Studio dei metodi di valutazione della pericolosità associata ai "debris flow" in ambiente alpino

The present work concerns with the study of debris flows and, in particular, with the related hazard in the Alpine Environment. During the last years several methodologies have been developed to evaluate hazard associated to such a complex phenomenon, whose velocity, impacting force and inappropriate temporal prediction are responsible of the related high hazard level. This research focuses its attention on the depositional phase of debris flows through the application of a numerical model (DFlowz), and on hazard evaluation related to watersheds morphometric, morphological and geological characterization. The main aims are to test the validity of DFlowz simulations and assess sources of errors in order to understand how the empirical uncertainties influence the predictions; on the other side the research concerns with the possibility of performing hazard analysis starting from the identification of susceptible debris flow catchments and definition of their activity level. 25 well documented debris flow events have been back analyzed with the model DFlowz (Berti and Simoni, 2007): derived form the implementation of the empirical relations between event volume and planimetric and cross section inundated areas, the code allows to delineate areas affected by an event by taking into account information about volume, preferential flow path and digital elevation model (DEM) of fan area. The analysis uses an objective methodology for evaluating the accuracy of the prediction and involve the calibration of the model based on factors describing the uncertainty associated to the semi empirical relationships. The general assumptions on which the model is based have been verified although the predictive capabilities are influenced by the uncertainties of the empirical scaling relationships, which have to be necessarily taken into account and depend mostly on errors concerning deposited volume estimation. In addition, in order to test prediction capabilities of physical-based models, some events have been simulated through the use of RAMMS (RApid Mass MovementS). The model, which has been developed by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) in Birmensdorf and the Swiss Federal Institute for Snow and Avalanche Research (SLF) takes into account a one-phase approach based on Voellmy rheology (Voellmy, 1955; Salm et al., 1990). The input file combines the total volume of the debris flow located in a release area with a mean depth. The model predicts the affected area, the maximum depth and the flow velocity in each cell of the input DTM. Relatively to hazard analysis related to watersheds characterization, the database collected by the Alto Adige Province represents an opportunity to examine debris-flow sediment dynamics at the regional scale and analyze lithologic controls. With the aim of advancing current understandings about debris flow, this study focuses on 82 events in order to characterize the topographic conditions associated with their initiation , transportation and deposition, seasonal patterns of occurrence and examine the role played by bedrock geology on sediment transfer.

A novel map-matching procedure for low-sampling GPS data with applications to traffic flow analysis

An extensive sample (2%) of private vehicles in Italy are equipped with a GPS device that periodically measures their position and dynamical state for insurance purposes. Having access to this type of data allows to develop theoretical and practical applications of great interest: the real-time reconstruction of traffic state in a certain region, the development of accurate models of vehicle dynamics, the study of the cognitive dynamics of drivers. In order for these applications to be possible, we first need to develop the ability to reconstruct the paths taken by vehicles on the road network from the raw GPS data. In fact, these data are affected by positioning errors and they are often very distanced from each other (~2 Km). For these reasons, the task of path identification is not straightforward. This thesis describes the approach we followed to reliably identify vehicle paths from this kind of low-sampling data. The problem of matching data with roads is solved with a bayesian approach of maximum likelihood. While the identification of the path taken between two consecutive GPS measures is performed with a specifically developed optimal routing algorithm, based on A* algorithm. The procedure was applied on an off-line urban data sample and proved to be robust and accurate. Future developments will extend the procedure to real-time execution and nation-wide coverage.

