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

冲积河流和基岩河流作为输沙能力和输沙能力之间变化关系的连续体的端部成员，其一般特性是众所周知的。 在河流是基岩和冲积层的组合的地方，对河流过程和形式的知识和理解存在差距。 本研究的目的是探索在德克萨斯州中部的瓜达尔卡尔特河和麦地那河的冲积抚育和基岩抚育河段的空间和时间变化，重点是不同粒度的泥沙输运能力。 这两条河都有河床，在主要是砾石和干净的基岩之间交替。 城市的影响，特别是在瓜达尔卡巴纳河修建小水坝方面，要比麦地那河流域大得多。 将研究一系列小的、河流运行的、堰式坝影响泥沙输运的程度以及由此产生的河道形态变化。 该项目的一个相关目标是比较瓜达尔卡卢佩河和麦地那河，以确定瓜达尔卡卢佩河的形态是否发生了重大变化，即浅滩的撤离。 为了实现这些目标，该项目将研究沉积物沉积和运输能力的历史，并通过历史分析，实地测绘和统计技术将自然河流过程与人类改变的过程进行比较。 该研究将调查混合冲积基岩渠道中的泥沙输运过程，试图解释观测到的床面形态、沉积地貌、渠道几何形状、渠道模式和特征的分布变化。 在比较瓜达尔卡卢佩河和麦地那河，预计瓜达尔卡卢佩河将有更多的情节，间歇性的泥沙输运事件在空间和时间上，在下游方向的泥沙纵向分布不均匀，上游和下游河段之间的差异更多，以及不规则的浅滩间距比麦地那河。 关于时间效应，据推断，在瓜达尔卡巴纳河显着的变化，在通道类型和形态发生后，立即安装大坝与缓慢的调整通道类型和形态，预计随着时间的推移。 预计在水坝间隔较近的路段，形态的动态性将低于水坝间隔较远的路段。 还预计，在两个渠道的几个地点，在50年至100年的回流间隔期内，半米至米大小范围内的大型碎屑的运输能力，或宏观湍流事件的潜力。这项研究提供了一个地理和时间的角度来看，输沙能力和渠道类型的分布达到在德克萨斯州中部的两个混合冲积基岩河流。对冲积-基岩混合河流的过程知之甚少。 这一研究项目将更好地了解冲积-基岩混合河道上运行的过程的空间变化，以及大坝建设造成的地貌变化和随后对沉积物输运速率和形态的变化。 虽然最终的结果将是在得克萨斯州中部的瓜达卢佩河和麦地那河的比较，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，本研究将有助于预测在冲积-基岩混合河道和河段中安装大坝后河道形态的变化。 本研究结果可供流域管理、河川径流分析及水坝间距调整之参考。 研究结果表明，大坝的安装或拆除的影响，为特定的河段可以与资源管理者，以帮助预测这种改变的影响。 对宏观湍流、泥沙输运能力和沉积地貌的空间分布的地理观点将增加对混合冲积-基岩河道的科学认识。该项目将有助于建立一个强有力的研究议程，并为地理学科的女博士生开创一个有前途的职业生涯。

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.