E3S Web of Conferences 415, 04001 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341504001

Debris-flow activity and sediment dynamics in the landslideinfluenced Lattenbach catchment, Austria
Philipp Aigner1*, Erik Kuschel2, Leonard Sklar3, Christian Zangerl2, Markus Hrachowitz4, Tjalling de Haas5, Johannes
Huebl1, and Roland Kaitna1
1Inst. of Mountain Risk Eng., Dept. of Civil Eng. and Natural Hazards, BOKU Vienna, Peter-Jordan-Straße 82, 1190 Wien
2Inst. of Applied Geology, Dept. of Civil Eng. and Natural Hazards, BOKU Vienna, Peter-Jordan-Straße 82, 1190 Wien
3

Dept. of Geography, Planning and Environment, Concordia University,1455 De Maisonneuve Blvd. W. Montréal, QC H3G 1M8

4Dept. of Civil Engineering, TU Delft, Stevinweg 1 / PO-box 5048, 2628 CN Delft / 2600 GA Delft1
5Dept. of Physical Geography, Utrecht University, Princetonlaan 8a, 3584 CB Utrecht

Abstract. Deep seated landslides are common phenomena in Alpine areas. In case of a direct connectivity
with the channel system, the catchment’s sediment yield and the probability of other forms of mass wastingprocesses such as debris flows may be increased significantly. Up to now, sediment dynamics related todeep-seated landslides and debris flows have not been quantified. The Lattenbach catchment (basin area 5,3km², relief 2134 m) in Grins (Tyrol, Austria), is an example for an active DF-site, where there isgeomorphological evidence of deep-seated landslide activity. In this study we shed light (1) on the locationand size of active landslides in the catchment, that may deliver sediment to the channel system. Furthermore,
we want to (2) quantify the contributed sediment volumes by these landslides (3) and estimate the exported
sediment by debris flow. We apply an image correlation algorithm to high resolution ALS and TLS terrain
models of derived over a period of 14 years to calculate surface movement rates within the catchment andlocate deep seated landslide activity. We further assess the sediment yield of these landslides to the channel
system and relate that with DF-volumes measured by a monitoring station at the catchment outlet. We findthat there are five deep-seated landslide bodies directly connected to the channel system in the catchment.
These are the largest source of sediment and significantly increases the overall sediment yield of thecatchment. Our study shall contribute to the limited knowledge about the importance of deep-seatedlandslides for sediment dynamics and debris-flow activity, as their presence is predicted to be more frequentin the wake of global warming.

1 Introduction
Deep-seated landslides are a common phenomenon
in Alpine areas [1]. Moving at speeds of less than one
meter per year, these mass wasting processes can beeasily overlooked and their influence on the sediment
dynamics underestimated as their appearance is lessobvious in nature than that of sudden, fast moving,
shallow landslides. The presence of such large mass
movements can significantly increase erosion rates [2]and thus the sediment yield from the catchment [3].
In case of a direct connectivity between the slowmoving material and the channel system, small shallow
failures at the intersection of the large landslide bodywith the channel (“inner gorge”) may be stochasticallytriggered by rainfall events to feed the channel withloose material. Subsequently, large amounts of sediment
may be relocated within the channel system during
periods of elevated discharge, with the potential toinitiate devastating debris flows or debris floods. The
volumes and timescales of these processes as well as
their importance for debris-flow initiation are not wellunderstood.

Expected changes of temperature and precipitation
pattern, as well as changes in high-mountain cryosphere,
deep-seated landslides are suspected to occur more
frequently in the coming decades [4,5]. To assessclimate change impact, it is very relevant to quantify thepotential amount of sediment contribution in affectedcatchments.
The Lattenbach catchment in Tyrol (Austria) is an
exceptionally well monitored site with a documentationof debris-flow activity dating back to 1900 and an
extensive monitoring carried out since 2005.
Geomorphological evidence indicates the existence ofdeep-seated landslides that may influence sediment
dynamics and debris-flow initiation. The focus of thisstudy is to (1) identify the location, size and speed ofactive landslides in the catchment, (2) assess the amountof material that is delivered to the channel system bythese landslides, and (3) compare this quantity with thedebris-flow exported volumes from the catchment.

* Corresponding author: philipp.aigner@boku.ac.at© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0(https://creativecommons.org/licenses/by/4.0/).

E3S Web of Conferences 415, 04001 (2023)
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https://doi.org/10.1051/e3sconf/202341504001

2 Study site

outlet, as the area upstream covers the all relevant
sediment sources and is the location of debris-flow
initiation.

