Document Actions

IJEGE-11_BS-Reid-et-alii

background image
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
367
DOI: 10.4408/IJEGE.2011-03.B-042
ENTRAINMENT OF BED SEDIMENT BY DEBRIS FLOWS:
RESULTS FROM LARGE-SCALE EXPERIMENTS
m
aRk
E. REID
(*)
, R
iCHaRd
M. IVERSON
(**)
, m
attHew
LOGAN
(**)
, R
iCHaRd
G. LAHUSEN
(**)
,
J
onatHan
W. GODT
(***)
& J
ulie
P. GRISWOLD
(**)
(*)
U.S. Geological Survey, 345 Middlefield Road, MS 910 - Menlo Park - CA 94025 USA;
Email: mreid@usgs.gov; tel: +1-650-329-4891
(**)
Cascades Volcano Observatory, U.S. Geological Survey, 1300 SE Cardinal Ct. #100 - Vancouver - WA 98683 USA
(***)
U.S. Geological Survey, Denver Federal Center, Box 25046, MS 966 - Denver - CO 80225 USA
INTRODUCTION
Debris flows that entrain sediment by scouring
channel beds or undermining channel banks can be-
come exceptionally mobile and destructive (H
unGR
et
alii, 2005). They typically inundate larger regions than
flows lacking entrainment, and they can originate in di-
verse geographic settings, including steep mountainous
regions (b
enda
, 1990; b
eRti
et alii, 2000; b
eRti
& s
i
-
moni
, 2005; b
Reien
et alii, 2008), volcano flanks (P
ieR
-
son
et alii, 1990), denuded post-wildfire watersheds
(C
annon
& R
eneau
, 2000; l
aRsen
et alii, 2006), and
post-timber harvest hillslopes (G
utHRie
et alii, 2010).
Moreover, debris flows that entrain sediment as they
descend channels can initiate by diverse processes,
including: mobilization of discrete landslides, coales-
cence of erosional rills, or exceptional concentration of
surface-water flow (C
annon
et alii, 2001; w
anG
et alii,
2003; G
odt
& C
oe
, 2007; C
oe
et alii, 2008).
Several hypotheses have been offered to explain
the mechanics of bed sediment entrainment by debris
flows. t
akaHasHi
(1978; 1991) proposed that saturated
bed sediment fails en masse, rather than through pro-
gressive downward scour, when loaded by an overrid-
ing debris flow. He quantified his hypothesis by using
an infinite slope-stability analysis that assumed steady,
slope-parallel groundwater flow to calculate the depth
of bed failure. In this approach, groundwater pressure
in the sediment is in equilibrium with the sloping water
table in the overriding debris flow, and no transient ex-
cess pore pressures develop. By contrast, Sassa and col-
ABSTRACT
When debris flows grow by entraining sediment,
they can become especially hazardous owing to in-
creased volume, speed, and runout. To investigate
the entrainment process, we conducted eight large-
scale experiments in the USGS debris-flow flume. In
each experiment, we released a 6 m
3
water-saturated
debris flow across a 47-m long, ~12-cm thick bed of
partially saturated sediment lining the 31º flume. Prior
to release, we used low-intensity overhead sprinkling
and real-time monitoring to control the bed-sediment
wetness. As each debris flow descended the flume, we
measured the evolution of flow thickness, basal total
normal stress, basal pore-fluid pressure, and sediment
scour depth. When debris flows traveled over relatively
dry sediment, net scour was minimal, but when debris
flows traveled over wetter sediment (volumetric water
content > 0.22), debris-flow volume grew rapidly and
flow speed and runout were enhanced. Data from scour
sensors showed that entrainment occurred by rapid
(5-10 cm/s), progressive scour rather than by mass
failure at depth. Overriding debris flows rapidly gener-
ated high basal pore-fluid pressures when they loaded
and deformed bed sediment, and in wetter beds these
pressures approached lithostatic levels. Reduction of
intergranular friction within the bed sediment thereby
enhanced scour efficiency, entrainment, and runout.
