DIFFERENTIATING FLASH FLOOD-BORNE SEDIMENTS IN A SMALL AGRICULTURAL HEADWATER SYSTEM USING ISOTOPIC TRACERS

使用同位素示踪剂区分小型农业水源系统中的闪洪沉积物

• 批准号: 0948750
• 负责人: Thanos Papanicolaou
• 金额: $ 4.89万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-04-01 至 2013-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0948750&HistoricalAwards=false
• 关键词: DIFFERENTIATING; FLASH; FLOOD; BORNE; SEDIMENTS

Flash flood events are geomorphically critical because they affect stream morphology and floodplain sediment redistribution, as well as lead to the formation of ephemeral gullies, which become key conduits of soils derived from the uplands and floodplain. The June 19th, 2009 flash flood event in the University of Iowa Clear Creek NSF testbed offers a unique opportunity to derive sediment rating data points that, to our best knowledge, do not exist in the literature. In addition, the pre-existing infrastructure in the NSF test bed allowed us to capture soils/ sediments of different origin, i.e., sediments that originate from hills, ditches, riparian zone, stream banks and bed. These unexpected measurements along with the availability of detailed hydrological measurements from radar and preexisting LiDAR data will help us quantify a sediment budget for the event.We propose: 1) to develop a sediment budget for a headwater system of Clear Creek, IA during the June 19th flash flood event; 2) to quantify the proportions of recently eroded surface soils and channel-derived sediment in the suspended load using established sediment tracing techniques that involve naturally occurring radionuclides (7Be and excess Lead-210, 210Pbxs) and stable isotopes (Carbon-13, 13C, and Nitrogen-15, 15N); and 3) to compare the budget with simulations of coupled upland erosion and 1D/ 2D sediment transport models to test their predictive ability for simulating flash flood events.For this study, we are seeking support to conduct isotopic tracer analysis for the samples collected prior to and during the flash flood event to provide a more detailed budget and for modeling of the event. Although an inventory of geochemical tracers is available for Clear Creek through past research, these tracers cannot identify the origin of mobilized sediments solely associated to the flood event of June 19th, 2009. A powerful and established tracer for identifying recently mobilized sediment is the naturally occurring radionuclide, Beryllium-7 (7Be). 7Be is produced continuously in the atmosphere but delivered to the landscape surface in high concentrations mainly during precipitation events. Moreover, 7Be has a relatively short half-life of only 53 days, meaning that it will not remain long in the soil before decaying. Thus, there is a strong relationship between a single erosion event and high signatures of 7Be in the eroded surface soils. Past research has shown the unique ability of 7Be to differentiate uplands from stream banks and bed sediments.The samples to be analyzed have already been collected, but time is critical because of the short 53-day half-life of 7Be. Radionuclide analysis of the samples must begin immediately and be completed within 4 half-lives in order to capture detectable activities of 7Be for differentiating upland and stream bank/bed sources to the sediment load of the June 19th event.As with any catastrophic flood, frequently asked questions include how much material (e.g., water and sediment) was moved during the event. For this study, we will supersede this primary question by addressing not only how much material (in this case, sediment) was mobilized during the June 19th flash flood, but also from where the transported material was derived. This research is transformative because it will provide sediment flux vs. flow data for

山洪暴发事件在地貌上是关键的，因为它们影响河流形态和洪泛平原沉积物的再分配，并导致短暂的冲沟的形成，这些冲沟成为来自高地和泛滥平原的土壤的关键管道。2009年6月19日在爱荷华大学Clear Creek NSF试验床发生的洪水事件提供了一个独特的机会来得出泥沙等级数据点，据我们所知，这些数据点在文献中是不存在的。此外，NSF试验台原有的基础设施使我们能够捕获不同来源的土壤/沉积物，即来自丘陵、沟渠、河岸带、河岸和河床的沉积物。这些意想不到的测量，以及来自雷达和现有激光雷达数据的详细水文测量的可用性，将有助于我们量化此次事件的泥沙收支。我们建议：1)在6月19日的洪水事件期间，为IA的Clear Creek水源系统制定泥沙收支；2)利用现有的泥沙示踪技术，量化最近被侵蚀的表层土壤和河道来源的泥沙在悬沙中的比例，这些技术涉及自然存在的放射性核素(7Be和过量铅-210、210Pbxs)和稳定同位素(碳-13、13C和氮-15、15N)；3)将模拟结果与高地侵蚀模拟和一维/二维泥沙运动模拟结果进行比较，以检验它们对模拟山洪事件的预测能力。在本研究中，我们正在寻求支持对山洪事件发生前和期间采集的样本进行同位素示踪分析，以提供更详细的预算和对山洪事件的模拟。尽管通过过去的研究，Clear Creek有一份地球化学示踪剂的清单，但这些示踪剂不能确定仅与2009年6月19日洪水事件有关的动员沉积物的来源。天然放射性核素铍-7(7Be)是识别最近动员的沉积物的一种强大和成熟的示踪剂。7Be在大气中持续产生，但主要在降水期间以高浓度的形式输送到地表。此外，7Be的半衰期相对较短，只有53天，这意味着它在腐烂之前不会在土壤中停留很长时间。因此，在侵蚀表层土壤中，单一侵蚀事件与7Be的高特征之间存在很强的相关性。过去的研究表明，7Be具有区分高地、河岸和河床沉积物的独特能力。要分析的样品已经收集完毕，但由于7Be的半衰期很短，时间非常关键。样品的放射性核素分析必须立即开始，并在4个半衰期内完成，以便捕捉7Be的可检测活动，以区分高地和河岸/河床来源与6月19日事件的泥沙负荷。与任何灾难性的洪水一样，常见的问题包括在事件期间移动了多少物质(例如水和沉积物)。对于这项研究，我们将取代这个主要问题，不仅解决在6月19日的山洪暴发期间动员了多少物质(在这种情况下，是泥沙)，而且还解决了运输的物质来自哪里。这项研究具有变革性，因为它将提供泥沙通量与水流数据