Giuseppe De Martino

Variability and Trend in Seasonal Precipitation in the Continental United States

AbstractUsing 92-year precipitation data from 400 rain gauge stations located in 48 states throughout the continental United States, the change in precipitation in space and time was investigated. The variability in precipitation was investigated using an entropy-based approach. The Mann-Kendall, Spearman’s rho, and Sen slope tests were applied to assess the existence of a trend in precipitation. Analysis showed that annual precipitation exhibited lower temporal variability than did its constituent seasonal series. The fall precipitation had the highest variability, and the spring precipitation the lowest. Not many stations exhibited trends, and they are concentrated in limited areas of the United States. The greatest part of those exhibiting statistically significant trends showed increasing trends both in precipitation and rainy days. Only in a few cases negative trends were found. Finally, analysis showed that no relationship can be established between trend and variability in precipitation.

Entropy approach for 2D velocity distribution in open-channel flow

In this paper, considering time-averaged velocity as a random variable, two-dimensional (2D) velocity distributions in open-channel flow have been derived based on the Shannon entropy concept and the principle of maximum entropy. The velocity distributions so derived have limited practical use, since they contain too many parameters that need to be experimentally calibrated and hence are not convenient to apply. This work develops a new entropy-based approach for deriving a 2D velocity distribution in open-channel flow, thereby investigating a rectangular geometric domain. The derived distribution is parsimonious, and the values determined using the proposed distribution are found to be in good agreement with the experimentally-measured velocity values.

Pollution Reduction in Receivers: Storm-Water Tanks

Urban runoff discharges in receiving water are a significant source of pollution. Storm-water tanks are one of the most effective facilities used for reducing the impact of first-flush pollution. Nevertheless, because the system performance depends on many parameters, design criteria for storm-water tanks are not completely consolidated in the literature. To assess the influence of the rainfall regime on the system performance, extensive numerical simulations from 45 rain gauges in Campania, Italy, were calculated. A typical Italian urban catchment was considered in simulations. Hydrographs and pollutographs were generated to analyze the operation of different sewer and tank configurations. All simulations showed a negligible influence of the rainfall regime on the phenomenon, thus suggesting a simplified approach to estimate the average pollution reduction by using storm-water tanks. The analysis shows good agreement between the values estimated from the proposed approach and the results provided by continuous simulations.

Experimental assessment of level pool routing in preliminary design of floodplain storage

Among control structures in flood management, floodplain storage represents one of the most effective measures, since it holds part of flood volume in a delimited area thus reducing the peak discharge. Sizing of floodplain storage, both on-stream and off-stream, is complex and several methodologies for preliminary design are available in literature, almost all assuming level pool reservoir routing, i.e. the water level in the floodplain is horizontal during the storage filling. Few studies examine the accuracy of that assumption. The present paper work reports an extensive experimental investigation to assess the reliability of level pool routing in the design of on-stream floodplain storages. The good agreement between numerical and experimental values during the filling phase confirmed the reliability of the hypothesis in the preliminary sizing of on-stream floodplain storage. In contrast, even significant differences can be shown during the floodplain draining, due to vegetation and bottom irregularities.

Simplified Approach for the Optimal Sizing of Throttled Air Chambers

AbstractAmong water hammer damping devices, air chambers are often used in pumping plants to reduce pressure surges to acceptable values. The chamber is more effective if a throttling device is used, resulting in a reduction of the required volume. Design charts for a simple and fast sizing of air volume and orifice diameter are available in the literature using the rigid column theory (incompressible flow) and the De Sparre rule. Nevertheless, in many cases the pressure pattern is far from being constant during the first quarter of the transient period and lower pressures can be attained; furthermore, the rigid column model is not able to reproduce elastic phenomena arising from throttling, and so water hammer equations should be used instead. Although orifice induced pressure waves are evident only in the first part of the transient, differences between air chamber pressure and pipe pressure can be quite significant. Negative pressure surge should be limited because column separation and cavitation coul...