K
ey
words
: debris flow, sediment entrainment, scour, large-
scale experiment, pore-fluid pressure, soil moisture
background image
M.E. REID, R.M. IVERSON, M. LOGAN, R.G. LAHUSEN, J.w. GODT & J.P. GRISwOLD
368
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
crete channel 95 m long and 2 m wide with a bumpy
bed and a smoother, nearly horizontal concrete runout
pad at the base (Fig. 1). Between 2006 and 2009, we
conducted eight entrainment experiments and two
control experiments without any erodible sediment in
the flume (i
veRson
et alii, 2011).
In each entrainment experiment, we placed 11±1
m
3
of sediment on the flume bed between 6 and 53
m downslope of the headgate; this loose sediment
formed a layer 47 m long and ~12 cm thick with a
mean porosity of 0.45 ± 0.04. We determined in-situ
porosity via a sediment excavation method. Using
low-intensity overhead sprinklers, we then wetted the
sediment and monitored its evolving volumetric water
content, θ, and pore-fluid suctions with 1-Hz sampling
of data from electrical capacitance soil-moisture sen-
sors (k
izito
et alii, 2008) and tensiometers. Using
sediment from our experiments, we calibrated soil-
moisture sensor response and found that variability in
measured volumetric water content was about ± 0.02.
In each experiment, we installed between 16 and 20
soil-moisture sensors in the bed sediment, distributed
at 2.5 m spacing downslope. Typically, 3 locations
contained nests of 2 sensors to monitor progression
of the infiltration front. With this system, we con-
trolled θ of the sediment layer so that its mean value
ranged between about 0.15 ± 0.03 and 0.28 ± 0.04 at
the time of debris-flow release. During sprinkling the
bed sediment settled slightly, likely reducing poros-
ity to ~0.4. We avoided fully saturating or generating
positive pore-fluid pressures in the bed sediment prior
to debris-flow release because such conditions led to
premature failure of parts of the bed.
leagues (s
assa
et alii, 1985; w
anG
et alii, 2003; s
assa
& w
anG
, 2005) suggested that loading by overriding
debris flows could transiently increase pore pressures
in saturated bed sediment. From results of laboratory
ring-shear tests, they inferred that excess pore pressures
might nearly liquefy the bed, greatly reducing bed-sedi-
ment shear strength and facilitating entrainment. A sim-
ilar hypothesis was offered by H
unGR
& e
vans
(2004)
to explain entrainment by rock avalanches. Analogous
undrained loading has been observed in other mass
movements (H
utCHinson
& b
HandaRi
, 1971).
Despite the importance of debris-flow entrainment
to hazard assessment and landscape change, clear un-
derstanding of the basic process remains elusive, ow-
ing partly to a lack of high-resolution, field-scale data.
Quantifying physical controls on entrainment through
field measurements is difficult because of the spo-
radic, irreproducible character of natural events. To
avoid the shortcomings of field investigations, some
researchers have used small-scale laboratory flumes to
examine debris-flow entrainment (R
iCkenmann
et alii,
2003; P
aPa
et alii, 2004). Direct application of results
from small experiments to natural debris flows, how-
ever, is hampered by the scale-dependent properties of
water-saturated debris (i
veRson
, 1997).
As an alternative to these approaches, we per-
formed a series of debris-flow entrainment experiments
in a unique, large-scale facility that minimized scaling
problems. Our experiments used reproducible initial
conditions with precisely placed instrumentation, and
thus enabled thorough evaluation of factors influenc-
ing entrainment. The experiments focused on testing
whether entrainment occurs by mass failure of the bed
and whether deformation caused by overriding debris
flows generates excess pore-fluid pressure in the bed
sediments. To help isolate these processes, we control-
led and systematically varied the water content of the
bed sediment. Here we present experimental results, dis-
cuss the influence of bed water content on entrainment,
and note that profound growth in debris-flow speed and
runout can accompany entrainment of wet sediment.
EXPERIMENTAL CONFIGURATION
We performed our experiments using the U.S.
