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Gully erosion and valley aggradation in the upper Republican River basin, Nebraska.

机译：内布拉斯加州共和党上游流域的沟壑侵蚀和山谷积聚。

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摘要

This dissertation examines mechanisms of sediment erosion and deposition in the upper Republican River basin, and uses results to characterize floodplain aggradation, valley incision and gully erosion in semiarid regions in general. Research demonstrates that tributaries to the upper Republican River have incised and aggraded in response to late Holocene climatic variability. Ages of incision and aggradation episodes appear to coincide with other Great Plains alluvial chronologies, suggesting widespread regional synchroneity. Floodplains within the study area underwent slow valley aggradation during the late Holocene until about 1200 to 800 yr B.P. Widespread valley incision during this period corresponds with regional climatic conditions of the Medieval Warm Period, in which multi-decadal droughts stressed grassland vegetation and increased runoff associated with convective storms.; Results also provide evidence for mechanisms of aggradation and pedogenesis on semiarid cut and fill floodplains. Sheetflow deposition on unchanneled valley floors represents an important mechanism of valley aggradation. Rates of sediment deposition on cut and fill floodplains strongly determine the degree to which pedogenic features develop within aggrading alluvium. Three pedofacies common to semiarid alluvial deposits correspond with increasing aggradation rates: (1) cumulic soils; (2) multiple buried soils; (3) no pedogenic features. Radiocarbon age determinations from multiple alluvial fills indicate that floodplain aggradation greater than approximately 0.5 cm yr−1 limits soil formation: this represents a threshold rate of pedogenic assimilation. Floodplain sediments and soils exhibit a strong positive relationship between aggradation rate and total CaCO 3 percent, and a negative relationship between aggradation rate and organic carbon percent.; This research also characterizes the morphology and distribution of contemporary gullies within the study area. No relationship exists between gully morphology and intrinsic geomorphic variables such as drainage area or channel order. Gully headcut morphology does reflect the hydraulic mechanisms of overland flow and/or shallow subsurface flow. Discharge records of small Nebraska watersheds provide insight into the runoff magnitudes responsible for driving valley-bottom gully incision. A record of sediment from an enclosed stock pond helps estimate total gully derived sediment yield in the study area at 0.43 Mg km −2 yr−1.
机译：本文研究了共和河上游流域的泥沙淤积和沉积机理，并利用结果来表征一般半干旱地区的洪泛区聚集，河谷切口和沟壑侵蚀。研究表明，响应晚新世气候变化，共和党河上游的支流已切开并逐渐积聚。切口和积水时代的年龄似乎与其他大平原冲积年代相吻合，表明广泛的区域同步性。研究区内的洪泛区在全新世晚期经历了缓慢的河谷沉积，直到约1200至800年B.P.在此期间，广泛的山谷切口与中世纪温暖期的区域气候条件相对应，在该气候条件下，数十年干旱加剧了草原植被，并增加了与对流风暴有关的径流。结果也为半干旱切割和填充泛滥平原上的凝结和成岩机理提供了证据。无通道谷底的表流沉积是谷底积聚的重要机制。 cut积洪泛平原上的沉积物沉积速率强烈决定着积积冲积层中成岩特征的发展程度。半干旱冲积沉积物常见的三种岩藻与增加的沉积速率相对应：（1）积土; （2）多个地下土壤; （3）没有成岩特征。通过多次冲积充填确定的放射性碳年龄表明，洪泛区的积聚大于约0.5 cm yr -1 会限制土壤形成：这代表了成岩同化的阈值速率。洪泛区沉积物和土壤的沉积速率与总CaCO 3 的百分比之间具有很强的正相关关系，而与有机碳含量的百分比则呈负相关。这项研究还表征了研究区域内当代沟壑的形态和分布。沟渠形态与内在地貌变量（如流域或河道阶数）之间不存在任何关系。沟渠沟渠形态确实反映了陆上流和/或浅层地下流的水力机理。内布拉斯加州小流域的出水记录可以深入了解造成谷底沟壑切口的径流大小。封闭式蓄水池的沉积物记录有助于估算研究区总沟源沉积物产量为0.43 Mg km -2 yr -1 。

著录项

  • 作者

    Daniels, James Michael.;

  • 作者单位

    The University of Wisconsin - Madison.;

  • 授予单位 The University of Wisconsin - Madison.;
  • 学科 Physical Geography.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 142 p.
  • 总页数 142
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 自然地理学;
  • 关键词

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