Gustavo Marini

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.

Experimental Assessment of a 2-D Entropy-Based Model for Velocity Distribution in Open Channel Flow

Velocity distribution in an open channel flow can be very useful to model many hydraulic phenomena. Among the others, several 1D models based on the concept of entropy are available in the literature, which allow estimating the velocity distribution by measuring velocities only in a few points. Nevertheless, since 1D models have often a limited practical use, a 2D entropy based model was recently developed. The model provides a reliable estimation of the velocity distribution for open channel flow with a rectangular cross section, if the maximum velocity and the average velocity are known. In this paper results from the proposed model were compared with measured velocities carried out from laboratory experiments. Calculated values were also compared with results inferred from a 2D model available in the literature, resulting in a greater ease of use and a more reliable estimate of the velocity profile.

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.

Derivation of 2D Power-Law Velocity Distribution Using Entropy Theory

The one-dimensional (1D) power law velocity distribution, commonly used for computing velocities in open channel flow, has been derived empirically. However, a multitude of problems, such as scour around bridge piers, cutoffs and diversions, pollutant dispersion, and so on, require the velocity distribution in two dimensions. This paper employs the Shannon entropy theory for deriving the power law velocity distribution in two-dimensions (2D). The development encompasses the rectangular domain, but can be extended to any arbitrary domain, including a trapezoidal domain. The derived methodology requires only a few parameters and the good agreement is confirmed by comparing the velocity values calculated using the proposed methodology with values derived from both the 1D power law model and a logarithmic velocity distribution available in the literature.

Real Time Control of a Prototype for Pressure Regulation and Energy Production in Water Distribution Networks

AbstractIn recent years, the opportunity of coupling a pressure management strategy with power generation in water distribution networks (WDNs) has attracted increasing interest. Numerical simulations developed for a number of real cases showed attractive profits and capital payback periods. Although many micro- and pico-hydro plants currently are operating along supply water mains, installations in WDNs are quite uncommon because of the high variability of flow and pressure patterns. Aiming at robust and effective industrial-based solutions, a laboratory prototype was developed for hydropower generation in WDNs. A pump as turbine (PAT) was used for generation, although a traditional turbine could be used as well. A control strategy was developed and implemented for automatic setting of regulating valves, aimed at both ensuring adequate pressure over the network and maximizing electric power. Experiments showed that the valves, equipped with the automatic control system previously described, can automatic...

Real-Time Control of a PRV in Water Distribution Networks for Pressure Regulation: Theoretical Framework and Laboratory Experiments

AbstractPressure-reducing valves (PRVs) are often used in water distribution networks (WDNs) to regulate pressure for leakage reduction. Optimal management would require the pressure to be constant...

Performance of vertical-axis pumps as turbines

ABSTRACT Hydropower generation in water distribution networks (WDNs) is an attractive topic in the field of management of water systems. Pumps as turbines (PATs) allow coupling pressure control with power generation. Although PATs have several advantages over traditional turbines, theoretical and experimental studies are still required to overcome the reduced knowledge about their performances, especially for vertical-axis pumps. To this end, laboratory experiments on three vertical pumps running in reverse, with different number of stages and motor efficiency classes, were carried out and discussed. Results were compared with theoretical models available in the literature for horizontal PATs, with maximum errors around 20% and 30% for head and power curve, respectively. Analytical relationships for vertical PATs were proposed for better agreement. The dependence of performances by the number of stages and the motor efficiency class was also discussed.

Derivation of 2D Velocity Distribution in Watercourses Using Entropy

AbstractExisting entropy-based methodologies for deriving two-dimensional (2D) velocity distributions in open-channel flow are based on the extension of one-dimensional (1D) formulations. Such exte...