Dynamics, rheology and critical properties of colloidal fluid mixtures

Liquids under the influence of external fields exhibit a wide range of intriguing phenomena that can be markedly different from the behaviour of a quiescent system. This work considers two different systems — a glassforming Yukawa system and a colloid-polymer mixture — by Molecular Dynamics (MD) computer simulations coupled to dissipative particle dynamics. The former consists of a 50-50 binary mixture of differently-sized, like-charged colloids interacting via a screened Coulomb (Yukawa) potential. Near the glass transition the influence of an external shear field is studied. In particular, the transition from elastic response to plastic flow is of interest. At first, this model is characterised in equilibrium. Upon decreasing temperature it exhibits the typical dynamics of glassforming liquids, i.e. the structural relaxation time τα grows strongly in a rather small temperature range. This is discussed with respect to the mode-coupling theory of the glass transition (MCT). For the simulation of bulk systems under shear, Lees-Edwards boundary conditions are applied. At constant shear rates γ˙ ≫ 1/τα the relevant time scale is given by 1/γ˙ and the system shows shear thinning behaviour. In order to understand the pronounced differences between a quiescent system and a system under shear, the response to a suddenly commencing or terminating shear flow is studied. After the switch-on of the shear field the shear stress shows an overshoot, marking the transition from elastic to plastic deformation, which is connected to a super-diffusive increase of the mean squared displacement. Since the average static structure only depends on the value of the shear stress, it does not discriminate between those two regimes. The distribution of local stresses, in contrast, becomes broader as soon as the system starts flowing. After a switch-off of the shear field, these additional fluctuations are responsible for the fast decay of stresses, which occurs on a time scale 1/γ˙ . The stress decay after a switch-off in the elastic regime, on the other hand, happens on the much larger time scale of structural relaxation τα. While stresses decrease to zero after a switch-off for temperatures above the glass transition, they decay to a finite value for lower temperatures. The obtained results are important for advancing new theoretical approaches in the framework of mode-coupling theory. Furthermore, they suggest new experimental investigations on colloidal systems. The colloid-polymer mixture is studied in the context of the behaviour near the critical point of phase separation. For the MD simulations a new effective model with soft interaction potentials is introduced and its phase diagram is presented. Here, mainly the equilibrium properties of this model are characterised. While the self-diffusion constants of colloids and polymers do not change strongly when the critical point is approached, critical slowing down of interdiffusion is observed. The order parameter fluctuations can be determined through the long-wavelength limit of static structure factors. For this strongly asymmetric mixture it is shown how the relevant structure factor can be extracted by a diagonalisation of a matrix that contains the partial static structure factors. By presenting first results of this model under shear it is demonstrated that it is suitable for non-equilibrium simulations as well.

Genetic dynamics across early life stages in the tropical tree Prunus africana (Rosaceae)

In many plant species, the genetic template of early life-stages is formed by animal-mediated pollination and seed dispersal and has profound impact on further recruitment and population dynamics. Understanding the impact of pollination and seed dispersal on genetic patterns is a central issue in plant population biology. In my thesis, I investigated (i) contemporary dispersal and gene flow distances as well as (ii) genetic diversity and spatial genetic structure (SGS) across subsequent recruitment stages in a population of the animal-pollinated and dispersed tree Prunus africana in Kakamega Forest, West Kenya. Using microsatellite markers and parentage analyses, I inferred distances of pollen dispersal (father-to-mother), seed dispersal/maternal gene flow (mother-to-offspring) as well as paternal gene flow (father-to-offspring) for four early life stages of the species (seeds and fruits, current year seedlings, seedlings ≤ 3yr, seedlings > 3yr). Distances of pollen and seed dispersal as well as paternal gene flow were significantly shorter than expected from the spatial arrangement of trees and sampling plots. They were not affected by the density of conspecific trees in the surrounding. At the propagule stage, mean pollen dispersal distances were considerably (23-fold) longer than seed dispersal distances, and paternal gene flow distances exceeded maternal gene flow by a factor of 25. Seed dispersal distances were remarkably restricted, potentially leading to a strong initial SGS. The initial genetic template created by pollination and seed dispersal was extensively altered during later recruitment stages. Potential Janzen-Connell effects led to markedly increasing distances between offspring and both parental trees in older life stages. This showed that distance and density-dependent mortality factors are not exclusively related to the mother tree, but also to the father. Across subsequent recruitment stages, the pollen to seed dispersal ratio and the paternal to maternal gene flow ratio dropped to 2.1 and 3.4, respectively, in seedlings > 3yr. The relative changes in effective pollen dispersal, seed dispersal, and paternal gene flow distances across recruitment stages elucidate the mechanisms affecting the contribution of the two processes pollen and seed dispersal to overall gene flow. Using the same six microsatellite loci, I analyzed genetic diversity and SGS across five life stages, from seed rain to adults. Levels of genetic diversity within the studied P. africana population were comparable to other Prunus species and did not vary across life stages. In congruence with the short seed dispersal distances, I found significant SGS in all life stages. SGS decreased from seed and early seedling stages to older juvenile stages, and it was higher in adults than in late juveniles of the next generation. A comparison of the data with direct assessments of contemporary gene flow patterns indicate that distance- or density-dependent mortality, potentially due to Janzen-Connell effects, led to the initial decrease in SGS. Intergeneration variation in SGS could have been driven by variation in demographic processes, the effect of overlapping generations, and local selection processes. Overall, my study showed that complex sequential processes during recruitment contribute to the spatial genetic structure of tree populations. It highlights the importance of a multistage perspective for a comprehensive understanding of the impact of animal-mediated pollen and seed dispersal on spatial population dynamics and genetic patterns of trees.

