Can morphological dredging help improving natural values in rivers and estuaries?

We should acknowledge that dredging has been quite often not taking properly into account the morphological and the ecological functioning of rivers and estuaries. Fortunately, things are changing, also because society recognizes that nature values are to be preserved. As the latter are strongly linked to the morphology, dredging could be a way to influence positively morphology and consequently ecology. Obviously, dredging has always to a certain degree an effect on morphology, but the concept “morphological dredging” should be restricted to that activity inducing positive effects for navigation, ecology and safety against flooding. It must rely on a sound understanding of the morphological functioning of the river system and the capability to predict changes. This method has been introduced in the project for improvement of navigation conditions on the powerful Congo River, in its maritime reach. It was applied routinely since the end of the sixties and was based on the prediction of the behaviour of channels and sandbars, working “with nature” instead of against it. However, in 1988 it had to be implemented in an emergency situation, working against an evolution that would result in halting navigation. The work was executed with the CSD Kallo (Dredging International) on the basis of a thorough analysis of the morphological behaviour, with a comprehensive survey programme. Dredging cuts as well as the disposal sites of the dredge material were chosen for helping reverse the negative morphological evolution. More recently, disposal of dredging material in the Westerschelde estuary was proposed as a means to revert a negative evolution of a sandbar and channel system (Peters et al. 2001). The proposed experiment started by the end of 2004 and is considered successful, so far. This disposal strategy has now been included in the future dredging operations and today, other disposal sites are considered. The monitoring goes on and helps better understanding the morphological and ecological functioning of a complex estuarine channel and bar system. Other experiments will be proposed about the use of dredging, not only disposal but also dredge cuts for improving port accessibility and for helping stopping the degradation of nature values, possibly improving them. The possibilities for using worldwide the dredging operations as a means to influence positively the morphological changes are discussed, as well as the benefit they might have on the nature values in rivers and estuaries