Geological Survey debris-flow flume, located in the
H.J. Andrews Experimental Forest in the Cascades
Range of Oregon, USA (i
veRson
et alii, 2010). The
flume, constructed on a 31º slope, consists of a con-
Fig. 1 - Schematic cross section of flume experiment con-
figuration showing upper headgate area (contain-
ing initial debris-flow material), erodible sediment
lining flume bed (between 6 and 53 m), overhead
sprinkler system, instrumented cross sections, and
runout area. Longitudinal distance is measured
from the gate at the head of the flume. Thickness
of bed sediment is exaggerated about 7X
background image
ENTRAINMENT OF BED SEDIMENT BY DEBRIS FLOWS: RESULTS FROM LARGE-SCALE EXPERIMENTS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
369
Electronic circuits were broken as the clasts were en-
trained, thereby signaling the time and depth of scour.
We also surveyed the bed sediment surface using either
graduated surface-contact probes or, later, a laser rang-
ing device (at minimum intervals of 0.2 m across the
flume and 2.5 m down the flume) before and after each
experiment. Using differences in the isopach surfaces
generated from these surveys, we obtained estimates of
the net sediment volume entrained by the debris flows.
RESULTS
Our experiments demonstrated that the water
content of the bed sediment had a profound effect on
entrainment and resulting debris-flow behavior. With
wetter bed sediment, conspicuous entrainment (> 60%
of the bed sediment) occurred and debris-flow runout
was enhanced (Figs. 3 and 7). With drier bed sediment,
minimal net entrainment (20-30%) occurred and de-
bris-flow runout was hindered. We found a roughly lin-
ear positive relation (over the range examined) between
overall bed-sediment volumetric water content, θ, and
normalized volume of sediment entrained, V
E
, defined
as the ratio of entrained volume to the control debris-
flow volume of 6 m
3
(Fig. 3). We also found that if θ >
0.22, then V
E
> 1, indicating that the entrained volume
exceeded the control debris-flow initial volume.
To understand the differences in behavior caused
by variable bed-sediment water contents, we first
examine scour and loading effects within wetter and
Following bed-sediment wetting, we released 6-m
3
water-saturated debris flows from a steel headgate at the
top of the flume (Fig. 2). Both the debris flows and bed
sediment averaged 37% sand, 56% gravel, and 7% mud-
sized (silt/clay) grains by dry weight. When in contact
with the bumpy flume bed, this “SGM” mixture, exten-
sively used in other USGS flume experiments, exhibits
a static basal friction angle equal to its internal angle of
friction of about 40º (i
veRson
et alii, 2010).
As the debris flows traveled down the flume, we
sampled at 500 Hz the evolving flow height, h, nor-
mal to the bed (using overhead lasers), total normal
stress, σ, on the bed (using force plates mounted in
the bed), and pore-fluid pressure, p, on the bed (using
pressure transducers mounted in the bed) at several
cross sections in the flume (Fig. 1). Our instruments
and methods of data processing are described in de-
tail by i
veRson
et alii (2010). We used time-stamped
video recordings, synchronized with the sensor data,
to precisely determine flow-front speeds. The video
recordings, indexed by experiment date, can be
viewed on-line at http://pubs.usgs.gov/of/2007/1315
(l
oGan
& i
veRson
, 2007).
At locations between 13 and 43 m, we installed
nests of scour sensors within the bed sediment. These
sensors consisted of artificial gravel-sized clasts, bur-
ied at depths from 2 to 10 cm (normal to the slope)
with a typical spacing of ~4 cm, connected by short
leashes to contact switches mounted in the flume bed.
Fig. 2 - Photographs showing debris-flow behavior during an experiment with wet bed sediment (vol. water content, θ =
0.28). (a) Release of flow from headgate with bed sediment still in place. (b) Close-up showing debris flow entraining
bed sediment; flow front is approaching measurement section at 32 m downslope from flume headgate, ~ 4 s after
release. (c) Debris flow crossing runout pad, ~ 10 s after release. Grid squares are 1 m. Experiment date: 21 June
2007. Videos of experiments can be viewed at http://pubs.usgs.gov/of/2007/1315
background image
M.E. REID, R.M. IVERSON, M. LOGAN, R.G. LAHUSEN, J.w. GODT & J.P. GRISwOLD
370
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
Detailed data from our sensors illuminate the in-
teractions between sediment entrainment and debris-
flow behavior with θ = 0.25 and θ = 0.18. At the 32-m
measurement section, the height, h (encompassing
both the debris flow and bed-sediment thickness), in-
creased rapidly in both experiments as the debris-flow
front passed (Figs. 5a and b). With θ = 0.25, h subse-
quently decreased to a level less than the pre-release
bed level, reflecting removal of bed material (Fig. 5a).
