Steady analysis of transcritical flows in collapsible tubes with discontinuous mechanical properties: implications for arteries and veins

We study the conditions under which discontinuous mechanical properties of a collapsible tube can induce transcritical flows, i.e. the transition through the critical state where the speed index (analogous to the Mach or the Froude numbers for compressible and free surface flows, respectively) is one. Such a critical transition may strongly modify the flow properties, cause a significant reduction in the cross-sectional area of the tube, and limit the flow. General relationships are obtained for a short segment using a one-dimensional model under steady flow conditions. Marginal curves delimiting the transcritical regions are identified in terms of the speed index and the cross-sectional area ratio. Since there are many examples of such flows in physiology and medicine, we also analyse the specific case of prosthesis (graft or stent) implantation in blood vessels. We then compute transcritical conditions for the case of stiffness and reference area variations, considering a collapsible tube characterized by physiological parameters representative of both arteries and veins. The results suggest that variations in mechanical properties may induce transcritical flow in veins but is unrealistic in arterie

Multiple states for flow through a collapsible tube with discontinuities

We study the occurrence of the multiple steady states that flows in a collapsible tube can develop under the effect of: (i)geometrical alterations (e.g.stenosis), (ii)variations of the mechanical properties of the tube wall, or (iii)variations of the external pressure acting on the conduit. Specifically, if the approaching flow is supercritical, two steady flow states are possible in a restricted region of the parameter space: one of these flow states is wholly supercritical while the other produces an elastic jump that is located upstream of the variation. In the latter case the flow undergoes a transition through critical conditions in the modified segment of the conduit. Both states being possible, the actual state is determined by the past history of the system, and the parameter values show a hysteretic behaviour when shifting from one state to the other. First we set up the problem in a theoretical framework assuming stationary conditions, and then we analyse the dynamics numerically in a one-dimensional framework. Theoretical considerations suggest that the existence of multiple states is associated with non-uniqueness of the steady-state solution, which is confirmed by numerical simulations of the fully unsteady proble

Il Museo dell’Osservatorio Vesuviano: dati statistici 2005

Il museo dell'Osservatorio Vesuviano, rinnovato nel 2000, nasce con l’obiettivo di informare la popolazione sui fenomeni vulcanici, sui pericoli connessi e sulla sorveglianza dei vulcani attivi in aree ad alto rischio; è situato nella sede storica dell’Osservatorio Vesuviano, il primo Osservatorio vulcanologico del mondo, attualmente sezione dell’Istituto Nazionale di Geofisica e Vulcanologia. Il percorso museale ha inizio con la presentazione delle diverse tipologie eruttive e dei fenomeni a esse associati e quindi dei pericoli per l’uomo e i manufatti. Si ripercorre la storia eruttiva del Somma-Vesuvio soffermandosi sulle eruzioni più note del 79 d.C. e del 1944, e sulle metodologie adottate dai vulcanologi per ricostruire la storia eruttiva di un vulcano attraverso lo studio dei suoi prodotti. Inoltre, sono esposti i prodotti delle eruzioni effusive ed esplosive, e i minerali che si formano in ambiente vulcanico. Il percorso è arricchito da documenti storici di notevole interesse vulcanologico quali: la carta vulcanologica di Henry James Johnston-Lavis e il volume “Campi Flegrei” di William Hamilton (in visione la riproduzione anastatica). Un altro tema portante della mostra riguarda il monitoraggio dei vulcani attivi. Sono esposti gli strumenti scientifici storici utilizzati per la sorveglianza, tra cui il primo sismografo del mondo costruito nel 1856 da Luigi Palmieri, direttore dell’Osservatorio Vesuviano dal 1855 al 1896. Una sala ospita monitor collegati in tempo reale alla sezione “segnali sismici” del sito web dell’Osservatorio Vesuviano. Si propongono inoltre filmati tratti da modelli fisico-matematici di simulazioni di eruzioni esplosive per la definizione degli scenari attesi in caso di eruzione. Infine, si affronta il problema del rischio mediante pannelli informativi sul piano Nazionale di emergenza al fine di promuovere atteggiamenti adeguati in caso di necessità. Gli strumenti utilizzati sono video, pannelli, webcam, internet. Nel rapporto sono presentati i dati statistici relativi al pubblico del museo nell’anno 2005

