Abstract
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.
Highlights
During the last decades the coast of the Emilia-Romagna region has been affected by a considerable beach retreat phenomena
Aiming at defining the behaviour of sediment-transport in these two rivers, this paper focuses on the analysis of threshold sediment transport condition
Hydraulic and sediment transport data were collected at fixed verticals, spaced along the active cross section
Summary
During the last decades the coast of the Emilia-Romagna region has been affected by a considerable beach retreat phenomena. Given the relevant economic role of the summer tourism, beach protection and reconstruction became crucial for, coastal management [1, 2]. In this region beach erosion is primarily due to the scarcity of sediment supplied by the small local rivers. Many factors contributed to the decrease in sediment supply and among them, anthropogenic interventions, such as an increase in deforestation, a change in land use, river bed mining and proliferation of dams, are the most evident [5, 6, 7, 8, 9, 10, 11]. Variations due to climate change such as decreasing of precipitation, runoff and water discharge, directly affected fluvial geomorphology and sediment supply [12]
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