With θ = 0.18, h ultimately returned to approximately
the pre-debris-flow bed level, indicating minimal net
erosion (Fig. 5b). In both cases, the primary flow front
was followed by a series of roll waves evidenced by
small transient increases in h (Figs. 5a and b).
With both θ = 0.25 and θ = 0.18, increased just after
the passage of the flow front (Figs. 5c and d). Similarly,
in both cases basal pore-fluid pressure, p, increased when
σ increased, but p increased significantly only with θ =
0.25 (Figs. 5e and f). In our control experiments, as well
as other field and laboratory observations without entrain-
ment, the increase in p and σ is typically delayed slightly
as the drained, dilated, coarse-grained debris-flow snout
passes, and the increase in p typically lags behind that of
σ (i
veRson
, 1997; m
C
a
Rdell
et alii, 2007; i
veRson
et alii,
2010; m
C
C
oy
et alii, 2010). Results shown in Fig. 5 do
drier bed sediments as they were overridden by debris
flows. Then, we summarize large-scale effects of bed
entrainment on overall debris-flow behavior, includ-
ing flow-front speeds and runout distances.
SEDIMENT SCOUR DURING DEBRIS-FLOw
LOADING
Results from two experiments, one with relatively
wet (θ = 0.25) and one with relatively dry (θ = 0.18)
bed sediments, illustrate the disparities in sediment
entrainment. With θ = 0.25, bed material was rapidly
and progressively scoured as the debris-flow front
moved down the flume (Fig. 4a). In this case, shallow
scour sensors (at 2-4 cm depth) at the upslope sec-
tion (13 m downslope from the flume headgate) were
eroded first, and scour proceeded rapidly downward
into the sediment at a rate of 5-10 cm/s. Complete ero-
sion of the bed sediment occurred within 1-2 seconds
without en masse failure at depth, and sensor nests
located within the right and left sides of the bed sedi-
ment responded almost identically. As the debris flow
traveled down the flume, scour occurred in a similar
manner farther downslope (Fig. 4a). Pore-fluid pres-
sures at the base of the sediment were transiently el-
evated during the 1-2 s of intense scour. (Compare,
for example, scour data with basal pore-pressure re-
sponse at the 32-m section (Fig. 4b)). In contrast, 16
scour sensors located within drier bed sediment (θ =
0.18) remained undisturbed as the debris flow over-
rode them. In this case, our post-flow excavation of
the bed sediment revealed that only 1-2 cm of scour of
the uppermost bed sediment had occurred.
Fig. 3 - Normalized volume of sediment entrained, V
E
,
(entrained volume/control debris-flow volume of
6 m
3
) as a function of bed-sediment volumetric
water content, . Normalization differs from that of
i
verSoN
, et alii (2011)
Fig. 4 - (a) Scour depth detected at 4 measurement sections
down the flume (13, 23, 33, and 43 m) during an
entrainment experiment with wet bed sediment (θ =
0.25). Each measurement section had a left- (triangle
symbols) and right-side (circle symbols) nest consist-
ing of two sensors at different depths. Left- and right-
side sensor nests were located 0.5 m from the left and
right flume walls, respectively. (b) Basal pore-pres-
sure responses at the 32-m measurement section. Ver-
tical dashed line denotes arrival of debris-flow front
at 32-m section. Experiment date: 13 May 2008
background image
ENTRAINMENT OF BED SEDIMENT BY DEBRIS FLOWS: RESULTS FROM LARGE-SCALE EXPERIMENTS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
371
not illustrate such a lag, because they depict conditions at
the base of the bed sediment - which do not necessarily
mirror those at the base of the debris flow.