The Lattenbach catchment is situated on the border ofthe northern calcareous Alps and the crystalline Alps in
Tyrol, Austria (Figure 1). The vertical relief amounts tomore than 2 km over 4.5 km map distance between theDawinkopf peak at 2,968 m and the confluence of theLattenbach and the river Sanna in the village of Pians at
858 m elevation. The total catchment area is about
5.3km². The monthly mean temperature ranges between-1.4 C° and 17.4 C° in the valley and between -5.2 C°and 6.1 C° on the Dawinkopf peak. Due to the shadingof the northern mountain range average annual
precipitation is low with around 750 mm.

3 Methods
3.1 Identification of active landslides
Since 2006 the Federal Government of Tyrol (Amt fürGeoinformation) repeatedly organizes airborne lidar(ALS) campaigns of the whole state area. TheLattenbach study catchment is covered in the surveys ofAugust 16, 2006, September 15, 2016 and September
21, 2019. Lower parts of the catchment have also been
covered in a 2012 survey, which we do not include inthis analysis. We carried out an additional survey of theidentified landslides using a Riegl VZ-4000 long-range
terrestrial laser scanner (TLS). To cover the whole areaof interest, we scanned from a total of 16 scan positions
within and outside the catchment. These different scans
were later put together to form a continuous point cloudand registered on the ALS point cloud of 2019, which
we considered to be the ground truth. These tasks wereperformed in the software package RIEGL RiSCAN
Pro [6].
The surface displacement was determined using theimage correlation algorithm implemented in the opensource software SAGA GIS [7] following procedures
described by Bremer [8] and Fey et al. [9]. In general,
the image correlation algorithm finds corresponding
features in two compared images. Through theapplication of this method a raster with the threedimensional displacement vectors in each of theevaluated pixels was calculated for each timestep
between 2006 and 2020. From this layer the active
landslide areas were delineated visually.

Fig. 1. a) Overview and b) geographic and geologic setting of
the Lattenbach catchment. Why use this yellow cyrcle when
we know where the landslides are (use maybe map from LeoSchranz).

There are two main channels in the upper part of thecatchment, the main stem of Lattenbach on the westernside and the Radunbach on the eastern side. Bothstreams merge at an altitude of 1,160 m around 1.7 km
from the catchment outlet. The Lattenbach channel runs
along a fault zone that has developed between thenorthern calcareous Alps and the crystalline Alps in thesouth. This caused a sequence of weak rocks andstronger formations in the areas near the channel. There
are large post glacial deposits (moraines) and scree
slopes in the sub-catchment of the Radunbach tributary.
In the Lattenbach tributary on the other hand only minor
amounts can be identified at first sight. Downstream of
the confluence, public mitigation works started in the1930ies. Since then, a series of check dams over a
stretch of about one kilometre were built and are
currently replaced. A monitoring station of the BOKU’s
Institute of Mountain Risk Engineering, measuring
timing, speed and flow depth of passing debris flows,has been installed at the lower end of this reach in 2005,
about one kilometre from the confluence with thereceiving river Sanna. For the scope of this research, wewill consider this monitoring station as the catchment

3.2 Sediment import
The downslope flux of sediment in the deep-seatedlandslide bodies was estimated using average velocities
across the delineated landslide bodies. The near channel
areas with very large calculated velocities have been
excluded due to the lack of visual features present incompared points in time. Without knowing the detailed
geometry of the landslide body, we defined the depth of
the incised gully at the landslide toe as the representative
depth of the landslide. Multiplying this average depthwith the average flow velocity and integrating along theaffected channel length provided volume estimates forevery timestep between the lidar surveys.
3.3 Sediment export
Sediment export was determined from data of a debrisflow monitoring station, which has been in operation
since summer 2005. Here, the flow stage during debris-2

E3S Web of Conferences 415, 04001 (2023)
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https://doi.org/10.1051/e3sconf/202341504001

flow events is measured by two radar sensors locatedabove well-defined cross sections. Using a rating curve
yields respective cross-section areas. The flow velocity
is estimated by measuring the time difference in the flow
stage hydrographs and then dividing the sensor distanceby this time interval. In 2014 a Doppler radar system
was installed, which measures the surface velocity over
the whole duration of the debris [10]. A volume estimate
is then calculated by multiplying the velocities with therespective wetted perimeter and then integrating overthe whole duration of the passing debris flow (see [11]for details).

last study period as vegetation cover made processing of
the respective parts in the TLS data impossible.
Table 1. Annual contributed volumes by landslides
LanslideNo.
123
45Total

3.4 Initiation zone
We performed UAV surveys after each debris flow in
the 2020 and 2021 season to locate the respective
initiation zones. These were carried out with a DJI
MAVIC 2 PRO and a DJI PHANTOM 4 RTK using theUAV mission planning software UGCS and AGISOFTMETASHAPE PRO to produce digital surface models.
We applied a coalignment-of-surveys approachdescribed in Cook et al. [12] and Nota et al. [13] andthen calculated and analysed differences between
surveys in QGIS 3.22.

