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

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Earth Surf. Dynam., 5, 571-583, 2017
https://doi.org/10.5194/esurf-5-571-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
18 Sep 2017
Possible threshold 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, 3012 Bern, Switzerland
2Grupo de Investigación en Geología Sedimentaria, Sección de Ingeniería de Minas, Departamento de Ingeniería, Pontificia Universidad Católica del Perú, Av. Universitaria 1801, San Miguel, Lima, Peru
Abstract. To determine possible controls on sediment grain properties, 21 coastal rivers located along the entire western Peruvian margin were analysed. This represents one of the largest grain size dataset that has been collected over a large area. Modern gravel beds were sampled along a north–south transect on the western side of the Peruvian Andes where the rivers cross the tip of the mountain range, and at each site the long a axis and the intermediate b axis of about 500 pebbles were measured. Morphometric properties of each drainage basin, sediment and water discharge, together with flow shear stresses, were determined and compared against measured grain properties. Pebble size data show that the values for the D50 are nearly constant and range between 2 and 3 cm, while the values of the D96 range between 6 and 12 cm. The ratios between the intermediate and the long axis range from 0.67 to 0.74. Linear correlations between all grain size percentiles and water shear stresses, mean basin denudation rates, mean basin slopes and basin sizes are small to non-existent. However, exceptionally large D50 values of 4–6 cm were measured for basins situated between 11–12 and 16–17° S latitude where hillslope gradients are steeper than on average or where mean annual stream flows exceed the average values of the western Peruvian streams by a factor of 2. We suggest that the generally uniform grain size pattern has been perturbed where either mean basin slopes or water fluxes exceed threshold conditions.

Citation: Litty, C., Schlunegger, F., and Viveen, W.: Possible threshold controls on sediment grain properties of Peruvian coastal river basins, Earth Surf. Dynam., 5, 571-583, https://doi.org/10.5194/esurf-5-571-2017, 2017.
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Short summary
This paper 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 basin properties. The resulting trends and differences in sediment properties seem to have been controlled by threshold conditions upon supply and transport.
This paper focuses on the analysis of the properties controlling the grain size in the streams...
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