Suspended sediment transport in the Magdalena River(Colombia,South America):Hydrologic regime,rating parameters and effective discharge variability

The Magdalena River has the greatest length（1612 km）and drainage area（257400 km2）of any river system in Colombia,and its watershed occupies 24%of the Colombian territory.The river originates in the Andean Cordillera at an elevation of 3685 m and flows to its mouth in the Caribbean Sea（Bocas de Cenizas）.For this study,information on daily flow discharge（Q）,suspended sediment transport(Qs and mean suspended sediment concentration（Cs）from 1990-2010 for the Magdalena River,based on measurements at the Caiamar gauging station（the closest station to the mouth）,was provided by the Institute of Hydrology,Meteorology and Environmental Studies of Colombia（IDEAM in Spanish）.The mean annual suspended sediment load was 169±73×10～6tyr-1for the period from 1990-1999 and145±47×10～6 t yr1 for the period from 2000-2010,amounting to a 14%reduction in the suspended sediment transport rate between the two periods.The sediment rating curve（Qs=aQb）was also evaluated for these two periods（1990-1999 and 2000-2010）.An analysis of the regression coefficients（a.b）for the two periods showed a decrease in b and an increase in a after 1999,which coincides with a decrease in suspended sediment transport.This change might be attributed to natural factors,including the accumulation of sediment in the Depresion Momposina and variation in hydro-climatological patterns in the Caribbean region.Decreases in effective transport were confirmed using three methods（Log-Normal and Normal distribution,and magnitude-frequency histogram）for the study period.