Assessment of “Carbopeaking” in a hydropeaking-impacted river in the Italian Alpine area

Hydropeaking (i.e., rapid and frequent artificial flow fluctuations caused by reservoir-operated hydropower production) is a much-investigated river stressor, and has been associated, among others, to sudden changes in temperature (“thermopeaking”), underwater soundscape (“soundpeaking”), total dissolved gas saturation (“saturopeaking”). We have recently started investigating the “carbopeaking”, i.e., variations of greenhouse gas (mainly CO2) concentrations and evasion fluxes through the water-air interface associated with hydropeaks. Here we report on the methodology and preliminary results from a field-measurement campaign conducted in a single-thread Alpine river (River Noce, Italy) during multiple hydropeaking events. The analysis of water samples collected in the upstream reservoir showed CO2 oversaturation in the hypolimnion, around the depth of the hydropower intake system. In the Noce reach upstream of the hydropower plant outlet (i.e., in a residual flow stretch), the CO2 concentrations displayed diel fluctuations around the atmospheric equilibrium concentration, likely driven by diurnal primary production. Conversely, water released at the hydropower outlet during hydropeaking were consistently oversaturated in CO2 relative to the atmosphere, in agreement with the concentrations in the reservoir’s hypolimnetic water. As a result, hydropeaking events were associated with an alteration of the sub-daily patterns of CO2 concentration downstream of the hydropower outlet which, combined with higher gas exchange velocities occurring during higher flow rates, can cause periods of enhanced CO2 emissions. The results highlight the potential impact of hydropeaking on greenhouse gas emissions, demonstrating the need to account for sub-daily variations of flow and gas concentration to accurately quantify carbon balances in rivers impacted by hydropower

An ecosystem service approach to license new run of the river hydropower plants

Freshwater ecosystems provide several services (ES) to society. Hydropower production is one of the most relevant ES supported by Alpine rivers, and it is often in conflict with other river uses and services. Recently, the demand by local authorities, public or private agencies for new small hydropower plants have been increasing, and new conflicts have been arousing. We propose an approach to model the alterations of selected ES which integrates hydrological and habitat models and evaluates possible variations of the selected ES under different withdrawal scenarios. The case-study is the Noce River, a gravel-bed river in the Italian Alps (Trentino, North East Italy) which is subject to hydropeaking. We selected four ES: habitat for juvenile and adult marble trout as biodiversity proxy, rafting as recreational services, and small hydropower production as provisioning service. We evaluated the variations of these services for maximum and no hydropower production, chosen as different boundary conditions. Moreover, we simulated the presence of four new different small hydropower plants with increasing withdrawals. Large hydropower is the key driver, affecting all the selected ES. Small hydropower decreases the potential for rafting up to 64%, while it is often negligible for other services

Can the discharge of a hyperconcentrated flow be estimated from paleoflood evidence?

