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Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
845
DOI: 10.4408/IJEGE.2011-03.B-092
AN ESTIMATE OF THE SEDIMENTS VOLUME ENTRAINABLE BY DE-
BRIS FLOW ALONG STROBEL AND SOUTH PEZORÌES CHANNELS
AT FIAMES (DOLOMITES, ITALY)
M. DEGETTO
(*)
, G. CRUCIL
(*)
, A. PIMAZZONI
(*)
, C. MASETTO
(*)
& C. GREGORETTI
(*)
(*)
University of Padua - Department of Land and Agro-Forest Environment – Padua, Italy
(hyperconcentrated flow) or a debris flow event.
In literature there are descriptions of different
methodologies applied to different environments and
contexts for the estimation of sediment volumes mobi-
lized by debris flow. These methodologies, for streams
or torrents characterized by debris flows, can be divided
into two groups: the first, empirical or semi-empirical,
carries out a statistical analysis of historical data of
measured sediment volumes in the deposition area
(d’a
Gostino
, 1996; b
ovis
& J
akob
, 1999; R
iCkenmann
,
1999; b
ianCo
& f
Ranzi
, 2000; d’a
Gostino
& m
aRCHi
,
2001; b
RoCHot
et alii, 2002; G
aRtneR
et alii, 2008),
while the second is based on geomorphological survey,
verifying the availability of sediment along the chan-
nel routed by debris flow (H
unGR
et alii, 1984; t
HouRet
et alii, 1995; s
PReafiCo
et alii, 1999; b
ovis
& J
akob
,
1999; b
RoCHot
et alii, 2002; d’a
Gostino
& m
aRCHi
,
2003; G
aRtneR
et alii, 2008; s
anti
et alii, 2008).
There are many factors involved in defining the
volumes that are mobilized during a flood event: the ba-
sin and stream’s slope, the drainage area and in particu-
larly that part which is a potential source of sediments,
the intensity of rainfall and thus runoff, the land cover,
the type of sediment (cohesive or not), the geology and
stratigraphy of soil layers, and many others. However,
in a geomorphological approach, some of these become
more important and require a very detailed survey.
From an operational standpoint, the geomorpho-
logical approach must be economical, fast, safe for
technicians but also sufficient to define with some pre-
ABSTRACT
The area of Fiames is located on a narrow and
flat valley, 2 km north to Cortina d’Ampezzo, and is
bounded on the right side by the Pomagagnon and
Pezorìes peaks. At the transition between rock vertical
cliffs and talus, about twenty debris channels originate
and affect the talus till the bottom of the valley. The
Strobel and South Pezorìes channels were recently
routed by debris flows in 2004 and 2006. Field sur-
veys, topographical and geo-morphological measure-
ments were carried out to recognize the sediments vol-
ume that the debris flow can entrain during triggering
and routing phases. The estimate of the erodible sedi-
ment volume was obtained through the measurements
of the geo-morphological and sediments features of
source areas including their locations (channel bank
or bottom). The resultant estimate can help in the de-
sign of the input debris flow hydrographs for dynamic
modelling of debris flow and retain basins.
K
ey
words
: sediment volume, geo-morphological measure-
ments, triggering, debris flow, field survey.
INTRODUCTION
Land management, using risk or hazard maps,
requires knowledge of the volumes of water and sedi-
ments mobilized during a flood events. So, the estima-
tion of sediment volumes potentially trasportable in a
basin, during particularly intense rainfall, is the start-
ing point for analyzing an intense sediment transport
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M. DEGETTO, G. CRUCIL, A. PIMAZZONI, C. MASETTO & C. GREGORETTI
846
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
channel, that runs along the intersection of two fans
with a meandering path (Fig. 2).
TEST BED AREA GEO-LITHOLOGICAL CHA-
RACTERISTICS
Both channels born at the transition between
rock walls and talus and run on a non-cohesive soil
with limestone scree. The area covered by vegetation
is very small and is restricted to Mugo Pine (Pinus
mugo
) upstream and, by Scots Pine (Pinus sylvestris)
and Mugo Pine, downstream.
