INFLUENCES OF POSITION IN A FORELAND BASIN ON MEANDER BELT MIGRATION PATTERNS ON THE MEGAFANS IN THE CENTRAL ANDEAN FORELAND BASIN

Identifying patterns and changes of the meanders in the Central Andean Foreland Basin centered around the Rio Beni river system could be key to understanding meander belt development on distributive fluvial systems (DFS) and how these systems adjust based on their placement within a tectonic region. We evaluated meander belt migration and patterns in the Central Andean Foreland Basin by (1) quantifying lateral movement of the meander loops in different parts of the basin, (e.g., foredeep, forebulge, and backbulge), (2) identifying different types of capture and avulsion of the river channels along the meander belt, and (3) identifying the downstream changes in the width of the active river channels from the apex. The river systems in this basin form megafans (DFS) as they enter the sedimentary basin. To conduct this work we are using Landsat and Google Earth imagery. Preliminary analysis using Google Earth imagery from 1986-2016 indicates that the Rio Beni system specifically displays (1) a difference in both density and number of meanders downstream from the apex with many meanders in the foredeep, few in the forebulge, and fewer still in the backbulge, (2) a decrease in sinuosity from the foredeep to the backbulge, (3) multiple types of river channel cut-offs (mostly in the foredeep), and (4) a decrease in number of meander loop cut-offs downstream of the apex (backbulge contains no cut-offs over 30 year analysis period ). This analysis shows a foredeep containing many meanders with almost yearly chute and/or neck cut-offs between the period of 1986-2016 while further away from the apex these cut-offs become very infrequent. Landsat imagery will be used to expand the period of coverage, assess change with higher temporal resolution, and evaluate how meander migration is affected by whether the river channel is in a distributive or incised reach. Further study into other rivers in this part of the Andean Foreland Basin will help determine whether changes in meander migration are due to the change from distributing to incising or do to a subsidence difference (ie. foredeep to forebulge).