1,721,754 research outputs found
Monitoring Rainfall Erosivity in the Sparacia Experimental Area by an Optical Disdrometer
No full textThe kinetic power of rainfall plays a fundamental role in soil erosion processes. Kinetic power can be determined by knowing both drop size distribution (DSD) and drop falling velocity. This paper reports the results obtained by the DSDs detected by an optical disdrometer installed in two Sicilian sites. In particular, the disdrometer was installed at Palermo in the period June 2006 – May 2014 and at Sparacia experimental station in the period March 2017 – December 2019. The DSDs, that are detected using a sampling time equal to 1 min, after aggregation by rainfall intensity classes, are presented highlighting the differences on DSDs characteristics for the two experimental sites. The rainfall kinetic power was calculated by combining DSDs and the falling velocity obtained by the relationship suggested by Ferro (Ferro, V.: Tecniche di misura e monitoraggio dei processi erosivi. Quaderni di Idronomia Montana (21/2), 63–128 (2001).). The reliability of the empirical relationships estimating kinetic power by only rainfall intensity proposed by Wischmeier and Smith (Wischmeier, W.H., Smith, D.D.: Predicting Rainfall Erosion Losses-A guide to conservation planning. Agriculture Handbook: United States Department of Agricolture, Washingtin, DC; 537 (1978).) and Brown and Foster (Brown, L.C., Foster, G.R.: Storm erosivity using idealized intensity distribution. Trans. ASAE 30, 379–386 (1987). https://doi.org/10.13031/2013.31957 ), is firstly verified. Furthermore, the relationship theoretically deduced by Carollo et al. (Carollo, F.G., Ferro, V., Serio, M.A.: Reliability of rainfall kinetic power- intensity relationships. Hydrol. Process 31, 1293–1300 (2016). https://doi.org/10.1002/hyp.11099 ), which allows to estimate the kinetic power by rainfall intensity and a characteristic diameter (median volume diameter), is tested. Finally, the comparison between the relation kinetic power – intensity detected in the two sites is presented
Opere di sistemazione idraulico-forestale
No full textIl volume illustra, nella visione unitaria del sistema “bacino idrografico”, i processi fisici, le problematiche applicative e le tipologie di intervento disponibili per la sistemazione del reticolo fluviale e dei versanti. Il trasporto solido delle correnti a pelo libero viene introdotto con l’intento di esaminare i processi evolutivi del cavo fluviale, di fornire indicazioni per la progettazione delle opere di correzione ed inalveazione del tracciato del corso d’acqua e di stabilire l’influenza dell’inserimento di manufatti sul delicato equilibrio del sistema fluviale. La trattazione, seguendo il percorso della corrente dalle propaggini più montane fino allo sbocco a mare, esamina opere convenzionali (briglie, pennelli, inalveazioni, etc.) e non (briglie aperte, rampe di massi, rivestimenti in gabbioni, etc.), e mette in relazione la produzione di sedimenti dei versanti con il trasporto solido fluviale. Un capitolo è dedicato, infine, alle opere di sistemazione idraulico-forestale realizzate con tecniche di ingegneria naturalistica
ADV measurements of velocity distributions in a gravel-bed flume
No full textVelocity measurements carried out by an acoustic doppler velocimeter (ADV) in a rectangular laboratory flume having a gravel bed are presented. The velocity profiles are measured in six verticals of the channel cross-section having an increasing distance (from 4 to 38.5 cm) from the flume wall. The experimental runs are carried out for five different bed arrangements, characterized by different concentrations of coarser elements, and for the two conditions of small- and large-scale roughness. For both hydraulic conditions, the velocity measurements are first used to test the applicability of the Dean profile and of the logarithmic profile corrected by a divergence function proposed in this paper. Then, for each value of the depth sediment ratio h/d84, the non-dimensional friction factor parameter is calculated by integration of the measured velocity distributions in the different verticals of the cross-section. Finally a semi-logarithmic flow resistance equation is empirically deduced. © 2003 John Wiley and Sons, Ltd
Flow resistance in gravel-bed channels with large-scale roughness
No full textA previously published mixing length (ML) model for evaluating the Darcy-Weisbach friction factor for a large-scale roughness condition (depth to sediment height ratio ranging from 1 to 4) is briefly reviewed and modified (MML). Then the MML model and a modified drag (MD) model are experimentally tested using laboratory measurements carried out for gravel-bed channels and large-scale roughness condition. This analysis showed that the MML gives accurate estimates of the Darcy-Weisbach coefficient and for Froude number values greater than 0·5 the MML model coincides with the ML one. Testing of the MD model shows limited accuracy in estimating flow resistance. Finally, the MML and MD models are compared with the performance of a quasi-theoretical (QT) model deduced applying the II-theorem of the dimensional analysis and the incomplete self-similarity condition for the depth/sediment ratio and the Froude number. Using the experimental gravel-bed data to calibrate the QT model, a constant value of the exponent of the Froude number is determined while two relationships are proposed for estimating the scale factor and the exponent of the depth/sediment ratio. This indirect estimate procedure of the coefficients (ba- b1 and b2) of the QT model can produce a negligible overestimation or underestimation of the friction factor. © 2003 John Wiley and Sons, Ltd
