Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 15 6 2008 10.5194/npg-15-999-2008 http://www.nonlin-processes-geophys.net/15/999/2008/ http://www.nonlin-processes-geophys.net/15/999/2008/npg-15-999-2008.html http://www.nonlin-processes-geophys.net/15/999/2008/npg-15-999-2008.pdf 999 1011 2008-12-16 Granulometric characterization of sediments transported by surface runoff generated by moving storms J. L. M. P. de Lima plima@dec.uc.pt C. S. Souza V. P. Singh Department of Civil Engineering, Faculty of Science and Technology – Campus 2, University of Coimbra, 3030-788 Coimbra, Portugal Institute of Marine Research – Coimbra Interdisciplinary Centre, Coimbra, Portugal Department of Biological and Agricultural Engineering, Texas A and M University, Scoates Hall, 2117 TAMU, College Station, Texas 77843-2117, USA Due to the combined effect of wind and rain, the importance of storm movement to surface flow has long been recognized, at scales ranging from headwater scales to large basins. This study presents the results of laboratory experiments designed to investigate the influence of moving rainfall storms on the dynamics of sediment transport by surface runoff. Experiments were carried out, using a rain simulator and a soil flume. The movement of rainfall was generated by moving the rain simulator at a constant speed in the upstream and downstream directions along the flume. The main objective of the study was to characterize, in laboratory conditions, the distribution of sediment grain-size transported by rainfall-induced overland flow and its temporal evolution. Grain-size distribution of the eroded material is governed by the capacity of flow that transports sediments. Granulometric curves were constructed using conventional hand sieving and a laser diffraction particle size analyser (material below 0.250 mm) for overland flow and sediment deliveries collected at the flume outlet. Surface slope was set at 2%, 7% and 14%. Rainstorms were moved with a constant speed, upslope and downslope, along the flume or were kept static. The results of laboratory experiments show that storm movement, affecting the spatial and temporal distribution of rainfall, has a marked influence on the grain-size characteristics of sediments transported by overland flow. The downstream-moving rainfall storms have higher stream power than do other storm types. Bagnold R. 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