Field investigation of bedforms and flow resistance in a large sand river

The paper refers to a field study of river bedforms and their effect on the flow resistance in a large sand river (i.e. river Po-Italy). Multibeam echosounder surveying was carried out, and different computational methods are applied and compared, in order to calculate bed form pattern (spatial distribution, height, wave length, steepness). The field data in terms of dune geometry have been compared with those calculated by means of different approaches. Linear approaches to flow resistance in presence of bed form are applied and compared with field observed data in terms of energy slope. Good results are obtained ac-counting for a recently proposed semi-analytical model for the bedform drag, considering the effects of a sudden expansion of a free surface flow rather than of a pressure flow.