Morphological Changes in Stretches of the São Francisco River due to Uncontrolled Agricultural Expansion in its Watershed

The springs of São Francisco River are in the State of Minas Gerais, Southeast of Brazil. It drains seven states, traveling 2,830 km towards the Northeast region. The river is perennial and has an 1,391 km navigable segment. Brazilian Government has invested in three fronts uses: (1) partial transposition of its waters to the Brazilian Northeastern Semi Arid region; (2) construction of hydroelectric plants: there are already six hydroelectric complexes in operation in its main course, with a total generation of 9,400 MW, and (3) expansion of Irrigation. The Iuiú Irrigation Basic Project, elaborated at the year 2000, intended for agricultural development of an area of 500 km², located at the mouth of Verde Grande River. A navigable 10.0 km stretch of the São Francisco River irrigation project, located between two hydrosedimentological stations: Manga 30.0 km upstream in Minas Gerais State, and Carinhanha, 20.0 km downstream, in the Bahia State, was considered. Assisted by Remote Sensing techniques, six sediment banks were analyzed during the period of 1985 to 2011. Annual images showed that some of the sediment banks were intermittent, while others were permanent. It also showed that some banks migrated to downstream, while others remained stationary but had annual morphological changes. The stretch of the Iuiú Irrigation Project gradated in the first period (1985-2001), and later (2003-2011) reached a sedimentological equilibrium. The challenge and, consequently, a great motivation to improve the morphodynamic studies on the São Francisco River has consisted in explaining the formation and disappearances of these movable banks. Based on this idea, the studies were extended in this article, for the subsequent period from 2011 to 2018, with the help of Landsat-5 and -8 images and Google Earth Engine JavaScript Application Programming Interface. The evolution of the watershed and river bed`s morphology were considered during this period of time, and the results are conclusive and surprising: (i) in a period of less than 10 years, there arose numerous projects of water withdrawal of tributaries of the São Francisco River; (ii) several of them dried up due to uncontrolled water outtake for agricultural development; (iii) the number of sediment banks multiplied; (iv) the 10.0 km of the Iuiú Project, which was in sediment balance between 2003 and 2011, presented new sediment banks and tendencies to braiding; (v) the soil use has changed, and (vi) conflicts have aroused between large landowners and peasants.