Many flood events involving water and sediments have been characterized using classic hydraulics principles, assuming the existence of critical flow and many other simplifications. In this paper, hyperconcentrated flow discharge was evaluated by using paleoflood reconstructions (based on paleostage indicators [PSI]) combined with a detailed hydraulic analysis of the critical flow assumption. The exact location where this condition occurred was established by iteratively determining the corresponding cross section, so that specific energy is at a minimum. In addition, all of the factors and parameters involved in the process were assessed, especially those related to the momentum equation, existing shear stresses in the wetted perimeter, and nonhydrostatic and hydrostatic pressure distributions. The superelevation of the hyperconcentrated flow, due to the flow elevation curvature, was also estimated and calibrated with the PSI. The estimated peak discharge was established once the iterative process was unable to improve the fit between the simulated depth and the depth observed from the PSI. The methodological approach proposed here can be applied to other higher-gradient mountainous torrents with a similar geomorphic configuration to the one studied in this paper. Likewise, results have been derived with fewer uncertainties than those obtained from standard hydraulic approaches, whose simplifying assumptions have not been considered. © 2011 by the American Geophysical Union.This work was funded by the Spanish Ministry of Science and Innovation within the framework of the CICYT Dendro-Avenidas project (CGL2007-62063) and the MAS Dendro-Avenidas project (CGL2010-19274). We are especially grateful to Robert D. Jarrett, Vern Manville, and one anonymous reviewer for their comments and helpful suggestions on previous versions of this manuscript.Bodoque, J.; Eguibar Galán, MÁ.; Diez-Herrero, A.; Gutierrez-Perez, I.; Ruiz-Villanueva, V. (2011). Can the discharge of a hyperconcentrated flow be estimated from paleoflood evidence?. Water Resources Research. 47(W12535). doi:10.1029/2011WR010380S47W12535Alcoverro, J., Corominas, J., & Gómez, M. (1999). The Barranco de Arás flood of 7 August 1996 (Biescas, Central Pyrenees, Spain). Engineering Geology, 51(4), 237-255. doi:10.1016/s0013-7952(98)00076-3Alexandrov, Y., Laronne, J. B., & Reid, I. (2007). Intra-event and inter-seasonal behaviour of suspended sediment in flash floods of the semi-arid northern Negev, Israel. Geomorphology, 85(1-2), 85-97. doi:10.1016/j.geomorph.2006.03.013BAAS, J. H., & BEST, J. L. (2008). The dynamics of turbulent, transitional and laminar clay-laden flow over a fixed current ripple. Sedimentology, 55(3), 635-666. doi:10.1111/j.1365-3091.2007.00916.xBallesteros, J. A., Bodoque, J. M., Díez-Herrero, A., Sanchez-Silva, M., & Stoffel, M. (2011). Calibration of floodplain roughness and estimation of flood discharge based on tree-ring evidence and hydraulic modelling. Journal of Hydrology, 403(1-2), 103-115. doi:10.1016/j.jhydrol.2011.03.045Bathurst, J. C. (1985). Flow Resistance Estimation in Mountain Rivers. Journal of Hydraulic Engineering, 111(4), 625-643. doi:10.1061/(asce)0733-9429(1985)111:4(625)BERZI, D., & JENKINS, J. T. (2008). A theoretical analysis of free-surface flows of saturated granular–liquid mixtures. Journal of Fluid Mechanics, 608, 393-410. doi:10.1017/s0022112008002401Biron, P. M., Lane, S. N., Roy, A. G., Bradbrook, K. F., & Richards, K. S. (1998). Sensitivity of bed shear stress estimated from vertical velocity profiles: the problem of sampling resolution. Earth Surface Processes and Landforms, 23(2), 133-139. doi:10.1002/(sici)1096-9837(199802)23:23.0.co;2-nBisantino, T., Fischer, P., & Gentile, F. (2009). Rheological characteristics of debris-flow material in South-Gargano watersheds. Natural Hazards, 54(2), 209-223. doi:10.1007/s11069-009-9462-4Bousmar, D., & Zech, Y. (1999). Momentum