Linking flow-stream variability to grain size distribution of suspended sediment from a satellite-based analysis of the Tiber River plume (Tyrrhenian Sea)

J Pitarch,F Falcini,S Marullo,W Nardin,A Di Cicco,V E Brando

doi:10.1038/s41598-019-56409-8

Abstract

Several coastal regions on Earth have been increasingly affected by intense, often catastrophic, flash floods that deliver significant amounts of sediment along shorelines. One of the critical questions related to the impact of these impulsive runoffs is “are flash floods more efficient in delivering non-cohesive sandy sediment along the coasts?” Here we relate flow stages (i.e., from erratic to persistent) to the grain size distribution of the suspended load, by performing a synergic analysis of in-situ river discharge and satellite-retrieved grain size distribution, from 2002 to 2014, covering the 2012 Tiber River (Italy) exceptional flood event. Our analysis shows novel and promising results regarding the capability of remote sensing in characterizing suspended sediment in terms of grain size distribution and reveals that erratic stages favour delivering of non-cohesive sandy sediment more than the persistent stages. This conclusion is supported by numerical simulations and is consistent with previous studies on suspended sediment rating curves.

Highlights

The hydrologic regime of the Tiber River basin plays an important role in sediment transport and, in turn, in the evaluation of medium- and long-term changes of the Mediterranean coastline of central Italy, called Laurentine Shore by the Romans[1,2]
Correlation between water discharge (Qw) and the satellite-based total volume concentration of suspended particles (VCtot) shows a comforting agreement, i.e., r = 0.55 (Fig. 1b); peaks of water discharge are always associated with high values of VCtot, which ranges from 1200 to 2500 ppm
By plotting the monthly η versus the coefficient of variation (CV) we find that CV and η correlate negatively, suggesting that more erratic river discharges relate to a larger proportion of large particles in suspension

Summary

Introduction

The hydrologic regime of the Tiber River basin (central Italy; Fig. 1a) plays an important role in sediment transport and, in turn, in the evaluation of medium- and long-term changes of the Mediterranean coastline of central Italy, called Laurentine Shore by the Romans[1,2]. We test consistencies between a model of sediment transport based on remote sensing observations, and a generic numerical model of sediment transport, by exploring the relation between GSD and stages (erratic vs persistent) of river outflows (Fig. 3).

Results

Conclusion