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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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doi:10.5194/esurf-2017-8
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
01 Mar 2017
Review status
This discussion paper is under review for the journal Earth Surface Dynamics (ESurf).
Multiple controls on sediment grain properties of Peruvian coastal river basins
Camille Litty1, Fritz Schlunegger1, and Willem Viveen2 1Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, CH- 3012 Bern
2Sección de Ingeniería de Minas e Ingeniería Geológica, Departamento de Ciencias Ingeniería, Pontificia Universidad Católica del Perú, San Miguel, Lima, Perú
Abstract. Twenty-one coastal rivers located on the western Peruvian margin were analyzed to determine the relationships between fluvial and environmental processes and sediment grain properties such as grain size, roundness and sphericity. Modern gravel beds were sampled along a north-south transect on the western side of the Peruvian Andes, and at each site the long a-axis and the intermediate b-axis of about 500 pebbles were measured. Morphometric properties such as river gradient, catchment size and discharge of each drainage basin were determined and compared against measured grain properties. Grain size data show a constant value of the D50 percentile all along the coast, but an increase in the D84 and D96 values and an increase in the ratio of the intermediate and the long axis from south to north. Our results then yield better-sorted and less spherical material in the south when compared to the north. No correlations were found between the grain size and the morphometric properties of the river basins when considering the data together. Grouping the results in a northern and southern group shows better-sorted sediments and lower D84 and D96 values for the southern group of basins. Within the two groups, correlations were found between the grain size distributions and morphometric basins properties. Our data indicates that fluvial transport is the dominant process controlling the erosion, transport and deposition of sediment in the southern basins while we propose a geomorphic control on the grain size properties in the northern basins. Sediment properties in the northern and southern basins could not be linked to differences in tectonic controls. On the other hand, the north-south trend in the grain size and in the b/a ratio seems controlled by a shift towards a more humid climate and towards a stronger El Nino impact in northern Peru. But, generally speaking, the resulting trends and differences in sediment properties seem controlled by differences in the complex geomorphic setting along the arc and forearc regions.

Citation: Litty, C., Schlunegger, F., and Viveen, W.: Multiple controls on sediment grain properties of Peruvian coastal river basins, Earth Surf. Dynam. Discuss., doi:10.5194/esurf-2017-8, in review, 2017.
Camille Litty et al.
Camille Litty et al.
Camille Litty et al.

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Short summary
This manuscript focuses on the analysis of the properties controlling the grain size in the streams of the western Peruvian Andes. Pebble size distributions in these streams have been compared to fluvial processes and basins properties. The resulting trends and differences in sediment properties seem to have been controlled by differences in the complex geomorphic setting along the arc and forearc regions.
This manuscript focuses on the analysis of the properties controlling the grain size in the...
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