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

暴洪事件在地貌上是关键的，因为它们影响河流形态和河漫滩沉积物的重新分布，以及导致形成短暂的冲沟，成为来自高地和河漫滩的土壤的关键管道。2009年6月19日，在爱荷华州大学的克利尔克里克NSF试验台山洪事件提供了一个独特的机会，以获得沉积物评级数据点，据我们所知，不存在于文献中。此外，NSF试验台中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，来源于丘陵、沟渠、河岸带、河岸和河床的沉积物。沿着这些意外的测量以及雷达和已有的LiDAR数据的详细水文测量的可用性将帮助我们量化事件的泥沙收支。我们建议：1）开发在6月19日山洪事件期间的Clear Creek，IA的源头系统的泥沙收支; 2）利用已建立的沉积物追踪技术，包括天然放射性核素，量化最近侵蚀的表层土壤和来自河道的沉积物在悬浮物中的比例（7 Be和过量的铅-210，210 Pbxs）和稳定同位素（碳-13，13 C和氮-15，15 N）; 3）将该模型与耦合的高地侵蚀模型和一维/二维泥沙输运模型进行比较，以检验其模拟山洪事件的预测能力。我们正在寻求支持，对在山洪暴发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，并为山洪暴发建模。尽管通过过去的研究，可获得Clear Creek的地球化学示踪剂清单，但这些示踪剂无法确定仅与2009年6月19日洪水事件相关的动员沉积物的来源。天然放射性核素铍-7（7 Be）是一种确定最近活动的沉积物的强有力的示踪剂。7 Be在大气中持续产生，但主要在降水事件期间以高浓度输送到景观表面。此外，7 Be的半衰期相对较短，只有53天，这意味着它在土壤中不会停留很长时间。因此，有一个很强的关系之间的一个单一的侵蚀事件和高签名的7 Be在侵蚀表层土壤。过去的研究显示，7 Be具有独特的能力，可以区分高地、河岸和河床沉积物。已经收集了要分析的样品，但由于7 Be的半衰期很短，只有53天，因此时间很关键。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，以捕获可检测的7 Be活动，从而将高地和河岸/河床来源与6月19日事件的沉积物负荷区分开来。与任何灾难性洪水一样，常见的问题包括有多少物质（例如，水和沉积物）在活动期间被移动。在这项研究中，我们将取代这个主要问题，不仅解决了多少材料（在这种情况下，沉积物）在6月19日山洪暴发期间被动员，而且还从哪里来的运输材料。这项研究是变革性的，因为它将提供沉积物通量与流量数据，

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