Collaborative Research: Beyond lithologic control of bedrock valley width: Investigating the role of persistent valley cover in bedrock valley width development, Buffalo River, AR

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Rivers shape landscapes by incising deep canyons and carving both wide and narrow valleys, determining where people live and where floodwaters go. Little is known about how, when, and why rivers carve wide vs. narrow valleys as they flow through landscapes where they can ‘touch’ the adjoining valley walls. For this project, the scientists will investigate controls on the development bedrock valleys on America’s first National River, the Buffalo in northwest Arkansas. This research represents an important step in advancing understanding of how rivers and their valleys respond and evolve. Understanding the how and why bedrock valleys widen will allow researchers, land use planners, and environmental scientists to interpret how river systems in the past, present, and future have and will respond to changes in river sediment or discharge. Additionally, the project scientists will engage with a diverse population of teachers and K-12 students in Kansas and Arkansas and develop an interactive mapping tool that highlights the intersection of places (the Buffalo River) and faces (the diverse peoples living in the Buffalo watershed over the past several millennia).Despite the intuitive conceptual model that soft bedrock makes for wide valleys and hard bedrock narrower valleys, new research suggests that two end members of bedrock valley width development are as important as bedrock lithology in determining bedrock valley width and widening rates. In the project, the PIs will study how bedrock valley width, widening rates, and associated valley bottom morphology are controlled by the persistence vs. mobility of collapsed valley wall material. The Buffalo River in northwest Arkansas is an ideal field site given the distinct lithologies that create both wide and narrow bedrock valleys. The project goals are 1) investigate the persistence of valley bottom cover as a function of the block sizes of collapsed bedrock wall material and 2) determine controls on the block size of collapsed material by characterizing fracture spacing in bedrock valley walls, using data from field measurements of valley and channel morphology and bedrock properties. The final goal of this project is 3) conduct a series of flume experiments to quantify how valley widening end members control valley widening rate, total valley width, and valley response to changes in key drivers. The data collected during this project will allow for re-evaluation of existing theories of bedrock valley widening and the advancement of processed-based understanding of bedrock valley evolution in response to external climate drivers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.