Annualcontributed
volume2006-2016
11,610
1,425
2,520
1,230
1,337
18,122

Annualcontributed
volume2016-201912,900
3,225
6,384
3,444
3,069
29,022

Annualcontributed
volume2019-2020
18,834no data
4,788
no datano data
23,622

Between 2005 and 2020, the monitoring station
registered 16 debris flows, i.e. an average of one eventper year (Table 2). Between 2011 and 2014, no debris
flows have been registered, which also fits to theunusually low storm frequency during this time. The
largest event happened in 2016 with a total volume of46,080 m³. Over the whole study period we estimate a
total debris-flow volume of 225,683 m³, with an averageof 15,712 m³ per year.
Table 2. Annual cumulative debris-flow volumes

4 Results
We find a total of four active landslide bodies in themain stem of Lattenbach creek as well as one at theconfluence with the tributary Radunbach (Figure 2).
Landslide 1, the largest of the mass movements had avariable depth of 35 m to 50 m, the smaller landslides 25 depths between 10 m and 25 m. The average
movement rates show a fairly constant movement forlandslide 1 and 2, whereas the smaller 3-5 behaved morevariable.

Year

Volume [m³]2005

14,5682007

22,2662008

14,0392010

10,0002015

35,1542016

46,0802017

55,2682018

16,308

2019

8,000

2020
Total

14,000235,683

Annual average

15,712A first analysis of the erosion and deposition patterns
in the catchment showed a clear connection between thepresence of deep-seated landslides and increasedmaterial relocation (Fig. 3). Especially in the parts of thechannel along landslides 1 and 2, significant erosion wasobserved.

Fig. 2. Displacement of the 5 landslides between 2006 and2016

Sediment volumes delivered to the channel(“contributed volume”) on an annual basis varied
between 1,230 m³ for landslide 4 and 18,834 m³ forlandslide 1 (Table 1). We calculated a total annual
sediment yield of 18,122 m³ between 2006 and 2016.
After an acceleration of landslides 3-5, the amount ofsediment delivered rose to 29,022 m³ per year between
2016 and 2019. Starting in 2019, the largest landslide –no. 1 – accelerated and contributed 18,834m³ alone,landslide 3 slightly slowed down and delivered 4,788m³.
The other three landslides could not be evaluated in theFig. 3. Erosion and Deposition between 2006 and 2016

3

E3S Web of Conferences 415, 04001 (2023)
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https://doi.org/10.1051/e3sconf/202341504001

5 Discussion and conclusion

11. J. Huebl, R. Kaitna, Environmental andEngineering Geoscience 27, 2 (2021)
12. K.L. Cook, M. Dietze, Earth Surf. Dynam. 7(2019)13. E.W. Nota, W. Nijland, T. de Haas, International
Journal of Applied Earth Observation andGeoinformation 109 (2022)
14. J.A. Coe, D.A. Kinner, J.W. Godt,Geomorphology 96, 3 (2008)
15. G.L. Bennett, P. Molnar, B.W. McArdell, P.
Burlando, Water Resources Research 50, 2 (2014)
16. F. Comiti, L. Marchi, P. Macconi ,M. Arattano, G.
Bertoldi, M. Borga, Natural Hazards 73, 3 (2014)

Our results indicate that debris-flow activity is stronglyconnected to deep-seated landslides located in the
Lattenbach catchment. This is in contrast to other wellmonitored sites [14-16], where material for debris-flow
initiation is mainly derived from channel refill byweathering and hillslope processes.
A first assessment of erosion and deposition at theintersection between the deep-seated landslides and thechannel (“inner gorge”) derived from the UAV surveys
indicates a rapid channel refill at the time scale of adebris-flow event.
For a detailed sediment budgeting at the catchment
scale, there are two main challenges at the current stageof the study. First, we did not assess the amount ofsuspended sediment and bedload that is exported out of
the catchment, when no debris flows are occurring.
Furthermore, there are substantial uncertainties about
the actual depth of the deep-seated landslides. Despite
these limitations, we conclude that the five deep seatedlandslides within the Lattenbach catchment deliver
sediment volumes to the channel system in the order ofmagnitude of material exported by debris flows. Thus,
landslide activity is the most important source of
sediment in the catchment and significantly increases
the overall sediment yield.

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