Statute laws concerning preventative archaeology adopted in France in 2001 for threatened sites required development of evaluation techniques. The common methodology used during the past 10?years has been extensive excavation. This method delivers a direct record of the discovered archaeological features and of their distribution. However, the success of visual observation can be variable, depending on geological context and the feasibility of envisaging the entire archaeological settlement from the part that is observed. We report here a case study from an early Middle Age settlement located on a floodplain. It was partially excavated and the alluvial context makes the features difficult to recognize for archaeologists. We show how the geophysical survey complemented the archaeological survey and allowed the detection of previously unrecognized features. In a second step, we compare the results of surveys with magnetic and electromagnetic methods on a topsoil stripped area and the neighbouring surface. From this analysis we conclude that a significant part of the unrecognized features discovered were present above the level of stripping. This example underlines that the practice of topsoil stripping has to be reconsidered, and should be integrated with geophysical survey to limit the potential loss of archaeological information. Copyright (C) 2012 John Wiley & Sons, Ltd.