Transfer for Practical Flow Computation in Compound Channels. Journal of Hydraulic Engineering, 125(7), 696-706. doi:10.1061/(asce)0733-9429(1999)125:7(696)Costa, J. E. (1984). Physical Geomorphology of Debris Flows. Developments and Applications of Geomorphology, 268-317. doi:10.1007/978-3-642-69759-3_9COUSSOT, P., & MEUNIER, M. (1996). Recognition, classification and mechanical description of debris flows. Earth-Science Reviews, 40(3-4), 209-227. doi:10.1016/0012-8252(95)00065-8Coussot, P., Laigle, D., Arattano, M., Deganutti, A., & Marchi, L. (1998). Direct Determination of Rheological Characteristics of Debris Flow. Journal of Hydraulic Engineering, 124(8), 865-868. doi:10.1061/(asce)0733-9429(1998)124:8(865)Desilets, S. L. E., Ferré, T. P. A., & Ekwurzel, B. (2008). Flash flood dynamics and composition in a semiarid mountain watershed. Water Resources Research, 44(12). doi:10.1029/2007wr006159Dietrich, W. E., & Whiting, P. (1989). Boundary shear stress and sediment transport in river meanders of sand and gravel. River Meandering, 1-50. doi:10.1029/wm012p0001Ervine, D. A., Willetts, B. B., Sellin, R. H. J., & Lorena, M. (1993). Factors Affecting Conveyance in Meandering Compound Flows. Journal of Hydraulic Engineering, 119(12), 1383-1399. doi:10.1061/(asce)0733-9429(1993)119:12(1383)Gaume, E., Livet, M., Desbordes, M., & Villeneuve, J.-P. (2004). Hydrological analysis of the river Aude, France, flash flood on 12 and 13 November 1999. Journal of Hydrology, 286(1-4), 135-154. doi:10.1016/j.jhydrol.2003.09.015Grant, G. E. (1997). Critical flow constrains flow hydraulics in mobile-bed streams: A new hypothesis. Water Resources Research, 33(2), 349-358. doi:10.1029/96wr03134Hessel, R. (2006). Consequences of hyperconcentrated flow for process-based soil erosion modelling on the Chinese Loess Plateau. Earth Surface Processes and Landforms, 31(9), 1100-1114. doi:10.1002/esp.1307House, P. K., & Baker, V. R. (2001). Paleohydrology of flash floods in small desert watersheds in western Arizona. Water Resources Research, 37(6), 1825-1839. doi:10.1029/2000wr900408House, P. K., & Pearthree, P. A. (1995). A geomorphologic and hydrologic evaluation of an extraordinary flood discharge estimate: Bronco Creek, Arizona. Water Resources Research, 31(12), 3059-3073. doi:10.1029/95wr02428Hungr, O. (s. f.). Classification and terminology. Springer Praxis Books, 9-23. doi:10.1007/3-540-27129-5_2Iverson, R. M. (1997). The physics of debris flows. Reviews of Geophysics, 35(3), 245-296. doi:10.1029/97rg00426Iverson , R. M. 2003 The debris-flow rheology myth, paper presented at debris-flow hazards mitigation: mechanics, prediction, and assessment 303 314 Millpress Rotterdam, Davos, SwitzerlandIverson, R. M., Logan, M., LaHusen, R. G., & Berti, M. (2010). The perfect debris flow? Aggregated results from 28 large-scale experiments. Journal of Geophysical Research, 115(F3). doi:10.1029/2009jf001514Jarrett, R. D. (1987). Closure to « Hydraulics of High‐Gradient Streams » by Robert D. Jarrett (November, 1984). Journal of Hydraulic Engineering, 113(7), 927-929. doi:10.1061/(asce)0733-9429(1987)113:7(927)Jarrett, R. D., & Tomlinson, E. M. (2000). Regional interdisciplinary paleoflood approach to assess extreme flood potential. Water Resources Research, 36(10), 2957-2984. doi:10.1029/2000wr900098Lavigne, F., & Suwa, H. (2004). Contrasts between debris flows, hyperconcentrated flows and stream flows at a channel of Mount Semeru, East Java, Indonesia. Geomorphology, 61(1-2), 41-58. doi:10.1016/j.geomorph.2003.11.005McCoy, S. W., Kean, J. W., Coe, J. A., Staley, D. M., Wasklewicz, T. A., & Tucker, G. E. (2010). Evolution of a natural debris flow: In situ measurements of flow dynamics, video imagery, and terrestrial laser scanning. Geology, 38(8), 735-738. doi:10.1130/g30928.1Pierson , T. C. 2005 Distinguishing between debris flows