Paolo La Barbera

Fractal relation of mainstream length to catchment area in river networks

Institute of Hydraulics, University of Genoa, ItalyMandelbrots (1982) hypothesis that river length is fractal has been recently substantiated byHjelmfelt (1988) using eight rivers in Missouri. The fractal dimension of river length, d, is derived herefrom the Hortons laws of network composition. This results in a simple function of stream length andstream area ratios, that is, d = max (1, 2 log RL/\og RA). Three case studies are reported showing thisestimate to be coherent with measurements of d obtained from map analysis. The scaling properties ofthe network as a whole are also investigated, showing the fractal dimension of river network, D, todepend upon bifurcation and stream area ratios according to D = min (2, 2 log RB/log RA). Theseresults provide a linkage between quantitative analysis of drainage network composition and scalingproperties of river networks.

The tracking and prediction of high intensity rainstorms

The paper addresses some concepts and issues relevant to the use of satellite imagery, as provided by the infrared radiometers flying on board geostationary orbiting platforms, in the tracking and prediction of typical mid‐latitude Mesoscale Convective Complexes (MCCs) associated with high intensity rainstorms over the Mediterranean area. The predictive content of sequences of Meteosat half‐hourly images is exploited in this work, aiming at the development of storm identification and cloud tracking procedures suitable for operational use in flash flood forecasting applications. Though relying essentially on image processing techniques, the cloud tracking approach seems quite useful in the short term prediction of the dynamics of MCCs as the resolution scale of the temporal sampling provided by the satellite sensor is short enough to ensure that abrupt changes in the cloud characteristics are not likely to occur between two subsequent images. Some studies are presented to show the potential of the procedur...

Early warnings and quantitative precipitation forecasting

Flash floods rank high in the list of major hazards in the Mediterranean environment. Early warnings in highly developed areas are the only non-structural remedial measures suitable to reduce the risk level, if properly diffused with enough lead time and acceptable reliability.

Modelling uncertainty in estimates of recharge to a shallow coastal aquifer

Due to the difficulty of field characterization, one is often forced to employ hydrological models in order to determine estimates of aquifer recharge. A Geographical Information System (GIS) and Digital Elevation Model (DEM) may provide the basic support for such hydrological models. Unfortunately, despite the availability of these tools, the values of many parameters within distributed models remain uncertain for application to real world problems. Using the Bisagno basin (100 km2) in the Liguria region of Italy, the role of model parameter uncertainty on estimates of recharge to the Bisagno Aquifer is demonstrated. Uncertainty estimation is achieved through Monte Carlo simulations with the aid of the Generalised Likelihood Uncertainty Estimation procedure of Beven & Binley (1992).

A green roof experimental site in the Mediterranean climate: the storm water quality issue.

Since 2007, the University of Genoa has been carrying out a monitoring programme to investigate the hydrologic response of green roofs in the Mediterranean climate by installing a green roof experimental site. In order to assess the influence of green roofs on the storm water runoff quality, water chemistry data have been included in the monitoring programme since 2010, providing rainfall and outflow data. For atmospheric source, the bulk deposition is collected to evaluate the role of the overall atmospheric deposition in storm water runoff quality. For subsurface outflow, a maximum of 24 composite samples are taken on an event basis, thus aiming at a full characterization of the outflow hydrograph. Water chemistry data reveal that the pollutant loads associated with green roof outflow is low; in particular, solids and metal concentrations are lower than values generally observed in storm water runoff from traditional rooftops. The concentration values of chemical oxygen demand, total dissolved solids, Fe, Ca and K measured in the subsurface outflow are significantly higher than those observed in the bulk deposition (p < 0.05). With respect to the atmospheric deposition, the green roof behaviour as a sink/source of pollutants is investigated based on both concentration and mass.

An Integrated GIS Approach to Assess the Mini Hydropower Potential

An analytical approach to assess the mini hydropower potential is proposed on a GIS platform. The mini hydropower potential is defined in terms of a synthetic index that measures the investment feasibility of a given hydropower plant. The investigation of the mini hydropower potential is performed at the catchment scale by integrating: catchment morphometric analysis; setting criteria for locating the weirs and powerhouses; hydrological modelling; engineering analysis; economic analysis and mapping. The integrated approach has been tested on the Arroscia catchment (Italy) where 27 weir sections have been examined thus resulting into 640 evaluated mini hydropower plant alternatives. Hydropower potential results indicate that in 14 over 27 sub-catchments it is possible to select at least a specific powerhouse location where the investment is affordable. The determination of MHP indexes in a simplified framework overcomes the typical problem due to the single prediction of hydropower potential for a specific plant configuration. The comprehensive MHP analysis allows to supports the energy management strategies while ensuring the sustainable water resource management at the catchment scale.

Enhancing the Retention Performance of a Small Urban Catchment by Green Roofs

In existing urban areas the drainage systems can be retrofitted in order to address flooding and water quality problems. In this study, the installation of green roofs is assumed as hypothetic retrofitting scenario according to a sustainable storm water mitigation strategy for a selected urban catchment. The modelling is undertaken using EPA SWMM; the simulations are performed over a continuous simulation of 26-years of rainfall records. The modelling results point out that the retrofitting scenario contributes to the storm water runoff mitigation mainly in terms of volume and peak reduction.

A dimensionless approach for the runoff peak assessment: effects of the rainfall event structure

The present paper proposes a dimensionless analytical framework to investigate the impact of the rainfall event structure on the hydrograph peak. To this end a methodology to describe the rainfall event structure is proposed based on the similarity with the depth–duration– frequency (DDF) curves. The rainfall input consists of a constant hyetograph where all the possible outcomes in the sample space of the rainfall structures can be condensed. Soil abstractions are modelled using the Soil Conservation Service method and the instantaneous unit hydrograph theory is undertaken to determine the dimensionless form of the hydrograph; the two-parameter gamma distribution is selected to test the proposed methodology. The dimensionless approach is introduced in order to implement the analytical framework to any study case (i.e. natural catchment) for which the model assumptions are valid (i.e. linear causative and time-invariant system). A set of analytical expressions are derived in the case of a constant-intensity hyetograph to assess the maximum runoff peak with respect to a given rainfall event structure irrespective of the specific catchment (such as the return period associated with the reference rainfall event). Looking at the results, the curve of the maximum values of the runoff peak reveals a local minimum point corresponding to the design hyetograph derived according to the statistical DDF curve. A specific catchment application is discussed in order to point out the dimensionless procedure implications and to provide some numerical examples of the rainfall structures with respect to observed rainfall events; finally their effects on the hydrograph peak are examined.