The pore-pressure ratio, λ, (commonly used in
groundwater analyses and defined as
p
/σ) specifies the
amount of the total normal load offset by basal pore-
fluid pressure; λ = 1 indicates a fully liquefied state in
which the pore pressure equals the lithostatic load, such
that the effective frictional strength is reduced to zero.
In our experiment with θ = 0.25, λ hovered around 0.9
during scour (Fig. 5g). In the drier bed experiment, λ
remained quite low (Fig. 5h). Thus, rapid loading and
deformation due to an overriding debris flow provoked
elevated basal pore-fluid pressures in wetter bed sedi-
ment, but had little effect in drier bed sediment.
EFFECT OF ENTRAINMENT ON DEBRIS-FLOw
BEHAVIOR
Our experimental debris flows that entrained wet bed
sediment traveled faster and farther than our control de-
bris flows on bare concrete beds. In all of the experiments,
the speeds of the debris-flow fronts exiting from the gate
at the head of the flume were similar for about 3 s (Fig.
6). Flows interacting with wetter bed sediment became
greatly agitated compared to those overriding drier sedi-
ment. Notable differences in flow-front speeds occurred
after the flows traveled beyond the extent of the bed sedi-
ment (at ~7-8 s). Flows that overrode wetter bed sediment
Fig. 5 - Responses measured at the cross section 32 m downslope from headgate during wet (θ = 0.25) and dry (θ = 0.18)
entrainment experiments. (a) and (b) Flow thickness, h. Horizontal dashed lines represent original bed-sediment
heights. (c) and (d) Total normal basal stress at the flume base, σ (e) and (f) Basal pore-fluid pressure, p. (g) and (h)
Basal pore-pressure ratio, λ (ratio of p/σ). wet experiment date: 13 May 2008. Dry experiment date: 2 June 2009
Fig. 6 - Debris-flow front position as a function of time
since flow release during 8 entrainment experi-
ments (solid and dashed lines) and 2 control ex-
periments (thick black lines)
background image
M.E. REID, R.M. IVERSON, M. LOGAN, R.G. LAHUSEN, J.w. GODT & J.P. GRISwOLD
372
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
water content is quantified by the peak λ (ratio of pore
pressure to total normal load) response during scour
(Fig. 8). We observed an abrupt transition in behavior
between wet bed sediment, where approached 1 and the
sediment could liquefy, and dry sediment, where re-
mained quite small (~0.1). Elevated pore pressures and
associated liquefaction effects reduced effective fric-
tional strength and encouraged sediment entrainment.
Rapid pore-pressure increase within the wet bed sed-
iment was likely caused by two mechanisms. As a debris
flow traveled over the sediment, its weight directly com-
pressed the sediment pores. Because compression was
considerably more rapid than the rate of equilibration of
pore-fluid pressure, undrained loading occurred. In ad-
dition, the loose sediment in the bed likely contracted as
it approached a critical-state density during shear defor-
mation. Our sensors indicated that scour, and therefore
shear deformation, occurred with increased pore-fluid
pressures (Fig. 4). Contraction and collapse during shear
failure can help transiently elevate pore-fluid pressures
and promote debris-flow mobilization (i
veRson
et alii,
1997; i
veRson
et alii, 2000; i
veRson
, 2005).
We observed that increased pore pressures devel-
oped in bed sediment without the pores being fully sat-
urated prior to loading by debris flows. Initial sediment
porosity after sprinkling was ~ 0.4 and rapid pressure
increases occurred if θ > 0.22. In such cases, water in
sediment pores was likely mostly continuous with air
mainly confined to isolated, entrapped bubbles. With
drier sediment (more air spaces), escape of air as the
sediment was compressed probably thwarted substan-
tial pore pressure increases. For our loose sediment, θ
> ~ 0.22 appears to be a threshold for rapid pressure
response and substantial sediment entrainment.
generally increased in speed (by 10-20%), whereas those
that overrode drier bed sediment had speeds similar to or
slower than the speeds measured in control experiments
(Fig. 6). Speeds of the flows that entrained wet sediment
exceeded those of the control flows even across the gen-
tly sloping runout pad. Debris flows that entrained wet
bed sediment traveled farther as well. There is a roughly
linear positive relation between overall bed-sediment
volumetric water content, θ, and normalized maximum
runout distance, D
R
, defined as the furthest runout dis-
tance relative to that of the control experiments (Fig. 7).
