch legal safety assessment regulations for water retaining structures. During recent high-water periods in 2011 and 2012 sand boils were observed along several Dutch rivers except at the dikes along the Maas. The striking absence of sand boils in the Maasvallei area raised the question if the failure mechanism piping is relevant for this specific area. In the recent assessment of the Dutch dikes, many of the dikes along the Maas in Limburg were found to be insufficiently safe against piping. The dilemma then becomes clear: the lack of early signs of piping contradicts the outcome of the safety assessment. Resources could be saved if the dikes do not need to be reinforced for piping, however, the safety should not be compromised. Within the thesis this dilemma is studied. The main question that is answered is: Is dike-failure due to piping realistic in the Maasvallei?