From the geological point of view, the study area
is covered by a pre-Quaternary formations in an in-
terval between the Carnian and Early Miocene. The
stratigraphic succession, from oldest to most recent,
is as follows:
· Saint Cassian formation with intercalations of marls,
shales and calcarenites;
· Cassian Dolomite that represents the massive white-
gray crystalline dolomite and is the basis of the
Pomagagnon and Pezorìes peaks;
· Durrenstein formation (upper Carnian) consists of
white dolomite with sandstone purposes, siltstones
and silty limestones;
· Raibl formation consists of sandstone and marl and
thin intercalations of gypsum;
· Main dolomite consisting of white and gray massive
dolomite representing the most developed outside
of the cliffs;
From a geomorphological point of view, we can
say that the weathering of limestone and dolomite
develops a thick debris layer, formed by particle size
ranging from sand to large boulders, which is easily and
often entrained by debris flows during the roaring storm
from July to October. Both the channels were routed by
debris flows the 19
th
of July 2004 and the 5th July of
2006 (G
ReGoRetti
& d
alla
f
ontana
, 2008).
cision the areas and volumes of sediment.
This paper will present a methodology adopted
for geomorphological field surveys, taking inspiration
from those proposed by some authors (H
unGR
et alii,
1984; t
HouRet
et alii, 1995) but differs from these for
the topographic approach and hydraulic considerations.
This methodology will be applied to estimate the vol-
ume of sediments in two debris flow channels at Fi-
ames, Eastern Dolomites. The results will be compared
with the volumes obtained from application of empiri-
cal and semi-empirical formulas
GENERAL SETTING
TEST BED AREA LOCATION.
The test bed area is in north to Cortina d’Ampezzo
(upper Boite River Valley, Eastern Dolomites, Italy)
on the western side of Pomagagnon and Pezorìes
peaks (Fig. 1).
Two channels, routed by debris flow, were sur-
veyed in summer 2010: “Strobel” channel (c06),
which runs almost linearly on a well developed fan,
and “South Pezorìes” channel (c07), north to Strobel
Fig. 1 - Test bed area: Fiames (Eastern Dolomites)
Fig. 2 - Overview of the two debris flow channels at Fia-
mes
Tab. 1 - Morphometric characteristics of channel c06
“Strobel”
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AN ESTIMATE OF THE SEDIMENTS VOLUME ENTRAINABLE BY DEBRIS FLOW ALONG STROBEL AND SOUTH PEZORÌES CHAN-
NELS AT FIAMES (DOLOMITES, ITALY)
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
847
the source areas of sediment. Figure 5, with a clas-
sic V-shape, shows a large bank erosion, fine debris
and boulders in riverbed, residues left by the tails of
previous debris flows. Figure 6 shows the channel
enlargement degree and the massive accumulation of
detritus consisting of gravel and small pebbles
Very similar is the situation for the second chan-
nel, South Pezorìes (Tab. 2), with the difference that
the channel runs along a more tortuous path charac-
terized by two wide bends. Even in this case the av-
erage slope of the channel is quite high (usually more
than 35%). In respect to the Strobel channel, the stor-
age area is very long and narrow (mean slope 32%)
because debris flows tend to entrench too much with-
TEST BED AREA MORPHOMETRIC CHARAC-
TERISTICS
The morphometric analysis of Strobel channel
(Tab. 1) shows that slopes along the channel are very
high (up to 48%): the deposition area is generally
very limited in length and is positioned at the end
of the fan (mean slope 31%), at its confluence with
the Boite river where the slope decrease too. Often,
debris flows can deposit in the upper part of the chan-
nel (slopes between 40-48%) due to a strong enlarge-
ment of the channel bed: indeed, it’s not unusual to
find large deposits of debris flow with slopes larger
than 40%. Strobel channel is very small in length
(about 1 km from the source at the end of the fan);
the catchment area can be divided into two parts: the
upstream drainage area closed to triggering section
of the debris flow (approximately 0.16 km
2
) almost
in rock and, downstream the routing area, that is lim-
ited to the path occupied by the flow, consist of scree
with some small piece of outcrop rock
The catchment area has a very small portion of
plant cover composed exclusively of Mugo pine.
Figure 3 shows the drainage basin closed at trig-
gering section and the fan area incised by Strobel
channel. The basin has undergone a thorough hy-
drological and morphological analysis by applying a
numerical model on a GIS support (G
eoGRaPHiC
i
n
-
foRmation
s
ystem
– a
d
bt
ool
b
ox
, 2010): a crucial
problem, when using a distributed hydrologic model,
is that the drainage area on the downstream part of
the fan allows more outlets preventing the software
to close the catchment area properly.