If D
R
> 1, then the maximum runout exceeded that of the
control experiments with no entrainment.
DISCUSSION
CONTROLS ON ENTRAINMENT
In our experiments, bed sediment entrainment by
overriding debris flows occurred through rapid pro-
gressive downward scour, rather than by mass failure
at depth. Progressive scour by debris flows has also
been documented in field settings (b
eRGeR
et alii,
2010). It is possible, however, that very thin, finite-
thickness layers of bed sediment could have failed in
rapid succession without detection in our experiments,
because the vertical spacing of our sensors typically
was ~4 cm. Nevertheless, initial failure did not com-
mence at the base of the bed sediment.
Our experiments revealed a remarkable sensitivity
of entrainment to the water content of the bed sediment.
Wet sediments (here θ > 0.22) responded to debris-flow
loading with rapidly elevated pore-fluid pressures that
promoted entrainment, whereas drier sediments did not
(Figs. 3 and 5). This acute sensitivity to bed-sediment
Fig. 7 - Normalized maximum debris-flow runout dis-
tance,
D
R
(runout distance relative to that of the
control experiments), as a function of bed-sedi-
ment volumetric water content, θ
Fig. 8 - Peak basal pore-pressure ratio, λ (= p/σ), as a func-
tion of bed-sediment volumetric water content, θ
background image
ENTRAINMENT OF BED SEDIMENT BY DEBRIS FLOWS: RESULTS FROM LARGE-SCALE EXPERIMENTS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
373
CONCLUSIONS
Using a series of well-controlled, large-scale ex-
periments, we investigated entrainment of bed sedi-
ment by overriding debris flows. Results from our
experiments support the following conclusions:
(1) Sediment entrainment is very sensitive to the vo-
lumetric water content of the bed sediment. Wet-
ter sediment is readily entrained, whereas drier
sediment is not.
(2) Entrainment occurs through rapid (5-10 cm/s)
progressive downward scour rather than by mass
failure at depth.
(3) Rapid loading by an overriding debris flow quic-
kly increases pore-fluid pressures within loose,
wet bed sediment, typically increasing basal pres-
sures to nearly lithostatic levels.
(4) Flows that entrain wet sediment can travel faster
and farther, and can be more hazardous, than
flows without entrainment. Rapid elevation of
pore-fluid pressures and the ensuing reduction of
intergranular friction (to near zero) within the bed
sediment facilitate this behavior.
ACKNOWLEDGEMENTS
We thank Kelly Swinford, Roger Denlinger, Scott
Henderson, David George, Cate Fox-Lent, Jeff Coe,
Bill Schulz, Brian McArdell, and Catherine Berger
for their assistance in performing entrainment ex-
periments. We also thank Scott McCoy and Kevin
Schmidt for helpful reviews.
IMPLICATIONS FOR DEBRIS-FLOw HAZARDS
Experimental debris flows that entrained wet
bed sediment traveled faster and farther than control
flows without bed sediment. The combination of in-
creased speed and flow volume implied increased flow
momentum. Simple physical reasoning dictates that
entraining sediment adds flow mass with zero veloc-
ity, which should reduce flow speed if momentum is
conserved and frictional resistance remains the same
(i
veRson
et alii, 2011). This behavior was clearly evi-
dent when flows encountered dry bed sediment and
slowed. On the other hand, in the wet-bed sediment
experiments, elevated pore-fluid pressures in the bed
sediment diminished frictional resistance (to almost
zero) and stimulated growth of both flow mass and
speed. This positive feedback promoted sustained en-
trainment and further growth. Increased flow speed
likely resulted from the development of a steeper and
deeper debris-flow front, as documented in our video
recordings. These processes combined to generate
faster flows with longer runouts (i
veRson
et alii, 2011).