Aeroelastic stability of structures: flutter analysis using Computational Fluid Dynamics

Thanks to the increasing slenderness and lightness allowed by new construction techniques and materials, the effects of wind on structures became in the last decades a research field of great importance in Civil Engineering. Thanks to the advances in computers power, the numerical simulation of wind tunnel tests has became a valid complementary activity and an attractive alternative for the future. Due to its flexibility, during the last years, the computational approach gained importance with respect to the traditional experimental investigation. However, still today, the computational approach to fluid-structure interaction problems is not as widely adopted as it could be expected. The main reason for this lies in the difficulties encountered in the numerical simulation of the turbulent, unsteady flow conditions generally encountered around bluff bodies. This thesis aims at providing a guide to the numerical simulation of bridge deck aerodynamic and aeroelastic behaviour describing in detail the simulation strategies and setting guidelines useful for the interpretation of the results.

Testing of subgrid scale (SGS) models for large-eddy simulation (LES) of turbulent channel flow

Sub-grid scale (SGS) models are required in order to model the influence of the unresolved small scales on the resolved scales in large-eddy simulations (LES), the flow at the smallest scales of turbulence. In the following work two SGS models are presented and deeply analyzed in terms of accuracy through several LESs with different spatial resolutions, i.e. grid spacings. The first part of this thesis focuses on the basic theory of turbulence, the governing equations of fluid dynamics and their adaptation to LES. Furthermore, two important SGS models are presented: one is the Dynamic eddy-viscosity model (DEVM), developed by \cite{germano1991dynamic}, while the other is the Explicit Algebraic SGS model (EASSM), by \cite{marstorp2009explicit}. In addition, some details about the implementation of the EASSM in a Pseudo-Spectral Navier-Stokes code \cite{chevalier2007simson} are presented. The performance of the two aforementioned models will be investigated in the following chapters, by means of LES of a channel flow, with friction Reynolds numbers $Re_\tau=590$ up to $Re_\tau=5200$, with relatively coarse resolutions. Data from each simulation will be compared to baseline DNS data. Results have shown that, in contrast to the DEVM, the EASSM has promising potentials for flow predictions at high friction Reynolds numbers: the higher the friction Reynolds number is the better the EASSM will behave and the worse the performances of the DEVM will be. The better performance of the EASSM is contributed to the ability to capture flow anisotropy at the small scales through a correct formulation for the SGS stresses. Moreover, a considerable reduction in the required computational resources can be achieved using the EASSM compared to DEVM. Therefore, the EASSM combines accuracy and computational efficiency, implying that it has a clear potential for industrial CFD usage.

Dynamics of Bora wind over the Adriatic sea: atmospheric water balance and role of air-sea fluxes and orography

The Bora wind is a mesoscale phenomenon which typically affects the Adriatic Sea basin for several days each year, especially during winter. The Bora wind has been studied for its intense outbreak across the Dinaric Alps. The properties of the Bora wind are widely discussed in the literature and scientific papers usually focus on the eastern Adriatic coast where strong turbulence and severe gust intensity are more pronounced. However, the impact of the Bora wind can be significant also over Italy, not only in terms of wind speed instensity. Depending on the synoptic pressure pattern (cyclonic or anticyclonic Bora) and on the season, heavy snowfall, severe storms, storm surges and floods can occur along the Adriatic coast and on the windward flanks of the Apennines. In the present work five Bora cases that occurred in recent years have been selected and their evolution has been simulated with the BOLAM-MOLOCH model set, developed at ISAC-CNR in Bologna. Each case study has been addressed by a control run and by several sensitivity tests, performed with the purpose of better understanding the role played by air-sea latent and sensible heat fluxes. The tests show that the removal of the fluxes induces modifications in the wind approching the coast and a decrease of the total precipitation amount predicted over Italy. In order to assess the role of heat fluxes, further analysis has been carried out: column integrated water vapour fluxes have been computed along the Italian coastline and an atmospheric water balance has been evaluated inside a box volume over the Adriatic Sea. The balance computation shows that, although latent heat flux produces a significant impact on the precipitation field, its contribution to the balance is relatively minor. The most significant and lasting case study, that of February 2012, has been studied in more detail in order to explain the impressive drop in the total precipitation amount simulated in the sensitivity tests with removed heat fluxes with respect to the CNTRL run. In these experiments relative humidity and potential temperature distribution over different cross-sections have been examined. With respect to the CNTRL run a drier and more stable boundary layer, characterised by a more pronounced wind shear at the lower levels, has been observed to establish above the Adriatic Sea. Finally, in order to demonstrate that also the interaction of the Bora flow with the Apennines plays a crucial role, sensitivity tests varying the orography height have been considered. The results of such sensitivity tests indicate that the propagation of the Bora wind over the Adriatic Sea, and in turn its meteorological impact over Italy, is influenced by both the large air-sea heat fluxes and the interaction with the Apennines that decelerate the upstream flow.