In the following, Figures 4, 5, 6 show three sec-
tions of the Strobel channel relative to the triggering
area, to the middle part and downstream respective-
ly: in the upstream part (Fig. 4) it can be observed
the large detrital grains and clusters that constitute
Fig. 3 - View of the “Strobel” channel (c06)
Fig. 4 - Upstream part of “Strobel” channel (c06)
Fig. 5 - Middle part of “Strobel” channel (c06)
Fig. 6 - Downstream part of “Strobel” channel (c06)
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M. DEGETTO, G. CRUCIL, A. PIMAZZONI, C. MASETTO & C. GREGORETTI
848
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
ume, potentially erodible and transportable during an
event, should be determined through observations, and
hydrologic and hydraulic considerations.
The methods proposed by other authors provide
the definition of a channel type (eg. A, B, C, D, ..) and
a minimum or a range of values for yield rate (m
3
/m)
that is distributed along all the channel length (H
unGR
et alii, 1984; s
PReafiCo
et alii, 1999; b
RoCHot
et alii,
2002). The proposed values are the result of assess-
ments, in torrents, which bring the geological sub-
strate, the average channel slope and some qualitative
stability conditions (eg. stable, unstable, eroded,...)
but, anyway, they don’t consider directly the hydro-
logical and hydraulic aspects.
The approach taken in this work can be summa-
rized in the following six stages:
- before carrying out a field survey, it’s necessary to
compute the runoff hydrograph corresponding to
out overflowing the banks. South Pezorìes channel
is very small like Strobel channel and the basin can
also, in this case, divided in two parts: the upstream
drainage area closed to triggering section of debris
flow (approximately 0.08 km
2
) is mostly rocky with
the presence of Mugo pine (20%). Downstream, in
the routing area, there is only scree, and at the foot
of the fan there are also Mugo pine and Scots pine.
Figure 7 shows the drainage basin closed at
triggering section and the fan area incised by South
Pezorìes channel.
Also in this case, the hydrological analysis presents
several problem for the inability to define a unique
flow path along the fan. Figg. 8, 9 and 10 show three
representative sections of the South Pezorìes channel:
in the upstream part (Fig. 8) it can be observed that
there are boulders and large detrital areas that are the
source areas of sediments. Figure 9, with a classic V-
shape, shows a narrow bank erosion, and a large sedi-
ment deposition. In the downstream part (Fig. 10) it is
evident the channel minor enlargement rate andm the
massive accumulation of detritus consisting of gravel
and small pebbles also in this case.
METHODOLOGY FOR THE ESTIMA-
TION OF SEDIMENT VOLUMES
The geomorphological approach emphasizes the
role of the field survey in the sense that sediment vol-
Tab. 2 - Morphometric characteristics of channel c07
“South Pezorìes”
Fig. 7 - View of “South Pezorìes” channel (c07)
Fig. 8 - Upstream part of “South Pezorìes” channel (c07)
Fig. 9 - Middle part of “South Pezorìes” channel (c07)
Fig. 10 - Downstream part of “South Pezorìes” channel
(c07)
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AN ESTIMATE OF THE SEDIMENTS VOLUME ENTRAINABLE BY DEBRIS FLOW ALONG STROBEL AND SOUTH PEZORÌES CHAN-
NELS AT FIAMES (DOLOMITES, ITALY)
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
849
error less than 0.2 m) and TOPCON system,
rover and base, with vertical error less than
0.02 m used on storage areas;
▪ laser rangefinder to measure the lengths and
slopes of the source areas located along the
banks or in the slope overhanging the banks
(eg. local landslides).
▪ a camera to photograph each source area: you
must have a feedback image for data analysis
that, some times, is made long after the event;
▪ sampler for sediment grain sizes (numeral method);
▪ sheets, prepared ‘ad hoc’, for the survey data of
source.areas of sediment.
- fourth step is to identify source areas of sediment,
homogeneous for litho-morphological, geotechnical
characteristics and for erosion phenomena (erosion/
deposition) These areas will be corrected or modi-
fied during data processing;
- fifth step is the collection of soil samples along the
channel for geotechnical analysis (eg. grain size
with weight method, cohesion, friction angle, etc.)
- sixth step is the digital input of all the collected data
in a GIS database in order to have georeferenced in-
formation and carry out the calculations. After that,
it’s possible to make all the computations regarding
some return periods (2, 5, 10, 100, 200 years) and
transform it in a debris flow hydrograph. Runoff is
computed by the hydrological model proposed by
G
ReGoRetti
& d
alla
f
ontana
(2008) which runs
on GIS platform (AdBToolBox, 2010). The trans-
formation of runoff hydrograph into debris flow hy-
drograph is carried out using the triggering model
of AbBToolBox (see also d
eanGeli
et alii, 2010).
