摘要：The Fiumi Uniti and Savio rivers are two small sandy-bed river
systems which sediment yield contributes feeds part of the EmiliaRomagna
beaches (Italy). Since the twentieth century the northern Adriatic
coast has been affected by well-known beach retreat phenomena. As the
sediment supply of these local rivers is not well known, an analysis of bedload
transport rates for the last 10 kilometres of the river has been done.
Multiple analysis, supported by direct field measurements of the 2005-06
and 2017 years (still ongoing) have been realized. Complementary
hydraulic investigation and modelling have been performed. Repeated bedmaterial
samplings have been carried out during different flood conditions,
obtaining a significant number of observations. Aiming at defining the
behaviour of sediment-transport in these two rivers, this paper focuses on
the analysis of threshold sediment transport condition. Several formulae
available in literature were used to test the field measurements. All these
criteria seem inappropriate to predict the threshold conditions for bed
particle entrainment in terms of the value of bed shear stress. The
inaccurate estimation given by these formulae is due to the fact that they
do not consider natural grain-shape factors or are mainly suitable for
gravel-bed rivers.
其他摘要：The Fiumi Uniti and Savio rivers are two small sandy-bed river systems which sediment yield contributes feeds part of the Emilia-Romagna beaches (Italy). Since the twentieth century the northern Adriatic coast has been affected by well-known beach retreat phenomena. As the sediment supply of these local rivers is not well known, an analysis of bed-load transport rates for the last 10 kilometres of the river has been done. Multiple analysis, supported by direct field measurements of the 2005-06 and 2017 years (still ongoing) have been realized. Complementary hydraulic investigation and modelling have been performed. Repeated bed-material samplings have been carried out during different flood conditions, obtaining a significant number of observations. Aiming at defining the behaviour of sediment-transport in these two rivers, this paper focuses on the analysis of threshold sediment transport condition. Several formulae available in literature were used to test the field measurements. All these criteria seem inappropriate to predict the threshold conditions for bed particle entrainment in terms of the value of bed shear stress. The inaccurate estimation given by these formulae is due to the fact that they do not consider natural grain-shape factors or are mainly suitable for gravel-bed rivers.
