RAPID: In-Channel Alluvial Benches and Their Environmental Controls

河道内冲积阶地是位于河床上方、主要泛滥平原表面以下的陆架状河流沉积物。它们的位置和形态可能会使漫滩阶段的常规确定复杂化，因此对河流恢复计划至关重要。它们的存在会影响水力和河岸栖息地的质量，而它们的质量预算是河流动态的重要指标。这项研究的重点是测量Kilpatrick和Barnes于1964年在美国东南部南皮德蒙特记录的旧海峡内长凳的改装情况，以及可能起源于过去十年山麓干旱条件下的较年轻长凳的改装。其他地方的研究人员发现，板凳可能在干旱期间产生，在更潮湿、洪水占主导地位的地区被破坏。因此，与过去十年的大部分时间相比，2009年降雨量恢复较高，有可能启动长凳的快速转变，影响整个区域的泥沙收支和河岸生境。或者，土地利用历史可能会取代洪水制度，成为控制台阶形成和破坏的主要因素。该项目旨在通过测量、地形测年技术、洪水数据分析和土地利用变化评估，区分台阶质量平衡的控制，以阐明山前溪流的台阶动态。该项目对时间很敏感，因为2009年到目前为止的降雨量远远大于过去十年南部皮埃蒙特地区每年的降雨量。最近从干旱到更潮湿条件的这一气象转变提供了一个无与伦比的机会，可以记录可能是在十年干旱期间产生的河道内长凳，并观察从一开始就向更高的溪流状况过渡的影响。这项研究有助于更好地了解河流中泥沙的储存，因为对河道内冲积阶地的形成和持久性作为泥沙储存特征的了解还不多。人们对冲积板凳的了解来自于在气候与美国东部温带地区显著不同的地区进行的研究。因此，这项研究将解决我们目前对板凳的理解是否普遍适用于不同气候环境下的系统。这项研究项目考察了一种特定类型的河流泥沙储存特征的发生、形成和持续。因此，这将有助于更好地了解导致河道内泥沙储存的原因、过程和条件，这具有相当大的潜力，有助于使泥沙预算在理解河流泥沙动力学方面更加准确和有意义。从应用河流地貌学的角度，这项研究将通过研究位于洪泛平原或主谷滩下方的具有水文意义的地貌面，为现场确定漫滩水位提供新的见解。最后，这项研究将通过研究干旱的潜在影响和更常见的河流沉积物动态变化的诱因，如土地利用/覆盖和地表水文的历史性变化，为景观和大气现象的耦合提供新的见解。研究成果将在会议报告和研究期刊上广泛传播。

In-channel alluvial benches are shelf-like deposits of river sediment that are located above the channel bed but below the main floodplain surface. Their positions and morphologies may complicate routine determinations of bankfull stage, so vitally important to stream restoration plans. Their presence can impact the quality of hydraulic and riparian habitat, while their mass budgets are important indicators of fluvial dynamics. This research focuses on measuring modifications of old in-channel benches documented by Kilpatrick and Barnes in 1964 in the Southern Piedmont of the southeastern United States, and of younger benches that may have originated during drought conditions occurring in the Piedmont over the last decade. Researchers elsewhere have found that benches may be produced during drought and destroyed during wetter, flood dominated regimes. The return to higher rainfall in 2009 relative to most of the last decade thus has the potential to initiate rapid transformation of benches, affecting sediment budgets and riparian habitat throughout the region. Alternatively, land use history may override flood regimes as the dominant control on bench formation and destruction. This project seeks to differentiate controls on bench mass balance to elucidate bench dynamics in Piedmont streams using surveying, landform dating techniques, flood data analysis and land use change assessment. This project is time sensitive because year 2009 rainfall to date has been much greater than that occurring annually for most of the last decade in the southern Piedmont. This recent meteorological transition from drought to wetter conditions presents an unparalleled opportunity to document in-channel benches that may have been created during decadal drought and to observe the effects of a transition to higher stream-flow regime at its beginning. This research contributes to better understanding about sediment storage in rivers, as not much is known about the formation and persistence of in-channel alluvial benches as sediment storage features. What is known about alluvial benches comes from studies conducted in locations with climates significantly different from those of the temperate Eastern United States. Thus, this research will address whether our current understanding of benches from previous research is generally applicable to systems in diverse climatic settings. This research project examines the occurrence, formation, and persistence of a specific type of river sediment storage feature. As such, it will result in a better understanding of causes, processes, and conditions leading to in-channel sediment storage, which has considerable potential to help make sediment budgets more precise and meaningful in terms of understanding sediment dynamics in rivers. From an applied fluvial geomorphology perspective, this research will provide new insight into the field determination of bankfull stage, by examining geomorphic surfaces located below the floodplain or main valley flat that are hydrologically significant. Finally, this research will provide new insight into the coupling of landscape and atmospheric phenomena by examining the potential impact of drought versus more commonly cited instigators of change in river sediment dynamics, such as historic alteration of land use /cover and surface hydrology. Research results will be widely disseminated in conference presentations and research journals.