Morphodynamic study of the lacustrine environment in Anavilhanas archipelago, Negro River, Amazon basin

Abstract

The Negro River before the confluence with the Amazon River presents a complex fluvial system composed of islands, channels and lakes interconnected to the floodplain, which is known as the Anavilhanas Archipelago. This study analyzed the morphodynamics characteristics of the lakes inside the Anavilhanas Archipelago using images from the Sentinel-1 (SAR sensor) and Landsat-5 (TM sensor) satellites. Bathymetric data, suspended sediment concentration and grain size from the Apacú Lake, the largest lake in Anavilhanas, are also presented. Based on images from the Sentinel1 satellite, a water surface ranging from 390 to 340 km2 was detected in the hydrological year 2017. The Anavilhanas fluvial complex has a surface of 2000 km2, of which 20% of this area is occupied by more than 300 lakes with elongated and narrow morphometry, with size ranging from 0.01 to 59 km2, where 63% are less than 0.53 km2. The annual hydrological dynamics of the Negro River causes low changes in the water surface of the Anavilhanas lake system, with a variation of 15% in the area occupied by the lakes between the period of high water and low water levels. The largest lake in Anavilhanas (Apacú Lake) has an annual average of suspended sediment concentration of 4.15 mg L-1, composed of fine particles (D50 0.02 mm). This paper presents to the scientific community a detailed morphometric survey of the Anavilhanas lakes and the analysis of their local characteristics in relation to the geomorphological style of the lower Negro River.