LANDSCAPE EVOLUTION MODELING OF GIA-ASSISTED CHANNEL AVULSIONS IN LOW RELIEF RIVERINE LANDSCAPES

Alluvial rivers normally avulse when the bed is aggraded above the channel banks and then those newly formed banks fail to contain discharges as the river shifts to find a preferential path. Here, the avulsion process is investigated when occurring in the presence of continuous, regional Glacial Isostatic Adjustment (GIA) using numerical Landscape Evolution Modeling and through case study of the Red River of the North, which has exhibited areas of avulsions since the existence of Lake Agassiz. These path changes are seemingly abrupt, and some of the former paths are marked by small streams in oversized river valleys that run roughly parallel to the Red River and by fluvial deposits preserved in the modern surficial geology. Occurrence abrupt channel avulsions are related to Holocene climate patterns, GIA motions that have impacted the drainage basin, and the subtle, low-relief topography of the former lake bottom. Here, the LandLab Landscape Evolution Modeling library was used to design a simple, low relief topography and model different scenarios of GIA motion and climate patterns using current numerical models. GIS was used to explore the Red River’s former paths that have avulsed to their present location. Simple, preliminary Landscape Evolution Modeling shows that continuous GIA motion with no climate or sediment variations lead to gradual shifting of channels and more relatively more widespread floodplain erosion to lower base-levels. Models with both GIA motion and climatic variance show more abrupt shifting during transitions from arid to less arid climate conditions and better preserve the elevation of the floodplains. With the trend of GIA motion being oriented to the northeast, and the net rebound and rate of rebound being greater toward the northeast most channel avulsions cause the river’s path to shift to the west. The lengths and paths of avulsions seem to rely on existing topography, the location and extent of historic fluvial sediments, and glacial moraines deposited during the late-Pleistocene.