DDRI: Spatial and temporal variation of sediment transport capacity and channel reach type in two mixed alluvial-bedrock rivers in central Texas

DDRI：德克萨斯州中部两条混合冲积基岩河流输沙能力和河段类型的时空变化

• 批准号: 0526101
• 负责人: Joanna Curran
• 金额: $ 1.15万
• 依托单位: Texas State University - San Marcos
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-05-01 至 2006-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0526101&HistoricalAwards=false
• 关键词: DDRI; Spatial; temporal; variation; sediment

As end members on a continuum of a varying relationship between sediment supply and transport capacity, the general behavior of both alluvial and bedrock rivers is well known. Where rivers are a combination of bedrock and alluvium, there is a gap in knowledge and understanding of river processes and forms. The objective of this research is to explore the spatial and temporal variation in alluvial tending and bedrock tending reaches in the Guadalupe and Medina Rivers in central Texas, with focus on the sediment transport capacity of varied grain sizes. Both rivers have channel beds that alternate between predominately gravel to clean bedrock. There is a much greater urban influence, particularly in the creation of small dams, in the Guadalupe than in the Medina watershed. The extent to which a series of small, run of the river, weir type dams affect sediment transport and the resultant changes channel morphology will be investigated. A related objective of the project is to compare the Guadalupe and Medina Rivers to determine if there is a significant shift in the morphology of the Guadalupe River in the form of the evacuation of riffles. To reach these goals, the project will examine the history of sediment deposition and transport capacity, and compare the natural river processes to human altered ones through historical analysis, field mapping, and statistical techniques. The research will investigate the sediment transport processes operating in mixed alluvial-bedrock channels in an attempt to explain observed changes in the distribution of bed forms, depositional landforms, channel geometry, and channel patterns and characteristics. In comparing the Guadalupe and Medina rivers it is expected that the Guadalupe River will have more episodic, punctuated sediment transport events over space and time, a less even longitudinal distribution of sediment in the downstream direction, more differences between upstream and downstream reaches, and less regular riffle spacing than in the Medina River. With respect to temporal effects it is inferred that in the Guadalupe River pronounced changes in channel type and morphology occur immediately following dam installation with slower adjustments of channel type and morphology expected over time. It is anticipated that in segments where dams are closely spaced, morphology will be less dynamic than where dams are farther apart. It is also expected that transport capacity for large clasts in the half meter to meter size range, or the potential for macroturbulent events, occurs at several locations in both channels at flows with return intervals between 50 and 100 years. This research offers a geographic and temporal perspective on sediment transport capacity and the distribution of channel type reaches in two mixed alluvial-bedrock rivers in central Texas. Little is known about processes operating on mixed alluvial-bedrock rivers. This research project will develop a better understanding of the spatial variation of processes operating on mixed alluvial-bedrock channels and the geomorphic changes resulting from dam construction and subsequent changes to sediment transport rates and morphology. While the final results will be a comparison of the Guadalupe and Medina Rivers in central Texas, the insight gained from this study will be applicable to the region. Based on a multi-scaled approach, this research will aid the prediction of change in channel morphology subsequent to dam installation in mixed alluvial-bedrock channels and reaches. Results of this study can be used to increase understanding for watershed management, in-stream flow analyses, and regulation on the spacing of dams. Research results illustrating the effects of dam installation or removal for specific reaches can be related to resource managers to lend to help predict impacts of such alterations. Geographic perspectives on the spatial distribution of the potential for macroturbulence, sediment transport capacity, and depositional landforms will add to the scientific knowledge on mixed alluvial-bedrock channels. The project will help establish a strong research agenda and launch a promising career for a female doctoral student in the discipline of geography.

作为泥沙供应和输送能力之间不同关系的连续体上的终端成员，冲积河流和基岩河流的一般行为是众所周知的。在河流是基岩和冲积层组合的地方，对河流过程和形态的认识和理解存在差距。本研究的目的是探讨德克萨斯州中部瓜达卢佩河和麦地纳河冲积和基岩发育段的时空变化，重点是不同粒度的泥沙输送能力。这两条河流都有河床，在以砾石为主的河床和清洁基岩之间交替。与麦地那分水岭相比，瓜达卢佩的城市影响力要大得多，特别是在建造小水坝方面。将调查一系列小型堰式堤坝对泥沙输送的影响程度，以及由此引起的河道形态变化。该项目的一个相关目标是对瓜达卢佩河和麦地那河进行比较，以确定瓜达卢佩河的形态是否发生了重大变化，其形式是疏散游荡者。为了实现这些目标，该项目将研究泥沙淤积和输沙能力的历史，并通过历史分析、野外测绘和统计技术将自然河流过程与人类改变的河流过程进行比较。这项研究将研究冲积-基岩混合河道中的泥沙输送过程，试图解释观测到的河床形态、沉积地貌、河道几何形状以及河道形态和特征的变化。通过比较瓜达卢佩河和麦地那河，预计瓜达卢佩河在空间和时间上将有更多的断断续续的泥沙输送事件，下游方向的泥沙纵向分布不那么均匀，上下游之间的差异更大，规则的冲沟间距比麦地那河小。关于时间效应，据推断，瓜达卢佩河的河道类型和形态在大坝安装后立即发生显着变化，预计随着时间的推移，河道类型和形态调整的速度会较慢。预计在大坝间距较近的地段中，地形将比大坝距离较远的地段更不动态。预计半米至米大小范围的大型碎屑的输送能力，或发生宏观湍流事件的可能性，在两个航道的几个位置以50至100年之间的重现间隔出现。这项研究为德克萨斯州中部两条冲积-基岩混合河流的泥沙输送能力和河段类型分布提供了一个地理和时间的视角。人们对在冲积-基岩混合河流上运行的过程知之甚少。这一研究项目将使人们更好地了解冲积-基岩混合河道上运行的过程的空间变化，以及大坝建设和随后的泥沙输移率和地形变化所引起的地貌变化。虽然最终的结果将是对德克萨斯州中部的瓜达卢佩河和麦地纳河的比较，但从这项研究中获得的见解将适用于该地区。基于多尺度方法，这项研究将有助于预测冲积岩-基岩混合河道和河段大坝安装后河道形态的变化。这项研究的结果可以用来增加对流域管理、溪流分析和大坝间距调节的理解。说明大坝安装或拆除对特定河段的影响的研究结果可能与资源管理者有关，以帮助预测此类变化的影响。对宏观湍流潜力、泥沙输送能力和沉积地貌的空间分布的地理观点将增加关于冲积-基岩混合河道的科学知识。该项目将帮助建立一个强有力的研究议程，并为地理学科的一名女性博士生开启一段充满希望的职业生涯。