Scaling properties of the turbidity and streamflow time series at two different locations of an intra-Apennine stream: Case study

The time scales of a catchment hydrologic response in a human impacted intra-Apennine basin, was assessed by a power spectral analysis. Turbidity and streamflow data, at high resolution (10 minutes) have been considered during four years. The turbidity and streamflow have heavy tails that follow approximately Pareto distributions. Both also display scaling Fourier power spectra of the form f-b, over different scaling ranges: from 10 minutes to one day for the turbidity and from 1 hour to 20 days for the streamflow data. For both locations the slope for the streamflow is close to b=1.7, whereas for turbidity the values b=1.68 and 2.25 are found for the upstream and downstream locations, respectively. The turbidity dataset at the downstream station has a steeper slope than the upstream station, implying a higher persistence of the turbidity fluctuations: this change of slope shows that the effect of the river channel and catchment is similar to a fractional integration from the upstream to the downstream data. Furthermore, the delay times of the turbidity dataset, and hence of suspended sediment, were calculated using a co-spectrum between the series and indicating characteristic transit times of 25 days and 145 days.