Water Discharge and Suspended Sediment Concentrations in the Amazon River: 1982–1984

Abstract

An equal‐width‐increment procedure was developed to measure water discharge and the suspended sediment load of the Amazon River and its principal tributaries. A variable speed hydraulic winch deploys an instrument array of a sounding weight, Price current meter, and collapsible bag sampler by lowering it from the surface to the bottom and back at a constant velocity. Eighteen verticals are taken at main stem stations (fewer on tributaries), with positioning determined by shipboard observation with a sextant monitoring angles from a three‐marker baseline on the shore. Confidence intervals (95%) for discharge and the fluxes of fine (< 0.063 mm) and coarse (> 0.063 mm) suspended sediments were 5%, 10%, and 20%, respectively. Water discharge varied from 31,700 m 3 /s to 69,700 m 3 /s upriver at Vargem Grande and from 91,700 m 3 /s to 203,000 m 3 /s downriver at Obidos. Concentrations of fine suspended sediments generally decreased downstream from 220–490 mg/L at Vargem Grande to 110–250 mg/L at Sao Jose do Amatari. Large concentrations of fines at high water in the Rio Madeira of 590–770 mg/L increased downstream concentrations of fines in the Amazon. Coarse suspended sediments had some of the same distribution and transport patterns as the fines but with only 20–30% of the concentration.