The computed peak discharge of debris flow is then
transformed in an equivalent debris flow depth us-
ing the formula proposed by H
unGR
(1984). In this
way it’s possible to get an idea of debris flow dis-
charge, strength and velocity along the channel (see
formulas in HunGR et alii 1984). Present meth-
odology assumes a correlation between the volume
mobilized by a debris flow and the return time of the
runoff that trigger it. The initial hypothesis is that
the increase of precipitation (related to the return
period) in mountainous areas with steep slopes cor-
responds to an increase in runoff and, consequently,
of its erosion capacity. The increase of erosion ca-
pacity means an higher mobilized solid volume. The
results are clearly approximated but are very useful
to assess the erosive capacity of debris flow;
- the second step is the analysis of the geo-lithological
and geomorphological mapping corresponding to
the area with technical data available in literature.
This work provides information about cohesion,
permeability, stability, erodibility of debris piles and
rock structures. All the maps data should be checked
by a preliminary survey of the entire basin. The pre-
liminary survey allows the knowledge of the real
situation which can help in the planning the follow-
ing surveys;
- third step is the field analysis along the channel. The
channel must be walked up to its beginning (the lim-
it beyond which point you can no longer walk) and
the main morphological features investigated. From
the upper point, the channel is walked down: topo-
graphic and morphological measurement are carried
out using the following instruments.
▪ GPS (Global Position System) to make a detailed
survey into the channel to improve the DEM
building. GPS was used also to capture several
points for geo-referencing the border of the
source areas (Fig. 11). We used GRS-1 TOP-
CON GPS with real time differential correction
(horizontal error less than 0.03 m and vertical
Fig. 11 - Measured GPS points in South Pezorìes channel
(a), in Strobel channel (b,) a detailed view (c) of
source sediment area and its many GPS points and
different homogeneous source sediment areas in
Strobel channel with proposed methodology
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M. DEGETTO, G. CRUCIL, A. PIMAZZONI, C. MASETTO & C. GREGORETTI
850
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
the basin characteristics and the source areas and
then, the estimation of sediments volume.
Figure 11 shows the GPS points measured in field
survey: 983 points were taken in South Pezorìes chan-
nel (Fig. 11.a) and 1031 points were measured in Strobel
channel (Fig. 11.b). The distribution of measured GPS
points allows us to build a DEM of the channels and of
the source sediment areas (Fig. 11.c and 11.d).
The survey must proceed from top to downstream
because, during the ascent, the operators must careful-
ly observe the channel, banks, sediment in the chan-
nel, the erosions or the landslides present along the
channel, in order to define with some precision homo-
geneous traits of source area (not the channel; this as-
pect differs from that proposed by previous authors).
In fact, we assume that the source area of sediment
should be homogeneous for geomorphological char-
acteristics and phenomena to which is subjected (ero-
sion, deposition) and not for the trait of channel. In a
same channel trait we can have one or more source ar-
eas. In fact in a channel trait we can distinguish one or
more source areas of sediment on the right bank, idem
on the left bank and idem on the bottom (Fig. 11.d).
This methodology is original and differs from
those proposed in literature; the formula proposed by
previous authors has the following form (H
unGR
et
alii, 1984; s
PReafiCo
et alii, 1999; b
RoCHot
et alii,
2002; d’a
Gostino
& m
aRCHi
, 2003):
where n = source areas; V
i
= erodible sediment vol-
ume of the single homogeneous trait of channel; V
tot
= the total volume. The volume V
i
is the result of the
product of the following factors: a reduction coef-
ficient k, the thickness of erodible layer d (m), the
bottom width b (m) and the length of the homoge-
neous channel trait L (m). The product of the last
two parameters is the erodible area in homogeneous
channel trait A = b·L (m
2
).
We propose the following relationship for the
sediment volume estimation:
in which the total volume V
tot
is obtained by the
product of As
i
, that is the source area numbered i
along the channel from upstream (m
2
), with the cor-
responding thickness d
i
.
