1,721,065 research outputs found
Experimental evidence from the triggering of debris flow along a granular slopeâ€
No full textThe instability of a granular slope, with seepage flow and low tail downstream water level, has been experimentally investigate to point out the conditions associated to the formation of a debris flow, excluding the case of the debris flow triggered by a failure due to the toe erosion. Material employed were uniform glass spheres (d = 0.003 m) and two different gravel (d50 = 0.007 m and d50 = 0.0022 m)
Influence of streamwise bed slope on sediment threshold under stream flow Discussion
No full textDiscussio
Inception Sediment Transport Relationships at High Slopes
No full textThis study proposes relationships between mean streamflow depth and cohesionless particle bed characteristics at the beginning
of the sediment transport at high slopes in low submergence conditions. The inception of sediment transport is theoretically
approached by the incipient motion condition. A previous theoretical analysis of the equilibrium of a gravel particle based on the exposure
of the particle itself to the streamflow is generalized by introducing the relative position of the exposed part of the particle with respect
to the bottom and by considering the case of a partially submerged particle. Using a low-submergence flow velocity profile in the particle
balance of forces at the limit of equilibrium leads to a relationship between the mean flow depth and the sediment size. Another velocity
profile of low-submergence flow is added to that used in the previous study, and two analytical expressions of flow depths corresponding
to the beginning of sediment transport are obtained for both fully submerged particles and partially submerged particles. The theoretical
flow depths given by the analytical expressions are then compared with those from previous experimental tests at the beginning of
sediment transport at high slopes with fully submerged particles. The comparison shows a satisfactory agreement between theoretical and
experimental values of flow depth corresponding to the degree of exposure and the relative position of the exposed part of the surface
layer bed particles
The initiation of debris flow at high slopes: experimental results
No full textDebris deposit laying over an impermeable high slope surface (e.g. in steep streams and gullies) could develop a water sediment mixture flow
(usually known as debris flow) when a high enough water flow is flowing over the sediment bed. In particular the rainfall first saturates the debris
deposit and then mobilizes it by an overland flow.
The mechanisms which make unstable the granular material layer in such a case were studied by experimental tests performed in a tilting flume
filled with uniformly distributed granular material.
The experimental results are compared with theoretical relationships on the occurrence of debris flow and with experimental findings pertinent to
sediment transport phenomena.
The material employed in the experiments was nearly uniform gravel of three different sizes with mean diameters respectively equal to d = 0.023,
0.029 and 0.034 m
Comparison between weather radar and rain gauges data of precipitations that triggered debris flows in the Dolomites (North Eastern Italian Alps)
No full textMODELLO DI INNESCO DI UNA COLATA DETRITICA ORIGINATA DALL'EROSIONE DI SEDIMENTI PER DEFLUSSO SUPERFICIALE E DELL'IDROGRAMMA SOLIDO-LIQUIDO
No full textLe colate detritiche si originano in ambiente alpino prevalentemente per la mobiliz-
zazione, causa deflusso superficiale, dei sedimenti posti al fondo di canali e corsi
d’acqua. Il presente lavoro propone un modello di innesco che si basa su di un mod-
ello idrologico per la determinazione dei deflussi superficiali; un metodo per deter-
minare le condizioni di innesco di una colata; un modello per il calcolo della portata
di picco di una colata; un modello di costruzione dell’idrogramma solido-liquido.
Per quest’ultimo si propongono due forme diverse: una che si appoggia alla forma
dell’idrogramma liquido ed una di forma triangolare. La prima corrisponde ad un
idrogramma solido-liquido nella zona di formazione della colata, la seconda ad una
colata giá sviluppata. Si riporta infine un caso di applicazione del modello per ri-
costruire lo scenario di una colata avvenuta a Fiames (Cortina d’Ampezzo, BL) il 25 Luglio 200
CALCOLO DELLA PORTATA DI UNA COLATA DETRITICA ORIGINATA DALL'EROSIONE DI UN LETTO DI SEDIMENTI PER DEFLUSSO SUPERFICIALE
No full textLe colate detritiche in ambiente alpino sono spesso causate dalla mobilizzazione, per
effetto del deflusso idrico superficiale, dei sedimenti posti a valle dei canaloni incisi
nelle pareti rocciose e nelle aste torrentizie che da essi si dipartono. E tuttavia, ad
oggi non esiste una teoria univoca che consenta di descrivere la formazione di tali
colate. Ad esempio, Takahashi (1978) ha sviluppato due diversi modelli per stimare le
caratteristiche di una colata detritica originata dalla movimentazione di un deposito
detritico soggetto all’azione di una corrente idrica. La presente nota intende ricon-
durre tali modelli entro un contesto razionale, evidenziando essi possono essere uti-
lizzati per descrivere due fasi distinte e consecutive del processo di formazione di una
colata. Essi, inoltre, se opportunamente semplificati, forniscono un’unica relazione
per il calcolo della portata di una colata, di comune uso nella pratica ingegneristica
per la stima dell’idrogramma solido-liquido. Questa relazione, viene qui confrontata
con i dati di una sistematica serie di esperimenti di laboratorio precedentemente con-
dotti. La sovrastima della portata complessivamente convogliata dalla colata detrit-
ica che risulta da tale confronto è verosimilmente associata alla composizione della
coda della colata, che risulta piú ricca d’acqua rispetto al corpo della colata. Al fine
di tenere conto di ció, la relazione sopra considerata viene corretta sulla base dei dati disponibil
Rainfall threshold for the initiation of debris flows by channel bed failure in the Dolomites
No full textThe most common process of initiation of debris flows in natural channel of high mountainous areas is the channel-bed failure. In this case the runoff, rather than infiltration, becomes the most important controlling factor of the occurrence of debris flow. The estimates of the critical values of runoff can be indirectly approached by the precipitation that generated them. The aim of this study is to define the threshold rainfall conditions that result in the initiation of debris flow by channel-bed failure. Historical and rainfall data from 28 debris-flow events that occurred in six watersheds in the Dolomites (Northeastern Italian Alps) were collected. Using information on the rainfall up to the time of occurrence of the debris flows a method to identify these events using an SCS based kinematic distributed hydrological response model is proposed. Precipitation intensities plotted against durations are used to define a threshold curves for the triggering of the debris flow by channel bed-failure in the Dolomite environment. The threshold curve is compared with eleven threshold curves for the triggering of debris flow reported in the literature and with the intensity-duration-frequency curves of two gauges stations next to the five study sites. Comparisons with reported thresholds do not show a distinction between rainfall conditions that result in landslide-triggered or channel bed failure-initiated debris flows. Comparison of thresholds with intensity-duration-frequency curves lead to the identification of two different precipitation regimes for the triggering of debris flows by channel bed failure
- …