Active processes, morphology, and dynamics of icy debris fans: Landform evolution along rapidly degrading escarpments in alpine regions undergoing recent deglaciation

In the past few decades the impacts of climate warming have been significant in alpine glaciated regions. Many valley glaciers formerly linked as distributary glaciers to high-level icecaps have decoupled at their icefalls, exposing major escarpments and generating a suite of dynamic landforrns dominated by mass wasting. Ice-dominated landforms, here termed icy debris fans, develop rapidly by ice avalanching, rockfall, and icy debris flow. Field-based reconnaissance studies at two alpine settings, the Wrangell Mountains of Alaska and the Southern Alps of New Zealand, provide a preliminary morphogenetic model of spatial and temporal evolution of icy debris fans in a range of alpine settings. The influence of these processes on landform evolution is largely unrecognized in the literature dealing with post-glacial landform adjustment known as the paraglacial. A better understanding of these dynamic processes will be increasingly important because of the extreme geohazards characterizing these areas. Our field studies show that after glacier decoupling, icy debris fans begin to form along the base of bedrock escarpments at the mouths of catchments and prograde over valley glaciers. The presence of a distinct catchment, apex, and fan morphology distinguishes these landforms from other landforms common in periglacial hillslope settings receiving abundant clastic debris and ice. Ice avalanching is the most abundant process involved in icy debris fan formation. Fans developed below weakly incised catchments are dominated by ice avalanching and are composed primarily of ice with minor lithic detritus. Typically, avalanches fall into the fan catchments where sediments transform into grainflows that flow onto the fans. Once on the fans, avalanche deposits ablate rapidly, flattening and concentrating lithic fragments at the surface. Icy debris fans may become thick enough to become glaciers with splay crevasse systems. Fans developed below larger, more complex catchments are composed of higher proportions of lithic detritus resulting from temporary storage of ice and lithic detritus deposits within the catchment. Episodic outbursts of meltwater from the icecap may mix with the stored sediments and mobilize icy debris flows (mixture of ice and lithic clasts) onto the fans. Our observations indicate that the entire evolutionary cycle of icy debris fans probably occurs during an early paraglacial interval (i.e., decades to 100 years). Observations comparing avalanche frequency, volume, and fan morphologic evolution at the Alaska site between 2006 and 2010 illustrate complex response between icy debris fans even within the same cirque - where one fan may be growing while others are downwasting because of differences in ice supply controlled by their respective catchments and icecap contributions. As ice supply from the icecap diminishes through time, icy debris fans rapidly downwaste and eventually evolve into talus cones that receive occasional but ephemeral ice avalanches.

Scheduler-dependent inter-cell interference and its impact on LTE uplink performance at flow level

The Long Term Evolution (LTE) cellular technology is expected to extend the capacity and improve the performance of current 3G cellular networks. Among the key mechanisms in LTE responsible for traffic management is the packet scheduler, which handles the allocation of resources to active flows in both the frequency and time dimension. This paper investigates for various scheduling scheme how they affect the inter-cell interference characteristics and how the interference in turn affects the user’s performance. A special focus in the analysis is on the impact of flow-level dynamics resulting from the random user behaviour. For this we use a hybrid analytical/simulation approach which enables fast evaluation of flow-level performance measures. Most interestingly, our findings show that the scheduling policy significantly affects the inter-cell interference pattern but that the scheduler specific pattern has little impact on the flow-level performance.