The thickness of the sediment layer in the source
area d
i
is determined through the following procedure:
- computation of the surface delimited by the GPS
points which border it;
- estimation of the minimum, average and maximum
values of slope of the source area (estimated di-
rectly in field or more accurately using GIS if GPS
points are enough);
- estimation of the impact angle, i.e. the angle be-
tween the prevailing direction of flow and the
surface area (even this estimation can be done
directly in the field or more precisely by GIS op-
erations);
- estimation of the average slope of the channel trait
adjacent to source area;
- computation of the average bottom width;
- estimation, with the most possible accuracy, of
the debris flow depth, velocity, force and impact
force (H
unGR
et alii, 1984) based on elaborated
field data collection, for events with different re-
turn times in order to define the erodible thick-
ness for different situations.
The first two operations provide the range of de-
bris thickness of the source area while the remain-
ders are necessary to define the specific thickness
corresponding to the flow erosion power. In fact, we
distinguish two thickness of source area: the first,
called erodible depth (d
e
) represents the erodible
thickness by an event with return period of ten years;
the second, called potentially erodible depth (d
p
) rep-
resents the erodible depth for an event of 100 years
return time. Furthermore, at the purpose of limiting
the subjectivity anddiscretion, each of the thickness
was further subdivided into aminimum, av erage and
maximum thickness.
The parameters that affect the determination of
the erodible or potentially erodible thickness are the
following:
- the erodible thickness increases with bank slope (up
to 40°) while, for larger bank slope values there
is a slight and progressive reduction of thickness.
- flow erosion power: it is evaluated through the av-
erage slope of the channel, the debris flow depth,
the impact angle between flow and source area, the
cross section of channel. The erodible thickness in-
creases with the increasing of impact angle and flow
(1)
(2)
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AN ESTIMATE OF THE SEDIMENTS VOLUME ENTRAINABLE BY DEBRIS FLOW ALONG STROBEL AND SOUTH PEZORÌES CHAN-
NELS AT FIAMES (DOLOMITES, ITALY)
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
851
2006 on both the channels, being distinguishable de-
posits, there were carried out measurements of sedi-
ment deposit thickness in the terminal part of the fan.
In this case, for each point detected by GPS in the stor-
age area, it was evaluated the thickness of the deposit.
The estimation of sediment deposit volumes is carried
out through the difference of the DEM obtained from
the surface of the GPS points and the subsurface cor-
responding to the quote of GPS points minus the es-
timated debris thickness. The areal average difference
between the two surfaces multiplied by the surface
area itself provides the overall volume of the deposit
Volumes obtained by topographic survey of sedi-
ment deposit after 2006 event for Strobel and South
Pezorìes depositional fans are. 3415 and 3058 m
3
re-
spectively. These values can be compared with those
computed by equation (2) to check the reliability of
the proposed methodology. In the case of the Strobel
channel the deposited volume (3415 m
3
) has an inter-
mediate value between the mean erodible (2908 m
3
)
and the maximum erodible volumes (4705 m
3
); In the
case of the South Pezorìes channel the deposited vol-
ume (3058 m
3
) coincides with the maximum erodible
volume (3034 m
3
). These results assure the reliability
of the proposed methodology.
COMPARING THE RESULTS WITH SEDI-
MENT VOLUMES COMPUTED BY EMPI-
RICAL RELATIONSHIPS OF PREVIOUS
AUTHORS
The method proposed and applied in this work
tries to compensate on the one hand the economic as-
pect and from another the quality of data (that must
be georeferenced) in order to make findings with past
events and/or future, ones.
The volumes obtained by present geomorphologi-
cal methodology, are then compared with those obtained
from the application of empirical or semi-empirical re-
lationships available in literature. In Table 4, the rela-
tionships are listed with their references. These formulas
use morphometric parameters and indices that must be
derived for each of the catchments shown in figure 3 and
7. The formulas are presented in the following:
discharge (and its related parameters, eg. velocity,
cross section, water level, impact force, etc.).
- the susceptibility to erosion (H
unGR
et alii, 1984):
it is evaluated considering vegetation cover, grain
size, sediments cohesion, location of the area,
the causes which leads to instability and stability
conditions. The erodible thickness increases from
soils covered with vegetation to bare soil, from
cohesive to not cohesive sediments, from large
to small grain size. The instability for foot ero-
sion produces more sediment than an uniformly
distributed erosion and, erodibility of deposited
sediments is easier than surface bank erosions.
The influence of these parameters on the erodible
thickness has been overall considered. In other words
the erodible depth is subjectively estimated consider-
ing all the aspect above. The average debris thickness
computed by the first two operation is assumed as the
average thickness d
e m.
