Energy head dissipation and flow pressures in vortex drop shafts

Vortex drop shafts are special manholes designed to link sewer channels at different elevations. Significant energy head dissipation occurs across these structures, mainly due to vertical shaft wall friction and turbulence in the dissipation chamber at the toe of the shaft. In the present study two aspects, sometimes neglected in the standard hydraulic design, are considered, namely the energy head dissipation efficiency and the maximum pressure force in the dissipation chamber. Different physical model results derived from the pertinent literature are analyzed. It is demonstrated that the energy head dissipation efficiency is mostly related to the flow impact and turbulence occurring in the chamber. Similarly to the drop manholes, a relation derived from a simple theoretical model is proposed for the estimation of the energy head loss coefficient. The analysis of the pressures measured on the chamber bottom allows to provide a useful equation to estimate the pressure peak in the chamber as a function of the approach flow energy head

Energy dissipation in sewer fall manholes

In the present literature review paper several experimental investigations on physical and numerical models of drop manholes and vortex drop shafts were considered. The examination of the experimental data led to the definition of a simple empirical equation, initially suggested for one type of drop manhole, to estimate the total head loss coefficient for both drop manholes and vortex drop shafts. The energy efficiency values, as detected by the corresponding physical and numerical tests, of all the drop structure models were also compared. The energy efficiency of vortex drop shafts is larger than in drop manholes, and it reaches easily the 90%. Drop manholes are, instead, characterized by a smaller energy efficiency, which was shown to increase as the drop height augments

The composite dataset of the present-day Infralittoral Prograding Wedges (IPWs) in the inner continental shelf of the Campania region (Central-Eastern Tyrrhenian Sea)

This article reports on the dataset gathered following the census of 83 present-day Infralittoral Prograding Wedges (IPWs), surveyed on the inner continental shelf of the Central-Eastern Tyrrhenian Sea. The purpose of the census was to explore their bathymetric range and assess the observational laws governing this variability. The ensued dataset (Campania Region IPW Dataset, CRID) includes geographic, topographic and morpho-bathymetric indices, descriptive of each IPW and more, the exposure of each IPW to wave forcing (Geographical fetch, Effective fetch and extreme significant wave height, HS). In this work, histograms contribute to describe all the variables and highlight the dominant features of each IPW. Location maps univocally links the geographic position of each IPW to the appropriate attribute record in the dataset. Further, thematic maps illustrate eight wave fields obtained by offshore-to-nearshore transformation by as many sea states scenarios with 200-year return period. Such wave fields are used as sources for significant wave height representing wave conditions over each IPW. This dataset could be implemented with new measures at a broader scale, by following analogue procedures for measurements, to enlarge the observational scale on IPWs and improve the numerical models which might eventually derive by the analysis of this dataset

Lifecycle Environmental Impact Assessment of an Overtopping Wave Energy Converter Embedded in Breakwater Systems

Overtopping breakwater systems are among the most promising technologies for exploiting wave energy to generate electricity. They consist in water reservoirs, embedded in piers, placed on top of ramps, higher than sea-level. Pushed by wave energy, seawater fills up the reservoirs and produces electricity by flowing back down through low headhydro turbines. Different overtopping breakwater systems have been tested worldwide in recent years. This study focuses on the Overtopping BReakwater for Energy Conversion (OBREC) system that has been implemented and tested in the harbor of Naples (Italy). The Life Cycle Assessment of a single replicable module of OBREC has been performed for analyzing potential environmental impacts, in terms of Greenhouse Gas Emissions, considering construction, installation, maintenance, and the operational phases. The Carbon Footprint (i.e., mass of CO2eq) to build wave energy converters integrated in breakwater systems has been estimated, more specifically the “environmental investment” (i.e., the share of Carbon Footprint due to the integration of wave energy converter) needed to generate renewable electricity has been assessed. The Carbon Intensity of Electricity (i.e., the ratio between the CO2eq emitted and the electricity produced) has been then assessed in order to demonstrate the profitability and the opportunity to foster innovation in the field of blue energy. Considering the impact for implementing an operational OBREC module (Carbon Footprint = 1.08 t CO2eq; Environmental Investment = 0.48 t CO2eq) and the electricity production (12.6 MWh/year per module), environmental benefits (avoided emissions) would compensate environmental costs (i.e., Carbon Footprint; Environmental Investment) those provided within a range of 25 and 13 months respectively