Hazards may increase when debris flows entrain wet
bed sediment and travel faster and further. Flows that gain
mass commonly have more destructive impact force and
inundate larger areas while delivering more sediment
downstream. Estimating the likelihood of sediment en-
trainment in a natural channel prior to a debris flow may
be difficult, but mapping the distribution and quantity of
saturated (or potentially saturated) channel sediment ca-
pable of being liquefied when loaded by overriding debris
flows could aid regional debris-flow hazard analyses.
REFERENCES
b
enda
L. (1990) - The influence of debris flows on channels and valley floors in the Oregon Coast Range, USA. Earth Surface
Processes and Landforms, 15: 457-466.
b
eRGeR
C., m
C
a
Rdell
b.w., f
RtisCHi
b. & s
CHluneGGeR
f. (2010) - A novel method for measuring the timing of bed erosion
during debris flows and floods. Water Resources Research, 46, doi: 10.1029/2009WR007993.
b
eRti
m., G
enevois
R., l
a
H
usen
R.l., s
imoni
a. & t
eCCa
P.R. (2000) - Debris flow monitoring in the Acquabona watershed on the
Dolomites (Italian Alps). Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, 26(9): 707-715.
b
eRti
m. & s
imoni
a. (2005) - Experimental evidences and numerical modelling of debris flow initiated by channel runoff.
Landslides, 2: 171-182.
b
Reien
H., f.v. d.b., e
lveRHoi
a. & H
oeG
k. (2008) - Erosion and morphology of a debris flow caused by a glacial lake outburst
flood, Western Norway. Landslides, 5: 271-280.
C
annon
s.H., k
iRkHam
R.m. & P
aRise
m. (2001) - wildfire-related debris-flow initiation processes, Storm king Mountain,
Colorado. Geomorphology, 39: 171-188.
C
annon
s.H. & R
eneau
s.l. (2000) - Conditions for generation of fire-related debris flows, Capulin Canyon, New Mexico. Earth
Surface Processes and Landforms, 25: 1103-1121.
C
oe
J.a., k
inneR
d.a. & G
odt
J.w. (2008) - Initiation conditions for debris flows generated by runoff at Chalk Cliffs, central
background image
M.E. REID, R.M. IVERSON, M. LOGAN, R.G. LAHUSEN, J.w. GODT & J.P. GRISwOLD
374
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
Colorado. Geomorphology, 96: 270-297.
G
odt
J.w. & C
oe
J.a. (2007) - Alpine debris flows triggered by a 28 July 1999 thunderstorm in the central Front Range,
Colorado. Geomorphology, 84: 80-97.
G
utHRie
R.H., H
oCkin
a., C
olQuHoun
l., n
aGy
t., e
vans
s.G. & a
yles
C. (2010) - An examination of controls on debris flow
mobility: Evidence from coastal British Columbia. Geomorphology, 114: 601-613.
H
unGR
o. & e
vans
s.G. (2004) - Entrainment of debris in rock avalanches: An analysis of a long run-out mechanism. Geological
Society of America Bulletin, 116(9/10): 1240-1252, doi: 10.1130/B25362.1.
H
unGR
o., m
C
d
ouGall
s. & b
ovis
m. (2005) - Entrainment of material by debris flows. In: J
akob
m. & H
unGR
o. (eds.) -
Debris-flow Hazards and Related Phenomena: 135-158, Springer, Berlin.
H
utCHinson
J.n. & b
HandaRi
R.k. (1971) - Undrained loading, a fundamental mechanism of mudflows and other mass
movements. Geotechnique, 21: 353-358.
i
veRson
R.M. (1997) - The physics of debris flows. Reviews of Geophysics, 35: 245-296.
i
veRson
R.M. (2005) - Regulation of landslide motion by dilatancy and pore-pressure feedback. Journal of Geophysical Research,
110: doi: 10.1029/2004JF000268.
i
veRson
R.m., l
oGan
m., l
a
H
usen
R.G. & b
eRti
m. (2010) - The perfect debris flow? Aggregated results from 28 large-scale
experiments. Journal of Geophysical Research, 115(F03005), doi: 10.1029/2009JF001514.
i
veRson
R.m., R
eid
m.e., i
veRson
n.R., l
a
H
usen
R.G., l
oGan
m., m
ann
J.e. & b
Rien
d.l. (2000) - Acute sensitivity of
landslide rates to initial soil porosity. Science, 290(5491): 513-516.
