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

山洪暴发事件在地貌学上至关重要，因为它们影响河流形态和洪泛区沉积物的再分配，并导致短暂沟渠的形成，这些沟渠成为高地和洪泛区土壤的关键通道。2009年6月19日，爱荷华大学Clear Creek NSF试验台的山洪暴发事件提供了一个独特的机会来获得沉积物评级数据点，据我们所知，这在文献中是不存在的。此外，NSF试验台已有的基础设施使我们能够捕获不同来源的土壤/沉积物，即来自山丘、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帮助我们量化该事件的沉积物预算。我们建议：1)在6月19日山洪暴发期间，为IA Clear Creek源头系统制定泥沙预算；2)利用已建立的沉积物示踪技术，利用自然产生的放射性核素（7Be和过量的铅-210、210Pbxs）和稳定同位素（碳-13、13C和氮-15、15N），量化近期侵蚀的表层土壤和河道泥沙在悬浮荷载中的比例；3)与陆面侵蚀耦合模型和一维/二维输沙模型的模拟结果进行比较，验证其对山洪事件的预测能力。在这项研究中，我们正在寻求支持，对山洪暴发事件之前和期间收集的样本进行同位素示踪分析，以提供更详细的预算和事件建模。虽然通过过去的研究，我们可以获得Clear Creek的地球化学示踪剂清单，但这些示踪剂无法确定与2009年6月19日洪水事件相关的移动沉积物的来源。一个强大的和建立的示踪剂，以确定最近移动的沉积物是自然产生的放射性核素，铍-7 （7Be）。be在大气中不断产生，但主要在降水期间以高浓度输送到景观地表。此外，7Be的半衰期相对较短，只有53天，这意味着它不会在土壤中停留太久就会腐烂。因此，单次侵蚀事件与被侵蚀表层土壤中7Be的高特征之间存在很强的关系。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。待分析的样品已经收集好了，但时间很关键，因为7Be的半衰期只有53天。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，以便捕捉可检测到的7Be活性，以区分6月19日事件的高地和溪流河岸/河床来源的沉积物负荷。与任何灾难性洪水一样，经常被问到的问题包括在事件中移动了多少物质（例如水和沉积物）。在这项研究中，我们将通过解决在6月19日的山洪暴发期间动员了多少物质（在这种情况下是沉积物），以及运输物质的来源来取代这个主要问题。这项研究具有变革性，因为它将提供沉积物通量与流量的数据

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