This value is then modified ac-
cording to the influence of the parameters listed above
to have the erodible and the potential erodible depths.
ESTIMATION OF SEDIMENT VOLUMES
FOR THE SURVEYED CHANNELS USING
THE PROPOSED METHODOLOGY
The sediment source areas number 14 for the
Strobel channel and 11 for the South Pezorìes channel.
Their surfaces range between 194 and 2167 m
2
for the
first channel and between 108 and 576 m
2
for the sec-
ond channel. The corresponding average erodible thick-
ness ranges between 0.1 and 0.7 m in the case of Strobel
channel and between 0.2 and 1.0 m for South Pezorìes
channel.
The values of the erodible and potential erodible
depths were estimated for all the source areas in the
two surveyed channels and the corresponding sediment
volumes of the numbered source areas were computed
using equation (2). The results are shown in Table 3.
For the debris flow event that occurred in July
Tab. 3 - Erodible sediment volumes (m
3
) obtained using
equation (2)
(3)
(4)
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M. DEGETTO, G. CRUCIL, A. PIMAZZONI, C. MASETTO & C. GREGORETTI
852
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
The values computed according to equations (3) to
(16) are in a wide range of value: from 4187 to 40098
m3 in the case of Strobel channel and from 1750 to
44296 m
3
in the case of South Pezorìes channel. The av-
erage erodible volume Ve m computed for the Strobel
channel is always overstimated by equation (3)-(16)
while that of South Pezorìes channel not. In this last
case the value of V
e m
nearly coincides with that given
by equation (6) given by d’a
Gostino
(1996). The av-
erage potential erodible volume V
p m
computed for the
Strobel channel is next to value given by equation (15)
given by b
ianCo
& f
Ranzi
(2000) while that of South
Pezorìes is next to the values computed by equation
(3) given by Kronfellner-Kraus (1984). These results
are of no use for a comparison due to their high vari-
ability explainable by the lack of homogeneity in data
used by the previous authors. The lack of homogeneity
mainly regards the use of data of volumes deposited by
debris flows corresponding to different return periods
of runoff that triggered them. There are two confirma-
tions of this, one direct and the other one indirect. The
direct is that equation (16) obtained by R
iCkenmann
&
k
osCHni
(2010) using data with the same return period,
approximates the maximum erodible volume values of
both the channels. The indirect confirmations is given
by the results of equation (15) that imputes larger vol-
umes to the South Pezorìes channel characterized by
minus sediment production.
The fact that equation (16) provides a set of val-
ues somehow in agreement with those computed here
could be a confirm of the reliability of the proposed
methodology.
CONCLUSIONS
A new methodology for the estimation of sedi-
ment volume that can be mobilized by debris flows
is presented and used in two channels of Dolomites
(Italy). Both the channels were surveyed and the
source area of sediments were identified and measured
(surface and thickness). These data were used to pro-
vide an estimate of the erodible sediment volumes in
the two channels. The reliability of this approach was
checked by comparing the results with the deposited
volumes due to antecedent debris flows and with the
results of an empirical equation obtained through data
characterized by the same return period.
Nevertheless, this approach should be tested in oth-
er channels toassess its validity.
where k
1
and k
2
are coefficients relative to sediment pro-
duction and for the surveyed channels assume the val-
ues 1150 and 0.014 respectively; A is the catchment area
(km
2
); i is the average slope along erodible channel (%);
IG is the geological index (1-5) that for the surveyed
channel assumes the value 1.66; IT is an index depend-
ing on the mass transport phenomenon (debris flows =
1, hyperconcentrated = 2 and bed-load =3); Igv is a geo-
lithological index (1-6) that for the surveyed channel is
3 (dolomite rock and scree). In the equations (12) and
(13)
i is expressed in m/m.
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
(15)
(16)
Tab. 4 - Erodible sediment volumes (m
3
) obtained by em-
pirical and semiempirical formulas application
background image
AN ESTIMATE OF THE SEDIMENTS VOLUME ENTRAINABLE BY DEBRIS FLOW ALONG STROBEL AND SOUTH PEZORÌES CHAN-
NELS AT FIAMES (DOLOMITES, ITALY)
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
853
structure related to mountainous hazards in a chang-
ing climate), within the Alpine Space 2007-2013
project. The writers wishes to thank the reviewers
for they useful comments.
ACKNOWLEDGEMENTS
This research has been financially supported by
European grant PARAmount (imProved Accessibil-
ity: Reliability and security of Alpine transport infra-
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