Sediment dynamic in tropical mountain regions : influence of climatic and anthropogenic disturbances on erosion and sediment transfer mechanisms
Description
Context
Sediment dynamics in tropical mountain regions are complex and highly sensitive to climatic and anthropogenic disturbances. Several studies have shown the importance of extreme climatic events, like tropical rainfall associated with ‘El Niño’, on sediment production and transport (e.g. Romero et al., 2007). Field studies measuring erosion rates in mountainous areas have highlighted the acceleration of erosion processes by human activities (Vanacker et al., 2007; Nyssen et al., 2008). There is no doubt that climatic and anthropogenic disturbances are controlling erosion and sediment flux. However the way this control is operating is still highly discussed.
Research question
This research project aims to bring a better comprehension of sediment dynamics in tropical mountain regions by analysing the influence of climatic and anthropogenic disturbances on erosion mechanisms and sediment transfer. We will focus on two specific hypotheses:
- Sediment dynamics in tropical mountains catchments are largely influenced by landslides
- Anthropogenic disturbances have little influence on sediment dynamics in tropical mountains with high sensitivity to extreme climatic events
The study sites are located in the Ecuadorian Andes where it is possible to find catchments subject to different climatic disturbances and land use histories.
Methodology
Research activities are divided into three parts.
(A) Sediment balance (including an estimation of the landslides contribution)
In order to quantify how landsliding contribute to the overall catchment-wide erosion rate, we will use the methodology developed by Hovius et al. (1997). A landslides database will be created for the three catchments by using field trip observations and aerial photographs (Demoulin, 2006). The displaced sediment volume will be quantified from width and depth measures on the field and on aerial photographs. As landslide frequency-magnitude distributions follow a power-law relation (Van Den Eeckhaut et al., 2007), we will be able to estimate the landslide contribution to the overall erosion rate.
(B) Impact of anthropogenic disturbances
It is possible that natural phenomena triggering landslides are amplified or accelerated by human activities leading to land use changes. In order to verify this idea, a natural experiment will be realised. We will select in each catchment (Río Pangor and Rio Llavircay), two sub-catchments with a different land use history. This will allow us to analyse changes in landslide activity comparatively with land use change (Vanacker et al., 2003). A temporal analysis of the landslide magnitude distribution will be done using aerial photographs (’62, ’72, ’89, ’95 and ’00).
(C) Impact of climatic disturbances
The Cordillera Occidental, where the catchments of the Rio Pangor and Alamor are located, is one of the most sensitive areas to El Niño. Moreover, the hydrological regime of those catchments is highly variable (Rossel et al., 1999). In general, it has been observed than mass movements are accentuated by high-intensity rainfall (Chen and Su, 2001). Until now, it has been difficult to quantify anthropogenic influence in those kinds of catchments. We hypothesize that human impact might be insignificant in catchments that are highly sensitive to extreme meteorological events. In order to test this hypothesis, we will analyse the consequences of a high variable hydrological regimes on sediment transport and erosion rates in two to three sub-catchments with different land use history. For the last fifty years, the periods of time with strong influence of ENSO will be identified based on climatic and hydrological data. A multi-temporal analysis of landslide occurrence will be done based on historical information (aerial photographs, newspapers …). Changes in overall erosion rates will be analysed using existing data on sediments in suspension from gauging stations.
This research is funded by the Fonds de la Recherche Scientifique - FNRS.
Contact
Main references
- Chen H et Su D. (2001) Geological factors for hazardous debris flow in Hoser, Central Taiwan, Environmental Geology, 40: 1114-1124.
- Demoulin A. (2006) Monitoring and mapping landslide displacements: a combined DGPS-stereophotogrammetric approach for detailed short- and long-term rate estimates, Terra Nova, 18 (4): 290-298.
- Hovius N., Stark CP., Allen PA. (2007) Sediment flux from a mountain belt derived by landslide mapping, Geology, 25: 231-234.
- Nyssen J., Poesen J., Haregeweyn N, Parsons T. (2008) Environmental change, geomorphic processes and land degradation in tropical Highlands, Catena, 75: 1-4.
- Romero C.C., Baigorria G.A., Stroosnijder L. (2007) Changes of erosive rainfall for El Nino and La Nina years in the northern Andean highlands of Peru, Climatic Change, 85 : 343-356.
- Rossel F., Le Goulven P., Cadier E. (1999) Répartition spatiale de l'influence de l'ENSO sur les précipitations annuelles en Equateur, Revue des sciences de l'eau, 12: 183-200.
- Vanacker V., Vanderschaeghe M., Govers G., Willems E., Poesen J., Deckers J. et De Bievred B.(2003) Linking hydrological, infinite slope stability and land-use change models through GIS forassessing the impact of deforestation on slope stability in high Andean watersheds, Geomorphology,52: 299-315.
- Vanacker V., von Blanckenburg F., Govers G., Molina A., Poesen J., Deckers J. et Kubik P. (2007)Restoring dense vegetation can slow mountain erosion to near natural benchmark levels, Geology,35 (4): 303-306.
- Van Den Eeckhaut M., Poesen J., Govers G., Verstraeten G. et Demoulin A. (2007) Characteristics of the size distribution of recent and historical landslides in a populated hilly region, Earth and Planetary Science Letters, 256 (3-4): 588-603