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

河流通过切割深深的峡谷和雕刻宽窄的山谷来塑造景观，决定人们居住的地方和洪水的去向。人们对河流如何、何时以及为什么在流经可以“接触”相邻谷壁的景观时雕刻出宽而窄的山谷知之甚少。在这个项目中，科学家们将调查美国第一条国家河流阿肯色州西北部的布法罗的基岩山谷的开发控制。这项研究代表了推进了解河流及其山谷如何响应和演变的重要一步。了解基岩山谷如何以及为什么会扩大，将使研究人员，土地利用规划者和环境科学家能够解释过去，现在和未来的河流系统如何应对河流沉积物或流量的变化。此外，项目科学家将与堪萨斯和阿肯色州的多元化教师和K-12学生接触，并开发一种强调地点交叉点的交互式地图工具（布法罗河）和面孔（过去几千年来生活在布法罗流域的不同民族）。尽管直观的概念模型认为软基岩使山谷变宽，硬基岩使山谷变窄，新的研究表明，在确定基岩谷宽和加宽率方面，基岩谷宽发展的两个端部成员与基岩岩性一样重要。在该项目中，PI将研究基岩山谷宽度，加宽率和相关的谷底形态如何受到坍塌谷壁材料的持久性与流动性的控制。阿肯色州西北部的布法罗河是一个理想的野外场地，因为独特的岩性形成了宽而窄的基岩山谷。该项目的目标是：1）调查谷底覆盖层的持续性，作为坍塌基岩壁材料块体尺寸的函数; 2）通过使用山谷和河道形态和基岩特性的现场测量数据，表征基岩山谷壁中的裂缝间距，确定对坍塌材料块体尺寸的控制。该项目的最终目标是3）进行一系列水槽实验，以量化谷宽端构件如何控制谷宽速率、总谷宽以及谷对关键驱动力变化的响应。在这个项目中收集的数据将允许重新评估现有的基岩山谷拓宽理论和促进基于过程的基岩山谷演变的理解，以应对外部气候驱动因素。这个奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.