E3S Web of Conferences 415, 05015 (2023)
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https://doi.org/10.1051/e3sconf/202341505015

Morphological characteristics of drainage networks related tolandslide cluster in the Colombian Andean
Karolina Naranjo1* , Edier Aristizábal1, and Johnnatan Palacio2
1Dept. Geociencias y Medio Ambiente, Facultad de Minas, Universidad Nacional de Colombia, Medellín, Colombia.
2Dept. Ingeniería Civil, Facultad de Minas, Universidad Nacional de Colombia, Medellín, Colombia.

Abstract. Debris flows are a highly destructive and common phenomena in Colombia. A large percentage
are triggered during seasonal rainfalls. And the Andean region is the most affected area, which exhibits adynamic landscape made up of weak and highly weathered materials and affected by tectonic stress. As aresult of this setting, sometimes many landslides are generated in clusters. Those hillslope landslides are thesediment source for the formation of debris flows. The main goal of this study is to know the state of thedynamics of 3 basins that have been affected by cluster landslides and their subsequent debris flows thathave occurred in the northern region of the Colombian Andes using diverse morphometric indices. In generalterms, the results show a transitory state into basins, with an evident migration along the margins of thenetwork drainages due to unbalance state. This means more susceptible areas with greatergeomorphodynamic activity.

1

Introduction

Debris flow is defined as a phenomenon with very rapid
to extremely rapid mobility, according to water content,sediments, and topography [1], [2]. Debris flows arecommon and highly destructive in tropical andmountainous environments like Colombia. In 30.730
compiled records, there were 138.290 people affected;
34.198 deaths, and economic losses of 654.517.292(USD). In addition, it is indicated that 87% of landslides
are triggered by rainfall [3].
Debris flows are formed generally from shallow translational - landslides triggered by rainfall. The
occurrence is favored by a dynamic landscape made up
of weak and highly weathered materials and affected bytectonic stress. Landslides are triggered by theimposition of body forces on hillslope materials. One ofthese forces comes from relative base-level fall whichoccurs in most active montane landscapes and provides
a sufficient condition for long-term hillslope erosion [4].
Morphology landscape reflects the interaction between
Earth's surface geomorphological processes, rock, andsoil. Longitudinal profiles of rivers retain aninterpretable signature of tectonic forcing and landslide
erosion rates can match high rates of landscapedenudation [5], [6].
Sometimes during strong and/or prolonged rainfall
events, a large number of landslides are generated fromtens to hundreds (cluster), in the same rain event andwithin a limited time and area; these events are called*“Multiple-occurrence regional landslide events” [7].
Those hillslope debris flows are the sediment source forthe formation of debris flows, called in Colombia as“Avenidas Torrenciales”. Those are described as a
mixture of water and sediment in different proportions,moving rapidly along channels in small and mountainbasins [8]. The availability of sediment on the hillslopes
and bottom of streams may be increased due to its
location in a tectonically active zone generating uplift
processes, rejuvenation of landscape, and reorganizationof drainage [9]–[13].
In this study, the objective is to know the state of thedynamics of the basins of interest where cluster
landslides and their subsequent torrential flows haveoccurred using diverse morphometric indices to survey
drainage rearrangement.

2

Study area and data

The Colombian Andean is the most affected region bylandslides during bimodal seasonal rainfalls. In thenorthern Andes, there have been some cluster-type
events with a subsequent debris flow. Some records
have occurred in the municipality of San Carlos (1990),Tarazá (2007), Salgar (La Liboriana - 2015), Yalí(2020), Anorí (2020), Dabeiba (2020) and SantoDomingo (2021). The study area focuses on the basins
associated with the events cluster shown in Figure 1;
San Carlos into the Nare basin, Salgar into the San Juanbasin and Dabeiba into the Riosucio basin.

Corresponding author: knaranjobe@unal.edu.co© 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, 05015 (2023)
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Fig. 1. Study area.

relationships between possible tectonic activity, rockstrength and topography.
χ parameter represents a solution for the stream powerlaw equation. Characterizes drainage topology andgeometry, it is sensitive to changes in upstream areas.
Calculating χ to drainage networks and comparing
values at a watershed divides, produce a snapshot ofdynamic remodeling of drainage basins. Anotherapplication is the transformed longitudinal profiles (χplots), which allow the comparison of profiles
independent of spatial scale.
The slope of the χ‐ elevation plot is the Ksn index which
has the main objective to highlight any external factor
that deviates the river profile from an equilibrium state
into a transient state.

Table 1 shows the number and frequency of drains
analyzed for each basin. In San Carlos, the largest
number of landslides and economic damage toinfrastructure occurred. However, the cluster event in
the municipality of Salgar caused the highest damage tothe population (104 deaths).
Table 1. Data study area.
Basin/ MunicipalityClusterRíosucio/ Dabeiba
El Mohan

N°Landslides

San Juan/ Salgar
La Liboriana∽160 [15]Nare/ San Carlos
La Arenosa∽170

699 [13]N° Deaths
5 [16]∽100 [17]
20 [18]43Geomorphic indices

Discussion and results

Colombia is a complex multi-hazard scenario [14].
Some areas are more susceptible than others according
to geological, geomorphological, and hydrologicalsettings. It is essential to understand why those areas are
more susceptible or have more active morphodynamic
processes than others, apparently similar.