Comments on “Mean velocity and turbulent characteristics of flow over half-cycle cosine sharp-crested weirs” by Salehi S., Esmaili K., Azimi A.H
No full textIn this paper the stage-discharge equation of a half-cycle cosine weir is theoretically deduced applying the Π-Theorem of dimensional analysis and the self-similarity theory. The coefficients of the new stage-discharge relationships are estimated using the results of the experimental runs by Salehi et al
Assessing flow resistance law in vegetated channels by dimensional analysis and self-similarity
No full textIn this paper experimental data collected by Kouwen et al., Wilson and Horrit, Raffaelli et al. and Carollo et al., using straight flumes having a bed covered by grass-like vegetation with different stem concentrations, were used to analyze flow resistance for flexible submerged elements. At first, the dimensional analysis and the incomplete self-similarity hypothesis was applied to deduce the flow velocity distribution and the resulting theoretical expression of the Darcy-Weisbach friction factor. Then, a relationship between the Γ function of the velocity profile and the biomechanical characteristics of vegetation, the channel slope, the Reynolds number and the flow Froude number was empirically deduced by the available measurements. This relationship was established distinguishing between the low stem concentration values and the highest values for which a quasi-smooth skimming flow occurs. Finally, the analysis showed that, in comparison with previous results, a more accurate Darcy-Weisbach friction factor estimate can be obtained by the theoretical approach based on a power-velocity profile
Evaluating overland flow sediment transport capacity
No full textAn equation for evaluating the sediment transport capacity of overland flow is a necessary part of a physically based soil erosion model describing sediment detachment and transport as distributed processes. At first, for the hydraulic conditions of small-scale and large-scale roughness, the sediment transport capacity relationship used in the WEPP model is calibrated by Yalin and Govers' equation. The analysis shows that the transport coefficient Kt depends on the Shields parameter, Y, according to a semi-logarithmic (Yalin) or a linear (Govers) equation. The reliability of the semi-logarithmic equation is verified by Smart's, and Aziz and Scott's experimental data. Then the Low's formula, whose applicability is also proved by Smart's, and Aziz and Scott's data, is transformed as a stream power equation in which a stream power coefficient, KSP, depending on Shields parameter, slope, sediment and water-specific weight, appears. A relationship between transport capacity and effective stream power is also proposed. Finally, the influence of rainfall on sediment transport capacity and the prediction of critical shear stress corresponding to overland flow are examined
Discussion of “simple flume for flow measurement in open channel ’’ by Zohrab Samani and Henry Magallanez
No full textThis paper is a Discussion of “simple flume for flow measurement in open channel"
Intermediate-duration-rainfall intensity equations. Discussion by Vito Ferro
No full textRainfall depth-duration relationships are presented
Is rainfall momentum the best index for estimating rainfall erosivity?
No full textThis paper shows the results of an experimental investigation carried out by the drop size distributions (DSD) measured in the period June 2006- April 2014 using an optical disdrometer installed at the Department of Agricultural, Food and Forest Sciences of University of Palermo and in the period July 2015-May 2016 at El Teularet experimental station in Spain. At first the DSDs are aggregated into intensity classes and then measured momentum values are determined by coupling at each raindrop of the aggregated DSD the corresponding terminal velocity, calculated by a relationship available in literature. For a fixed rainfall intensity the measurements show that both DSD and rainfall momentum measured at the two experimental sites are not coincident. However both datasets present a threshold value of rainfall intensity over which the rainfall momentum becomes quasi constant. Using the raindrop size distribution proposed by Marshall and Palmer a theoretical relationship is deduced, according to which the ratio between the rainfall momentum and rainfall intensity depends only on the median volume diameter of the distribution. The available measurements detected in different climatic contests by different measurement techniques allow to conclude that: (i) this theoretically deduced relationship allows reliable rainfall momentum estimates; (ii) the rainfall momentum is strictly correlated to the kinetic power of the precipitation
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