Doctoral Dissertation Research: Responses of Gully Erosion and Sedimentation to Environmental Change in the Upper Republican River Basin, Nebraska

博士论文研究：内布拉斯加州共和河流域上游沟渠侵蚀和沉积对环境变化的响应

• 批准号: 0100859
• 负责人: James Knox
• 金额: $ 1万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-03-15 至 2002-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0100859&HistoricalAwards=false
• 关键词: Doctoral; Dissertation; Research; Responses; Gully

Many fluvial systems of the central Great Plains have flashy discharge regimes and high sediment yields. As a result, their sedimentary processes are extremely sensitive to changing hydrologic conditions. Evidence in the form of cut-and-fill terraces and alluvial stratigraphy with high resolution depositional units suggests that both hydrologic and sedimentologic adjustments have taken place throughout the Holocene. Morphologic properties of currently active gullies and valley fills also indicate that contemporary gully erosion rates are sensitive to changes in modern environmental conditions. This general objective of this doctoral dissertation research project is to quantify gully erosion and valley aggradation rates in the upper Republican River basin of western Nebraska and to determine how these rates have varied in response to environmental change. This research will examine how gully systems have (1) activated and stabilized on decadal time scales in the late 20th century; (2) incised and aggraded in response to climate changes of the Holocene; and (3) extended headward to shape watershed morphology during late Quaternary. This research will integrate field, laboratory, and GIS analyses. Historical gully erosion will be documented by examining aerial photographs to determine the magnitude of headward gully migration on a decadal time scale since the 1950s. The spatial distribution of gully-derived sediment downstream from active headcuts will be established using a 137-Cs sediment tracing technique. Holocene valley aggradation rates will be estimated on the basis of radiocarbon age determinations of organic matter within alluvial fills and terraces. Sedimentologic and pedologic analyses of these same fills will permit interpretation of the depositional and soil-forming processes active during aggradation. Extension of drainage networks will be investigated by using soil-stratigraphic and morpho-stratigraphic evidence to infer the headward limits of networks at various times throughout the late Quaternary. These limits can define network planforms that will be analyzed in a GIS environment to determine changes in hydrologically significant drainage network parameters over millennial time- scales.Results of this research will help document the response of semi-arid fluvial systems to environmental change. As scientific concern mounts over the potential impact of future climate change in sensitive semi-arid regions like the Great Plains, realistic appraisals of past hydrologic variability become increasingly necessary. This research will improve understanding of that variability by examining its impact on gully erosion and valley aggradation. By investigating these processes over temporal scales ranging from decades to millennia, the project will establish a better understanding of the complete range of potential process rates, and will document the many factors that may govern changes in these rates. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.

大平原中部的许多河流系统都具有快速的流量和高的沉积物产量。 因此，它们的沉积过程对水文条件的变化极为敏感。 以高分辨率沉积单元的切割和填充阶地和冲积地层的形式提供的证据表明，水文和沉积调整在整个全新世都发生了。 目前活跃的冲沟和山谷填充物的形态特征也表明，当代冲沟侵蚀速率对现代环境条件的变化很敏感。 这个博士论文的研究项目的总体目标是量化沟侵蚀和山谷加积率在上共和党河流域西部内布拉斯加州，并确定这些利率如何变化，以应对环境变化。 本研究将探讨沟系统如何（1）在世纪后期的十年时间尺度上激活和稳定;（2）在全新世气候变化的响应下切割和加积;（3）在第四纪晚期向前延伸形成流域形态。 这项研究将整合现场，实验室和GIS分析。 历史上的沟蚀将通过检查航空照片来记录，以确定自20世纪50年代以来的十年时间尺度上的溯源沟迁移的规模。 将使用137-Cs沉积物示踪技术确定来自主动头切下游的冲沟沉积物的空间分布。 将根据冲积充填物和阶地内有机物的放射性碳年龄测定，估计全新世河谷的沉积速率。 这些相同的填充物的沉积学和土壤学分析将允许沉积和土壤形成过程的解释在加积期间活跃。 排水网络的延伸将通过使用土壤地层和地貌地层证据来推断网络在整个晚第四纪的不同时期的源头限制进行调查。 这些限制可以定义网络平面图，将在GIS环境中进行分析，以确定水文重要的排水网络参数的变化在千年的时间scale.Results的研究将有助于文件的半干旱河流系统对环境变化的响应。 随着科学界越来越关注未来气候变化对大平原等敏感半干旱地区的潜在影响，对过去水文变化的现实评估变得越来越必要。 这项研究将通过检查其对沟蚀和山谷加积的影响，提高对这种变化的理解。 通过在几十年到几千年的时间尺度上调查这些过程，该项目将更好地了解潜在过程速率的全部范围，并将记录可能控制这些速率变化的许多因素。 作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立的研究生涯。