Morphometry is the measurement and mathematicalanalysis of the configuration of the Earth's surface. Ariver basin is the fundamental geomorphic unit in which
important information is found regarding its formationand evolution. This stored information is key tounderstanding geomorphic activity.
Indices are commonly used to visualize andquantify changes in morphometry, dynamics andevolution of drainage networks of basins. We use three
indices to identify possible correlations betweenchanges in the drainage network and cluster events.
Those include Hack index (SL), integrated position
function in the drainage network (χ) and Normalized
channel steepness index (Ksn).
SL index is based on detecting abrupt variations inslope angle of the longitudinal profile of rivers causedby an anomaly (knickpoint). It is generally very
sensitive to changes in slope and it is applied to assess

Figure 2 and Figure 3 show the longitudinal profileof the main drainage with the distribution of slope andSL index values on the right and left lateral sides of thestream; top and bottom in Figure. In the three basins, it
is observed an unusual distribution of high slopes, as itis expected that high values will be in the upper part ofthe basin, in this case, the high slope values are
distributed along the drainage, also reflected in bothsides of the basin. The distribution of SL values (Figure3) is not uniform along the riverbed. High values arefound in the middle part of the Nare and Sucio riverbasins, while the highest values in the San Juan river areconcentrated in the final part of its way. There is no2

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https://doi.org/10.1051/e3sconf/202341505015relationship between the distribution of SL index values
and the presence of clusters.

Fig. 4. χ map with cluster landslide in red circle.
Fig. 2. Longitudinal profiles with slope values on bothmargins of the main drainage. The red circle represents local
basin associated with the cluster type event.

Figure 5a, 5b and 5c show χ-plots for each basin.
The presence of disturbances within the basins can beobserved, expressed in high values of the variable Ksn (> 2.8). Figure 5d shows fluvial network reorganization
represented in the movement of divides of the basins
towards high values of the χ index (see the direction ofarrows).
In the Nare River basin on the western and northernsides, there is a reduction of catchment area as a resultof the advance of the watershed divides (see [19]). In theSucio River basin, the divide advances in an East-Westdirection with implications of loss in the area; theopposite is the case in the northern boundary where thedivide is gaining area from the neighboring basin. Thesepatterns are reflected in Figure 5a y Figure 5b. The
approximate location of the local tributary where eachof the cluster events occurred is indicated by a black dot(Dabeiba y San Carlos).

Fig. 3. Longitudinal profiles with SL index values on bothmargins of the main drainage. The red circle represents local
basin associated with the cluster type event.

In both cases, the affected drainages would be under
the condition of loss of area. Regarding the San Juanriver basin, the advance of the watershed is in an EastWest direction as a way of gaining area over theneighboring basin. The location of the Salgar cluster
event would be influenced by the presence ofknickpoints within nearby higher-order drainage
systems (Figura 5c).

Figure 4 shows distribution of the χ-index indrainage network. Indicated with a red circle the local
basin associated with the cluster type event. In the areas
close to the cluster events analyzed, high values of thechi index are observed in the drainage network.

In the basins where the cluster-type events occurred,the χ showed a transitory state, with an evident
unbalance in the margins of the drainages presentingthat they are migrating. This means more susceptible
areas with greater morphodynamic activity.
Having a better compression of morphodynamics
from morphogenesis is important to assess landslide anddebris flow susceptibility conditions regarding3

E3S Web of Conferences 415, 05015 (2023)
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https://doi.org/10.1051/e3sconf/202341505015

The results of the indices were not strongly
correlated with the occurrence of cluster events. In
future research, a more detailed scale analysis is neededin the local watersheds where cluster events occurred. It
is also necessary to carry out analyses in basins with andwithout the presence of clusters to obtain a better
comparative analysis.

landscape characteristics and evolution. In addition, ageneral characteristic of this type of event is thesubsequent torrential flow, hence the importance ofdeepening the determination of morphometric indicesthat delve into determining the torrentiality of the basins
as an additional analysis to the knowledge of themorphodynamic processes that have occurred in it.

Fig. 5. Morphometric indices. a) χ plot Nare River b) χ plot Sucio River c) χ plot San Juan River d) Unbalance divides around study
basins.

in XVIII Congreso Colombiano de Geología(2021)
11. J. Palacio, E. Aristizábal, M. Mergili, O.
Echeverri, Shallow landslide occurrence andpropagation in tropical mountainous terrain with
open source models. A case study in theColombian Andes, in EGU General Assembly
2021 (2021)
12. E. Aristizábal, J. I. Vélez, H. E. Martínez, M.
Jaboyedoff, Landslides 13, 3 (2016)
13. E. Aristizábal, E. García, H. Martínez, Nat.
Hazards 78, 1 (2015)
14. A.L. Densmore, N. Hovius, Geology 28, 4 (2000)
15. D. Ruiz-Vásquez, E. Aristizábal, Landslide
susceptibility assessment in mountainous andtropical scarce-data regions using remote sensing
data: a case study in the Colombian Andes.
Medellín, p. 27 (2017) [Online]. Available:
https://repository.eafit.edu.co/handle/10784/1347.
16. Noticias RCN, Cinco muertos y 16 heridos por
deslizamientos en Dabeiba, Antioquia (2020).
https://www.noticiasrcn.com/nacional/tresmuertos-y-12-heridos-por-deslizamientos-endabeiba-antioquia-365686A.F. Hernández,Avenida Torrencial en Salgar, Antioquia(Colombia). In ERNtérate. ern.com.mx (2015)17. M. Hermelin, O. Mejía, E. Velásquez, Bulletin ofthe International Association of Engineering Geology 45, 1 (1992)
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C.Y. Chen, Science 343, 3175 (2014)

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