Bedload transport rates for coarse-bed streams in an Atlantic region (Narcea River, NW Iberian Peninsula)

Rivers from northern Cantabrian Mountain Range (NW Spain) are emplaced in an Atlantic region, draining to the Bay of Biscay and saving 2000 m in a short path. Thus, high gradient streams normally develop with coarse-bed sediment and a strong importance of bedload transport processes in their morphosedimentary dynamics. In the present work, tagged clasts (painted and with inserted magnets) were used as tracers in order to estimate bedload transport rates in two of those coarse bed streams (River Pigüeña and River Coto) belonging to River Narcea drainage basin. Four methodological steps were followed: (1) grain size analysis of bed sediment; (2) preparing tracer clasts in the laboratory; (3) seeding the studied reaches with the tracers, measuring their displacements after flood events; and (4) analysis of data. Ten flood episodes with the ability to disturb tracer position were registered along two hydrological years (2009–2010 and 2010–2011); bedload transport rates were estimated for six of these episodes. Values ranging from 1.1 to 4.1 kg/s were obtained for Pigüeña, and values ranging from 0.20 to 0.28 kg/s were obtained for Coto. Also, an attempt at analysis of threshold conditions was tried, and a regression model between bedload transport rates and shear stress was built.