Collaborative Research: Quantifying Sediment Storage Transit Times For Geomorphically Explicit, Watershed Scale Suspended Sediment Routing

合作研究：量化地貌明确的流域规模悬浮沉积物路线的沉积物储存运输时间

• 批准号: 1424969
• 负责人: James Pizzuto
• 金额: $ 24.8万
• 依托单位: University of Delaware
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1424969&HistoricalAwards=false
• 关键词: Collaborative; Research; Quantifying; Sediment; Storage

Nontechnical Explanation of the Project's Broader Significance Suspended sediment and associated contaminants and nutrients are leading causes of environmental degradation in rivers, but predicting the movement of fine-grained material through watersheds remains difficult. Most watershed management planning treats fine-grained suspended sediment as "washload" that is rapidly transported to receiving waters once particles enter stream channels. However, sediment particles actually move downstream by a series of discrete jumps, with each jump punctuated by a period of resting in floodplains and other alluvial deposits. According for this view, particle travel times from upland sources to estuarine sinks may be very long (up to 1000 years for the Chesapeake Bay watershed, for example). The disparity between these two views is most critical where Best Management Practices are used to reduce the contribution of sediment and other contaminants from upland watershed sources to downstream receiving waters, such as the Chesapeake Bay. Sediment travel times are not currently incorporated into existing watershed modeling schemes used to evaluate and design Best Management Practices, so the time required for them to achieve their maximum effectiveness is unknown. During this project, particle waiting times will be determined for a sub-basin of the Chesapeake Bay watershed, and these results will be incorporated into a new modeling framework for predicting the movement of particles through watersheds that explicitly incorporates measured particle waiting times. These results will help evaluate restoration schemes designed to reduce loading of sediment and other particles from watersheds to ecologically damaged receiving waters. Technical Description of the ProjectGeomorphologists widely acknowledge that suspended sediment routing through large (100-1000 km spatial scales) watersheds must account for the 100-10,000 year timescales associated with alluvial storage, but this knowledge is rarely reflected in watershed models. A few recent modeling schemes include both sediment transport and storage, but the necessary reach averaging introduces a new variable, the sediment-storage (waiting) time distribution that is virtually undocumented. This study will use pollen analyis, optically-stimulated luminescence, radiocarbon dating, and fallout radionuclide concentrations to measure contemporary waiting time distributions for all significant alluvial storage reservoirs in a mid-Atlantic Piedmont watershed where rates of erosion, deposition, and transport are well-constrained. The measured waiting time distributions will be used with a suspended-sediment routing model in a series of scenarios designed to illustrate timescales required for suspended sediment to move from upland sources to basin outlet in the Chesapeake Bay watershed. The results will improve existing theory concerning sediment waiting time distributions and sediment budgets within fluvial systems. The results will also help interpret the complex histories of watershed disturbance amd provide a means for a more accurate prediction of future changes. This study is designed to test the following hypotheses: 1) sediment storage or waiting time distributions can be quantified using measured erosion rates, geomorphic mapping, radiometric dating, and reservoir theory; 2) sediment waiting times for mid-Atlantic upland watersheds range from months to millennia, with characteristic values on the order of 1000 years, implying very long timescales to transport most suspended particles from upland sources to basin outlets; 3) observed waiting time distributions are not exponential, suggesting that valley storage reservoirs are not well-mixed.

悬浮沉积物和相关的污染物和营养物是河流环境退化的主要原因，但预测细颗粒物质在流域中的运动仍然很困难。大多数流域管理规划将细颗粒悬浮泥沙视为“冲刷量”，一旦颗粒进入河道，就会迅速输送到接收沃茨。然而，沉积物颗粒实际上是通过一系列离散的跳跃向下游移动的，每一次跳跃都被在洪泛平原和其他冲积物中的一段时间所打断。 根据这一观点，颗粒从高地源到河口汇的传播时间可能很长（例如，切萨皮克湾流域长达1000年）。 这两种观点之间的差异是最关键的最佳管理做法是用来减少沉积物和其他污染物的贡献，从高地流域来源的下游接收沃茨，如切萨皮克湾。 沉积物的传播时间目前还没有纳入现有的流域建模方案，用于评估和设计最佳管理措施，因此，所需的时间，他们实现其最大的有效性是未知的。 在这个项目中，颗粒等待时间将被确定为一个子流域的切萨皮克湾流域，这些结果将被纳入一个新的建模框架，用于预测颗粒的运动通过流域，明确纳入测量的颗粒等待时间。 这些结果将有助于评估旨在减少流域沉积物和其他颗粒物向生态受损的受纳沃茨的负荷的恢复方案。 项目的技术说明地貌学家广泛承认，通过大流域（100-1000公里的空间尺度）的悬浮泥沙路由必须考虑到100- 10000年的时间尺度与冲积存储，但这方面的知识很少反映在流域模型。一些最近的建模方案包括泥沙输运和储存，但必要的到达平均引入了一个新的变量，沉积物存储（等待）时间分布，这是几乎没有记录。 本研究将使用花粉分析，光激发光，放射性碳测年，放射性核素浓度，以测量当代的等待时间分布的所有重要的冲积水库在大西洋中部的皮埃蒙特流域的侵蚀，沉积和运输率受到很好的限制。所测得的等待时间分布将被用来与悬浮泥沙路由模型在一系列的情况下，旨在说明悬浮泥沙所需的时间尺度移动从高地来源的流域出口在切萨皮克湾流域。研究结果将改进现有的理论，泥沙等待时间分布和泥沙收支的河流系统。研究结果也将有助于解释流域扰动的复杂历史，并为更准确地预测未来变化提供一种手段。本研究旨在验证以下假设：1）沉积物储存或等待时间分布可以通过测量侵蚀速率、地貌制图、放射性测年和水库理论来量化; 2）大西洋中部高地流域的沉积物等待时间从几个月到几千年不等，特征值大约为1000年，这意味着很长的时间尺度，以运输大多数悬浮颗粒从高地源到流域出口; 3）观察到的等待时间分布不是指数，这表明山谷水库没有很好地混合。