LTE uplink scheduling - flow level analysis

Long Term Evolution (LTE) is a cellular technology foreseen to extend the capacity and improve the performance of current 3G cellular networks. A key mechanism in the LTE traffic handling is the packet scheduler, which is in charge of allocating resources to active flows in both the frequency and time dimension. In this paper we present a performance comparison of three distinct scheduling schemes for LTE uplink with main focus on the impact of flow-level dynamics resulting from the random user behaviour. We apply a combined analytical/simulation approach which enables fast evaluation of flow-level performance measures. The results show that by considering flow-level dynamics we are able to observe performance trends that would otherwise stay hidden if only packet-level analysis is performed.

Optical projection tomography reveals dynamics of HEV growth after immunization with protein plus CFA and features shared with HEVs in acute autoinflammatory lymphadenopathy

The vascular-stromal compartment of lymph nodes is important for lymph node function, and high endothelial venules (HEVs) play a critical role in controlling the entry of recirculating lymphocytes. In autoimmune and autoinflammatory diseases, lymph node swelling is often accompanied by apparent HEV expansion and, potentially, targeting HEV expansion could be used therapeutically to limit autoimmunity. In previous studies using mostly flow cytometry analysis, we defined three differentially regulated phases of lymph node vascular-stromal growth: initiation, expansion, and the re-establishment of vascular quiescence and stabilization. In this study, we use optical projection tomography to better understand the morphologic aspects of HEV growth upon immunization with ovalbumin/CFA (OVA/CFA). We find HEV elongation as well as modest arborization during the initiation phase, increased arborization during the expansion phase, and, finally, vessel narrowing during the re-establishment of vascular quiescence and stabilization. We also examine acutely enlarged autoinflammatory lymph nodes induced by regulatory T cell depletion and show that HEVs are expanded and morphologically similar to the expanded HEVs in OVA/CFA-stimulated lymph nodes. These results reinforce the idea of differentially regulated, distinct phases of vascular-stromal growth after immunization and suggest that insights gained from studying immunization-induced lymph node vascular growth may help to understand how the lymph node vascular-stromal compartment could be therapeutically targeted in autoimmune and autoinflammatory diseases.

Speciation reversal and biodiversity dynamics with hybridization in changing environments

A considerable fraction of the world's biodiversity is of recent evolutionary origin and has evolved as a by-product of, and is maintained by, divergent adaptation in heterogeneous environments. Conservationists have paid attention to genetic homogenization caused by human-induced translocations (e.g. biological invasions and stocking), and to the importance of environmental heterogeneity for the ecological coexistence of species. However, far less attention has been paid to the consequences of loss of environmental heterogeneity to the genetic coexistence of sympatric species. Our review of empirical observations and our theoretical considerations on the causes and consequences of interspecific hybridization suggest that a loss of environmental heterogeneity causes a loss of biodiversity through increased genetic admixture, effectively reversing speciation. Loss of heterogeneity relaxes divergent selection and removes ecological barriers to gene flow between divergently adapted species, promoting interspecific introgressive hybridization. Since heterogeneity of natural environments is rapidly deteriorating in most biomes, the evolutionary ecology of speciation reversal ought to be fully integrated into conservation biology.

Influence of inspired oxygen on glucose-lactate dynamics after subdural hematoma in the rat

The mechanisms causing brain damage after acute subdural hematoma (SDH) are poorly understood. A decrease in cerebral blood flow develops immediately after the hematoma forms, thus reducing cerebral oxygenation. This in turn may activate mitochondrial failure and tissue damage leading to ionic imbalance and possibly to cellular breakdown. The purpose of this study was to test whether a simple therapeutic measure, namely increased fraction of inspired oxygen (FiO2 100), and hence increased arterial and brain tissue oxygen tension, can influence brain glucose and lactate dynamics acutely after subdural hematoma in the rat. Twenty-five male Sprague-Dawley anesthetized rats were studied before, during and after induction of the SDH in two separate groups. The Oxygen group (n = 10) was ventilated with 100% oxygen immediately after induction of the SDH. The Air group (n = 10) was ventilated during the entire study with 21% oxygen. Brain microdialysate samples were analyzed for glucose and lactate. All rats were monitored with femoral arterial blood pressure catheters, arterial blood gas analysis, arterial glucose, lactate and end tidal CO2 (EtCO2). Five male Sprague-Dawley rats were sham operated to measure the effect of oxygen challenge on glucose-lactate dynamics without injury. Arterial oxygen tension in the Oxygen group was 371 +/- 30 mmHg and was associated with significantly greater increase in dialysate lactate in the first 30 min after induction of SDH. Dialysate glucose initially dropped in both groups, after SDH, but then reverted significantly faster to values above baseline in the Oxygen group. Changes in ventilatory parameters had no significant effect on dialysate glucose and lactate parameters in the sham group. Extracellular dialysate lactate and glucose are influenced by administration of 100% O2 after SDH. Dialysate glucose normalizes significantly quicker upon 100% oxygen ventilation. We hypothesize that increased neural tissue oxygen tension, in presence of reduced regional CBF, and possibly compromised mitochondrial function, after acute SDH results in upregulation of rate-limiting enzyme systems responsible for both glycolytic and aerobic metabolism. Similar changes have been seen in severe human head injury, and suggest that a simple therapeutic measure, such as early ventilation with 100% O2, may improve cerebral energy metabolism, early after SDH. Further studies to measure the generation of adenosine triphosphate (ATP) are needed to validate the hypothesis.