i
veRson
R.m., R
eid
m.e. & l
a
H
usen
R.G. (1997) - Debris-flow mobilization from landslides. Annual Review of Earth and
Planetary Sciences, 25: 85-138.
i
veRson
R.m., R
eid
m.e., l
oGan
m., l
a
H
usen
R.G., G
odt
J.w. & G
Riswold
J.P. (2011) - Positive feedback and momentum
growth during debris-flow entrainment of wet bed sediment. Nature Geoscience, 4, doi: 10.1038/NGEO1040.
k
izito
f., C
amPbell
C.s., C
amPbell
G.s., C
obos
d.R., t
eaRe
b.l., C
aRteR
b. & H
oPmans
J.w. (2008) - Frequency, electrical
conductivity and temperature analysis of a low-cost capacitance soil moisture sensor. Journal of Hydrology, 352: 367-378.
l
aRsen
i.J., P
edeRson
J.l. & s
CHmidt
J.C. (2006) - Geologic versus wildfire controls on hillslope processes and debris flow
initiation in the Green River canyons of Dinosaur National Monument. Geomorphology, 81: 114-127.
l
oGan
m. & i
veRson
R.m. (2007) - Video documentation of experiments at the USGS debris-flow flume, 1992-2009. U.S.
Geological Survey Open-file Report 2007-1315, version 2.0.
m
C
a
Rdell
b.w., b
aRtelt
P. & k
owalski
J. (2007) - Field observations of basal forces and fluid pore pressure in a debris flow.
Geophysical Research Letters, 34, doi: 10.1029/2006GL029183.
m
C
C
oy
s.w., k
ean
J.w., C
oe
J.a., s
taley
d.m., w
asklewiCz
t.a. & t
uCkeR
G.e. (2010) - Evolution of a natural debris flow: In situ
measurements of flow dynamcis, video imagery, and terrestrial laser scanning. Geology, 38(8): 735-738, doi: 10.1130/G30928.1.
P
aPa
m., e
GasHiRa
s. & i
toH
t. (2004) - Critical conditions of bed sediment entrainment due to debris flow. Natural Hazards and
Earth System Sciences 4(3): 469-474.
P
ieRson
t.C., J
anda
R.J., t
HouRet
J.-C. & b
oRReRo
C.a. (1990) - Perturbation and melting of snow and ice by the 13 November
1985 eruption of Nevado del Ruiz, Columbia and consequent mobilization, flow and deposition of lahars. Journal of
Volcanology and Geothermal Research, 41: 17-66.
R
iCkenmann
d., w
ebeR
d. & s
tePanov
b. (2003) - Erosion by debris flows in field and laboratory experiments. In: R
iCkenmann
d.
& C
Hen
C.-l. (eds.) - Debris-flow Hazards Mitigation: Mechanics, Prediction, and Assessment: 883-894, Millpress, Rotterdam.
s
assa
k., k
aiboRi
m. & k
iteRa
n. (1985) - Liquefaction and undrained shear of torrent deposits as the cause of debris flows. In:
t
akei
A. (ed.) - Proceedings of the International Synposium on Erosion, Debris Flows and Disaster Prevention: 231-236,
The Erosion-control Engineering Society, Japan, Tokyo.
s
assa
k. & w
anG
G. (2005) - Mechanism of landslide-triggered debris flows: Liquefaction phenomena due to the undrained loading
of torrent deposits. In: J
akob
m. & H
unGR
o. (eds.) - Debris-flow Hazards and Related Phenomena: 81-104, Springer, Berlin.
t
akaHasHi
T. (1978) - Mechanical characteristics of debris flow. Journal of Hydraulics Division, ASCE, 104(HY8): 1153-1169.
t
akaHasHi
T. (1991) - Debris Flow. IAHR Monograph. A. A. Balkema, Rotterdam
w
anG
G., s
assa
k. & f
ukuoka
H. (2003) - Downslope volume enlargement of a debris slide-debris fow in the 1999 Hiroshima,
Japan, rainstorm. Engineering Geology, 69: 309-330.
Statistics