Variability of gravel movement on the Virginio gravel-bed stream (Central Italy) during some floods.

A continuous-operation bed load measuring station was installed on the Virginio gravel-bed stream (central Italy), which has a median grain size of about 16 mm (-5 phi) and a straight channel with alternate bars. The slope of the stream at this point is about 0.008 and the basin has an area of 40 kms^2. The introduction of a marked sample of about 4,000 pebbles upstream from the measuring station made it possible to study the relationships between bed load transport and the passage of pebbles through the reach above the station. It was possible after each flood to measure the position of the pebbles remaining on the surface of the river bed. The results of this study confirm the pulsating nature of bed load transport and its poor correlation with grain-size distribution and water discharge. For each grain-size class, the distance travelled by the pebbles, and their embedding were measured.