G.R. 1322/2006), based on the ratio between the volume of the discharge and the volume of the input rainfall ( Puppini, 1923 and Puppini, 1931). The storage PARP activity method connects the delay of the discharge peak with the full capacity of the basin to accumulate the incoming rainfall volume within

the hydraulic network, and it uses as main parameter the storage capacity per unit area of the basin ( Puppini, 1923 and Puppini, 1931). Aside from the rainfall patterns, the basin area and the capacity of the basin to retain or infiltrate a part of the precipitation, the delay and dispersion between the precipitation and the transit of the outflows at the outlet are due to the variety of hydraulic paths, and to the availability of volumes invaded that delays the flood wave ( Puppini, 1923 and Puppini,

1931). Given this preface, to quantify the effects of network changes we developed a new indicator named Network Saturation Index (NSI) that provide a measure of how long it takes for a designed rainfall to saturate the available storage volume. Given a designed rainfall duration and rainfall amount, we simulated a hyetograph to describe the behavior of the rainfall during time. We assume that the amount of rainfall is homogeneous over the surface, and at every time step we computed the percentage of storage volume that is filled by the rainfall. The NSI is then the first time step at which the available storage volume is 100% reached (Fig. 6). The NSI has one basic assumption, also main assumption of

the Puppini, selleck products 1923 and Puppini, 1931 method, that is the synchronous and autonomous filling of volumes stored in the network: the water does not flow in the channels – null slopes–, and each storage volume is considered as an independent unit that gets filled Vasopressin Receptor only by the incoming rainfall. With reference to the mechanisms of formation of the discharge, the idea is that in the considered morphological and drainage condition, the water flows in the channels are entirely controlled by the work of pumping stations, and we assume a critical condition where the pumps are turned off. One must note that the NSI is an index that is not meant to be read as an absolute measurement, nor with a modelistic claim, rather it is defined to compare situations derived for different network conformations. To compute the index, as in many drainage design approaches (Smith, 1993), we based the evaluation on synthetic rather than actual rainfall events, and we considered some Depth–Duration Frequency curves (DDF). A DDF curve is graphical representation of the probability that a given average rainfall intensity will occur, and it is created with long term rainfall records collected at a rainfall monitoring station. DDF curves are widely used to characterize frequency of rainfall annual maxima in a geographical area (Uboldi et al., 2014). Stewart et al. (1999) reviewed actual applications of estimates of rainfall frequency and estimation methods.