Dynamics and kinematics of eruptive activity at Fuego volcano, Guatemala 2005-2009

Volcanoes are the surficial expressions of complex pathways that vent magma and gasses generated deep in the Earth. Geophysical data record at least the partial history of magma and gas movement in the conduit and venting to the atmosphere. This work focuses on developing a more comprehensive understanding of explosive degassing at Fuego volcano, Guatemala through observations and analysis of geophysical data collected in 2005 – 2009. A pattern of eruptive activity was observed during 2005 – 2007 and quantified with seismic and infrasound, satellite thermal and gas measurements, and lava flow lengths. Eruptive styles are related to variable magma flux and accumulation of gas. Explosive degassing was recorded on broadband seismic and infrasound sensors in 2008 and 2009. Explosion energy partitioning between the ground and the atmosphere shows an increase in acoustic energy from 2008 to 2009, indicating a shift toward increased gas pressure in the conduit. Very-long-period (VLP) seismic signals are associated with the strongest explosions recorded in 2009 and waveform modeling in the 10 – 30 s band produces a best-fit source location 300 m west and 300 m below the summit crater. The calculated moment tensor indicates a volumetric source, which is modeled as a dike feeding a SW-dipping (35°) sill. The sill is the dominant component and its projection to the surface nearly intersects the summit crater. The deformation history of the sill is interpreted as: 1) an initial inflation due to pressurization, followed by 2) a rapid deflation as overpressure is explosively release, and finally 3) a reinflation as fresh magma flows into the sill and degasses. Tilt signals are derived from the horizontal components of the seismometer and show repetitive inflation deflation cycles with a 20 minute period coincident with strong explosions. These cycles represent the pressurization of the shallow conduit and explosive venting of overpressure that develops beneath a partially crystallized plug of magma. The energy released during the strong explosions has allowed for imaging of Fuego’s shallow conduit, which appears to have migrated west of the summit crater. In summary, Fuego is becoming more gas charged and its summit centered vent is shifting to the west - serious hazard consequences are likely.

Analyzing the effects of vertical acceleration and deceleration in multi-phase, debris-flow sediment-column experiments / by Christine Marie Williams.

Water-saturated debris flows are among some of the most destructive mass movements. Their complex nature presents a challenge for quantitative description and modeling. In order to improve understanding of the dynamics of these flows, it is important to seek a simplified dynamic system underlying their behavior. Models currently in use to describe the motion of debris flows employ depth-averaged equations of motion, typically assuming negligible effects from vertical acceleration. However, in many cases debris flows experience significant vertical acceleration as they move across irregular surfaces, and it has been proposed that friction associated with vertical forces and liquefaction merit inclusion in any comprehensive mechanical model. The intent of this work is to determine the effect of vertical acceleration through a series of laboratory experiments designed to simulate debris flows, testing a recent model for debris flows experimentally. In the experiments, a mass of water-saturated sediment is released suddenly from a holding container, and parameters including rate of collapse, pore-fluid pressure, and bed load are monitored. Experiments are simplified to axial geometry so that variables act solely in the vertical dimension. Steady state equations to infer motion of the moving sediment mass are not sufficient to model accurately the independent solid and fluid constituents in these experiments. The model developed in this work more accurately predicts the bed-normal stress of a saturated sediment mass in motion and illustrates the importance of acceleration and deceleration.