Detecting mass sediment transport and movement tainted by decades of mining activities in river Quito, Western Colombia

Sediment supply in rivers is the dominant material source for ecosystems, which have been undergoing large variations globally. The objective of this research was to study the spatial distribution of runoff and sediment load in river Quito (Choco, Colombia), which is affected by extreme gold mining practices. Long-term daily mean discharge data from gauging stations were analyzed. The runoff values of 297, 210 and 141 m3/s have exceeded (in %) 50, 70 and 90 during 2001–2011 in the river Quito. In river Atrato 976, 706 and 500 m3/s have occurred (in %) 50, 75 and 90 during 1984–2015. Suspended sediment concentrations were measured using a linear equation derived from the results obtained from laboratory analysis of field samples and acoustic doppler current profiler. Minimum and maximum flow discharge (Q) observed using ADCP instrument was 0.59 m3/s at the tributary and 370 m3/s at the downstream of main river indicating that the tributaries play an important role in sediment supply. Spatially distinct trends in suspended sediment load, with an increasing trend from the upstream (73.73 tons/day) to downstream (3140.82 tons/day) in the main channel is observed. Significant correlation (r2 = 0.79 and 0.85 for tributary and main river, respectively) between the SSL and Q suggests that the SSL depends on the intensity of runoff, governed by the extreme rainfall condition. In contrast, no significant correlation was observed between Q and SSC due to the continuous migration of mining dredges and dumping of mine tailing piles at the riverbank. The results provide support for river management to engineers, where the best conservation/management practices that can be implemented.