and floods from field evidence Small Watersheds U.S. Geological Survey 2004 3142Pierson, T. C. (s. f.). Hyperconcentrated flow — transitional process between water flow and debris flow. Springer Praxis Books, 159-202. doi:10.1007/3-540-27129-5_8Pierson, T. C., & Costa, J. E. (1987). A rheologic classification of subaerial sediment-water flows. Reviews in Engineering Geology, 1-12. doi:10.1130/reg7-p1Pierson, T. C., & Scott, K. M. (1985). Downstream Dilution of a Lahar: Transition From Debris Flow to Hyperconcentrated Streamflow. Water Resources Research, 21(10), 1511-1524. doi:10.1029/wr021i010p01511Rico, M., Benito, G., & Barnolas, A. (2001). Combined palaeoflood and rainfall–runoff assessment of mountain floods (Spanish Pyrenees). Journal of Hydrology, 245(1-4), 59-72. doi:10.1016/s0022-1694(01)00339-0Roca, M., Martín-Vide, J. P., & Moreta, P. J. M. (2009). Modelling a torrential event in a river confluence. Journal of Hydrology, 364(3-4), 207-215. doi:10.1016/j.jhydrol.2008.10.020Ruiz-Villanueva, V., Bodoque, J. M., Díez-Herrero, A., & Calvo, C. (2011). Triggering threshold precipitation and soil hydrological characteristics of shallow landslides in granitic landscapes. Geomorphology, 133(3-4), 178-189. doi:10.1016/j.geomorph.2011.05.018Shiono, K., & Knight, D. W. (1991). Turbulent open-channel flows with variable depth across the channel. Journal of Fluid Mechanics, 222(-1), 617. doi:10.1017/s0022112091001246Shu, A., & Fei, X. (2008). Sediment transport capacity of hyperconcentrated flow. Science in China Series G: Physics, Mechanics and Astronomy, 51(8), 961-975. doi:10.1007/s11433-008-0108-4Siviglia, A., & Cantelli, A. (2005). Effect of bottom curvature on mudflow dynamics: Theory and experiments. Water Resources Research, 41(11). doi:10.1029/2005wr004475Sleiti, A. K., & Kapat, J. S. (2008). Effect of Coriolis and centrifugal forces on turbulence and transport at high rotation and density ratios in a rib-roughened channel. International Journal of Thermal Sciences, 47(5), 609-619. doi:10.1016/j.ijthermalsci.2007.06.008SMITH, G. A. (1986). Coarse-grained nonmarine volcaniclastic sediment: Terminology and depositional process. Geological Society of America Bulletin, 97(1), 1. doi:10.1130/0016-7606(1986)972.0.co;2Sohn, Y. K., Rhee, C. W., & Kim, B. C. (1999). Debris Flow and Hyperconcentrated Flood‐Flow Deposits in an Alluvial Fan, Northwestern Part of the Cretaceous Yongdong Basin, Central Korea. The Journal of Geology, 107(1), 111-132. doi:10.1086/314334Sosio, R., & Crosta, G. B. (2009). Rheology of concentrated granular suspensions and possible implications for debris flow modeling. Water Resources Research, 45(3). doi:10.1029/2008wr006920Svendsen, J., Stollhofen, H., Krapf, C. B. ., & Stanistreet, I. G. (2003). Mass and hyperconcentrated flow deposits record dune damming and catastrophic breakthrough of ephemeral rivers, Skeleton Coast Erg, Namibia. Sedimentary Geology, 160(1-3), 7-31. doi:10.1016/s0037-0738(02)00334-2Tinkler, K. J. (1997). Critical flow in rockbed streams with estimated values for Manning’s n. Geomorphology, 20(1-2), 147-164. doi:10.1016/s0169-555x(97)00011-1Trieste , D. J. R. D. Jarrett 1987 Roughness coefficients of large floodsVan Maren, D. S., Winterwerp, J. C., Wu, B. S., & Zhou, J. J. (2009). Modelling hyperconcentrated flow in the Yellow River. Earth Surface Processes and Landforms, 34(4), 596-612. doi:10.1002/esp.1760Wan, Z., Wang, Z., & Julien, P. Y. (1994). Hyperconcentrated Flow. Journal of Hydraulic Engineering, 120(10), 1234-1234. doi:10.1061/(asce)0733-9429(1994)120:10(1234)Winterwerp, J. C. (2001). Stratification effects by cohesive and noncohesive sediment. Journal of Geophysical Research: Oceans, 106(C10), 22559-22574. doi:10.1029/2000jc000435Jiongxin, X. (1999). Erosion caused by hyperconcentrated flow on the Loess Plateau of China. CATENA, 36(1-2), 1-19. doi:10.1016/s0341-8162(99)00009-